=" OL? iN © LIBRARY ¢ oj es “) Cornell University Library Dthaca, New York BOUGHT WITH THE INCOME OF THE SAGE ENDOWMENT FUND THE GIFT OF HENRY W. SAGE 1891 ng EXPERIMENTAL ENGINEERING AND MANUAL FOR TESTING FOR ENGINEERS AND FOR STUDENTS IN ENGINEERING LABORATORIES BY ROLLA C. CARPENTER, M.S., C.E., M.M.E., AND HERMAN DIEDERICHS, M.E. PROFESSORS OF EXPERIMENTAL ENGINEERING IN CORNELL UNIVERSITY SEVENTH EDITION, REVISED AND ENLARGED TOTAL ISSUE FIFTEEN THOUSAND NEW YORK JOHN WILEY & SONS Lonpon: CHAPMAN & HALL, Limirep 1913 A.2 2 SAO 2, 2 ORS CoryRiGHT, 1892, 19c6 BY ROLLA C. CARPENTER e AND CopyRIGHT, 1911 ne BY RC, CARPENTER anv H, DIEDERICHS | Stanbope Press : eH, GILSON_ com PANY BOSTON U.S.A. PREFACE TO SEVENTH EDITION. Tuis edition of ‘Experimental Engineering,” as compared with the earlier editions, has been rewritten and enlarged to such an extent that it may be considered substantially a new book. The work of revision has been done principally by Professor H. Diederichs, whose name appears on the title-page, in connection, with that of the original author. - 3 A “Experimental Engineering” was first written by Professor Carpenter in 1892; its object, in brief, was to serve as a textbook for students in mechanical engineering and as a reference book for engineers on the subject of testing. The book was an outgrowth of an earlier work entitled “Notes on Mechanical Laboratory Practice,” published in 1801. : The work -was received. with general favor and it has been exten- sively used in colleges as a textbook and by engineers as a reference book on the subjects of which it treats. More than 10,000 copies have been published and sold in this country and abroad. It has been revised from time to time, and a considerable amount of. new material has been added since the publication of the first edition. The first edition, published in 1892, contained about 550 pages, - while the sixth edition, published in ee contained nearly 850 pages. - .-The rapid deistonments in mechanical engineering and the numer- ous improvements in the methods of investigation and in the appa- ratus for conducting investigations have been such as to make it desirable to rewrite and republish the entire work. Fortunately the original author was able to secure the codperation of his col- league, Professor Diederichs, in this work, and to induce him to assume charge of the revision. Professor Diederichs, from his train- ing and.experience,.and also from his acquaintance with European practice, was especially well qualified for this task. It is believed iii iv PREFACE that the new edition will be found to give practically all the in- formation required by the mechanical engineer for testing in any field of work which has received consideration from engineering or scientific societies. . In the revision the general plan of the original work has been followed. Some portions of the old work have been cut out as obsolete or practically unnecessary, and a large amount of new matter has been added. Every attempt has been made to bring the new edition up to date in every department which it covers. The field embraced by the work is large, since it covers nearly all departments of testing, with the exception of electrical; and although every effort was made to state all explanations and directions as _ concisely as possible, consistent with clearness, and to eliminate all apparently unnecessary matter, it was not found possible to keep the size of the book within the limits of the preceding edition. In spite of every effort of this kind, the work is over 200 pages larger than the sixth edition. The principal increase in size is due to the extended treatment given the subjects relating to gas engines and producers, steam: turbines, refrigerating and hydraulic machin- ery, the first two of which are comparatively late developments. By the use, however, of a thinner grade of paper, the thickness of the book will not be greater than that of the earlier edition con- taining about 250 pages less, so that the reader will find that the increase in the number of pages of the book to 1100 will not .make it inconvenient to handle or consult, nor will it detract from its use as a textbook. The book is intended chiefly for use in engineering laboratories and presents information which the experience of the authors has shown to be necessary to carry out experiments intelligently and without great loss of time on the part of students. For this pur- pose it gives a brief statement of the theoretical principles involved in connection with each experiment, with references, where neces- sary, to more complete demonstrations, short descriptions of the various classes of engineering apparatus or machinery, a full state- ment of methods of testing, and of preparing reports. For a few cases, where references cannot be readily given, demonstrations of the fundamental principles are given in full. PREFACE Vv This work deals principally with educational methods, the use of apparatus, and the preparation required for making a skilled observer. It is believed, however, that the volume will not be without value as a reference book to the consulting and practising engineer, since it contains in a single volume the principal standard methods which have from time to time been adopted by various engineering societies for the testing of materials, engines, and other machinery, and an extensive series of tables useful in computing results. It also contains a description of the apparatus required in testing and directions for taking data and deducing results in engineering experiments as applied in nearly every branch of the art. An attempt has been made, by dividing the book into several chapters of moderate length and making the paragraphs short, to make references to the book easy to those who care to consult it. The full list of subjects treated in the book is given in the Table of Contents, which immediately follows the Preface. Some of the more important divisions of the work are as follows: Experimental Methods of Investigation. Reduction of Experimental Data. The Slide Rule; the Planimeter. Strength of Materials, Including General Formule, Testing Machines, and Methods of Testing. Methods and Instruments for Measurement of Pressure. Methods and Instruments for Measuring Temperature. Methods and Instruments for Measuring Speed. Friction and the Testing of Lubricants. Measurement and Transmission of Power. Heat and Properties of Gases and Vapors. Measurement of Liquids, Gases and Vapors. Combustion and Fuels. Methods of Determining the Amount of Moisture in Steam. The Engine Indicator. The Indicator Diagram. The Testing of Steam Boilers. The Testing of Steam Engines, Pumping Engines and I.ocomotives. Steam Turbines. Injectors. Gas Engines and Gas Producers. Hot Air Engines. Air Compressing Machinery. Mechanical Refrigeration. Hydrauitic Machinery. vi PREFACE The authors desire to express their thanks for assistance in the preparation of this edition to Assistant Professor G. B. Upton, who has revised and rewritten the portion of the book relating to Mate- rials, and afforded valuable assistance in other portions of the book. They also desire to express their thanks for the help rendered by various colleagues and assistants in Sibley College, particularly to Professor C. F. Hirshfeld, Mr. A. G. Kessler, and Mr. G. L. Currént. The subject-matter of the book comes, of course, from a great variety of sources. It has been the aim in every case to give due credit, in the body of the book, to the authorities from whom infor- mation has been obtained in connection with the subject-matter under discussion. R. C.C. Ivwaca, N. Y., October, rgrt. TABLE OF CONTENTS ‘CHAPTER I. INTRODUCTORY. ARTICLES PAGE Objects of Engineering Experiments. . Relation of Theory to Experiment. . SSR ieteab eee sa i sho grace yee . Method of Investigation... 00.0.0. ccc ee ce ee ce ce ce ee en ee teas Classification of Experiments. .. 2.2.2... 06 cbc ee ce cee ce cn eee eens Efficiency Tests. . ‘ ese ais Classification of Bzceriniental ‘Eeroee.. . Probability of Errors.. serrqeeen . Errors. of Stile Obetiidens-« dace ce ook hae aie aS Ain RES eed eet alee Example. . genase : Comb lection os Eaorey, i. 39 . Deduction of Empirical: ronuale bg . Rules and Formule for Approsinate Calculation. . The Rejection of Doubtful Observations... . When to Neglect Errors. Seat Gn ee . Accuracy of Numerical Calculations). . Methods of ee Experiments Graphical. . Autographic Diagrams. . eiind eve Re Be 8 Sw ANP OD H et 99 H H ONT ANNE WW DID H HHH kB wWn HH H O° Ht mn 4 an Hw is} H ~ Hw - CHAPTER II. APPARATUS FOR REDUCTION OF EXPERIMENTAL DATA AND FOR ACCURATE MEASUREMENT. 18. The Slide Rule. . es 5626 A EN RAS FA SVE KE RE EE euae se TO Ig. Direction fr Using the Slide Rule. Re AI MEN eons geaits, SF 20. The Vernier. . st Jot atin Raprsanrateamreceate ers ecietis te ase as are natn AE Oy ai. The Polar Plantmeter .. selnradiuet teesenace Wack bye Rar eo AVReN NER ease ety «SRI 22. Theory of the Instrument... Wiese aod ere wemaeteay ester eee mn. 223 23. Fariisia’ Pols Plauiinetérs.. 58 Le Madu pitied. ay et ersiominns-. J2O 24, The Mean Ordinate by the: Polar Plapimetet, er ipeusigus has ease 29 25. The Suspended Planimeter. . ef Wa ete Meoketeewk: BR 26. The Coffin Planimeter and Averaiag Instrument. . dimmer ah, AOE 27. Theory of the Coffin Planimeter. . Phe Mead RANGA Md eee aes | Bit 28. Bie Wl laeectet oan cacahGesuce 4 cco escaanetentansee. 34° vii viii TABLE OF CONTENTS ARTICLES PAGE 29. 30. Bi. 32. 33- 34- 35- 36. 37- 38. 39- 40. . Notation.. : Ke oh RMA RASS Gee eo ete GES 42. 43- 44. 45. 40. 47. 48. 49- 50. Ste 52 53- 54: 55+ 56. 57- 58. 59- 60. 61. 62. 63. 64. 65. The Roller Planimeter.. : spimiaay esau ascdtin) 635 Directions for Care and se of Plaiiheters; Side tye ete a. 30 isis aie ick (he TSMR CREA: 2 ad ue cuedwin ewe nee wrenia aug 37 Errors of Different Planimeters.......... 0.0. cee cee eee rete ee eee GO ee ena 42 Vernier Caliper ing nsisuty aie sboy eed saad eeligde ee nee Hae Selo nanoamak Aa The Micrometer. Be dala alee ep caches abide Vat sbac cis Sa ewes High ay mera nie Mamet. CHAD, The Micometer Celine... Leen ee eee et ee rete e eee tere ee ee AG aE OB INeISS acho cae aup agate el kcal och wens 47 Aidsto: Computations 2. 200544 44 Si Geenteese ea caeeicimimieaeuee tess 48 CHAPTER III. STRENGTH OF MATERIALS. — GENERAL FORMULA, Definitions. ....... sei Meso organs ba tata Gent inaione dyctctaiigAeumeeks KG Streaedelownarion Disgesmes, Hee MEDI wh edEtaThevas Mawes O58 Bomnuleton eaion Roading. CURR ERE RGR eee Y eR cei Seay. SS iscravia top Clemip vesstord Mecieditud av ae ave assoc airecraren nce 56 Formule for Transverse Loading......... 0... 0... cece cece ee eee sete eee 57 Formuls for Direct Shéarzd.c.5 occeseasds os deeand ae beesae wean seereea OL Formiule: for VOrsiony: j.ic cio sac Revere oe Sansa av een ey GA eres Gaines eae OOK DeCOndaLy Stresses aisha oid la ta Sieur d deamigipy Raa baamnanee Meas ids TIOZ CHAPTER IV. STRENGTH OF MATERIALS. — TESTING-MACHINES. Testing-machines and Methods of Testing ............... 00000 ce cece eR es eiai tate ii sseset aia 68 Wepiae ae nee iin ahcoes Ha Seg ey Meare TEE ABE A EEN Reagan 70 Shackles... Miia ee es ae wnedes ih oe Briedttica tions for Goverment? sTesGnecnachines, Pipa selAMeae ses", TES Riehlé Brothers’ ea ee 2 bd Miata dasa ae ieee Oe Riehlé Power Machines... iain otOARTA Ge at ys ai ea tencre foe ME Pada hoes ae Olsen Testing-machine. . fs ee ie edie ee oul os eRe See, SO Thurston’s Torsion Mestivigrnaching.. is aM Anes MMS ainsi ease. ia Power Torsion-machines...2 sess. 00s ecstseseeeeestsceersnsecns Impact-testing Machine. . Gti He Ba Akeni Gi gaia uh Fosea deat may wake Machines for Testing Cennenit.. ee imei sekea a 96 General Requirements of insteumaenta lor NMeasiving Steines. Various Forms of Extensometers.. A Eee UN Mae aac ARRAS Combined Extensometer and itagesohte derparatae, ae hates Instruments for Measuring Torsion, Deflection, and Compressicns, Ico 107 vs IIt CHAPTER V. 4 STRENGTH OF MATERIALS. — METHODS OF TESTING. ARTICLES 66. Standard Methods. . 67. Tension Testing. . 68. 69. 70. 71. 72. 73: 74- 75: 76. 77- 78. 79- 80. 81. 82. 83. 84. 85. 86. SF 88. 89. go. QI. 92. 93- 94. 95: 96. 97. 98. 99. Too. Tor. 102. TABLE OF CONTENTS Test-pieces of Special Materials, , Directions for Tension-tests. . Compression Testing. . eee Directions for Gori gressibertesteu. Transverse Testing. . ‘i Directions for Tianaverse Tests. Rhepott- of Diaieeverse Tesises. 0. ee ee Porsion’ Testing ies: s siacsis sisting ogg Soe nati ce so alee eA OSG Deen ee aS Directions for Torsion-tests...........- 0. ec ee ce ee cnet eee ence ee ee arene Testing. in Direct Shéar:saees.0 vacc eves ss se ee erase Oe Ne He eka EAE AD ae eS ee Drop-tests. . Minor Tests... 4 Special Tests anil Spectticnvions., Tests of Building Stone and Brick, Tests of Paving Material, a ad Ballast, ‘Natural aad Artificial. Testing Cements and Mortars.. aug Sets sasscentucs CHAPTER VI. MEASUREMENT OF PRESSURE. Pressure, Definitions and Units.... 2.2... 0... ccc ccc ce eee eee e ee Measurement:Of Pressures oc sccisccace ian ene ebs ah dos wa ene su ae See ea na Manometers.. U-shaped Manomister: Cistern-manometer. . Mercury Columns. . Multiplying and Differential Manotweters. Presstites Ban dune cua aa acoucavace va ap azgncnue acanasonnecnens Via CUUM=BaUS ES 6 20 sea aitcit bree waned swank anvareh aes toate sane aan Recording-gauges .......... Gauge Calibration . Correction of Ciioees <4 SwRI ROS Forms for Calibration of ‘Coupes, CHAPTER VII. MEASUREMENT OF TEMPERATURE. Temperature. . Thermometers ind Thermoneeus Niaterials., Thermometric Scales and Thermometric Standards, Leiner suk weeeews ah we Gas Thermometers.. ‘ Thermometers Employing iyuids.. PAGE II5 IIs 117 118 125 125 126 127 127 129 129 132 132 133 134 138 152 155 156 167 168 168 169 171 172 174 181 185 185 188 192 192 193 193 195 196 201 x TABLE OF CONTENTS ARTICLES PAGE 103. Thermometers Employing Solids.. Seema datagram eae ces «205 104. Calorimetric Pyrometers..:..... shiva mkwest wees 68 oe 200 105. Electrical Methods of Measuring WEverbtteacaosu ce es 209 106. Optical and Radiation Pyrometers. . os bea, 216 107. Calibration of Thermometers and pytainetete: Ce teh eaoaarepeasonmamenee 216 CHAPTER VIII. THE aie OF SPEED. 108. Counting Devices. . ca cba. dy tush Rane te Orem eesataatanaeh oayegae aan! 2a tog. Speed Indicators: Tavhometers... lg andl ah ee be Gade thas, Sar eues Sea iab aa $22O) ito. The Chronograph. . nied Lee MOA esa Ie (WBS i111. Measurement of Bead Vastation within Revdliton:, - 235 ; CHAPTER IX.. 4 FRICTION. — TESTING OF LUBRICANTS. 112. Friction. RWS Sah star sods Siow diete dn ubeuaneanaaen Gd 4 Snares Yanaiersin aed sunecdus 4230 i13. Classification. sisicdgie 8 aA aai ac love, Rania ROTO Aen AS aE Ade ae ay Ae II4. Pormube and Noigtion, ior on casa i We ede tela ocala eee Dasaaten we eee SBT. 115. Friction of Pivots. . sesh Sapa esti eang inc a viata hak aS ead nee a” 238 116. Filton of Catlsand. Belts, ‘Belt Drive. Meer aser Meare tere 238 #17: Friction Of Blidsiicte sire ses aioe ae Bes BANS PRS SBA LE RO EAE OAT 118. Tibbetts yale yeh eels cel gal te a 242 119. Determinations Required. ... 0.00.00. occ e ee ee ee ees 243 120. ee oe enter eat ir 243 121. Acid Tests.. Hise bath an OLN Rahal eae ate maeaenenias Wo sea aaea on ad anne 24S) 122, Guraming ar Drying... Je pRe, Waa eag Nels Beenie eee ance DAS 123. Density of Oils. . Hugh eden s epee Rae ee RRs tay weve He EE ve Hee ee 4O 124. Method of Finding Density... Ae OE Ha Sh is Ea eae uae da «ia eur! BAT 125. Viscosity. . issih amekewe (24S 126. Method of ‘Measuring Viscosity with Olsen. Apparatus. sew aia ae aur, 252) 127. Chill-point.. Rn tae AS. aemalent wa eae es ISD 128. Method of Finding the Chill-point... died@einteeareabeis sees g. BEA! 129. The Flash-point. . Bene Gear okt 254 130. Method of Testing for Flash-point.., Be ane eed Pie ee eRONS a aiideas de (GREE 131. Burning-point........ doit wieatttie sie WEA mated ucieewr Gers ges 1250 132. Mbtlicd of Testing for Burcing-nsine Pins Mena en pele neoaees 256 133. Volatility. . ne Leo mpe guanine ed staal a 0 256 134. Coefficient of ‘Fiction, — Oil eating Machines... ae 256 135. Directions for Obtaining Coefficient of Friction wit Tyurston’s s Oil- testing Machines... sto ng ereee navees - 1264 136. Instructions op Use of Thurston's R, ‘R. Tnbsleantetenten,, Sawada wise, (260 137. Durability of Lubricants.. S500 PEs wale ey Meu Ge Galt eames» 260 138. Durability-testing Machine... : «207 139. Directions for Durability Test 3 Oils with Boult’s Oil- testing Machine, . . 270 140. Friction of Ball- and Roller-bearings ..... 00-0. 00000. ccc cece ce ccceeeee 271 I4I. Fotime:for Report iss vi si o2ae-240- neve tes cscscavee od adecscccn. 273° TABLE OF CONTENTS xi CHAPTER X. he or MEASUREMENT AND TRANSMISSION OF POWER. ane ARTICLES a 142. Definitions: -. ciutiians 143. Megsurement'of Bower... sain ROA LUA ba a Ree on padoe a apr Si MEMer a EW 144. Absorption Tiyninsaneeers . risers West anne Sale Gee eee ees aera eer oy 145. The Design of Prony Bakes >. ge tin Gee ihe 146. Cooling and Lubricating a Bilin: Bike 147. Other Forms of Friction ee Selé-reguatng ‘Frakes, , 148. Alden Brake. . 149. Brakes Sinployiag the. Fr riction of Lauds. 150. Other Forms of Brakes: — Brakes.. 151. Fan Brakes. waive vacate aN ss 152. eid Bribe. 153. Traction Dyniamometers, . shits s #4. Transmission Dynimieneiers General’ 1 Types 155. Morin’s Rotation Dynamometer.. 156. Steélyard Dynamometer.. Rauf N i A CISA ck cited Tacertaghhenty sity casimen etieberteene ce 187. Pillow-block Dynamometer......... 0... 00s cece ee cnet eee cee eens 158. The Lewis Dynamometer. ........0. 5c cbc cee ee lence tees cece cies 159. The Differential Dynamometer......2 060. .lec ce cece cece cee teen neces 160., Emerson’s Power Scale ..cc sy caencns og oa $e oa wee ee te te de ta ee one 161. The Van Winkle Power Meter.... 1.2.0... 0. cece cece cece ete ee te ee ans 162. Belt Dynamometers.........0.0. 00 cece cece ce cece be cece sete ucts en anes 163. Sp a ali Sk a a a 164. Torsion Dynamometers.. 165. Cradle Dynamometers. . 3 Setters 166. Electrical Measurement i Power Input and: Output, 167. Methods of Connecting Up, etc.. 168. The Testing of Belts. sd ti nae aeg8 rele asrovieney Sug aah esos 169. The Sibley College Belt- testing Machine, . Grd deieysteeideenca acca 170. Methods of Making Tests and Computations... velages ava hina olen Ue wae Ges Gyo GGBO CHAPTER XI. HEAT AND THE PROPERTIES OF GASES AND VAPORS. T7i. _Purpose-6b Chapters ioccnecsou cia an ia aasuun demons ped an ROMS Eg 325 172. Notation and General Definitions.. ‘ samamanrete ae (325 173. The Heat Unit and the Mechanical Equivalent ak Heit; siegigase. 9328 174. Specific Heat. . ‘ Sud se teag ee ae eee sate at ahasnmedcae es B20 175. Boyle’s Law, Chivtles's Law, ele Spee denedee dete be oe das. alan 176. Specific Heat of Gases. . fe ee Laaeabe Saree i Seen Mea alias 1232S 177. Pressare and Volume Changes in Gases. a OR ease aes ee domuaseaie. 320) 178. Entropy of Gases. . fannie eG MEAN SEK We lad Cae ma ae ie Miemenaseng’y 392 179. Vaporization........ Hepresesri seme eedewaae ye 333 180. Superheating nil Specific Heats GE Vanes, Sayehet ws sear as oeees a. 335 181. Use of Steam Tables and Diagram. ........ 0.0... cece eee ne ete eens 337 182. BeeapaGr VEO aie re ee es ee os 340 xii TABLE OF CONTENTS ARTICLES 183. 184. 185. 186. 187. 188. 189. Igo. IgI. 192. 193. 194. 195. 196. 197. 108. 199. 200. 201. 202. 203. 204. 205. 207. 208. 209. 210. 211. 212. 213. 214. 215. 216. 217. 218. 2109. 220. 221. 222. 223. 224. The Temperature-Entropy Diagram for Steam........... 0.00. se se eeee Pressure and Volume Changes in Vapors...... 2.0.0. cceeeeceeeeeceeees Cyeles and ‘Their Efficiencies...6.660i, 2.426000 540g wee eave ee ce ae wa oH eed CHAPTER XII. THE MEASUREMENT OF LIQUIDS, GASES, AND VAPORS. General Considerations. ...... Classification of Available Methods... Methods Used.. aay ah 88 Sources of Error i in Ween. Submerged Orifices.. Value of the Coefident ot Dischatve.. Method of Calibrating an Orifice. . ; aeigin we Use of Orifices for Measuring Contauéus Flow. Measurement by Means of Nozzles.. The Venturi Tube or Venturi Meter fou Measoring Waters or Other Linuid. The Flow of Water over Weirs. . 2 Methods of Measuring the Henge over sr Walt: Conditions Affecting the Accuracy of Weirs. supduedee lens Effect of Disturbing Causes and Error in Weir Measurements. 2 Directions for Calibrating Weirs, Nozzles, and Venturi Meter............ Calibrated, Taiks ncicciw eo-ae tide de oa aces eave we laren gas Ze wise Bawa SPA MEER Sas ay excuse gene Gis ce ah Raulo ee Me cae Miele Mee eee adils aorta Yabeee we Water Meters. Hot-water Meter. The Calibration of Water Meters, eee Measurement of Average Velocttirs in Open ‘Channels aad Streams... Floats.. Sait eh Niet eee Stic ie chal Hydro- dgamnemneteis al Hydvometric Pendubums, Tachometers and Current Meters.. Calibration of Current Meters anal “Methods ae Detemsining Averene Velocity in Cross Sections. . The Pitot Tube. ae Measurement of rae Velodity’: in 1 Closed ‘Pines anid Conduits, Conditions Affecting the Value of the Constant C in the Best Bork of Pitot Tube.. Calibration of Pitot Tubes... Method of Making a ‘Tranense and Obteining the Duccoat or “Mean Valodiey Relation between Center Velocity and Mean Velocity.. . The Flow of Water in Pipes. . Measurement of Gases . Theoretical Velocity sal. Weight Discharged .. Value of the Pressure P2.. Formulas for the Flow of Air.. Value of the Coefficient of Discharge C. sa: GuadenGnMnd adaate cee BS shai Necessary Precautions in Orifice Methods, . Jeb ine apne Ga PAGE 341 343 346 356 357 357 360 361 362 365 366 368 369 372 378 - 379 380 380 383 383 385 394 396 397 397 400 402 404 405 406 407 409 41 412 412 417 419 421 422 424 429 TABLE OF CONTENTS xl ARTICLES ; PAGE ae “The GasOmeter ssa cs)0 5 22 sea nen ga cee wins subsrnswowma gee wes Oxlade we eins - 430 226. Gas Meters. i Wurpne die uemaedvenamerereseene, ABZ 227. Dry Meters ef ‘Laree ‘Capacity... 3 435 228. Calibration of Meters and the Raélative aeounaicy ‘of Wet ‘and Dry Meters 437 229. Gas-meter Capacities........ b tadeyke at anda saan ABT 230. Reservoir Method of of Measuring Mes or ther Bases, tiewidginwe sea: AST 231. Anemometers.. CLEAREST ee my ase ~430 232. Precautions Necessary in the ‘Use o Acremmeinaekarat MEoa eee AGE 233. Measurement of Gas by Means of Pitot Tubes.................0.05--+- 441 234. Measurement of Gas by Venturi Meter............ 0.020. ce cece rece eee 442 235. Measurement of Gas by estas cateeeewaueeye swe esouee Gere AAs 236. Measurement of Vapors. . é ue Junho Seater ee kote te ates eae “AAS 237. Determination of Weight of Linuld. aeeeee’ suite orade AAS 238. Measurement of Vapors by Means of Gece, General Gaz. ia 446 239. Method of Determining Theoretical Velocity for Steam from the Hen Chart 447 240. Value of the Pressure P2. . rail de uaitarasTelaui dew oN chatiage aa ast oh ek aaa. AAS 241. Weight -of Vapor Discharced... brits wea ee, bid Raa eR ews ee oa nae: “AAO: 242. Value of the Coefficient of Dischaere C. weeceeees 440 243. Approximate Formule for the Flow of Steam through Orilices, oo nln ASD 244. Measurement of Vapors by determining Average Velocity..........----- 453 245. Steam Meters. Nis Wiha etiadee ieee s We epee RE RL SB. ASS! 246. (Culormieene Meisitement of Vator. Laie MOG GA die mites aeemeaenoe ° AOS) 247. The Flow of Steam in Pipes. .......... 0. ce cece cece ete ete tenet ee es 463 CHAPTER XIII. COMBUSTION AND FUELS. 248. Combustion. . os Boe balalec BATA eset nue Mommie eartgkinenae Cues ee pair TAOS 240. Weight and Volume Relations... sie Gob caspian albehe ee apna Baa). “AOS 250. Heat of Combustion’ 6 alone Rowen: Bileetemaetenand eaeaee, 400 251. Combustion of Elementary Fuels. Shari setpeseasyeem! 4O6 252. Combustion of Hydrogen or of F els Confataine’ Epavoneny, Fipher and Lower Heating Value of Fuels. .... 0.0.0.0... cece eee eee eee es 467 253. i res 468 254. Calorimetry. . idol ao aine setae aay Randa eeding palody age da Sahai ieee dees, ee ecalan ee < AGO) 255. The Bomb. Calorimeter. es shwncelnt Asal Mra hiitek Adena piteanat | AL 256. Method of Opertings Bomb Culéaincter: siviatinase Mispiatiean eee apt ec ATS 257. Fayre wid Sitiernuinn Wael Calotinaton, .. .< iN eew eae seca aie sh ba! BBS 258. Carpenter Calorimeter......... ie thas otanpse rd odee Beever ABS 259. Calculations with the Carpenter Caloraster.., sates cit uchaseoene ne te cater, ASO 260. CT Eis rls e tines ce. eo dave wees aioe as bairaeats sa ccc anced 490 261. Continuous Calorimeters... .. 0.0.0.2. cece ee eect te ee eee tee tenes 4O4 262. Composition of FuelSs: Jsasues sc: teed ey ey eens ae Hae Dew e e Neale © 408 263. Se rear a nee ne rene een eee 501 264. Sampling. . Bite hie Sdn der a RR Ne BEE SETS TS ae Abe Nt beets SOL 265. Moisture.. CURLER ae MRE MEA MAAR ek cue a bare Uae “GOD 266. Valauilé Matter., SGALNd tye ee tay oeaeay Sa A ieeatiaeagineee ce Sam ANeeaiee hs GOS xiv TABLE OF CONTENTS ARTICLES PAGE _267. Determination of Fixed Carbon.......... 0.0... ce eee eee ee eee ees 504 268. The Ash Determination. . acdiceie. ste Cab en PAs Vion aie eae SRE Rea. OS 269. Determination of Heating Value. Eda MINS Th vada aad hata Mae ae es La OS 270. Chemical Analysis. . Dicamanounleeders vases Saarnicnnalnanaassenaans 507 271. Sulphur Detenaihe tion. at neice ini Meee de. AG OO 272. Methods of Computing the Heating Value ae Biiels.. Hee the dyes tes, | ISTO 273. Buying Coal by Analysis. . 4 512 274. Flue-gas Analysis and Combustion ‘Gelcalations, 2 ing BAO Roe nee ge Se) 275. Sampling. . i dra aise aco ftlaf Dra NNR RTiN a tal iain Ue ante aus ratio Ine eae 5 LS 276. Araly aie ol Bhiewas Da aer keen wae wie ee Ae etwas wea ae aN A Oye 277. Absorbing Power of ‘he: Pleawenties : . 520 278. General Forms of oe ae Apraraies ‘nil Method af Operation, 520 279. Elliot’s Apparatus. . Sah sit-in bane 4 eae Sa CAE oy et SoG Mapas. 522 280. The Oreat Apparatus, ae i ised sie tater ead: S24: 281. The Hempel Apparatus lor Gad pace ei iMate ee +525 282. Automatic Flue Gas Analysis Apparatus: CO» Racnideté., nama GSM 282. Assumptions and Accuracy of Flue Gas Analysis.. . + 530° 284. Losses in Commercial Combustion. The Computation ‘of the Flue Tose, - 531 285. Errors in the Flue-gas Calculations as “Above Carried Out.. pbadesay 598 286. The Excess or Dilution Coefficient... 2.0... 6... cece gece eee ee eee ee 538 287. Smoke Determinations...........-. 600 ee ee ee eee etre teen ee ce ees 540 ot y CHAPTER XIV. METHODS OF DETERMINING THE AMOUNT OF MOISTURE IN STEAM. 288. Meaning of the Term “ Quality of Steam”. . 2... oe eee eee 543 289. Importance of Quality Determinations............ 0... 0. css ee eeee ee es 544 290. Methods of Determining the Quality. ...... 0... 0.0... cece eee ee eee 544 291. Classification of Calorimeters... 2... 0.2... 0 ce cee cece tee eee eee 545 292. Use of Steam Tables. . sn sitibsicaas eee ate ie ele eMintindn shy etn SAS 293. Method of Obtaining a Sample wf Sicam, . ive nas oe wnameeer yes 540 294. Method of Inserting Thermometers............ 0.0.00 0e cesses ee ee ences S47 295. Condensing Calorimeters. . el iweid eee tar en | 848 296. Determination of the Water Equivalent af the Calorimeter. Rede d hades.” BAO 297. Forms of Condensing Calorimeters... .... 0.0... 6.0200 ce eee ee cece eee 550 298. Directions for Use of the Barrel Csladmeter., ee ee ee 299. The Continuous Jet Condensing Calorimeter. . sities ei iostinetiniee dy a veaat | 52 300. The Hoadley Calorimeter .. btaceywsiease aed w ea oes eae ts Gian or SRA 301. The Barrus Continuous Galismneter, wala wee pete ches Aiken RIGO: 302. Superheating Calorimeters. . oe Piva oa Pa RASA ck eane, 5 5B 303. The Barrus Superheating Caloeinaater, PRATER ES EE Ly yess, 55S 304. The Throttling Calorimeter . si sreseeerees 560 305. Graphical Solutions for Throttling Calorimeter Computations. wemieh) “568, 306. Limits of the Throttling Calorimeter . i iin ten daca I504 307. Throttling Calorimeter Constructed fronn Bipe Fittings. pakiedeane: (668 308. The Thomas Electric Superheating Calorimeter........ 2.6.2... 0.0.2... 566 ARTICLES a PAGE 309. Methods of Direct Determination of Moisture in Steam. The Separating Calorimeter .. sua dian durheeee coming eae SON 310. Formule for itise swith, the Separating Calorineeer. Rik Aenea eM ASTD 311. The Limits of the Separating Calorimeter. . ia age eR san tony S73 312. General Method of. Using the Separsiing Calorinaatetes seqeassyeemm S94 313. The Chemical Calorimeter. . sie Sea eassitnayaus sanceling due casa Boonen Mes aseeea AEUDS 314. Universal or Combination. Calorimeters. . seliesd) ual pehielts Bena eRe ete? SUT 315. Comparative Value of Calorimeters. Lael aan the ceils Bowen bin keen 3678) CHAPTER xv. THE ENGINE INDICATOR. 316. Uses of the Indicator. . die auns 317. Indicated and Dynainamende Power, ¢ sweats 318. Early Forms of the Steam-engine ae alata sivas aa dhretenteait 319. The Richards Indicator... .. 0.0... 0.0. cece cee ce ee ee ee eee 320. yaa erie dit tus. Fee aor avehanee pale Be shewan sina ipa ae ave ne dae 321. The Tabor Indicator. . 322. The Crosby Indicator. eee ce + 323. Indicators with Ficterneil: Springs: : Saar As 324. Indicators facAwimonia Machines... erat Entiat eae Vecdia asdee ag ke M602 a0. Small. Piston Indicators, «2 s30 ip ccc etalad Meee dota raw aneesesaeen 5O2 326. Large and Small Indicators. ...0.. 0.020600 sede e cece eee ee eee ee ees $93 327. The Continuous Indicator. . Sieor's air bites Jat eunein a om etn vee code ye wou < & 9/503 328. The Errors of the Piston Tachoaten oe Ae e Gee ves iewsy - SOL 329. Calibration of Indicator Springs. . : 597 330. Comparison of Dead-weight and Fluid-y ieee - Methods “of ‘Calbextion. ‘ and Hot vs. Cold Calibration. . 3 605. 331. Determination of Scale of Spring ‘andl ‘the jieaiiation ‘at Disevame Taken with Faulty Springs. ....-...+.+-ree- 608 332. Other Errors in. Tudicators au Methods at Detemining T. Their Magnitude 612 333- Method of, Attaching the Indicator.to the ee toners eiase 620° 334. Reducing-motions for Indicators......... ine or GY Sede a eee | OAT 335- Reducing Wheel. . fae Buatnacnaeeaiay (030 336. The Inidicatorcond and “Methods af Cornenting up.. 632 337- Electrical Attachments for Taking a Number of Cards at ithe Satiic ‘Tinie: 635 338. Care of the Indicator.. a vette eter eee ee en 636, 339. Diréctions for Taking Indicator Disgrams.. Neen cera dahe dy sand wit s | 1636 340., The Optical Indicator. . eh RD canes we ase she uageeanens oreresaevess 637° ' CHAPTER XVI. : THE INDICATOR-DIAGRAM. Og? 2 341. Definitions. . sti ee tee eae 342. Meagisewenisdvaw the Dingrenis’, i ahadem ign ater tidc shat perae zante wareey OMS 343. Indicated Horse Power.. gute diastase slabsateh tae loenet a anaes tiacnte cde Sekar’ OA 344. Form of the Trlieatordiaerat oe sek ous wide PRED Eee hoes acer eee OAS 3452 Methods of Drawing an Hyperbola... sok Iocithne ner edad a eh PS AB TABLE OF CONTENTS XV xvi TABLE OF CONTENTS ARTICLES PAGE 346. Construction of Saturation and Isentropic Curves for Steam............. 650 347. Clearance Determined from the Diagram. . z 652 348. Weight of Steam Accounted for by the Indicatordiagram. “The Didecam Water-rate. . igid ae eae oa! OSS) 349. The Diagram Woatet-exte for Malticylinder Engines. 26 did mae manera ae ea? - “O55 350. Approximate Formulas for the Diagram Water-rate . feo Heer Smareee atte) UO5O 351. Re-evaporation and Cylinder Condensation . ee faieoaaik ae OST 352. Various Forms of Actual Steam Engine Indicator diagrams wwieees O87 353. The Combining of Diagrams for Multicylinder Engines.. bee secrecy OO 354. The Actual Entropy Diagram for a Steam Engine.....................- 670 355. Steam-chest and Steam-pipe Diagrams............. 0. ee ee ee cece ee ee ee 675 356. Displaced Diagrams and Time Diagrams. . Barents he ood a ctenneea dite ee OO 357- Theoretical and Normal Gas Engine Uisaraeis sik asc seezacee. (078 358. The Actual Entropy Diagram for a Gas or a Mixture of ‘Cn wee. 685 CHAPTER XVII. THE TESTING OF STEAM BOILERS. 359. Methods of Testing Steam Boilers......... 0.0... 0... ce cece ee eee eee 691 360: Notes Omsthes Rules cs siatssee dis ddrie scee ki ics nettle Baca Eheencins eee Beem FIO CHAPTER XVIII. THE TESTING OF STEAM ENGINES, PUMPING ENGINES, AND LOCO- MOTIVES. 361. The Testing of Steam Engines. General Considerations and Definitions. 725 362. Rules for Conducting Steam-engine Tests, Code of 1902 ................ 732 363. The Testing of Pumping Engines (Steam ae Sliema Me ana ants PA, 364. The Testing of Locomotives.. é dk amageeiwmawemeen a 780 365. Calorimetric Methods of Bagiae Testing. Khe wee aaa meee FOO 366. Valve Setting on Steam Engines............. 0.0. 0c ce cece eee eee. 807 CHAPTER XIX. STEAM TURBINES. 367. General Considerations. ........ 0. eee cece cece eee ences. 808 368. Types of Turbines. . ‘ hohe ed ghee sear ae Meee WEEE E Re cee BOS 369. The Single-stage Tip titse ‘Tarbine, : Se Beis Sow ce guuadinaa | 4OLO 370. The Multi-stage (Compound) Fnpatae! Turbines » Silo @ataeuateame a. IO Le 371. The Multi-stage Reaction Turbine. : antecaenee, | GOES 372. Turbines of the Pelton Type (Onmi-dane ¢ or Bucket Thrhines.. exces 816 373. The Testing of Steam Turbines. . oR gid awe iia etuatese a: 2OLF, 374. Computations in Connection a Sirametuthine Tests,. Pouch weabahink o, CIO 375. Separation and Estimation of Steam-turbine Losses. tinh 822 376. Method of Correcting the Results of Steam-turbine ‘Tests fe Standand< or Guarantee Conditions. .. 0.0... 0... cc ce cece cece ce cece ce ueeeuecnues 824 TABLE OF CONTENTS CHAPTER XX. THE TESTING OF INJECTORS. ARTICLES 377- 378. 379. 380. 381. 382. 383. 384. 385. 386. 387. 388. 389. 390. 391. 392. 393 394- 395: 396. 397- 398. 399- 400. 4ol. 402. 403. 404. 405. 406 General Theory of the Instrument... 00.0... eee eee ce ee ee ee eee Practical Construction and Operation. brain asin urea. tine Sela derseceti tars Efficiency: of, Injectors,.o4 sac a oaeae ge apne oh ey Academe Mh Bes Pees Testing ‘of Injectors). sieeve ww eis ex 24454 Gah wx empiea re eh tee eee eR CHAPTER XXI. GAS ENGINES AND GAS PRODUCERS. Types of Gas aie Seeks Gas-engine Fuels.. Producer Gas. . Types of Gas Prodiicers,. Data Relating to Gases, Fuels, © etc. ., Generally ied 3 in > iiciency Geren tations. ee i eae Analysis at Fuel Gases and Determination at ‘Heating Value. Analysis of Exhaust Gases and Computation of Heat Lost in Tichaust,, Experimental Determination of Exhaust Loss. . Determination of the Quantity of Producer Gas Made per : Bound of ud, The Testing of Gas Producers and of Gas Engines...............-2+6-- Directions for Testing a Gas Producer. ........-. 0... cece cece eee eee? Heat Balance for a Gas Producer... ...... 0... cece cee cee nes Computation of Gas Producer Efficiency... ...... 0.0.0.0. ce cece ee ee ee es Testing of Gas Engines... : Saute hea Heat Balance for an Tntersall Gombiation: oe elcadaGhetea as The Computation of Gas-engine Efficiencies.............. 0. cece eee eee CHAPTER XXII. HOT-AIR ENGINES. eo ee ee ee sh ashen eee gona eondhaseaes The Ericsson Engine. . Mnideaaeae The Rider Engine.. The Vestine of Hot-oin Hasines wihya gas aay abs yavanna SP asec kee: 64 Computations and Report....... 2... cece cee cee eee teen ee be ee ne _CHAPTER XXIII. AIR-COMPRESSING MACHINERY. Types of Air-compressing Machinery.............. 00.20. ce cece eee cee Piston. Compressors; «sisi ciuse eyes ne eas gh RR Eee Oe EE Gee tee epg Rotary or Positive Blowers...... 0.0.00. ci ccc ce cee ce teens teenies Centrifugal or Volume Blowers... 0.2.0.0... 000 cc cece cece cece ee eees Turbine Compressors... ...... 00 cece cece cee ce ce ce cece ne ee aes PAGE 827 829 833 835 841 846 847 850 855 8638 877 883 884 891 801 899 903 905 920 g2r 925 926 929 933 934 938 938 942 943 045 xviii TABLE OF CONTENTS © ARTICLES PAGE 407. Injector Blowers. . 946 408. Hydraulic Compressors. Pin be ERG Mel ae aie WIE Heese 6 OAT 409. Physical (Characteristies of Air... dtehietid he sua beak BER ee Beene: AO 410. Determination of Humidity. . eg : 951 411. The Theoretical Work of Catnrscaseing “Air 054 412. Theoretical Compressor Horse Power . 206 veetpet 961 413. Effect of Clearance, Volumetric Efficiency, sind Slip. es 963 414. The Efficiency of Compression and the Methantialt Eiicienes: af THE THATCHER Rou. : The instrument is similar’ to ‘the straight slides rule previously: described,. the scale, on. the. ‘triangular bars corresponding to the bidlicaaly scale, that on ‘the cylinder to the sliding scale, and a triangular index J to the sliding pointer or runner. The method of using is essentially similar to that of the plain slide-rule, thus, to solve an example of the form a/b, put the runner J on the trian- gular scale at the number corresponding to a, bring the number corresponding to 6 on the cylindrical scale to register with a on the triangular scale; the respective numbers on the triangular scale and cylinder will in this position all be in the ratio of @ to b, and the quotient will be read by noting that number on the triangular scale which registers with 1 on the cylindrical scale. The product of this quotient by any other number will be obtained by reading the number on the triangular scale registering with the required multi- plier on the cylindrical scale. Fuller’s slide-rule, Fig. 3, consists of a cylinder C which can be moved up or down and turned around a sleeve which is attached to the handle H. A single logarithmic scale, 42 feet in length, is gradu- ated around the cylinder spirally, and the readings are obtained by means of two pointers or indices, one of which, A, is attached to the handle, and the other, B, to an axis which slides in the sleeve. This instrument is not well adapted for multiplying or dividing a series of numbers by a constant, since the cylinder must be moved for every result. The instrument is, however, very convenient for ordinary mathematical computations, and the results may be read accurately to four decimal places, 20 EXPERIMENTAL ENGINEERING The method of using the instrument is as follows: Call the pointer A, fixed to the handle, the fixed pointer, the other, BB’, which may be moved independently, the movable index. To use the instru- ment, as for example in performing the operation indicated by (a X b) + ¢, set the fixed pointer A to the first number in the num- erator, then bring the movable index B to the first figure in the de- nominator; then move the cylinder C until the second figure in the numerator appears under the movable index; finally read the answer on the cylinder C underneath the fixed pointer A. C . : D = rE PEEP te 8 ‘ H o Offa ) _R—=z-— == = Fic. 3. — THE FULLER SLIDE-RULE. In general, to divide with this instrument move the index B; to multiply, move the cylinder C; read results under the fixed pointer A. The movable index BB’ has two marks, one at the middle, the other near the end of the pointer, either of which may be used for reading, as convenient, their distance apart corresponding to the entire length of the scale on the cylinder C. 20. The Vernier. —The vernier is used to obtain finer sub- divisions than is possible by directly dividing the main scale, which in this discussion we will term the limb. The vernier is a scale which may be moved with reference to the main scale or limb or, vice versa, the vernier is fixed and the limb made to move past it. The vernier has usually one more subdivision for the same dis- tance than the limb, but it may have one less. The theory of the vernier is readily perceived by the following discussion. Let d equal the value of the least subdivision of the limb; let » equal the number of subdivisions of the vernier which are equal to — 1 on the limb. Then the value of one subdivision on the vernier is ie APPARATUS 2I. The difference in length of one subdivision on the limb and one on the vernier is g= a(* eee n )- n’ which evidently will equal the least reading of the vernier, and indicates the distance to be moved to bring the first line of the vernier to coincide with one on the limb. In case there is one more subdivision on the limb than on the vernier for the same distance, the interval between the graduations on the vernier is greater than on the limb, and the vernier must be behind its zero-point with reference to its motion, and hence is termed retrograde. The formula for this case, using the same notation as before, gives a(" * ‘) -—d= “ for the least reading. The following method will enable one to readily read any vernier: 1. Find the value of the least subdivision of the limb. 2. Find the number of divisions of the vernier which corresponds to a num- ber one less or one greater than that on the limb: the quotient obtained by dividing the least subdivision of the limb by this num- ber is the value of the least reading of the vernier. The following tules for reading should be carefully observed: Firstly. Read the last subdivision of the limb passed over by the zero of the vernier on the scale of the limb as the reading of the limb. Secondly. Look along the vernier until a line is found which coincides with some line on the limb. Read the number of this line from the scale of the vernier. This number multiplied by the least reading of the vernier is the reading of the vernier. Thirdly. The sum of these readings is the one sought. Thus, in Fig. 5, page 22, (1) the reading of the limb is 4.70 at a; (2) that of the vernier is 0.03; (3) the sum is 4.73. 21. The Polar Planimeter. — The planimeter is an instrument for evaluating the areas of irregular figures, and in some one of its numerous forms is extensively used for finding the areas of indicator and dynamometer diagrams. The principal instrument now in use for this purpose was in- vented by Amsler and exhibited at the Paris Exposition in 1867. This form is now generally known as Amsler’s Polar Planimeter; 22 EXPERIMENTAL ENGINEERING as most of the other instruments are modifications of this one, it is important that it be thoroughly understood. The general appearance of the instrument is shown in Fig. 4, from ‘which it is seen that it consists of two simple arms PK and FK, Fic. 4.— AMSLER’s POLAR PLANIMETER. « pivoted together at the point K. The arm PK during use is free to rotate around the point P, and is held in place by a weight. The arm KF carries at one end a tracing-point, which is passed around the borders of the area to be integrated. It also carries a wheel, whose axis is in the same vertical plane with the arm KF, and which may be located indifferently between K and F, or in KF produced. It is usually located in KF produced, as at D. The rim of this wheel is in contact with the paper, and any motion of the arm, except in the direction of its axis, will cause it to revolve. 0.010 In. @ @ D Fic. 5.— RECORD WHEEL, AMSLER POLAR PLANIMETER. A graduated scale with a vernier denotes the amount of lineal travel of its circumference. This wheel is termed the record-wheel, Fig. 5. The wheel D is subdivided into a given number of parts, APPARATUS 23 usually 100; the value of one of these parts is to be obtained by dividing the circumference of the rim of the wheel which is in contact with the paper by the number of divisions. This result will give the value of the least division on the limb; this is sub- divided by an attached vernier, in this particular case to tenths of the reading of the limb, so that the least reading of the vernier is one thousandth of that of one revolution. 22. Theory of the Instrument. — There are a number of methods of developing the theory of the planimeter, two of which will be given. The first of these is due to Mr. G. B. Upton, and was published in the “Sibley Jour- nal” for 1905-06. If a straight line mm move ina plane, it will generate an area. This area may be considered positive or negative according to the direction of motion of the line. In Fig. 6, let the paths of the ends m and x of the line be the perimeters of the areas A and B respectively, m and m travelling clockwise about these perimeters. The areas A, B, and C between A and B, are then generated by the line as shown by the arrows. Call- ing A a positive area, it is at once apparent that the net area generated is A+C—C-—B,orA —B. Fic. 6. The immediate corollary to this is that if the area B be reduced in width to zero, as in Fig. 7, i.e., becomes a line along which » travels back and forth, the area swept over will be A, around which m is carried. Analyzing a differential motion of the line from mn to m/n‘/ Fic. 7. 24 EXPERIMENTAL ENGINEERING (Fig. 8), it may be broken up into three parts: a movement perpendicular to the line, giving area Jdp; a movement in the direction of the length of the line, | 4 giving no area; and a movement of rotation about one end, giving as area (re Were ng en 4?d0. The total differential of area m’ dpi isthen dd =Idp + 4Pd0. 1 is always a constant during the operation of a eae planimeter, so that A= faanifap + ye fae. The common use of a planimeter is that typified in Fig. 7, where the tracing-point is carried around the area to be measured, while the other end of the tracing-arm is guided back and forth along some line. The guide-line is usually either a straight line or an arc of a circle. When the tracing-point has returned to its initial position the net angle turned through by the tracing-arm, or | dO, is zero. Hence A = / f dp simply. But f dp is the net distance the arm has moved perpendicular to itself. Call this R, and there results the equation of the planimeter A = IR. (1) The Zero-circle (see Fig. 9). —If the two arms be clamped so that the plane of the record-wheel intersects the centre P, and be revolved around P, the graduated circle will be continually travelling in the direction of its axis, and will evidently not revolve. A circle generated under such a condition around P as a centre is termed the zero-circle. If the instrument be unclamped and the tracing-point be moved around an area in the direction of the hands of a watch outside the zero-circle, the registering wheel will give a positive record; while if it be moved in the same direction around an area inside the zero-circle, it will give a negative record. This fact makes it necessary, in evaluating areas that are very large and have to be measured by swinging the instrument completely around P as a centre, to know the area of this zero-circle, which must be APPARATUS 25 added to the determination given by the instrument, since for such cases that circumference is the initial point for measurement. If the polar planimeter is so used ‘as to bring in the zero-circle, the case is that of Fig. 6, each end of the line describing an area. The tracing-arm sweeps over the difference between the area described by T (Fig. 9) and the circle made by G about Pasacentre. This difference-area is not, however, recorded by the plahimeter be- cause the f. 26 is now 2z instead of zero, Fic. 9. T making a complete revolution about P. The linear turning of the edge of the recording-wheel is f dp — 2xn, where 7 is the dis- tance from guided point G to the plane of the wheel. The effect on the reading is the same as if the radius PG were increased. The zero-circle is traced by T when the plane of W passes through P. Then f dp = 27m, and the wheel records zero. In practice the area described by the tracing-point is found by adding to the area of the zero-circle the area recorded by the wheel, taking account of the algebraic sign of the latter. The second demonstration of the theory of the planimeter is given by Professor A. G. Greenhill, published in his “ Differential and Integral Calculus,” p. 228. The planimeter in its most usual form, that invented by Amsler of Schaffhausen, consists of two bars OA, AP, jointed at A, and carrying in PA produced a small graduated roller R, with axis fixed parallel to PA (Fig. 10). To explain the theory of the instrument, let OA = a, AP =}, AR = ¢, and the radius of the roller = 7; and let the direction of a positive rotation of the roller, as marked by the graduations, be that of rotation on a right-handed screw on the axle of R, which would give a motion in the direction AR. Drop the perpendicular OJ from O on AR, and first suppose the joint A clamped. 26 EXPERIMENTAL ENGINEERING Then if J is in AR produced, a rotation of the instrument about O with angular velocity a will give to R the component velocities Or a in the direction JR andIR a perpendicular to JR, and there- fore compel the roller to turn with angular velocity at a ; but when J is on the other side of R, the angular velocity of the roller Mitpase 3 r dt Therefore, keeping A clamped, the roller will turn through an RI RI ‘ : : angle ey 0 or — — 6, according as J is not or is on the same side of R as A, when the instrument is rotated through an angle 0 about O. When 7 coincides with R, the roller will not turn, and then P describes a circle called the zero-circle, represented by the middle dotted circular line (Fig. 10) of radius V(OR? + RP) =V f@ —2 + b+ ePt =V(ELTPE + 2 bo). APPARATUS (27 Next unclamp the joint A, and clamp O; the roller will turn with db angular velocity — < ©? when the bar AP turns with angular r dt velocity e so that the roller will turn through an angle — <$ while AP turns through an angle ¢. Now suppose P to travel round the finite circuit PP,P,P, by a combination of the preceding motions in the following order: 1. Clamp the joint A, and move P to P,, and A to A,, on ares of circles with center O; then the roller will turn through an angle a 6, if the angle AOA, = POP, = 8. 2. Unclamp A and clamp O, and move P, to P, on the arc of a circle of center A,; then the roller will move through an angle € i a g, if the angle P,A,P, = ¢. 3. Unclamp O and clamp A, and move P, backwards to P, and A, to A on arcs of circles with center O, through an angle 0; then the roller will move through an angle — ae 6, if OI, is the per- pendicular from O on P,A. 4. Unclamp A and clamp O, and move P, to P on the arc of a circle of center A, and consequently through an angle 4; the roller will turn through an angle < $, which cancels the angle due to motion (2). In completing the finite circuit PP,P,P, the roller will then have turned through an angle (RI — Rr,)* But the area PP,P,P, = area PP,Q,Q = sector OPP, — OQQ,. = 4(OP? — OP,’)6. = 4(0A? + AP? + 2AI+AP — OA? — AP’ —2 Al,+ AP)O. = (AI — AI,)b0. = br times the angle (in cm.) turned through by the roller. -- 28 EXPERIMENTAL EN GINEERING The area PP,P,P, is therefore b times the travel of the circum- ference of the roller, so that by altering the length b by an adjust- ment on the instrument, the area can be read off in any required units. Any irregular area must be supposed to be built up of infinitesimal elements found in the same manner as PP,P,P,, and will be accu- rately measured by the roller when the point P completes a circuit of the perimeter, both joints being now free to turn simultaneously. If, however, the origin O is inside the area, the area of the zero- circle must be added to the reading of the roller. 23. Forms of Polar Planimeters. — Polar planimeters are made in two forms: 1. With length of tracing arm PA, Fig. to, fixed. 2. With length of tracing arm PA adjustable so that J, Eq. (1), may be varied. Since the area is in each case equal to the length of this arm multiplied by the lineal space R moved through by the record- wheel, we have in the first case, since / is not adjustable, the result always in the same unit, as square inches or square centimeters. In this case it is customary to fix the circumference of the record- wheel and compute the arm / so as to give the desired units. For example, the circumference of the record-wheel is assumed as equal to 100 divisions, each one-fortieth of an inch, thus giving us a distance of 2.5 inches traversed in one revolution. The diameter corresponding to this circumference is 0.796 inch, which is equal to 2.025 centimeters. The distance from pivot to tracing-point can be taken any convenient distance: thus, if the diameter of the record-wheel is as above, and the length of the arm be taken as 4 inches, the area described by a single revolution of the register- wheel will be 2.5 X 4 = 10.0 square inches. Since there were too divisions in the wheel, the value of one of these would be in this case 0.1 square inch. This would be sub- divided by the attached vernier into ten parts, giving as the least reading one one-hundredth of a square inch. By making the arm larger and the wheel smaller, readings giving the same units could be obtained. The formula expressing this reduction is as follows: Let d equal the value of one division on the record-wheel; let / equal the length of the arm from pivot to tracing-point; let A equal the area, which APPARATUS 29 must evidently be either 1, 10, or 1oo in order that the value of the readings in lineal measures on the record-wheel shall correspond with the results in square measures. Then by equation (1) we shall have, supposing 100 divisions, too dl = A; (2) A [S 100d) (3) _If A = 10 square inches and d = 4, inch, foe 2.5 If A = 10 square inches and d = ;; inch, poe — g The length of the arm from center to the pivot has no effect on the result unless the instrument makes a complete revolution around the fixed point E, in which case the area of the zero-circle must be considered. It is evident, however, that this arm must be taken sufficiently long to permit free motion of the tracing-point around the area to be evaluated. The second class of instruments, shown in Fig. 4, is arranged so that the pivot can be moved to any desired position on the tracing- arm KF, or, in other words, the length can be changed to give readings in various units. The effect of such a change will be readily understood from the preceding discussion. 24. The Mean Ordinate by the Polar Planimeter. —If we let p equal the length of the mean ordinate, and let Z equal the length of the diagram, Fig. 11, then the area A = Lp, but the area A = IR [Eq. (1), p. 24]. Therefore Lp = IR, from which 1+L=p-+R. (4) In an instrument in which / is adjustable, it may be made the length of the area to be evaluated. Now if / be made equal L, p=R. That is, if the adjustable arm be made equal to the length of the diagram, the mean ordinate is equal to the reading of the record- wheel, to a scale to be determined. 30 EXPERIMENTAL ENGINEERING The method of making the adjustable arm the length of the diagram is facilitated by placing a point U on the back of the planimeter at a convenient distance back of the tracing-point F and mounting a similar point V at the same distance back of the pivot C; then in all cases the distance UV will be equal to the length of the adjustable arm/. ‘The instrument is readily set by loosening the set-screw S and sliding the frame carrying the pivot and record- wheel until the points UV are at the respective ends of the diagram _to be traced, as shown in Fig. 11. Fic. 11.— METHOD oF SETTING THE PLANIMETER FOR FINDING THE MEAN ORDINATE. In the absence of the points U and V the length of the diagram can be obtained by a pair of dividers, and the distance of the pivot C from the tracing-point F made equal to the length of the diagram. In this position, if the tracing-point be carried around the dia- gram, the reading will be the mean ordinate of the diagram ex- pressed in the same units as the subdivisions of the record-wheel; thus, if the subdivisions of this wheel are fortieths of one inch, the result will be the length of the mean ordinate in fortieths. This distance, which we term the scale of the record-wheel, is not the distance between the marks on the graduated scale, but is the corre- sponding distance on the edge of the wheel which comes in con- tact with the paper. The scale of the record-wheel evidently corresponds to a linear distance, and it should be obtained by measurement or computa- tion. It is evidently equal to the number of divisions in the circumference divided by zd, in which d is the diameter, or it can be obtained by measuring a rectangular diagram with a length APPARATUS 31 equal to /, and a mean ordinate equal to one inch, in which case the reading of the record-wheel will give the number of divisions per inch. A diameter of 0.795 inch, which corresponds to a radius of one centimeter, with a hundred subdivisions of the circumference, cor- responds almost exactly to a scale of forty subdivisions to the inch, and is the dimension usually adopted on foreign-made instruments. 25. The Suspended Planimeter. — In the Amsler Suspended Pla- nimeter, as shown in Fig. 12, pure rolling motion without slipping Fic. 12. — SUSPENDED PLANIMETER. is assumed to take place. The motion of the record-wheel, not clearly shown in the figure, is produced by the rotation of the cylinder c in contact with the spherical segment K. The rotation of the segment is due to angular motion around the pole O, that of the cylinder c to its position with reference to the axis of the segment. This position depends on the angle that the tracing arm, ks, makes with the radial arm, BB, the area in each case being, as with the polar planimeter, equal to the product of the length of the tracing arm from pivot to tracing point multiplied by a constant factor. 26. The Coffin Planimeter and Averaging Instrument. — The instrument is shown in Fig. 13, from which it is seen that it consists of an arm supporting a record-wheel whose axis is parallel to the line joining the extremities of the arm. This instrument was invented by the late John Coffin, of Johnstown, in 1874. The record-wheel travels over a special surface; one end of the arm travels in a slide, the other end passes around the diagram. 27. Theory of the Coffin Instrument. — This planimeter may be considered a special form of the Amsler, in which the point P, see 32 EXPERIMENTAL ENGINEERING o | C) i: ——S Fic. 13.—- COFFIN AVERAGING INSTRUMENT. Fig. 14, page 33, moves in a right line instead of swinging in an arc of a circle, and the angle CPT is a fixed right angle. The differ- ential equation for area therefore is dA = Indé, (s) and the differential equation of the register becomes dR = ndo. (6) Hence, as in equation (1), A =I]1R. (7) That is, the area is equal to the space registered by the record-wheel multiplied by the length of the planimeter arm. APPARATUS 33 This instrument may be made to give a line equivalent to the mean ordinate (M. 0.) by placing the diagram so that one edge is in line with the guide for the arm; starting at the farthest portion of the diagram, run the tracing-point around in the usual manner to the point of starting, after which run the tracing-point perpen- dicular to the base along a special guide provided for that purpose until the record-wheel reads as at the beginning. This latter distance is the mean ordinate. Fic. 14.— CoFFIn AVERAGING INSTRUMENT. To prove, take as in Art. 24 the M. O. = 4, the length of dia- gram = L, the perpendicular distance = S. Then A = pL =IR. (8) Let C be the angle, EPT, that the arm makes with the guide, Fig. 14. In moving over a vertical line this angle will remain con- stant, and the record will be R=SsinC. (9) For the position at the end of the diagram snC=L +]; therefore R= SL +1. 34 EXPERIMENTAL ENGINEERING Substituting this in equation (8), pL = IR = ISL +1 = SL. Hence p = S, which was to be proved. From the above discussion it is evident that areas will be meas- ured accurately in all positions, but that to get the M. O. the base of the diagram must be placed perpendicular to the guide, and with one end in line of the guide produced. It is also to be noticed that the record-wheel may be placed in any position with reference to the arm, but that it must have its axis parallel to it, and that it registers only the perpendicular dis- tance moved by the arm. 28. The Willis Planimeter. — This planimeter is of the same general type as the Amsler Polar, but in place of the record-wheel for recording-arm it employs a disk or sharp-edged wheel free to slide on an- axis perpendicular to the tracing-arm. The distance moved perpendicular to this arm is read on the graduated edge of a triangular scale which is supported in an ingenious manner, as shown in the accompanying figure. The planimeter-arm can be adjusted as in the Amsler Planimeter so as to read the M.E.P. direct. An adjustable pin, EZ, is employed for the purpose of set- ting off the length of the diagram. Fic. 15. — THE WILLIS PLANIMETER. The mathematical demonstration is exactly as for the Amsler Planimeter, but in this case it is evident that the perpendicular distance which is registered on the scale is independent of the cir- cumference of the wheel. The only conditions of accuracy are, that the axis of the scale shall be at ‘right angles to the arm of the APPARATUS 35 planimeter, and that its graduations shall be equal to the area to be measured divided by the length of the arm. 29. The Roller Planimeter. — This is the most accurate of the instruments for integrating plane areas, and is capable of measuring the area of a surface of indefinite length and of limited breadth. This instrument was designed by Herr Corradi of Ziirich, and is manufactured in this country by Fauth & Company of Washing- ton, D.C. - Fic. 16.— ROLLER PLANIMETER. A view of the instrument is shown in Fig. 16. The features of this instrument are: first, the unit of the vernier is so small that surfaces of quite diminutive size may be determined with accuracy; secondly, the space that can be encompassed by one fixing of the instrument is very large; thirdly, the results need not be affected by the surface of the paper on which the diagram is drawn; and, fourthly, the arrangement of its working parts admits of its being kept in good order a long time. The frame B is supported by the shaft of the two rollers R,R,, the surfaces of which are fluted. To the frame B are fitted the disk A, and the axis of the tracing-arm Ff. The whole apparatus is moved in a straight line to any desired length upon the two rollers resting on the paper, while the tracing-point travels around the diagram to be integrated. Upon the shaft that forms the axis of the two rollers R,R, a minutely divided miter-wheel R, is fixed, which gears into a pinion R,. This pinion, being fixed upon the 36 EXPERIMENTAL ENGINEERING same spindle as the disk A, causes the disk to revolve, and thereby actuates the entire recording apparatus. The measuring-roller Z, resting upon the disk A, travels radially thereon in accord with the motion of the tracing-arm F, this measur- ing-roller being actuated by another arm fixed at right angles to the tracing-arm and moving freely between pivots. The axis of the measuring-roller is parallel to the tracing-arm F. The top end of the spindle upon which the disk A is fixed pivots on a radial steel bar CC,, fixed upon the frame B. 30. Directions for Care and Use of Planimeters. — The revolv- ing parts should spin around easily but at the same time accurately, and the various arms should swing easily and show no lost motion. The pitch-line of the record-wheel should be as close as possible to the vernier, but yet must not touch it; the counting-wheel must work smoothly, but in no way interfere with the motion of the record-wheel. Oil occasionally with a few drops of watch or nut oil. Keep the rim of the record-wheel clean and free from rust. Wipe with a soft rag if it is touched with the fingers. Prepare a smooth level surface, and cover it with heavy drawing- paper, for the record-wheel to move over. Stretch the diagram to be evaluated smooth. Handle the instrument with the greatest care, as the least injury may ruin it. Select a pole-point so that the instrument will in its initial position have the tracing-arm perpendicular either to the pole- arm or to the axis of the fluted rollers, as the case may be; for in this position only is the error neutralized which arises from the fact that the tracer is not returned to its exact starting-point. Then marking some starting-point, trace the outline of the area to be measured in the direction of the hands of a watch, slowly and carefully, noting the reading of the record-wheel at the instant of starting and stopping. It is generally more accurate to note the initial reading of the record- wheel than to try to set it at zero. Special Directions. —To obtain the mean ordinate with the polar planimeter, make the length of the adjustable arm equal to the length of the diagram, as explained in Art. 24, page 29, and follow directions for use as before. In using the Coffin planimeter, the grooved metal plate is first APPARATUS 37 attached to the board upon which the apparatus is mounted, as shown in the cut, page 32, being held in place by a thumb-screw applied to the back side. The diagram will be held securely in place by the spring-clips adja- cent, A and C, Fig. 13. The area may be found by running the tracing-point around the diagram, as described for the polar plani- meter, for any position within the limits of the arm. The mean ordinate may be found by locating the diagram as shown in the cut, with one extreme point in the line of the metal groove produced, and the dimensions representing the length of the diagram perpen- dicular to this groove. Start to trace the area at the point of the dia- gram farthest from the metal groove produced, as shown in Fig. 13; pass around in the direction of the motion of the hands of a watch to the point of beginning; then carry the tracing-point along the straight-edge, AK, which is parallel to the metal groove, until the record-wheel shows the same reading as at the instant of starting: this vertical distance is the length of the mean ordinate. 31. Calibration of the Planimeter.—In order to ascertain whether the instrument is accurate and graduated correctly, it is necessary to resort to actual tests to determine the character and amount of error. It is necessary to ascertain: 1. Whether the axis of record-wheel is parallel to axis of tracing-arm. 2. Whether the position of the tracing-arm vernier is correct, and agrees with the constants tabu- lated or marked on the tracing-arm. These tests are all made by comparing the readings of the instru- . ment with a definite and known area. To obtain a definite area, a small brass or German-silver rule, shown at L, Fig. 17, is used; this rule has a small needle-point near one end, and a series of small holes at exact distances of one inch or one centimeter from one another, starting at unit distance from the needle-point. To use the rule the needle-point is fixed on a smooth surface covered with paper, the planimeter is set with its tracing-point in one of the holes of the rule, and the pole-point fixed as required for actual use. With the tracing- point in the rule describe a circle, as shown by the dotted lines (Fig. 17), around the needle-point as a centre. Since the radius of this circle is known, its area is known; and as the tracing-point of the 38 EXPERIMENTAL ENGINEERING planimeter is guided in the circumference, the reading of the record- wheel should give the correct area. The method of testing is illustrated in Figs. 17, 18, 19, and 20. Figs. 17 and 19 show the method with reference to the polar plani- meter; Figs. 18 and 20 show the corresponding methods of testing the rolling planimeter. In Figs. 17 and 19, P is the position of the pole, B the pole-arm, and A the tracing-arm. In Figs. 18 and 20, B is the axis of the rollers and A is the tracing-arm. \ 7 Sy y \ < sw K_-- E Fic. 18. First Test. This operation, see Figs. 17 and 18, consists in locating the planimeters as shown, and then slowly and carefully revolving so as to swing the check-rule as shown by the arrow. Take readings of the vernier at initial point, and again on returning to the starting-point: the difference of these readings should give the area. Repeat this operation several times. Fic. 19. The instrument is now placed in the position shown in Figs. 19 and 20when the circle K appears on the right-hand side of the tracing- APPARATUS 39 arm A, and the passage of the tracer takes place in exactly the same way. If the results obtained right and left of the tracing-arm be equal to one another, it is clear that the axis ab of the measuring-wheel is parallel to the tracing-arm, and, this being so, the second test may now be applied. But if the result be greaéer in the first case, that is to say, when the circle lies to the left of the tracing-arm, the extremity a of the axis of the measuring-wheel must be farther removed from the tracing-arm; if it be Jess, that extremity must be brought nearer to the tracing-arm. Second Test. The tracing-arm is adjusted by means of the ver- nier on the guide and by means of the micrometer-screw, in accord- ance with the formule for different areas; it then is fixed within the guide by means of the binding-screw. ‘The circumferences of circles of various sizes are then traveled over with the check-rule, and the results thus obtained are multiplied into the unit of the vernier corresponding to the area given for that particular adjustment by the formula. The figures thus obtained ought to be equal to the calculated area of the circles included by the circumferences. If the results obtained with the planimeter fall short of the calculated areas I to the extent of — of those areas, the length of thetracing-arm, that is n to say, the distance between the tracer and the fulcrum of the tracing- I arm,must be reduced to the extent of ; of that length; in the opposite case it must be increased in the same proportion. The vernier on the guide-piece of the tracing-arm shows the length thus defined with sufficient accuracy, usually in half-millimeters, or about fiftieths of an inch, on the gauged portion of the arm. In order to test the accuracy of the readings according to the two methods just described, some prefer the use of a check-plate in lieu of the check-rule. The check-plate is a circular brass disk upon which are engraved circles with known radii. It is advisable to apply the second test also to a large diagram drawn on paper and having a known area. The instrument having been found correct or its errors determined, it may now be used with confidence. 40 EXPERIMENTAL ENGINEERING The following form is used to record the results of the test: DEPARTMENT OF EXPERIMENTAL ENGINEERING. SIBLEY COLLEGE. Calibration of .......... 00 eee e eee eters Planimeter. Length of Tracing Arm =J=........- Ithaca, N. Y.,......--.-000- 19.. Diameter of Register Wheel = d =..... Byveccicse a5 dioedé. Saag gs orice Fes oe a % Error from Calibration ...... 0.66.05 cee eee eee eter teen enter ete eee % Error from ld = 2... eee cece nee cee eee een eee tere e ete tes PARALLELISM. (First Test.) Instrument Area from N Instrument Area from No: Reading. Instrument. a Reading. Instrument. ACCURACY. (Second Test.) Length of Arm Tree t in Error, %. No nstrumen Area from Aetaal Avex SC Reading. Instrument. Too long. Too short. ZERO-CIRCLE. Instrument Reading. Area from Instrument. Guide Circle Dia. Area. Area of Zero-Circle. 32. Errors of Different Planimeters. — Professor Lorber, of the Royal Mining Academy of Loeben, in Austria, made extensive experiments on various planimeters, with the results shown in the following table: APPARATUS 41 The error in one passage of the tracer amounts on an average to the fol- lowing fraction of the area measured by — Area in — . Sue. Rolling Planimeter — The ordinary | Stark’s Linear| Suspended S Polar Plani- Planimeter. Planimeter. meter. Unit | Unit of Ver- i - 5 ‘ Be ad : s vat 2 if ver Unit of Ver- | Unit of Ver- of Vernier: niler: nier: e ¥ r1osq. mm. =| I sq. mm. = Isq.mm,. = niche sues Square | Square of fa ee a Be an Isq.mm. = | .1sq.mm. = em. |inches.| °°75 $4 1 ai8cs. TNs . areas Ans .0015 Sq. in. | .coor sq. in. 1 1 19 1-55 ts BEE B25 335 ooo 20 3-10) rte 00 Itit T0090 BOOT 5° 7-75 395 1853 2500 2050 BOOT Too | 15-50 rE ZEST F167 3353 30T0 2007 || 23209 T27E a253 7133 B128 7853 300 46 FO. eee ee ee ee fe eee ee ee eee Das B00 T0000 The absolute amount of error increases much less than the size of the area to be measured, and with the ordinary polar planimeter is nearly a constant amount. The following table is deduced from the foregoing, and shows the error per single revolution in square inches: Error in one passage of the tracer in square inches — Area in — . s Rolling Planimeter — Polar Planimeter. | Suspended Plani- Unit of Vernier: meter. Unit of ro sq.mm.= | Vernier: 1sq.mm.| Unit of Ver.:| Unit of Ver.: Square Square .ors sq. in. = .oors sq.in. | 1sq.mm. = | .1sq. mm. = cm. inches. é Z .0015 sq in. -ooor sq. in. 10 1.55 v.0207 0.0025 0.0025 0.00155 20 3-10 0.0216 0.0028 ©.0031 0.00158 5° 7395 0.0221 0.0031 0.0038 0.00258 100 15.50 0.0227 0.0035 0.0043 0.00310 200 31.00 v.0243 0.0043 0.0060 0.00403 300 AOBO: |b cikiaaseces 0.0049 0.0058 0.00465 These errors were expressed in the form of equations, as follows, by Professor Lorber. Let f equal the area corresponding to one complete revolution of the record-wheel; let dF be the error in area 42 EXPERIMENTAL ENGINEERING due to use of the planimeter. Then for the different planimeters we have the following equations: Lineal planimeter, dF = 0.00081 f + 0.00087 \/Ff; Polar planimeter, dF = 0.00126 f + 0.00022 »/ Ff; Precision polar planimeter, dF = 0.00069 f + 0.00018 /Ff; Suspended planimeter, dF =0,0006f + 0.00026 \/Ff; Rolling planimeter, dF = 0.0009 f + 0.0006 /Ff. 33- Special Planimeters. — These, much more complicated than those described, have been made for special purposes. Among these we may mention Amsler’s mechanical integrator for finding the moment of inertia, and Corradi’s mechanical integraph for draw- ing the derivative of any curve, the principal curve being known, thus giving a graphic representation of moment. rc aver i Ro ee A Fic. 21.— VERNIER CALIPER. 34. Vernier Caliper. — This instrument consists of a sliding-jaw, which carries a vernier, and may be moved over a fixed scale. The form shown in Fig. 21 gives readings to yy inchon the limb, and + this amount or to one-thousandth of an inch on the vernier. The reading APPARATUS 43 of the vernier as it is shown in the figure is 1.650 on the limb and 0.002 on the vernier, making the total reading 1.652 inches. This instrument is useful for accurate measurements of great variety; the special form shown in the cut has a heavy base, so that it will stand in a vertical position and may be used as a height-gauge. To use it as a caliper, the specimen to be measured is placed between the sliding-jaw and the base; the reading of the vernier will give the required diameter. 35. The Micrometer. — This instrument is used to determine dimensions when great accuracy is desired. It consists of a finely cut screw, one revolution of which will advance the point an amount equal to the pitch of the screw. The screw is provided with a gradu- ated head, so that it can be turned a very small and definite portion of a revolution. Thus a screw with forty threads to the inch will advance for one complete revolution #5 of an inch, or 25 thousandths. If this be provided with a head subdivided to 250 parts, the point would be advanced one ten-thousandth of an inch by the motion sufficient to carry the head past one subdivision. ; The micrometer is often used in connection with a microscope having cross-hairs, and in such a case represents the most accurate instrument known for obtaining the value of minute subdivisions; it is also often used in connection with the vernier. The value of the least reading is determined by ascertaining the advance due to one complete revolution and dividing by the number of subdivisions. The total advance of the screw is equal to the advance for one revolu- tion multiplied by the number of revolutions plus the number of sub- divisions multiplied by the corresponding advance for each. The accuracy of the micrometer depends entirely on the accuracy of the screw which is used. Accuracy of Micrometer-screws.— The accuracy attained in cutting screws is discussed at length by Professor Rogers in Vol. V. of “Transactions of American Society of Mechanical Engineers,” from which it is seen that while no screw is perfectly accurate, still great accuracy is attained. ‘The following errors are those in one of the best screws in the United States, expressed in hundred-thousandths of an inch, for each half-inch space, reckoned from one end. 44 EXPERIMENTAL ENGINEERING CORNELL UNIVERSITY SCREW. Total Errors in Hundred-thousandths of an Inch. No. of Space. | Total Error. No. of Space. | Total Error. No. of Space. | Total Error. ° ° 12 — 4 24 —8 I +6 13 = 25 —7 2 +8 14 — 9 26 =7) 3 +9 15 = 7 27 —9 4 +7 16 —I10 28 —9 5 +9 17 —1r 29 =] 6 Pe: 18 II 30 —7 7 +4 19 —I0 31 —6 8 +5 20 —I0 32 7 9 ° 2r —9 33 7 10 —I 22 II 34 -3 II a2 23 —10 35 —2 36 ° An investigation made by the author on the errors in the ordinary Brown and Sharpe micrometer-screw failed to detect any errors except those of observation, which were found to be about 4 hundred- thousandths of an inch for a distance equal to three-fourths its length. The errors in the remaining portion of the screw were greater, the total error in the whole screw being 12 hundred-thousandths of an inch. As the least reading was one ten-thousandth, the screw was in error but slightly in excess of the value of its least subdivision. In another screw of the same make the error was three times that of the one described. 36. The Micrometer Caliper consists of a micrometer-screw shown in Fig. 22, which may be rotated through a fixed nut. To the screw is attached an external part or thimble, which has a graduated edge subdivided into 25 parts. The fixed nut is prolonged and carries a cylinder, termed the barrel, on which are cut concentric circles, cor- responding to a scale of equal parts, and a series of parallel lines, which form a vernier with reference to the scale on the thimble, the least reading of which is one-tenth that on the thimble. If the screw be cut 4o threads per inch, one revolution will advance the point 0.025 inch; and if the thimble carry 25 subdivisions, the least read- ing past any fixed mark on the barrel would be one-thousandth of an inch. By means of the vernier the advance of the point can be read to APPARATUS 45 ten-thousandths of an inch. Thus in the sketches of the barrel and thimble scales in Fig. 22 the zero of the vernier coincides in the upper 1 Thimble Barrel sete 10 <—_—_-15 Thimble Fic. 22. — MICROMETER CALIPER. 27 4218 37.5781 FZ 294581 63s J 35.5468 S81 4843-83 516 HH sketch with No. 7 on the thimble; but in the lower figure the zero of the vernier has passed beyond 7, and by looking on the vernier we see that the 4th mark coincides with one on the thimble, so that the total reading is 0.007 + 0.0003, which equals 0.0073 inch. This number must be added to the scale-reading cut on the barrel to show the complete reading. The principal use of the instrument is for measuring external diameters less than the travel of the mi- crometer-screw, usually less than 2 inches in this type. The Sweet Measuring- machine. — The Sweet meas- uring-machine is a type of micrometer caliper arranged for measuring larger diam- eters than the one previously described. The general form of the instrument is shown in Fig. 23. The micrometer- screw has a limited range of motion, but the instrument is furnished with an adjustable tail spindle, which is set at each observation for distances in even Fic. 23.—SWEET’s MEasuRING-MACHINE. 46 EXPERIMENTAL ENGINEERING inches, and the micrometer-screw is used only to measure the fractional or decimal parts of an inch. The instrument is furnished with an external scale, graduated on the upper edge to read in binary fractions of an inch and on the lower edge to read in decimals of an inch; this scale can be set at a slight angle with the axis to correct for any error in the pitch of the micrometer-screw. The graduated Fic. 24. disk is doubly graduated, the right-hand graduations corresponding to those on the lower side of the scale. The scale and graduated disk are shown in Fig. 24,and the readings corresponding to the posi- from the ten-thread screw. in Fig. 25 is seen. tions shown in the figure are 0.6822, the last number being estimated. The back or upper side of the scale, and the left-hand disk, are for binary fractions, the figures indicating 32ds. Fig. 25 shows the arrangement of the figures. Beginning at o and following the line of cords to the right, the numbers are in regular order, every fifth one being counted, and coming back to o after five circuits. This isdone to eliminate the factor five In Fig. 24 the portion to the left of o APPARATUS 47 The back side of the index-bar is divided only to 16ths, the odd 32ds being easily estimated, as this scale is simply used for a “finder,” thus: In the figure the reading line is very near the }4 mark, or six 32ds beyond the half-inch. This shows that 6 is the significant figure upon this thread of the screw. The other figures belong to other threads. ‘The fig- ure 6 is brought to view when the reading line comes near this division of thescale. Bring the 6 to the front edge of the index-bar, and the meas- urement is exactly 42 without any calculation. Thus every 32d may be read, and for 64ths and other binary fractions take the nearest 32d bciow and set by the intermediate divisions, always remem- bering that it requires five spaces to count one. 37. The Cathetometer. — This instrument is used extensively to measure ¢ differences of levels and changes from a horizontal line. Primarily it consists of one or more telescopes sliding over a vertical scale, with means for clamping the telescope in various positions and of reading minute distances. The one shown in the engraving (Fig. 26) consists of a solid brass tripod or Fic. 26. — CATHETOMETER. 48 EXPERIMENTAL ENGINEERING base supporting a standard of the same metal, the cross-section of which is shown at different points by the small figures on the left. A sliding-carriage, upon which is secured the small level- ing instrument and which has also a vernier scale as shown, is balanced by heavy lead weights, suspended within the brass tubes on either side by cords attached to the upper end of the carriage, and passing over the pulleys shown at the top of the columns The column is made vertical by reference to the attached plumb-line. The movable clamping-piece below the carriage is fixed at any point required, by the screw shown at its side, after which the tele- scope can be raised or lowered by rotating the micrometer-screw attached to the clamp. The telescope is provided with cross-hairs, which can be adjusted by reversing in the wyes and turning 180 degrees in azimuth. The vertical scale is provided with vernier and reading-microscope. 38. Aids to Computation may be of three kinds: graphical, tabu- lar, or mechanical. Graphical methods for multiplying and dividing are usually given in treatises on geometry and are often sufficiently accurate for engi- neering purposes. Tabular aids are of two kinds: arithmetic, such as product, quo- tient and reciprocal tables, and logarithmic. The Rechentafeln of A. L. Crelle give one million products and will be found of much value in multiplication and division. ‘There are a number of good logarithmic tables, the standard being those of Vega, but any good four or five place table is sufficient for engineering work. As com- pared with graphical methods, the use of tables usually gives more accurate results with a smaller expenditure of time. Mechanical aids may be either computing machines or slide-rules. Several very excellent machines for multiplying and dividing which give accurate results to from 14 to 17 places are now made. Of these we may mention the calculating machine of George B. Grant of Boston; the Brunsvega of Grimme-Natlis & Co., Brunswick, Germany; the Comptometer, made by the Comptometer Co. of Chicago; and the adding machine made by the Burroughs Adding Machine Co., Detroit, Mich. Slide-rules of compact form but with APPARATUS 49 scales 4o feet in length, as designed by Thatcher or Fuller, can also be obtained of the principal stationers. . The processes of arithmetical calculation are almost entirely mechanical and involve no reasoning powers, yet they are of utmost importance in connection with experimental work. Unless the obser- vations of the experiment are correctly recorded and the necessary calculations for expressing the result made accurately, the experi- mental work will either be of no value, or, what is worse, positively misleading. For these reasons mechanical methods of computation, which involve at best small errors of known magnitude, are to be adopted whenever possible in reducing engineering experiments. The calculating machine is of special value, since if the mechanical processes are correctly performed the results will be given with accu- racy for the number of places within limits of the machine. Numer- ous calculating machines have been designed, the most noted of which is the ‘difference engine ” designed by Babbage in 1822 and on which the English Government expended more than $85,000 without bringing it to perfection. The first practical machine which accomplished anything worthy of permanent record was invented by Thomas de Colmar in 1850, and since that time numerous others, designed on similar lines, have appeared, of which should be men- tioned those invented by Tate, Burkhardt, Grant, Baldwin, and Odhner. The Grant machine, developed from 1874 to 1896, had reached a high degree of perfection, but is no longer sold. The Odhner or Brunsvega, referred to above, was shown at the World’s Fair in 1893, and differs from the Grant principally in the arrange- ment of parts, and in the fact that, as now sold, it possesses an index or counter to register the multiplier during the process of multiplication. In the Brunsvega the result is read on a series of wheels arranged on the same axis and so connected that ten revolutions of one of lower denomination are required for one of the next higher, etc., these wheels being readily and simultaneously set at zero. Series of digits from 1 to 9 are engraved in vertical parallel columns on a keyboard. By setting a lever opposite any number and turning a crank once, the number will appear on the result-wheels; by turning the crank twice, the result-wheels will show twice the number, etc. 50 EXPERIMENTAL ENGINEERING The shaft carrying the result-wheels can be shifted several places, so that it is possible to multiply by numbers of any denomination with less than ten revolutions of the crank. Subtraction is performed by starting with the larger number on the result-wheels and the smaller number on the keyboard and revolving the crank in the opposite direction from that required for addition. Dividing is done as a sort of continued subtraction, and is a more complicated operation. The machine is readily worked as a difference engine, thus permitting its use for computing complicated tables. A trial made in the U. S. Coast Survey of the relative rapidity and accuracy of the Grant calculating machine and a seven-place table of logarithms, in multiplying seven figures by seven figures and retaining seven figures in the result, showed the average time of multiplication with the machine as 56 seconds, and with logarithms 157 seconds; the number of errors in roo trials, with the machine 7, with logarithms 12. A trial made at Sibley College showed more favorable for the machine, probably because the observers were not so expert with logarithms. CHAPTER III. STRENGTH OF MATERIALS.— GENERAL FORMULZ. In this chapter a statement is made of the principal definitions and formule required for the experimental work in “Strength of Mate- rials.” The full demonstration of the formule and discussion of “Strength of Materials ”’ is to be found in “ Mechanics of Engineer- ing,” by I. P. Church, or by Mansfield Merriman; “Strength of Materials,” by D. V. Wood; ‘“‘ Materials of Construction,” by R. H. Thurston; ‘Materials of Construction,’ by J. B. Johnson; “The Testing of Materials of Construction,” by Unwin; “ Materialien- kunde fiir den Maschinenbau,” by A. Martens. The object of experiments in ‘“‘Strength of Materials” is to ascertain the resistance of different materials to stresses of various character; to find the characteristics distinguishing the different qualities, i.e., the good from the bad; to obtain experimental proof of laws deduced theoretically; and to discover the general laws of variation of properties as dependent on form, kind, and quality of material. The more general tests may be classified under the heads of: (1) tension; (2) compression; (3) transverse loading; (4) direct shear; (5) torsion; (6) impact; (7) repeated loading and unloading, or fatigue testing. 39. Definitions. — Stress is the force applied to a material. Séress, used in the sense of stress intensity, means force per unit area, or in English units, pounds per square inch. Stresses are fundamentally of two kinds: normal stress, conceived of as acting perpendicular to an imagined exposed section of the material; and tangential or shearing stress, acting parallel to an exposed section. Deformation is the distortion or change of shape of a material which accompanies the action of a stress. Deformation is mainly elongation or compression, if the stress is normal; or is angular, if the stress is a shear. (See Figs. 27 and 28.) With normal stress, unit 51 52 EXPERIMENTAL ENGINEERING deformation is measured in inches change of length per inch of original length, or in percentage of the original length. With shear stress angular deformation is measured in z (radian) measure. t | Ba/ ~ ~ Fic. 27.— NoRMAL STRESS Fic. 28.— SHEAR STRESS ANGULAR ELONGATION. DEFORMATION. Up to acertain point, called the elastic limit, stress and deformation are proportional to each other. If stressed within the limit, once or many times, the recovery to original size and shape is perfect when the load is taken off. If the stress exceeds the elastic limit the material experiences a permanent change of shape and no longer returns entirely to its original dimensions when the stress is removed. Such permanent deformation is called a seé. Many materials can be stressed far beyond the elastic limit, under- going during this stressing a considerable permanent deformation. Such materials are called ductile. The ultimate strength of a material is the maximum load the piece carries before breaking, divided by the original area. ‘The elastic limit strength is similarly found from the load at the elastic limit. The ductility, for tension loading, is the permanent set at the breaking load expressed as a percentage of the original length. The reduction of area is the per- centage difference between initial and final areas of section of the tension test piece, computed on the initial area. There are two important secondary quantities depending on both stress and deformation. The modulus of elasticity measures the stiff- ness of a material; it is equal to the ratio of stress to corresponding deformation, in unit quantities, under conditions of elastic loading. The resilience measures the work which the material can absorb in being stressed to a certain value. So long as the loading is elastic, the resilience of a piece is the half product of load and deformation of the piece. The modulus of resilience of the material is the work STRENGTH OF MATERIALS 53 done upon unit volume (one cubic inch) in stressing to the elastic limit; it is the half product of elastic limit strength by corresponding unit deformation. Working loads must always be within the elastic limit. The ratio of ultimate strength to working stress is called the factor of safety. It measures the safety of a structure against rupture. The ratio of elastic limit strength to working stress measures the safety for con- tinued operation of the structure. 40. Stress-deformation Diagrams are curves showing the relations between stress and deformation as load is applied to a piece of material. These diagrams show by inspection the general nature of a material. The diagrams are plotted with deformations as abscisse and stresses as ordinates. The general form of the diagram for certain typical materials is shown in Figs. 29 to 31. a So 8 Stress, pounds per square inch 8 8 3 oOo m o Deformation (elongation), inches per inch. Fic. 29. A, Fig. 29, marks the elastic limit found only in worked materials; B, Figs. 29 and 30, is the yield point, where the material suddenly begins to take large permanent set; C is the maximum and D the breaking load. The modulus of elasticity is the slope of the elastic line OA, Fig. 29. The modulus of resilience is represented by the 54 EXPERIMENTAL ENGINEERING area bounded by the axis of abscissas, the elastic line OA, and a per- pendicular dropped from A to the axis of abscissas. In commercial practice, B, the yield point, is taken as the practical elastic limit in the 60 000 50 000 Dotted curve magnified horizontally|100 times 40 000 a 30 000 20.000 a no wo Stress, pounds per square inch = 10.000 to -" — oe" 0,10 0.20 0.30 Deformation (elongation), inches per inch. Fic. 30. 40000 380 000 o 20.000 LZ 10000 ZL ic Stress, pounds per square inch 0.001 0.002 0.003 0.004 0.005 Deformation (elongation), inches per inch, Fig. 31. case of ductile materials; for brittle materials, as cast iron, either the breaking point, C-D (Fig. 31), or some arbitrarily chosen point on the curved load line, is taken as the working elastic limit. STRENGTH OF MATERIALS 55 41. Notation. — The notation used is similar to that of Church’s “ Mechanics,” and is as follows: Symbol. Quantity. General. Elastic limit. | Maximum. Todd Applied yi. ns ene gk sannedancnsios ice eos P Pt Pin SLTeSS INCE DSIEY aes seco etacaad menace ateCa wear aan p Pp pm Total elongation or compression ......... A v am Increment of elongation ................ Ad aus ae Relative elongation .................... é ef Em Bending or twisting moment ............ M M’ Mm Total angle of torsion ..............-..- a a’ am Relative shear distortion................ 0 o om Vertical shear, total ..............0.000. Jors Jt Jm ShearintenSityos.sm sans canes aeisntewatewtants 5 s! Sm Tension. Compression. Shear. Modulus of elasticity ................00. Et Ec Es Modulus of resilience .................. Ut Ue Us Area of section, Square inches: ...cs550eessa sa ndeenorsneeees paweRes FB Original, length; nchescemees sj +n2se sss eeeen see orate me ees es L Breadth Of Séetiony INCHESi joc. 2 5 so.eccee a caeioaace Fai ea ee soma vajetaedeae ema © b Height: of: SECHOH,, INCHES Ss 4. uiy dda daeay sivamtseinbelanase oycd.evanud atoneneiaueuasd. oe Boren h Diameter of a circular section, inches. .......... 00.0. eee eee eee eee d Radius of a circular section, Inches. ....0cccs00ceee coer ewes eee enn ce r Rectangular moment of inertia, about gravity axis of section............. I Polar moment of inertia, about gravity center of section................- Ip Maxinitim: fbré: distance. «:s.cccass aned ices seed oy sa ceed Meaweeeee x e 42. Formule for Tension Loading. — Since in a properly con- structed tension test-piece the stress is uniformly distributed, have » II ® Il es wee & l ee OI wrx byl ty l al so long as the loading remains elastic; U=he= 5) + Be we (r) (2) (3) (4) 56 EXPERIMENTAL ENGINEERING 43. Formule for Compression Loading. —For short columns, or those pieces which fail by crushing down without bending, the for- mule are the same as for tension: iP) p ee (5) en's (6) and, E.= ene a? (7) U,=tpe =4 (0) + Ep (8) For long columns, which fail because of the occurrence of bending, the formule in common use are four: The Rankine or Gordon: P Pn= Fpm*> (<+ mes); (9) The Ritter or Merriman: ’ p P P = Fp + (1+ moe : =); (10) The Johnson: ’ , p P p= Fp (x mie * Bg my The Euler: 47EI are a me P a ee m+ — RB In these formule P’, Pm, ~’, Pm have the meanings given in Art. 41, ~’ and p, referring here to the results of short column tests of the material; @ is a constant characteristic of the material; & is the radius of gyration of the cross-section of the column (# = =) mis a factor o end condition, having the numerical value 1 for “square- ended SONS, if for one “square end” and one “round end,” and 4 for a “round-ended” column. “Square ends” are those STRENGTH OF MATERIALS 57 which are rigidly held in line at the point of support; “round ends ” are free to hinge at the supports. It will be seen that formule (9) and (10) are convertible in form , by making @= a ; but (11) cannot possibly be converted into (9) or (0), and, given the same values of p’, EZ, / and k, (11) will give a lower value of P’ than (10). The Euler formula, while mathematically and experimentally true for very long columns, is d useless for any actual case, for it gives too high values of Pm if i is less than 150 to 200. The Mcrriman formula is valid over the 1 widest range of Z values, beginning with short columns and becom- ing tangent to the Euler at infinity. Suitable design values of p,, and # in the Rankine formula are as follows: Material. Pm. 8. Castiirons wna Gxmetero wesc eee clan bs wignlany ein ted 80,000 I-- 6,400 Wrought trons ssissxcrseney i eaamrrenyegee eden ee ees 36,000 I+ 36,000 Mild Steel a. ic cinaa caonass Oct AUR eM Gay Bee Re 50,000 I 50,000 Timber (oak or similar)... 2... 00.6 ce cece cece eee ee tees 7,500 I+ 3,000 44. Transverse Loading. — In pure transverse loading all the ex- ternal forces applied are perpendicular to the principal dimension —the length — of the material used. As a result of this loading the beam becomes curved. Layers of material parallel to the length of the beam are then distorted, those on the concave side of the beam being shortened and those on the convex side lengthened. The amount of this distortion or deformation is proportional to the dis- tance of a layer from the instantaneous center of curvature, and hence varies in a straight-line law with distance from one curved surface of the beam to the other (Fig. 32). Consequent on this deformation are set up internal tension and compression forces in the direction of the length of the beam. Because there is no external force in the direction of the length, the internal tension and compres- 58 EXPERIMENTAL ENGINEERING sion forces must balance each other. The only possible distribution of elastic stresses which satisfies the two conditions of (1) linear variation of intensity in passage from one curved Confer a surface to the other, and (2) zero resultant in Curyalture the direction of the length, is shown in Fig. 33. Both stress and deformation are zero at o, which can be shown to be the gravity axis of the cross-section. A surface through o and parallel to the two curved surfaces of the beam is called the neutral surface, and its intersection with a cross-section is the neutral axis of the section, The curve assumed by the neutral surface due to the forces acting is called the elastic curve. The internal stresses (Fig. 33) have a moment about o which balances the moment of external forces about the same point. Writing # for the stress in either outer fiber, e for the distance from neutral axis to outer fiber, 7 for the rec- Convex Surface = tangular moment of inertia of the cross-section pl e The moment M of external forces about any section is found by considering one or the other end of the eiauederoene beam from that section as a free body. ane FIG. 32. about the neutral axis, the moment M= M usually varies from point to point of : : Neutral Surface a beam, and as the cross-section dimen- 6S sions of the beam are usually constant, ad . ’ ens the only section at which p need be os} : : f : Cc Surf investigated is that corresponding to the eee ger maximum value of M. Corresponding to the value of p in outer fiber we need a value of «, the deformation. For this we measure the deflection of the beam at that same point of maximum moment at which we compute p. Text- books on “ Mechanics” (see tables below) give values of E in terms of the deflection A and load and dimensions of the beam. Using then pe the relation «= z the unit deformation ¢ is readily computed. Fic. 33. STRENGTH OF MATERIALS 59 By plotting the unit quantities p and ¢ against each other, the curve of the transverse test is the same as that of tension and compression tests, up to the elastic limit. Beyond that point the formule are no longer valid. It has been customary, however, to continue to use the elastic formule up to the failure of the beam. To distinguish the fictitious values of stress p so computed from a real stress in the material, a special name is given to the value of p at rupture — it is called the modulus of rupture. The modulus of ruptureis useful in the comparison of one material with another. In addition to the tension and compression stresses, transverse loading sets up in a beam a system of primary shears. These are called the horizontal and vertical shears. The horizontal shear occurs in surfaces parallel to the neutral surface; the vertical shear in planes perpendicular to the neutral surface. At any given point of a section the intensities of horizontal and vertical shear are identical. The shears are of zero intensity at either outer surface of the beam and of maximum intensity at the neutral surface. The variation of shear intensity across the section is parabolic if the sec- tion does not change in width. The éotal vertical shear at any section is the resultant of external forces perpendicular to the beam on one or the other side of that section. The intensity of primary vertical or horizontal shear stress at the neutral axis is area above the distance of the center Qm= — X +4 (or below) + X } of gravity of that area e neutral axis from the neutral axis. J = total vertical shear, b, = width of beam at the neutral axis, L = rectangular moment of inertia. For a rectangular cross-section this becomes 3a 2 bh’ Im or the intensity is fifty per cent greater than if the shear were uni- formly distributed over the cross-section. It is only in the case of 60 EXPERIMENTAL ENGINEERING I-beams or similar shapes that the primary shears have sufficient intensity to be a possible cause of failure of the beam. The following tables will be useful in working up tests: TABLE I. Sect} Rectangular Mo- Maximum Fiber eetion: ment of Inertia J. Distance e. Rectangle, width 6, depth #................ lz bh th Hollow rectangle. ... 6.0.0... cece cece ee eee pe (byh,? — b,h,*) th, Cliclé «: seagseiyaeevers pheeaKs Ree eae ty r : b Square with side 0 vertical................. Pz bt . Square with side b at 45°...............0.. qe 4 2/3 TABLE II. gy ¢ & @ S ad. ~ : a am oS o 7 a a Eq 88 G s 5 bs ‘a’ 9 28 33 a3 35/28 ES Ag 3¢e 556 | see Beam and Loading. = g = oe i as = 3 = j .4 ga | Sau | Bee = = = Bea | ESS Ba ay Ak Cantilever-beams fixed at one end. 1. Loaded at ex- PB treme end with Pl a ee 3 EI os P anywhere. a iP. (5) .d P \bs. : free end. , 2. Uniform load | Wi wi of intensity rae fed 3 zr * W at fixed 5) Ww (3) d o=W+ i. end. free end. oe, ar Pye Beams supported at both ends. : PB Zero at cen- 3. Single load P | Pi —— at fer “elees. (Ye tneenter, 7 atcenter.| 48 EI ee se a) Pp (334) d center. P+92 4. Uniform load Wi 5 Ww ead 8 384 ET 2 (55) Ww Gea A wo=W+l. at center. center. at ends. ne gf STRENGTH OF MATERIALS 61 45. Formule for Direct Shear. — This stress acts across a piece, without an arm, and tends to produce a square break. It is sensibly uniform over the section, so that S=s-F, (13) where S = total shear, s = intensity of stress, and F = area of section acted on. This stress produces in an element of material an angular distortion which is measured in z measure (see Art. 39 and Fig. 28), and is denoted by 6. The modulus of shear elasticity or modulus of rigidity = E, = (14) The modulus of resilience pate s~ y 2B The ultimate shear strength S,, can be obtained by direct experi- ments, using the specimen in the form of pins or rivets holding links together, the links being held and pulled in a tension-testing machine. A plate can be tested by forcing a punch through, measuring the compression load on the punch. The elastic strength and the angu- lar deformation carinot be measured in the direct testing, but may be accurately determined by tests in torsion, as described below. Direct shear tests must be very carefully conducted, making sure that no arm is given to the load, in order to be satisfactory. 46. Formule for Torsion. — The stress produced by torsion is primarily a shear stress on the elements of the material. The torque, or twisting moment (measured in inch-pounds), is applied in planes at right angles to the length of the specimen. The outer fibers of the specimen are twisted into helices, each making an angle with its initial position equal to the angular deformation 6. Any section of the specimen, distant 7 from the fixed end, is turned in its own plane through an angle a. This angle « is the external deformation which is measured in testing. From the arc which, in Fig. 34, is common to a and 6, we have arc = ea =/ tan 6. Since e and / do not change more than ;/5 % up to break, tan 6 = : (15) e ‘ j°% may be used throughout the test. If we consider the piece 62 EXPERIMENTAL ENGINEERING twisted through a certain value of a, the above equation shows that 6 varies with e; that is, d is zero at the center of the section, and increases in direct proportion to distance from the center. Within the elastic limit, stress and de- formation are proportional to each other. Hence, until the elastic limit is passed, the shear stress is zero at the center and increases in direct proportion to distance from the center to the maximum in the outer surface of the piece. This variation of stress is similar to that in transverse loading, and leads to a similar formula between moment and stress intensity in outer fiber, viz.: sa fe. (16) fi, Fic. 34. 7 . e Tu For a solid circular section e=r7 and Ip= — r*, so that 2 2 16 s=(—,).M=(—)M (=) (- 3) (27) where d = diameter of specimen. s’ 2 Us= Fs" =4 . , (18) E,= : along an elastic line. (19) The resilience of the test-piece is 4 M’a’. (20) As in transverse loading, these formule are derived for elastic loading and are not valid when the elastic limit is passed. Beyond the elastic limit the values of s computed from = are higher than the actual values of s in outer fiber of the test-piece. It is customary, however, to continue the computation by the elastic formulz up to the break. The value of s,, so computed is fictitious, and under the name of modulus of rupture in torsion loading is used in comparison of materials. STRENGTH OF MATERIALS 63 47. Secondary Stresses. —In the preceding sections the stresses described have been those which are directly produced by the loadings, z.¢., what may be called primary stresses. Of equal importance to or of greater importance Pp than these primary stresses in determining the yield and failure of materials (but not their elastic action) are the secondary stresses. In Fig. 35 is represented a body in tension. The P P 4 intensity of the primary stress is p= F’ P being Fe the total end force and F the area of the normal Sn section. If any other section than the normal be investigated, as F, at an angle @ with the normal, it will be found to carry a tension P’ and a shear S, so related that the resultant of P’ and S is P. P’ is less than P (equals P cos @) and F, is greater than F (equals F + cos @), so that the tension stress perpendicular to F, is much less than the stress F P p=-—onthe normal plane. But the shear stress, Ff Fic. 35. ge Sa 2M ead de Peeea aes (21) FF, F+cos@ F may be acause of failure. In general, with every tension or compres- sion stress of intensity p there goes at 6 degrees with the normal to p a shear stress of intensity s = p sin 0 cos 6. The expression sin 0 cos @ has a maximum value of 4 when @ = 45°. At 45° with 9, oe 2 For instance, in torsion loading of a soft steel the elastic failure in shear is found at about s = 15,000 pounds per square inch. If the same material be loaded in tension, the secondary shear will reach the critical intensity when the primary tension stress is 30,000 pounds per square inch. The material will break down sharply and begin to elongate; it will show slip lines of failure at 45 degrees to the axis. It is said the steel has passed its yield-point. The permanent sets in ductile materials in tension loading are due to failure occurring through the secondary stressing in shear. 64 EXPERIMENTAL ENGINEERING In compression loading of brittle materials the problem is com- plicated by a sliding over each other of surfaces under pressure. Friction then occurs. It can be shown that friction will change the angle of failure from 45 to 45 + é degrees where ¢ is the friction 2 angle for the material sliding on itself. For instance, cast tron on cast iron has a coefficient of friction corresponding to a friction angle of 20 degrees; the angle in cast iron “short columns ”’ between the planes of failure and the normal plane is oO 20 45° = = 55 2 ’ If the primary stress is a shear, the secondary stresses are tension and compression. The mathematical relation between the primary and the secondary stresses is mot the same as in the case above, with the direct stress as the primary stress. Consider first a unit cube of material (Fig. 36) to which a shear S, is applied. To balance this and prevent translation horizontally there must be on the opposite face an' equal and opposite stress S, But S, and S, constitute a couple; to balance the couple requires S; and S,. This shows that when shear is applied as a primary stress the shears come in pairs at right angles to each other. One cannot have a horizontal shear without having at any given point a vertical shear of the same intensity as the horizontal. Sie Si S Ss S4| x Sq 4 Fic. 36. Fic. 37. Now consider Fig. 37 made from Fig. 36 by cutting on a diagonal. S, and S; can be balanced by P; the value of P, by summation of vertical components, is Pan gee S=5)or Po on , sin 45° sin 45° (22) STRENGTH OF MATERIALS 65 If the area on which S, or S, is applied is F, the area over which P ae ea . = eee ; ; Si _ Ss is distributed is FV2. Theintensity of primary sheariss = 7 F the intensity of the secondary stress (compression in this case) is P S S es = = Es. 2 FV2 FsinasV2 F : If the other diagonal of the cube had been used, we should have found tension for the secondary stress. When the primary stress is shear of intensity s, there goes with it at 45 degrees a secondary stress (tension or compression) of intensity p = Ss. An application comes in'the case of brittle materials in torsion loading. The tensile strength of cast iron is about 20,000 pounds per square inch. If loaded in torsion, the iron will snap with a brittle fracture at s = 20,000 pounds per square inch, and the direc- tion of the break will be found to be at 45 degrees with the helices or planes perpendicular to the helices in which shear failure is found. The break has been due to the secondary stressing in tension. The real shear strength of a brittle material cannot be found from torsion loading. 66 EXPERIMENTAL ENGINEERING Fic. 38.— THe Emrery TESTING-MACHINE AT THE UNITED STATES ARSENAL AT WATERTOWN. CHAPTER IV. STRENGTH OF MATERIALS — TESTING-MACHINES. 48. Testing-machines and Methods of Testing. — The testing. machines consist essentially of, first, a device for weighing or regis- tering the power applied to rupture material; second, head and clamps for holding the specimen; third, suitable machinery for applying the power to strain the specimen; and fourth, a frame to hold the various parts together, which must be of sufficient strength to resist the stress caused by rupture of the specimen. Machines are built for applying tensile, compressive, transverse, and torsional stresses; they vary greatly in character and form; some are adapted for applying more than one kind of stress, while others are limited to a single specific purpose. In all machines the weighing device should be accurate and sufficiently sensitive to detect any essential variation in the stress, and every laboratory should be provided with means for calibrating testing-machines from time to time; the weighing system is usually independent of the system for applying power, although in certain early machines a single lever mounted on a fulcrum was used, as Fic. 39. — OLD Form. Fic. 40. — THURSTON, POLMEYER. shown in Figs. 39 and 40, and in which the power system and weigh- ing system were combined, the power applied being measured by multiplying the weight by the ratio of the lever-arms b/a. The power system, when independent of the weighing system, usually consists of a hydraulic press (Fig. 41), or screws driven by a 67 68 EXPERIMENTAL ENGINEERING train of gears (Fig. 42). The principal advantage of having the power system independent from the weighing system is due to the fact that under such conditions the stretching of the specimen, which almost invariably takes place, does not affect the accuracy of weighing. Fic. 41. — HypRAULIC PREss. Fic. 42. — Form or GEARING. The shackles or clamps for holding the specimen vary with the stress to be applied. The clamps for tension-tests usually consist of truncated wedges which are inserted in rectangular openings in the heads of the testing-machines, and between which the specimen is placed. The interior face of the wedges is, for flat specimens, plane or slightly convex and serrated, but for round or square specimens is provided with a triangle or V-shaped groove into which the head of the specimen is placed. When the strain is applied to the specimen the wedges are drawn close together, exerting a pressure on the specimen somewhat in proportion to the strain and often injurious to itsstrength. In many instances shackles with internal cut threads are used, into which specimens provided with a corresponding ex- ternal thread are screwed; this latter construction is much prefer- able to the former, though adding much to the expense of preparing the specimen. It is very important that the shackles should hold the specimens firmly and accurately in the axis of the machine and should not exert a crushing strain, which is injurious to the material. 49. General Character of Testing-machines. — Testing-machines are classified as vertical or horizontal, depending upon the position of the specimen; this, however, is not an important structural difference, STRENGTH OF MATERIALS — TESTING-MACHINES 69 although certain classes of machines are better adapted for the one method of testing than the other. Machines may also be classified as tension, compression, or transverse machines, depending upon whether they are better suited to apply one class of stresses than the other, but as the method of testing is generally dependent simply upon the method of supporting the specimen, this classification is of little importance structurally. Machines can perhaps be best classified by the form and character of weighing mechanism, it being generally understood that power may be applied through the medium of gears or by a hydraulic press, as desired, and with any class of machine. Under this classification we have: First, the simple-lever machines, forms of which have been shown in Figs. 39 and 4o, in which the power for breaking was obtained from the weighing mechanism. Fig. 43 shows a single-lever machine much used at the present time in England, in which the power is applied to the specimen at B, and the amount of stress is determined by the position of the jockey weight w and the amount of weight on the poise R. Fic. 43. — WICKSTEAD, MARTENS, Fic. 44. — THOMASSET. MICHAELIS, BUCKTON. A single-lever machine in which the lever is of the second order is shown in Fig. 44. The specimen is placed between the fulcrum and the weighing mechanism. The latter consists of a hydraulic cylinder with diaphragm and attached gauge, and is interesting as being the prototype of the Emery testing-machine. Second, differential-lever machines, one kind of which is shown 79 EXPERIMENTAL ENGINEERING in Fig. 45. This consists of a single lever with poise, to which the draw-head is connected by links placed at unequal distances from the fulcrum. A machine of this form was manufactured at one time by Riehlé Brothers.* d- —t Perry ii i ne ft Fic. 45. — RIEHLE HypRavtic. Fic. 46. — FarrBaNKS MACHINE. Third, compound-lever machines. ‘These have been much used in America for the last twenty years, and are manufactured by Riehlé Brothers, Olsen, and Fairbanks. In these machines power is usually applied by gearing; at least,such a construction is generally preferred in this country. The diagram, Fig. 46, shows the arrange- ment of levers adopted in the Fairbanks machine. The movable plate F of the machine, operated by the power device, either exerts a pull P or acompression C upon the stationary plate F’, F’, through the medium of the Hidi: Si metcieeuy Gee Ramen specimen, which in the first case is under tension, in the second case under compression. Fig. 47 shows arrangement of levers adopted in the Olsen and Riehlé machines, the action being otherwise the same as in the Fairbanks machine. * The forces acting in this machine can be represented by the following equation : EF Rd + we = fa (af —bg). STRENGTH OF MATERIALS — TESTING-MACHINES 71 Fourth, direct-acting hydraulic machines. Fig. 48 shows a simple form of a hydraulic machine, in which power is applied by liquid pressure to move the piston R, the specimen being located at s for tension and at a’b’ for compression. Machines of this kind have Fic. 48. — KELLoGG, ee been built of the very largest capacity; for instance, that designed by Kellogg at Athens, Pa., has a capacity of 1,250,000 pounds, and that at the Phoenix Iron Works has a capacity of 2,000,000 pounds, while one built by Professor Johnson at St. Louis has a capacity of about 750,000 pounds. In all these machines the stress is meas- ured by multiplying the readings of the gauge by a constant de- pending upon the area of the cylinder, the effect of friction being eliminated by keeping the piston rotating, or in other cases neglecting it or determining its amount, and correcting the results accordingly. Such machines are not adapted for accurate testing, but are suited for testing of a character which permits consider- able variation from the correct results. A modified form of the simple hydraulic machine was designed by Werder in 1852, having a capacity of 100 tons, the principle of Fic. 49. — WERDER, 1852. its construction being shown in Fig. 49. In this machine the line of action of the stress is in RF, while that of the resistance is in the line Ad which is to one side of RF. These forces are balanced by adjust- 7 2 EXPERIMENTAL ENGINEERING ing the weights on the scale-beam, thus providing means of weighing the force applied to the specimen. Fig. so is a sketch of the working parts of the Maillard machine, in which the weighing apparatus consists of a fluid which is put under D Zea —— (LLL Ver oe. Fic. 50. — MAILLARD. pressure by means of a diaphragm against which the stress applied to the specimen reacts. This force is measured on a hydraulic gauge similar in many respects to the weighing apparatus of the Emery testing-machine. Fifth, the Emery machine. The general principle of the Emery testing-machine is shown in Fig. 51. Power is applied by means of " AS oh ho F Fic, 51. — EMERY. the double-acting hydraulic press R so as to break the specimen either in tension or compression, as desired. The specimen is placed at s, and the stress transmitted is received, if in tension, first by the draw- head BB, thence transmitted to the draw-head B’B’, thence in turn to the fluid in the hydraulic support v through a frictionless dia- phragm, from which the fluid pressure is transmitted to the vessel with the smaller diaphragm d, the pressure of which is balanced and weighed on the weighing-scale w. If the specimen is in compression STRENGTH OF MATERIALS — TESTING-MACHINES 73 the force is transmitted by the draw-head BB to the bottom of the hydraulic support v, thus crowding the hydraulic support and its contents against the diaphragm, which in turn causes a liquid pres- sure which is measured on the weighing-scale as before. The springs which receive the pressure of the liquid are adjusted by screws 17, connected to the frame, and of sufficient strength to resist the greatest stress applied in compression. In order that the levers of a testing-machine may transmit the force to the weighing poise with as little loss as possible, and in such a manner that a large force can be balanced by a small weight, a knife-edge bearing is in nearly every case provided for each lever. The knife-edge as usually constructed is a piece of hardened steel with a sharp edge which is inserted rigidly in the weighing-lever and rests upon a hardened steel plate fastened to the fulcrum, although in some cases the positions of knife-edge and plate are reversed. The knife-edge should be as sharp as it can be made without crumbling or cutting the contact-plate, and it should be kept clean and free from dirt or rust in order to keep the friction at the lowest possible point. In practice the angle of the knife-edge is made from 30 to 110 degrees, depending upon the load. Machines of the type shown in Fig. 47 have been constructed in which the friction and other losses, as shown by trial, did not exceed 100 pounds in 100,000. The fulcrums for supporting the levers in the Emery testing- machine are thin plates of steel rigidly connected to both the lever and its support, as shown in Fig. 51. A flexure of the fulcrum-plates is produced by an angular motion of the levers; but as this motion in practice is small, and as the fulcrums are very thin, the loss of force is inappreciable and all friction is eliminated. The plate fulcrums also possess the advantage of holding the levers so that end motion is impossible, and thus preventing any error in weighing due to change of lever-arm. The peculiar form of the plate fulcrums is such as to be unaffected by dirt; furthermore in practice a higher degree of accuracy in weighing has been obtained than is possible with knife-edge levers. ‘The principal characteristics of the Emery machine are, first, the hydraulic supports, which are vessels filled with a liquid and having a flexible side, or diaphragm, which transmits the pressure to a similar support in contact with the weigh- 74 EXPERIMENTAL ENGINEERING ing apparatus. The detailed construction of a hydraulic support as used in a vertical machine is shown in Fig. 59, its method of opera- tion in Fig. 51. Second, the peculiar steel-plate fulcrums, which have been described. These, together with excellent workmanship throughout, have served to make the Emery testing-machine an instrument of precision with a greater range of capacity and an accuracy far superior to that of any other machine. > STM ta | NSA ENG oa bias SLL ath oe Cet — an A? Cf 7 Fic. 52. — Emery HorizontaL MacuHINE. Fig. 52 gives a perspective view of the Emery machine with the working parts marked the same as in the diagram. In this figure M is the pump for operating the hydraulic press, hh’ the connecting piping, 77 screws forming a part of the frame and used for adjusting the position of the press for different lengths of specimens and of sufficient strength to withstand the shock due to breaking; P is the weighing-case, which contains a very elaborate system of weights which can be applied without handling, as described in detail later. 50. Weighing System. — The weighing system in the present Engiish machines, and in former ones built in this country, con- sists of a single lever or scale-beam, along which can be moved a poise, and which can be connected by one or more levers to the test STRENGTH OF MATERIALS — TESTING-MACHINES 75 specimen. Such machines are objectionable principally on account of the space occupied. The weighing device in nearly all recent machines consists of a series of levers, arranged very much as in platform-scales, finally ending in a graduated scale-beam over which a poise is made to move. The machines are usually so constructed that the effect of the strain on the specimen is transmitted into a downward force acting on the platform, and the effect of a given stress is just the same as a given load on the platform. The weighing-levers usually consist of cast-iron beams carrying hardened steel knife-edges, which in turn rest on hardened-steel bearing plates. This is the system adopted by most scale-makers for their best scales. In the Emery testing-machines, which are especially noted for their accuracy and sensitiveness, the knife-edges and bearing plates are replaced by thin plates of steel, the flexibility of which permits the necessary motion of the levers. The weighing device should be accurate, and sufficiently sensitive to detect any essential variation in the stress. The amount of sensi- tiveness required must depend largely on the purposes of the test. An amount less than one.tenth of one per cent will rarely make any appreciable difference in the result, and probably may be taken as the minimum sensitiveness needed for ordinary testing. Means should be provided for calibrating the weighing device. This can be done, in the class of machines under consideration, by loading the lower platform with standard weights and noting the corresponding readings of the scale-beams. Testing-machines may be calibrated with a limited number of standard weights by the use of a test- specimen, which is not to be strained beyond the elastic limit. The weights are successively added and removed, and strain is maintained on the test-piece, equal to the reading on the calibrated portion of the scale-beam. 51. The Frame.— The frame of the machine must be sufficiently heavy and strong to withstand the shock produced by a weight equal to the capacity of the machine suddenly applied. The weighing levers must sustain all the stress or force acting on the specimen, without sufficient deflection to affect accuracy of the 76 EXPERIMENTAL ENGINEERING weighing, and the frame must be able to sustain the shock conse- quent upon the sudden removal of the load, due to breaking, without permanent set or deflection. 52. Power System. — The power to strain or rupture the speci- men is usually applied through the medium of a train of gears or by a hydraulic press, operated by power or hand. The hydraulic machine is very convenient when the stress is less than 50,000 pounds; but if there is any leakage in the valves, the stress will be partially relieved the instant the pump ceases to operate, and difh- culty may be experienced in ascertaining the stretch for a given load. 53. Shackles. — The design of shackles or clamps for holding the specimen varies with the strain to be applied. Clamps for tension- tests usually consist of truncated wedges which are inserted in rectangular openings in the heads of the testing-machines and between which the specimen is placed. The interior face of the wedges is for flat specimens plane and serrated, but for round or square specimens it is provided with a triangular or V-shaped groove, into which the head of the specimen is placed. When the strain is applied to the specimen these wedges are drawn closer together, exerting a pressure on the specimen somewhat in proportion to the strain and often injurious to its strength. In tensile testing it is essential to the correct determination of the strength of the specimen that the force shall be applied axially to the material; in other words, it shall have no oblique or transverse component. This requires that the wedge-clamps shall be parallel to the specimen, and that the heads which contain the clamp shall separate in a right line and parallel to the specimen. This construction is well shown in the following description of the clamps used in the Olsen and Riehlé testing-machines. A plan and section of the draw-heads used with the Olsen machine are shown in Fig. 53. AA is a counterbalanced lever used to prevent the wedges falling out when the strain is relieved; BB, are screws connected to plungers for adjusting the space into which the wedge-clamps are drawn. A lateral motion of the speci- men is obtained by unscrewing on one side and screwing up simul- taneously on the other side: this adjustment is of advantage in some instances in centering the specimen. STRENGTH OF MATERIALS — TESTING-MACHINES 77 3 [O (EE © [elfiis) ne SNH WW mia: UN Wr ee : y SS SY VS ie YY Fic. 53. — DRAW-HEAD OLSEN MAcHINE. The clamps used by Riehlé Brothers for holding flat specimens are shown in Figs. 54 to Fig. 56, as follows: Fig. 55 is a plan view of the draw-head, with specimen in posi- tion: CC, curve-faced wedges; D, specimen; A, draw-head; and BB, tension-rods. Fig. 56 is a sectional view of same. Fig. 54 is a separate view of the wedge. The inclinations of the outside surfaces of the wedges are exaggerated in the drawings, so as distinctly to show the con- struction. Wedges have been made with spherical backs, and a portion of the draw-heads mounted on spherical surfaces in order to insure axial strain. Special holders into which screw-threads have been cut have been used with success, and in many instances the specimens 78 EXPERIMENTAL ENGINEERING have been fastened to the draw-heads by right and left threaded screws. The wedge-fastening is the most widely used in American com- mercial testing. It has, however, been found impossible to get a really accurate centering and uniform stressing with this fastening, and in any work of importance screw-ends must be used on the test- piece, with ball and socket supports. Fic. 54. Fic. 55. Fic. 56. 54. Specifications for Government Testing-machine. — The large machine in use by the United States Government at the Watertown Arsenal was built by Albert H. Emery. The machine is not only of large capacity, but is extremely delicate and very accurate. A perspective view of the machine is shown in Fig. 38. The requirements of the United States Government as expressed in the specifications, which were all successfully met, were as follows: 1st. A machine with a capacity in tension or compression of 800,000 pounds, with a delicacy sufficient accurately to register the stress required to break a single horse-hair. 2d. The machine should have the capacity of seizing and giving the necessary strains, from the minutest to the greatest, without a large number of special appliances, and without special adjustments for the different sizes. 3d. The machine should be able to give the stresses and receive the shocks of recoil produced by rupture of the specimen without injury. The recoil from the breaking of a specimen which strains the machine to full capacity may amount to 800,000 pounds, instantly -STRENGTH OF MATERIALS — TESTING-MACHINES 79 Fic. 57. — LONGITUDINAL SECTION oF WEIGHING HEap, Emery TEstinc MAcHINE. \\ | Mn Mm i —_t Ba 80 EXPERIMENTAL ENGINEERING applied. The machine must bear this load in such a manner as to be sensitive io a load of a single pound placed upon it, without readjustment, the next moment. 4th. The parts of the machine to be at all times accessible. sth. The machine to be operated without excessive cost. Description of Emery Testing-machine. — These machines are now constructed by Wm. Sellers & Co. of Philadelphia, under a license from the Yale & Towne Mfg. Co. of Stamford, Conn. The following description will serve to explain the principle on which the machine acts: The machine consists of the usual parts: 1. Apparatus to apply the power. 2. Clamps for holding the specimen. 3. The weighing device or scale, 1. The apparatus for applying power consists of a large hydraulic press, which is mounted on wheels as shown in the engravings, Fig. 38 and Fig. 57, and can be moved a greater or less distance from the fixed head of the machine. Two large screws serve to fix or hold this hydraulic press in any position desired, according to the length of the specimen: and when rupture is produced the shock is received at each end of these screws, which tend to alter- nately elongate and compress, and take all the strain from the foundation. 2. Clamps for holding the specimen. These are peculiar to the Emery machine, and are shown in Fig. 57 in section. This figure also shows a section of the fixed head of the machine, and a portion of the straining-press, with elevation of the holder for the other end of the specimen. The clamps, numbered 1484 in Fig. 57, are inserted between two movable jaws (1477), which are pressed together by a hydraulic press (1480), resting on the fixed support (1476). By this heavy lateral pressure force equal to 1,000,000 pounds can be applied to hold the specimen. The amount of this force is shown by gauges connected to the press cylinder, and can be regulated as required. For the vertical machines these shackles or holders are arranged so as to have sufficient lateral motion to keepin the line of the test-piece. 3. The weighing device. This is the especial peculiarity of the Emery machine: instead of knife-edges, thin plates of steel are used STRENGTH OF MATERIALS — TESTING-MACHINES 81 which are flexed sufficiently to allow the necessary motion of the levers. The steel used varies from 0.004 to 0.05 inch thick, and the blades are so wide that the stress does not exceed 40,000 to 60,000 pounds per square inch. Fig. 58 shows the form of fulcrums used for light forces when the steel fulcrums are in tension:: Fic. 58.—Emery Knire Epce Furcruu, Lhe method of measuring the load is practically that of the hydraulic press reversed, but instead of pistons, diaphragms having very little motion are used. Below the diaphragm is a very shallow chamber connected by a tube to a second chamber covered with a similar diaphragm, but of a different diameter. Any downward pressure on the first diaphragm is transmitted to the second, giving a motion inversely as the squares of the diameters. This latter motion may be farther increased in the same manner, with a corre- sponding reduction in pressure, or it may at once be received by the system of weighing levers. The total range of motion given the first diaphragm in the 5o-ton testing-machine is gyqu5q Part of an inch, but the indicating arm of the scales has a motion of y$5 of an inch for each pound. This increase of motion and corre- sponding reduction of pressure is accomplished practically without friction. The above mentioned parts may be understood from a study of Figs. 59, 60, and 61. Fig. 59 shows the base frame and abutments of the vertical machine. The diaphragm is placed between the frames EE, the whole being supported on springs d, so as to have an initial tension on the test piece. The pressure on the diaphragm between the frames EE is com- municated by the tube f to a similar diaphragm in communication with the weighing-levers, Figs. 60 and 61. In case a diaphragm is used it is placed beneath the column A, Fig. 61; the motion of the column A is communicated to the scale-beams by a system of levers as shown. The scale-beam mechanism of the testing-machine is so arranged 82 EXPERIMENTAL ENGINEERING that by operating the handles on the outside of the case the weights required to balance: the load can be added or removed at pleasure. The device for adding the weights is shown in Fig. 62. a, 5, ¢, d, e, and fare the weights, which are usually gold-plated to prevent rust- ing. ‘These when not in use are carried on the supports A and B- Fic. 59. — THE BASE FRAME AND ABUTMENTS. by means of pins. When needed, these supports can be lowered by the outside levers,.-and as many weights as are needed are added to the weighing-poise CD. 55. Riehlé Brothers’ Hydraulic Testing-machines. — The testing- machines built by Riehlé Brothers of Philadelphia vary greatly in principles and methods of construction. In the machines built by this firm, power is applied either by hydraulic pressure or by gearing, and the weighing device consists of one or more levers working on steel knife-edges, as in the usual scale construction. STRENGTH OF MATERIALS — TESTING-MACHINES 83 Fic. 60. — SCALE-BEAM AND CASE. te W 4 = $ — ae SEO = I : SS L - mt S] | | Fic. 61. — Bram ror PLATFORM-SCALE. 84 EXPERIMENTAL ENGINEERING Machines have been built by this firm since 1876. The form of the first machine constructed was essentially that of a long \- — e A == AN A TAT a va WZ y-/" DZ \_] S oe a LY LE } Se Fic. 62.— DEviIcE For ApDD- ING AND REMOVING WEIGHTS. DAT] LA 2 “a weighing-beam suspended in a frame and connected by differential levers to the specimen, the power being applied by a hydraulic press. The latter forms are more compact. The standard hy- draulic machine as constructed by this firm is shown in Fig. 63. In this machine the cylinder of the hydraulic press, which is situated directly beneath the specimen, is movable, and the piston is fixed. This motion is transmitted through the specimen, and is resisted by the weighing levers at the top of the ma- chine, which are connected by rods and levers to the scale-frame. Two plat- forms connected by a frame are carried by the weighing levers: the upper one is slotted to receive the wedges for holding the specimen; the lower one forms a plane table. The intermediate platform, or draw-head, can be adjusted in differ- ent positions by turning the nuts on the screws shown in the cut. For tension- strains the specimen is placed between the upper and intermediate head; for compression it is placed between the intermediate and lower heads. An attachment is often added to the lower platform, so that transverse strains can be applied. The hydraulic cylinder is connected by two screw rods to the in- termediate platform or draw-head, and when it is forced down- ward by the operation of the pump this draw-head is moved in the same direction and at the same rate. 56. Riehle Power Machines. — The machines in which power is applied by gearing are now more generally used than hydraulic Fic. 63. — RIEHLE TESTING-MACHINE FOR TENSION, COMPRESSION, AND ‘TRANSVERSE LOADING. FRONT VIEW. TM Ld CTT Ink Fic. 64. — RIEHLE TESTING-MACHINE FOR TENSION, COMPRESSION, AND TRANSVERSE LOADING. BAcK VIEW. 86 EXPERIMENTAL ENGINEERING machines. Fig. 64 shows the design of geared machine now built by Riehlé Brothers. In this machine both the gearing for applying the power and the levers connected with the weighing apparatus are near the floor and below the specimen, thus giving the machine great stability. The heads for holding the specimen are arranged as in the hydraulic machine, and power is applied to move the intermediate platform up or down as required. The upper head and lower platform form a part of the weighing system. The intermediate or draw-head may be moved either by friction-wheels or spur-gears at various speeds, which are regulated by two levers convenient to the operator standing near the scale-beam. The poise can be moved backward or forward on the scale-beam, without disturbing the balance, by means of a hand-wheel, opposite the fulcrum on which the scale-beam rests. The scale-beam can be read to minute divisions by a vernier on the poise. 57. Olsen Testing-machine. — The machines of Tinius Olsen & Co. of Philadelphia are all operated by gearing, driven by hand in the machines of small capacity, and by power in those of larger capacity. The general form of the machine is shown in Fig. 65, from which it is seen that the principles of construction are the same as in the machine last described. The intermediate platform or draw-head is operated by four screws instead of by two, and there is a marked difference in the arrangement of the weighing-levers and in the gearing. The machine can be operated at various rates of speed in either direction, and is readily controlled by convenient levers. 58. Thurston’s Torsion Testing-machine. — Both the breaking- strength and the modulus of rigidity can be obtained from the auto- graphic testing-machine invented by Professor Thurston in 1872. In this machine, Fig. 66, the power is applied by a crank at one side, tending to rotate the specimen, the specimen being connected at the opposite end to a pendulum with a heavy weight. The resistance offered by the pendulum is the measure of the force applied, since it is equal to the length of the lever-arm into the sine of the angle of inclination, multiplied by the constant weight P, STRENGTH OF MATERIALS — TESTING-MACHINES 87 Fig. 67. A pencil is carried in the axis of the pendulum produced, and at the same time is moved parallel to the axis of the test-piece by a guide curved in proportion to the sine of the angle of devia- tion of the pendulum, so that the pencil moves in the direction of the axis of the specimen an amount proportional to the sine of this Fic. 65.—THE OLSEN TESTING-MACHINE, FOR TENSION, COMPRESSION, AND TRANSVERSE LOADING. angle. A drum carrying a sheet of paper is moved at the same rate as the end of the specimen to which the power is applied. Now if the pencil be made to trace a line, it will move a distance around the drum which is equal to the angle of torsion (a) expressed in degrees or z measure, and it will move a distance parallel to the 88 EXPERIMENTAL ENGINEERING li i ng \\ ee ei ‘ai Hi Wf Ta ren ue REN AW h\ Fic. 66. — THuRSTON’s TORSION TESTING-MACHINE : ee P seat L TEST-PIECE Fic. 67. STRENGTH OF MATERIALS — TESTING-MACHINES 89 axis of the test-piece proportional to the moment of external forces, Pa. The diagram, Fig.67, from Church’s “‘ Mechanics of Engineering,” shows the working portions of the machine very clearly. In the figure, P is the pendulum, the upper end of which moves past the guide WR, and is connected by the link FA with the pencil AT. The diagram is drawn on a sheet of paper on the drum, which is rotated by the, lever 6. The drum moves through the angle a, relatively to the pendulum which moves through the angle 6. The test-piece is inserted between the pendulum and drum. The value of a in degrees can be found by dividing the distance on the diagram by the length of one degree on the surface of the paper on the drum, which may be found by measurement and calculation. Application of the Equations to the Strain-diagram. —For the breaking-load, equation (16) of Chapter III, may be written. ae, é The external moment M equals Pr sin 8, in which P is the fixed weight, r the length of the pendulum, £ the angle made with the vertical. Hence Pr sin 8 = sIp = @. In this equation P and ¢ are constant, and depend upon the machine; Ip and e are constant, and depend upon the test-piece. Sin f is the ordinate in inches on the autographic strain-diagram, and can be measured; knowing the constant, s may be computed from s = Pre sin 8 + Ip. For the modulus of rigidity, apply equation (19), Chapter III, page 62. E,= ola The modulus of resilience (see equation (18), page 62) is the area of the diagram within the elastic limit, expressed in absolute units. U.= 1’0’ for unit of material. gO EXPERIMENTAL ENGINEERING The Helix Angle 6 = ea + J, in which / is the length of the specimen in inches. Machine Constants. — To Obtain the Constants of the Machine. — First, the external moment Pa. This is obtained on the principle that it is equal to any other external moment which holds it in equi- librium. Swing the pendulum until its centre-line is horizontal; support it in this position by a strut resting on a pair of scales; the product of the corrected reading of the scales into the distance to the axis on thearmwill give @. Check this result by trials with the strut at different points. Second, the value of the scale of ordinates can be obtained by measuring the ordinate for 8 = go° and for B = 30°, since sine 90° = 1 and sine 30° = 4. Third, the value of the scale of abscisse can be obtained by dividing the abscissa on the diagram by the circumference of the drum including the paper. This may be expressed in degrees by considering the. circumference = 360°. Constants of the Material are obtained by measuring the dimensions of the specimen. The values of J, and e are given on page 62. Conditions of Accuracy. — In obtaining these values, the following conditions are assumed: Firstly, the test-piece is exactly in the center of motion of the pendulum and of the drum; secondly, the pencil is in line of the pendulum produced; thirdly, the curve of the guides is that of the sine of the angle of deviation; and, fourthly, the specimen is held firmly from rotation by the shackles or wedges, and yet allowed longitudinal motion. These constitute the adjust- ments of the machine, and must be carefully examined before each test. Any eccentricity of the axis of the specimen will lead to serious error. 59. Power Torsion-machines.— The Riehlé power torsion-machine is shown in Fig. 68. Power is applied at various rates of speed by means of the gearing shown. The specimen is held by means of two chucks: the one on the left is rotated by the power applied; the one on the right is prevented from rotating by a system of levers, so connected to the scale-beam that when it is bal- anced the reading is proportional to the torsional force or external moment transmitted through the specimen, expressed in foot-pounds, inch-pounds, or any other units desired. The weighing STRENGTH OF MATERIALS — TESTING-MACHINES gI head is suspended so as to permit free elongation of the specimen. The chucks used have self-centering jaws which will hold the speci- men rigidly and central during application of the stress. In the Riehlé machine shown, the adjustment for specimens of various lengths is made by moving the weighing head. Fic. 68.— Rren~E Power Torsion Testinc MAcuIne. It is in general not best to determine the angle of torsion from a graduated scale on the movable chuck unless the slip of the specimen in the jaws is corrected for. The Riehlé Co. make a torsion indica- tor, which is applied directly to the specimen and thus obviates any inaccuracy due to slip. The construction of this indicator is shown in Figs. 69 and 7o and needs no further explanation. Two of these are used, clamped to the specimen any desired distance apart. ‘The reading of the dial near the weighing head is subtracted from that near the power head. Fig. 71 shows the Olsen power torsion-machine. Were the mov- able or power chuck is shown at the right, the stationary or weighing chuck at the left. In the particular machine shown, that at Sibley College, the scale beam shows the force in pounds acting at an arm of 20", EXPERIMENTAL ENGINEERING g2 Fic. 7o. Fic. 69. RIEHLE Torsion METER. Fic. 71.— OLsen Torsion TESTING-MACHINE, STRENGTH OF MATERIALS — TESTING-MACHINES 93 ' In the Olsen machine the angle of torsion may be measured by clamping dogs on the specimen at each end so as to engage the projections, shown at b, Fig. 71, of the index-rings, which are free to move over the graduated scales of the chucks. The angle of torsion of the specimen, for a length represented by the distance between the centers of the dogs, is the angle turned through by the movable chuck less the sum of the angles through which the index-rings are pushed by the dogs. Let a, =angle through which movable chuck is rotated, a, = angle through which index-ring on the movable chuck is pushed by the dog, a, = angle through which index-ring on fixed chuck is pushed by the dog, and a = angle of torsion. Then a= a, — (a, + a). This angle may also be measured through short ranges by means of two index-arms clamped to the specimen, as shown at c, Fig. 71. One arm carries a pointer which plays over an arc (d), graduated in inches, whose center of curvature is the center of the specimen. The distance traversed by the pointer divided by the radius of the arc gives the angle of torsion in circular measure. The constant of the Olsen machine, or the value of the gradua- tions on the scale-beam, may be found as follows (see Fig. 72): The fixed chuck is rigidly connected to link K asshown. The tor- sion moment (Pa) on the specimen tends to rotate the chuck and link as indicated by the arrow. The only additional forces acting on K are the vertical forces of strut P, and of the frame through the knife-edges at R. The right end of link K is pre- vented from dropping down, when no load is on the specimen, by a strut acting upward at R (not shown in figure). R Ae may therefore act either upward or i | downward, depending upon the intensity : - 7 of Pa. The weight of K may, however, Fic. 72.— Werrcutnc Heap oF be entirely neglected, since the counter- O1SEN_“TORSION-wACHINE. poise of the machine may be so set that the system is in equilibrium with no stress on the specimen. With the dimensions shown, weight of poise = 4o pounds, length 94 EXPERIMENTAL ENGINEERING between divisions on scale-beam = 2 inch, consider K as a free body. Then X(Pa)=0 and S¥Y=o0. From which Pa =12P,+8Rand P, =k, or Pa = 20P, (1) P, acts at a lever-arm of 2 inches on the lower lever G, and P, acts at a lever-arm of 30 inches. Then 2P, =30P,andP, =15 P, (2) P,acts on scale-beam at a lever-arm of 2 inches, and this moment must be balanced by moving the poise W along a distance x. From which 2P, = Wx (3) From (1), (2), and (3) we have Pa = 20 X 15 X 20%. Make « = 1 scale division = 2 inch, then Pa = 4000 inch-pounds. Since the value of each division as marked on scale-beam is 200, the constant of the machine is 20. For an accurate determination of the angle of torsion, it is impor- tant that the specimen be kept straight during the application of stress, and that the angle of torsion be measured from arcs or scales having the same center as the specimen. 60. Impact-testing Machine. —The Drop Test — Testing by Impact. — This test is recommended for material used in machinery, railroad construction, and generally whenever the material is likely to receive shocks or blows in use. It is usually performed by letting a heavy weight fall on to the material to be tested. The Committee on Standard Tests of the American Society of Mechanical Engineers recommend that the standard machine for this purpose consist of a gallows or framework operating a drop of twenty feet, the weight to be 2000 pounds, the machine to be arranged substantially like a pile-driver. The impact machine designed by Mr. Heisler, Fig. 73, consists of a pendulum with a heavy bob, which delivers a blow on the center of a bar securely held on two knife-edge supports affixed to a heavy mass of STRENGTH OF MATERIALS — TESTING-MACHINES 95 metal. This machine is especially designed for comparative tests of cast iron; it is furnished with an arc graduated to read the vertical fall of the bob in feet, and a trip device for dropping the ram from any point in the arc. A paper drum can be arranged for automati- cally recording the deflection of the test-pieces. Fic. 73. HEIsLtER Impact TESTING-MACHINE. Let W = the weight of the bob; h = the distance fallen through; P = centre-load; A = deflection. Then bo v Fis Wh = Hence, P=2Wh+.i. 96 EXPERIMENTAL ENGINEERING 61. Machines for Testing Cement. —Cement mortar can be formed into cubes, and after hardening can be tested in the usual testing-machines for compression; but tensile tests are usually required, and for this purpose a delicate machine with special shackles is needed. In order that the tests may give correct results, it is necessary that the power be applied uniformly, and absolutely in the line of the axis of the specimen; and to make different tests comparable, the specimen, or, as it is called, the briquette, must be Fic. 74. FarrBANKS’ CEMENT-TESTING MACHINE. always of the same shape and size, and made in exactly the same manner. The engraving (Fig. 74) shows Fairbanks’ Automatic Cement-tester, in which the power is applied by the dropping of shot into the pail F. The specimen is held between clamps, which are regulated at the proper distance apart by the screw P. At the instant of rupture the scale-beam D falls, closes a valve, and stops the flow of shot. In Fig. 74 S is a closed mould for forming a bri- quette, and U a briquette ready for test. STRENGTH OF MATERIALS — TESTING-MACHINES 97 Directions. — Hang the cup F on the end of the beam D, as shown in the illustration. See that the poise R is at the zero-mark, and balance the beam by turning the counter weight L. Place the shot in the hopper B, place the specimen in the clamps NN, and adjust the hand-wheel P so that the graduated beam D HINTON Pere a eh eT SF Fic. 75.— OLSEN’S CEMENT-TESTING MACHINE. will rise nearly to the stop K. Open the automatic valve I so as to allow the shot to run slowly. Stand back and let the machine make the test. When the specimen breaks, the beam D drops and closes the valve J. Remove the cup with the shot in it, and hang the counier- 98 EXPERIMENTAL ENGINEERING poise-weight G in its place. Hang the cup F on the hook under the large balance-ball E, and proceed to weigh the shot in the ordinary way, using the poise R on the graduated beam D and the weights H on the counterpoise-weight G. The result will show the number of pounds required to break the specimen. Owing, apparently, to a certain give in the shackles and lever, it sometimes becomes necessary to turn the wheel P to prevent D from striking the lower stop before the test is complete. Under Fic. 76, — RrmuLt CEMENT-TESTING Macuine. high loads it becomes difficult to do this uniformly by hand. In the later forms of this machine an attachment is now located in the base of the machine whereby P can be turned through gear- ing, making the action more uniform and less apt to affect the strength of the specimen by jars. Automatic Machines, similar in their action to the Fairbanks, are also built by Tinius Olsen & Co., and by Riehlé Bros. Testing Machine Co., both of Philadelphia. These firms also make cement- testing machines of a different type, of which Figs. 75 and 76 are examples. STRENGTH OF MATERIALS — TESTING-MACHINES 99 The Olsen Cement-tester is shown in Fig. 75. The power is applied by the hand-wheel and screw, so that it strains the briquette very slowly. The poise on the scale-beam is moved by turning a crank so that the beam can readily be kept floating. The Riehlé Cement-tester is shown in Fig. 76. The briquette to be tested is placed between two shackles mounted on pivots so as to be free to turn in every direction. Power is applied to the specimen through belts and gearing as shown, and is measured by the reading on the scale-beam at the position of the poise. TESTING-MACHINE ACCESSORIES. 62. General Requirements of Instruments for Measuring Strains. — In the testing of materials it is necessary to measure the amount of strain or distortion of the body, in order to compute ductility, mod- ulus of elasticity, etc. The ductility or percentage of ultimate deformation, since the latter is usually a large quantity, can often be obtained by measurement with ordinary scales and cal- ipers. Thus, in the tension-test of a steel bar 8 inches long, it will increase in length before rupture nearly or quite 2 inches; if in the measure of this quantity an error equal to one-fiftieth of an inch be made, the resulting error in ductility is only one-half of one per cent, In the measurement of deformation occurring within the elastic limit the case is very different, as the deformation is very small, and conse- quently a very small error is sufficient to make a great percentage difference in the result. The instruments used for the purpose of measuring elongation are called extensometers, and vary greatly in form and in principle of construction. The instrument is generally attached to the test- piece, either on one or on both sides, and the deformation is obtained by direct measurement with one or two micrometer-screws, or by the use of levers which multiply the deformation so that the results can be read on an ordinary scale. As a rule, instruments which attach to one side of the test-piece will give erroneous readings if the test-piece either be initially curved, or deformed so as to draw its axis out of a right line, and this error may be large or small, as the conditions vary. 100 EXPERIMENTAL ENGINEERING The extensometers in use generally consist of some form of multiplying-lever the free end of which moves over a scale which may or may not be provided with a vernier, or of a micrometer- screw, which is used to measure the distance between fixed points attached to the specimen or of some form of mirror apparatus, or various forms of cathetometers. Fic. 77. WEDGE SCALE. 63. Various Forms of Extensometers. The Wedge Scale. — The wedge-shaped scale, Fig. 77, which could be crowded between two fixed points on the test-piece, was one of the earliest devices to be used. In using the scale two projecting points were attached to the specimen, and as these points separated, the scale could be inserted farther, and the distance measured. The Bauschinger Roller and Mirror Extensometer. —'To Professor Bauschinger belongs the credit of first systematically taking double measurements on opposite sides of a test-bar. The general principle n if Fic. 78. — BAUSCHINGER’s Mrrror APPARATUS. of his apparatus is shown in Fig. 78. It is seen to consist of two knife-edged clips, 6, 6, which are connected to the specimen and carry two hard ebonite rollers, d, d, which turn on accurately centered spindles. The spindles are prolonged, and support mirrors, STRENGTH OF MATERIALS — TESTING-MACHINES I01 g, g, which rotate in the plane of the figure as the spindles rotate. Clips, a, a, are fastened to each side of the test-piece at the opposite extremity, and are connected by spring-pieces, with the rollers. The spring-pieces are slightly roughened by file, and turn the rollers by frictional contact, so that the least extension of the test-piece causes a rotation of the mirror through an angle. If a scale be placed at 5, 5, and telescopes at e, e, the reflection of the scale will be seen in the mirror in looking through the telescope, and any extension of the test-piece will cause a variation in the reading of the scale as seen in the mirror. The apparatus is equivalent to a lever apparatus having for a small arm the radius of the roller g, and for a long arm the double distance of the scale from the mirror. With this instrument it is evidently possible to obtain very accurate measurements, but on the other hand the instrument is very cumbrous and difficult to use. The mean of the two readings with the Bauschinger instru- ment is the true extension of the piece. Professor Unwin obviates the use of two mirrors and two telescopes by attaching clips to the center of the speci- men and having the single mirror revolve in a plane at right angles with the plane pass- ing through the clips and the axis of the specimen. Strohmeyer’s Roller Extensometer, Fig. 79, was designed in 1886, and is a double-roller extensometer. The apparatus consists of a roller carrying a needle, which is centered with respect to a graduated scale. The roller moves between side-bars extending to clips which are fastened to each end of the specimen. The tension between these side- F!6- 79.—THE Strou- bars can be regulated by a spring with a ee screw adjustment. ‘The objections to this form of extensometer are due, first, to slipping of side-bars on the roller, and second, to the difficulty in making the roller perfectly round. Regarding the various forms of extensometers, the writer would say that his experience has covered the use of nearly every form mentioned, and none have proved to be superior in —j L—~ 2 102 EXPERIMENTAL ENGINEERING uracy to that with the double micrometer-screw, and few can acc be applied so readily. . The Paine Extensometer.— This instrument, shown in Fig. 80, operates on the principle of the bell-crank lever, the long arm moving a vernier over a scale at right angles to the axis of the speci- men. It reads by the scale to thousandths of an inch, and by means of the vernier to one ten-thou- sandth of aninch. Points on the instrument are fitted to indentations in one side of the test-piece, and the instrument is held in place by spring clips. It is of historical importance, having been in- vented by Colonel W. H. Paine, and used in the tests of material for the Brooklyn Bridge, and also on the cables of the Niagara Suspension Bridge when, a few years since, the question of its strength was under investigation. Buzby Hair-line Extensometer. — This is an extensometer in which the deformation is utilized to rotate a small friction-roller connected with a graduated disk as shown in Fig. 81. A projecting pin placed in the axis of the graduated disk is held between two parallel bars, each of which is con- nected to the specimen. The deformation is magnified an amount proportional to the ratio of diameters of the disk and pin. The amount of deformation is read by noting the number of AlliTr! subdivisions of the disk passing the hair-line. | To prevent error of parallax in reading, a small mirror is placed back of the graduations, and a readings are to be taken when the graduations, i vad AINE the cross-hair, and its reflection are in line. TENSOMETER- In the late styles of this instrument the disk is made of aluminum, with open spokes, to reduce its weight. To operate this instrument it is on!’ necessary to clamp it to the specimen, to adjust the mirror ane «Yss-hair, and then to revolve the disk by hand until the a ptresponds with the cross-hair a STRENGTH OF MATERIALS — TESTING-MACHINES 103. and its reflection. Stress is then applied to the specimen, and read- ings taken as desired in the manner described. Fic. 81. — Buzpy Hatr-LINE Fic, 82. — JoHNSON EXTENSOMETER. EXTENSOMETER, Johnson Extensometer. — Johnson extensometer, shown in Fig. 82, is a modification of the Strohmeyer, the elongation being denoted by the motion of a needle over a'graduated scale. The elongation for each side is shown separately, and the algebraic sum of the two readings gives the total elongation. Thurston’s Extensometer. —'This extensometer was designed by Prof. R. H. Thurston and Mr. Wm. Kent, and was the first to employ two micrometer-screws, at equal distances from the axis of the specimen. These were connected to a battery and an electric bell in such a manner that the contact of the micrometer-screws was indicated by sound of the bell. The method of using this instrument is essentially the same as that of the Henning and Marshall instrument, to be described later. 104 EXPERIMENTAL ENGINEERING With instruments of this nature a slight bending in the specimen will be corrected by taking the average of the two readings. The accuracy of such extensometers depends on — 1. The accuracy of the micrometer-screws. 2. The screws to be compensating must be two in number, in the same plane, and at equal distances from the axis of the specimen. 3. The framework and clamping device must hold the micrometers rigidly in place, and yet not interfere with the application of stress. The Henning Extensometer. —'This instrument, which was de- signed by G. C. Henning and C. A. Marshall, is shown in Fig. 83. It is constructed on the same gen- eral principles as the Thurston Extensometer, but the clamps which are attached to the speci- men are heavier, and are made so that they are held firmly in posi- tion by springs up to the instant of rupture. ‘This extensometer is furnished with links connecting the two parts together. The links are used to hold the heads exactly eight inches apart, and are un- hooked from the upper head before load is applied to the specimen. The micrometer is connected to an electric bell in the same manner as the Thurston extensometer. Henning’s Mirror Extensometer** —In 1806 Gus. C. Henning designed a mirror extensometer differing in several particulars from that of Bauschinger. The instrument is intended for accurate measurements of the extension or compression on both sides of the test-piece within the elastic limit, and is said to fulfl the following conditions: (a) It is applicable for measures of extension or com- pression. () Readings in either direction, negative or positive, can be taken without interruption or adjustment. (c) The instrument * See Transactions American Society Mechanical Engineers, Vol. xvitt. Fic. 83. — HENNING EXTENSOMETER. STRENGTH OF MATERIALS — TESTING-MACHINES 105 is free from changes of shape during the test. (d) There is neither slip nor play of the working parts. The instrument consists of two parts; the first is a telescope provided with levelling-screws, mounted on a horizontal and vertical axis and furnished with supports for two linear scales, which may be arranged so that the reflection will show in mirrors attached to the specimen. ‘The second part consists of a frame which can be fas- tened to the test-specimen near one end by opposing, pointed screws, and which is connected to spindles carrying the mirrors by spring side-bars. A portion of each mirror-spindle is double knife-edged, and when adjusted is brought in contact on one side with the test- piece, and on the other with the spring side-bar. The elongation of the test-piece causes an angular motion of the mirror, which in turn causes a multiplied motion of the reflection of the scale as seen from the telescope. The mirrors are so arranged that the reflections from both scales can be seen continually and without adjustment of the telescope, and the apparatus as a whole has fewer parts and is more readily adjusted than the Bauschinger. It is limited to a total elongation of about 0.04 inch and hence is accurate only for measure- ments within the elastic limit. The Marshall Extensometer. —'This ex- tensometer, shown in Fig. 84, is the latest design of the late Mr. C. A. Marshall. Its principal difference from the Thurston extensometer is in the convenient form of clamps, which are well shown in the cut, and in the spring apparatus for steadying the lower part. The micrometer-screw used with this instrument has a motion of only one inch. When the motion exceeds the range of the micrometer-screws, the movable bars BP, B’P’ are changed in position, and a new series of readings can be taken with the F!- 84.— Tue MarsHatt a EXTENSOMETER. micrometer-screw. The following are the directions for connecting up the electric bell circuits used with extensometers of this type: 106 EXPERIMENTAL ENGINEERING Run wire (Fig. 84) from one terminal of battery to lower clamp at A, from B and B’ to binding-post C on the electric bell, from the Fic. 85.— Boston EXTENSOMETER. other binding-post marked D to switch E, and from there back to the other terminal of battery. To measure deformation, screw up the microm- eter screw on one side until the bell indicates contact, then back off very slowly until the circuit breaks, then take the reading. After this, back off the same screw a little more to prevent its making contact when working with the other side, and repeat the same process with the other screw. Boston Micrometer Extensometer.— This instru- ment consists, as shown in Fig. 85, of the grad- uated micrometer-screw, reading in thousandths up to one inch, and having pointed extension- pieces attached, for gauging the distance between the small projections on the collars fastened to the specimen at the proper distance. These collars are made partly self-adjusting by the springs which help to centralize them. They are then clamped in place by means of the pointed set-screws on the sides, and meas- urements are made between the projec- tions on opposite sides of the specimen and compared, to denote any changes in shape or variations in the two sides. The Brown and Sharpe micrometer | Fic. 86.— OLs—En NEw ExTENSOMETER. D A B ae = Cc To) E == G == ke] =} = 7 K === can readily be used with similar collars, thus forming an exten- someter; the accuracy of this form is considerably less than those STRENGTH OF MATERIALS — TESTING-MACHINES 107 in which the micrometers are fixed, but it will, however, be found with careful handling to give good results. The New Exten- someter,— This is a type which is finding extended use. Fig. 86 shows its con- struction, method of attachment and of op- eration without fur- ther explanation. By the use of auxiliary sleeves, the same type of instrument may also be used in the testing of wire, Fig. 87. Of the various extensometers de- scribed, the Paine, Buzby, and Marsh all, Fic. 87.— OLSEN NEw WIRE EXTENSOMETER. are manufactured by Riehlé Bros., Philadelphia; the Thurston and New by Olsen of Philadelphia; the others, by the respective designers. 64. Combined Extensometer and Autographic Apparatus.— Various methods have been devised whereby the stress and strain diagram may be obtained directly by action of the testing ma- chine. All of these devices consist essentially of a drum which carries the paper upon which the diagram is to be drawn and whose movement about its own axis is usually determined by the deforma- tion of the test-piece multiplied in some ratio. Thus motion around the drum records strain. The pencil drawing the diagram is moved along the drum in some proportion to the movement of the poise along the weighing beam. Thus the combined motion of drum and of pencil produces the diagram. Some of this autographic apparatus is quite elaborate. The Riehlé Gray apparatus built by Riehlé Bros. is able to produce 108 EXPERIMENTAL ENGINEERING a double diagram, one showing the entire curve to the breaking point of the specimen; the other, by multiplying the elongation within the elastic limit, shows the characteristics of the material up to the yield point. The type of diagram ob- tained is shown in Fig. 88. RIEHLE-GRAY EXTENSOMETER DOUBLE PENCIL CARD A simpler type of autographic monte sa apparatus, also built by the same Length 7.97” aaa company, is shown attached to diipiliiee oe the machine in Fig. 89. Here 4 times the deformation movement of the specimen is converted into circular motion of -the drum, while the pencil moves up along the drum in proportion to the load. The Olsen autographic device is shown attached to the ma- chine in Fig. 90. The drum is - here supported parallel to the Scale for Force .6950 Lbs, per Inch beam. The pencil is carried by a fine threaded extension of the beam screw. Thus movement parallel to the drum represents load. The deformation of the specimen is followed by contact fingers by means of which the movement is multiplied five times and converted into the rotary motion of the drum. This mechanism is used to draw the entire diagram for the detection of the yield point, the determination of the breaking load, etc. For the more accurate work required within the elastic limit an auxiliary attachment is furnished which multiplies the deformation 500 times. Concerning any autographic apparatus of this type the fol- lowing points should be kept in mind. Owing to slip in the jaws in the case of tension and yielding of the supports in the case of com- pression, that part of the apparatus recording the deformation should never be attached to or rest against the heads of the ma- chine. Instead of this, collars on the specimen should always be used. Further, the more elaborate the apparatus, the greater the Elongation Magnified 347 times Zero Line 347 Magnificati Zero Line 4 Magnification Fic. 88. — AUTOGRAPHIC RECORD. STRENGTH OF MATERIALS — TESTING-MACHINES _ 109 Fic. 90. OLSEN TESTING-MACHINE WITH AUTOGRAPHIC APPARATUS. 110 EXPERIMENTAL ENGINEERING chance for error of adjustment, for lost motion in the bearings and for bending and yielding in the levers. All these things affect the result, and while errors thus induced may not seriously affect the determination of the yield point, maximum load, breaking load, and total elongation, the results for the modulus of elasticity as deter- mined from the magnified curve should always be used with caution, Bus tes Fic. 91. — KENERSON AUTOGRAPHIC EXTENSOMETER. muy! mm amy [ii 7 | === The autographic apparatus so far described may be considered an integral part of the machine. Another type merely forms an auxiliary attachment to the ordinary extensometer. To this class belong the Henning pocket recorder and the Kenerson extensom- eter, the latter of which is shown in Fig. 9. In this instrument the upper clamp carries a drum whose motion about its axis is controlled by the movement of the poise on the weighing beam by means of a cord. The pencil is carried by a weight which can move up or down between two guide rods also carried by the upper clamp. This weight is suspended by means of two cords which pass over small STRENGTH OF MATERIALS — TESTING-MACHINES III guide sheaves and which are wrapped around two small pulleys carried by the micrometer screws. The rest of the apparatus is like an ordinary extensometer. As the specimen stretches and the contact points tend to separate, the weight pulling on the cords rotates the pulleys and maintains contact. Thus motion of the pencil downward is proportional to the deformation. | i | = i iy At Fic. 92. — RIEBLE COMPRESSION MICROMETER. 65. Instruments for Measuring Torsion, Deflection, and Com- pression.— Instruments for measuring the angle of torsion have already been discussed under Torsion Machines, see Art. 58. In- struments for measuring the deflection of a specimen subjected to transverse stress are termed deflectometers. 112 EXPERIMENTAL ENGINEERING The deflectometer usually used by the author consists of a light metal-frame of the same length as the test-piece, and arched or raised sufficiently in the center to hold a micrometer above the point to which measurements are to be taken. In using the deflectom- eter it is supported on the same bearings as the test-piece, and Fic. 93. — OLSEN COMPRESSION MICROMETER measurements made to a point on the specimen or to a point on the testing-machine which moves downward as the specimen is deflected. This instrument eliminates any error of settlement in the supports. There are a number of different types of instruments which may be used to measure compression. Some of these are modifications of the extensometer idea, see Figs. 92 and 93. Both of these are STRENGTH OF MATERIALS — TESTING-MACHINES 114 Fic. 96. — OLSEN COMPRESSION MICROMETER. II4 EXPERIMENTAL ENGINEERING apparently open to the objection that they do not allow for the settling of the supports. The instrument shown attached to the cylindrical specimen in Fig. 94 avoids this source of error. Figs. 95 and 96 show two instruments which work on a some- what different principle. The first does not allow for the yielding of the supports, while the second works between collars on the specimen and is therefore independent of any movement of the supports. The instrument shown in Fig. 95 is also often used as a deflectometer in transverse testing. CHAPTER V. STRENGTH OF MATERIALS.— METHODS OF TESTING. 66. Standard Methods. — The importance of standard methods of testing material can hardly be over-estimated if it is desired to pro- duce results directly comparable with those obtained by other experimenters, since it is found that the results obtained in testing the strength of materials are affected by the methods of testing and by the size and shape of the test-specimen. To secure uniform practice, standard methods for testing various materials have been adopted by several of the engineering societies, as well as by asso- ciations of the different manufacturers. The general and special standard methods adopted by these associations form the basis of methods described in this chapter. 67. Tension Testing. — Form oj Test-pieces. — The form of test- pieces is found to have an important bearing on the strength, and for this reason engineers have adopted certain standard forms to be used. The form recommended by the Committee on Standard Tests and Methods of Testing, of the American Society of Mechani- cal Engineers, is as follows: * “Specimens for scientific or standard tests are to be prepared with the greatest care and accuracy, and turned as nearly as possible according to the following dimensions. The tension test-pieces are to have different diameters according to the original thickness of the material, and to be, when expressed in English measures, exactly 0.4, 0.6, 0.8, and 1.0 inch in diameter; but for all these different diameters the angle, but not the length, of the neck is to remain constant. This neck is a cone, not a fillet connecting the shoulders and body. The length of the gauged or measured part to be 8 inches, of the cylindrical part 8.8 inches. The length of the coned neck to be 2} times the diameter, increasing in diameter from * See Vol. XI. of Transactions. IIs 116 EXPERIMENTAL ENGINEERING the cylindrical part to 1} times the cylindrical part. The shoulders to have a length equal to the diameter, and to be connected with a round fillet to a head, which has a diameter equal to twice that of the cylinder, and a length at least 14 the diameter.” tie s-— = ——-—290 millimetres — -— -—->l-—50—- eo j-25-4| ry t | | i # 3 aS o8e I-8-; — -——¢ ~ BE - Tote 1 fea + | { Nrullet 0.1’R. t ka—t vasrfe- 2 4. —--—— 8.8:inches— - ee eee --beakea| Fic. 97.—STANDARD TEST-PIECE IN TENSION. Fig. 97 shows the form of the test-piece recommended for tension; the numbers above the figure give dimensions in millimeters, those below in inches. For flat test-pieces the shape as shown in Fig. 98 spoke = 29 = =" oe eaoed #127 <— 30—> -O- | | 4, | | | L = 4 isa ce Fic. 98.— TEST-PIECE FOR FLAT SPECIMENS. is recommended: such specimens are to be cut from larger pieces; the fillets are to be accurately milled, and the shoulders made ample to receive and hold the full grip of the shackles or wedges. If wedges are used for fastening, the ends to be gripped should be at least 2 inches long. The length for rough bars when such are used as test-pieces is to be the same as for finished test-pieces, but the length of specimen from the gauge-mark to the nearest holder is to be not less than the diameter of the test-piece if round, orone and a half timesthe greatest side if flat. For commercial testing the standard form cannot always be adhered to, and no form is recommended. The commonest form of test section in commercial work is } inch diameter and 2 inches gauge length. The ductilities found on this form of piece are much greater than would be given by the same material in the standard test-piece STRENGTH OF MATERIALS — METHODS OF TESTING 117 form. Ductility is always a function of the ratio of length to diame- ter of the test section. The strength determinations are nearly independent of the shape of the test section so long as the gauge- length exceeds twice the diameter; with a shorter gauge-length the strengths will be too high. 68. Test-pieces of Special Materials.— Wood.— Wood is a difficult material to test in tension, as the specimen is likely to be crushed by the shackles or holders. The author has had fairly good success with specimens, made with a very large bearing-surface in the shackles, of the form shown in Fig. 98, for flat specimens, but with the breadth of the shoulders or bearing-surfaces increased an amount equal to one-half the width of thespecimen over thatshown in Fig. 98. Cast iron. — Cast-iron specimens of the usual or standard forms are very likely to be broken by oblique deformations in tension-tests -much before the true tensile strength has been reached. To insure perfectly axial strains Riehlé Bros. propose a form of specimen Fic. 99. — CastT-IRON SPECIMEN AND SELF-CENTERING GRIPS. shown in Fig. 99, A, B, and C, cast with an enlarged head, the pro- jecting portion of which, as shown in C, has a knife-edge shape. The specimen is carried in holders or shackles, A and B, which rest on knife-edges extending at right angles to those of the specimen. 118 EXPERIMENTAL ENGINEERING This permits free play of the specimen in either direction, and ren- ders oblique deformation nearly impossible. Chain. — In the case of chain, large links are welded to the ends, as shown in Fig. 100; these are passed through the heads of the test- ing-machine and held by pins. Fic. 100. — CHAIN TEST-PIECE. Hemp Rope. — A similar method is used in testing hemp rope, the specimen being prepared as shown in Fig. 101. Special hollow conical shackles have also been used with success for holding the rope. Fic. ro1.— Rope TEST-PIECE. Wire Rope. — Wire-rope specimens may be prepared as shown in Fig. 102 or heads may be made by pouring a mass of melied Fic, 102, — WIRE RoprE TEST-PIECE. babbitt metal around the ends of the wires arranged in an iron cone as in Fig. 103. ie tt bent ZZ Fic, 103. —MeErHop oF Hotpinc Rops, 69. Directions for Tension-tests. —Examine the test-piece carefully for any flaw, defect, irregularity, or abnormal appearance, and see that it is of correct form and carefully prepared. Indentations from STRENGTH OF MATERIALS — METHODS OF TESTING II9g a hammer often seriously affect the results. In wood specimens, abrasions, slight nicks at the corners, or bruises on the surface will invariably be the cause of failure. Next, carefully determine the dimensions, record total length, gauge-length (or length on which measurements of strains are made), also form and dimensions of shoulders. Divide the specimen between the gauge-marks into inches and half inches, which may be marked with a special tool, or by rubbing chalk on the specimens and marking each division with a steel scratch. Special gauges, as shown in Figs. 104, 105, and 106, are convenient for this purpose. These A. ee Yee g Z = Fic. 106. — RIEHLE MarkING GAUGE. marks serve as reference points in measuring the elongation after rupture, and this elongation should be measured, not from the center of the specimen, but either way from the point of rupture, as explained below. The matter of properly holding the specimen is of the greatest importance. Unless special forms of test-pieces or self-aligning 120 EXPERIMENTAL ENGINEERING grips are used, great care should be taken in the proper position of the wedges. Fig. 107, a to e, published by the Riehlé Co. shows the conditions that may exist when ordinary wedges are used. Fig. a shows the proper position, both wedges and specimen bear- ing the whole length. Fig. 6 shows what may occur with a thin Fic. 107. — WEDGE ADJUSTMENTS. specimen. ‘This grip may hold if the load is not too high, but it is better to improve it by the use of liners, as in Fig. c. Fig. d shows a condition that should never be allowed to exist. The grip is almost sure to fail before the test is complete by the crushing of the top of the specimen, and above all the severe wedge action taking place may split the head of the machine. ‘A cure for the trouble is indicated in Fig. e, but the grip is not likely to stand high loads. See that the testing-machine is level and balanced before each test; insert the specimen in a truly axial position in the machine. Attach the auxiliary apparatus for measuring stretch, or obtaining autographic diagrams. The method of attaching extensometers will depend on the special form used, but this act should always be carefully performed, and the specimen exactly centered in the exten- someter, and the gauge-points arranged 8 inches apart. The fol- lowing directions for applying and using the Henning extensometer will serve to show the method to be used in all cases. The Henning extensometer (see Fig. 83) is attached and used as follows: Before attaching the instrument, adjust the knife- edges in the clamps by means of the two milled nuts so that they are equally distant from the frame and a distance apart a little smaller than the diameter of the test-piece. Then, since the springs acting on the knife-edges are of equal strength, the instrument will adjust itself in the plane of the screws symmetrically with respect to the STRENGTH OF MATERIALS — METHODS OF TESTING 121 test-piece. Advance or withdraw the set-screws until their points are equally distant from the frame and far enough apart to admit the test-piece. Separate the upper portion of the instrument, put it around the test-piece (already inserted in the machine), near the upper shoulder, with the smaller part to the right, force together and fasten securely. Advance the set-screws simultaneously until their points indent the test-piece. Separate the lower portion, put it around the test-piece with the vertical scales to the front, force together and secure. Hang the links on the proper bearings on both portions of the instru- ment. Then advance the set-screws as above. Throw the links out, take readings of the micrometers, apply the first increment of load, and proceed with the test as directed. ‘To read the microme- ters make the electrical connections; advance one micrometer until the bell rings announcing contact, back off barely enough to stop ringing. Read that side of the instrument. Back that side off further, and run up the other side and read as with the first. Read break of circuit. The vertical scale and the micrometer head are graduated so that readings to to¢en inch can be obtained directly. Calculate from the supposed coefficients of the material the probable load at elastic limit. Take one-tenth of this as the in- crement of load. The Committee on Standard Tests, American Society of Mechanical Engineers, recommend that the increment be one-half or one-third that of the probable load at the elastic limit, thus giving larger strains but fewer observations. Apply one in- crement of load to the specimen before measurements of elonga- tion are made, since by loading specimens up to ro00 or 2000 pounds per square inch the effect of initial errors, such as occur generally at the commencement of each test, are lessened. The auxiliary apparatus adjusts itself somewhat during this period of loading, and the specimen assumes a true position should any slight irregularity exist. After passing the elastic limit, which will be indicated by the jump in stretch as shown by the extensometer, the test is run by apply- ing the stress continuously and uniformly without intermission until the instant of rupture, only stopping at intervals long enough to make the desired observations of stretch and change of shape. The stress should at no time be decreased and reapplied in a standard 122 EXPERIMENTAL ENGINEERING test, but should be maintained continuously. The auxiliary appara- tus for measuring strain must be removed before rupture takes place, except it is of a character not likely to be injured. It should usually be taken off very soon after the elastic limit Is passed; although for ductile material it may be left in place for a longer time after the elastic limit has been passed than for hard and brittle materials. After the removal of the extensometer the stretched length of the test section may be measured with dividers. The material is to be loaded until fracture takes place, keeping the beam floating, after which the distortion for each part is to be measured by comparison with the reference divisions on the test-piece, measured from the point of rupture as previously explained. It is to be noted that measurements within the elastic limit are of especial impor- tance, since materials in use are not to be strained beyond that point. Remove the fractured piece from the machine; make measure- ments of shape, external and fractured surface; give time required in making the test.* In recording the results of tests, loads at elastic limit, at yield- point, maximum, and instant of rupture are all to be noted. The load at elastic limit is to be that stress which produces a change in the rate of stretch. The load at yield-point is to be that stress under which the rate of stretch suddenly increases rapidly. The maximum load is to be the highest load carried by the test- piece. The load at instant of rupture is often not the maximum load, but a lesser load carried by the specimen at the instant of rupture. In giving results of tests it is not necessary to give the load per unit section of reduced area, as such figure is of no value: (1) because it is not always possible to obtain the load at instant of rupture; (2) because it is generally impossible to obtain a correct measurement of the area of section after rupture; (3) lastly, because the amount of reduction of area may be dependent upon local and accidental con- ditions at the point of rupture. The modulus or coefficient of elasticity is to be deduced from measurements of deformation ob- served between fixed increments of load per unit section; as between * See Report of Committee on Standard Tests, Vol. XI., Am. Society Mech. Engrs. STRENGTH OF MATERIALS — METHODS OF TESTING 123 2000 pounds per square inch and 12,000 pounds per square inch; or between ooo pounds per square inch and 11,000 pounds per square inch. With this precaution several sources of error are avoided, and it becomes possible to compare results on the same basis. The character of the fracture often affords important information regarding the material. The structure of the fractured surface should be described as coarse or fine, either fibrous, granular, or crystalline. Its form, whether plane, convex, or concave, cup- shaped above or below, should in each case be stated. Its location should be accurately given, from marks on the specimen one-half inch or less apart. The reduction of diameter which accompanies fracture should be accurately measured. Accompanying the report should be a sketch of the fractured specimen. Fracture occurs usually as the result of a gradual yielding of the particles of the specimen. The strain, so long as the stress is less than the maximum load, is distributed nearly uniformly over the specimen, but after that point is passed the distortion becomes nearly local; a rapid elongation with a corresponding reduction in section is manifest as affecting a small portion of the specimen only. This action in materials with sensible ductility takes place some little time before rupture; in very rigid materials it cannot be perceived at all. This peculiar change in form is spoken of as ‘‘necking.” 6 4132 119 8765 4 38 21 [0128 hI Pay iyi tei et Lier Hh 19 1817 16 15 4131221109 8 7 65 4 3 2 1 Fic. 108. The drawing, Fig. 108, shows the appearance of a test-specimen in which the “necking” is well developed. Rupture occurs at b—b, a point in the neck which may be near one end of the specimen. In order to measure the elongation of the specimen fairly, a cor- rection should be applied, so that the reduced elongation shall be the same as though the stretch either side of the point of rupture were equal. This can only be done by dividing up the original specimen into equal spaces, each of which is marked so that it can be identified after rupture. 124 EXPERIMENTAL ENGINEERING Suppose that twenty spaces represent the full length between gauge-marks: then if the rupture be at b—%, nearest the mark o, Fig. 108, three spaces to the left of the nearest gauge-mark, the total length to compare with the original length should be o to 3 on the right, plus 0 to to on the left, plus the distance 3 to to on the left. These spaces are to be measured, and the sum taken as the total length after rupture. The stretch is the difference between this and the original length; the per cent of stretch, or elongation, is the stretch divided by the original length. Report of Tension-tests. —In the report describe the testing- machine and method of testing, the form and dimensions of the specimen, the character and position of rupture. Make a sketch of the break. Submit a complete log of test (see blank form below). Calculate strength at elastic limit, maximum strength, and breaking strength, and moduli of elasticity and resilience. Plot a stress-defor- mation diagram on squared paper. Two scales for deformation should be used, one such that the elastic line shall have a slope of about 45° actual on the paper and the other such as to show the whole test. Both abscissa scalings should use the same scaling of ordinates. The following form is used in Sibley College, Cornell University, for both tension- and compression-tests: MECHANICAL LABORATORY —SIBLEY COLLEGE, CORNELL UNIVERSITY. , Test of....... : ssosayailDV"va tavasibra cee gus vatinanadelote andst tue vbteniold Oe rau e tie Kind of Test. sence iee tech pews eee Aveugs Seat ces Scan aoe ence cabanas Miaterial: froma; veer ites aiaccendivn taae does ph ermaces a panes abana © pemnaiaes BRD NIE oreteletale as Machine used... Yiaaigs algigaitonn oStale gin elneee a 19 Time of Testing 4... eekieks 2a ws in. TEM Pi ais swage es degrees F. Load. Extensometer Readings. Extension. Modulus No. = of Elas- : er Ditfer- é ticity. Actual! qin. | Right. | Left. | Mean, | Actual | “ence. | Per in. E ie. P AA 1 serageselecseeeesleceeesealereeereed/eeresteesfescrsenee [oessecseeelecsscevenslecetereeas/eaetaeeees #25 gota nah wna Pacer stenoses rs [ane es ah hae decane bel vcs take ones ean nist pe ta mend esawtts [et eae Ain] pemeeeneel |vomen saanelatns eeanalyshseniaysayenany naira ra aatany seep ann |ownnsicss/evwnanel annnrnnns | Eanes oho) suena ons asichinn|e vantage eda ene ads eanene STRENGTH OF MATERIALS — METHODS OF TESTING 125 Original Length iene cesmieenee aceon in. sq. in Final 7 8 ageing taracoenenevans * Form of Section............. site » Rharacte rss, csiex aie seonasens Modulus: of résillente s.csvesesucsteeds eerseeenaseaweiawenemeade@arerg eswewes Load per sq. inch, Elastic limit... .. 5 ING ceinavgeace es Equivalent elongation for 8 inches. ...... inches. Ductility.............. per cent, Reduction area. vseeeeees.sper cent. Local elongation each half inch, from top, Sts svavesecs Bis cinerea disneiecs : qth eter Btls. icsmcenece Gt edunitieees WU a cgnssac Pisin x gth...... Tothis aca Lithvccces P2thiecmee < T3ths os oe TAtB acne r5th...... TOth v.05 70. Compression Testing.—form oj Test-pieces.—'Test-pieces are in all cases to be prepared with the greatest care, to make sure that the end surfaces are true parallel planes normal to the axis of the specimen. 1. Short Specimens. — The standard test-specimens for metals are to be cylinders 2 inches in length and 1 inch in diameter, when ultimate resistance alone is to be determined. 2. Long Specimens. —For all other purposes, especially when the elastic resistances are to be ascertained, specimens 1 inch in diameter and 10 or 20 inches long are to be used in the case of metal testing. Standard length on which deformation is to be measured is to be 8 inches, as in the tension-tests. Greatest care must be taken in all cases to insure square ends and that the force be applied axially. The specimens are to be marked and the compression measured as explained for tension-test pieces. 71. Directions for Compression-tests. —1. Short Pieces.—In case of short pieces, measurements of deformation cannot be made on the test-piece itself, but must be made between points on the heads of the testing-machine. It is necessary to ascertain and make a correction for the error due to the yielding of the parts of the testing-machine. This is done as follows: Lower the moving-head until the steel com- pression-plate presses on the steel block on the lower platform with a force of about 500 pounds. Attach the micrometers to a special frame, which is supported by the upper platform, and read to a point on the movable head. With load at 500 pounds, read both microm- eters. Apply loads by increments of tooo pounds up to three-fourths the limit of the machine, taking corresponding readings. Plota curve of loads and deflections with ordinates 1 long division = 1000 pounds, and abscisse 1 long division = 0.001 inch. From this curve obtain corrections for the deflections caused by the loads used in the compression-test. In making the test calculate the increment of load as explained for tensile test, Article 69. Conduct the experi- 126 EXPERIMENTAL ENGINEERING ment in the same manner as for tension, except that the stress is applied to compress instead of to stretch the specimen. If the material tested is hard or brittle, as in cast iron, care should be taken to protect the person from the pieces which sometimes fly at rupture. Report and draw curves as for tension-tests. 2. Long Pieces. —In this case the extensometers used for tension- tests can be connected directly to the specimen, and the measure- ments taken in substantially the same way, except that the heads of the extensometer will approach instead of recede from each other; this makes it necessary to run the screws back each time after taking a measurement a distance greater than the compression caused by the increment of load. In case large specimens are tested horizon- tally, initial flexion is to be avoided by counterweighting the mass of the test-piece. Calculate the increment of load as one-tenth the breaking-load given by Rankine’s formula, Article 43, page 56. Apply the first increment and take initial reading of micrometers; continue this until after the elastic limit has been passed, after which remove the extensometer, and apply load until rupture takes place. Protect yourself from injury by flying pieces. Compute the breaking coefficient C by Rankine’s formula, and compare with the value usually assumed. Compute the modulus of elasticity by Z é€ Note in the report load at elastic limit, yield-point, and ultimate resistance, as well as increase of section at various points, and total: compression, are calculated as explained for tension. Submit a load-deformation diagram, and follow the same gen- eral directions as prescribed in the report for tension-testing. 72. Transverse Testing. — Form oj Test-pieces.— For standard transverse tests, bars one inch square and forty inches long are to be used, the bearing blocks or supports to be exactly thirty-six inches apart, center to center. For standard or scientific tests of cast iron, such bars are to be cut out of a casting at least two inches square or two and a quarter inches in diameter, so as to remove all chilling effect. For routine tests, bars cast one inch square may be used, but all possible precautions must be taken to prevent surface-chilling and porosity. as in the tension-test. STRENGTH OF MATERIALS — METHODS OF TESTING 127 Test-bars of wood are to be forty inches in length, and three inches square in section. 73. Directions for Transverse Tests. — Arrange a tension-compres- sion machine for the transverse test by putting in supporting abut- ments and a loading head in the center, or use a special transverse- .testing machine. The test-piece is usually a prismatic beam, loaded on a three-foot length, the load being applied at the center. The data required are loads and deflections at the center. Sharp edges on all bearing-pieces are to be avoided, and the use of rolling bearings which move accurately with the angular deflec- tions of the ends of the bars is recommended; otherwise the distance between fixed supports measured along the axis of the specimen is continually changing. Place the test-bar upon the supports, and adjust the latter thirty- six inches apart between centers, and so that the load will be ap- plied exactly at the middle. Obtain the necessary dimensions, and calculate the probable strength at elastic limit and at rupture by means of the formula p = Ple+4J. (See Article 44, page 60.) Adjust the specimen in the machine in a horizontal plane, and apply the stress at the center, normal to the axis of the specimen. Measure the deflections at the center from a fixed plane or base, allowing for the settling of the supports, or by a special deflect- ometer. (See Article 65, page 111.) Balance the scale-beam with the test-bar in position and the deflectometer lying on the platform. Set the poise for one increment of load and apply stress until the beam tips. Place the poise at zero, and balance by gradually removing the load. Place the deflectometer in position on the supports, and with the micrometer at zero make contact and record zero-reading and zero-load. Apply the load in uniform increments equal to about one-tenth the calculated load for the elastic limit, stopping only long enough to measure the deflections. Wrought-iron is to be strained only until it has a sensible permanent set, but cast iron and wood are to be tested to rupture. 74. Report of Transverse Tests.—In the report describe the machine, method of making test, form of cross-section, peculiarities of the section, and make a sketch showing position and form of rupture. 128 EXPERIMENTAL ENGINEERING Submit a complete log of the test together with a stress-deformation curve. Calculate the unit stresses and deformations by the formu- las given in Article 44, table 1, page 60. The following is a form for data and results of a transverse test: MECHANICAL LABORATORY —SIBLEY COLLEGE, CORNELL UNIVERSITY. Log and Report of Transverse-test. Materialloss. 2 2c2snncaedaets at seas oes PrOMi Says coe Sis deseo v ns a uamingaenies Breadth Biscay a4. aanadeuge daiacd ete in. Height, h,........---- essence in. Length between supports, J,........... in. Max. Fiber distance, ¢,............ in. Moment of inertia, J,.............00005 Load applied at centerof test length, ir ee eee ete te ee eee eee Testing Machine ............0.-00- eee Observers Jocccccetctettettce PMNE ss tig gure eager ATS iiatesse eens: coarsieg min. SENT A. ct cal endl pie uialatess. a pRAeAe Datos geceania wears ees owe kOe eee, . , . Neves amtcbadan Waaumal dye. arent giedie Relative Deforma- Stress Deflection, tion in Load, |Per "in Outer Fibers. Modulus of Elas- No. P ? oe a ticity, : ‘iber : ‘otal De- Corrected | Ibs. per sq. in., Z. p- Penne flection, Caleniated for Zero P 4 ’ " in., d. - Error, e. 1 Actual | Deflec- Load, tion, lbs. inches. Stress per sq. in.|Relative Deform-| Greatest Vertical or in Outer Fiber, | 2tion in Outer Horizontal Shear Fiber. Stress, Ibs. per sq. in. sense eee Semen relrcecrcercccceseceelecccsecenseseres weeee we ecelecceneenocee Gece c ew eee At Maximum Load STRENGTH OF MATERIALS — METHODS OF TESTING 129 Modulus of Elasticity, Z,............4. Ibs. per sq. in. Modulus of Resilience, Usgevereneweessa in. lbs. per cu. in. e 6 L Formulas (for = 7 ei = (s:) Mabe ga? central loading): 1s 6h é=—--d=—-d These formulas are BP L true only for elas- tic action of the e=e material. E= Ae + U =}.p.eat elastic limit (at break for brittle materials). 75. Torsion Testing.— Form of Test-pieces. —For standard tests, cylindrical specimens with cylindrical concentric shoulders are to be used; the two are connected by large fillets. The speci- men is to be held in the heads of the machine by three keys, inserted in key-ways $ inch deep, cut in the shoulder. In commercial testing the ends of the specimen are usually held in self-centering jaw-chucks on the heads of the testing-machine. 76. Directions for Torsion-Tests. —1. Wuth Olsen or Riehlé Ma- chines. —'The general method of test is like that of the transverse test, as to choice of increment of load, etc. For measuring elastic deformations arms are attached to the piece as described in Article 59, page 93. For measuring the deformation at the break there should be scribed on the piece before loading a line parallel to the axis. After the break the distance along the piece in which this line makes one or more complete turns can easily be measured, and by proportion the number of turns, or angle of twist, in the test- length can then be computed. The final dimensions of the test- section should be taken. The report should describe the test-piece and testing-machine, method of test, and action of the material under stress. Note position and character of fracture. Calculate the unit stress and deformation in the outer fiber. Submit a log of test (see form below) and a curve showing the variation of unit stress against unit deformation, similar to the tension-test. Calculate the mod- uli of elasticity and resilience in shear. The following is a form for reporting a torsion-test: 130 EXPERIMENTAL ENGINEERING MECHANICAL LABORATORY — SIBLEY COLLEGE, CORNELL UNIVERSITY. Log and Report of Torsion-test. Materials. cis canto toned one ad + antes Promivnnc os begin wentenanie iste asgomiien Diameter, d,........--- in. Max. Fiber distance, 7,..........-..- in. Length between measuring arms, Des Naseer in. Length of measuring arms, Z,...... ..ip. Testing machines .esyecaeocomserueese fp te ete trae sete ne ttre TiGs. os nee wai d+ Wie betexseueesd min. Observerg 4 °°" * See ee ee eee Tite ccdaonow ska cucnentt mens 1Qii2 1+ Seas seeder ate Moment of eens pe ene ane Modulus of No. | TOO Iyer ty inch) | seate | Distynee | totarn lat Surtaco] UEiaity, = at surtace Reading, inches’ Measure m Measure sq. ta R, =¢ inches. ey =a = 1. noes ii ec Haha avn i 909A NEN ARENAS ERIE Hochst . et statin emacs ni no see ee ni a H sig ane ah enna arte | shoe | nat Sener nines Seas eR A Hi ado olnn a esi steel tee uhdoasslstn ase | tianeas Vivant | tecelopntencntas tna] areata aii ou aS antetsteatoaae hasnpgins| sxonnse cea] vetenesh Nas tans et: | ahamibsanbion oasis #= [ess Sina ss eaemeeanaana wa ig lig Sete v aun OH 1 a KA ei) i wa eae eRe vd ga emanate | nevis gn |e NE: oie AERA] ampere ot Moment of angle of | Shearing Stress, lbs.| Helix Angle Torsion Torsion |persq.in.at Surface.| at Surface. Modulus of Rigidity, Es, average,.......... Ibs. per sq. in. Modulus of Resilience Giga 2e rah soa in. lbs. per cu. in. , Within or near elastic limit. At maximum load (break) 2 16 q= sa M=TAM gm = modulus of rupture = =, + Mp r A Formulas } 6 = 7 ia cs gs = true shear stress in surface, for Aq ductile materials, = (gm — 4) Es NGS 3 —ly U = 345, ne i Pe STRENGTH OF MATERIALS — METHODS OF TESTING 131 2. With Thurston Autographic Machine. — Special test-pieces are used, generally with a test section about $ inch diameter and 2 inches or less long, with the ends of the piece square to hold in the wedges. The pieces are generally turned from square stock of size somewhat greater than the desired diameter of test section. Determine first the maximum moment of the pendulum. This may be done by swinging the pendulum so that its center-line is horizontal, supporting it on platform-scales and taking the weight and the distance of the point of support from the center of suspen- sion of the pendulum. The product of these two quantities is the maximum moment of the pendulum. Make three determinations, using different lever-arms, and take the mean for the true moment of the pendulum. A correction for the friction of the journal of the pendulum must be made. When hanging vertically, measure with a spring-balance, inserted in the eye near the bob, the force necessary to start the pendulum. Add this moment to that obtained above, and the result is the total maximum moment of the pendu- lum. From this the value of the moment for any angular position may be calculated. Note the variation of position of the pencil-point between the vertical and the horizontal positions of the pendulum. This distance laid down on the Y-axis of the record-sheet corresponds to the max- imum moment obtained above, whence calculate the value of one inch of ordinate. Calculate the length corresponding to one degree on the surface of the paper drum, parallel to the X-axis. This will be the unit to be used in calculating the angle of torsion. Fix the paper on the drum and draw the datum-line or X-axis. Insert the test-piece between the centers and screw in the center until the neck of the test-piece is about midway between the jaws. Wedge the test-piece between the jaws as firmly as possible by hand, and then tap the wedges slightly with a copper hammer. Throw the worm into gear and turn the handle slowly and steadily until rup- ture occurs, unless set-lines are taken. Take the record of all the test-pieces on the same sheet with the same origin of co-ordinates. The diagram is drawn by attachment to the working parts of the frame, and consequently any yielding of the frame or slipping of the jaws appears on the diagram as a strain or yield of the 132 EXPERIMENTAL ENGINEERING specimen. The angular deformation a, as obtained from the dia- gram, is likely to be too great, especially within the elastic limit. The characteristic form of diagram given by the torsion-machine is shown in Fig. 109, in which the results of tests of several materials are shown. In these diagrams the ordinates are moments of torsion (M), the abscissee are developments of the angle of torsion (a). wrO'T IRON MOM.TORS. ANG.TORSION 60° Fic. 109. Save that measurements from these autographic diagrams take the place of data and curves of the usual testing, the method of working up the test is as given above. 77. Testing in Direct Shear. — Satisfactory direct-shear tests are difficult to make. In the commonest form of this test, a pin of material is broken in double shear, by fitting it through three links, pulling or pushing the outer links past the centralone. The arrange- ment must be rigid and must not allow either shearing force to acquire a lever-arm; yet friction between the links themselves must be small. More information about the properties of a material under shear stressing can be had from a torsion-test than from a test in direct shear. The latter test gives the ultimate strength only; the torsion-test gives the elastic strengths and moduli. 78. Impact Testing. — No universally acceptable impact-testing machine has yet been devised. The results of impact tests vary from machine to machine, as well as from material to material. The following are directions for testing cast-iron with Heisler’s impact-testing machine. (See Article 60, p.95.) Take a transverse test-bar of cast-iron and place it in the machine, cope side out, so that the blow will be struck in the middle of its length. Arrange the autographic device so thatit will register the deflection of the bar. STRENGTH OF MATERIALS — METHODS OF TESTING 133 Place the tripping device or “dog” for a fall of two inches. Catch the bob at this point, and trip at every notch above successively until the bar breaks. Note the maximum height of fall. Report on the experiment the behavior of the test-bar and character of its fracture, and the number of impacts and the force in inch-pounds of the last blow. Compute the resilience of the test-piece. Try a similar bar at same ultimate fall, and observe the number of blows required to break it. Draw conclusions. Write complete report, and give moduli and coefficients. 79. Drop-tests. — Drop-tests are a form of impact test used on railway materials, as car wheels, axles, etc. The specification calls for the taking without rupture of a certain number of blows from a certain height. The following method of making drop-tests has been recommended by the Committee on Standard Methods of Testing appointed by the American Society of Mechanical Engi- neers, and is substantially the same as adopted by the German Engineers at Munich in 1888: Dro p-tests are to be made on a standard drop, which is to embody the following essential points: a, Each drop-test apparatus must be standardized. b. The “ball” (falling mass) shall weigh 1000 or 1500 pounds; the smaller is, however, preferable. c. The “ball” may be made of cast iron, cast or wrought steel; the shape is to be such that its center of gravity be as low as possible. d. The striking-block is to be made of forged steel, and is to be secured to the “ball” by dovetail and wedges in a rigid manner, and so that the striking-face is placed strictly symmetrical about and normal to its vertical axis passing through the center of gravity. Special permanent marks are to indicate the correctness of the face in these respects. Special marks should be made to indicate the center of the anvil- block. e. The length of guides on the ball should be more than twice the width between the guides, which are to be made of metal; i.e., rails so placed that the ball has but a minimum amount of play between them. Graphite is recommended as lubricant. 134 EXPERIMENTAL ENGINEERING f. The detachment or shears must not cause the ball to oscillate between the guides, and must be readily and freely controllable, with the point of suspension truly above the center of gravity of the ball; and a short movable link, chain, or rope is to be fixed between the ball and shears or detachment. g. When a constant height of drop is used, an automatic detach- ing device is recommended. h. The bearings for the test-piece are to be rigidly attached to the scaffold or frame, and they should be, wherever possible, in one piece with it. i. The weight of frame, bearings, and anvil-block should be at least ten times that of the ball. j. The foundation should be inelastic, and consist of masonry, the dimensions of which are to be determined by the locality and subsoil. k. The surface struck should always be accurately level; therefore proper shoes or bearing-blocks are to be provided for testing rails, axles, tires, springs, etc., etc., to insure a proper level upper surface; these blocks are to be as light as possible. The exact shape of these bearing-blocks is to be given in each test report. 1. The gallows or frame should be truly vertical and the guides accurately parallel. m. The height of fall of ball should be 20 feet clear, between striking and struck surfaces. n. Drops which by friction of ball on guides absorb two per cent of the work due to impact are to be discarded. o. For tests on large specimens a ball weighing 2000 pounds is to be used. p. A sliding-scale is to be attached to the frame, and in such a manner that the zero-mark can always be placed on a level with the top of the test-piece. 80. Minor Tests: The Welding-test. —The welding is to be done with a hammer weighing eight to ten pounds, with a given number of blows. The weld is to be a simple scarf weld, made in a coke or gas flame without fluxes. Each bar to be tested is to be treated in the same way, using in each case two or three samples of iron; one weld STRENGTH OF MATERIALS — METHODS OF TESTING 135 is to be tested on the tension-machine, the other to be nicked to the depth of the weld and then bent or broken, to show the character of the welded surfaces. The Bending-test. — This affords a ready means of finding the ductility of metals. The test-piece is to be bent about a stud having a diameter twice that of the specimen. The piece is to be bent with a lever, and no pounding is permitted. If the plate hold- ing the stud is graduated, the angular deflection at time of perma- nent set may be read at once. A modification of the bending-test is often used to determine the property of toughness, by bending the specimen, first hot and then cold, until it is doubled over on itself. The Drijting-test. —This tests the softness and ductility of metals. It is made by driving a “drift,” a tapered steel punch, so as to enlarge a hole drilled in a plate. The measurement is in the amount of enlargement of the hole before the edges crack and tear. The Punching-test.— Find the least material that will stand be- tween the edge of the plate and the hole punched, by measurement. The Forging-test. —'The material is brought to a red heat and hammered until cracks begin to show, the relative amount of flattening indicating the red-shortness of the material. Useful principally with rivet-rods. The Hammer-test. —This is made with a light hammer, and the character of the material is determined by the sound emitted. Is useful in locating defects in finished products, but of little value on test-specimens. The Hardening-test is made by heating a specimen to cherry- red heat and plunging it in water having a temperature of 32 to 4o degrees. The specimen so treated is tested by bending or torsion, the same as an unhardened specimen. Used for boiler plate and similar materials to find whether the carbon content is too high. The Abrasion-test. —Find the amount of wear from a given amount of work. For testing paving-brick and similar material special abrasion-testing machines have been devised, and the test is standardized. These machines are of barrel form. A charge is 136 EXPERIMENTAL ENGINEERING put in consisting of a certain number of brick and of hard cast-iron cubes of 1-inch or 2-inch face. The charged barrel is rotated a certain number of times at a certain speed, such that its contents get a thorough mixing and shaking. The measurement is in per- centage of weight lost by the brick. Abrasion-tests of metals, generally bearing metals, are made by holding a block of the metal against a hardened steel wheel of large diameter, using a certain pressure between the block and the wheel, running the wheel a definite number of revolutions, and measuring the loss of weight or thickness of the block tested. The Hardness-test. —The “hardness” of a material is usually understood as a relative property, having reference to the ability of one material to cut another. Hardness is a composite property, depending partly on density and on tensile and shear strengths. Hence the machines devised to measure hardness are also strength- measuring devices. Two types of hardness-testers are likely to be met with by the engineer, the pressure and the impact types, represented respectively by the Brinell ball-tester and the Shore “Scleroscope.”’ 1. The Brinell Ball-testers. —For the Brinell ball-tester a flat of an inch or so in diameter is prepared on the surface of the material to be tested. Then a hard steel ball, usually five-eighths of an inch in diameter, is pressed into the material with a certain load. The depth or diameter of the impression made in the material is then measured with a special micrometer. From this, the load used, and the size of the ball used, the “hardness” is computed. These same data have been found to be so intimately connected with the ultimate strength of the material that this quantity also can be computed with good accuracy from the ball-test. The close connection with the ultimate strength can be understood when one considers that to displace the material and make the permanent impression which is measured the material must have been stressed considerably beyond its yield-point. The ball-test thus gains unexpected importance, for it becomes a field-test of the strength of materials (steels and iron), which can be applied at any time, without appreciable injury to the material or taking the material out of its place in a structure. STRENGTH OF MATERIALS — METHODS OF TESTING 137 2. The Scleroscope.—The Shore ‘“Scleroscope” drops onto a small flat surface of the material to be tested a tiny diamond- pointed steel hammer. If the material were perfectly elastic and no work were done on it (perfect hardness), the hammer would rebound to the height from which it fell. If some of the energy of the hammer is used up in doing work on the material tested, making an impression in the material, then the rebound of the hammer is not complete. The softer the material, the less is the rebound. Hence the ratio of height of fall to height of rebound of the hammer measures the hardness of the material. On account of the rapidity of the blow and the smallness of the area of material affected, the strength with which the material resists deformation by the scleroscope hammer is the elastic strength of the material. On brittle materials, where the elastic strengths and ultimate strengths are close together, the two types of hardness-testers will give parallel results. On ductile materials the ball-tester seems to get nearer to the cutting hardness. The impact type of testers will show a “hardness” more than proportionate to the cutting hardness on cold-worked metals, on account of the elevation of the elastic strength by cold working. The Fatigue-test. —Fatigue-tests are made to determine the resistance of materials to repeatedly applied loads, either with or without reversal of stress. No commercially satisfactory fatigue- test has yet been devised. It is well established that failure will occur under repeated loads of much less intensity than is needed for failure under single loading. This is due to (1) the time factor in shear failure, so that the material tested in an ordinary “single- loading” tensile test does not break down at the yield-point at as low a stress as it should; (2) the nonhomogeneity of nature of the metals, being different in properties in adjacent crystals of their make-up, and the repeated loadings searching out the weak spots as a single loading cannot. It is proper to note here that rest, or removal of stressing, for a time may restore strength and elasticity to a material beginning to be fatigued; a complete recovery, unless cracks have begun to form, can be brought about by heat treatment in the case of steels, 138 EXPERIMENTAL ENGINEERING 81. Special Tests and Specifications. —In general the material is to be tested in such a manner as to develop the same properties that will be called forth in the peculiar use to which it is devoted. The table below shows the tests that are prescribed for materials for various uses, by the Committee on Standard Tests and Methods of Testing of the American Society of Mechanical Engineers: TABLE SHOWING TESTS REQUIRED. Required Test Denoted by x. ¢ . ; 8 3 ob ~ | B18 : ~ 1S a |” Material used for g oe ale12)e/ 8) 2] 2 = a/e(aite)a/S/2/e] Pls] 3 Si gle eles lal le) ss Railroad rails......... : a wcialtsite dll) Bo [Reel BE lewtetelin ccs dates se car-axles........ x scbotallicna alt ORE Netessl) Foe dlasstiate teas sift ss “ATES osiecu es x sen danas 082 | cated aes Gal] a ose es softs Shatiing’ .we0es caeseeeesa x 6! || | Diese hace | oes seca’, os ‘aint Building — wrought iron. . x} wx] w].... x | m|....[-... athe ee low steel...... |) 798 x jcc] EW SEEM aS ari ae high steel..... | £2) 2 awe BE], ME arcs si Boiler — wrought iron..... Seslose9| sees eer eect ayaa wat a ee ee Plates... cs cce ees a eee Re gas | BOP saves | Oe x ss shape-iron....... DO | ual ceatiaes 2) 26: lagen]. He x ef rivet-rods....... BE AW oievens' | dcmesus gel! AE bakead. 25 ee low steels....... Oo Abe aa col taaneis | | ee Shipmaterials ....¢¢<454%5 feces sesfewes cnt Reta | a ae SO plates is j.-tak eatemaerns OG: Is sia.ci) sealer x BES MTIVE tS \azciit 28 deri gate Mecsas. al Soave sides Bede x Wires iui aun ssoeo eats 6 leases all apavete'| Saco ed sg angle a ail MF agli a eae [eeaoa ead Wire Tope ss wie hese es ciine 0 Micon a afd ene if. Beles eahoaes Allee maleate eel 5 abo Cast irOnscera sees ss aes Bl 6 lees Saul gy gall) 6 Copper and soft metals... . 6) H |ewys x Wo0dsS)..45 secure e oSuk. ees we] xe || 2 SONS iis eis ha eS juceanpere anes ae] 8 * Repeat in both directions — also by winding, t Longitudinal, Many of the Engineering Societies and of the different associ- ations of manufacturers have formulated and adopted specifications for, and methods of test of, the different engineering materials. These rules differ more or less among themselves even in the case of materials intended for the same purposes. It is therefore neces- sary to determine, before testing, just what set of specifications a material is to meet. Some of the more important sets of rules are STRENGTH OF MATERIALS — METHODS OF TESTING 1 39 given below, but, as these rules are modified from time to time, those cited must be considered rather as examples of what to expect than as specifications to be used in any individual case without further investigation. MANUFACTURERS’ STANDARD SPECIFICATIONS, (Revised to Feb. 6, 1903.) 1. STRUCTURAL STEEL. Process of Manufacture. 1. Steel may be made by either the Open-hearth or the Bessemer process. Testing and Inspection. _ 2, All tests and inspection shall be made at the places of manufacture prior to shipment. Test-pieces. 3. The tensile strength, limit of elasticity and ductility, shall be determined from a standard test-piece cut from the finished material. The standard shape of the test-piece for sheared plates shall be as shown by the following sketch (Fig. II0). | About 3” ee Parallel Section ————————_—_—* ' Not less than 9” 1 ' 1 1 = + eg tt ~~ I 1 | $e tHe 4! tne Ete. 5 About 18” { Piece to be same thickness as the plate : Fic, 110. On specimens cut from other material the test-piece may be either the same as for sheared plates, or it may be planed or turned parallel throughout its entire length, and in all cases where possible, two opposite sides of the test-piece shall be the rolled surfaces. The elongation shall be measured on an original length of 8 inches except as modified in section 12, paragraph c. Rivet rounds and small bars shall be tested of full size as rolled. Two test-pieces shall be taken from each melt or blow of finished material, one for tension and one for bending; but in case either test develops flaws, or the tensile test-piece breaks outside of the middle third of its gauged length, it may be dis- carded and another test-piece substituted therefor. 140 EXPERIMENTAL ENGINEERING Annealed Test-pteces. 4. Material which is to be used without annealing or further treatment shall be tested in the condition in which it comes from the rolls. When material is to be annealed or otherwise treated before use, the specimen representing such material shall be similarly treated before testing. Marking. 5. Every finished piece of steel shall be stamped with the blow or melt number, and steel for pins shall have the blow or melt number stamped on the ends. Rivet and lacing steel, and small pieces for pin plates and stiffeners, may be shipped in bundles securely wired together, with the blow or melt number on a metal tag attached. Finish. 6. Finished bars shall be free from injurious seams, flaws or cracks, and have a workmanlike finish. Chemical Properties. 7a. Steel for buildings, train sheds, highway bridges and similar Maximum phosphorus, 0.10 per cent. structures. 7b. Steel for railway bridges: Maximum phosphorus, 0.08 per cent. Physical Properties. 8. Structural steel shall be of three grades: Rivet, Railway Bridge and Medium. Rivet Steel. g. Ultimate strength, 48,000 pounds per square inch. Elastic limit, not less than one-half the ultimate strength. Percentage of elongation, ——~4°%°0°__ 8 8 ’ Ultimate strength Bending-test, 180 degrees flat on itself, without fracture on outside of bent portion. Steel for Railway Bridges. to. Ultimate strength, 55,000 to 65,000 pounds per square inch. Elastic limit, not less than one-half the ultimate strength. Percentage of elongation. a : S S ” Ultimate strength Bending-test, 180 degrees to a diameter equal to thickness of piece tested without fracture on outside of bent portion. Medium. Steel. 11. Ultimate strength, 60,000 to 70,000 pounds per square inch. Elastic limit, not less than one-half the ultimate strength. Percentage of elongation, ——40%000 _ 8 8 ” Ultimate strength STRENGTH OF MATERIALS — METHODS OF TESTING I4I Modifications in Elongation for Thin and Thick Material. 12, For material less than 7 inch and more than } inch in thickness, the fol- lowing modifications shall be made in the requirements for elongation: a. For each increase of § inch in thickness above } inch, a deduction of I per cent shall be made from the specified elongation, except that the minimum elongation shall be 20 per cent for eye-bar material and 18 per cent for other structural material. b. For each decrease of #s inch in thickness below 3; inch, a deduction of 2} per cent shall be made from the specified elongation. c. In rounds of $ inch or less in diameter, the elongation shall be measured in a length equal to eight times the diameter of section tested. d, For pins made from any of the before-mentioned grades of steel, the required elongation shall be 5 per cent less than that specified for each grade, as determined on a test-piece, the center of which shall be one inch from the surface of the bar. Variation in Weight. 13. The variation in cross-section or weight of more than 24 per cent from that specified will be sufficient cause for rejection, except in the case of sheared plates, which will be covered by the following permissible variations: a, Plates 123 pounds per square foot or heavier, up to 100 inches wide, when ordered to weight, shall not average more than 24 per cent variation above or 24 per cent below the theoretical weight. When 100 inches wide and over, 5 per cent above or 5 per cent below the theoretical weight. b. Plates under 123 pounds per square foot, when ordered to weight, shall not average a greater variation than the following: Up to 75 inches wide, 24 per cent above or 2 per cent below the theoretical weight. Seventy-five inches wide up to 100 inches wide, 5 per cent above or 3 per cent below the theoretical weight. When roo inches wide and over, 10 per cent above or 3 per cent below the theoretical weight. 2. STRUCTURAL Cast [RON. 1. Except when chilled iron is specified, all castings shall be tough gray iron, free from injurious cold-shuts or blow-holes, true to pattern, and of a workmanlike finish. Sample pieces, one inch square, cast from the same heat of metal in sand moulds, shall be capable of sustaining on a clear span of 4 feet 8 inches a central load of 500 pounds when tested in the rough bar. 3. SPECIAL OPEN-HEARTH PLATE AND RIVET STEEL. Testing and Inspection. 1. All tests and inspections shall be made at the place of manufacture prior to shipment. Test-pieces. 2. The tensile strength, limit of elasticity and ductility, shall be determined from a standard test-piece cut from the finished material. The standard shape: 142, EXPERIMENTAL ENGINEERING of the test-piece for sheared plates shall be as shown by the following sketch (see Fig. 111): On specimens cut from other material the test-piece may be either the same as for sheared plates, or it may be planed or turned parallel throughout its entire length, and, in all cases where possible, two opposite sides of the test-piece shall be rolled surfaces. The elongation shall be measured on an original length of 8 inches, except as modified in section 12, paragraph ¢. Rivet rounds and small bars shall be tested of full size as rolled. Four test-pieces shall be taken from each melt of finished material, two for tension and two for bending; but in case either test develops flaws, or the tensile test-piece breaks outside of the middle third of its gauged length, it may be dis- carded and another test-piece substituted therefor. Annealed Test-pieces. 3. Material which is to be used without annealing or further treatment shall be tested in the condition in which it comes from the rolls. When material is to be annealed or otherwise treated before use, the specimen representing such material shall be similarly treated before testing. Marking. 4. Every finished piece of steel shall be stamped with the melt number. Rivet steel may be shipped in bundles securely wired together, with the melt number on a metal tag attached. Finish. 5. All plates shall be free from injurious surface defects and have a workmanlike finish. Chemical Properties. Maximum phosphorus, 0.06 per cent. Maximum sulphur, 0.04 per cent. Maximum phosphorus, 0.04 per cent. Maximum sulphur, 0.04 per cent. 6a. Flange or boiler steel. 6b. Extra-soft and fire-box steel. i Physical Properties. 7. Special Open-hearth Plate and Rivet Steel shall be of three grades : Extra- soft, Fire-box and Flange or Boiler Steel. Extra-soft Steel. 8. Ultimate strength, 45,000 to 55,000 pounds per square inch. Elastic limit, not less than one-half the ultimate strength. Elongation, 28 per cent. Cold and quench bends, 180 degrees flat on itself, without fracture on outside of bent portion. Fire-box Steel. 9. Ultimate strength, 52,000 to 62,000 pounds per square inch. Elastic limit, not less than one-half the ultimate strength. Elongation, 26 per cent. Cold and quench bends, 180 degrees flat on itself, without fracture on outside of bent portion. STRENGTH OF MATERIALS — METHODS OF TESTING 143 Flange or Boiler Steel. to. Ultimate strength, 55,000 to 65,000 pounds per square inch. Elastic limit, not less than one-half the ultimate strength. Elongation, 25 per cent. Cold and quench bends, 180 degrees flat on itself, without fracture on outside of bent portion. Boiler-rivet Steel. 11. Steel for boiler rivets shall be made of the extra-soft grade specified in paragraph No. 8. Modifications in Elongation for Thin and Thick Material. 12. For material less than 3; inch, and more than ? inch in thickness, the following modifications shall be made in the requirements for elongation: a. For each increase of 3 inch in thickness above ? inch, a deduction of 1 per cent shall be made from the specified elongation. b. For each decrease of # inch in thickness below #, inch, a deduction of 24 per cent shall be made from the specified elongation. : c. In rounds of % inch or less in diameter, the elongation shall be measured in a length equal to eight times the diameter of section tested. , Variation in Weight. 13. The variation in cross-section or weight of more than 2} per cent from that specified will be sufficient cause for rejection, except in the case of sheared plates, which will be covered by the following permissible variations: a, Plates 124 pounds per square foot or heavier, up to 100 inches wide, when ordered to weight, shall not average more than 2} per cent variation above or 24 per cent below the theoretical weight. When 100 inches wide and over, 5 per cent above or 5 per cent below the theoretical weight. bd. Plates under 123 pounds per square foot, when ordered to weight, shall not average a greater variation than the following: Up to 75 inches wide, 23 per cent above or 2} per cent below the theoretical weight. Seventy-five inches wide up to 100 inches wide, 5 per cent above or 3 per cent below the theoretical weight. When 100 inches wide and over, 10 per cent above or 3 per cent below the theoretical weight. AMERICAN BOILER MANUFACTURERS’ ASSOCIATION SPECIFICATIONS (Adopted 1898). 1. Cast Iron. — Should be of soft, gray texture and high degree of ductility. To be used only for hand-hole plates, crabs, yokes, etc., and manheads. It is a dangerous metal to be used in mud drums, legs, necks, headers, manhole rings, or any part of a boiler subject to tensile strains; its use is prohibited for such parts. 2. Steel. —Homogeneous steel made by the open-hearth or crucible processes, and having the following qualities, is to be used in all boilers. 144 | EXPERIMENTAL ENGINEERING Tensile Strength, Elongation, Chemical Tests. — Shell plates not exposed to the direct heat of the fire or gases of combustion, as in the external shells of internally fired boilers, may have from 65,000 to 70,000 pounds tensile strength; elongation not less than 24 per cent in 8 inches; phosphorus not over 0.035 per cent; sulphur not Over 0.035 per cent. Shell plates in any way exposed to the direct heat of the fire or the gases of combustion, as in the external shells or heads of externally fired boilers, or plates on which any flanging is to be done, to have from 60,000 to 65,000 pounds tensile strength; elongation not less than 27 per cent in 8 inches; phosphorus not over 0.03 per cent; sulphur not over 0.025 per cent. Fire-box plates, or such as are exposed to the direct heat of the fire, or flanged on the greater portion of their periphery, to have 55,000 to 62,000 pounds tensile strength; elongation, 30 per cent in 8 inches; phosphorus not over 0.03 per cent; sulphur not over 0.025 per cent. For all plates the elastic limit to be at least one-half the ultimate strength; per- centage of manganese and carbon left to the judgment of the steel maker. Test Section to be 8 inches long, planed or milled edges; its cross-sectional area not less than one-half of one square inch, nor width less than the thickness of the plate. Bending-test. — Steel up to } inch thickness must stand bending double and being hammered down on itself; above that thickness it must bend round a mandrel of diameter one and one-half times the thickness of plate down to 180 degrees. All without showing signs of distress. Bending test-piece to be in length not less than sixteen times thickness of plate and rough, shear edges milled or filed off. Such pieces to be cut both lengthwise and crosswise of the plate. All tests to be made at the steel mill. Three pulling-tests and three bending- tests to be made from each heat. If one fails the manufacturer may furnish and test a fourth piece, but if two fail the entire heat to be rejected. Certified copies of tests to be furnished each member of A. B. M. A. from heats from which his plates are made. 3. Rivets. — All rivets to be of good charcoal iron, or of a soft, mild steel, having the same physical and chemical properties as the fire-box plates, and must test hot and cold by driving down on an anvil with the head in a die; by nicking and bending, by bending back on themselves cold, without developing cracks or flaws. 4. Boiler Tubes, of charcoal iron or mild steel specially made for the purpose and lap-welded or drawn; they should be round, straight, free from scales, blisters, and mechanical defects, each tested to 500 pounds internal hydrostatic pressure. This fact and manufacturer’s name to be plainly stenciled on each tube. Standard Thicknesses by Birmingham wire gauge to be No. 13 for tubes 1 in., 1} in., 13 in. and 13 in. diameter. No. 12 for tubes 2 in., 2} in. and 24 in. diameter. No. rr for tubes 2? in., 3 in., 34 in. and 3} in. diameter, No. 10 for tubes 3$ in. and 4 in. diameter. No. 9 for tubes 43 in. and gs in. diameter. STRENGTH OF MATERIALS — METHODS OF TESTING 145 Tests. — A section cut from one tube taken at random from a lot of 150 or less must stand hammering down cold vertically without cracking or splitting when down solid. Length of test-pieces: 4 in. for tubes from 1 in. to 13 in. diameter. 1 in. for tubes from 2 in. to 24 in. diameter. 1} in. for tubes from 23 in. to 3} in. diameter. 14 in. for tubes from 33 in. to 4 in. diameter. 1} in. for tubes from 4} in. to 5 in. diameter. All tubes must stand expanding flange over on tube plate and bending without flaw, crack, or opening of the weld. 5. Stay Bolts to be made of iron or mild steel specially manufactured for the purpose, and must show on: Test Section, 8 inches long, net: For Iron, tensile strength not less than 46,000 lIbs.; elastic limit not less than 26,000 lbs.; elongation not less than 22 per cent for bolts of less than one (1) square inch area, nor less than 20 per cent for bolts one (1) square inch and more in net area. For Steel, tensile strength not less than 55,000 lbs.; elastic limit not less than ~ 33,000 Ibs.; elongation not less than 25 per cent for bolts of less than one (r) square inch area, nor less than 22 per cent for bolts one (1) square inch and more in net area. Tests. — A bar taken from a lot of 1000 lbs. or less at random, threaded with a sharp die ‘“V” thread with rounded edges, must bend cold 180 degrees around a .. bar of same diameter, without showing any crack or flaws. = Another piece, similarly chosen, and threaded, to be screwed into well-fitting nuts formed of pieces of the plates to be stayed, and riveted over so as to form an exact counterpart of the bolt in the finished structure; to be pulled in testing- machine and breaking stress noted; if it fails by pulling apart the tensile stress per square inch of net section is its measure of strength; if it fails by shearing the shear stress per square inch of mean section in shear is this measure. The mean section in shear is the product of half the thickness of the plate by the circumfer- ence at half height of thread. 6. Braces and Stays. — Material to be fully equal to stay-bolt stock, and tensile strength to be determined by testing a bar not less than ten inches (ro in.) long from each lot of 1000 lbs. or less. LLOYD’S SPECIFICATIONS FOR QUALITY AND TESTING OF SHIP STEEL (1907-1908). 1. Process of Manufacture. — Steel for shipbuilding shall be made by the open- hearth process, acid or basic. 2. Freedom from Defects. — The finished material shall be free from cracks, sur- face flaws and lamination. It shall also have a workmanlike finish, and must not have been hammer-dressed. 146 EXPERIMENTAL ENGINEERING 3. Testing and Inspection. — The following tests and inspections shall be made at the place of manufacture prior to dispatch; but, in the event of any of the material proving unsatisfactory in the course of being worked into vessels, such material shall be rejected, notwithstanding any previous certificate of satisfactory testing, and such further tests of the material from the same charge may be made as the Surveyor may consider desirable. 4. Tensile Test-pieces.— The tensile strength and ductility shall be determined from standard test-pieces cut lengthwise or crosswise from the rolled material. When material is annealed or otherwise treated before dispatch, the test-pieces shall be similarly and simultaneously treated with the material before testing. Plates. — Wherever practicable the rolled surfaces shall be retained on two opposite sides of the test-piece. The elongation shall be measured on a standard test-piece having a gauge-length of 8 inches. For material more than 0.875 inch in thickness the width of the test-piece between the gauge-points shall not exceed 14 inches; for material less than 0.375 inch thickness the width shall not be more than 24 inches. In other respects the test-pieces shall conform generally to the standard test-piece A (Fig. 111). Any straightening of test-pieces which may be required shall be done cold. ' ” «—______—_—_—_________—1——'Total Length about 18 | \ te , Parallel for a length not less than 9’) I 5 <_____—-8"Gauge Length ———_— ) ' eae, 4 “ For Thickness over 0.875: Maximum Width allowed=1!4 0 ” ” =2 YW 2% n For Thickness 0.375 to 0.875: Maximum Width allowed For Thickness under 0,375 ; Maximum Width allowed: Fic. 111. 5. Mechanical Tests and Selection of Test-pieces, — Plates and bars for ship- building shall comply with the following mechanical tests. All test-pieces shall be selected by the Surveyor and tested in his presence and he shall satisfy himself that the conditions herein described are fulfilled. 6. Tensile Tests.— Plates. — The tensile breaking strength of steel plates, determined from standard test-pieces, shall be between the limits of 28 and 32 tons (of 2240 pounds each) per square inch. For plates specially intended for cold flanging and marked for identification the lower limit shall be 26 tons per square inch. In the case of material for purposes in which tensile strength is not STRENGTH OF MATERIALS — METHODS OF TESTING 147 important, the tensile test may be dispensed with and the bend-test only be made, if so specified by the builders and approved by the Committee. The elongation, measured on a standard test-piece having a gauge-length of 8 inches, shall not be less than 20 per cent for material of 0.375 inch in thickness and upwards, and not less than 16 per cent for material below 0.375 inch in thickness. Angles, Bulb Angles, Channels, etc. — The tensile breaking strength of sectional material, such as angles, bulb angles, channels, etc., shall be between the limits of 28 and 33 tons (of 2240 pounds each) per square inch. In the case of material for purposes in which tensile strength is not important, the tensile test may be dis- pensed with and the bend-test only be made, if so specified by the builders and approved by the Committee. The elongation measured on a standard test-piece having a gauge-length of 8 inches shall not be less than 20 per cent for material of 0.375 inch in thickness and upwards, and not less than 16 per cent for material below 0.375 inch in thickness. Rivet Bars. — The tensile breaking strength of rivet bars, when required by the Committee to be tested, shall be between the limits of 25 and 30 tons (2240 pounds) per square inch of section, with an elongation of not less than 25 per cent of the gauge-length of eight times the diameter of the test-piece, measured on the stand- ard test-piece B (Fig. 112). The bars may be tested the full size as rolled. (With enlarged ends: Parallel for a length of not less than 9 times the reduced diameter [{$--—_—__—_______——————- Gauge Length —= Parallel for a length of not less than 8 times diame ——— Fic. 112. When the Surveyor is in constant attendance at the steel works the following requirements are to be complied with: 7. Number of Tensile Tests. — Plates and Sectional Material. — One tensile test for plates or sectional material shall be taken from the finished material of each charge. When the quantity of the material from one charge exceeds 25 tons, a second tensile test will be required; also additional tests shall be made for every variation in thickness of 0.15 of an inch in the plates or sectional bars from each charge. Rivet Bars. — When required by the Committee, one tensile test shall be taken from each charge used for rivet bars; but when the weight of the bars, as rolled, from one charge exceeds to tons, an additional tensile test shall be made for each further ro tons or portion thereof. Should a tensile-test piece break outside the middle half of its gauge-length, and the elongation be less than that required by the Rules, the test may, at the maker’s option, be discarded and another test be made of the same plate or bar. —! 148 EXPERIMENTAL ENGINEERING 8. Bend-tesis. — Cold Bends. — Test-pieces shall be sheared lengthwise or crosswise from plates or bars, and shall not be less than 14 inches wide, but for small bars the whole section may be used. For rivet bars bend-tests are not required. Temper Bends. — The test-pieces shall be similar to those used for cold-bend tests. For temper-bend tests the samples shall be heated to a blood-red and quenched in water at a temperature not exceeding 80 degrees Fahr. The color shall be judged indoors in the shade. In all cold-bend tests, and in temper-bend tests on samples 0.5 inch in thickness and above, the rough edge or arris caused by shearing may be removed by filing or grinding, and samples 1 inch in thickness and above may have the edges machined, but the test-pieces shall receive no other preparation. The test- pieces shall not be annealed unless the material from which they are cut is simi- larly annealed, in which case the test-pieces shall be similarly and simultaneously treated with the material before testing. For both cold and temper bends the test-piece shall withstand, without fracture, being doubled over until the internal radius is equal to 1} times the thickness of the test-piece, and the sides are parailel. For small sectional material these bend-tests may be made froma flattened bar. Bend-tests may be made either by pressure or by blows. 9. Number of Bend-tests.— A cold or temper-bend test ‘shall be made from each plate or bar as rolled, and these tests shall be in about equal numbers from each charge; but a cold-bend test shall be made from all plates which are specially marked for cold flanging. - to. Tests for Manufactured Rivets. — Rivets selected by the Surveyor from the bulk shall withstand the following tests: (a) The rivet shanks are to be bent cold, and hammered until the two parts of the shank touch in the manner shown in Fig. 113, without fracture on the out- side of the bend. Fic. 11q. (6) The rivet heads are to be flattened, while hot, in the manner shown in Fig. 114, without cracking at the edges. The heads are to be flattened until their diameter is 24 times the diameter of the shank. 11. Additional Tests before Rejection. — Should any of the test-pieces first selected by the Surveyor not fulfil the test requirements, two further tests may be STRENGTH OF MATERIALS — METHODS OF TESTING 149 made from the same plate or bar, but should either of these fail, the plate or bar from which the test-pieces were cut shall be rejected. In all such cases further tests shall be made before any material from the same charge can be accepted. 12. Branding. — Every plate and bar shall be clearly and distinctly marked by the maker in two places with the Society’s brand, indicating that the material has complied with the Society’s tests. No plates or bars bearing this brand shall be forwarded from the steel works until the prescribed tests have been made by the Surveyor, and the mill sheets have been signed by him. All plates and bars shall also be legibly stamped in two places with the maker’s name or trade-mark and the place where made. They shall also be stamped with numbers or identification marks by which they can be traced to the charge from which the material was made. 13. Maker’s Certificate. — Before the mill sheets are signed by the Surveyor, the maker shall furnish him with a certificate guaranteeing that the material has been made by the open-hearth process, and that it has been subjected to, and withstood satisfactorily the tests above described in the presence, of the Surveyor. The following form of certificate will be accepted if printed on each mill sheet with the name of the firm, and initialed by the test-house manager: “We hereby certify that the material described below has been made by the open-hearth process, and is that which has been satisfactorily tested in the presence of the Surveyor in accordance with the Rules of Lloyd’s Register.” ' 14. Rejected Material. — In the event of the material failing in any case to withstand the prescribed tests, the Surveyor shall see that the Society’s brand stamped on the plates and bars by the maker has been defaced by punch marks extending beyond the brand in the form of a cross, denoting that the material has been rejected. AMERICAN FOUNDRYMEN’S ASSOCIATION STANDARD SPECIFICATIONS FOR TESTING GRAY CAST IRON. (June 4, 1g01.) 1. Unless furnace iron, dry sand or loam moulding, or subsequent annealing is specified, all gray-iron castings are understood to be of cupola metal; mixtures, moulds and methods of preparation to be fixed by the founder to secure the results desired by purchaser. 2. All castings shall be clean, free from flaws, cracks, and excessive shrinkage. They shall conform in other respects to whatever points may be specially agreed upon. ; 3. When the castings themselves are to be tested to destruction, the number selected from a given lot and the tests they shall be subjected to are made a matter of special agreement between founder and purchaser. 4. Castings made under these specifications, the iron in which is to be tested for its quality, shall be represented by at least three test-bars from the same heat. 150 EXPERIMENTAL ENGINEERING 5. These test-bars shall be subjected to a transverse-breaking test, the load applied at the middle with supports 12 inches apart. The breaking-load and deflection shall be agreed upon specially on placing the contract, and two of these bars shall meet the requirements. 6. A tensile-strength test may be added, in which case at least three bars for this purpose shall be cast with the others in the same moulds respectively. The ultimate strength shall also be agreed upon specially before placing the contract, and two of the bars shall meet the requirements.* (See Fig. 115 for shape of tension-test piece.) nO INN * 7. The dimensions of the test-bars shall be as given herewith. There is only one size for the tensile bar and three for the transverse. For the light and medium weight castings the 14-inch round bar is to be used, heavy castings the 2-inch, and chilling irons the 2$-inch test-bar. 8. Where the chemical composition of the castings is a matter of specification in addition to the physical tests, borings shall be taken from all the test-bars made, well mixed, and any required determination, combined carbon and graphite alone excepted, made therefrom. g. Reasonable facilities shall be given the inspectors to satisfy themselves that castings are being made in accordance with specifications, and, if possible, tests shall be made at the place of production prior to shipments. 1o. The following are the sizes of bars selected for tests as a result of our investigations: For all tension tests a bar tumed to 0.8 inch in diameter, corresponding to a cross-section of } square inch. (Fig. 115.) Results, therefore, multiplied by two give the tensile strength per square inch. For transverse test of all classes of iron for general comparison, a bar 1} inches diameter on supports 12 inches apart, pressure applied in middle and deflection * The remarkably wide range of values for the ultimate strength and modulus of rupture which are really good for the various classes of iron precludes the giving of definite upper limits in the specifications. It will therefore remain a matter of mutual agreement in each case, the requirements of service and price per pound paid regulat- ing the mixtures which can be used. { There should really be no necessity for this test, for the requirements of the physi- cal tests presuppose a given chemical composition. It may, however, sometimes be expedient to know the total carbon, silicon, sulphur, manganese, and phosphorus of a casting to insure good service conditions. STRENGTH OF MATERIALS — METHODS OF TESTING I51 noted. Similarly, for ingot-mould, light machinery, stove-plate and novelty iron a 14-inch diameter bar; that is to say, for irons running from two per cent in silicon upward, or from 1.75 per cent silicon upward where but little scrap is in the mixture. For dynamo frame, sash weight, cylinder, heavy machinery, and gun-metal irons, similarly a 2-inch diameter bar is recommended; that is, for irons running from 1.50 to 2 per cent in silicon, or where the silicon is lower and the proportion of scrap is rather large. For roll irons, whether chilled or sand, and car-wheel metals, a 24-inch diameter bar is recommended; that is, for all irons below 1 per cent silicon, and which may therefore be classed as the chilling irons, AMERICAN WATER-WORKS ASSOCIATION STANDARD SPECIFI- CATIONS FOR CAST-IRON WATER-PIPE. (Philadelphia, 1891.) 1. Length. — Each pipe shall be of the kind known as “socket and spigot,” and shall be 12 feet long from bottom of the socket to the end of the pipe. 2. Metal and Treatment,— The metal shall be best quality neutral pig-iron, with no admixture of cinder, cast in dry-sand moulds, placed vertically, numbered and marked with name of maker and date of making. The shell to be smooth and round, without imperfections, and of uniform thickness. All pipes to be thoroughly cooled when taken from the pit, afterward thoroughly cleaned without the use of acid, then heated to 300 degrees F., and plunged into coal-pitch varnish. When removed, the coating to fume freely and set hard within an hour. Templates to be furnished by the maker; the weight of pipe to vary. not over 3 per cent from the standard; all tests to be made at expense of maker. 3. Testing. — The pipes to be tested after the varnish hardens with hydrostatic pressure of 300 pounds per square inch for all sizes below 12 inches diameter, and 250 pounds for all above that diameter, and simultaneously to be struck with a 3-pound hammer. 4. Test-bars. — Test-bars to be 26 inches long, 2 inches wide, and 1 inch thick, and to be tested for transverse strength. These bars shall stand, when carried flatwise on supports 24 inches apart, a center load of 1900 pounds, and show a deflection of not less than 0.25 inch before breaking. ‘Test-bars are to be cast when required by the inspector, and to be as nearly as possible the specified dimensions. PENNSYLVANIA RAILROAD COMPANY’S TEST FOR CAST-IRON CAR-WHEELS, Car-wheels are usually subjected to the drop-test, The following method is employed by the Pennsylvania Railroad Company for testing cast-iron wheels: For each fifty wheels which have been shipped, or are ready to ship, one wheel is taken at random by the railroad company’s inspector, either at the railroad com- pany’s shops or at the wheel-manufacturer’s, as the case may be, and subjected 152 EXPERIMENTAL ENGINEERING to the following test: The wheel is placed flange downward on an anvil-block weighing 1700 pounds, set on rubble masonry two feet down, and having three supports not more than five inches wide for the wheel to rest on. This arrange- ment being effected, the wheel is struck centrally on the hub by a weight of 140 pounds, falling from a height of 12 feet. Should the wheel break in two or more pieces before nine blows or less, the fifty wheels represented by it are rejected. If the wheel stands eight blows without breaking in two or more pieces, the fifty wheels are accepted. 82. Tests of Building Stone and Brick. — These materials are prin- cipally used in walls of buildings and for foundations. For this use they are subjected principally to compression or crushing stresses. The important properties are strength and durability. Stone is usually tested for compressive and transverse strength, brick for compressive strength. 1. Testing Stones. — The specimens for compressive strength are cubes of various sizes, depend- ing principally on the capacity of the testing-machine. These cubes are to be nicely made with the opposite sides perfectly parallel to provide a uniform bearing-sur. face. It is found that the larger the blocks the greater the strength per unit of area.* ‘i To test Stone for Compressive Strength. — Have the specimen dry and dressed, and ground to a cube — inches on each edge, and with the opposite faces parallel planes. This is important, as imperfect or wedge-shaped faces concentrate the stress ona small area. In testing, use a layer of wet plaster of Paris between the specimen and the faces of the machine, to distribute the stress. To test Stone for Transverse Strength. —In this case the specimen is dressed into the form of a prism 8 inches long and 2 by 2 inches in section. It is supported on bearings 6 inches apart, and a center load applied. The strength is com- puted as explained under head of Transverse Testing, page 60. Durability of stone is tested accurately only by actual trial. Some idea can be formed by noticing the effect of the weather on the exposed rocks in the quarry from which the specimen came. In the method of standard tests adopted in Munich, in 1887, the following additional tests are recommended: Trial method with (a) a jumper or drill, (0) by rotary boring. The amount of work done by the drill to be determined by the momentum of drop, its velocity of rotation, and the shape or cutting angle of the drill or cutting tool. These qualities are to be determined by comparison with a standard drill working under definite conditions. Examine the stone for resistance to shearing as well as to boring. * See Unwin, “Testing of Materials.” STRENGTH OF MATERIALS — METHODS OF TESTING 153 Find when possible the position in the quarry originally occupied by the speci- men tested. Find out the intended use of the stone, and determine the character of tests largely from that. Dry the stone until no further loss of weight occurs at a tem- perature of 30° C. (86° F.), and test in a dry condition. Make the tests for strength as described, using as large specimens as possible. Also, test by compression rectangular blocks. Test also for tension and bending. Obtain the specific gravity, after drying at a temperature of 86° F. Examine the specimen for resistance to frost by using samples of uniform size, 7 cm, (2.76 inches) on each edge. The frost-test consists of: a. The determination of the compressive strength of saturated stones, and its comparison with that of dried pieces. b. The determination of compressive strength of the dried stone after having been frozen and thawed out twenty-five times, and its comparison with that of dried pieces not so treated. c. The determination of the loss of weight of the stone after the twenty-fifth frost and thaw. Special attention must be had to the loss of those particles which are detached by the mechanical action, and also those lost by solution in a definite quantity of water. d, The examination of the frozen stone by use of a magnifying-glass, to deter- mine particularly whether fissures or scaling occurred. Yor the frost-test are to be used: Six pieces for compression-tests in dry condition, three normal and three parallel to the bed of the stone, provided these tests have not already been made, in which case it is permissible, on account of the law of proportions, to use cubical test-blocks larger than 7 cm. (2.76 inches). Six test-pieces in saturated condition — not frozen, however; three tested nor- mal to and three parallel to bed. Six test-pieces for tests when frozen, three of which are to be tested normal to and three parallel to bed of stone. When making the freezing-test the following details are to be observed: a. During the absorption of water the cubes are at first to be immersed but 2 cm. (0.77 inch) deep, and are to be lowered little by little until finally submerged. b. For immersion, distilled water is to be used at a temperature of from 15° C. (59° F.) to 20° C. (68° F.). c. The saturated blocks are to be subjected to temperatures of from — 10° to —15°C. (14° to 5° F.). This can be done in a vessel surrounded with melting ice and salt. d. The blocks are to be subjected to the influence of such cold for four hours, and they are to be thus treated when completely saturated. e. The blocks are to be thawed out in a given quantity of distilled water at from 59° F. to 64°F. 154 EXPERIMENTAL ENGINEERING An investigation of weathering qualities — stability under influences of atmos- pheric changes — can be neglected when the frost-test has been made. However, the effects in this respect, in nature, are to be carefully observed and compared with previous experience in the use of similar material. Observe — a. The effect of the sun in producing cracks and ruptures in stones. b. The effect of the air, and whether carbonic-acid gas is given off. c. The effect of rain and moisture. d. The effect of temperature. 2. Testing Bricks or Artificial Building-stone. —Bricks are tested for strength, principally by compression. They should be ground to a form with opposite parallel faces, and are tested between layers of thin paper, or, without grinding, between thin layers of plaster of Paris, as explained for stone. The variation in size of specimen, and whether the brick is tested on end, side-ways, or flat-ways, will make a great difference in the results. The test, to be of any value, must state the method of testing. Whole bricks are stronger per unit of area than portions of bricks, and should be used when practicable. It is also recommended that brick be tested for compression in the shape of two half-bricks superimposed, united by a thin layer of Portland cement, and covered on top and bottom with a thin layer of such paste to secure even bearing- surfaces.* The transverse test for brick is believed to be a valuable index to its building properties. Support the brick on knife-edges 6 inches apart, and apply the load at the center. Compute the modulus of rupture: 3 Wi 2 bd? in which W equals the center-load, / the length, 6 the breadth, d the depth, all in inches. Dry as for stone, and determine the specific gravity. Test hard-burned and soft-burned from the same kiln. Determine the porosity of the brick as follows: Thoroughly dry ten pieces on an iron plate; weigh these pieces; then sub- merge in water to one-half the depth for twenty-four hours; then completely sub- merge for twenty-four hours, dry superficially, and weigh. Determine porosity from the weight of water absorbed, which should be expressed as per cent of volume. Express absorption as per cent of weight. Determine resistance against frost, as previously explained for stones, using five specimens, and repeating the operation of freezing and thawing twenty-five times for each specimen. Observe the effect with a magnifying-glass. After freezing, test for compression, and compare the results with those obtained with a dry brick. R= * See Vol. XI (Standard Method of Testing), Transactions of American Society Mechanical Engineers. STRENGTH OF MATERIALS — METHODS OF TESTING 155 To test brick for soluble salts, obtain samples from an underburned brick and grind these to dust. Sift through a sieve 4g0o meshes per square cm. (31,360 per square inch). The dust sifted out is lixiviated in 250 c.c. of distilled water, boiled for about one hour, filtered, and washed. The amount of soluble salts is then determined by boiling down the solution and bringing the residue to a red heat for a short time. The amount is determined by weight and expressed in percentage; its composition is determined by a chemical analysis. Determinations of the presence of carbonate of lime, mica, or pyrites are to be made by chemical analysis. 83. Tests of Paving Material, Stones, and Ballast, Natural and Arti- ficial. —In this case the following observations and tests should be made: ; Information in regard to petrographic and geologic classification, the origin of the samples, etc., etc.; also: Statement in regard to utilization of same. Specific gravity of the samples is to be determined. All materials used in the construction of roads, provided they are not to be used under cover or in localities without frost, are to be tested for their frost- resisting qualities by tests similar to those prescribed for natural stone. Stones or brick used for paving are tested most satisfactorily in a manner representing their mode of utilization by determining the wearing qualities by an abrasion-test standardized by the National Brick Manufacturers’ Association. (1900) as follows: The Rattler Test. — The standard rattler shall be 28 inches in diameter and 20 inches in length, inside measurements. Other dimensions may be employed between 26 and 30 inches diameter and 18 to 24 inches length, in which case the dimensions should be stated in reporting the test. Longer rattlers may be em- ployed by the insertion of a diaphragm. The barrel shall be supported on trunnions at the ends, with no shaft running through the rattling chamber. The cross-section shall be a regular polygon of 14sides. The heads shall be of gray cast iron, not chilled or case-hardened. The staves shall preferably be composed of steel plates, as cast-iron peens and ulti- mately breaks from the wearing action on the inner side. There shall be a space of one-fourth of an inch between the staves for the escape of dust and small pieces. Machines having from 12 to 16 staves may be employed, with openings from } to # inch, but these variations from the standard should be mentioned in an official report. The Charge shall consist of but one kind.of brick at a time, nine paving blocks or twelve bricks * being inserted, together with 300 pounds of cast-iron blocks. *The number of bricks should be that number which most nearly gives the total cubic contents of the brick charge equal to 8 per cent of the total cubic con- tents of the rattler. 156 EXPERIMENTAL ENGINEERING These shall be of two sizes, 75 pounds being of the larger and 225 pounds of the smaller size. The larger size shall be about 23 inches square and 43 inches long, with slightly rounded edges, and shall weigh at first 7 pounds. The smaller size shall be 13-inch cubes, with rounded edges. All blocks shall be replaced by new ones when they have lost 10 per cent of their normal weight. The Number of Revolutions shall be 1800 for a standard test, at a speed between 28 and 30 per minute. The Bricks shall be fhdeauiatiy dried before testing. The Loss shall be calculated as a per cent of the weight of the dry bricks com- posing the charge, and mo result shall be considered as official unless it is the average of two distinct and complete tests on separate charges of bricks. The uniformity of wearing qualities of brick for parts more or less distant from the exterior surface is determined by repeating the trial on the sarhe piece, and not merely testing one, but a greater number of pieces. It is, moreover, necessary to test samples of the best, the poorest, and the medium qualities of bricks in any one kiln. Obtain the transverse strength as explained. Obtain the per cent of water absorbed after the bricks have been thoroughly dried at 30° C. (86° F.), as explained in Art. 2, p. 154. Test materials for ballast in a similar manner. In some cases it may be desirable to test stones as to the capacity for receiving a polish. Examinations of asphalis can only be made in an exhaustive manner by the construction of trial roads. An opinion coinciding with the results of .such trial may be formed by — (a) Determination of the quantity and quality of the bitumen contained therein (whether the bitumen be artificial or natural). (0) By physical and chemical determination of the residue. (c) By determination of the specific density of test-pieces of the material used by means of a needle of a circular sectional area of 1 sq. mm., carrying a weight of 300 grams. (See Cement Testing, p. 160.) _ (d) By the determination of the wear of such test-pieces by abrasion or grind- ing trials. (e) By the determination cf the resistance to frost of these test-pieces. (See Building Stone, Frost-test.) 84. Testing Cements and Mortars. —The following descriptions will serve to distinguish the different classes of bonding materials: 1. Common limes are produced by roasting at bright red heat limestones containing little clay or silicic acid. When moistened with water limes become wholly or partly pulverized and slaked. They are sold, when unslaked, as lumps of “quick-lime”; when slaked, in the form of fine flour. After mixing with water (and sand) to STRENGTH OF MATERIALS — METHODS OF TESTING 157 make mortar, the setting or hardening of the lime cement takes place by chemical combination with CO, from the atmosphere, and simultaneous rejection and evaporation of the water used in mixing. 2. Water limes and Roman cements are products obtained by burning clayey lime marls or limestones below the melting temper- ature. They do not disintegrate on being moistened, but must be powdered by mechanical means. ‘Their setting or hardening is sim- ilar to that of the hydraulic cements rather than to that of common lime. 3. Hydraulic cements are products obtained by burning at a temperature of incipient fusion clayey marls or limestones or arti- ficial mixtures of materials containing clay and lime (or lime, silica, and, alumina), the clinker so made being crushed and ground to the fineness of flour. The hydraulic parts of a hydraulic cement are silicates and aluminates (or ferrates) of lime. In setting or hard- ening of the cement the hydraulic parts combine chemically with part or all of the water added in mixing; the water disappears as water, and becomes part of the cement. Hence the name “hydraulic cement.” Be 4. Hydraulic fluxes are natural or artificial materials which in general do not harden of themselves, but do so in presence of caustic lime, and then in the same way as a hydraulic material; i.e., puzzuo- lana, santorine earth, trass produced from a proper kind of volcanic tufa, blast-furnace slag, burnt clay. . 5. Puzzuolana cements are products obtained by most carefully mixing hydrates of lime, pulverized, with hydraulic fluxes in the condition of dust. 6. Mixed cements are products obtained by most carefully mixing existing cements with proper fluxes. Such bond materials should be particularly marked ‘‘ Mixed Cements,” at the same time naming the base and ‘the flux used. 7. Mortar is made by mixing three or four parts of sharp sand with one part of quick-lime or cement, and adding water until of the proper consistency. Mortar made from quick-lime will neither set nor stay hard under water; that made from /ydraulic- or water- lime, if allowed to set in the air, will not be softened by water; while that made from hydraulic cements will harden under water. 158 EXPERIMENTAL ENGINEERING 8. Method of Testing Cements. — The principal properties which it is necessary to know are: (1) fineness; (2) time of setting; (3) tensile strength; (4) soundness or freedom from cracks after set- ting; (5) heaviness or specific gravity; (6) crushing strength; (7) toughness or power to resist definite blows. The following standard method of testing cements was adopted by a committee of the American Society of Civil Engineers and of the American Society for Testing Materials in 1903 and 1904. Selection of Sample. — The sample shall be a fair average of the contents of the package; it shall be passed through a sieve having 20 meshes per lineal inch before testing to remove lumps. In obtaining a sample from barrels or bags, an auger or sampling-iron reaching to the center should be used. A chemical analysis, if required, should be made in accordance with the directions in the Journal of the Society of Chemical Industry, published Jan. 15, 1902. Specific Gravity. — This is most conveniently made with le Chatelier’s appa- ratus, which consists of a flask (D), Fig. 116, of 120 cu. cm. (7.32 cubic inches) capacity, the neck of which is about 20 cm. (7.87 inches) long; in the mid- dle of this neck is a bulb (C), above and below which are two marks (F and £); the volume between these marks is 20 cu. cm.(1.22 cubic inches). The neck has a diameter of about 9 mm. (0.35 in.), and is graduated into tenths of cubic centimeters above the mark F. Benzine (62° Baumé naph- tha), or kerosene free from water, should be used in making the deter- mination. WL The specific gravity can be deter- Fic. 116. —Le CHAtetter’s Specrric. Mined in two ways: (1) The flask is GRAVITY APPARATUS. filled with either of these liquids to the lower mark (£), and 64 gr. (2.25 ounces) of powder, previously dried at 100° C. (212° F.) and cooled to the temper- ature of the liquid, is gradually introduced through the funnel (B) [the stem of which extends into the flask to the top of the bulb (C)], until the upper mark (F) is reached. The difference in weight between the cement remaining and the original quantity (64 gr.) is the weight which has displaced 20 cu. cm. (2) The whole quantity of the powder is introduced, and the level of the liquid rises to some division of the graduated neck. This reading plus 20 cu. cm. is the STRENGTH OF MATERIALS — METHODS OF TESTING 159 ‘volume displaced by 64 gr. of the powder. The specific gravity is then obtained from the formula: . eee Weight of cement RBCS eran Weight of volume of liquid displaced © The flask during the operation is kept immersed in water in a jar, A, in order to avoid variations in the temperature of the liquid. Different trials should agree within 1 per cent. The apparatus is conveniently cleaned by inverting the flask over a glass jar, then shaking it vertically until the liquid starts to flow freely. Repeat this opera- tion several times. / Fineness. — The fineness is determined by the use of circular sieves, about 20 cm. (7.87 inches) in diameter, 6 cm. (2.36 inches) high, and provided with a pan 5 cm. (1.97 inches deep) and a cover. The wire cloth should be woven (not twilled) from brass wire having the fol- lowing diameters: No. 100, 0.0045 inch; No. 200, 0.0024 inch, This cloth should be mounted on the frames without distortion; the mesh should be regular in spacing and be within the following limits: No. 100, 96 to 100 meshes to the linear inch; No. 200, 188 to 200 “SO so 50 to 100 gr. dried at a temperature of 212° F. prior to sieving should be used for the test, the sieves having previously been dried. The coarsely screened sample is weighed and placed on the No. 200 sieve, which is moved forward and backward, at the same time striking the side gently with the palm of-the other hand, at the rate of about 200 strokes per minute. The operation is continued until not more than one-tenth of one per cent passes through per minute. The work is expedited by placing in the sieve a small quantity of large shot, or, better, some flat pieces of brass or copper about the size of a cent. The residue is weighed, then placed on a No. 100 sieve and the operation repeated. The results should be reported to the nearest tenth of one per cent. Normal Consistency. — The use of a proper percentage of water in mixing the cement or mortar is exceedingly important. No method is entirely satisfactory, but the following, which consists in the determination of the depth of penetration of a wire of a known diameter carrying a specified weight, is recommended. The apparatus recommended is the Vicat needle, shown in Fig. 117, which is also used for determining the time of setting. This consists of a frame, K, bearing a movable rod, L, with a cap, D, at one end, and at the other the cylinder, G, 1 cm. (0.39 inch) in diameter, the cap, rod and cylinder weighing 300 gr. (10.58 oz.) The rod, which can be held in any desired position by a screw, F, carries an indi- cator, which moves over a graduated scale attached to the frame, K. The paste is held by a conical hard-rubber ring, J, 7 cm. (2.76 inches) in diameter at the base, 4 cm. (1.57 inches) high, resting on a glass plate, J, about 10 cm. (3.94 inches) square. 160 EXPERIMENTAL ENGINEERING In making the determination, the same quantity of cement as will be subse- quently used for each batch in making the briquettes (but not less than 500 grams) is kneaded into a paste and quickly formed into a ball with the hands, completing the operation by tossing it six times from one hand to the other, maintained 6 inches apart; the ball is then pressed into the rubber ring, through the larger open- ing, smoothed off, and placed (on its large end) on a glass plate and the smaller end smoothed off with a trowel; the paste, confined in the ring, resting on the plate, is placed under the rod bearing the cylinder, which is brought in contact with the surface and quickly released. Qa | Ati 6 ar SSS J AME, lis, A. WS. CE Me oo it Fic. 117. — VicatT NEEDLE. The paste is of normal consistency when the cylinder, released from contact with the surface, penetrates to a point in the mass ro mm. (0.39 inch) below the top of the ring and there stops. Great care must be taken to fill the ring exactly to the top. The trial pastes are made with varying percentages of water until the correct consistency is obtained. The committee has recommended, as normal, a paste the consistency of which is rather wet, because it believes that variations in the amount of compression to which the briquette is subjected in moulding are likely to be less with such a paste. Time of Setting. — The object of this test is to determine the time which elapses until the paste ceases to be fluid and plastic, called the initial set, and also the time required for it to acquire a certain degree of hardness, called the final set. STRENGTH OF MATERIALS — METHODS OF TESTING 161 For this purpose the Vicat needle, which has already been described, should be used. -In making the test, a paste of normal consistency is moulded and placed under the rod (L), Fig. 117; this rod when bearing the cap (D) weighs 300 gr. (10.58 0z.). The needle (), at the lower end, is 1 mm. (0.039 inch) in diameter. Then the needle is carefully brought in contact with the surface of the paste and quickly released. The setting is said to have siataeaiee when the needle ceases to pass a point 5 mm. (0.20 inch) above the upper surface of the glass plate, and is said to have terminated the moment the needle does not sink visibly into the mass. The test-pieces should be stored in moist air during the test. This is accom- plished by placing them in a rack over water contained ina pan and covered with a damp cloth, the cloth to be kept away from them by means of a wire screen, or preferably they may be stored in a moist box or closet. The determination of the time of setting is only approximate, since it is mate- tially affected by the temperature of the mixing water, the percentage of the water used, and the amount of moulding the paste receives. Standard Sand. — The committee recommend at present the use of a natural sand from Ottawa, IIl., screened to pass a sieve having 20 meshes per lineal inch and retained on a sieve having 30 meshes per lineal inch; the wires to have diame- ters of 0.0165 and o.o1z2 inch respectively. This sand will be furnished by the Sandusky Portland Cement Co., Sandusky, Ohio, at a moderate price. This sand gives in testing considerably more strength than the crushed quartz of the same size formerly employed for this purpose. Form of Briquette. — The form of briquette recommended is shown in Fig. 120. It is substantially like that formerly used except that the corners are rounded. Moulds. — The moulds should be made of brass, bronze, or some equally non- corrodible material, and gang moulds of the form shown in Fig. 118 are recom- mended. They should be wiped with an oily cloth before using. Mixing. — All proportions should be stated by weight; the quantity of water to be used should be stated as a percentage of the dry material. The metric system is recommended because of the convenient relation of the gram and the cubic centi- meter. The temperature of the room and the mixing water should be as near 21° C. (70° F.) as it is practicable to maintain it. The sand and cement should be thoroughly mixed dry. The mixing should be done on some non-absorbing surface, preferably plate glass. If the mixing must be done on an absorbing surface, it should be thoroughly dampened prior to use. The quantity of material to be mixed at one time depends on the number of test- pieces to be made; about 1000 gr. (35.28 oz.) makes a convenient quantity to mix, especially by hand methods. The material is weighed, dampened, and roughly mixed with a trowel, after which the operation is completed by vigorously kneading with the hand for 14 minutes. Moulding. — Having worked the mortar to the proper consistency it is at once placed in the mould by hand, being pressed in firmly with the fingers and smoothed off with a trowel without ramming, but in such a manner as to exert a moderate 162 EXPERIMENTAL ENGINEERING pressure. The mould should be turned over and the operation repeated. The briquettes should be weighed prior to immersion, and those which vary in weight more than 3 per cent from the average should be rejected. DETAILS FOR GANG MOULD Fic. 118. ers = 4 FORM OF CLIP DETAILS FOR BRIQUETTE Fic. 119. FIG. 120. STANDARD CLIP AND BRIQUETTE ADOPTED BY THE AMERICAN SOCIETY FOR TESTING MATERIALS, 1904. Storage of the Test-pieces. — During the first twenty-four hours after mould- ing, the test-pieces should be kept in moist air to prevent them from drying out. A moist closet or chamber is so easily devised that the use of the damp cloth should be abandoned if possible. Covering the test-pieces with a damp cloth is objec- tionable, as commonly used, because the cloth may dry out unequally, and, in con- sequence, the test-pieces are not all maintained under the same condition. Where a moist closet is not available, a cloth may be used and kept uniformly wet by immersing the ends in water. It should be kept from direct contact with the test- pieces by means of a wire screen or some similar arrangement. A moist closet consists of a soapstone or slate box, or a metal-lined wooden box —the metal lining being covered with felt and this felt kept wet. The bottom of the box is so constructed as to hold water, and the sides are provided with cleats for holding glass shelves on which to place the briquettes. Care should be taken to keep the air in the closet uniformly moist. After twenty-four hours in moist air the test-pieces for longer periods of time should be immersed in water maintained as near 21° C. (70° F.) as practicable; they may be stored in tanks or pans, which should be of non-corrodible material. STRENGTH OF MATERIALS — METHODS OF TESTING 163 Tensile Strength. — The tests may be made on any standard machine. A solid metal clip, as shown in Fig. 119, is recommended. This clip is to be used without cushioning at the points of contact with the test-specimen. The bearing at each point of contact should be } inch wide, and the distance between the center of contact on the same clip should be 1} inches. Test-pieces should be broken as soon as they are removed from the water, the load being applied uniformly at the rate of about 600 pounds per minute. The average tests of the briquettes of each sample should be taken as the strength, excluding any results which are manifestly faulty. Constancy of Volume, — The object is to develop those qualities which tend to destroy the strength and durability of a cement. As it is highly essential to deter- mine such qualities at once, tests of this character are for the most part made ina very short time, and are known, therefore, as accelerated tests. Failure is revealed by cracking, checking, swelling, or disintegration, or all of these phenomena. A cement which remains perfectly sound is said to be of constant volume. Tests for constancy of volume are divided into two classes: (1) normal tests, or those made in either air or water maintained at about 21° C. (70° F.), and (2) accelerated tests, or those made in air, steam, or water at a temperature of 45° C. (115° F.) and upward. The test-pieces should be allowed to remain twenty-four hours in moist air before immersion in water or steam, or preservation in air. For these tests, pats, about 73 cm. (2.95 inches) in diameter, 1} cm. (0.49 inch) thick at the center, and tapering to a thin edge, should be made, upon a clean glass plate [about 10 cm. (3.94 inches) square], from cement paste of normal consistency. Normal Test. — A pat is immersed in water maintained as near 21° C. (70° F.) as possible for 28 days, and observed at intervals. A similar pat is maintained in air at ordinary temperature and observed at intervals. Accelerated Test. — A pat is exposed in any convenient way in an atmosphere of steam, above boiling water, in a loosely closed vessel for three hours. To pass these tests satisfactorily, the pats should remain firm and hard, and show no signs of cracking, distortion, or disintegration. Should the pat leave the plate, distortion may be detected best with a straight-edge applied to the surface which was in contact with the plate. In the present state of our knowledge it cannot be said that cement should necessarily be condemned simply for failure to pass the accelerated tests, nor can it be considered entirely satisfactory if it has passed these tests. AMERICAN SOCIETY FOR TESTING MATERIALS’ SPECIFICATIONS FOR CEMENT (Nov. 14, 1904). 1. General Conditions — (a) All cement shall be inspected. (b) Cement may be inspected either at the place of manufacture or on the work. (c) In order to allow ample time for inspecting and testing, the cement should be stored in a suitable weather-tight building having the floor properly blocked or raised from the ground. 164 EXPERIMENTAL ENGINEERING (d) The cement shall be stored in such a manner as to permit easy access for proper inspection and identification of each shipment. (e) Every facility shall be provided by the contractor and a period of at least twelve days allowed for the inspection and necessary tests. (f) Cement shall be delivered in suitable packages with the brand and name of manufacturer plainly marked thereon. (g) A bag of cement shall contain 94 pounds of cement net. Each barrel of Portland cement shall contain 4 bags, and each barrel of natural cement shall con- tain 3 bags of the above net weight. (h) Cement failing to meet the seven-day requirements may be held awaiting the results of the twenty-eight-day tests before rejection. (¢) All tests shall be made in accordance with the methods proposed by the Committee on Uniform Tests of Cement of the American Society of Civil Engineers, presented to the Society January 21, 1903, and amended January 20, 1904, with all subsequent amendments thereto. (j) The acceptance or rejection shall be based on the following requirements: 2. Natural Cement. — Definition. — This term shall be applied to the finely pulverized product resulting from the calcination of an argillaceous limestone at a temperature only sufficient to drive off the carbonic acid gas. (a) Specific Gravity. — The specific gravity of the cement thoroughly dried at 100° C. shall be not less than 2.8. (b) Fineness. — It shall leave by weight a residue of not more than ro per cent on the No. roo sieve, and 3o per cent on the No. 200. (c) Time of Setting. — It shall develop initial set in not less than ten minutes, and hard set in not less than thirty minutes nor more than three hours. (d) Tensile Strength. — "The minimum requirements for tensile strength for briquettes one inch square in cross-section shall be within the following limits, and shall show no retrogression in strength within the periods specified:* Ages NEAT CEMENT. Strength. D4 OUTST MOIST AIT stuns. cya alain in@acare erate a ramen vets 50-100 lbs. 7 days (x day in moist air, 6 days in water)......... 100-200 “ 28 days (x day in moist air, 27 days in water)......... 200-300 ‘* ONE PART CEMENT, THREE PARTS STANDARD SAND. 7 days (1 day in moist air, 5 days in water) ......... 25-75 “ 28 days (x day in moist air, 27 days in --ater).......... 75-150 “ (e) Constancy of Volume.— Pats f neat cement about three inches in dia- meter, one-half inch thick at center, tapering to a thin edge, shall be kept in moist air for a period of twenty-four hours. * For example, the minimum requirement for the twenty-four-hour neat-cement test should be some specified value within the limits of 50 and 100 pounds, and so on for each period stated. STRENGTH OF MATERIALS — METHODS OF TESTING 165 ~ 3, A pat is then kept in air at normal temperature. 2. Another is kept in water maintained as near 70° F. as practicable. These pats are observed at inicrvals for at least 28 days, and, to satisfactorily pass the tests, should remain firm and hard and show no signs of distortion, check- ing, cracking or disintegrating. 3. Portland Cement. — Definition. — This term is oe to‘the finely pul- verized product resulting from the calcination to incipient fusion of an intimate mixture of properly proportioned argillaceous and calcareous materials, and to which no addition greater than 3 per cent has been made subsequent to calcination. (a) Specific Gravity. — The specific gravity of the cement, thoroughly dried at 100° C., shall be not less than 3.10. (0) Fineness. — It shall leave by weight a residue of not more than 8 per cent on the No. roo sieve, and not more than 25 per cent on the No. 200. (c) Time of Setting. — It shall develop initial set in not less than thirty minutes, but must develop hard set in not less than one hour nor more than 10 hours. (@) Tensile Strength.— The minimum requirements for tensile strength for briquettes one inch square in section shall be within the following limits, and shall show no retrogression in strength within the periods specified:* Age. NEAT CEMENT. - Strength. 24 Hours in) MOIlst GIP sscucwedne vemse sada see nese 150-200 lbs. 7 days (x day in moist air, 6 days in water).......... 450-550 “ 28 days (x day in moist air, 27 days in water).......... 550-650 “ ONE PART CEMENT, THREE PARTS SAND. 4 days (1 day in moist air, 6 days in water).......... 150-200 “ 28 days (z day in moist air, 27 days in water).......... 200-300 “ (e) Constancy of Volume. — Pats of neat cement about three inches in diame- ter, one-half inch thick at the center, and tapering to a thin edge, shall be kept in moist air for a period of twenty-four hours. 1. A pat is then kept in air at normal temperature and observed at intervals for at least 28 days. 2. Another pat is kept in water maintained as near 70° F. as practicable, and observed at intervals for at least 28 days. 3. A third pat is exposed in any convenient way in an atmosphere of steam, above boiling water, in a loosely closed vessel for five hours. These pats, to satisfactorily pass the requirements, shall remain firm and hard and show no signs of distortion, checking, cracking, or disintegrating. (f) Sulphuric Acid and Magnesia. — The cement shall not contain more than 1.75 per cent of anhydrous sulphuric acid (SO,), nor more than 4 per cent of mag- nesia (MgO). * For example, the minimum requirement for the twenty-four-hour neat-cement test should be some specified value within the limits of 150 and 200 pounds, and so on for each period stated. EXPERIMENTAL ENGINEERING 166 Report Blank. — The following is a blank for reporting the results of cement testing: Qa Lend , te A cp iJ Slee lee)e |e tml a |e it |e] & 4) 2) 25 |eed| 3 | & B | EB| 88 2 | & e |" | ea |Bag] 2 | = |8s| 8° e = | 002 | ovr | og | & © | sss 5 2 e 2 Se | SBE a B | & |aeqsow e:1 *qUOUI8D 4¥ONT sp 4m g 2s} % g ¢ ; § g 3 a : H} 2 | jo Surpuy a s ‘ oO durx ur pesn . “0 yo ate m o Batsted | ysout guano | 7 AS | seuseul ap yo-an Z ssoupunog seSe ye 44800148 O]ISUeT, jo Surppe |. Gass rad ‘ssouo uly ewy) 4v O14 FOJEM JO “JAL a wosy ‘aw -e19duey, quedo 10g 2uI105 Jimpiaceapeididiwieanamenmaiee °°. iene gigs giiaud 2 egestas aed stiiniieentne nieve eeeeeia naeiee . svn eee We ceiiinsaaee TEAL le ee enee SRR Phat Aas AemeieR perew eee eee pana DEER ars SE TES g ne whan RN SERA ee ea TE Eek e A Hee Fete Ke Haidures Pe ee ee) Aq paisa, a CURE ERT STS YS PRR RRR DEERME NATE A Sterne eee ORE GA ORT ‘sjatreqs st Buyueseidar yuauiaZ jo adures jo jsay, ‘yar yuemay ‘KLISUAAINA TTANUYOO ‘ADATION AATIAIS ‘ONIVAANIONA IVLINAWIYadXa AO LNAWLYVdad CHAPTER VI. MEASUREMENT OF PRESSURE. 85. Pressure, Definitions and Units.— The term pressure, as employed in engineering, refers to the force tending to compress a body, and is generally expressed as follows: (1) In pounds per square inch; (2) In pounds per square foot; (3) In inches of mer- cury; (4) In feet or inches of water. The values of these different units of pressure are as follows: TABLE SHOWING RELATION BETWEEN PRESSURE EXPRESSED IN POUNDS, AND THAT EXPRESSED IN INCHES OF MERCURY, OR FEET OF WATER. fe] Pressure in Pressure in 70° Fahr. Pounds per Sq. Pounds per Sq. Inch. Foot. Inches Gf Mets | sas aif Water) Tnchenol Water cury. I 144 2.0378 2.307 27.68 2 288 4.0756 4.614 55-36 3 432 6.1134 6.921 83.04 4 576 8.0512 9.23 II0.72 5 720 10.1890 Il.54 138.40 6 864 12.2268 13.85 166.08 7 1008 14.2646 160.15 193-76 8 I1§2 16. 3024 18.46 221.44 9 1296 18.3402 20.76 249.12 Io 1440 20.3781 23.07 276.80 The barometer pressure is that of the atmosphere in inches of mercury reckoned from a vacuum. At the sea-level, latitude of Paris, the normal reading of the barometer is 29.922 inches of mer- cury at 32° F. corresponding to a pressure of 14.7 pounds per square inch. Gauge or Manometer pressure is reckoned from the atmospheric pressure. Absolute pressure is measured from a vacuum, and is equal to the sum of gauge-pressure and barometer readings expressed in the 167 168 EXPERIMENTAL ENGINEERING same units. Absolute pressure is always meant unless otherwise specified. Pressure below the atmosphere is usually reckoned in inches of mercury from the atmospheric pressure, so that 29.92 inches would correspond to a perfect vacuum at sea-level, latitude 49°. 86. Measurement of Pressure. — Pressure is always measured as a difference, that is, as pressure above or below some other pressure. Although there are apparent exceptions, no instrument has really been devised which actually measures absolute pressure. It would seem at first sight as though the barometer measured the absolute pressure of the atmosphere and thus formed an exception to this rule. What it really does is to measure the difference between the atmospheric pressure and the pressure of mercury vapor and any other gas present in the upper part of the barometer tube. The correction thus made necessary is, however, always negligible. The common pressure measurements are all made from the atmos- pheric pressure as a base, that is, they are pressures in pounds, or feet or inches of water or mercury above or below atmosphere. For a knowledge of absolute pressure it is therefore necessary to add to or subtract from the atmospheric pressure at the time of measurement. . The instruments for measuring pressures divide themselves naturally into two classes, those for low pressures, say up to about 15 pounds above atmosphere, and those for higher pressures. To a certain extent the types used for measuring the higher pressures are also used below 15 pounds, but they become less accurate as the pressure to be measured decreases. ‘The low-pressure measur- ing devices generally take the form known as Manometers; those for higher pressures are generally some form of gauge. 87. Manometers. —The term manometer is frequently applied to any apparatus for the measurement of pressure, although it is the practice of American engineers to use this term only for short columns filled with mercury, water or other liquid and used to measure small pressures. The pressure is measured in the ordinary case either above or below the atmosphere. To convert this into absolute pressure, find the sum of barometer and manometer readings in the first case and the difference between them in the second case. All readings must be in the same units. MEASUREMENT OF PRESSURE 169 The manometers in common use are glass or metal tubes, either U-shape in form, as in Fig. 121, or straight and connected to a cistern of considerable cross-section, as shown in Fig. 122. Li i Fic. 121. — TYPE OF ORDINARY Fic. 122. —CISTERN MANOMETER. MANOMETER. . ‘Pressures below the atmosphere can be measured equally well by connecting to the long branch of the tube and leaving the short branch open to the atmosphere. 88. U-shaped Manometer. —In the U-shaped tube, with any form, as shown in Fig. 121, mercury, water, or other liquid is poured in both branches of the tube and the pressure is applied to the top of one of the tubes. When no pressure is applied, the liquid will stand at the same level in both tubes; when pressure 170 EXPERIMENTAL ENGINEERING is applied, it is depressed in one tube and raised in the other. The pressure above or below atmosphere corresponds to the vertical distance between the surface of the liquid in the two tubes and can be reduced, as explained in Article 85, to pounds pressure per square inch. An inch of water at a temperature of 70° F. corresponds to a pressure of 0.0361 pound; an inch of mercury, to 0.4905 pound. The principle of action of the U-shaped manometer-tubes is as follows: Consider the atmospheric pressure as acting on one side of the tube, and the pressure which is to be measured and which is greater or less than atmospheric as acting on the other side. The total absolute pressure in each branch of the tube must be equal, consequently enough liquid will flow from the side of the greater to the side of the less to maintain equilibrium. Thus let p be the atmospheric pressure and #, the absolute pressure to be measured, both expressed in inches of water or mercury; / the height of the column on the side of the atmosphere; h, the height on the side of the pressure, the latter both measured above some reference line. Then, if # and p are expressed in the same units, pt h= Py t+ h,, from which PH h = he A very important measurement commonly made by means of U-shaped manometers is that of chimney draught. So important is this use that many special types of such manometers have been produced for the purpose. They are generally known as Draught- gauges. . A very complete draught-gauge of the U-shaped manometer type, with attached thermometer and a movable scale the zero of which can be set to correspond to the lower water surface, is shown in Fig. 123 as designed by J. M. Allen of the Hartford Boiler Insur- ance Co. A draught-gauge designed by the author is shown in Fig. 124. This gauge is arranged so that one scale will give difference in eleva- tion of the liquid in the two columns. This is accomplished by set- ting the collar F to the lower meniscus of the liquid by the screw E; MEASUREMENT OF PRESSURE 17I then by setting the collar H to the meniscus of the liquid in the other column by means of the micrometer-screw R, the height of the column may be read on the attached scale and the micrometer- screw R. The reflection from the two edges of the meniscus enables Fic. 123. — DRAUGHT-GAUGE. Fic. 124. DRAUGHT-GAUGE. the scales to be set with great accuracy. The inches and tenths of inches are read on the attached scale, the hundredths of inches by the graduations of the micrometer-screw R. 89. Cistern-manometer. —In the case of a manometer of the form of Fig. 125, the cistern or vessel into which the tube is con- nected has a large area relative to that of the tube. Pressure is applied to the top of the liquid in the cistern, the surface of which will be depressed a small amount, and the liquid in the tube will be raised an amount sufficient to balance this pressure. The pressure above atmosphere corresponds to the vertical distance from the surface of the liquid in the tube to that in the cistern. 172 éc 1 Fic. 125. MERCURY CoLuMN. EXPERIMENTAL ENGINEERING As the liquid is not usually in sight ‘in the cistern, a correction is necessary to the readings in order to find the correct height corresponding to a given pressure. This correction is calculated as-follows: Let A equal the area of surface of the liquid in the cistern, a the area of the manometer-tube, H the fall of liquid in the cistern, # the corresponding rise of liquid in the tube, } the height required for one pound of pressure (see Article 85), the number of pounds of pressure. We have then H+h b a; B and since the tube is supplied by liquid from the cistern, HA = ha. Eliminating H in the two equations, oo Apb ; A+a If » = one pound, _ _Ab A+a which is the length the graduation should be made to allow for fall of mercury in the cistern and give a value equal to one pound of pressure. To make this correction applicable the area of cross-section of both tube and cistern should remain uniform. 90. Mercury Columns.— Mercury columns, as used in the laboratories, are usually made on the principle of the cistern-manometer. The tube is a very long and made of glass or steel carefully bored out to a uniform diameter. If the tube is of glass, the height of mercury can be readily perceived and read; if of steel, the height of the mercury is MEASUREMENT OF PRESSURE 173 usually obtained by a float, which in some instances is connected to a needle which moves around a graduated dial. In some of these instruments electric connections are broken whenever the mercury passes a certain point, and an automatic register of the reading is made. Fig. 125 shows the usual form of the mercury column, in which the pressure is applied in the upper part of the cistern, so as to come directly on the top of the mercury. In the case of a glass column the graduations are usually made on an attached scale,‘and are corrected as explained in ettigle 89 for the fall of mercury in the cistern. Corrections to the Mercury Column. —The mercury column is usually the ultimate standard by which all pressure-gauges are compared, and its accuracy should be thoroughly established in every particular. The requirements for an accurate | mercury column are: 1. Uniform bore in cistern and tube. 2. Accurate graduations. The corrections to the readings are: 1. For Inaccuracies of Graduation. — As it is impossible to make the graduations perfectly accurate, the error in this scale should be carefully determined, and the readings corrected accordingly. 2. For expansion of the mercury, tube and scale due to increase of temperature. The method of correcting for expansion of the mercury and the material enclosing it would be as follows: Let A equal the coefficient of lineal expansion of the mercury, and 34 that of the cubical expansion per degree Fahr.; let 0 equal the coefficient of lineal expansion of the metal of the cistern, and 0” that of the material of the tube. Let H’ equal the depression in the cistern, 4’ the corresponding elevation in the tube corresponding to a pressure of one pound, and a difference of level of 6’. Let 6 equal the difference of level corresponding to a pressure of one pound at a temperature of 60° F. Then, as before, Al’ A(a +: 2. 0)b(r + 34) a +A’ att+20’)+ A(t +20) t — 174 EXPERIMENTAL ENGINEERING 3. For the Capillary Action of the Tube. — This force depresses the mercury in the tube a distance which decreases rapidly as the diam- eter increases. The amount of this depression is given in Loomis’s Meteorology as follows: Diameter of Depression, Diameter of ‘Depression’ Tithe. Inch aupe Inch. Inch. : Inch. 0.05 0.295 0.40 0.015 0.10 ©.I41 0.45 0.012 0.15 0.087 0.50 0.008 0.20 0.058 0.60 0.004 on25 0.041 0.70 0.0023 v.30 0.029 0.80 0.0012 0.35 ©.021 Variations in the bore of tube might cause slight variations in the value of this correction. 4. There should also be considered a very slight correction, due to the fact that the force of gravity in different latitudes varies some- what. Since the weight of a given mass of mercury is equal to the product of the mass into the force of gravity, it will vary directly as the force of gravity, or, in other words, the assumed weight of mercury may not be exactly correct. While it is well to give all these corrections their true weight, yet a false impression should not be incurred concerning their impor- tance. It is hardly probable that the corrections for change in temperature, or corrections for the difference in the force of gravity from that at the sea-level on the equator, would in any event make a sensible difference in the readings of any account in engineering practice. 91. Multiplying and Differential Manometers. —In many cases the ‘ordinary U-shaped manometer does not indicate sufficiently small pressure variation for the work in hand. For such purposes it is customary to use multiplying manometers. These divide roughly into two classes: mechanical multiplying manometers and differential multiplying manometers. Descriptions of both types are given below. MEASUREMENT OF PRESSURE 175 As in the case of the U-shaped instruments, many of the best forms of multiplying manometers have been produced for measuring chimney draughts and are known as draught-gauges. 1. Mechanical Multiplying Manometers. —A form of multiply- ing manometer, commonly known as Peclé?’s Draught-gauge, is shown in Fig. 126. It consists of a bottle, 4, with a mouthpiece near the bottom into which a tube, EB, is— inserted with any convenient in- clination. The upper end of the tube is bent upward, as at BK, and connected with a rubber tube, KC, leading to the chim- Fic. 126. — DRAUGHT-GAUGE. ney. The tube is fastened to a convenient support, and a level, D, isattached. To use the instrument, first level it, note reading of scale, then attach it to the chimney, and take the reading, which will be, if the inclination is one to five, five times the difference of level in the bottle and tube. The scale should be graduated to show differences of level in the bottle, and thus give the pressure directly in inches of water. A commercial form of this gauge is shown in Fig. 127. Fic. 127.— MULTIPLYING DRAUGHT-GAUGE. An ingenious modification of this instrument, known as the Sar- gent Draft-gauge, is shown in Fig. 128. The functions of the bottle, A, of Fig. 126 are performed by the nickeled brass tube about which the spiral is wound. The spiral which takes the place of the inclined tube of Peclét is made of transparent celluloid and the height of the liqu.d in it is read by means of the scale carried on the metal reservoir. 176 EXPEPIMENTAL ENGINEERING Another form of this class of manometers is shown in Fig. 129, as designed by Mr. C. P. Higgins, of Philadelphia. The gauge is filled with water above the level of the horizontal tube, in such a manner as to leave a bubble of air about one-half inch long near one end of the horizontal tube when the water is level in the side tubes. The inside diameter of the vertical tubes being the same, say one- half inch, and that of the horizontal tube one-eighth of an inch, a draught or pressure equivalent to one inch in water, or which will cause the water-level in the vertical tubes to vary one inch, will cause the bubble in the tube to move eight inches in the horizontal tube. In general, the air-bubble moves a distance inversely proportional to the area of the tubes, and hence this gauge can be read more accurately than the ordinary manometer. 49" Te Fic. 128.— SARGENT Fic. 129. — Hiccrns’s Fic. 130.— KENT’s DRAUGHT-GAUGE. DRAUGHT-GAUGE. DRAUGHT-GAUGE. Fig. 130 shows a draught-gauge designed by Prof. Wm. Kent, the dimensions of which are marked on the figure, although they are not material for its operation. The gauge consists of a cup, B, which is partly filled with water, and an inverted cup, A, suspended above the cup, B, by a spring, C, with the lower and open end sub- merged in the water of the cup, B. The tube, E, extends through the side of the cup, B, with its upper end projecting above the surface MEASUREMENT OF PRESSURE 177 of the water in the cup, B, and is extended by suitable connection to the flue. By this connection the pressure in the inverted cup, A, is reduced to that in the flue where the pressure is to be measured, putting a greater load on the spring, C, which causes it to elongate. The amount of elongation will be proportional to the reduction in pressure and can be determined by the use of a suitable scale, the values of which are found by calibration. It is evident that the distance through which the cup, A, will move is dependent upon the area of its cross-section and the strength and length of the spring, C, and the immersion in the water. Commercial forms of this type of in- strument, in which the movement of the cup, A, is magnified by various means, are now made. 2. Differential Multiplying Manometers. —A class of multi- plying manometers in which two liquids of different specific gravities are used are known as differential manometers. Their theory can Area A Fic. 131. be best approached by first considering a simple but impracticable mechanical multiplying manometer, as shown in Fig. 131. It consists of a U-tube enlarged at the upper ends and fitted with the 178 EXPERIMENTAL ENGINEERING small frictionless piston, P, as shown. The device is filled to the level indicated with any liquid, such as water. If now the same unit pressure p exist above each surface, pthe =pt+h~; hd =h,~, where 6 stands for density of liquid. Increasing the pressure above the left-hand surface by Ap, that surface will sink a distance « and the piston will move down a dis- A ; A tance greater in the proportion —, that is, x a a Writing the equation for equilibrium for these conditions A A pt Ap+ho- xd +x — pa pe he pe am a) a and since ho =h 1 it follows that Ap = 2x0, which is exactly the same result as for the ordinary U-tube. If instead of reading the fall or rise of the upper surface, the fall F ; : : A or rise of the piston is read, the actual distance read will be — greater a than x; therefore the indication of the instrument can be made larger than that of the ordinary U-shaped manometer for the same pressure difference. The use of the solid piston is of course impracticable, so that all actual instruments substitute the film between two non-mixable liquids in its place. In general, however, the two liquids will not have the same densities and the theory of the instrument is then as follows: To develop the equation for this case, imagine a liquid of density 0,, to occupy the space above the piston in Fig. 131, and some other liquid with greater density, 6,, and not mixable with the first, to occupy the rest of the space in the manometer, that is, the right leg and the part of the left leg below the piston. Now remove the piston. With the same external pressure on both legs the surface MEASUREMENT OF PRESSURE 179 of contact will move upward or downward, as the case may be, until ho, = 1D», the heads h, and h, being measured above the surface of contact as they were previously measured above the piston. Applying Ap to the left leg the equation for equilibrium will now be A A PEALE AS, My Te 8 HP hl, tae Oy giving A ap = «$2, +9, + “@- 9) . In practice the enlargements at the upper ends of the tubes are usually made of metal, so that the movement x cannot be observed. The measurement may be transferred to the dividing surface be- tween the two liquids, provided this surface can be clearly recog- nized. Where the liquids used are both water-white, as is the case with the pair most commonly used, that is, alcohol and gaso- line, it is possible to clearly define this surface and its movement by coloring either one of the liquids. Since »“ then becomes the quantity observed, a better form for the equation of the instrument would be Ap == $0, pas + (3, -3)t. The result, since the densities © are expressed with reference to water, is Ap in water-inches, if « is expressed in inches. Note that the smaller the factor in brackets, the greater will be “ for the same value of Ap; that is, the smaller this factor the more sensitive will the instrument be. To get a big multiplication, therefore, make © as small as possible, and choose two liquids whose densities are very close together. 180 EXPERIMENTAL ENGINEERING ‘Fhe-actual value of the pressure difference which causes a given movement of the surface of contact may be determined by calcu- lation from the equation above or by actual calibration. The latter method is always preferable. Another modification of this type is shown in Fig. 132. The heavier liquid, density 4,, is placed in the lower part of the manometer Fic. 132. and the lighter with density 0, in the upper part. The two enlarge- ments are connected, as shown, by a tube containing a valve. By opening the valve when the pressure is the same on both upper surfaces the two upper surfaces will assume the same level and the two surfaces of contact will assume the same level. If the valve is then closed and additional pressure Ap applied to the left leg the equation for equilibrium is A A A pt Apth~,—xd,+* - 8, =P+hp, +x, e— 3, + ga— 2, a a and 4 a Ap= i ha, i +(d, — 9) 5 MEASUREMENT OF PRESSURE 181 : A, : . In this case 2X — is the total difference in level between the two a contact surfaces in the two branches of the tube and is the quantity usually observed. The factors controlling the magnitude of the movement for any given Ap are the same as for the multiplying manometer described just above. The principles of this type of manometer are embodied in the instrument known as Hoadley’s Draught-gauge and shown in Fig. 133. This gauge was used in the trials of a warm-blast apparatus, described in Vol. VI, Transactions American Soci- ety Mechanical Engineers, page 725. It consists of two glass tubes, as shown in Fig. 133, about 30 inches long, and about o.4 inch inside diameter and o.7 inch outside, joined at each end by means of stuffing-boxes to suitable brass tube connections, by which they are secured to a backing of wood. The glass tubes can be put in communication with each other at top and bottom by opening a cock in each of the brass connections. Directly over each tube is a brass drum-shaped vessel 4.25 inches in diameter and with heads formed of plate-glass. These drums are connected to the tubes, and also provided with stop-cocks and nipples to which rubber tubes can be attached. Two sliding-scales are ar- ranged along the tubes, one to measure the de- pression, the other the elevation, of the surface of a liquid filling the lower halves of the tubes. In the use of the instrument two liquids of different densities were used, a mixture of water and alcohol ; : ; Fic. 133. with specific gravity about 0.93 being used for the Hoapzev’s heavier liquid, and crude olive-oil with a specific DRavcat GAUGE. gravity of o.916 for the lighter. 92. Pressure-gauges.— Pressure-gauges in general use are of two classes, known respectively as the Bourdon and the Diaphragm gauges. 1. The Bourdon Gauge. —In the Bourdon gauge the pressure is exerted on the interior of a tube, oval in cross-section, bent to fit 182 EXPERIMENTAL ENGINEERING the interior of a circular case; the application of pressure tends to make the cross-section round and thus to straighten the tube. This motion communicated by means of sectors and gears rotates an arbor carrying a needle or hand. . The various forms of levers used for transmitting the motion of the tube to the needle are well shown in the accompanying figures, 134 to 138. The levers are in general adjustable in length so that the rate of motion of the needle with respect to the bent tube can be increased or diminished at will. Thus, in Fig. 134, and also in Fig. al ( it ae Fic. 134.— Bourbon GavuceE. Fic. 135.— BouRDON GAUGE. 135, the lever carrying the sector is slotted where it is pivoted to the frame; by loosening a set-screw the pivot can be changed in position, thus altering the ratio of motion of hand and spring in different parts of the dial. Fig. 136 shows a gauge with a steel tube for use with ammo- niacal vapors which attack brass. A double tube construction is shown in Fig. 135. In nearly all these gauges lost motions of the parts are to some extent taken up by a light hair-spring wound around the needle- pivot. 2. The Diaphragm-gauge. —In the diaphragm-gauge the pres- sure is resisted by a corrugated plate, which may be placed in a hori- zontal plane, as in Fig. 137, or in a vertical plane, as in Fig. 138, MEASUREMENT OF PRESSURE 183 “obs = IN — wr Tj 184 EXPERIMENTAL ENGINEERING The motion given the plate is transmitted to the hand in ways similar to those just explained. In Fig. 137 the pressure is exerted on the corrugated diaphragm below the gauge, and the motion is transmitted to the hand by the rods and gears shown in the engraving. The construction shown in Fig. 138, in which the diaphragm is , vertical, is as follows: the lever is in two parts which are pivoted at Fic. 138.— Draparacm GAUGE. the center; one end is fixed to the frame, the other connected to the sector. ‘The center pivot is pressed outward by the action of the diaphragm, drawing the free end downward and rotating the sector, which in turn moves the needle. ‘ In gauges of usual construction of either class, when there is no pressure on the gauge, the needle rests against a stop, which is placed somewhat in advance of the zero-mark, so that minute pressures are not indicated by the gauge. In the use of the instrument the needle sometimes gets loose on the pivot, or turned to the wrong position with reference to the graduations; in such a case the needle MEASUREMENT OF PRESSURE 185 is to be removed entirely, and set when the gauge is subjected to a known pressure. ‘These gauges are also affected by heat. Hence, when set up for use with a heated medium, such as steam, a bent tube or a vessel which will always contain water should be inter- posed between the gauge and the hot material. All the devices used for thus protecting gauges are termed siphons. The principal types are shown in Fig. 139. ES Fic. 139. — GaucE SYPHON. 93. Vacuum-gauges. — Vacuum-gauges are constructed in the same way as the Bourdon or diaphragm gauges; the removal of pressure from the interior of the bent tube or diaphragm causes a motion which is utilized to move the needle. These gauges are graduated to show pressure below that of the atmosphere corre- sponding to inches of mercury, zero being at atmospheric pressure. The difference between the reading by such a gauge and that of the barometer, taken at the same time, would be the absolute pressure in inches of mercury. 04. Recording-gauges. — Recording-gauges are arranged so that the pressure moves a pencil or pen over a chart which.is moved at a uniform rate by clock-work. The Edson recording-gauge is shown in Fig. 140. In this gauge the steam-pressure acts on a diaphragm which operates a series of levers giving motion to a needle moving over a graduated arc showing pressure in pounds; also to a pencil- arm moving parallel to the axis of a revolving drum. 186 EXPERIMENTAL ENGINEERING. This instrument has an attachment, which is furnished when re- quired, to record fluctuations in the speed of an engine, consisting of a pulley on a vertical axis below the instrument, which pulley is put in motion by a belt from the engine-shaft. On the small pulley- ui FEE TEED PRET H ic ct a B) q 5) Fic. 140.— EDSON RECORDING Fic. 141.— RECORDING GAUGE. PRESSURE-GAUGE, shaft are two governor-balls which change their vertical position with variation in the speed, giving a corresponding movement up or down to a pencil near the lower:part of the drum. A diagram is drawn on which uniform speed would be shown by a straight line. Fig. 141 shows Schaeffer & Budenberg’s recording-gauge. This is arranged with a pressure-gauge below the recording mechanism. The drum B is operated by clock-work, the piston-rod C, which carries the pencil, being moved by the pressure. The pencil- movement is much like that on the Richards steam-engine indicator. MEASUREMENT OF PRESSURE 187 Fig. 142 shows a portion of a diagram made by a recording- gauge. The drum is operated by an eight-day clock, and arranged to rotate once in twenty-four hours. In the diagram the ordinates show pressure, and the abscisse time in hours and fractions of an hour. 2 3 4 5 6 7 8 9 Fic. 142.— DIAGRAM FROM PRESSURE-RECORDING GAUGE. Fic. 143.— BristoL RECORDING GAUGE. 188 EXPERIMENTAL ENGINEERING Figs. 143 and 144 show one type of Bristol recording-gauge. In this instrument the chart is circular and rotates about its center, the pressure ordinates being measured on radiating arcs, as shown. inti / l ) Nn \ | : yi Y ViG e fires I S Fic. 144. BrisTOL RECORDING GAUGE. 95. Gauge Calibration. — Gauges are calibrated in two ways: by comparison with other gauges with known error or by comparison with mercury columns or standard weights. 1. Calibration by Comparison with Other Gauges. —For this purpose some form of pump is necessary. It generally consists of a cylinder into which a plunger can be driven by rotating a hand- wheel and is fitted with connections for the standard gauge and the gauge to be tested. Fig. 145 shows a portable form of this appa- MEASUREMENT OF PRESSURE 189 ratus. The device shown in Fig. 146 may be used for a similar purpose by putting a standard gauge in place of the manometer shown. Fic. 145.— PortaBLeE Gauce TESTING APPARATUS. 2. Comparison with Mercury Column or Standard Weights. — Mercury Column. — The apparatus shown in Fig. 146 may be used for this purpose, connecting the mercury column at #,. This instrument consists essentially of the cylinder Ccontaining a plunger operated by the hand-wheel D. The cylinder is filled with water or other suitable liquid through the cup shown and then the same pressure applied to both gauge and test column by driving the plunger inward. Another convenient method is to attach the gauge and the mer- cury column to a drum in which the pressure can be varied by ad- mitting steam or water under pressure through a throttle-valve. In all cases the gauge should be tapped before reading and com- parison should be made with the standard both with the pressure rising and with the pressure falling. This is necessary to minimize errors due to friction and lost motion in the gauge. The readings of the mercury column should be corrected in accu- rate work as outlined in Art. go. 190 EXPERIMENTAL ENGINEERING ‘Test Gauge Fic. 146.— GAaucE TESTER witH MERcuRY COLUMN, Vacuum gauges are practically always calibrated by comparison with a mercury column. The necessary vacuum may be obtained by means of any suitable air-pump or by connection to a condenser. The U-shaped manometer shown in Fig. 121 is a convenient form for this purpose, but it is necessary that each branch of the tube exceed 30 inches in length. Comparison with Standard Weights. —There are two forms of this apparatus for this purpose on the market; in one of these the pressure is received on a round piston, and in the other on a surface exactly one square inch in area. The friction in both cases is prac- tically inappreciable; the errors in areas can be determined by comparison with a standard mercury column. MEASUREMENT OF PRESSURE 19! One of the forms with round piston is known as the Croshy Gauge-testing Apparatus and is shown in Fig. 147. It is seen to consist of a small cylinder in which works a nicely fitted piston; this cylinder connects with a U-shaped tube ending in a pipe tapped and fitted for attaching a gauge. The tube is filled with glycerine, or oil, in which case a known weight added to the piston produces an equal pressure on the gauge, less the friction of the piston in the tube. This is almost entirely overcome by giving the weight and piston a slight rotary motion. Ca a eT He ue a Cy QUIK TTT Weight of Tray, Piston and Rod =5 Lbs. HTT i La VM \ oa | Fic. 147.— STANDARD WEIGHT GAUGE TESTER. The Square-inch apparatus consists of a tube the end of which has an area of one square inch enclosed with sharp edges. This tube is connected to the test-pump in place of the standard (see Fig. 146); a given weight is suspended from the center of a smooth plate which rests on the square-inch orifice. The gauge to be tested is connected at E, and the pressure applied until the plate is lifted and water escapes from the orifice. 192 EXPERIMENTAL ENGINEERING 96. Correction of Gauges. — If the calibration shows errors in the gauge, they may generally be corrected; if the error is a constant one, the hand may be removed with a needle-lifter, and moved an amount corresponding to the error, or in some gauges the dial may be rotated. If the error is a gradually increasing or diminishing one, it can be corrected by changing the length of the lever-arm between the spring and the gearing by means of adjustable sleeves or the equivalent. It is to be noted that the pin to stop the motion of the hand is not placed at zero, but in high-pressure gauges is usually set at from three to five pounds pressure. 97. Forms for Calibration of Gauges. CALIBRATION OF STEAM-GAUGE BY COMPARISON, WITH THE MERCURY COLUMN. Maker and: No.of (Gauteng ocagrie savored aeien Deak Od een Gee amnemee aa TR PAE scomaulvaiviecen’ 19 Ciseneis, } Stieaciepdseoe se OMA He ae es SREY BS ay Mercury Column. No. Gauge. Inches. Error. Ibs. é dbs. Pounds. Up. | Down. | Mean. Temperature of Room...... deg. Fahr. Center of Gauge above o of column...... ft. Correction to column reading...... lbs. CALIBRATION OF STEAM-GAUGE BY COMPARISON WITH THE SQUARE-INCH GAUGE, OR WITH CROSBY’S GAUGE- TESTING APPARATUS. Maker aid ING: Of tGaiger oi.- 0's 33 qin, Susan Ho 5.5 ad oo aie eaters eunansaneae soe aeeyeies Date vey 5 seme sas 19. Observers, | AEG TSS SES EES AEE OEE YORE GS 8 RISE Actual Pressure lbs. per sq. in. CHAPTER VII. MEASUREMENT OF TEMPERATURE. 98. Temperature. —The term “temperature” is not easy to define. As a matter of fact no definition strictly accurate has ever been given, but to say that temperature is a measure of the tendency for one body to transmit heat to another is probably open to least objection.* 99. Thermometers and Thermometric Materials. — Instruments designed to measure temperature are generally called thermom- eters, but, depending upon the materials used or the principle of operation, special names are often assigned to the different instruments. In general, what is really done in measuring temperature is to observe the temperature of the material of which the instrument is made, the construction being such that the thermometer acquires the temperature of the medium in which it is placed. There are certain properties of matter, like lineal or volume expansion, electrical resistance, or the electromotive force set up in a thermopyle, which vary continuously with the temperature, and any of these may therefore be used to measure temperature. As a consequence, the number of available thermometric materials, as well as the variety of methods by which they may be employed, is quite large. The former comprise gases, liquids and solids, and as far as the methods are concerned the following is a fairly com- plete list: ‘ 1. Expansion of a gas under constant or under variable pressure. This method is very little used. 2. Increase in the pressure of a gas when heated at constant volume. Of this class are all of the well-known gas thermometers, such as the air and the hydrogen thermometer. * See Edser, Heat, for Advanced Students. 193 194 EXPERIMENTAL ENGINEERING 3. Expansion of a liquid under constant or variable pressure. The ordinary mercury and alcohol or ether thermometers belong to this class. . 4. Increase in the pressure of a completely confined liquid, such as mercury. This method is also little employed. s. A method utilizing the relation existing between the vapor- pressure of a given liquid and its temperature. Instruments built on this principle are known as thalpotasimeters, but are not much used. 6. Expansion of solids. This usually consists in noting the rela- tive expansion of two dissimilar solids with respect to each other. The instruments are usually known as expansion pyrometers and quite widely employed. 4. Fusion methods, which usually consist in exposing a series of materials of known fusing-points to the effect of the temperature to be measured and noting which of the series fuse. 8. Calorimetric methods, in which a body whose temperature is to be measured is mixed with a liquid having a different temper- ature. The temperature of the body may then be computed by the law of mixtures from the variation in temperature of the liquid. 9. Electric methods, either determining the change in resistance of a given length of conductor as the temperature changes, or measuring the electro-motive force set up when a thermo-couple is exposed to the temperature to be measured. The former are usually known as resistance thermometers, the latter as electric pyrometers. These instruments with proper handling are very accurate and much used. to. Optical methods. The instruments based upon optical methods may be of two kinds: those measuring fotal radiation from a given area of the hot body, and those which depend for their action upon the intensity of the Juminous radiation given off. The former are often called radiation pyrometers. It will thus be noted that there is a great variety in the methods which may be used to measure any given temperature. But, depending upon where this temperature is located in the range, that is, low, moderate or high, it will usually be found that one or two methods should have the preference. The most reliable range MEASUREMENT OF TEMPERATURE 195 for each method or instrument will be pointed out in what follows. It will also be noted that the range of thermometric materials is quite wide, comprising, as it does, gas, liquids and solids. 100. Thermometric Scales and Thermometric Standards. —In all methods of measuring temperature, it is usual to establish, by arbitrary selection, two fixed standard temperatures, and then to divide the interval between them into a certain number of parts, called degrees. Temperatures higher or lower than these are then stated in the same thermometric scale, by simply continuing the subdivision into degrees above or below the two standard fixed points. For the great majority of engineering work in this country the scale used is the Fahrenheit. In this scale the interval between the two standard fixed temperatures, which are usually the temper- ature of melting ice and that of water boiling under standard atmospheric pressure, is divided into 180 equal parts or degrees. The temperature of melting ice (the freezing-point) being called 32 degrees in this scale, the boiling-point of water under the conditions stated will then be 212 degrees. In the Centigrade scale the freez- ing-point is called o degrees and the boiling-point 100 degrees, there being 100 equal divisions or degrees in this range. The latter scale is much used for scientific work. Finally, there is a third scale, that of Réaumur, in which the freezing is again called o degrees, but the interval between the two standard temperatures is divided only into 80 divisions or degrees, so that in this scale the boiling- point of water under standard atmospheric pressure is 80 degrees. This scale is now very little employed. It is very often necessary to change temperatures from the Fahrenheit into the Centigrade or vice versa. If T, = temper- ature on the Fahrenheit scale, and 7, the same temperature as read on the Centigrade scale, then we may write the conversion formula Lee % DT, gas (r) Te =% ap — 82): (2) Since all of our temperature measurements depend upon the variation of a certain property of the thermometric material with a \ 196 EXPERIMENTAL ENGINEERING change of temperature, the choice of a proper thermometric material to be used as a standard for comparing the action of all other thermo- metric materials under the effect of varying temperature becomes very important. It has been found in this connection that hydrogen gas shows a remarkably constant change in the pressure or in the volume, as the case may be, over a very wide range of temperature changes, and this, combined with the fact that the gas is fairly easy to obtain in a pure state, has caused the hydrogen-gas thermometer to be accepted as the primary standard. This instrument, however, is rather delicate and requires a skilled observer, so that it will probably always remain a laboratory standard. For this reason a high-grade mercury thermometer, or other high-grade tem- perature indicator of less delicate nature than the hydrogen-gas thermometer, is often very carefully compared with the latter, and instruments so calibrated are then often used as standards of comparison, called secondary standards. In ordinary labora- tory or engineering practice the calibration of thermometers by comparison with secondary standards is by far the more usual case. 1o1. Gas Thermometers. — One of the simplest forms of gas thermometers is shown in Fig. 148. It consists of a bulb C one end of which is drawn out into a rather fine tube which is usually bent at right angles at F. The rest of the apparatus consists of a manometer /BE and a source A of supply of mercury or other liquid to measure the pressure of the gas volume confined in C. At a there is either a scratch on -he glass or, in the better grade of instruments, a black glass tip is iused in the side of the tube, to serve as an indicator for the constant volume of gas. The bulb C for the lower temperature range is usually of glass; for the higher ranges generally of porcelain. The principle of the constant-volume gas thermometer is very simple. For any two states of a perfect gas we may write ey - 7 , (3) where p, V and T represent absolute pressure, volume and absolute temperature respectively. MEASUREMENT OF TEMPERATURE 197 , Now in the constant-volume gas thermometer, V = V, for any two observations, hence ey TT; (4) and if T, is the temperature to be determined, we finally have p Lg = m (5) E Cr Le U 3 U uot Poitif Petiti TEMP TTT TTT TTT TTT ye ch Pii?is TT FrSu Fic. 148.— PRESTON ArR-THERMOMETER, It is therefore necessary merely to observe p for any convenient absolute temperature JT and to observe p, for the temperature T, to be determined. A convenient way to obtain T and # is to use melting ice, in which case T =-460 + 32 = 492°. p and p, are absolute pressures, consequently it becomes neces- sary to take barometric readings when using the instrument. The only reading that is really observed on the instrument is the differ- ence in level of the liquid in the branches of the manometer after the bulb has attained the temperature of the medium to which it 198 EXPERIMENTAL ENGINEERING is exposed and after the level in the left-hand branch, Fig. 148, has been adjusted to stand at the mark a. Equation (5) may be modified as follows: Let m, and m, be the height of the liquid levels from any convenient datum line, M, on the side of the bulb. If the pressure exerted by the gas is p and the barometer pressure is b, both expressed in the same units as m, and m., then we must have ptm, =b+m, or p=b+m,—-—™, But m, — m, = h = difference in level, hence p=b+h. For any other state Pp =o, + hy where b, may or may not be equal to 6. Therefore b+h p T b, a h, Py T, or b,+h tL = 7 + 6 ; b+h - For the case where melting ice is used to determine T, this reduces to b+h 1 (b, a h,) = Kb, i h,), (6a) where K is a constant for any given instrument. Different investigators have used varying forms of the gas ther- mometer, but the principle is the same in all. The gases commonly employed are air, nitrogen or hydrogen. For reasons already pointed out, the hydrogen-gas thermometer has been accepted as the primary standard temperature-measuring instrument. The range of the hydrogen thermometer is from about — 375° F. to + 2700° F. The great objection to the gas thermometer in practice is the MEASUREMENT OF TEMPERATURE 199 great care with which it has to be handled and the fact that tem- perature determinations with it take considerable time. The following rules and directions pertain primarily to the air- thermometer, but they hold equally well for any other gas: Construction of the Air-thermometer.—The bulb of the air- thermometer must be filled with perfectly dry air, as any vapor of water will vitiate the results. To accomplish this, the bulb is provided with a small opening opposite the capillary tube, which is fused after the dry air is intro- duced. To effect the introduction of dry air, all the mercury is drawn into the bottle A, Fig. 148; the end of the tube Z is con- nected to a U-tube about 6 inches long in its branches and about 2 inch internal diameter, filled with dry lumps of chloride of calcium and surrounded by crushed ice; the opening in the end of the air- chamber is connected by a rubber tube to an aspirator (a small in- jector supplied with water would act well as an aspirator), and air is drawn through for three or four hours; at the end of this time the bulb and tube should be filled with dry air. While the current of air is still flowing, the cock B is opened and mercury allowed to pass into the tubes until it rises to the point a in the tube BF; the opening in the air-chamber is then hermetically sealed with a blow-pipe, and the connections to the chloride-of-calcium tube removed. This operation fills the bulb with air at atmospheric pressure. By closing the cock B before the mercury has risen to the point @ the pressure will be increased; by closing it after it has passed the point a@ it will be diminished. Packing the bulb C in ice, or heating it, will also increase or diminish the pressure as required. Corrections to Determinations by the Air-thermometer. —The corrections to the air-thermometer are all very small, and affect the results but little if considered. They are: 1. Capillarity, or adhesion of the mercury to the glass. In general the mercury in the two tubes BF and BE (Fig. 148) is moving in opposite directions, and the effect of adhesion is neutral- ized. 2. Expansion of the glass. This is a small amount, and may usually be neglected. The coefficient of surface expansion of 200 EXPERIMENTAL ENGINEERING glass is o.oooo1 per degree F.; it is entirely neutralized if the column of mercury is not reduced in area at the point of meeting the air from the bulb. 3. Expansion of the mercury should in every case be taken into account by reducing all observations to 32° F., the coefficient of expansion being o.ooo1 per degree F. Reduce all observations before applying formule. 4. Errors in the fixed scale should be determined and observa- tions reduced before applying formule. Directions for Use of the Air-thermometer. First. To obtain the Constants of the Instruments. — Surround the air-bulb with crushed ice, arranged so that the water will drain off. Note the reading of the mercury column of the air-thermom- eter h and of the barometer 6; by means of the attached ther- mometers reduce these readings for a temperature of the mercury corresponding to 32°F. Correct for errors of graduation. Divide 492 by the sum of these corrected readings for the constant of the air-thermometer. Call this constant K. Second. To Measure any Temperature t,.—Note the corre- sponding reading of the mercury column h,, and that of a barometer b, in the same room. The reading of the mercury column plus that of the barometer will correspond to 6, + h, in the formula 402 5 ; (by + hy) = Kb, + hy). To obtain from this the actual temperature ¢,, subtract 460. Third. To Compare a Mercurial Thermometer. —Make simul- taneous readings of the thermometer, when hanging in the chamber which surrounds the air-bulb, and the height of the mercury column. Perform reduction, and plot a calibration curve for each 10° of graduation. Fourth. For general use of the air-thermometer, arrange the bulb so that it can be inserted into the medium whose tem- perature is to be measured with the manometer in an accessible position. MEASUREMENT OF TEMPERATURE 201 Form for Reducing Air-thermometer Determinations. TEMPERATURE DETERMINATIONS WITH AIR-THERMOMETER, BY sun eg vi celnin ee autre ess enaseds MoRoR eae! Sadyaweadhiee gasps TQsseeee DETERMINATION OF CONSTANT. Symbol. | Ii II. | III. | IV. Tempeérature-of air-bulDicecswceneveccenedleaeveaonel yy ee mel csdcselres enelecaace Barometer;—. Reading s.s.0+ cane xeacaeste| om aiomamel|lax sieeve tres lane. aveaillanecsepoats TL HEE OUNCE E 4c 9 sas cee $55) ove [haw sard d si snteen dbase. eeanace| leav severed ova aceseeat) Be consoarnets Reduced to 32°...........-. BS” Nhe dcsaearel asec Gare teean here lle Geay Air-thermometer — Reading. .............[o. cece ee epee eee efe ee eecle sees clecsces CECFIOH TIN OC CET s.fants cai: toiss tanh bs vitesse ncensllketssnd ariel beads stapes sopan a asses Reduced to 32°........ Te © \lsevectsoaileicasseenal tert ace 63) ittueneese Constant = 492 + (D+ h)............4.. IS illest gece tame Ge elect DETERMINATION OF TEMPERATURE. t, = K (6,+ hy) — 460. Barometer. Air-thermometer. Mercury i Thermometer. by + hy] Tem- |——]{— No. b h, Sum i Read- ‘ Read- a um. | pera- | Read- j Ther. re- i Ther. Te- ture. < Error. ne: duced ng duced ane ET deans ci A ees sss | aps ase ete Se tec neg ein neces tS gece cag edie decountentte's [lee Weavers HS) ah gi sat sane Mes Brig oa case | an ab tsa cbioaa a [ eae cwcde Sas se Sy Raver PL gat lN sigan! eotoavae | setsules Se) dare] Sacsbvaan date fol [ane ata tn ceiteh |r eked Bid | [ie stesrcct Paste ater Baactlaca eta ene diaauall sealed ced eae wets te oeteaiell ehanecmcrae oe gah A | Weescesuireane Hewes well holes aacoveess au de busneiceua bed cetesel|poaettd exis | veteber fll barefeet el abt IB | Wie cay nae |b steriern teens cate [iatccecetl istantatae R acckeriy laren maacneys Gd i dechaacrel ate ens GO feaeniubowsr ddl eeudag ee eedes paeelasaee mas aay ei alee mallee exe W|I ictantahora | secacrateudl| aentiaie vs ohare nis s-edeia le watotne tpt |a ances teancareacal|l ays eras Slain meena eel ture ealne tamed eis sgigedleaaa wel omeeal aamacelleea maeileasna. so @ lesseseleseues| saaensl sevecel cen sndlees assesses eee tele arnonlaumara TQS. | sscoacsseareshay | dep cebsowads.ins (as sek alah abbots ved ceca aps etoay gn gies eae [day gest, “an | apa ini ao | es ana aerosol cesta calor ern fete EE Placa evcescapee | cet serve: at || gi bscxt vcore lf reaceoemee pp ehieiier aed] od eaneze | a eyreaye vedas quauiet ht atl dee ani Gralla ae EZ hecceiep arcana edvecateer avs: | wusmy'arse oe) erceice vance Paes ah 9 cet espa decorw anced] ahaa eed [lea a asia teas ana aa | wena ane 102. Thermometers employing Liquids. — Under this general head may be classed several temperature-measuring instruments of radically different type. Vapor-pressure Pyrometers or Thalpotasimeters make use of the fact that certain liquids when heated evolve vapors which, if con- fined, will exert a certain pressure for a definite temperature. Thus in the mercury thalpotasimeter an iron tube is partly filled 202 EXPERIMENTAL ENGINEERING with mercury which, if heated above a certain point, will give off a vapor which is made to exert a pressure upon a diaphragm, the motion of this diaphragm being communicated to a pointer, moving over a scale graduated directly to degrees by calibration, the entire construction being very similar to a diaphragm steam-gauge. De- pending upon the range of temperature to which the instrument is to be used, different liquids are used as per following table: Range, °F. Liquid. —85 to +55 Liquid CO,. +14 to +ar2 Liquid SO,. 95 to 250 Ether. 212 to 440 Water. 420 to 680 Heavy hydrocarbons. 680 to 1200 Mercury. The main objection to these instruments probably is that they must be exposed full length to the temperature to be measured. Somewhat similar to the above is the liquid-pressure pyrometer, which differs only in that the tube is completely filled with the liquid and strong enough to stand the bursting strain resulting from the tendency to expand. The recording mechanism is the same as in the vapor-pressure instrument. By connecting the reservoir holding the liquid to a very fine capillary tube, the pressure due to expansion may be transmitted some distance (up to 150 feet). In this case varying temperature of the capillary would affect the accuracy of the readings and it would be necessary to apply a cor- rection similar to the stem correction in mercury thermometers. In this instrument it is also necessary to expose the entire length of tube containing the liquid to the action of the temperature to be measured. ‘The mercury-pressure thermometer may be used in the range of — 10 to + 1000° F. Mercury and Alcohol Thermometers. —Neither one of the two instruments above described are much used, but the third kind under the general head of thermometers using liquids, those employing the expansion of liquids, are very extensively used. To this class belong the ordinary mercury and alcohol ther- mometers. MEASUREMENT OF TEMPERATURE 203 The mercurial thermometer consists of a bulb of thin glass con- nected with a capillary glass tube; on the best thermometers the graduations are cut on the tube, and an enameled strip is placed back of them to facilitate the reading. When the mercury is inserted, every trace of air must be removed in order to insure per- fect working.* There are certain defects in mercurial thetrmom- eters due to permanent change of volume of the glass bulb, with use and time, that result in a change of the zero-point. In a good thermometer the bore of the tube must be perfectly uniform, which fact can be tested by separating a thread of mercury and sliding it from point to point along the tube, and noting by careful measurement whether the thread is of the same length in all por- tions of the tube: if the readings are the same, the bore is uniform or graduated by trial. In most thermometers the graduations are made with a dividing engine; in some thermometers the principal graduations are obtained by the thread of mercury, as described; in the latter case change in diameter of bore would be compensated. To determine the accuracy of temperature measurements ther- mometers used should be frequently tested for freezing-point and boiling-point. The accuracy of intermediate points should be determined by comparison with a standard mercurial or air- thermometer. Mercury freezes at —39°C. ( —38.2° F.) and boils at 357°C. (675.6° F.) under atmospheric pressure, so that these tempera- tures represent the extreme limits of use of the ordinary mer- cury thermometer. In practice the space above the mercury in a thermometer is very often freed from air in order to prevent oxidation of the mercury. In this case the boiling-point is even lower than 675° F., and the range of use is correspondingly narrower, 550° F. being about the upper practical limit. In order to increase the range, so-called high-reading mercury ther- mometers are now made of high-grade glass and have the space above the film filled with some neutral gas like nitrogen or carbon dioxide under considerable pressure. The pressure varies, depending upon the range to which the instrument is to be * For a detailed discussion concerning the manufacture of mercury thermometers and the errors involved in their use, see Edser, Heat, for Advanced Students. 204 EXPERIMENTAL ENGINEERING ~ used.* This method of construction of course raises the boiling- point of the mercury and it is thus possible to make thermometers which read up to 1300°F. They are very delicate to handle, however, the glass sometimes breaking from the induced tem- perature strains alone, to say nothing of the effect of any accidental rough handling. For these reasons 850 or goo° F. is probably about the upper commercial limit of use of such thermometers. Experiments have recently been successfully made to substitute quartz for glass in order to produce a hardier instrument, and mercury-quartz ther- mometers have been made to read up to 1350°F., but at present they are rather too costly for ordinary use. The construction of the alcohol thermometer is very similar to that of the mercury thermometer. The expansion of a given volume of alcohol is about ten times that of the same volume of mercury for the same temperature change, and hence an alcohol thermometer is a much more sensitive instrument than a mercury thermometer having the same bulb and tube. Alcohol further possesses the advantage over mercury that it remains liquid down to — 130° C. (—202° F.) and may therefore be used for reading extremely low temperatures. On the other hand, it boils at about 78°C. (172° F.), so that its upper limit is not much above 150° F. Rules for the Care of Mercurial Thermometers. —'The following tules for handling and using mercurial thermometers, if carefully observed, will reduce accidents to a minimum: 1. Keep the thermometer in its case when not in use. 2. Avoid all jars; exercise especial care in placing in thermom- eter-cups. 3. Do not expose the thermometer to steam heat unless the graduations extend to or beyond 350° F. 4. In measuring heat given off by working-apparatus, or in continuous calorimeters, do not put the thermometers in place until the apparatus is started, and take them out before it * See the Bulletin entitled Heat Treatment of High Temperature Mercurial Ther- mometers, Department of Commerce and Labor, Bureau of Standards, Reprint No. 32, H. C. Dickinson, MEASUREMENT OF TEMPERATURE 205 is stopped. Be especially careful that no thermometer is over- heated. 5. In general do not use thermometers in apparatus not fully understood or which is not in good working condition. 6. Never carry a thermometer wrong end up. 7. See that the thermometer-cups are filled with cylinder-oil or mercury. If cylinder-oil is used, keep water out of the cups or an explosion will follow. 8. After a thermometer is placed in a cup, keep it from contact with the metal by the use of waste. 103. Thermometers employing Solids. — Expansion and Fusion Pyrometers. —Expansion pyrometers are often called metallic pyrometers. The ordinary instruments sold under this name are made of two metals which have different rates of expansion, copper and iron being generally used. The difference in the rate of expan- sion is employed by means of levers and gears to rotate a needle over a dial graduated to degrees. In using the metallic pyrometer no reading should be taken until it has had sufficient time to arrive at the temperature of the medium to which it is exposed. When the instrument is first exposed, the needle may be stationary on the dial, or even have a retrograde motion, the heat at first affecting the outside tube only. In order to obtain readings to correspond with the scale on the dial, it is neces- sary to insert the tube its entire length into the medium whose temperature is to be measured. This is often not convenient and constitutes one of the disadvantages of this type of instrument as usually made. The metallic pyrometer is usually calibrated by immersing in a pipe filled with steam under pressure and comparing the tem- perature with that given by a calibrated mercurial thermometer. The scale so obtained is assumed to be uniform throughout the range of the pyrometer and beyond the limits of the calibration. Com- parison might be made with an air-thermometer. The extreme range of such pyrometers is about 1200°F., but they are probably of little value for temperatures exceeding 1000° F. Wedgewood’s Pyrometer is based on the permanent contraction of clay cylinders due to heating. This contraction is determined 206 EXPERIMENTAL ENGINEERING by measurement in a metal groove with plane sides inclined towards each other. This pyrometer does not give uniform results. The type of fusion pyrometer is best exemplified by the so-called “Seger Cones.”” These consist of a graduated series of clay pyra- mids about 24 inches high. The composition of the clay differs from number to number in the series. The range of temperature covered is from about 600 to 3400°F., the difference between consecutive numbers being in the neighborhood of 40°F. The method of using these cones consists in exposing a series covering the estimated temperature to the effect of the heat and noting which of them melt down or fuse. Softening on the edges or slight bending over is not to be taken as failure. The last of the series fused is taken to indicate the temperature attained. It will be seen that this method does not give a positive measure- ment, but it is often used to indicate the temperature of pottery furnaces. 104. Calorimetric Pyrometers. — Pyrometers of this class deter- mine the temperature by heating a metal or other refractory sub- stance to the heat of the medium whose temperature is to be meas- ured. Suddenly dropping the heated body into a large mass of water, the heat given off by the body is equal to that gained by the water; from this operation and the known specific heat of the sub- stance the temperature is computed. Thus, let K equal the specific heat of the body, M its weight; let W equal the weight of water, ¢ its temperature before, and 7?’ after, the body has been immersed; let T equal the temperature of the heated body, #’ its final temper- ature. Then KM(T -?’) =W@ —- 2). From which a Sw itg —t)+?. MK In connection with pyrometrical work, the specific heat of the substance used often has to be determined. The best means of doing this is to heat a piece of the substance of known weight to a known temperature and then to cool it off in a calorimeter as above explained. With proper correction for radiation and water equiv- MEASUREMENT OF TEMPERATURE 207 alent of calorimeter, K may then be computed from the above equation. The metals best suited for pyrometrical purposes are those with a high melting-point and a uniform and known specific heat. The obvious losses of heat in (1) conveying the heated body to the calorimeter, and (2) radiation of heat from the calorimeter, may be considerable, and should be ascertained by radiation-tests and the proper correction made. Nearly all metals are oxidized, or acted on by the furnace-gases, long before the melting-point is reached; so that, in general, whatever metal is used, it should be protected by a fire-clay or graphite crucible. Platinum, copper and iron are usually employed. The following table gives deter- minations of melting-points and specific heats: TABLE OF MELTING-POINTS AND SPECIFIC HEATS OF METALS. Melting-point. Metal. —_—__—_—_—_—-——| Specific Heat. Degrees Degrees Low Temperatures. Fahr. Centigrade. PISA UM 2 si cceccivets widen 4464 SE VINGOS 3110 1710 0.034 SEED co.cc: aconsuanidca is faioatanleveaanides fone See 3) SASS al pe AY oI sbnataimoesitaanens 0.118 Wrought-iron ................0 eee 2900 1590 0.110 Castaronhie 2 acceded vcckiraraie sess ced actians ., 2400 1310 0.14 COppetiicsrattirensictmnvmcaceaeters seat acetate ape ~ 198Q ~ 1083 0.094 Ponce latina sinc tatetardesiesasoachernlegen aie sh an gv seceannanersta'e.§ Dots) eamse a ee 0.170 BrasSive exvenvaw aware aes 1870 1020 0.094 AMCs arsegetseaten tind sass 4 780 419 0.093 Dead eccse I eset dlc ayes eS 621 327 0.030 Bismuth... ote cmeates eeseee eens 507 264 0.030 Tit cies Ts dasa civees doer ACEC GEER ELA 450 232 0.047 IM CE CUE Y Sue Seeyaricicescsteusres dt passianeoreecieens Be | iaiashine vaguest’ 0.030 Saphir: 3. Mezauane dierimaceasaises . 230 115 0.200 Antimony...... Betas aevwlo ero aanaainapies 797 | AZS | Glheswecccncdcatensvs aivaoeaee The mean specific heat of Platinum* has been the subject of careful investigation. It was found to vary from 0.03350 at 100° C. to 0.0377 at 1100°C., by Poullet, the experiment being made with a platinum reservoir air-thermometer. The following table gives some figures for both platinum and copper: * See Encyclopedia Britannica, art. Pyrometer. 208 EXPERIMENTAL ENGINEERING Platinum. Copper. Range of Temperature. Mean Specific Range of Temperature. Mean Specific Degrees Centigrade. Heat. Degrees Centigrade. Heat. oto 100 ¥.03350 15 to 100 0.09331 o * 200 03392 16 “ 172 0.09483 o 300 03434 17 ‘° 247 0.09680 o “ 400 -03476 0 “500 .03518 o © 600 -03560 eo 966 -03602 o “ 800 -03644 o goo .03686 © “ T000 .03728 o “ r100 +03770 For wrought-iron the true specific heat at a temperature ¢ on the Centigrade scale is given as follows by Weinbold: Ct = 0.105907 + 0.00006538 ¢ + 0.000000066477 ?. Porcelain .or Fire-clay having a specific heat from 0.17 to 0.2, although not a metal, is well adapted for pyrometrical purposes. Hoadley Calorimetric Pyrometer.—The Hoadley pyrometer is described in Vol. VI., page 712, ce hr eo >, 0 od ° 7 a _ {eo 0 od 90 OO0}0 SFP a Transactions of the American Fic. 149. — HoaDLEY PyRoMETER. Society of Mechanical Engineers. It consisted of a vessel, Fig. 149, made of several concentric vessels of copper, with water in the inner MEASUREMENT OF TEMPERATURE 209 one, eider-down in the intermediate spaces, and a cover of sim- ilar construction. Also a substance to be heated consisting of balls of platinum, or wrought-iron and copper covered with platinum. These balls were heated in a crucible, conveyed to the calorimeter and suddenly dropped in. The calorimeter was provided with an agitator made of hard rubber, with a hole in the center for a thermom- eter. The balls used as heat-carriers weighed about three-quar- ters of a pound each; the vessel held about twelve pounds of water. The balls were heated in crucibles and conveyed to the calorimeter in a fire-clay jar as shown in Fig. 150. The cover of this jar was CSA Si \ Fic. 150. — PLATINUM BALLS AND CRUCIBLE. quickly removed and the balls dropped into the water in the calo- rimeter. With proper handling, calorimeters should give reliable results. There is, however, great danger of error in the transfer of the heated body to the calorimeter, and this, combined with the fact that the indications are slow and require computation, has prevented this method of measuring temperature from becoming general in engi- neering practice. 105. Electrical Methods of Measuring Temperature.* — There are two classes of electrical pyrometers: resistance thermometers and thermo-couples. The former depend for their action upon the change of resistance of electrical conductors with a change of temperature, the latter upon the fact that the current set up at the junction of a thermo-couple is a function of the temperature to * For an extended discussion on Electrical Pyrometers, see High Temperature Measurements by le Chatelier and Boudouard, translated by Burgess. 210 EXPERIMENTAL ENGINEERING which it is heated. Both methods of temperature measurement are susceptible of great refinement, and of late years several forms of these instruments have appeared which are suited to the require- ments of engineering practice. Resistance Thermometers. —It has been observed that the resistance of electrical conductors generally increases with a rise in temperature. This interrelation may be mathematically ex- pressed so that it is possible to draw a curve between temperature and resistance for any given conductor. It hence becomes neces- sary merely to determine the resistance in order to read the tem- perature directly from a curve, but, while this method has been used, commercial instruments are usually so arranged that the scale of the indicating instruments reads directly in degrees. Such a scale may be constructed by direct comparison with a hydrogen-gas thermometer, or by comparison with a secondary standard. In order to make the instrument reliable it is necessary to use as the conductor a metal which will successfully resist the action of high temperatures and which at any given temperature always has the same resistance. It is found that platinum best meets these conditions, and platinum is therefore widely used. The best form of platinum-resistance thermometer is probably that of Professor Callendar, who finds that if a coil of pure annealed ‘platinum wire is wound about a mica framework, the whole being protected against the action of gases by an outer tube of hard glass or porcelain (depending upon the temperature‘to be determined), then the temperature as deduced from an observation of the resist- ance of the wire will seldom be in error by more than 735°C. at 500° C., while at 1300° C. the error need not be more than 7° C. Callendar’s method of using the resistance thermometer is described by Edser * as follows: “The thermometer is supplied with two exactly similar sets of leads, one set T (Fig. 151) being connected to the ends of the spiral of fine platinum wire, while the other set C (called the compensating leads) are joined at their ends within the containing-tube of the thermometer. The Wheatstone-bridge arrangement com- prises two equal conjugate arms Pand Q. Of the other two arms, one com- prises the platinum spiral, the leads T connected across the terminals AB, and * Heat, for Advanced Students, p. gor. MEASUREMENT OF TEMPERATURE 2EI the right-hand part of a stretched wire FB; the other arm comprises a set of resist - ance coils R, the compensating leads C connected across EF, and the left-hand part of the wire FB. Let X represent the resistance of the platinum spiral, R that of the resistance coils, C and T the resistances of the two sets of leads, and 2 a the resistance of the wire FB, while x is the resistance of that part of this wire between its middle point and the galvanometer connection, so that the two parts of FB have resistances (2 + x) and (¢ — x). Then, since P and Q are equal, the resistances in the other two arms of the bridge must be equal when no galva- nometer deflection is produced; in these circumstances R+C+a+x=X4+T+a-x. The two sets of leads are exactly similar, being made of the same material and lying side by side, so that their temperatures are always equal, and there- fore C is always equal to T. Thus X = R + 2x.” This method determines the resistance of the thermometer in terms of R and xX. Ii, however, the galvanometer circuits were left connected to the middle point of FB, and the resistances so adjusted. that with the thermometer cold the galvanometer stands a at zero, then with the thermometer at some F'- ge Lenina Bis other temperature the galvanometer would aca show a deflection, which latter can be expressed directly in degrees, as explained. This is the method ordinarily used in commercial instruments. In the use of these instruments the following sources of error should be noted: (a) Heating of the Wire by the Measuring Current Itself.— This makes it necessary to keep the current down below a certain limit, as the heating due to the passing current would make the readings too high, or the heating effect must be corrected for. The more sensitive the galvanometer or voltmeter, the smaller need the cur- rent be to give a good reading. (b) Lag. — For most work the platinum wire must be protected, usually by porcelain. This makes the wire slow to assume the tem- 212 EXPERIMENTAL ENGINEERING perature and causes a Jag. In general, with the same kind of in- -sulation or protection, the thinner the wire, the less the lag, but of course a very fine wire is apt to fuse more easily. Diameters used are from 0.1 to 0.3 mm. (0.004 to 0.01 inch). (c) Compensation for Resistance of Leads.— In order to prevent the formation of currents at the junction of the leads with the thermometer proper, these junctions must be placed in the cooler part of the circuit. It is usual to employ platinum-lead wires of larger diameter for some ways back than the thermometer wire itself, but even in such a case the varying resistance of these lead wires is apt to cause an error, which is further complicated by the fact that varying degrees of immersion will also have an effect. Hence the use of compensators, one type of which is shown in the sketch, Fig. 156. Thermo-couple Pyrometers. —The action of electric pyrometers employing ¢hermo-couples depends upon the fact that if two strips of dissimilar metals are joined at both ends so as to form a closed circuit, and if one end is heated while the other is kept cool, an electric current is set up which may flow in either direction, depend- ing upon the metals used, the strength of the current depending upon the kind of metals employed and upon the temperature difference between the two ends. We thus have given a direct method of measuring temperature, for, as in the case of the resistance thermom- eter, a scale for the instrument indicating the current strength may be constructed to read directly in terms of degrees by comparing with any standard temperature indicator. A variety of metals may be used in the construction of couples, but they are not equally good. The metals should possess a high melting-point and be of uniform composition, and platinum at once suggests itself. As a matter of fact, this is one of the metals used in the high-class high-resistance type of instrument, while for the companion metal an alloy of platinum with 10 per cent of rhodium is found to be best. Such couples are usually quite deli- cate and must be protected by porcelain and iron tubes, as shown in Fig. 152. The rest of the industrial high-resistance electrical pyrometer consists merely of a delicate current indicator, Fig. 153, showing a complete Le Chatelier outfit. The resistance of the MEASUREMENT OF TEMPERATURE 213 outside circuit in an instrument of this type is made purposely high in order to counteract the considerable increase in the resistance LIZZ dg LAR \ AS ad NSS I “\\ SSSSSSS OZ SS LLL \ ny, of the couple itself as it is being heated. Thus, LITE . : SSSSSS Y| for instance, the resist- ZEEE ance of a platinum plat- inum-rhodium couple, I meter long, the wires Fic. 152.— ELEMENT OF LE CHATELIER’S 0.02 inch diameter, is PYROMETER. about 2 ohms whencold, but will increase to 4 ohms at 1800° F. If the outside resistance is 200 ohms and the change in the resistance of the couple is neglected, the error made will be ss =1 per cent. This will be even less if the couple is not completely immersed. Many industrial instruments, however, have outside resistances of 4oo ohms, so that in such a case neither the vari- ation of resisé- ance in the couple, varying depth of immer- Sion, varying length of outside leads, which are usually of much larger diameter than the couple- wires, or a mod- erate change in the temperature of the cold junction can have any serious effect upon the correctness of the indications. On the other hand, because of the small size of couple- wires used and on account of the high total resistance of Fic. 153.— LE CHATELIER’S ELECTRICAL PyYROMETER. the circuit, the current set up is very small and the indi- cating instrument must hence be rather delicate, and must be care- fully set up and handled. For these reasons successful efforts have lately been made to construct so-called base-metal couples which are used in the low- 214 EXPERIMENTAL ENGINEERING resistance type of electrical pyrometer. Several different makes of such instruments are now on the market, and while they may per- haps not be as accurate as the high-resistance type, they are much hardier and cost quite a little less. The metals used in the couples are usually alloys of tungsten, iron, nickel and copper of composition depending upon the temperatures to be read. The main point in the making of such alloys is to get them of uniform composition, otherwise so-called parasite currents will be set up in various parts of the circuit which may render the instrument useless. Since these metals are cheap as compared with platinum, the couples are made of wire of considerable cross-section. This means that the current set up will be comparatively large and that the change in resistance of the couple with change in temperature will be comparatively small. Hence an ordinary low-resistance type of indicating instru- ment may be used, and the total resistance in such a circuit does not exceed about 10 ohms in most of the industrial pyrometers. The Bristol type of low-resistance pyrometer with portable instru- ment is shown in Fig. 154, while Fig. 155 shows the construction Portable Indicating Instrument Fic. 154.— BristoL PyROMETER. of the couples. The latter for protection are in most cases inserted into three-eighth or one-half-inch iron pipe closed at one end. The leads marked in Fig. 154 are of the same metal as the couples, so Fic. 155. that the cold junction is really at the points of connection with the indicating instrument. It is possible in most cases to keep the latter near the temperature at which the cold junction was main- MEASUREMENT OF TEMPERATURE 215 tained when the instrument was calibrated (usually 75° F.). If this cannot be done, either some correction must be made or compen- sators must be used, for a considerable variation in the temperature of the cold junction causes a much greater error in the low-resistance than in the high-resistance type of instrument. For very accurate work it is of course desirable to take steps to maintain the cold junction at calibration temperature, whatever that may have been, in either type of instrument. If this is not done and compensating devices are not used, it is sufficiently accurate for the low-resistance type to proceed as follows: If / =temperature of cold junction of the instrument in use, and # = temperature of cold junction at standardization, then add t’—¢ to the reading of the instrument if ¢’>¢, and subtract ¢ — 7’ from the reading if¢ > 7’. This correction, however, becomes of doubtful value if ¢’ very much exceeds 100° F., if the standard- ization temperature was in the neighborhood of 75 degrees. Compensating devices automatically take care of the change of resistance in the low-resistance type of instrument for change of tem- perature in the outside leads. The device used by the Bristol Co. is shown in Fig. 156. It consists sim- ply of a glass bulb shaped as shown and partly filled with mercury. A platinum-wire loop in series with ‘the outside circuit is fused into the sides of the tube and dips into the mercury. As the temperature in the outside circuit falls, the E.M.F. of the couple would increase on ac- count of the greater range of tem- perature between hot and cold junc- tion. At the same time, however, the mercury contracts, short-circuiting less of the platinum resistance in the compensator. This increases the resistance in the circuit and thus counteracts the effect of the greater E.M.F. If the temperature of the cold junction increases, the reverse action takes place. Fic. 156. COMPENSATOR. 216 EXPERIMENTAL ENGINEERING 106. Optical and Radiation Pyrometers.* — The action of the optical pyrometer usually depends upon the comparison of the intensity of the light emitted from the body whose temperature is to be measured with the intensity of the light from a standard source. In order to get rid of difficulties due to color differences and because the laws connecting the temperature of the body with the intensity of the emitted light are simpler, it is usual to deal with only a single wave-length (red is commonly retained). The Le Chatelier, the Wanner and the Fery absorption pyrometers are based on this principle, and the construction is usually such that it is merely necessary to adjust the instrument until two adjacent fields of vision, each illuminated by one of the sources of light, show the same intensity. From the relative displacement of cer- tain parts of the instrument necessary to produce this result, the temperature may be read directly or may be easily computed. The Morse thermo-gauge and the Holborn pyrometer, which are very similar in their construction, also belong to this class, although their operation is somewhat different. The former instrument is shown in the conventional sketch, Fig. 157. It employs an incandescent lamp with a rheostat arranged so that the current flowing through Spiral Filament Rheostat [rise it and its consequent bright- = =~" =, ‘ness may be regulated. The u4tf Dial No . eae amount of current flowing pcg through is shown by a milli- Fic. 157.— Tae Morse Trrmo-Gavor, Voltmeter connected in circuit, the reading of which can be referred to a scale for the determination of temperature. The lamp is adjusted from an experimental scale for its degree of brightness at different ages. In using this instrument the incandescent lamp is located between the eye and the object whose temperature is to be measured, and the current is regulated until the lamp filament becomes invisible. * For detailed information concerning optical and radiation pyrometers see le Chatelier’s and Boudouard’s “High Temperature Measurements.” MEASUREMENT OF TEMPERATURE 217 This instrument is designed for use in tempering furnaces and has an extensive use in that industry. Still another type of optical pyrometer is the Mesuré and Nouel pyrometric telescope, Fig. 158, by which the temperature is deter- mined by the direct observation of the light emitted from the hot body. TIIIPILIT ITIP IPOS Fic. 1 58. — Mesure AND NOUVEL PYROMETRIC TELESCOPE. This instrument measures the temperature by taking advantage of the rotation of the plane of polarization of light passing through a quartz plate cut perpendicular to its axis. The angle of rotation is directly proportional to the thickness of the quartz, and approx- imately inversely proportional to the square of the wave-length. Light from an incandescent object, passing through the slightly ground diffusing-glass G enters a polarizing nicol P, and, traversing the quartz plate Q, strikes the analyzer A, and is seen through the eye-piece OL. In the use of the instrument the analyzer is turned until the object appears to have a lemon-yellow color. The position of the analyzer is indicated by the graduated circle C, the reading of which may be referred to a temperature scale. On account of the fact that the change of color from red through lemon yellow to green, or vice versa, which is seen when the analyzer is turned, is not sharply defined, different observers are apt to obtain different results with this instrument and the error may amount to 100° C. For that reason, although the instrument is easy to handle, it should not be depended upon for close results. In radiation pyrometers the energy of total radiation, that of the long invisible rays as well as that of the shorter luminous rays, is measured by the heat effect it produces. The latter may be deter- mined either by thermo-couples, by the expansion of a compound metal strip or by a very delicate resistance thermometer. The 218 EXPERIMENTAL ENGINEERING Fery radiation pyrometer, which uses a thermo-couple, may serve as an example of this type, and the following description is taken from the catalogue of the manufacturing company: “The heat rays given out by a hot body fall on a concave mirror in the pyrometer telescope and are brought to a focus. At this focus is the hot junction of a thermo-couple, and this junction is heated by the focussed heat rays, the hotter the body the hotter the junction. Referring to Fig. 159, a section of the pyrometer telescope is shown on the right. The mirror M receives the heat rays and Fic. 159.—- FERY RADIATION PyROMETER. brings them to a focus at F. Here is the hot junction of a little thermo-couple. The cold junction is quite near the hot junc- tion, but is screened from the focussed heat rays. Thus the two junctions are equally affected by changes in air temperature, and the difference in temperature which causes a current to flow will be due to the temperature of the hot body. The instrument is designed so that within wide limits it is inde- pendent of the size of the hot body, or the distance at which it is used. To guide the pointing of the telescope an eye-piece E is provided at the rear end of the telescope through which a reflected image of the hot body can be seen. In the center of the field of view, as MEASUREMENT OF TEMPERATURE 219 seen in the eye-piece, the hot junction of the thermo-couple is seen as a black spot, and this has to be overlapped all around by the image of the hot body. The telescope may be taken as much nearer as is desired without altering the temperature-reading. As the telescope gets nearer to the hot body the mirror M receives more heat, but at the same time this greater amount of heat is spread over a larger image, and the intensity of heat remains the same. Thus the only effect of going nearer to the hot body is to increase the amount of overlapping of the image beyond the black spot. The distance can be as much as thirty times the diameter of hot body. The telescope is focussed by turning the milled head H at the side, and this is very simple. The indicating outfit is provided with an indicator, which is joined to the telescope by a flexible cable. This indicator meas- ures the current generated by the thermo-couple in the telescope, but instead of reading in current it is made to read aueets in tem- perature of the hot body. , ee For use when the temperature reading reaches the top of the scale, a second scale for higher temperatures is provided, and to use this the diaphragm D is swung over the mouth of the telescope. The stock instrument has two scales, one from 1000° to 2400° F. and the second from 1800° to 3600° F.”’ 107. Calibration of Thermometers and Pyrometers. — The ulti- mate standard of comparison in the standardization of thermom- eters and pyrometers is some form of gas thermometer. On account of the fact, however, that such a standard is not easy to handle, secondary standards such as thermometers or pyrometers, which have been compared with the primary standard gas thermometer, are ordinarily used. The comparison may be made by placing the instrument to be calibrated in a medium which can. be slowly heated or cooled, as the case may be, together with the standard. This is probably the usual method for instruments reading to less than 500 or 600° F., as ordinary mercury thermometers. For the latter it is usual also to determine the freezing- and boiling-points of water by methods described below. For high-reading instruments, however, stand- 220 EXPERIMENTAL ENGINEERING ardizing laboratories, like the Bureau of Standards at Washington, use a high-temperature scale reproduced in terms of certain fixed freezing- and boiling-points of various chemical elements. This temperature scale is not absolutely fixed in the upper ranges, awaiting the results of further investigations, but the provisional scale now used by the Bureau * is as shown in the following table. The scale above 1200° C. is based on the laws of black-body radia- ‘tion. *C, oF, PLAT, asi se 4 Asdusvenlusisons freezing... ....... 232 449.5 DNAs os eostet strat denen aie freezing......... 419 786 Sul Phits..2. cscnaaiaans Holling. 2c. 444.7 832.5 Antimony.......... freezing......... 630.5 1167 Goldcsecmiiiendt warenness melting, ers aanaa 1064 1947 Coppenicans t. sanar FOEZIN Gis ics ss. 5040 1084 1983 Nickel). sais cen nase melting........ 1435 2615 Palladium.......... melting.... .... 1546 2815 Platinum. «3:05.92 c00% melting......... 1753 3187 Tin, zinc, lead, antimony and copper must be protected from oxidation, which can be done by melting in graphite crucibles and protecting the surface by powdered graphite. The presence of oxides appears to depress the freezing-points. ‘The freezing-points of lead (327°C.) and of aluminum (658°C. for 99.7 per cent purity) as well as the boiling-point of naphthalene (218° C.) are also often used in standardizing pyrometers. Calibration of Mercury Thermometers. 1. To Test for Boiling-point.— Suspend the thermometer so ‘that it will be entirely surrounded up to or beyond the reading point in the vapor of boiling water at atmospheric pressure but will not be in contact with the water. Notethe reading. From the barom- ‘eter-reading calculate the boiling-point for the same time. The difference will be the error in position of the boiling-point. The engraving (Fig. 160) shows an instrument for determining the boiling-point. The bulb of the thermometer is exposed to steam at atmospheric pressure, which passes up to the top of the instrument around the tube, and down on the outside, discharging * Bureau Circular No. 7, Oct. 1, 1908, Bureau of Standards. MEASUREMENT OF TEMPERATURE 221 into the air, or it may be returned directly to the cup, thus obviating the need of supplying water. In the form shown, the parts tele- scope into each other for convenience in carry- ing, which is entirely unnecessary for laboratory uses. 2. To Test for Freezing-point. — Surround the thermometer to the reading point by a mixture of water and ice, or water and snow; drain off most of the water. The difference between the reading obtained and the zero as marked on the thermometer (32° for Fahr. scale) is the error in location of freezing-point. 3. For any other temperatures place the ther- mometer in a liquid bath, such as high-flash- point oil from which all traces of water have been previously removed by heating it, along with a standard which may be a standardized mercury thermometer, resistance thermometer or thermo-couple. Obtain simultaneous readings while heating or cooling slowly. Great care must be taken to thoroughly stir the bath in order to make the temperature uniform through- out. 4. Film or Stem Correction. —The scale on most mercury thermometers is constructed by first locating the freezing- and boiling-points of water under standard atmospheric conditions, and in locating these points both bulb and stem F!6- 160. — Bortinc- : ‘i POINT APPARATUS. are immersed up to the respective points. In practice, therefore, a thermometer stem should be immersed in the medium whose temperature is being read up to the point where the mercury column in the stem ends. In many cases, however, this is not possible, especially in case thermometer wells or cups are used. In such cases it is always advisable to compute a stem correction because, since the projecting mercury film is at a different temperature than the mercury in the rest of the bulb and stem, the thermometer will be in error by a certain = ae == 222 EXPERIMENTAL ENGINEERING amount. In many cases such a correction is negligible, but in others it is not, and it is in any important case not safe to depend upon guess work. The correction may be computed from the following equation: Stem correction = .o0016 m(T — #) for C scale. Stem correction = .o00088 » (T — #4) for F scale. Where n = number of degrees projecting, T = temperature of bulb, t = mean temperature of emergent stem. ll tis usually found by hanging a small auxiliary thermometer about halfway up the emergent stem; 7, however, is unknown, and it is usual to substitute for T the temperature as read from the ther- mometer. The error thus made is small. It is possible to take care of the stem correction automatically when the thermometer is subsequently calibrated by immersing it in the bath to the depth to which it was used on the test, while the standard is handled in the proper way. This method, however, assumes that the air temperature surrounding the stem is the same during calibration as during use. Calibration of Pyrometers. —The general method has already been outlined above. The practice of the Bureau of Standards is given in the following extracts from the Bulletin already cited: Thermo-cou ples, Calibration and Precautions in Use. (2) Homogeneity. — For work of precision it is important that each wire of a thermo-couple be of exactly the same chemical composition and physical proper- ties throughout, otherwise the indications of the thermo-couple will vary with the depth of immersion in the heated (or cooled) region. When requested, a special test of the homogeneity of the wires will be made, the results being expressed in terms of the electro-motive forces generated when successive short lengths of the wire are exposed to a constant high temperature. (b) Annealing. — Before calibration and use all high-temperature thermo- couples should be annealed by heating them throughout their length, preferably by means of an electric current, to a temperature higher than any to which they may subsequently be exposed. This eliminates the electro-motive forces developed between the hard and soft portions of the wires. When platinum couples have been contaminated by long-continued use they may often be restored to their origi- nal condition by annealing (for an hour or more) at high temperatures (1500° or 1600° C.). MEASUREMENT OF TEMPERATURE 223 (c) Precautions in Use. — The wires of the couple should be fused together at the hot junction, not tied or twisted, as such connections are liable to develop high resistance or to interrupt the circuit when the wires become oxidized. In general the wires of the thermopyle should be protected from the action of hot furnace gases, silicon, metallic vapors, etc. The cold junctions should be so placed that their fluctuations of temperature are negligible. The electrical resistance of the pyrometer galvanometer should be so high that the errors resulting from the resist- ance of the leads and the variation of the resistance of the couple with temperature and depth of immersion may be neglected. In work of the highest precision at high temperatures (above r100° C.), contamination of the couples due to the evapora- tion of rhodium and especially of iridium must be carefully avoided. A great many of the reported failures of thermo-couples to fulfil the practical requirements of technical applications have been traced to neglect of one or the other of these precautions. Re-tests made by this Bureau of platinum platinum- thodium couples that have been subjected to long and severe usage in the indus- tries have shown that, after annealing the couples, the new calibrations are in practical agreement with the old. (d) Calibration. — Thermo-couples are usually calibrated at the Bureau of Standards, after a thorough annealing, by comparison at four or more tempera- tures with two standard couples, the couples being immersed for about 25 cm. of their length in an electric furnace, and the cold junctions being kept-at 0° C. When a couple is to be used with its cold junction at some temperature other than o° C., the necessary correction will be indicated in the certificate. For the usual forms of thermo-couples made of platinum and its alloys, this correction is approximately + 44, where ¢ is the Centigrade temperature of the cold junction, and in general this correction lies between + $4 and + ¢ for practically all types of thermo-couples. (e) Use of a Pyrometer Galvanometer of Low Resistance. — In many industrial forms of thermo-electric pyrometer, the electrical resistance of the thermo-couple wires and accompanying leads is not negligible in comparison with the resistance of the indicating instrument. When this is the case the galvanometer does not in general indicate the true E.M.F. of the thermo-couple. If R, is the resistance of the thermo-couple wires and attached leads, R, that of the galvanometer, and E the true E.M.F. of the thermo-couple, then the E.M.F. = E,, as indicated by the R, R, +R, the increase in R, due to-the increase in the resistance of the heated wires and will, therefore, vary with the depth of immersion of the thermo-couple in the heated space. Electrical-resistance Thermometers. Calibration. — We may define temperature on the scale of the platinum resist- ance thermometer as given by pyrometer galvanometer, will be Z, = E E, will thus depend also upon R= Ro (a) pt = 100 a= Re’ 224 EXPERIMENTAL ENGINEERING where R is the measured resistance at some unknown temperature #, and R,,,, Ro, are the resistances at 100° C. and o° C., respectively. The relation between the platinum temperature #¢ and the Centigrade temperature ¢ from — 100°C. to t100° C. is very exactly given by Callendar’s equation t t r-prao( 1), (b) where ¢ is characteristic of the kind of metal. For pure platinum ¢ = 1.50, and it is larger for impure platinum. The calibration of a platinum resistance thermometer, which is to be used in the range — 100° C. to 1100° C., usually consists in measuring its resistance in melting ice (0° C.), in steam (100° C.), and at one other temperature, usually that of the vapor of boiling sulphur (444.7° C.), and computing other temperatures by means of formule (a) and (b). The values of Ro, the fundamental interval (Rio — Ro), and of 0 will be given in the certificate furnished by the Bureau. The work of many investigators has shown that a platinum resistance thermometer calibrated at these temperatures may be used to reproduce gas-scale temperatures throughout the range — 100° C. to rroo° C. with a degree of accuracy equal to that at present attainable in gas thermometry. For example, when such a calibration is extra- polated to the melting-point of gold, it gives a value (1062° C.) which differs from the true value by an amount which is no greater than the present uncertainty (5°) in our knowledge of this temperature. If a resistance thermometer is to be used at very low temperatures, the boiling- point of liquid oxygen (— 182.5° C.) may be used to advantage as the third cali- bration temperature, since the value of 0 found from the sulphur boiling-point cali- bration does not hold exactly at these very low temperatures. Resistance thermometers which are to be used in calorimetric work for measure- ment of small temperature changes with high precision will be calibrated at 0°, 100° and 32.384°, the transition temperature of sodium sulphate. When the construction of a platinum resistance thermometer does not permit of calibration by the above method of using three fixed temperatures, the instrument will be compared directly with the standards of the Bureau at several temperatures in an electric furnace. This method is not in general capable of so high pre- cision as the previously described one. This is the procedure followed when a resistance thermometer and its direct-reading temperature indicator are sub- mitted for test as a single instrument, . Calibration of Optical and Radiation Pyrometers. — The radiation emitted by substances depends on the nature of the substance and condition of its surface as well as upon the temperature. The only body whose radiation depends only on its temperature is the “‘black body,” which is approximately realized by a uniformly heated enclosure. If an optical pyrometer has been calibrated in terms of the radiation from a black body, it will not, therefore, in general give the true temperature of the incandescent body under observation, but nevertheless it will define a consistent MEASUREMENT OF TEMPERATURE 225 temperature scale for any one substance, which in very many cases is all that is necessary in the control of an industrial operation. Where the equivalent black- body temperature is not sufficient, true temperatures may be found by applying a suitable correction, the magnitude of which will depend on the emissive power of the body and on its temperature, or by taking the measurements in such a way that the radiation is very approximately black-body radiation. For example, if the problem at hand is the measurement of the temperature of a furnace or hardening bath, then by inserting a closed-end tube, of suitable material, such as magnesia, porcelain, or tungsten steel, of sufficient length so that the end and some distance along the tube is at the temperature of the furnace or bath, the radiation coming out of this tube is a close approximation to black-body radiation, and the optical pyrometer will then give true temperatures. Again, within many furnaces the conditions approximate fairly close to black-body conditions and the temperatures found by the use of an optical or radiation pyrometer will then differ but little from the true temperature. The readings of optical pyrometers and, to a much greater degree, of radiation pyrometers will be influenced by the presence of flames, vapors, and furnace gases. The temperature scale defined by the several radiation laws is in agreement with the gas scale throughout the widest range of measurable temperatures, and when these laws are extrapolated to the highest attainable temperatures they are still in satisfactory agreement. An optical pyrometer may be calibrated by sighting either upon a black body or upon another body whose emissive properties are known. It is, however, neces- sary to determine the calibration temperatures by some auxiliaty means, as a thermo couple; or carrying out the calibration at certain known temperatures, such as the fusing point of gold, palladium, and platinum; or, what is usually the more convenient in the case of industrial instruments, comparing the indications of the pyrometer to be tested with that of a standard instrument, both being sighted upon the same source, which may be a clear furnace, or, in the case of the two instru- ments using the same colored light, a graphite or metal strip mounted in vacuo and heated electrically. This use of an electrically heated strip permits of a very rapid calibration of sufficient accuracy for industnal and many scientific purposes. With a graphite strip such a calibration may be made up to 1900° to 2000° C. With a strip of tungsten sucha calibration might be carried several hundred degrees higher. The calibration formula for these optical pyrometers which are of the pho- tometer type, and in which light of a single color is used, is very simple. The intensity J of a monochromatic light source, approximating a black body, varies with its absolute temperature T (= ¢ + 273° C.), as follows: b log I= a7, where a and 6 are constants. Such a pyrometer may, therefore, be calibrated completely by finding its readings at two temperatures only, if its construction is 226 EXPERIMENTAL ENGINEERING otherwise mechanically correct. Often with such pyrometers the monochromatic light is obtained by means of colored glasses which are but approximately mono- chromatic. In this case the calibration should be carried out at several tempera- tures, the number depending on the glass used and the accuracy sought. The relation between the current C through the filament of the lamp of the Morse or Holborn-Kurlbaum type of pyrometer and the temperature ¢ of an approximately black-body source is C=a+b+4 ct’, (a) where a, b and ¢ are constants, so that measurements at three temperatures, at least, are necessary to calibrate such pyrometers. The pyrometer lamps should be aged before calibration for some twenty hours at a temperature of about 1800° C. In order to extend the range of any optical pyrometer above 1500° C. absorp- tion glasses, mirrors, diaphragms, or rotating sectors may be used. It is then necessary to determine the absorption coefficient for the screen used, by the measurement of one or more known temperatures with and without the screen interposed. : The indications of total radiation pyrometers, such as the Fery thermo-electric telescope, obey approximately the law BT = TN (b) where £ is the energy received by the instrument at a temperature T, from a black-body source whose temperature is T, and & is a constant. For the measurement of high temperatures, 7,‘ may usually be neglected in comparison with T*. The industrial forms of these instruments usually give readings de- parting somewhat from equation (b), so that it is necessary to calibrate them empirically at several points over the range for which they are intended to be used. A relatively large area is usually required upon which to sight these pyrom- eters. These instruments may be used with recording galvanometers and thus give a permanent record of temperatures. CHAPTER VIII. THE MEASUREMENT OF SPEED. UNDER this head is to be understood the determination of strokes or revolutions of any mechanism per unit of time, and not the measurement of the speed of moving masses in general. In prac- tically alt pump and engine tests such speed determinations are necessary, for determining either delivered capacity, variation with load, or power. The number of strokes of a moving mechanism can be counted quite accurately without an instrument if the speed is not too great. This is best done by holding a stick in the hand in such a position that it is struck periodically by some moving part, such as the cross-head of an engine. The instruments in use for speed determinations fall approxi- mately into three classes: 1. Counting devices. 2. Indicating devices, or Tachometers. 3. Chronographs. 108. Counting Devices. — These are all arranged so that a part of the instrument is moved by direct attachment to the moving machine and they record continuously from the time of attachment until the connection is again severed. For this reason they must always be used in conjunction with a clock or watch if the record is to be reduced to strokes or revolutions per unit of time. 1. Hand Speed-counter.— One form of this device is shown in Fig. 161. It consists of a counter operated by holding the pointed end of the instrument against the end of the rotating shaft which should have a so-called “center.” In using the instrument, the time is noted by a watch at the instant the counting gears are put in operation or are stopped. A stop-watch is very convenient for obtaining the time. The errors to be corrected are principally 227 228 EXPERIMENTAL ENGINEERING those due to slipping of the point on the shaft, and to the slip of the gears in the counting device in putting in and out of operation. The best counters have a stop device to prevent this latter error, and the gears are engaged or disengaged with the point in contact Fic. 161, — DOUBLE-ENDED HAND SPEED-COUNTER.. with the shaft. To prevent slipping of the point, the end of the instrument is sometimes threaded and screwed into a hole in the end of the shaft. 2. Continuous Speed-counter. —The continuous counter con- sists of a series of gears arranged to work a set of dials which show the number of revolutions. The arrangement of gearing in such Fic. 162.— Stroke Counter. an instrument is shown in Fig. 162. The instrument can usually be made to register by either rotary or reciprocating motion, and MEASUREMENT OF SPEED 229 can be had in a square or round case. The reading of the counter is taken at stated intervals and the rate of rotation calculated. 109. Speed Indicators: Tachometers. — All these instruments in- dicate directly the speed at which the machine to which they are attached is operating. ‘They are thus independent of a time determi- nation and are often more convenient for certain purposes. 1. Centrifugal Tachometers. —These instruments utilize the centrifugal force in throwing outward either weights or a liquid. The motion so caused moves a needle or column of liquid a distance proportional to the speed, so that the number of revolutions is read directly from the position of the needle or other indicator. Fic. 163.— SCHAEFFER AND BUDENBERG HAND TACHOMETER. One form of the instrument is shown in Fig. 163. It is arranged with a pointed end to hold against the shaft whose speed is to be determined. A belt-driven type is shown in Fig. 164. The movement of the needle over the dial is caused by weights moving under the action of centrifugal force. These instruments are all subject to wear and should always be checked or cali- brated for accurate work. Brown’s Speed Indicator consists of a U-shaped tube joined to a straight tube at the center of the bend. The revolution of the U-tube around the center tube induces a centrifugal force which elevates mercury in Fic. 164. —- BELTED ‘TACHOMETER. 230 EXPERIMENTAL ENGINEERING the revolving arms and depresses it in the center tube. A calibrated scale gives the number of revolutions corresponding to a given depression. The Veeder Tachometer, Fig. 165, another liquid tachometer, consists essentially of a small centrifugal pump discharging into a Fic. 165. — VEEDER Liquip TACHOMETER. vertical tube. The pump is driven from the machine under test and raises the liquid in the tube to an extent proportional to the speed of rotation. The speed is read on a properly graduated scale attached to the tube. Autographic Tachom- eters. — Variations in speed are shown autographically in several instruments by recording on a strip of paper moved by clock-work the variation in centrifugal force of revolving weights. In the Moscrop speed-re- corder, shown in Fig. 166, the shaft B is connected with the shaft whose speed is to be measured. The variation in the height of the balls near B, caused by variation in speed, gives the arm C a reciprocating motion, so that an_at- tached pencil makes a diagram, FED, on the strip of paper moved by clock- work, The ordinates of this diagram are proportional to the speed. MEASUREMENT OF SPEED 231 2. Frahm’s Resonance Tachometer.* — This instru- ment now made in a great number of forms depends upon the principle of reson- ance, that is, the property of a body to vibrate in unison with another which has a like period. It consists of a num- ber of steel reeds of different lengths and differently loaded, so that each one of the series has a unique period, mounted in the order of their periodicity, Fig. 167. The variation of period, or of number of vibra- tions per minute between ad- jacent reeds, is fixed to suit the purpose for which the instrument is intended. In use it may rest directly upon the frame of a moving mechanism, it may be con- er nected by belt or mechanical % i linkage or it may be connected : electrically. When resting directly on the frame of an engine the impulses due Fic. 166.— THE Moscrop SPEED-RECORDER. al Fic. 167.— REEDS OF FRAHM’S RESONANCE TACHOMETER. * See Zeitschrift des Vereins Deutscher Ing. Oct. 15, 1904. 232 EXPERIMENTAL ENGINEERING to slight under- or over-balancing are sufficient to set the proper reed in motion. When belted the shaft of the tachometer carries either a small magnetic or a mechanical device for imparting vibrations to the proper reed. When connected electrically the reeds are set in vibration by the variation of a magnetic field set up by an alternating current, the alternating current being obtained from a generator driven by or connected to the mechanism of which the speed is to be measured. 110. The Chronograph. — The chronograph,* Fig. 168, consists of a drum revolved by clock-work so as to make a definite number Mn a mn Ma Fic. 168. — CHRONOGRAPH. of revolutions per minute. A carriage having one or two pens, h, g, as may be required, is moved parallel to the axis of the cylinder by a screw which is connected with the chronograph-drum A by gearing. The pen in its normal condition is in contact with the paper, and it is so connected to an electro-magnet that it is moved axially on the paper whenever the circuit is broken. The circuit may be broken automatically by the motion of a clock, or by hand with a special key, or by any moving mechanism. Two pens are usually * See Thurston’s Engine and Boiler Trials, page 226. MEASUREMENT OF SPEED 233 employed, one of which registers automatically the beats of a stand- ard clock; the other may be arranged to note each revolution or fraction of a revolution of a revolving shaft. The distance between the marks made by the clock gives the distance corresponding to one second of time; the distance between the marks made by break- ing the circuit at other intervals represents the required time which is to be measured on the same scale. This instrument has been in use by astronomers for a long time for minute measurements of time, and by its use intervals as short as one one-hundredth (.o1) part of a second can be measured accu- rately. Tuning-fork Chronograph. —A tuning-fork emitting a musical note makes a constant and known number of vibrations. The number of vibrations of the fork corresponding to the musical tones are as follows: INGLE dicen wdisdasns Cc D B&B F G&G A EB G, Vibrations per second..128 144 160 170% 192 213% 240 256 If now a small point or stylus be attached to one of the arms of a tuning-fork, as shown in Fig. 169, —in which F is one of the arms of the tuning- fork, and CAED a piece of elastic metal to which the stylus, AP, is attached, — and if the fork be put in vibration and the stylus permitted to come in contact with any surface that can be marked, as a smoked and varnished cylinder moved at a : uniform rate, the vibrations of the tuning- Fic. 169.—Srvy.us ror fork will be recorded on the cylinder by a FUNENE HORE, series of wavy lines, as shown in Fig. 170; the distance between Fic. 170. — SPEED-RECORD FROM CHRONOGRAPH. the waves corresponding to known increments of time. If each 234 EXPERIMENTAL ENGINEERING revolution or portion of a revolution of the shaft whose speed is required be marked on the cylinder, the distance between such marks, measured to the same scale as the wavy lines made by the tuning-fork, would represent the time of revolution. Fig. 171 (from Thurston’s Engine and Boiler Trials) represents the Ranson chronograph; in this case the tuning-fork is moved Fic. 171.— TUNING-FORK CHRONOGRAPH. axially by a carriage operated by gears, and is kept in vibration by an electro-magnet; the operation of the instrument is the same as already described. The form of the record being shown in Fig. 170; the wavy marks being those made by the tuning-forks, those at right angles being made at the end of a revolution of the shaft whose speed is required. The tuning-fork with stylus attached,* as in Fig. 169, can be made to draw a diagram on a revolving cylinder connected directly to the main shaft of the engine, or the shaft itself may be smoked and afterward varnished. If the fork be moved axially at a per- fectly uniform rate, the development of the lines drawn will be for uniform motion, straight and of uniform pitch; but for variations in speed these lines will be curved and at a varying distance apart. From such a diagram the variation in speed during a single revolu- tion can be determined. * See Engine and Boiler Trials, page 234. MEASUREMENT OF SPEED 235 111. Measurement of Speed Variation within a Revolution. — It is sometimes necessary to measure the variation of engine speed within a revolution. The most convenient method is to use some constant-speed mechanism running at much higher speed than the engine, allowing it to scratch the face of the engine flywheel at equal intervals of time. A tuning-fork has often been used, but is somewhat difficult to handle under these conditions unless arranged so that it is kept in vibration electrically. In commercial practice an electric motor fitted with a heavy fly- wheel and driven from a constant-voltage supply, such as a storage battery, has proven satisfactory. It runs at a much higher speed than the engine under test and is arranged to scratch the face of the engine flywheel every time its own flywheel makes one com- plete revolution. The constancy of angular speed of the engine may then be obtained by measuring the distance between successive marks on the face of its flywheel. CHAPTER IX. FRICTION —TESTING OF LUBRICANTS. 112. Friction.— This subject is of great importance to engineers, since in some instances friction causes loss of useful work, and in other instances it is utilized in transmission of power. The sub- ject is intimately connected with that of measurement of power by dynamometers, treated in Chapter X. In connection with these two chapters, the student is advised to read Friction and Lost Work in Machinery and Mill-work, by R. H. Thurston. Definitions. — Friction, denoted by F, is the resistance to motion offered by the surfaces of bodies in contact in a direction parallel to those surfaces. The normal force, denoted by N, is the force acting perpendicular to the surfaces, tending to press them together. The coefficient of friction, f, is the ratio of the friction, F, to the normal force, N; that is, f= F + N. The éotal pressure, R, is the resultant of the normal pressure, N, and of the friction, F, and its obliquity or inclination to the common perpendicular of the surfaces is the angle of friction, whose tangent is the coefficient of friction. The angle of repose, , is the inclination at which a body would start if resting on an inclined plane. It is easy to show * that for that condition, if W is the weight of the body, W cos¢ = N; also, W sing = F; and since f = F + N, W sin Wing | W cos ¢ See Table 1, Appendix, for values of f and ¢. tan ¢. * See Mechanics, by I. P. Church; p. 164. 236 FRICTION — TESTING OF LUBRICANTS 237 It has been shown by experiment that for sliding friction (1) the coefficient f is independent of N; (2) it is greater at the instant of starting than after it is in motion; (3) it is independent of the area of rubbing surfaces; (4) it is diminished by lubrication; (5) it is inde- pendent of velocity. 113. Classification. — The subject of friction is naturally divided into the following sub-heads, all of which are intimately connected with methods of lubrication: A. Friction of rest, occurring when a body is about to start. It is the resistance to change of position. B. Friction of motion, occurring while two bodies are in relative motion, and being less than the friction of rest. The second kind, or friction of motion, is of principal importance, and consists of — 1. Sliding friction, occurring usually in one of the following forms: a. Bodies sliding on a surface. b. Axles or journals revolving in boxes. c. Pivots turning on steps. 2. Rolling friction. a. One body rolling over a plane. b. One body rolling on another not plane. 114. Formule and Notation. a = angle of inclination of plane ; 1 = length of journal; ¢ = angle of friction; n = revolutions per minute. 6 = arc of contact on journal; V = velocity of rubbing in ft. per min, & = inclination of force with plane; p = intensity of pressure per sq. in. N = normal force on a plane; P = total pressure; f = coefficient of friction; W = weight of the body. = radius of journal; The most important formule relating to friction can be tabulated as follows: 238 EXPERIMENTAL ENGINEERING TABLE OF USEFUL FORMUL2 FOR UNIFORM MOTION. . g Force of friction............ F JN = Ntana= WN tan¢. © | Coefficient of friction........] f Tana = tang =VW?— Ni+N. , _ 3] Square of reaction of bearing.) N? |W?—F?=W? (1 —sin? ¢) = W? cos? ¢. y 2° S| Weight on journal (squared).| W? |N?+F? =N?(1+f*) =F? (r+f?) +f ga Z Moment of friction......... M |Fr=Wrsing =fWr + V1 +f. | Work of friction per minute...) U |FV=2nnrWsing=22nrfW+V 14 f?. +0 . | Weight on journal (general)..| W f ‘i pir cos 6d8. E Intensity of pressure at 9=9g0° pr oe 3 <, | Weight, perfect fit of journal.| W | pr Jce8 6d0 = 1.57 p'lr. 2 Pressure per square inch..... ? 0.64 W cos 6 + Ir. & Maximum pressure per sq.in.| pm | 0.64W + oe = | Total pressure on bearing....| P 0.64 W f aces 0d0 = 1.27 W. & | Total force of friction. ...... F | fP=127fw. 2 Moment of friction......... M | Pfr=Fr=1.27fWr. Work of friction per minute...) U | FV = 1.27fWV = 2.542 fnrW. 115. Friction of Pivots. —Intensity of pressure = p; total pres- sure = P. Moment of friction, M = 2 fPr. For a conical pivot, U = 4 xnfPr + sin a. U = $ anfPr. angle of cone. Work of friction, a= For Friction on a Flat Collar.— Moment of friction, U = $anfP (f° —7°)+(? — 1”); 7 = radius of collar; 7’ = radius of shaft on which it is fitted. 116. Friction of Cords and Belts, Belt Drive. — Suppose, referring -to Fig. 172, that a belt passes around a pulley so that T, is the tension on the tight side and T, the tension on the slack side, the tractive effort, P, of the belt is then T,—T,,. The frictional resistance to slip is best determined by con- sidering an infinitesimal part ds of the entire arc of contact, S. This small length of arc ds is that subtended by the angle 00 in Fig. 172. This FRICTION — TESTING OF LUBRICANTS 239 arc is reproduced in Fig. 173 for the sake of clearness. The resist- ance to slipping offered by any two surfaces in contact is the product of the normal pres- sure, p, on these surfaces multiplied by the coefficient of friction, f, That is, the frictional resistance offered is F = pf. At one end of the arc db =os in Fig. 173, the tension is T, at the other end it may be considered equal to T + OT, although for our purpose 67 may es be neglected. The normal | pressure, #, is the resultant ee of the tensions at the ends of this arc ds = arc db. If ad and ab represent these two tensions, the resultant, p, is represented by the line ac. 60 Now the angle ade = angle oe and ae = = ac =< P; ae, 00 also —-=sin —, ad 6 ae = ad ga =T ene 2 a : . 06 from which p =20¢e—27 sin—-- This for our purpose may be written p = Toe. (1) The normal force, p, with which the belt presses against the pulley is, however, decreased by the centrifugal force acting on the 240 EXPERIMENTAL ENGINEERING belt at the same time. The centrifugal force of the infinitesimal arc ds may be expressed by Os Z. Vv g - (2) where g = the weight of belt one foot long, v = velocity of belt in feet per second, r = radius of pulley in feet, and g = 32.2. Now since 6s = 700, (2) may be written ; | Centrifugal force = 700 = ==+v"d0. g er (3) The net normal force, p, is therefore ~ = T2 = evo 2 (7 as 8) 9, g Multiplying this by the coefficient of friction, f, we have the total frictional resistance p= (7-2) oof (4) On the assumption that any further increase in the tension T causes complete slipping, we must have oT = (7 s ty) a0f, (5) from which foo = tN ts (6) (49 Integrating (6) between the limits of T, and T,, we have re Ley foo =log ————- (7) FRICTION — TESTING OF LUBRICANTS 241 Tf the effect of centrifugal force had been neglected, equation (7) would have been T 00 = log —, 8 f br (8) in which simpler form the theoretical result is most frequently stated. Equation (8) is safe for moderate speeds where the action of centrifugal force is much less felt. By putting the tractive force Pat, f, and without entering into the details of the reduction, the following equations may be derived from equation (7): ef? q i P(=_) ae (9) Tica (4) +h, (a0) fo P - (7-0) 4 (11) where e = base of natural logarithms = 2.718. Again neglecting centrifugal force, equation (11) might have been written P= r,(1 = +) . (12) 117. Friction of Fluids (1) is independent of pressure; (2) pro- portional to area of surface; (3) proportional to square of velocity for moderate and high speeds and to velocity for low speeds; (4) is independent of the nature of the surfaces; (5) is proportional to the density of the fluid, and is related to viscosity. Based upon the above laws, the resistance encountered in the case of fluid friction may in general be expressed by Vy? 242 EXPERIMENTAL ENGINEERING in which f = coefficient of fluid friction (abstract number). A = area of rubbing surface. V = velocity of motion of fluid over the surface. y = heaviness (density) of fluid. ll ll 2 In this expression, ve head producing the velocity V, hence 2 28 Ar e = weight of an ideal prism of height # on area A, and this 2§ therefore represents a force which if multiplied by /, the coefficient of friction, gives the frictional resistance. The work of friction per minute, casey. 28 if V is expressed in feet per minute. Viscosity and density of fluids do not affect to any appreciable extent the retardation by friction or the rate of flow, but have some influence upon the total expenditures of energy. Molecular or internal friction also exists. 118. Lubricated Surfaces. — Lubricated surfaces are no doubt to be considered as solid surfaces, wholly or partially separated by a fluid, and the friction will vary, with different conditions, from that of liquid friction to that of sliding friction between solids. Dr. Thurston gives the following laws, applicable to perfect lubrica- tion only: 1. The coefficient of friction varies inversely as the intensity of the pressure, and the resistance is independent of the pressure. 2. The coefficient varies with the square of the speed. 3. The resistance varies directly as the area of journal and bearing. 4. The friction is reduced as temperature rises, and as the vis- cosity of the lubricant is thus decreased. Perfect lubrication does not usually exist, and consequently the laws governing the actual cases are likely to be very different from the above. The coefficient of friction in any practical case is likely to be made up of the sum of two components, solid and fluid friction. FRICTION — TESTING OF LUBRICANTS 243 Testing of Lubricants. 119. Determinations required. — The following determinations are required in a complete test of lubricants: The detection of adulteration. The detection of acids. The detection of tendency to gum. The measurement of density. The determination of viscosity. The determination of chill point. The determination of flash point. The determination of burning point. The determination of volatility. The measure of the coefficient of friction. 11. The determination of durability and heat-removing power. PEMA RE po H 9 120. Adulteration of and Impurities in Oils. — Quantitative determinations of adulteration can be made only by chemical analysis, but there are certain simple tests by which the engineer can sometimes detect adulteration. It should be stated, how- ever, that admixtures are not in all cases to be considered as adulteration.* Mineral Oils. —The most common case of adulteration in these oils is found in the addition of animal and vegetable oils or mineral soaps to cylinder oils. The presence of animal or vegetable oils in cylinder oils is objectionable because when subjected to the heat and moisture occurring in such service they decompose, yielding fatty acids as one of the decomposition products. Such acids sometimes attack the metal of cylinder and piston and are therefore undesirable. The presence of mineral soaps is objectionable only because they give an erroneous impression of the value of the oil as a lubricant, increasing its viscosity without increasing its lubricating powers. Adulteration by animal or vegetable oils is detected by mixing with a sample of the oil to be tested an alcoholic solution of sodium hydroxide or potassium hydroxide and then gradually heating to about 200° F. The metal of the hydroxide saponifies the fatty acid of the adulterant and the soap formed separates out. * See Friction and Lost Work, by R. H. Thurston. 244 EXPERIMENTAL ENGINEERING The presence of mineral soaps can only be detected by incinerating asample of the oil and judging the purity from the quantity of ash. This should not exceed about 0.1 per cent with a pure mineral oil. Poorly refined mineral oil may contain sulphur compounds. Their presence may be detected by heating a sample of the oil toa temperature of about 300° F. for fifteen minutes, under which con- ditions the presence of sulphur is indicated by a considerable darken- ing of color. Animal and Vegetable Oils. —Owing to ‘the fact that mineral oils are generally cheaper than those of animal and vegetable origin the former are often used as adulterants for the latter. Their presence can be detected by the saponification method above out- lined. In some cases the admixture of mineral oil may be so great that it can be detected by the bloom or sheen which all mineral oil naturally possesses. Under such conditions the saponification test is unnecessary. The detection of bloom is made easy by dropping a small quantity of oil on a “black plate”; when looking at the sample at an angle the iridescent coloring will show strongly if undebloomed oil is present. Since mineral oil may be debloomed by the addition of nitro- compounds, as nitro-naphthalene or bi-nitro-benzol, the optical test must not be regarded as absolute and in important cases the saponification method must be resorted to. The common way of detecting the adulteration of animal and vegetable oils among themselves is by using the saponification method and making quantitative determinations. It is necessary for this purpose to accurately determine the quantity of hydroxide necessary to completely saponify the oil and to check with that theoretically necessary for the particular oil under consideration. This is evidently a matter for the chemist and is seldom attempted by the engineer. Each animal and vegetable oil has a definite specific gravity at a given temperature, and variation from this figure may be taken as an indication that impurities are present. There are several oils, how- ever, whose specific gravity is very nearly the same at the same tem- perature, and hence this method of identification sometimes fails. FRICTION — TESTING OF LUBRICANTS 245 Animal oils may be distinguished from those of vegetable origin by the fact that chlorine gas will turn animal oils brown and vege- table oils white. 121. Acid Tests. —Tests for acidity may be made by observing the effects on blue litmus-paper; or better by the following method described by Dr. C. B. Dudley: Have ready (1) a quantity of 95 per cent alcohol, to which a few grains of carbonate of soda have been added, thoroughly shaken and allowed to settle; (2) a small amount of turmeric solution; (3) caustic-potash solution of such strength that 314 cubic centimeters exactly neutralize 5 c.c. of a solution of sulphuric acid and water, containing 4o milligrams H,SO, per c.c. Now weigh or measure into any suitable closed vessel —a four-ounce sample bottle, for example — 8.9 grams of the oil to be tested. To this add about two ounces No. 1, then adda few drops No. 2, and shake thoroughly. The color becomes yellow. Then add, from a burette graduated to c.c., solution No.3 until the color changes to red, and remains so after shaking. The acid is in proportion to the amount of solution (3) required. The best oils will require only from 4 to 30 c.c. to be neutralized and become red. 122. Gumming or Drying. —Gumming or drying is a conver- sion of the oil into a resin by a process of oxidation, and occurs after exposure of the oils to the air. In linseed and the drying oils it occurs very rapidly, and in the mineral oils very slowly. Methods of Testing. —Nasmyth’s Apparatus. — An iron plate six feet long, four inches-wide, one end elevated one inch. Six or less different oils are started by means of brass tubes at the same instant from the upper end: the relative distances covered in a given time constitute a measure of the gumming property. Bailey's Apparatus consists of an inclined plane, made of a glass plate, arranged so that it may be heated by boiling water. A scale and thermometer is attached to the plane. Its use is the same as the Nasmyth apparatus. This effect may also be tested in an oil-testing machine by apply- ing fresh oil, making a run, and noting the friction; then exposing the journal to the effect of the air for a time, and noting the increase of friction. In all cases a comparison must be made with some standard oil. 246 EXPERIMENTAL ENGINEERING 123. Density of Oils. — The density or specific gravity is usually obtained with a hydrometer (see Fig. 174) adapted for this special purpose, and termed an oleometer. The distance that it sinks in a vessel of oil of known temperature is measured by the graduation on the stem; from this the specific gravity of the oil may be found. The standard temperature for measuring of the density of oils is 60° F. The density is often expressed in Beaumé’s hydrometer-scale, which can be reduced to corresponding specific gravities as com- pared with water by Table 2 given in the Appendix. Beaumé’s hydrometer is graduated in degrees to accord with the density of a solution of common salt in water; thus, for liquids heavier than water the zero of the scale is obtained by immersing in pure water; the five-degree mark by immersing in a five-per-cent solution; the ten- degree mark in a ten-per-cent solution; etc. For liquids lighter than water the zero-mark is obtained by immersing in a ten-per-cent solution of brine; the ten-degree mark by immersing in pure water. After obtaining the length of a degree the stem is graduated by measurement. The tendency to-day is to avoid the use of arbitrary scales, like the Beaumé, and to refer to the standard specific gravity scale. The density may be found by obtaining the loss of weight of the same body in oil and in distilled water. The ratio of loss of weight will be the density com- pared with water. It may also be obtained by weighing a given volume on Fic. 174. @ pair of chemical scales. Hyprom- In connection with the methods of finding density “™*- above outlined it is well to remember that if a sample of oil is composite and has stood in a graduate for a considerable length of time the upper part of the oil column may be lighter than the lower, in which case the hydrometer may fail to give the correct result. This difficulty can usually be overcome by thorough stirring immediately before taking the reading. The following table gives average results of density determinations for the most common oils. FRICTION — TESTING OF LUBRICANTS 247 SPECIFIC GRAVITY (AVERAGE) OF OILS AT 60° F, : Animal and Vegetable Oils. CASTOR st: ido seure sacs Suketaaux Gaaeatendd Mobeiacth 0. 966 Cotton-seed (refined)...........0..0.2..0002. 0.923 Cod-liver:(puie). ec wiraawreaien oda vee van 0.927 Lard (Wilt?) siocuw sauna secwinws pars wkawan aed 0.917 Linseed (raw) ......... 0... c cece eee ee 0.929 Linseed (boiled)... 0.0... 20... ccc cee cee e ees ©. 941 Olive........ iRoaaconaninsan cited dash pana navn eee meas 0.914 Rape-seed (white winter)............ ray 0.914 Resin) (third: Punt) scsi sarige eae eheewiedges 0. 988 Seal} ini edro-asdie Avaaun pee eu nang hloaen een 0.924 Sperm: (Wintet)ins wacdeodeawenewwawia aes ae 0. 881 Vallow's cidresa ij reetvalsusuunymadiestiescsess ©. 904 Whale (GWint)®)) oss: cscincsnesuiaid ann peed 0.925 Mineral Oils. Rhigolen@ sc vac vnersdsadeeds teks ee cena ne 0.622 BON Zi 6s os. ccaresinespstd -siahseas pane sinless ale seranated 0.630 to 0.670 GaSOlENE sisi s sissces end eee ee niaye LabM oak acne 0.680 to 0. 700 Illuminating oils (average) ................. 0.780 to 0.860 Lubricating oils... 0.0... eee eee eee 0.860 to 0. 960 Parafline waxssssacxwes aes ee cava ewe eases 0. 8go- 124. — Method of Finding Density. —A. With Hydrometer Ther- mometer and with Hydrometer Cylinder. 1. Clean the cylinder thoroughly with benzine, then fill with dis- tilled water. Set the whole in a water-jacket, and bring the tem- perature to 60° F. Obtain the reading of the hydrometer in the distilled water and determine its error. 2. Clean out the cylinder, dry it thoroughly, and fill with the oil to be tested; heat in a water-jacket to a temperature of 60° F., and obtain reading of hydrometer; also obtain reading, at temperatures of 40°, 80°, 100°, 125°, and 150°, and plot a curve showing relation of temperature and corrected hydrometer-reading. Reduce hydrometer-readings, if in Beaumé degrees, to correspond- ing specific gravities, by table given in Appendix. B. Weigh on a chemical balance the same volume of distilled water at 60° F., and of the oil at the same temperature; and compute the specific gravity. 248 EXPERIMENTAL ENGINEERING C. Weigh the same metallic body by suspending from the bottom of a scale-pan of a balance: 1. In air; 2. In water; 3. In the oil at the required temperature. Carefully clean the body with benzine after immersing in the oil. The ratio of the loss of weight in oil to that in water will be the density. 125. Viscosity. — Viscosity of oil is closely related but not pro- portional to density. It is also closely related, and in many cases it is inversely proportional, to the lubricating properties. The rela- tion of the viscosities at ordinary temperatures is not the same as for higher temperatures, and tests for viscosity should be made with the temperatures the same as those in use. The less the viscosity, con- sistent with the pressure to be used, the less the friction. The viscosity test is considered of great value in determining the lubricating qualities of oils, and it is quite probable that by means of it alone we could determine the lubricating qualities to such an extent that a poor oil would not be accepted nor a good oil rejected. It is, however, in the present method of performing it, to be considered as giving comparative rather than ab- solute results. There are several methods of determining the viscosity. It is usual to take the viscosity as in- versely proportional to the rate of flow of the oil through a standard nozzle while maintaining a constant or constantly diminishing head and constant temperature, a comparison to be made with water or with some well-known oil, as sperm, lard, or rape-seed, under the same con- ditions of head and temperature. Viscosimeter, — A pipette sur- rounded by a water-jacket, in which the water can be heated by an auxiliary lamp and maintained at any desired temperature, is often used as a viscosimeter. F ig. 175 shows the usual arrangement for this test. E is the heater for the Fic. 175.— VISCOSIMETER. FRICTION — TESTING OF LUBRICANTS 249 jacket-water, BB the jacket, A the pipette, G a thermometer for determining the temperature of the jacket-water. The oil is usually allowed to run partially out from the pipette, in which case the head diminishes. ‘Time for the whole run is noted with a stop-watch. In the oil-tests made by the Pennsylvania Railroad Company the pipette is of special form, holding 100 c.c. between two marks, — one drawn on the stem, the other some distance from the end of the dis- charge-nozzle. Tagliabue’s Viscosimeter.—In Tagliabue’s viscosimeter, shown in Figs. 176 and 177, the oil is contained in a basin C, and trickles i Fic. 176.— TAGLIABUE’S Fic. 177. — TAGLIABUE’S VISCOSIMETER. VISCOSIMETER. downward through a metal coil, being discharged at the faucet on the side into a vessel holding so c.c. The oil is maintained at any desired temperature by heating the water in the vessel B surrounding the coil; cold water is supplied from the vessel A, as required to main- tain a uniform temperature. The temperature of the oil is taken by the thermometer D. Gibbs’ Viscosimeter. —In the practical use of viscosimeters it is found that the time of flow of too c.c. of the same oil, even at the same temperature, is not always the same, — which is probably due 250 EXPERIMENTAL ENGINEERING to the change in friction of the oil adhering to the sides of the pipette. To render the conditions which produce flow more constant, Mr. George Gibbs of Chicago surrounds the viscosimeter, which is of the pipette form, with a jacket of hot oil. A circulation of the jacket-oil is maintained by a force-pump. The oil to be tested is discharged under a constant head, which is insured by air-pressure applied by a pneumatic trough. The temperature of the discharged oil is meas- ured near the point of discharge. Perkins’ Viscosimeter.—The Perkins’ viscosimeter consists of a cy- lindrical vessel of glass, surrounded by a water or oil bath, and fitted with a piston and rod of glass. The edges of this piston are rounded, so as not to be caught by a slight angularity of motion. The diam- eter is one-thousandth of an inch less than that of the cylinder. In practice the cylinder is filled nearly full of the oil to be tested, and the piston inserted. The time required for the piston to sink a certain distance into the oil is taken as the measure of the viscosity.* Stillman’s Viscosimeter. — Prof. Thomas B. Stillman of Stevens Institute uses a conical vessel of copper, 6 inches in length and 13 inches greatest diameter, surrounded by a water-bath, and connected to a small branch tube of glass, which is graduated in cubic centi- meters; the time taken for 25 c.c. to flow through a bottom orifice #z of an inch in diameter is taken as the measure of the viscosity, during which time the head changes from 6 to 5 inches. Prof. Stillman makes all comparisons with water, which is the most con- venient and uniform standard. The temperature of the oil is taken at about the center of the viscosimeter. Viscosimeter with Constant Head, — A form of viscosimeter which possesses the advantage of having a constant head for flow of oil regardless of the quantity in the instrument, as made by Tinius Olsen & Co. of Philadelphia, is shown in the next figure. It is simple in form and can be very readily cleaned. It is provided with a jacket, and oils may be tested at any temperature. This instru- ment is now the principal standard used in the Sibley College Laboratories. * See paper by Prof. Denton, Vol. IX., Transactions of Am. Society of Mechanical Engineers. FRICTION — TESTING OF LUBRICANTS 251 Description. —A, Fig. 178, is a cup similar in construction to that of the kerosene reservoir of a students’ lamp, with a capacity of about 125 c.c., and is surrounded with a jacket D, in which may be placed ‘insulating materials or water to maintain a constant tem- perature while the oil is flowing; C is a ther- mometer-cup, to the bottom of which is secured a small cap containing the orifice F; N is a channel connecting the chamber con- taining A with C; B is one of four small tubes which admit air to the interior of the cup A and thus maintain atmospheric pressure on oil in it; this action secures a constant level of the surface of the oil in the cup C and the sur- rounding space, at the height of the lower opening in the tube B. 4H isa valve to retain oil in A while placing it into D. M is a bracket serving as a guide for valve-stem K. The mechanism L, G, G is a device for opening and closing the orifice F readily, and Fic. 178. is held in a closed position by spring catch L. VISCOSIMETER. The instrument is supported by three legs about eight inches in length. Operation. — Withdraw cup A, fill it in an inverted position with the oil, hold valve H on its seat, reinvert A and place in position in the instrument. The latter operation raises valve and the oil is allowed to flow out of A until chambers NV and C are filled a little above lower opening of tube B. A beaker graduated in c.c.’s, of capacity of about 110 c.c., is placed under F; L is released and G allowed to drop, permitting oil to flow through F freely into the beaker. When oil in C falls below the bottom of tube B, air is admitted to the top of the oil in A and oil flows out until it again rises a little above the lower end of tube B, when flow out of A is stopped until the level again falls below B. This action continues throughout entire run, intermittently but so rapidly that a practically constant head is maintained at F. In C a thermometer is suspended so that its bulb is immersed in 252 EXPERIMENTAL ENGINEERING the oil, by which means the temperature of oil can be observed immediately before flowing out of orifice F, which is essential in ascertaining the relative viscosity of the oil. The oil may be heated in the viscosimeter by applying a Bunsen burner, but it is usually more conveniently heated in a separate vessel until it has attained the proper temperature. Other Forms of Viscosimeters. — A simple form of viscosimeter has been used with success by the author, consisting of a copper cup in form of a frustum of a cone, having dimensions as follows: bottom diameter 1.25 inches, top diameter 1.95 inches, depth 6 inches. The flow takes place through a sharp-edged orifice in the centre of the bottom 7; inch in diameter. The whole height is 64 inches. The instrument when made of copper requires a glass oil-gauge, showing the height of the oil in the viscosimeter. ‘This should be connected to the viscosimeter 3 inches from the bottom. The time for the flow of 100 c.c. is taken as the measure of the viscosity, during which time the head changes from 6 to about 3.5 inches; the area of exposed surface diminishes at almost exactly the rate of decrease of velocity of flow, so that the fall of level is very nearly constant. The comparative number of vibrations of a pendulum swinging freely in the air, and when immersed in an oil during a given time, is also said to afford a valuable means of determining the viscosity. 126. Method of Measuring Viscosity with Olsen Apparatus. — If the viscosimeter has a water-jacket fill it and arrange for the main- tenance of the same at any desired temperature. This is most conveniently done by circulation from a water-bath. Fill the cup with the oil and insert in the instrument. Allow the oil to run out, noting accurately with the stop-watch the exact time required to discharge a given amount. Make determinations at 60°, 100°, and 150° F., two for each temperature. Clean the apparatus thoroughly at the beginning and end of the test, using benzine or alkali to remove any traces of oil. The ratio of time of flow of a quantity of oil to time of flow of an equal quantity of water measures the relative viscosity of the given sample of oil to that of water at the given temperature. 127. Chill-point. — Cold tests are made to determine the behavior of oils and greases at low temperatures. By chill-point is meant FRICTION — TESTING OF LUBRICANTS 253 the temperature of solidification. The method of test is to expose the sample while in a wide-mouthed bottle or test-tube to the action of a freezing mixture, which surrounds the oil to be tested. Freezing mixtures may be made with ice and common salt, with ice alone, or with 15 parts of Glauber’s salts, above which is a mixture of 5 parts muriatic acid and 5 parts of cold water. The temperature is read from a thermometer immersed in the oil. The chill-point is to be found by first freezing and then determining the melting temperature. Tagliabue’s Cold-test Apparatus. —'Tagliabue has a special ap- paratus for the cold test of oils shown in section in Fig. 179. The apt ww | FIG. 179. — TAGLIABUE’S COLD-TEST APPARATUS. oil is placed in the glass vessel, which is surrounded with a freezing mixture. The glass containing the oil can be rocked backward and forward, to insure more thorough freezing. A thermometer is inserted into the oil and another into the surrounding air-chamber; the oil is frozen, then permitted to melt, and the temperature taken. In making this test considerable difficulty may be experienced in determining the melting-point, since many of the oils do not suddenly 254 EXPERIMENTAL ENGINEERING freeze and thaw like water, but gradually soften, until they will finally run, and during this whole change the temperature will continue to rise. This is no doubt due to a mixture of various constituents with different melting-points. In such a case it is recommended that an arbitrary chill-point be assumed at the temperature that is indicated by a thermometer inserted in the oil, when it has attained sufficient fluidity to run slowly from an inverted test-tube. The temperature at the beginning and end of the process of melting is to be observed. 128. Method of Finding the Chill-point. — Pour the sample to be tested into a test-tube or other vessel, in which insert the thermometer; surround this with the freezing mixture, which may be composed of small particles of ice mixed with salt, with provision for draining off the water. Allow the sample to congeal, remove the test-tube or vessel from the freezing mixture, and while holding it in the hand stir gently with the thermometer. The temperature indicated when the oil is melted is the chill-point. In case the operation of melting takes place over a range of temperature, note the temperature at the beginning and also at the end of the process of melting. In report describe apparatus used and the methods of testing. 129. The Flash-point. — The Flash-test determines the temper- ature at which oils discharge by distillation vapors which may be ignited. The test is made in two ways. Firstly. With the open cup. —In this case the oil to be tested is placed in an open cup of watch-glass form, which rests on a sand- bath. A’ thermometer is suspended with the bulb immersed in the oil. Heat is applied to the sand-bath, and as the oil becomes heated a lighted taper or match is passed at intervals of a few seconds over the surface of the oil, and at a distance of about one-half inch from it. At the instant of flashing the temperature of the oil is noted, which temperature is the “ flash-point.” Fig. 180 shows Tagliabue’s form of the open cup, in which heat is applied by a spirit-lamp to a water or sand bath surrounding the cup containing the oil. The method of applying the match is found to have great ‘influence on the determination of the flash-point, and should be dis- FRICTION — TESTING OF LUBRICANTS 255 tinctly stated in each case. When the vapor is heavier than air, a lower flash-point will be shown by holding near one edge of the cup. Fic. 180.— OPEN CUP. Fic. 181.— CLosED CUP FOR FLASH-POINT. Secondly. With the closed oil-cup. —Fig. 181 is a view of Tag- liabue’s closed cup for obtaining the flash-point; in this instrument the oil is heated in a sand-bath above a lamp. ‘The thermometer gives the temperature of the oil. The match is applied from time to time at the orifice d, which in the intervals can be covered by a slide. The open cup is generally preferred to the closed one as giving more uniform determinations, and it is also more convenient and less likely to explode than the closed one. 130. Method of Testing for Flash-point. — Put some dry sand or water in the outer cup and some of the oil to be tested in the small cup. Light the lamp and heat the oil gently —at the rate of about 50°F. ina quarter of an hour. At intervals of half a minute after a temperature of 100° F. is attained, pass a lighted match or taper slowly over the oil at a distance of one-half inch from the surface. The reading of the thermometer taken immediately before the vapor flashes is the temperature of the flash-point. 256 EXPERIMENTAL ENGINEERING With the closed cup the method is essentially the same. The lighted taper is applied to the tube leading from the oil vessel, the valve being opened only long enough for this purpose. 131. Burning-point. — The burning-point is determined by heat- ing the oil to such a temperature that when the match is applied as for the flash-test the vapors above the surface burn continuously. The reading of the thermometer just before the match is applied is the burning-point. 132. Method of Testing for Burning-point. — The burning-point is found in the same manner as the flash-point, with the open cup, the test being continued until the oil takes fire when the match is applied. The last reading of the thermometer before combustion commences is the burning-point. 133. Volatility. — Mineral oil will lose weight by evaporation, which may be ascertained by placing a given weight in a watch-glass and exposing to the heat of a water-bath for a given time, as twelve hours. The loss denotes the existence of volatile vapors, and should not exceed 5 per cent in good oil. Other oils often gain weight by absorption of oxygen. 134. Coefficient of Friction. — Oil-testing Machines. — Measure- ments of the coefficients of friction are made on oil-testing machines, of which various forms have been built. These machines are all species of dynamometers, which provide (1) means of measuring the total work received and that delivered, the difference being the work of friction; or (2) means of measuring the work of friction directly. Machines of the latter class are the ones commonly employed for this especial purpose. Rankine’s Oil-testing Machine. — Rankine describes two forms of apparatus for testing the lubricating properties of oil and grease. I. Statical Apparatus. — This consists of a short cylindrical axle, supported on two bearings and driven by pulleys at each end. In the middle of the axle a plumber-block was rigidly connected to a mass of heavy material, forming a pendulum. The lubricant to be tested was inserted in the plumber-block attached to the pendulum, and the coefficient of friction determined by the deviation of the pendulum from a vertical. In this machine the axle was provided with reversing-gears, so that it could be driven first in one direction FRICTION — TESTING OF LUBRICANTS 257 and then in the opposite. With this class of machine, if 7 equal the radius of the journal, R the effective arm of the pendulum, P the total force acting on the journal, ¢ the angle with the vertical, we shall have the product of the force P into the arm R sin ¢ equal to the moment of resistance Fr. That is, Fr = PR sin 4, from which _F PRsin ?_ Rsin b Pp Pr r : II. Dynamic or Kinetic Apparatus. —In this case a loose fly- wheel of the required weight is used instead of the pendulum. The bearings of journals and of fly-wheel are lubricated; then the machine is set in motion at a speed greater than the normal. The driving- power is then disengaged, and the fly-disk rotates on the stationary axis until it comes to rest. The coefficient of friction is obtained by measuring the retardation in a given time. Let the initial number of turns per second = n the final number of turns per second = ,, , and w, = the corresponding angular velocities, W = weight of the wheel, k = radius of gyration, f= Nie = moment of inertia of the wheel, D> y = radius of the journal, and t = time of retardation in seconds. Then the loss in kinetic energy mii Wp (w? — w). 28 The work of friction during ¢ seconds =F.on (~—*) t 2 These two expressions must be equal, and, remembering that w = 2 mn, the equation will reduce to _2n(n,—n,) WR rt g F 258 EXPERIMENTAL ENGIN EERING Now F = fW, where f is the coefficient of friction. Hence finally Pe 2 (nm, — M,) Re rt g Thurston’s Standard Oil-testing Machine. —'This machine per- mits variation in speed and in pressure on the journal; it also affords means of supplying oil at any time, of reading the pressure on the journal, and the friction on graduated scales attached to the machine. This machine, as shown in the following cuts, Figs. 182 and 183, consists of a cone of pulleys C, for various speeds, fastened on ii — eT ir Ty nt SEN TOK Fic. 182.— SEcTION OF THURSTON’S Fic. 183. — PERSPECTIVE VIEW OF THURS- OIL-TESTING MACHINE. TON’S OIL-TESTING MACHINE, shaft A between two bearings B, B’. The shaft carries an over- hanging journal, F, about which the pendulum H swings. The latter is supported by brasses which are adjustable and which may be set to exert any given pressure by means of an adjusting screw K’, acting on a coiled spring within the pendulum. The pressure so exerted can be read directly on the scale M, attached to the pendulum; a thermometer Q in the upper brass gives the tem- perature of the bearings. The deviation of the pendulum is measured by a graduated arc PP’, fastened to the frame of the machine. The graduations of the pendulum scale M show on one side the total pressure on the journal P, and on the other the pres- FRICTION — TESTING OF LUBRICANTS 259 sure per square inch 9; those on the fixed scale PP’ show the total friction F; this, divided by the total pressure P, gives f, the coeffi- cient of friction. From the construction of the machine, it is at once perceived that the pressure on the journal is made up of equal pressures due to action of the spring on upper and lower brasses, and of the pressure due to the weight of the pendulum, which acts only on the upper brass. This latter weight is often very small, in which case it can be neglected without sen- sible error. Thurston’s Railroad Lu- bricant-tester. —The Thurs- ton machine is made in two sizes; the larger one, having axles and bearings of the same dimensions as those used in standard-car construction, is ‘termed the “Railroad Lubricant-test- ing Machine.” A form of this machine is shown in the following cut, arranged for testing with a limited supply of lubricant. (See Fig. 184.) Explanation of symbols: T, thermometer, giving temperature of bear- ings. R, S, rubber tubes for circulation of water { apes i Cg ; ¥ Ein Oy Lh a7 cf in a HH through the bear- Fic. 184.—THurston’s RAILROAD LUBRICANT- ings. N, burette, furnishing supply of oil. TESTING MACHINE. M, siphon, controlling supply of oil. P, candle-wicking, for feeding the oil. H, copper rod, for receiving oil from P. 260 EXPERIMENTAL ENGINEERING The railroad testing- -machine, which is shown in section in Fig. 185, differs from the Standard Oil-testing Machine principally in the construction of the pendulum. This is made by screwing a wrought- iron pipe J, which is shown by solid black shading in Fig. 185, into the head K, which embraces the journal and holds the bearingsa,a’ in their place. In this pipe a loose piece b is fitted, which bears a P ‘MUM — ‘Ut Fic. 185.—SECTION OF RAILROAD LUBRICANT-TESTING MACHINE. against the under journal-bearing a’. Into the lower end of the pipe J a piece cc is screwed, which has a hole drilled through the center, through which a rod f passes, the upper end of’ which is screwed into a cap d; between this cap and the piece cc a spiral spring is placed. The upper end of the rod bears against the piece b, which in turn bears against the bearing a’. The piece b has a key i, which passes through it and the pipe J. This key bears against a nut 9, screwed on the pipe. By turning the nut o the stress on the N FRICTION — TESTING OF LUBRICANTS 261 journal produced by screwing the rod f can be thrown on the key J, and the bearing relieved of pressure, without changing the tension on the spring. A counterbalance above the pendulum is used when accurate readings are desired. The “ brasses” are cast hollow, and when necessary a stream of water can be passed through to take up the heat, and maintain them at an even temperature. The graduations on the machine show on the fixed scale, as in the standard machine, the total friction; and on the pendulum, the total pressures (1) on the upper brasses, (2) on the lower brasses, and (3) the sum of these pressures. Theory of the Thurston Oil-testing Machines. The mathematical formule applying to these machines are as follows: Let P equal the total pressure on the journal; / the pres- sure per square inch on projected area of journal; T the tension of the spring; W the weight of the pendulum; ¢ the radius of the journal; R the effective arm of the pendulum; @ the angle of devia- tion of the pendulum from a vertical line; F the total force of friction; f the coefficient of friction; / the length of bearing-surface of each brass. : Since in this machine both brasses are loaded, the projected area of the journal bearing-surface is 2 (27)1 = 4/7. We shall evidently have P=2T+W, (1) P T+wWw GE ee (2) 4lr 4 By definition f = F + P. Since the moment of friction is equal to the external moment of forces acting, Fr =Pfr=f(2T+ W)r = WR sin 6. (3) From which EF WR sin 6 f= ao = (4) In the machines WR sin 0 + 7 is shown on the fixed scale, and the graduations will evidently vary with sin 0, since WR ~ r is constant. 4 262 EXPERIMENTAL ENGINEERING P, the total pressure, is shown on the scale attached to the pendu- lum. In the standard machine the weight of the pendulum is neglected, and P =2T; but in the railroad oil-testing machine the weight must be considered, and P = 2 T + W, as in equation (1). Constants of the Machine. As the constants of the machine are likely to change with use, they should be determined before every important test, and the final results corrected accordingly. 1. To determine the constant WR, swing the pendulum to a horizontal position, as determined by a spirit-level; support it in this position by a pointed strut resting on a pair of scales. From the weight, corrected for weight of strut, get the value of WR; this should be repeated several times, and the average of these products obtained. 2. Obtain the weight of the pendulum by a number of careful weighings. 3. Measure the length and radius of the journal; compute the projected bearing-surface 2 (2 Jr). 4. Compute the constant a" which should equal twice the reading of the arc showing the coefficient of friction when the pendu- lum is at an angle of 30°, since sine of 30° equal 4. Riehlé’s Oil-testing Machine. —This machine consists of an axle revolving in two brass boxes, which may be clamped more or less tightly together. The machine as shown in Fig. 186 has two scale-beams, — the lower one for the purpose of weighing the pres- sure put upon the journal by the hand-screw on the opposite side of the machine, the upper one for measuring the tendency of the journal to rotate. The upper scale-beam shows the total friction, or coefficient of friction, as the graduations may be arranged. A thermometer gives the temperature of the journal; a counter the number of revolutions. The Olsen-Cornell Oil-testing Machine. —In both the Thurston and Riehlé machines pressure is applied to both halves of the bear- FRICTION — TESTING OF LUBRICANTS 263 ing and there are consequently two points of maximum pressure on the journal. This is an unusual condition in actual practice and in this respect these machines fail to represent true conditions, although the results obtained with them can of course be compared among themselves. In the Cornell testing machine, Fig. 187, the test bearing is a block resting on the top of the test journal, which in turn is supported by a bearing on each side. The driving pulley is placed next to the test journal. The test bearing is held by a 1600 1800. 2000 _2200 290 "400 600" 800 Tuv0 12 Li () ee 250 400 "600 800 1000\( 1200 1400 1600 1800 2000 2200 h, i | Fic. 186.— RiEHLE’s Om-resTING MACHINE. yoke which is supported on knife-edges in the axis of the test journal. Pressure is applied to the bearing by pulling down the yoke by means of a strong helical spring contained in the cylindrical case near the base of the machine. ‘The force of friction tends to swing the yoke about its knife-edges, which tendency is balanced by means of the scale beam. The total pressure is determined by calibrat- ing the load spring, the figures being given on a scale attached to the spring case. . As in the other machines, the coefficient of friction is equal to 264 EXPERIMENTAL ENGINEERING the force of friction, in this case read directly from the beam, divided by the total pressure. A test bearing of the kind used in this machine represents more nearly the conditions existing in an actual bearing. Fic. 187.— OLSEN-CORNELL OIL-TESTING MACHINE. 135. Directions for Obtaining Coefficient of Friction with Thurs- ton’s Oil-testing Machines. — Cleaning. —In the testing of oils great care must be taken to prevent the mixing of different samples, and in changing from one oil to another the machine must be thoroughly cleaned by the use of alkali or benzine. In the test for coefficient of friction the loads, velocity, and tem- perature are kept constant for each run; the oil-supply is sufficient to keep temperature constant, the journals being generally flooded. The load is changed for each run. The following are the special directions for the test of Coefficient of Friction, as followed in the Sibley College Engineering Laboratory. Apparatus. —Thurston’s Standard Lubricant-testing Machine; thermometer; attached revolution-counter. FRICTION — TESTING OF LUBRICANTS 265 Method. — Remove and thoroughly clean the brasses and the steel sleeve or journal by the use of gasolene. Determine the con- stants of the machine as explained in Article 134, measure the pro- jected area of journal bearing-surface, and the weight and moment of the pendulum. Ascertain the error, if any, in the graduation of the machine, and correct the results obtained accordingly. Put the sleeve on the mandrel; place the brasses in the head of the pen- dulum and see that the pressure spring is set for zero and pressure as indicated by the pointer on the scale. Slide the pendulum care- fully over the sleeve, put on the washer, and secure it with the nut. See that the feeding apparatus is in running order. Belt up the machine for the high speed and throw on the power, at the same time supplying the oil at a rate calculated to maintain a free supply. By deflecting the pendulum and using a wrench on the nut at the bottom increase the pressure on the brasses gradually until the pointer in- dicates 50 pounds per square inch. Make a run at this pressure, and also for pressures of 100, 150, and 200 pounds; but do not in general permit the maximum pres- sure in pounds per square inch to exceed 44,800 + (v + 20). Begin by noting the time and the reading of the revolution-counter; take readings, at intervals of one minute, of the arc and the tem- perature until both are constant. At the end of the run read the revolution-counter and note the time. The velocity, v, of the rubbing surface in feet per minute should be computed from the number of revolutions and circumference of the journal. Make a second series of runs, with constant pressure and variable speed. In report of the test state clearly the objects, describe apparatus used and method of testing. Tabulate data, and make record of tests on the forms given. Draw a series of curves on the same sheet, showing results of the various tests as follows: 1. With total friction as abscisse, and pressure per square inch as ordinates; for constant speed. 2. With coefficient of friction as abscissz, and pressure per square inch as ordinates; for constant speed. 266 EXPERIMENTAL ENGINEERING 3. With coefficient of friction as abscissze, and velocity of rubbing in feet per minute as ordinates; pressure constant. 136. Instructions for Use of Thurston’s R. R. Lubricant-tester. —Follow same directions for coefficient of friction-test as given for the standard machine, applying the pressure as explained in Article 135. Water or oil of any desired temperature can be forced through the hollow boxes by connecting as shown in Fig. 184, and the temperature of the bearings thus maintained at any desired point. With this arrangement the machine may be used for testing cylinder- stock, as explained in directions for using Boult’s machine. The concise directions are: 1. Clean the machine. 2. Obtain the constants of the machine; do not trust to the graduations. 3. Make run under required conditions, which may be with each rate of speed. a. With flooded bearings, temperature variable. b. With flooded bearings, temperature regulated by forcing oil or water through hollow brasses. c. Feed limited, temperature variable or temperature regu- lated. Tn all cases the object will be to ascertain the coefficient of friction. 137. Durability of Lubricants. —In this case the amount of oil supplied is limited, and it is to be used for as long a time as it will continue to cover and lubricate the journal and prevent abrasion. To give satisfactory results, this requires a limited supply or a per- fectly constant rate of feed, an even distribution of the oil, and the restoration of any oil that is not used to destruction; these require- ments present serious difficulties, and present methods do not give uniform results.* The method at present used is to consider the endurance or durability proportional to the time in which a limited amount, as one-fourth c.c., will continue to cover and lubricate the journal without assuming a pasty or gummy condition, and with- out giving a high coefficient of friction. The average of a number * See paper by Professor Denton, Vol. XI., p. 1013, Transactions of American Society of Mechanical Engineers. FRICTION — TESTING OF LUBRICANTS 267 of runs is taken as the correct determination. In this test care must be taken not to injure the journal. The time or number of revolutions required to raise the tempera- ture to a fixed point — for instance, 160° F. —is in some instances considered proportional to the durability. 138. Durability-testing Machines. — The Ashcroft and the Boult machines are especially designed for determining the durability of oils —from the former by noting the rise in temperature, from the latter by noting the change in the coefficient of friction. The difficulty of properly making this test no doubt lies in the loss of a very slight amount of oil from the journals, which is sufficient, how- ever, to make the results very uncertain. oy mn; ‘ on i= ii q rill q (c ue TH Faas samen SSS SSS SS SS ein AACA == i = == Fic. 188.— ASHCROFT OIL-TESTING MACHINE. Ashcroft’s Oil-testing Machine. —This machine (Fig. 188) con- sists of an axle revolving in two brass boxes; the pressure on the axle is regulated by the heavy overhanging counterpoise shown in the engraving. The tendency to rotate is resisted by a lever which is 268 EXPERIMENTAL ENGINEERING connected to the attached gauge. The gauge is graduated to show coefficient of friction. The temperature is taken by an attached thermometer, and the number of revolutions by a counter, as shown in the figure. In this machine the weights and levers are constant, the variables being the temperature and coefficient of friction. It is used exclusively with a limited supply of oil, the value of the oil being supposed to vary with the total number of revolutions required to raise the temperature to a given degree — for instance, to 160° F, Boult’s Lubricant-testing Machine. —'This machine, designed by W. S. Boult of Liverpool, is a modification of the Thurston oil- a tester, yet it differs in several essential features. A general view of the machine is shown in Fig. 189, and a section of its boxes and the surrounding bush in Fig. go. The machine is designed to accom- = , rt i = (i ay ie _ lr: t ; my) ea Fic. 189. Fic. 190. FRICTION — TESTING OF LUBRICANTS 269 plish the following purposes: 1. Maintaining the testing journal at any desired temperature. 2. Complete retention on the rubbing surfaces of the oil under test. 3. Application of suitable pressure to the rubbing surfaces. 4. Measurement of the friction between the rubbing surfaces. To secure the complete retention of the oil, a complete bush with internal flanges is used instead of the brasses employed in other oil- testing machines. On the inside of the bush is an expanding journal DD, Fig. 190, the parts of which are pressed outward against the surrounding bush by the spring £, or they may be drawn together by the set-screws BB, compressing the spring E. A limited amount of oil is fed from a pipette or graduated cylinder onto the journal, with the bush removed. This oil, it is claimed, will be maintained on the outer surface of the journal and on the interior surface of the metallic bush, so that it may be used to destruction. The bush is hollow, and can be filled with water, oil, or melting ice and brine. The oil to be tested can be maintained at any desired temperature by a burner F, which heats the liquid CC in the surrounding bush. The temperature of the journal can be read by a thermometer whose bulb is inserted in the liquid CC. The friction tends to rotate the bush; this tendency is resisted by a lever connected by a chain to an axis carrying a weighted pendulum G, Fig. 189. The motion of the pendulum is communicated by gearing to a hand, passing over a dial graduated to show the total friction on the rubbing surfaces. The formule for use of the instrument would be as follows: Let f equal coefficient of friction; G the weight of the bob on the pendu- lum, R its lever-arm; a the angle made by the pendulum with the vertical; a the length of the connecting lever; c the radius of the axis to which the pendulum is attached; 7 the radius of the journal; A the projected area of the journal; P the total pressure on the journal. Then aR -—.-Gsina =fAP, r ¢ from which ee aGRsina sing — X aconstant. rcAP P 270 EXPERIMENTAL ENGINEERING In this instrument the total pressure P is usually constant and equal to 68 pounds, so that the graduations on the dial must be proportional to sin a. If the graduations are correct, the coefficient is found by dividing the readings of the dial by P (68 pounds). The work of friction is the product of the total space travelled into the total friction, and this space in the Boult instrument is two-thirds of a foot for each revolution, or two-thirds of the number of revolutions. The instrument cannot be used with a constant feed of oil, nor can the pressures be varied except by changing the spring £. 139. Directions for Durability-test of Oils with Boult’s Oil-testing Machine. — To fill cylindrical oil-bath, take out the small thumb- screw and insert a bent funnel. Pour in oil —any sort of heavy oil may be used — until it overflows from the hole in which funnel is inserted, and replace thumb-screw. 1. See that the friction surfaces are perfectly clean. These can be examined by tightening the set-screws in order to compress the spring. This will enable the cylindrical bath to be lifted away. After seeing that the surfaces are perfectly clean, pour on a measured quantity of the lubricant to be tested, and set the bath in position. Slacken set-screws so as to allow the spring to have full pressure. The set-screws should not be removed entirely when slackening, 2. Light the Bunsen burner. 3. Heat the oil-jacket until the temperature at which the oil is to be used is reached. 4. Read revolution-counter, start machine and note initial friction reading. Continue run until friction has increased 50 per cent above its initial value. In some cases it is preferable to run the tester until there is a rise of 100 per cent of the friction first indicated. There does not appear to be any advantage in going beyond this, as the oil is then practically unfit for further use, and there is danger of roughening the friction surfaces. 5. When it is considered desirable to ascertain the distance travelled by the friction surfaces during a test, read off the counting- indicator before and after the test, subtract the lesser from the greater total, and the difference will represent the number of revo- lutions made during the test. As the friction surfaces travel two- FRICTION — TESTING OF LUBRICANTS 271 thirds of a foot during each revolution, the number of feet travelled is arrived at by simply deducting from the number of revolutions made, one-third thereof. The value of the oil is proportional to the number of feet travelled by the rubbing surfaces. The speed at which the tester should be run should be about five to six hundred revolutions per minute. For high-speed engine-oil the speed may be increased to about a thousand per minute. 140. Friction of Ball- and Roller-bearings. — Within recent years ball- and roller-bearings have come into great prominence because of their low coefficient of friction and their capacity to endure abuse of various kinds. The common tests of such bearings may be divided into two classes: 1. Tests made to determine useful life of bearing under given load, and 2. Tests made to determine the coefficient of friction under different conditions. For the purpose of the first test any machine by means of which a known load can be maintained on the bearing to be tested and which will record the total number of revolutions up to the point of failure, may be made to give satisfactory results, A machine for the second test is, however, much more difficult of construction, as the friction loss to be measured is relatively very small, necessitating light, accurate parts, while the loads applied may be great, calling for stiff and heavy mechanism. Machines have been built along two distinct lines and the success or failure of either type depends to a great extent upon conditions. In the first type several similar bearings of the type to be tested support a rotating member which is driven by an accurately cali- brated motor. Means are provided for applying loads as desired and the test-bearing friction loss is found from the electrical input corrected for motor losses. The total friction loss divided by the number of bearings is assumed to be the loss due to each bearing. The second type of machine operates in much the same way as the Thurston and Riehlé machines just described, the rotating part of bearing and shaft being driven in any convenient way and the 272 EXPERIMENTAL ENGINEERING frictional resistance being determined by measuring or weighing the tendency of the outer or stationary parts of the bearing to turn. A very complete machine of this type was recently developed by Henry Hess of Philadelphia, and described in a paper before the A. S. M. E,, in 1908. This machine is capable of meas- uring the bearing capacity and the fric- tional resistance of a ball- or roller-bear- ing loaded radially or axially or both. The line drawings, Fig. 191 and Fig. 192, show the method of operation. In Fig. ror, A is the bearing to be tested, @ \ mounted on the end of a shaft. The outer member is held in a strap AB, hinged to the rod BC, which is, in turn, hinged to a weighing system represented by CE. With the bearing at rest the points A,B and C are in a vertical line, but if the shaft is rotated in the direction of the arrow the various E cq oe FIG. 191. ep ee Fic. 192. links assume a position similar, although much exaggerated, to that shown in the figure. The deflection of the point B, or any similar point B’, is a measure of the tendency to turn, or of the journal friction, and the machine is so arranged that this deflec- tion may be accurately read to o.coor inch by means of a micro- scope and cross-hairs. FRICTION — TESTING OF LUBRICANTS 273 Fig. 192 shows the arrangement for applying axial loads. G is a wire which serves to draw the yoke F against the bearing with any desired force and also resists the tendency of the yoke to turn by twisting to such a point that its torsional resistance is sufficient for the purpose. The amount of frictional resistance can be meas- ured by dropping weights into one or other of the pans P so as to bring the pointer which is carried by the yoke back to the zero reading. When the journal is submitted to combined radial and thrust loads the deflection of the point B, Fig. 191, measures the total friction. 141. Forms for Report. — The following are the forms used in Sibley College for data and results of lubricant-tests: SIBLEY COLLEGE, DEPARTMENT OF EXPERIMENTAL ENGINEERING. VISCOSITY-TEST. Kind Of Oilsissecsercacameartner see sg seeneae enn DAL Cpe sass cikchsitasenevane 1gI Received front ys asx s sane eked teinemmde e taeiddnianscs tenndanm died acmanamsateumey uo derbhavkiee GOLGI a ate dis tng it essere OVE Maer snetsaiciiereis Specific Gravity at............ oF; sBeaume: Seales sianemaauninse ed's °B, sg haha oaeeesa oa (¢ Water as 1.000 ....... 2.0.0.0 cee ASI 5. dsnatcroeaieg ave Oe Dats amaancrererncete % Chill-point ................ oF, Flashing-Pt jis. ic viesnecurgwiaes ME, Los8abenicsscc above equation is a constant, and it becomes necessary merely to determine G and ». The latter may be found by any of the many types of speed counters. In the determination of G for the type of brake shown in Fig. 193 and in Fig. 194 A it should be noted that G is the net reaction on the scale or other apparatus used to measure it, and not the total weight shown, because the latter is too large by the action of the weight of the arm and of the support. For small and medium sized brakes, or whenever the machine whose output is measured can be slowly rotated in either direction, the 278 EXPERIMENTAL ENGINEERING simplest way of determining the brake-zero, as it is called, is to pro- ceed as follows: Let W be the weight of whatever support for the brake-arm there may be on the scale. W, be the downward force due to the weight of the brake- arm. F be the force of friction generated between the strap and the wheel when turning the wheel in either direction at the same speed. Fic. 194.——A To C. Various Types or Prony BRAKES. Turn the wheel first in the direction of the arrow in Fig. 193, we have G,=W+W,4+F. Next, turn in the opposite direction; then G,=W+W,-F. Therefore, by addition, G,+ G,=2(W+W,) and Cac Wt W= Se, (7) W, can now be obtained by itself by determining the actual weight W of the support. In most cases, however, it is not necessary to MEASUREMENT AND TRANSMISSION OF POWER 279 know this, and W + W, is usually known as the brake-zero reading. This must be subtracted in all cases from the total scale reading to obtain G for formula (6). In case it should not be possible to turn the machine over slowly in either direction, as above indicated, the following procedure may sometimes be used. Place a man on the scale and let him slowly raise and depress the brake-arm through a small angle above and below its normal position and against a small friction. Care should be taken to apply the pressure to the brake-arm exactly below or above the knife-edge support with which all brake-arms should be furnished near the end. Determine the two reac- tions on the scale. The sum of these divided by 2 will then be the weight of the man plus the partial weight .of the brake-arm resting on the scale. Sub- tract the weight of the man and add that of the support or pedestal for the arm, if one is used. The result will be the brake-zero. In the case of the brake shown in Fig. 194 B, rota- tion as indicated by the Fic. 195. — Rove BRAKE. arrow gives a reading on the balance equal to G, = F — W,, while if the wheel is turned in the other direction, the balance must be placed above the brake- arm, and its reading will be G.=F +W,. From this again G : : ‘ W,= at, but in this case, when the brake is used as shown in Fig. 194 B, W, must be added to, not subtracted from, the read- ing of the balance. In this construction W = o. In Fig. 194 C we have what is known as a balanced brake, i.e., W, = 0, and the brake-zero is then merely the weight W of what- ever support there may be on the scale. 280 EXPERIMENTAL ENGINEERING Fig. 194 D shows a very simple form of strap or band brake in which a weight G is placed in a scale box or pan, which weight is held floating off the floor by the friction acting on the strap laid over the pulley, as shown. The left-hand end of the strap is usually also fastened to the floor, but except as a matter of safety or convenience this is not necessary. It merely helps to guide the strap and to prevent the weights from crashing to the floor should the wheel wn» stop. If the left-hand end is se- ) ° cured, care must be taken to see that the friction alone is able to overcome the weight G, that is, that there is no tension in the left side of the strap. To make sure of this a spring balance B is some- times interposed as shown. The - active force acting in this brake is evidently the weight G+ the weight of the pan or box, while the brake (O) arm is equal to the diameter of the wheel + 4 the thickness of strap or as rope. The scale pan should be fastened by means of a stout wire, as shown, to prevent the weight being pulled over the wheel by accident. The brakes shown in Figs. 195 a and 196, usually constructed as rope Tie: sad — Bann) ok Rose Deane: brakes, are modifications of the fun- damental type of Fig. 194 D. 145. The Design of Prony Brakes. — The material for the brake may be anything that is sufficiently flexible and strong. For small brakes, leather belting, either directly in contact with the surface of the wheel or serving as a holder for a number of narrow wood cleats which are in contact with the face of the wheel, is extensively used. For medium power brakes, rope which is held in place by a number of wooden retainers, see Fig. 197, often takes the place of leather. For very heavy work, sheet steel may be employed. In MEASUREMENT AND TRANSMISSION OF POWER 281 such cases the contact pieces are made of wood and fastened to the inside of the steel band, or, as is done in the case of the 150-H.P. Sibley College Corliss engine, there is first a sheet-steel lining bond which is in contact with the face of the wheel and takes all the wear. This is next surrounded by a copper water jacket through which water is circulated to keep the fric- tion strap cool, and the latter is in turn held to the Fie. 107. wheel by the sheet-steel band which carries the brake- —Metxop arm, drawing up-clamps, and acts as the brake-strap . eae proper. There are two or three essential: points to con- " sider in the design of Prony brakes, — the stresses in the strap, the method of keeping the brake cool, and the method of lubricating. The stresses in the brake-strap may be computed as follows: Let T, represent the greatest tension, T, the least tension, ¢ the percentage that the arc of contact bears to the whole circumference, N the normal pressure, F the resistance of the brake, and f the coefficient of friction. Then T,-—T,=F and N=F +f. Now it can be shown that a = 107-78f — Number whose log is 2.7288 fe = B 2 From which i a L (8) and T,-5— (0 The actual process of designing a brake* is as follows: There are given the power to be absorbed, number of revolutions, diam- eter and face of the brake-wheel. In case a special brake-wheel is to be designed, the area of bearing surface is to be taken so that the number obtained by multiplying the width w of the brake in inches by the velocity v of the periphery of the wheel in feet * See “Engine and Boiler Trials,” by R. H. Thurston, pages 260 to 282; also “Friction and Lubrication.” 282 EXPERIMENTAL ENGINEERING per minute, divided by the horse power H, shall not exceed 500 to tooo. Call this result K. Then wu, K=— Io a (10) 400 to 500 is considered a good average value of K. The value of the coefficient of friction f should be taken as the lowest value for the surfaces in contact (see table of coefficient of friction in Appendix). ‘This coefficient is about 0.2 for wood or leather on metal, and about 0.15 for metal on metal. Let HZ be the work to be transmitted in horse power, ” the number of revolutions of the brake-wheel, D its diameter. Then the resistance F of the brake must be A F = 3308. II zDn ee) The arc of contact is known or assumed, and may be expressed as convenient in circular measure 0, degrees a, or in percentage of the whole circumference c. Example. — Assume the arc of contact as 180 degrees (¢ = 0.5), the diameter of brake-wheel 4 feet, coefficient of friction (f = 0.15), face of brake-wheel ro inches, revolutions 90, horse power 70. Find the safe dimensions of the brake-strap and working parts of the brake. From page 281 B = 102-788f6 = 100-2048, That is, B equals the number whose logarithm is 0.2046; or, B = 1.602. Since the brake-wheel is 4 feet in diameter and revolves at 90 revolutions per minute, we get from Eq. (11) =e = 2043 pounds. Taking B as above, and substituting in equations (8) and (9), we have T= —— 1602 )- 5436; = 2043 _ .602 N= seer = 131620. = 3395; From the value of T,, the maximum tension, we next compute the required area of the brake-straps, assuming a safe working stress for the material used. MEASUREMENT AND TRANSMISSION OF POWER 283 Tf the latter is steel, we may assume a stress of 10,000 lbs. per sq. inch, in which case Section of brake-straps = 5436 + 10,000 = 0.55 square inch. The assumed width of brake-wheel is 10 inches; this gives for the value of K, by equation (10), page 282. K = (10) (1132) + 70 = 162; a low value. If it is proposed in this brake to use 3 straps, each 2 inches wide, the thick- ness will be 0.55 + 6 = 0.091 inch. 146. Cooling and Lubricating a Prony Brake. — Water is the usual agent for keeping a Prony brake cool. It may be used either inside of the flanged rim of the brake-wheel, or in special forms of brakes it may be circulated through jackets surrounding the strap. In case the rim of the wheel is flanged on the inside, it may in some cases be sufficient simply to throw some water into the rim from time to time, producing the cooling action by evaporation, but where the power taken off is considerable it is better to arrange a method for supplying water to the rim and for scooping it out continuously, thus producing a constant circulation. Concerning lubrication, it is better to use a constant quantity of oil or grease than to use either intermittently, because with inter- mittent supply the adjustment is disturbed every time the strap is oiled or greased. It should also be remem- bered in this connection, when supplying water for cooling purposes, that water will act as a lubricant if it is accidentally thrown under the strap, and will momentarily de- stroy the adjustment of the brake. 147. Other Forms of Friction Brakes: Self- regulating Brakes. — Brakes with automatic regulating devices are sometimes made; in this case the direction of motion of the wheel must be such as to lift the brake-arm. If %- 198.—Sezr-recu- et aa ‘ LATING BRAKE, the tension is too great the brake-arm rises a short distance, and this motion is made to operate a regulating device of some sort, lessening the tension on the brake-strap; if the tension is not great enough, the brake-beam falls, producing the opposite effect. A very simple form of self-regulating brake 284 EXPERIMENTAL ENGINEERING is shown in Fig. 198; in this case the arm is maintained at an angle with the horizontal. If the friction becomes too great, the weight G rises, and the arm of the brake swings from A to £, thus increasing the lever-arm from BC to LC; if the friction diminishes, the lever-arm is correspondingly diminished, thus tending to main- tain the brake in equilibrium. Another form of self-regulating brake is shown in Fig. 199. If this brake is to be constantly loaded with the weight P, it is adjusted at A until P floats and until all the slack has just been taken out of the string s. Now if the friction should momentarily increase, the weight P will rise, but this causes s to exert a pull at A’. This extends the spring S and separates the brake levers. Ss E 5\\ b as vs l , ote Fic. 199. SELF-REGULATING BRAKE. A decrease in the friction causes P to drop, which allows the spring to again exert its full force and tightens the brake. A number of various forms of automatic Prony brake may be found described in technical literature, but they are little used because in laboratory practice or for testing floors other more con- venient forms, like the magnetic brake, have been invented, while in practice a single application of a brake would hardly warrant the cost of construction of a complicated form. 148. Alden Brake. — The Alden brake (see Figs. 200-203) is an absorption dynamometer in which the rubbing surfaces producing the friction are separated by a film of oil, and the heat is absorbed by water under pressure. It is constructed by fastening a disk of cast iron, A, Fig. 200, to the power-shaft; this disk revolves be- tween two sheets of thin copper E E, joined at their outer edges, from which it is separated by a bath of oil. Outside the copper MEASUREMENT AND TRANSMISSION OF POWER ~ 285 sheets on either side is a chamber which is connected with the water supply at G. The water is received at G and discharged at H, maintaining a moderate temperature. Any pressure in the chamber causes the copper disks to press against the revolving plate, producing friction which tends to turn the copper disks. As these are rigidly connected to the outside cast-iron casing and brake- arm P, the turning effect can be balanced and measured the same as in the ordinary Prony. brake. The pressure of water is auto- matically regulated by a valve V, Figs. 201, 202 and 203, which Fics. 200-203. — ALDEN BRAKE. is partially closed if the brake-arm rises above the horizontal, and is partially opened if it falls below; with a constant head this brake gives exceedingly close regulation. Fig. 204 * shows the construction of the Alden brake more clearly than the more or less conventional sketch in Fig. 200. Here plates AA are the movable cast-iron disks, on each side of which are located the copper plates BB. The spaces between A and B are, as before, filled with oil, while the cooling water, entering through D and leaving through £, circulates through the spaces CC. This is one of the 400-H.P. brakes used in connection with * Trans, A. S. M. E., Vol. 25, p. 861. 286 EXPERIMENTAL ENGINEERING the locomotive-testing plant at Columbia University. The method of determining the tendency to rotation of the case is shown in the conventional sketch of the lever system in Fig. 205. 149. Brakes employing the Friction of Liquids. — Brakes have been constructed in which the friction of liquids has been substituted for the friction of solids. There are two distinct designs. In the CW Fic. 204. — ALDEN BRAKE, one a revolving member, notched or corrugated, disk, drum, or wheel is made to throw water against the similarly shaped inner surface of the case in which it runs. The resistance is produced by friction and impact and the power is converted into heat which may heat the water to boiling. In most cases, however, enough water may be circulated to prevent this. The outer casing is free to turn about its shaft, and the power delivered may be determined MEASUREMENT AND TRANSMISSION OF POWER 287 by measuring the tendency to turn just as in a Prony brake. The brake used by the Westinghouse Machine Company for testing its steam turbines is of this type. Figs. 206 and 207, reproduced from Power, June 30, 1908, show the general features. The rotor, pro- vided with projecting ridges, as shown, has internal and external flanges. Water is supplied through a funnel to the interior of the rotor and is thrown outward by centrifugal force. It flows through holes bored in the projections to the outside of the rotor and strikes the ridges on the inner surface of the casing, producing resistance as above described. Such brakes are very powerful, but subject to very rapid wear. A rotor about twenty-two inches in diameter and eight inch face C 1 ) ee Fic. 205. — LEVER System ALDEN Brake. LocomorivE-TEstInc PLantT, CoLumBIA UNIVERSITY. will absorb about 2000 H.P. at 3600 R.P.M. The power varies ap- proximately as the cube of the peripheral velocity. For a discussion of the wear encountered, see the above-mentioned article in Power. The second type of liquid friction brakes is adapted only for high speeds, and differs from the former in that smooth disks, usually without any projections whatever, are used in place of corrugated or notched disks and drums. The inside of the case is usually also left smooth, although not machine finished. When water is supplied to the case and fills it up so that the lower edge of the rapidly revolving disks commences to cut through it, the water is set in motion, following the disks around, and soon will be formed into rings which travel around with the edge of the disks but at a somewhat slower rate. The friction produced between water and 288 EXPERIMENTAL ENGINEERING disk on the one hand and water and casing on the other tends to rotate the casing, which tendency is measured as before. A brake of this type, designed by Professor Stumpf, is shown in Figs. 208 and 209.* This was used to test a 2000-H.P. turbine at from 1200 to 3400 R.P.M., a series of disks of different diameters being used. The disk shown in the picture has a diameter of roo cm. (3.28 ft.). In other designs of this brake the number of disks was greater and the brake was supported on both sides, which would tend to quieter operation. In either type of liquid friction brake, the power output may be A Lk S LE aL UW TTL SS SNS A Fics. 206-207. WESTINGHOUSE FRICTION BRAKE. easily controlled by means of regulating the water supply, and the operation of these brakes has proven very satisfactory. 150. Other Forms of Brakes: Pump Brakes. — A rotary pump which delivers water through an orifice that can be throttled or enlarged at will has been used with success for absorbing power. If the casing of the pump is mounted so as to be free to revolve, it can be held stationary by a weighted arm, and the absorbed power measured, as in the case of the Prony brake. If the casing of the pump is stationary, the work done can be measured by the weight of water discharged multiplied by the height due to the greatest velocity of its particles multiplied by a coefficient to be determined by trial. * F, Rotscher in the Zeitschrift des Vereins deutscher Ingenieure, April 20, 1907. MEASUREMENT AND TRANSMISSION OF POWER 289 A special form of the pump-brake, with casing mounted so that it is free to revolve, has been used with success on the Owens College experimental engine by Osborne Reynolds. In this case the brake is practically an inverted turbine, the wheel delivering water to the guides so as to produce the maximum resistance. The water forced through the guides at one point is discharged so as to oppose the motion of the wheel at another point. 151. Fan-brakes. — A fan or wheel with vanes revolved in water, oil, or air will absorb power, and in many instances forms a con- venient absorption-dynamometer. - Fics. 208-209. —Stumpr Friction BRAKE. The resistance that may be obtained from a fan-brake is ex- pressed by the formula V? Rl=1KDA 2g (12) 2 in which Ri equals the moment of resistance; V the velocity in feet per second of the center of vane; A the area of the vane in square feet; 1 equals the distance from center of vane to axis in feet; D the weight per cubic foot of fluid in which the vane moves. K is a coefficient, found by experiment by Poncelet to have for air the value 1.6244 VA ; = (13) K = 1.254 + in which s is the distance in feet from the center of the entire vane to the center of that half nearest the axis. When the vanes are set 290 EXPERIMENTAL ENGINEERING at an angle i with the direction of motion the value for RI must be multiplied by 2sin?é 1 +sin’z 152. Electro-magnetic Brake. — If a metal disk or wheel is made to cut the field of an electro-magnet, it will experience a certain resistance which may be utilized to put machines under load. For this purpose two of these magnets are fastened to a yoke which fits over the brake wheel, as shown in Fig. 210. The resistance or drag encountered tends to revolve the yoke about the center i | ee =] Ta T=] = = anne \ ioe y= F Ce |e | W Fic. 210.— Tyre oF ELECTRO-MAGNETIC BRAKE. of the wheel and its force may be measured by holding the yoke stationary. The method of computing the power is otherwise the same as for the Prony brake. Figs. 211 and 212 show a somewhat more complicated commer- cial form of this type of brake.* Here a number of electro-mag- nets a are so held in an aluminum spider c, which is free to turn about the shaft, that the magnetic lines are forced to pass through two copper disks d, driven by the prime mover. The tendency of * A, Heller in the Z. d. V. D. I., Oct. 5, 1907. MEASUREMENT AND TRANSMISSION OF POWER 291 the spider to turn is measured by balancing it by means of weights along the arm 8. It will be noted that in these brakes all of the power measured ma | (a= i | | | all i UK tu ll L SSS y Ula) Fic. 213, — ELEcTric GENERATOR ABSORPTION DyNAMOMETER. is destroyed in eddy currents, appearing finally in the form of heat. The increase of temperature in the parts concerned changes the electrical resistance, lowering the capacity, and makes it necessary to stay below a certain temperature to prevent injury. There is 292 EXPERIMENTAL ENGINEERING no good way to keep such a brake cool. On the other hand, the power output may be easily regulated by varying the resistance in the circuit, and the first form at least may be so built as to be quickly adjusted to different sizes of flywheel. ; A fundamentally similar form of magnetic brake, used where the speed variation of the prime mover is not very great, is that illustrated in Fig. 213.* Here the prime mover drives the armature of the generator, whose output is best regulated by a water rheostat. The field housing of the generator is carried by ball bearings which surround the armature bearings. The reaction between armature and field tends to turn the housing in a direction opposite to that in which the armature turns. This tendency is counterbalanced as shown. The computation of power is the same as for the Prony brake. 153. Traction Dynamometers.— Dynamometers for simple trac- tion or pulling are usually constructed as in Fig. 214. Pull is applied at the two ends of the spring, which rotates a hand in proportion to the force exerted. Recording Traction Dynamometers. — These are constructed in various 5 forms. Fig. 215 shows a simple form, Fic. 214.— Smerur Traction designed by C. M. Giddings. Paper DYNAMOMETER OR SPRING . eee Baraece: is placed on the reel A, which is op- erated by clockwork; a pencil is con- nected at K to the hand, and this draws a diagram, as shown in Fig. 216, the ordinates of which represent pounds of pull, the abscisse the time. The drum may also be arranged to be operated by a wheel in contact with the ground; then the abscissa will be proportional to the space, and the area of the diagram will rep- resent work done. It should be noted that these instruments are not strictly dyna- mometers, that is, not strictly measurers of power unless by some means the velocity with which the instrument itself is bodily moved through a given distance is also recorded. This may be done by an attachment which may be an integral part of the instrument * A. Heller, Z.d. V. D.1., Oct. 5, 1907. 1 CTT ry Suited Ss oe MEASUREMENT AND TRANSMISSION OF POWER 293 itself, but in many cases the deter- mination of the velocity factor is accomplished entirely independ- ently. 154. Transmission Dynamom- eters, General Types.* — Trans- mission dynamometers are of different types, the object in each case being to measure the power which is received without absorb- ing any greater portion than is necessary to move the dynamom- eter. They all consist of a set of pulleys or gear wheels, so ar- ranged that they may be placed between the prime movers and machinery to be driven, while the power that is transmitted is gen- erally measured by the flexure of springs or by the tendency to ro- tate a set of gears, which may be resisted by a lever. 155. Morin’s Rotation Dyna- mometer.—In Morin’s dyna- mometer, which is shown in Fig. 217, the power is transmitted through springs, FG, which are thereby flexed an amount propor- tional to the load. The flexure of the springs is recorded on paper V by a pencil Z fastened to the rim of the wheel EZ. A second pencil is stationary with reference to the frame carrying the paper. The paper is made to pass under 4 op ges Ss 4538 6 ah 5O Fic. 215.— RECORDING TRACTION DYNAMOMETER. * See Thurston’s “‘ Engine and Boiler Trials,” p. 264; also Weisbach’s “ Mechan- ics,” Vol. II, pp. 39-73; also Rankine’s “‘Steam-engine,” p. 42. 2904 EXPERIMENTAL ENGINEERING the pencil by means of clockwork driven by the shafting, which can be engaged or disengaged at any instant by operating a lever. The springs are fastened at one end rigidly to the main axle, which is in communication with the prime mover, and at the other end to the rim of the pulley Z, which otherwise is free to turn on the main shaft. The power is taken from this last pulley, and the re- sistance acts to bend the springs as already described. In the figure, A is a loose pulley, B is fixed to the shaft. Power is sup- plied through B and taken off through E. The autographic recording apparatus of the Morin dynamometer consists essentially of a drum, which is rotated by means of a worm gear K cut on a sleeve, which is concentric with the main axis. This sleeve slides longitudinally on the axis, and may be engaged with or disengaged from the gear train of the frame at any instant Fic. 216.— REcoRD FROM DyNAMOMETER. by means of a lever. When the sleeve is engaged with the gear train, the recording apparatus is putin motion. The pencil attached to the spring will then trace a diagram on the paper whose or- dinates, as measured from a base line drawn by the stationary pencil, are proportional to the force transmitted. The rate of rotation of the drums carrying the paper, with respect to the main axis, is determined in the same manner as though the gears were at rest — by finding the ratios of the radii of the respective wheels. Thus the amount of paper which passes off from one drum on to the other can be proportioned to the space passed through, so that the area of the diagram may be proportional to the work transmitted. To find the value of the ordinates in pounds the dynamometer must be calibrated; this may be done by a dead pull of a given weight against the springs, thus obtaining the deflections for a MEASUREMENT AND TRANSMISSION OF POWER 295 given force; or, better, connect a Prony brake directly to the rim of the pulley Z, make a series of runs with different loads on the brake, and find the corresponding values of the ordinates of the diagram. Calibration of the Morin Dynamometer. — Apparatus. — Speed indicator, dynamometer paper, and Prony brake. 1. Fasten paper on the receiving drum, wind off enough to pass over the recording drum, and fasten the end securely to the winding drum. See that the gears for the autographic apparatus are in perfect order, and that both pencils give legible lines. Adjust Aili: Fic. 217.— Morin DyNAMOMETER. the pencil fixed to the frame of the clockwork so that it will draw the same line as the movable pencil when no load is applied. 2. With the recording apparatus out of gear apply the power. Take a diagram with no load. This will show the friction work of the dynamometer. 3. Apply power and load, take diagrams at intervals; these will represent the total work done. This, less the friction work, will be the power transmitted. The line traced by the pencil affixed to the frame of the clockwork is in all cases to be considered the zero line, or line of no work. 4. To calibrate the dynamometer, attach a Prony brake to the same shaft and absorb the work transmitted. This transmitted work must equal that shown by the Prony brake. 296 EXPERIMENTAL ENGINEERING 5. Draw a calibration curve, with pounds on the brake-arm reduced to an equivalent amount acting at a distance equal to the radius of the driving pulley of the dynamometer, as abscisse, and with the ordinates of the diagrams as ordinates. Work up the equation of this curve. 6. In report of calibration make record of time, number of revolutions, brake-arm, equivalent brake-load for arm equal to radius of dynamometer pulley, length of ordinate, scale of ordinate. Describe the apparatus. 7. In using the dynamometer, insert it between the prime mover and resistance to be measured. Determine the power transmitted from the calibration. Form of Report. —The following form is useful in calibrating this dynamometer: CALIBRATION OF MORIN DYNAMOMETER. Kind of brake used. ............0. 00 0c eee Length of brake-arm.............. ft. Weight of brake-arm............ Ibs. Zero reading of scales.................1bs. Radius of driving pulley.......... ft. ODSEFVETS 5.2. cz teaetatet tae emnnae f DATE, aania.gesti bats es anole ates TOO Ss): «ssi ata cn anenducaa dasa hres vraunndosgs Papen png apn Revolutions per Minute. . Equivalent Ordinate, Inches. Effective = No Brake- Load on Brake i Driving H.P. Up. | Down.| Mean. | load, Ibs. Pulley, the: Up. | Down.| Mean. Remarks: Equation of Curve, A, = ney svete se oceania OS ety Aowghinnenss 156. Steelyard Dynamometer. — In this dynamometer, Fig. 218, the pressure Z on the axle of a revolving shaft is determined by shifting the weight G on the graduated scale-beam AC. The power is applied at P, putting in motion the train of gear- wheels, and is delivered at Q. Denote the applied force by P, the delivered force by Q, the MEASUREMENT AND TRANSMISSION OF POWER 207 radius KM by a, KE by r, LF by r,, NL by b, the force existing at E by R, that at F by R,. We shall have Rr = Pa, also R,r,= Qb. But R(ED) = R,(FD); and since ED = FD, R= R,. The resultant foreeZ = R+R,=2R, « R=42Z; P=%32Zr +a; (14)Q =4274,+6. (r5) A }f i Fic. 218. — STEELYARD DyNAMOMETER. If we know the number of revolutions, the space passed through by each force can be readily calculated, and the work found by taking the product of the force into the space passed through. Consideration of Friction. —The friction of the axle and gear- teeth will increase the force R and decrease the force R, Let pz be the experimental coefficient expressing this friction. Then P=4(1+p2Zr+4a; Q=3(1 — ») Zr, + 0; Par,— Qor. = ——L_xc_ vs Par, + Qobr 157. Pillow-block Dynamometer. — The pillow-block dynamom- eter operates on the same principle as the steelyard dynamometer, but no intermediate wheel is used. This dynamometer, shown in 298 EXPERIMENTAL ENGINEERING Fig. 219, consists of the fixed shaft L, which is rotated by the power Q applied at N. The power rotates the gear-wheel EL, which com- municates motion to the wheel KEon the same shaft with the wheel KM. This shaft is supported on a pair of weighing scales so that the force Z acting on the bearing can be weighed. Let P equal the force delivered, let a equal the angle this force makes with the horizontal, KM equal a and KE equal Fic. 219.—PILLow-BLOCK =», G equal the weight of shaft and wheel ppeec ns at K. Taking wheel KE as a free body and placing the summation of vertical forces = 0, we have Z=G+Psna+R=Gt Psina+

4 ‘. i el | 3 & rr © al 320 EXPERIMENTAL ENGINEERING shaft is fitted with a universal joint to eliminate transverse strain on the dynamometer, and to allow some freedom of motion trans- verse to the shaft to the carriage which supports pulley EZ. The tension carriage, so called, pivots near the floor upon sheet-steel fulcrums, like those used in the Emery testing machine. From the driving pulley Z the power is transmitted to the driven pulley F, whose shaft is mounted on solid pedestal bearings on the movable carriage M. By shifting the latter along the floor and securing it rigidly, any desired initial tension may be put into the belt.. The shaft of F also carries a brake wheel J, the power transmitted being regulated by means of the Prony brake. ‘The rest of the apparatus consists of a slip disk so constructed that the slip may be read directly in per cent. The auxiliary shaft J is driven from the shaft on which pulley P is placed through worm gearing having a ratio of too to1. At the opposite end, near the brake carriage (see enlarged detail figure), J carries a disk S, whose circumference is divided into too parts. Next to S, but loose on the shaft Z and driven by a worm W on the driven shaft, is the gear LZ. The ratio between W and L is again 100 to 1. A pointer V moving over the circum- ferential scale of S is carried by the hub of LZ, and may be secured in any position desired by the set screw JT. Now suppose that the machine is running and that V is set to any point on S._ If there is no difference in the position of V on S when S has made one com- plete revolution, L is moving just as fast as S, and there is no slip. If, however, V has lagged behind say X divisions on the scale, the slip will be X per cent, because as constructed each division on the scale is equal to a lag of 1 revolution in roo, that is, to a slip of 1 per cent. Platform scales are provided at B, to obtain the net brake load, at C to determine the reaction of the tension carriage, and at A to find the net load on the dynamometer. In what follows, B will be called the brake scale, C the tension scale, and A the dynamometer scale. Means should also be provided for accurately determining the speed of the driving pulley E. 170. Methods of making Tests and Computations. — 1. With test belt off, run the machine at speed desired and determine the zero readings of dynamometer and tension scales. Determine also the zero reading of the brake scale as outlined in Art. 144, p. 276. MEASUREMENT AND TRANSMISSION OF POWER = 321 2. Put test belt in place under very moderate tension and run for a few turns until it adjusts itself properly to the pulleys. Then shut down and move brake carriage outward until the desired initial tension in the belt is obtained. This is determined by means of the tension scale as follows: Initial Tension. —In Fig. 240, E is the driving pulley. The belt tensions are 7, and T, respectively, each acting at an army. The i +] v — at ais SF 8 — athe ; Er Fic. 240. — TENSION CARRIAGE, BELT-TESTING MACHINE. shaft couple is represented by Px. The vertical arm of the brake carriage is d, the horizontal arm is ¢ and C the net reaction on the tension scale. Then, taking moments about O, = 7 Ci DLR E=—H + P(d +) — P( -*) 2 or Co=d(T, +7, —r(T,—T,) + Px. But r (Y, — T,) is the couple due to the belt, while Px is the same couple on the shaft. Hence —r (T, — T,)+ Px = 0, and we have Cc = d(T, + T,) from which T,+T,=C5. (26) But in this case, since the belt is standing still, 7, = T, and therefore Cc T=CcS. 322 EXPERIMENTAL ENGINEERING This is the ¢otal initial tension, JT in each side of the belt, and is usually divided either by the width of the belt to reduce it to initial tension per inch of width, or by the cross-sectional area of the belt to reduce it to initial tension per square inch of belt. 3. Start machine and take a series of observations, varying the brake load,.i.e., the horse power delivered, from an amount as low as the brake will carry, until the slip becomes excessive, which point is indicated either by screeching and flopping of belt or by belt leaving the driven pulley. For each brake load, as soon as condi- tions become constant, observe reading of dynamometer scale, tension scale, brake scale, speed of driving shaft, the arc of contact, and slip. To cover the entire field a series of initial tensions should be taken and the same operation repeated for each, A te b + — -— — — Fic. 241. BRAKE CARRIAGE, BELT-TESTING MACHINE. 4. Computations. — (a) Horse-power Input. —See description of Lewis dynamometer, Art. 158. (6) Initial Tension per inch of width or per square inch of cross section; see 2 above. (c) Running Tensions, T, in driving or tight side of belt and T, in slack side. It was shown under 2 that the sum of the tensions is T,+ T,=C, Fig. 241 shows the moments involved in the brake scale mech- anism. Here F is the driven pulley, J the brake wheel, the MEASUREMENT AND TRANSMISSION OF POWER = 323 radius of F is Dag the length of the brake arm = 0 ft., and the net 2 a brake load = Blbs. With moments above the center of wheel F we have Bb + 7,21 =7,2:, from which 2b D, (27) Combining this with equation (26) above, we finally have ¢ 2b Cc Z +B D, T,= —————: (28) - . (29) These equations give the fofal tensions 7, and T,, which are usually reduced to pounds per inch of width or per square inch of cross section by proper division. (d) Coefficient of Friction, f. — This may be obtained from equa- tion (7), Art. 116. Usually, however, the equation is simplified to the following form: T ft — loge > 6, (30) 2 where @ is the arc of contact in radians. (e) Delivered Horse Power is computed from the constants of the Prony brake and the brake load; see Art. 144. (f) Efficiency of Transmission = Delivered Horse Power : Horse-power Input It should be noted here that the efficiency as above computed takes into account the friction of the bearings and is consequently not the net efficiency of transmission by the belt alone. 5. The following form used at Sibley College shows the manner of recording data and of arranging the results. EXPERIMENTAL ENGINEERING 324 *S8019 10 JOU JOYIOUM + | | 1 ta) a | ft lecete| te | te fet cfr] o | a] ye | o | af sy we] w i peeq|— = a 7 ee aes seFlegklet] | 2 leslie?) 2 leflez] § | © | P/E lege 2): Elpeles|s FS je Sle 5) 8 ibolag |= = B pelsel & |RSS) ¢ t+ 121 8 Blo Bl BIS olaelral sy [Felyz ah cee ll 63/28 rH 4 = e ° 4 g(a 5 old mir w o Ziv Zz nog 3/2 S| © o|* 6 XS | 8 WIS oI§ a) 8 SPF oto ss old ne|> a Ti)wols 8 > lns|ns , o\4 Ble WIS O12 Oly 8 9: eo: TREES ele |] WIPES] 3 [EBlEE = Bla gibe; gi" gis elg | Bee a @ 2.) o.. fe ‘ S - 2e8)F eo SlEel . ag) &| g [7 8/*8 Séla| 8] glasie | gly a2 ® aoe ny i ei | | BIS g a AIS gy a 2S g4 4 8 . ie 3 “sq] Ul sduIpeoy ow a | | 7 g . = e apeog: tt |e 8 8 4 o@+(@L +L) 807 AW] =f [fcc “sq|— a[eog rajouomreu A Jo o1a7Z}|""" "yy ‘Aay[Ng waalq] souaraywnsity |) "°°" (p)* *ayeog uolsuay, UO WIY “eA ERA ee Burpurys ‘apeog worsuay, Jo osaz| [oor |e spasn Aaqing Jo pury|| °° °° + "| ay ‘Aang Sutarsq eouasayumnomD||***"****| (2)"**efeog WoysuaT, Wo uLTW “JOH FE eS ee Suruuny ‘ayeog worsuay, jo o1az||""*** °°") saysut— Aay[ng waar jo seq}} (ig) 077+ Saying waatig "merq||" 97] (gy qed Auoig jo wiy eae ne perm eee aes Sq[— a[B9S ayRIg Jo o19zZ]|"*******/seyour— Aay[ng Zutatiq jo soeq]|"" (q) 0771 AayNg Sarat “weiq||"*"*"** "| (2) Aang Jayamoureusg jo ‘werd ‘ANIHOVIW AO SLNVLSNOO T6I°**** ee sete ew eae enee tur tt ++ +ssouHONT, reeeescgqedrerssssss ‘ul’ oe teers ss myBuaT “ONILTAA AO ISAL ‘AOATION AMTAIS —ONIMAANIONA TVINGWIAad xa dO INAWLYVdad +++ +sTaarasqQ uontpuos “"3pa JO pursdt CHAPTER XI. HEAT AND THE PROPERTIES OF GASES AND VAPORS. 171. The purpose of this chapter is to bring together in one place all the necessary definitions, conceptions, and laws concern- ing gases and vapors and thus to avoid loading down the chapters dealing with the testing of prime movers with elementary and theo- retical discussions.* 172. Notation and General Definitions. — Throughout this Chapter the following notation will be used: Q = Quantity of heat in British Thermal Units, B.t.u. = Work in foot-pounds. = Joule equivalent = 778. p= Specific heat at constant pressure in B.t.u. Specific heat at constant volume in B.t.u. ua Ga ah = Absolute pressure in pounds per sq. in. = Absolute pressure in pounds per sq. ft. = Volume of a gas or vapor in cu. ft. = Volume of one pound of gas or vapor in cu. ft. ( = specific volume). t! = Temperature in degrees Fahrenheit. T = Absolute temperature in degrees Fahrenheit. W = Weight of gas or vapor involved in a given change or process. I AQ &» SB | ! | ll HH to 00 on s 2 aot ryt 173.. The Heat Unit and the Mechanical Equivalent of Heat. — Heat has to be measured by an arbitrary unit, and the unit adopted in the English system is the quantity of heat required to raise one * The main exception to this statement is the discussion concerning specific heat, in Chap. XXI, in connection with gas-engine testing. 325 326 EXPERIMENTAL ENGINEERING pound of water through one degree Fahrenheit. This is known as the British thermal unit (B.t.u.). In the metric system the unit is taken as that quantity of heat required to raise one kilogram of water through one degree Cen- tigrade.* This unit is known as the Jarge calorie, and is the usual engineering unit, the physicist’s unit being the small calorie, which is the one-thousandth part of the large calorie. The ratio between the B.t.u. and the large calorie is 1 B.t.u. = .252 kilogram calorie. It is of the greatest importance in some engineering calculations to be able to transpose heat units into equivalent mechanical units or vice versa. ‘The determination of the relation existing between them is entirely experimental, and from the first investigator who determined a definite value for the British thermal unit the con- version factor has obtained the name Joule’s equivalent. Joule found the mechanical equivalent of one heat unit equal to 772 foot- pounds. This value was later changed to 778 foot-pounds, which is the figure now generally used, although some uncertainty still exists as to the true value. The mechanical equivalent of heat in the metric system is 1 calorie = 424 meter-kilograms. 174. Specific Heat. — Specific heat is generally defined as the quantity of heat required to raise unit weight of a substance through one degree of temperature. In this country the units. are one pound and one degree Fahrenheit. From the nature of the defini- tion of the heat unit given above, the specific heat of water is 1.00. The expansion of liquids and solids under a temperature rise of one degree is extremely small, so that practically all the heat furnished goes to increase the intrinsic energy of the substance. There is in the case of such material, therefore, no practical distinction between the specific heat at constant volume, C,, and that at constant pres- sure, C,. With gas the case is different. Here the volume of the gas may be kept constant while it is being heated through one degree or the gas may be allowed to expand in the process. In the first * On account of the fact that the specific heat of water varies slightly with tem- perature, it becomes necessary in the definition of the heat unit to fix the one degree of temperature through which the heat is supplied. In the older definitions this was taken at from 60 to 61° F. or from 15 to 16° C., but lately the unit is based upon a mean value obtained for the entire range from freezing to boiling points of water. HEAT AND THE PROPERTIES OF GASES AND VAPORS 327 case no external work is done and C, is consequently always smaller than C, by the amount of heat required to do the work of expansion against the external pressure.* LAWS OF GASES. 175. Boyle’s Law, Charles’s Law, etc. — An ideal gas is defined as one which, at constant temperature, follows Boyle’s law, pu = constant. (x) No gas as far as known follows this law strictly, departing from it especially near the region of liquefaction, but for all engineering purposes and in the range usually covered it expresses pressure and volume relation with sufficient accuracy. Pressure and volume, however, are only two of the criteria which define the state of a gas, the third being temperature. The relation of pressure or volume to temperature is expressed by Charles’s law, ek when the volume remains constant (2) Ld un vou : To 7 When the pressure remains constant. (3) 1 The interrelation of the three variables, p, v,and T, may be expressed by a combination of the laws of Boyle and of Charles as follows: oe T fT, Equation (4) is generally known as the equation of state or condition of the ideal gas. So far nothing has been said concerning units, and as a matter of fact any units may be used, provided only that p and T are absolute pressure and temperature respectively. The constant in equation (4) will of course have a different value depending upon the units in which g, v, and J are expressed and upon the weight and volume of gas concerned. It has, however, become usual in Eng- lish practice to express the pressure in pounds per square foot, in which case it is designated by P, to take absolute temperature in degrees Fahrenheit, and to take the volume v equal to that of = constant. (4) * For distinction between mean and instantaneous specific heat see discussion in Chap. XXI. Heat calculations for a given temperature range should be made by use of the mean specific heat for that temperature range, unless the simple assump- tion that specific heat is constant is made. 328 EXPERIMENTAL ENGINEERING one pound of the gas under the existing conditions of pressure and temperature, that is = v’. With these units the constant in equa- tion (4) is generally designated by the symbol R and equation (4) becomes Py’ oR (3) For any one gas, R is constant and is the foot-pounds of work done by one pound of gas when it is heated through one degree Fahrenheit. See Table below for values of R for the most common gases. 176. Specific Heat of Gases. — The distinction between specific heat at constant pressure, C,, and that at constant volume, C,, was made in Art. 174. For any given gas the specific heat varies with temperature, increasing as the temperature increases. The laws of this increase are not as yet definitely fixed, and for ordinary engineering calculations it is still usual to consider specific heat a constant quantity for a given gas. Enough information is now, however, available to make such an assumption unwarranted ex- cept for rough calculation. The subject is discussed at length in Chap. XXI in connection with gas-engine calculations. The ratio of the specific heats a8, which decreases with tempera- v ture, is designated by the lettery. It is in all cases computed from the instantaneous values of specific heat. The following table gives values of C,, C,, y, and R for a series of the more common gases. Weight per Specific Heat per lb.* Constant R ak cu. a at in equation 29.92 Hg. Py’ 32° FR. Cp Cy — a Hydrogen... cs ssacce eens He .00562 3.380 2.380 775.6 Carbon Monoxide........ CO .07807 +243 +174 55-23 Methane ies is ave cae ss CHy .04464 593 468 97-25 Ethylene vx sce oeeweawau na CoH, .07809 »404 +333 55-23 Acetylenev+ 2.1 ana caees v2 CoHe .O7251 -346 +270 59-13 Butylene:, ¢zsccaesha ats C,He -15590 «404 33a: | | dibedeaaiy NUtTO BED 5.20. 5, dce.cuesciecsinesecsusie No -07831 +243 +173 55-23 ORY BE Nise see sicors ware oa arocans Ox .08921 +217 +153 49-79 Alpes sxe wn smariweacetie _ .08072 2375 - 1684 53°75 Water vapor. .........06e H2.0 .05016 -455 - 34 85.58 Carbon Dioxide.......... COz -12268 201 +155 35-01 * These are instantaneous values for a temperature of about 60°F. HEAT AND THE PROPERTIES OF GASES AND VAPORS 329 177. Pressure and Volume Changes in Gases. — (a) Change at Constant Pressure.—In the rectangular coérdinate system, Fig. 242, let OX = axis of volumes v, and OY = axis of absolute pressure P. Let the point 1 define the initial state of v, cubic feet of gas at F,%1T3 3 1 2 P Pvt, Rv,T, | Is | Sthern, ia 4 lag P.4,T, 2tig 4h 1 | 5 | Feu5Ts | 0 ' 3 a Fic. 242. a pressure P, and a temperature T,. Heat is supplied and the gas is allowed to expand at constant pressure to the point 2, where the state is defined by P,v,T,. This change is called isopiestic or isobaric. Equation of state “= 2. quation of state TT. (6) Work done E = P, (v,— »,) ft.-Ibs. (7) Heat supplied Q = - + WC, (T,— T,) Btu. (8) or Q= WC, (T,-— T, Btu. (9) For the reverse of this change, that is, for a compression from 2 to 1, the same equations hold, except that E and Q will be negative, i.e. work is done upon and heat is rejected by the material changing volume. 330 EXPERIMENTAL ENGINEERING (b) Change ai Constant Volume. — With the material again at point 1 in Fig. 242, assume heat supplied and the volume of the gas maintained constant. The pressure rises to the point 3, where the state is defined by P,v,7,, according to Charles’s law. This change is called isometric or isovolumic. Py, Equation of state T, 7 tT. (10) Work done E =o, since there isno volume change. (11) Heat supplied Q = WC, (T, — T,) B.t.u. (12) For the reverse change there is a pressure drop, the quantity of heat, Q, becomes negative, showing that heat must be removed. (c) Isothermal Change. — The gas is expanded from the point 1, Fig. 242, to the point 4, heat being supplied to keep the temperature constant. At point 4 the state is defined by P,v,T7,. This change is called isothermal, and the expansion line described is known as an isothermal line. Since 7 is constant, Equation of state P,v, = P,v,= constant. (13) Work done E= f "Pdv = Py, log. UY 1 = P,v, log, r ft.-lbs., (14) where ¢ is the ratio of expansion. Heat supplied Q= . B.t.u. (15) For the reverse change, that is, isothermal compression, E and Q become negative, i.e., work must be done upon the gas and heat must be removed. (d) Adiabatic (or Isentropic) Change.* — The gas expands from point 1, Fig. 242, to point 5, but no heat is supplied or rejected. This process is known as adiabatic, and if reversible, also as isen- tropic, meaning constant entropy. For definition of the latter term see page 332. Let the final state of the gas be defined by P,v,T,,. Since the work done during the change must be done at the expense * See note, page 344. HEAT AND THE PROPERTIES OF GASES AND VAPORS 331 of the sensible heat in the gas, the temperature must drop, and hence the pressure must drop more rapidly than during an isothermal change. é P,v, — Pv fit 2s, 16 Equation of state T, T, (16) Equation of adiabatic line P,v,7 = P,v,”. (17) From equations (16) and (17) the interrelation of the three vari- ables may be expressed by yt a T, \W, P, Work done, £ -{" Pdv = pu, f "2 _ Pv. — Pov; 1 U1 vy yo D — RT Ee, y-1 T ear g) = a mA rf" = Us eo ya P.\ 7 a er,|-—(2)" | ft.-Ibs. (x9) y-1 Heat supplied QO = oB.t.u. (20) For the reverse change, i.e., adiabatic compression, E is negative, that is, work is expended in compressing the gas. (e) Changes represented by Pu" = constant. —The equations rep- resenting work done, as well as those showing the interrelation of pressure, volume, and temperature for these changes, are the same as those given for the adiabatic change under (d) except that m is substituted for y. As a matter of fact, the adiabatic change is a special case of Pu" = constant, in which nm =y. Similarly for the 332 EXPERIMENTAL ENGINEERING isothermal change » =1, for the change at constant volume n = oo, and for that at constant pressure ” = o. Heat supplied g= lc G= 754 B.tu. (20a) 178. Entropy of Gases. — When heat is supplied to a gas, the result may be a simultaneous change of pressure, volume, and tem- perature. In other words, the addition of heat may produce, first, additional internal energy of the gas, involving rise of temperature, and second, it may produce an external effect which is equivalent to the work done by the gas expanded between its containing walls. Mathematically expressed, these changes may be written 80 = COT + = by. ai) By substituting for P in this equation it reduces to 00 = C,0T + (C, — C,) re, (22) and if we write the general equation for entropy, 0 ag = 8, (23) we will finally have 70 dp = = C2 + (Cr-C) %, (24) which is the general a for entropy of a gas. According to the simultaneous interrelation between the three factors pressure, volume, and temperature, equation (24) undergoes certain modifications which make it directly applicable to each case. Case a. Change of Entropy at Constant Volume. — Under this condition dv! (C, — C,) ye We shall have from equation (24) op = ac, 2 (25) T. p, —h=Cy loge Tt (26) 1 HEAT AND THE PROPERTIES OF GASES AND VAPORS 333 Case b. Change of Entropy at Constant Pressure. —From Pv’ = / RT and Pév’ = ROT we may derive = = a which by substitution in equation (24) gives a0 ag ee 6 = = Oo (27) T. b2— $i= Cp log. T. (28) Case c. Change of Entropy with Simultaneous Change of Pressure and Volume. — From equations Pv’" = P,v’,” and P = aS we may derive a vw T(n—1)’ which by substitution in general equation (24) changes the latter to the form ge ue oe Oa ay oe 5 (29) This equation may be simplified by the aid of the relation C,= yC,, the final form being ap = C.F (2=1), (30) b.—- t= Cy (* = Nog. 7 (31) LAWS OF VAPORS. 179. Vaporization. — The conversion of liquid to vapor takes place at a definite and different temperature for every different pressure, provided the space above the liquid is limited. For the case of free evaporation, as for instance in the open cooling tower, the evaporation does not take place at atmospheric pressure, as might be supposed, but at a pressure determined by the tempera- ture of the liquid. This fact must be remembered when making computations for such a case. 334 EXPERIMENTAL ENGINEERING To raise unit weight of the liquid to these different tempera- tures requires in any given case a quantity of heat, called heat of the liquid, equal to p= tat, — 2) Bim, (32) in which C, is the mean specific heat of the liquid between the temperatures T, and T,, T, being the temperature of the liquid before the addition of heat. This is generally assumed 32° F. T, is the temperature at which vaporization takes place. It would seem more rational to assume T, at the freezing point of the liquid for every substance, although engineering practice still generally assumes T, at 32° F., probably because of the much more general use of steam as compared with other vapors. For ammonia vapor, for instance, this basis of computations results in negative heat quantities for the values of g, and in latent heat values r partly negative and partly positive for temperatures below 32°. After heating the liquid to the temperature of vaporization, the addition of a quantity of heat known as the latent heat of vaporiza- tion will convert all the liquid to dry saturated vapor at the same pressure and temperature previously possessed by the liquid. This heat is represented by 7. The latent heat of vaporization can be imagined to consist of two parts, the imternal latent heat, p,and the external latent heat, Apu. The internal latent heat is that part of the total latent heat which is used to do the interna] work coincident with the molecular re- arrangement during the change of state from liquid to vapor. The external latent heat is that part of the total latent heat which is used for doing the external work necessitated by the enormous volume increase during the change of state. The total heat above 32° per pound of dry saturated vapor is, then, Q=A=qtot+Apu=q+er. (33) If the process of vaporization ceases when a fraction, x, of each pound of liquid has been converted into vapor, the mixture is known as wet saturated vapor, and the heat above 32° per pound of mixture is Qu= 9+ (o + Apu)= q + xr. (34) HEAT AND THE PROPERTIES OF GASES AND VAPORS 335 As the pressure and the quantities g, o,7, Apu, and A all vary with the temperature, it is customary to tabulate them and other useful properties of the material in so-called vapor tables. See the Steam and Ammonia Vapor Tables in the Appendix. 180. Superheating and Specific Heats of Vapors. — After vaporiza- tion, as outlined in Art. 179, is complete, the further addition of heat results in raising the temperature above that corresponding to the pressure, if liquid were present. This is known as superheating. Vapor may be superheated at constant volume, at constant pres- sure, or under a simultaneous change of both pressure and volume. The usual method, however, is practically that at constant pres- sure, and this will therefore be the only case necessary to consider. Experiment shows that the specific heat of vapors varies with pressure and temperature, and recently fairly accurate determina- tions of this quantity have been made in the case of water vapor (steam). Among these the results of Knoblauch and Jakob, slightly modified at low pressures and at temperatures near satura- tion by Marks and Davis,* seem to be the most reliable. Fig. 243 f shows a graphical representation of Knoblauch and Jakob’s results so modified. The ordinates of this diagram represent what are called ‘instantaneous ”’ specific heats, that is, the progressive values which vary from degree to degree at constant pressure and from pressure to pressure at constant temperature. In Fig. 243 the curve AB may be called a saturation curve, since it is a curve obtained by plotting corresponding conditions of saturated steam. A more useful way of plotting specific heats, however, is to plot the “mean ”’ specific heat for given temperature ranges, because most engineering calculations in this field call for the determination of heat content of superheated steam at a certain definite pressure and temperature. This may be done by means of the data for superheated steam contained in the Tables of Marks and Davis. The result for a number of pressures is shown in Fig. 244. Thus for a pressure of too lbs. absolute and a degree of superheat equal to 200°, the mean * Tables and Diagrams of the Thermal Properties of Saturated and Superheated Steam, L. S. Marks and H. N. Davis, Longmans, Green & Co. t Tables and Diagrams, p. 97. 336 EXPERIMENTAL ENGINEERING specific heat is found to be C, = .515. Hence the B.t.u. represented by this degree of superheat will be 200 X .515 = 103 B.t.u. B 1.00 Cp 80 70 ‘> 100 I 700° 900° Fic. 243. —RELATION BETWEEN Cp (INSTANTANEOUS VALUES) AND TEMPERATURE FOR SUPERHEATED STEAM. (The numbers on the curves represent absolute pressure in Ibs./sq. inch.) To obtain the same result from the diagram of Fig. 243 we would have had to proceed as follows: The saturation temperature of steam at too Ibs. absolute is 327.8° F. (from Steam Table, Appendix). ce Ss © Ss ay Quay] ogloedg uvoyy 0.5 1nn HEAT AND THE PROPERTIES OF GASES AND VAPORS 337 With 200° of superheat the steam temperature would then be 527.8°F. It will next be necessary to obtain, in Fig. 243, the mean ordinate for that part of the C,-curve for 100 lbs. between the abscissee 327.8 and 527.8. This will be found to be .515, but the great advantage of Fig. 244 is at once apparent. 181. Use of Steam Tables and Diagram.* — Table No. I in the Appendix is computed with steam temperatures as a basis and gives the values of the various quantities from 32° to 165° F. It is intended to be used mainly for condenser work, the absolute pres- sure range covered being from .2’’ to 10.86” Hg. Table No. II is based on pressures and will serve for all ordinary steam calculations. The items in both tables are clearly enough set forth in the head- ings to the columns and need no further explanation. The diagram, Fig. 245, is of course constructed from steam table data, and the legends and directions it contains should be sufficient to explain its meaning. Some of its uses will be apparent in the following examples: Example 1.— Steam pressure 125 lbs. absolute, feed water temperature 72°, quality of steam 95 per cent, find total heat per pound of steam above feed water temperature. General equation: Heat per pound of steam = [xr + ¢ — (f—32)] B.t.u. From Table IT, for 125 lbs. pressure, r = 874.7, ¢ = 315.5, therefore heat per pound of steam = [(.95 X 874.7) + 315.5 —(72 — 32)] = 1106.4 B.t.u. Example 2.— How much heat is required to heat boiler feed water from 75° to vaporization at a boiler pressure of 150 lbs. by gauge? For the solution of this problem it is necessary to know the barometric pressure, since the tables are based on absolute pressure. Assume that the * Both tables and diagrams were taken from the “Tables and Diagrams of the Thermal Properties of Saturated and Superheated Steam,” by special permission of the ; authors, Prof. L. S. Marks and Mr. H. N. Davis, and of the publishers, Longmans, Green & Co. The tables were much shortened, and this is true especially of the temper- ature tables, which in the original covered the range from 32° to 689°. The pressure table is cut down less. The diagram was reduced from a large chart approximately 16 X 20 inches. The book mentioned also contains an extended table of the prop- erties of superheated steam. 338 EXPERIMENTAL ENGINEERING barometer stands at 29.3’’, equivalent to a pressure of 14.4 lbs. The abso- lute pressure will then be 150.0 + 14.4 = 164.4 lbs. From Table II: At 165 lbs. absolute, g = 338.2 B.t.u. above 32°. At 164 lbs. absolute, Gj sep Oh AP Ae ee Difference, 5 Hence at 164.4 lbs., g = 337.7 + (.4 X .5) = 337-9 B.t.u. above 32°. From this value must be subtracted the value of g for feed water at 75°. This is best found from Table I, from which g = 43.05 B.t.u. Hence the net amount of heat required is in this case equal to 337.9 — 43.05 = 294.85 B.t.u. It is quite customary for ordinary calculations, especially if no temperature table is available, to assume the specific heat of water equal to 1.0, in which case the heat in the feed water at 75° above 32° would be 43 B.t.u., and the heat required for the case under discussion would then have been 337.9— 43 = 294.9 B.t.u. It will be noted that the difference is very small. Example 3. — The total heat contained in a pound of steam is found to be 1175 B.t.u. The absolute pressure is 180 lbs. Find the quality of the steam. We have xr -+q = 1175. From the steam table, for 180 Ibs.,7 = 850.8, g = 345.6, hence 850.8 « + 345.6 = 1175, from which *% = 97.5 per cent The same result could have been obtained very quickly from the diagram, Fig. 245, by following the 1175 B.t.u. line to the right to its intersection with the 180 lbs. pressure line. This point will be found to lie halfway between the 97 and 08 per cent quality lines. Suppose, next, that at the same absolute pressure the steam had contained 1260 B.t.u. per pound; find «. Here 850.8 x + 345.6 = 1260, and 4% = 1.075. Evidently the steam is superheated, and the amount of superheat should next be expressed either in B.t.u. or in degrees. To obtain the B.t.u. of super- heat, the quickest way is to subtract from 1260 B.t.u. the total heat in dry and saturated steam at 180 lbs. absolute, equal to 1196.4 B.t.u. from the table. This shows 63.6 B.t.u. of superheat. The next step is to determine the degree of superheat, i.e., the steam temperature. We have Cp (T: — T;) = B.t.u. of superheat, where Cp = mean specific heat in the range T, to Ta, T, = actual temperature of steam, JT, = saturation temperature of steam. 1,54 1,20 1550 Velocity Btu, feet per second = 0 += 600 TEMPERATURE OF SATURATED STEAM [4000 ateach pressure for which a curve is drawn Pressure Pressure We.per TEP /doeper TPT ibs per TeMP- 1500 gq. in, oF Bq. F aq. in, F 450 0. 30 | 1% 219 347 75-92 | 19 RB 553 102 359 116 al 126 184 141 148 163 158 162 170 177 183 Reason ome eaea PRESS PES 198 206 213 Total Heat B.t.u, & oO ms 30 1.34 : Entropy. 1.68 1.62 TOTAL HEAT-ENTROPY DIAGRAM (“THE MOLLIER DIAGRAM") FOR SATURATED AND SUPERHEATED STEAM Sor use in the aolition of problems involving adiabatic expansion, throttling and the flow of lines are lines of constant entropy. lines are lines of constant total heat. running diagonally are lines of constant pressure, ing nearly hori: lly are lines of superheat or of constant quality, MARKS AND DAVIS, STEAM TABLES AND DIAGRAMS i 750 0 174 1.78 1.82 1.86 1.90 1.94 1.98 2.02 2.06 2.10 HEAT AND THE PROPERTIES OF GASES AND VAPORS 339 In this case, Cp (T2 — 373.1) = 63.6, T, =-3 If the only information available concerning the interrelation of Cp and T, is that contained in the curves of Fig. 244, the last equation will have to be solved by trial, since both Cy and T, are unknown. From Fig. 244 it will be found that when the degree of superheat = 111, Cp = .573 for 180 lbs. absolute, and this pair of values closely satisfies the above equation. Hence the steam temperature is 373.1 + 111 = 484.1° F. Again the diagram, Fig. 245, would have given this result without computa- tion, for following the 1260 B.t.u. line to the right until it crosses the 180 lbs. pressure line, it will be seen that the point of intersection is just about halfway between the 100° and the 120° lines of superheat. Example 4. — The vacuum gauge on a condenser shows 26” Hg, while the temperature in the condenser is 110°. The barometer shows 29” at the same time. What proportion of the absolute pressure in the condenser is due to the presence of air? | A temperature of 110° inthe condenser, if steam alone were present, calls for an absolute pressure of 2.589’’ Hg, according to the temperature table in the Appendix. The absolute pressure really is 29 — 26 = 3’’ Hg, and the excess pressure, or .411’’ Hg, is therefore due to the presence of air. Example 5. — One pound of steam at an absolute pressure of 150 lbs. anda temperature of 460° F. is exparided isentropically to a pressure of 30 lbs. abso- lute. What is the state of the steam at the end of the expansion and what is the difference in heat content of steam at beginning and end? The saturation temperature of the steam is 358.5° F., hence the steam is superheated to an extent of 460 — 358.5 = 1o01.5°. The problem is best solved by means of the diagram, Fig. 245. Since in this diagram the abscissa represent entropy, an isentropic change is represented by a vertical line, Starting, therefore, on the 150 lbs. pressure line at a point representing 101.5° of superheat, drop a vertical line to an intersection with the 30 lbs. pressure line. The point of intersection indicates a quality of 95.1 per cent, the steam having changed its state from that of superheat to 4.9 per cent wet. For 150 lbs. absolute pressure and 1o1.5° of superheat, the B.t.u. scale at the left shows a heat content of 1255 B.t.u. per pound. At 30 lbs. and 95.1 per cent quality, the scale shows a heat content of 1118 B.t.u. Hence the difference of heat content is in this case 1255 — 1118 = 137 B.t.u. Example 6. — Find the heat required to superheat 1 pound of steam from 425 to 500° F. at a constant pressure of 200 lbs. absolute. The saturation temperature for 200 lbs. is 381.9°, hence, the above tempera- ture ranges call for a degree of superheat increasing from 43.1° to 118.1° F. Fig. 244 shows that at 43.1° and 200 lbs. mean Cp = .642, hence the heat required to superheat up to that point is 43.1 X .642 = 27.67 B.tu. At 340 EXPERIMENTAL ENGINEERING 118.1° and 200 lbs., Cp = .582, hence the heat required up to this temperature is 118.1 X .582 = 68.72 B.t.u. The net expenditure of heat to raise the tem- perature from 425° to 500°, therefore, is 68.72 — 27.67 = 41.05 B.t.u. per pound. The same result would have been obtained much more quickly from the dia- gram, Fig. 245, by reading off the difference in the heat content of steam at 43° and 118° of superheat, following the constant pressure line 200, although this chart cannot give the result quite so closely. 182. Entropy of Vapors. — Defining entropy by the equation d dp = x (35) a finite entropy change must be dQ ag = f2. $ 7 (36) During the heating of a liquid preparatory to vaporization dQ os CaT, (37) where C; = specific heat of the liquid. Substituting this value of dQ in equation (36), we have the entropy change of the liquid T2 Ab= fi oe, (38) Ti i which, in case C; is assumed constant or taken as the mean value through the temperature range, can be written T2 Adi= cf oF = Cr loge (39) In the so-called ‘‘ entropy of the liquid ” in the steam tables, as computed above 32°, the value of 7, in the above equation is equal to 492, while T, is the temperature of vaporization. During vaporization of a liquid at constant pressure the tem- perature remains constant, and the heat added is the latent heat of vaporization, 7, so that the entropy change during vaporization is ag= [2-5 (40) If vaporization is incomplete, i.e., if the vapor formed has the quality, x, less than unity, the heat added during vaporization is only xr, and the entropy change is d aga= fe == (41) HEAT AND THE PROPERTIES OF GASES AND VAPORS 341, The total entropy change, therefore, experienced by a liquid when heated from any temperature 7,, and vaporized at a given constant pressure at a temperature T,, will be De er A¢,= C, log, + =—- p 1108. x 7 Tr (42) If the vapor is dry and saturated, this equation becomes T r Adsat= Cy log, + =: Psat = Cr log T.*T, (43) If the vapor is next superheated at constant pressure (usual case) dQ in equation (36) may be written = C,dT, and ts. dF age= J OT £ = Ga log. Tp (44) 2 where C, is the mean specific heat for the temperature range T,—T,=T, The total entropy change per pound of liquid changed from a temperature 7, into superheated vapor at a tem- perature T, will be Ag= Clog. 2+ % + Cylog. 2 (45) re dex oth provided the vapor has been superheated at constant pressure. The vapor table for steam in the Appendix gives the entropy of the liquid, the entropy of vaporization, and the total entropy of dry and saturated steam. If the steam is superheated, the third member in equation (45) will have to be computed. 183. The Temperature-Entropy Diagram for Steam. — In a rec- tangular system of codrdinates, Fig. 246, let the abscisse represent entropy, designated by ¢, and the ordinates represent absolute temperatures, T. Entropy changes of the liquid will in such a diagram be represented by a line a-b-b,, etc., called the liquid or water curve, the data for which line may be obtained either by solving equation (39) or by use of the steam table in the Appendix. The diagram is constructed for one pound of water. Suppose that vaporization begins at the point 6, where the absolute tempera- ture is 653.2°, corresponding to an absolute pressure of 10 Ibs. At 342 EXPERIMENTAL ENGINEERING this point the entropy of the liquid above 32° is 0.2832. See steam table. During vaporization the temperature is constant, until the point c is reached, where all of the water has been evaporated. The heat of vaporization during this change is 982 B.t.u., and the en- tropy change, therefore, is ae = 1.5042, which, added to the entropy at b, makes a total entropy change above 32°, equal to 1.7874. If only a part of the water is vaporized, only a proportionate part ea ce by 150*Abs. i THA Ds, & £ f & a by 8 S/d, 30*A bs. g& |e g 3 3 b 10*Abs. e i C < | | a ' | | | (2832 Tatnapese 1.637 1.7874 Fic. 246. — Entropy DIAGRAM FOR STEAM. of the heat of vaporization is used. For instance, assume that the quality of the vapor is 90 per cent. Then the heat rendered latent in the vaporization process = .go X 982 = 883.8, and the entropy 883.8 653.2 above 32°, therefore, is 1.6370. This locates the point e on the diagram. The line be is equal to .9 of the line bc, and, in fact, the quality of steam in this diagram may be determined by finding the ratio of actual length of the vaporization line to what would be the length if vaporization were complete. change, therefore, is = 1.3538. The total entropy change HEAT AND THE PROPERTIES OF GASES AND VAPORS 343 If, on reaching the point c, the vapor is next superheated, the temperature again rises with an increase in ¢ as represented by the line cd, the data for which may be computed from equation (44). For any other pressure, as 30 lbs., the process will be determined by the line a6,c,d,, the data for which is obtained in exactly the same manner. If the points ¢, ¢,, ¢,, .. . are joined by a smooth curve, the resulting line is the so-called saturation curve for steam. In the region to the right of this line the material must be super- heated, while to the left it must consist of wet vapor until the line abb, is reached, where all the vapor is condensed. 184. Pressure and Volume Changes in Vapors. — (a) Change at Constant Pressure. Case of Saturated Vapor. — During a volume change at constant pressure, with a saturated vapor, the temperature remains constant. Hence, for such a vapor the isothermal line and the isobar are identical. Also, since a change of volume at constant pressure with a saturated vapor can only occur during vaporization or con- densation, every such change is accompanied by a change in the quality of the vapor. Equation of the line, P = constant. (46) Work done, E=P(v,— vu, ft. lbs. (47) Heat supplied during an expansion from y% to v, in which the quality of the vapor changes from x, to x, = 0 = (q+ %F.) — (Qt %7) Btu. (48) in this case g,= 4, and 7,= 7, hence, OQ =r(x,- %,) B.tu. (48a) Case of Superheated Vapor. —The conditions accompanying a change of volume at constant pressure in a superheated vapor are best defined by the lines representing the entropy changes during superheating in Fig. 246. Accordingly, any such change is accompanied by a rise or drop in temperature, depending upon whether there is expansion or contraction, and such temperature changes are perhaps most easily considered by the construction of 344 EXPERIMENTAL ENGINEERING a curve similar to cd. In pressure-volume coérdinates, the follow- ing approximate formula of Tumlirz may be used in the case of steam: T v =.5962 a= .256, (49) in which v = specific volume of the superheated steam, T = absolute temperature in F degrees, p = absolute pressure in lbs. /sq. in. Equation for the line, P = constant. (50) Work done, E = P (v,— v,) ft.-lbs. (51) Heat supplied during an expansion from 4, to v,, Q-C,(T,— T) Btu, (52) where T, and T, may be obtained by use of Tumlirz’s equation. (b) Constant Volume Changes. Case of Saturated Vapor: Equation of line v = constant. (53) Work done, E = o ft.-lbs. (54) Heat supplied Q = (¢,+%,0,) — (Q,+,0,) B.tu. (55) Case of Superheated Vapor: Equation of line, v = constant. (56) Work done, E = o ft.-lbs. (57) Heat supplied, Q = C, (T,— T,) B.t.u. (58) Constant volume changes actually occurring are, however, usually cases of chang- ing mass, and the equations above do not then apply. (Example, toe of indicator card after release in steam or gas engines.) (c) Isentropic Change.* —An idea of the volume, pressure, temperature, and quality changes which accompany an isentropic * An adiabatic process is one in which interchange of heat, as heat, between the working medium and other bodies does not occur, —in other words the working body is thermally isolated. An isentropic change is defined as one during which the en- tropy remains constant. It has been held that, in the case of vapors, these two terms are not necessarily synonymous. It is clear however that in the great majority of cases, when the engineer uses the word adiabatic, he refers to the condition of con- stant entropy, ze. to the isentropic process. HEAT AND THE PROPERTIES OF GASES AND VAPORS 345 change, say expansion, in a vapor, is best gained from a preliminary study of the entropy-temperature diagram. In Fig. 246, aa’ is the liquid line for steam and cc’ the saturation line for steam. Since, during a reversible adiabatic change, there is no change in the total entropy of the vapor, such a change will be indicated by a straight line parallel to the axis of temperatures. For instance, starting at the point c,, on the 150 pound pressure line, an isentropic expansion to 10 lbs. pressure is indicated by the line c,e. During this change the quality of steam, which was equal to unity at c,, steadily decreases until at 10 lbs. pressure it is measured by the ratio i Similarly, at any other pressure, as 70 lbs., the quality will be es, and it will be noticed that the quality decreases as the pres- 2°2 sure drops. The quality variations during isentropic expansions vary with different initial qualities, and no simple law which expresses these quality changes can be given. For this reason it is again best to resort to the 7¢ diagram when studying any particular case. This diagram shows the entropy, temperature, pressure, and quality changes, but does not directly show the volume changes. Since most of the actual engineering calculations are based on pressure-volume changes, it becomes necessary to find a means of determining the volumes corresponding to the different points €, &, €, etc. Neglecting the volume occupied by water, which in all real cases is almost vanishingly small, the volume occupied by a pound of wet steam is to the volume occupied by a unit weight of dry and saturated steam at the same pressure as the quality of the wet steam is to unity, that is, Vz i 3 Vv HIS where vz is the volume occupied by one pound of steam at quality x, and v is the volume occupied by one pound of dry and saturated steam at the same pressure, that is, the specific volume, which latter may be found from steam tables. 346 EXPERIMENTAL ENGINEERING From this it follows that the volume occupied by steam with. conditions shown by any point such ase in the T¢ diagram, Fig. 246, is equal to the corresponding quality multiplied by the specific volume, that is, be ‘ : ve times specific volume. It is therefore possible to plot a Pv curve representing isentropic changes of saturated steam by means of the T¢ diagram and the specific volumes given in the steam tables. For superheated conditions the isentropic change must also be represented by a vertical line in the T7¢ diagram. Here, again, this diagram shows temperature and pressure variations accompany- ing the isentropic change, but it gives no indication of the volumes attained. These are best computed from the equation of Tumlirz (49). Equation of the line: For isentropic expansion of steam, approximate formule of the form Pu" = constant, have been developed. For saturated steam with initial quality, x, between 0.7 and 1.0, Py 1:035 + 0.18 constant. (59) For steam remaining superheated Pv'** = constant. (59 a) Work done is P,v, — Poy. for saturated steam with initial E = ——i4+—22 _ ft-lbs. ee - (60) (1.035 to.1 %) —1 qualities between 0.7 and 1.0 for saturated steam with E= 78 +2x7,—-9,—.",) f{t.-lbs. 778 (Qi + X11 — Gy % 91) : | any initial quality |. x) In all cases the heat supply is Q = o B.t.u. by definition of an adiabatic. 185. Cycles and Their Efficiencies. — The cycles discussed under this head are purely theoretical, so that the efficiency formule developed and the efficiences computed from them show the highest theoretically obtainable by ideal engines which operate upon these HEAT AND THE PROPERTIES OF GASES AND VAPORS 347 cycles. In any actual case, owing to various losses, the real cycles only approximate the theoretical cycles, so that the theoretical efficiency may serve as a standard and the ratio of the efficiency actually obtained to the theoretical efficiency may be taken as a measure of the degree of perfection of actual operation. This ratio has in some cases a specific name. ‘Thus, in the case of the reciprocating steam engine, it has been called the ‘cylinder effi- ciency;” in the case of the turbine the name “ potential efficiency ” has been used. Gas Cycles. — (a) Carnot Cycle, shown in Figs. 247 and 248. Vv $ Fics. 247, 248. CaRNot Cycle For GAs. € Heat supplied per lb. of gas=P4V 4 log, Ee RT, log, + ft.-lbs. (62) Fa =T, (ba — pa) B.tu. (63) Heat discharged pay ie. i ft-lbs. = RT, log,? B.t-u. D (64) =T,(¢c— $n) B.t.u. (6s) Work done =R(T,—T,) log,¢ B.t.u. (66) =(2 = 73) y= Ga) Bata (67) : KRUW,—T,) log? 7 TL) @e— ba) He Effi = 1 =) 1 2. = 1 2 ene RT, log. F Gaba t, (68) 348 EXPERIMENTAL ENGINEERING (6) Stirling Cycle (used in hot-air engines). Figs. 249 and 250. Fics. 249, 250. — STIRLING CYCLE. All the formule for this cycle are the same as those developed above for the Carnot cycle. The heat discharged along BC is stored in the regenerator, which is a part of the engine, and is restored to the working substance along DA. (c) Ericsson Cycle (used in hot air engines). Figs. 251 and 252. - essed Cc Fics, 251, 252.— Ericsson CycLe, The formule for this cycle also are the same as for (a) or (0). The action of the regenerator along AB and CD is the same as under (0). HEAT AND THE PROPERTIES OF GASES AND VAPORS 349. (d) The Otto Cycle. Figs. 253 and 254. Fics. 253, 254. Otro Cycte. Heat supplied per Ib. of gas (along AB) Te =| GéT=C (Ty-Th Baw (69) La Heat discharged per Ib. of gas (along CD) Tc = f CAP =a he) Bi, (70) Tp Work done =C,(Tg-—Tag—Tet Tp) Btu. (77) : Coiled let tp pa 2a de ie Effi = = clency = C.(fs— Fa Thy (72) = Pe pe Be =1 Ts I wt ' (73) In the development of these equations, C, is assumed constant. The last form of equation (73) is derived by the aid of the adiabatic equation Pv’ = constant. (e) Brayton Cycle. Figs. 255 and 256. Vv. 2. 3 \ } Fics. 255, 256. — BRAYTON CYCLE. 350 EXPERIMENTAL ENGINEERING Heat supplied per lb. of gas (along AB) Tes = C,dT = C, (Tp —T,4) B.t.u. (74) Ta Heat discharged (along CD) Tc Su C,dT =C, (Te—Tp)B.t.u. (75) D Work done = C, (Tg — T4 — Tc + Tp) B.t.u. (76) : C, (Tp — Ta — Te + To) Efficienc = : : C, (Tz — T4) ct This reduces to exactly the same form as equation (73). The assumption is again made that specific heat is constant. (f) Diesel Cycle (modified Brayton). See Figs. 257 and 258. Pp T V ? Fics. 257, 258. — DiesEL Cycte. Heat supplied per lb. of gas (along AB) TR = C,dT = Cc; (Tz ce T 4) B.t.u. (78) Ta Heat discharged per lb. of gas (along CD) Tec = C,dT =C, (Te — Tp) B.t.u. (79) Tp Work done = [C, (Tp — T4) — C, (Te — Tp)] B.t.u. (80) HEAT AND THE PROPERTIES OF GASES AND VAPORS 351 Efficiency = C (Te a2 SoD). I ae a ae ie In the last equation roe, a=T8, and y = G2 Vapor Cycles. —'The behavior of vapors when subject to cyclic variations under differing conditions of saturation or of superheat differs very much, depending mainly upon the nature of the vapor used. To discuss even a few of the vapors would lead to consider- ations somewhat beyond the scope of this book. Fortunately, in engineering practice we find only two, steam and ammonia vapor, used to any considerable extent, and the discussion will therefore be confined to these two vapors. The behavior of ammonia vapor is probably more easily understood in connection with machines in which it is used, and consequently the consideration of ammonia vapor (refrigerating) cycles will be taken up under refrigerating machines. Cycles for Steam — (a) Carnot Cycle for Saturated Steam. Figs. 259 and 260. . a Isothermal 4 Ti a. b d Isothermal ¢ d ! Paord $ Prore Fics. 259, 260.— CaRNoT CycLE FoR STEAM. Heat supplied per lb. of vapor = 7, (*%,—%q) = T, (b5—¢,4) B.t-u. (83) The first expression of the above equation generally reduces to %pr,, because it is usually assumed that at a the material is liquid at 352 EXPERIMENTAL ENGINEERING the temperature corresponding to the pressure Py. % stands for the latent heat of vaporization at pressure P, = Py. The factor x, with proper subscript, expresses the quality of the vapor. Heat discharged per lb. of vapor =7, (x,— Xa) = T, (fe- ga) B.teu. (84) Here r, is the latent heat of vaporization at the pressure Pg= P.. The work done is of course equal to the heat supplied less the heat discharged, and the efficiency may be written: Xe — 7, (Ko— Ka) _ (T,— T,) (¢o- $a) Efficiency = Xe T, (Ps— $a) oe utile) HT, =e — F; I T. (85) Note: Carnot Cycle with Wet, Dry, or Superheated Vapor. It must be evident from an examination of the derivation of the above efficiency formula that the efficiency depends only upon the shape of the Carnot cycle in the T¢ diagram and not upon the properties of the working substance. Since the Carnot cycle must always be made up of two reversible isothermals crossed by two reversible adiabatics, it must always have the same shape when drawn to T¢ codrdinates irrespective of the prop- Ti—T:2 erties of the working substance. Hence the efficiency must be for all cases. 1 (b) Clausius Cycle with Saturated Steam, Figs. 261 and 262. | 1 4 Pa > Prore : i j ~~. -Fics..261, 262. CLausIus CYCLE, SATURATED STEAM. Heat supplied per Ib. of steam -— =o ht B= C, y= Ty) Tg ba) B.Lu., (86) assuming that.C; is constant. Heat discharged = x7,= T, (6.— $a) B.tu. (87) HEAT AND THE PROPERTIES OF GASES AND VAPORS 353 The work done is again the difference between equations (86) and (87), and the efficiency consequently is: Ci(T,— T,) + Ti (bo— be) — Ti (Ge— $a) = OME, T) + TG $0) i SS eo sas (de— ga) “3 hy Cy = tS + T, (Pe oe, fa) It can be shown by inspection of areas in the T¢ diagram that at pe eae ae aot is greater than the term —’ C-T)+T.b- 6)” * T and hence that the efficiency of this cycle is less than the efficiency of the Carnot cycle between the same temperature limits. _ (©) Clausius Cycle with Superheated Steam. Figs. 263 and 264. Efficiency = (88) (89) the term Ts 5 2! i a bb’ Ts a \ tN 1 Ng a a T 7 \ ly, \ P Bog " \ Te y Ne d Cc d ! : iC i 1 ! Vv $, $, $, Plone Fics. 263, 264. CLausius CycLE WITH SUPERHEATED STEAM. Heat supplied =g—g,P n+ @, 7 y- Fa. (go) = Ci (T,— T,) + Ty @o— $a) + Cp (T,— T;) Btu, (91) again assuming that C: is constant, and that C, is constant. Heat discharged = x7,= T,(¢,— a) B.t.u., | 2 (92) Work done = equation (91) — equation (92) Efficiency Ss Cy (T,— T,) + T, (dy— a) oF or (Le= T,) au Tes (¢.— ga) Cl ,— Tt 1, Gr Ga) + C= Ta) oe x, (de= $a) . : C, (fa T,) cue a (bo- Pa) 1 Cg (ea T;) = 1 (93) 354 EXPERIMENTAL ENGINEERING (d) Rankine Cycle with saturated steam. Figs. 265 and 266. xf Pp Lig Latin ’ cf Te d c c " a ct oe i { Vv by Pa $ Pe Py ore Fics. 265-266. — RANKINE CYCLE WITH SATURATED STEAM. Heat supplied =h- Gt wi= Ci(Ti— T,) + T, (bo— $0) B.tu. (94) Heat discharged (along c’c) = (get %e pe) — Ge+ wee) = C, (Te— T,). (95) In equation (95) ~. and x, are best determined from the T¢ diagram. C, is what might be called the mean constant volume specific heat of the wet steam in the temperature range Ty to T,. Heat discharged (along cd) = x,r,= T, (6,— $a) B.t.u. (96) The work done in the cycle is in this case equal to the sum of the quantities in equations (95) and (96) subtracted from the heat quantity in equation (94). ‘The efficiency may be written: Efficiency es C; i= T,) a T, (gy — pa) = C, (Ty az T.) = T, (dbe— $a) Cr(— Tp + T= oa ope Te TA+T, = 6a, C,(T,— T,) + T, ($o- $2) (97) An inspection of the areas developed will show that the Rankine cycle is less efficient than the Clausius cycle, since the work equiva- lent to the area cc’ c’’ is not obtained in the former cycle. HEAT AND THE PROPERTIES OF GASES AND VAPORS 355 (e) Rankine Cycle with Superheated Steam. Figs. 267 and 268. Fics. 267-268. — RANKINE CycLE wiTtd SUPERHEATED STEAM. Heat supplied = Gy tt nt Gy Ty = Ci(T,— T,) + T, (gs — $a) + Cp (T,— T,) B.t.u. (98) Heat discharged (along c’c) = (qv + Xv pv) — (Get %ebe) = C,(T,~ T,) B.t.u. (99) Heat discharged along (cd) = x,7,= T, (¢,— $a) B.t.u. (100) Work done is again equal to the sum of the heat quantities in equations (99) and (100) subtracted from the quantity in equation (98), and the efficiency equation in the final form will be C(Te— T,) oF Ly (b-— $a) Efficiency =1— . a2 Py oo Oe (ror) Nore. In this cycle the point c’, Fig. 268, is of course not necessarily on the steam curve, as indicated. The steam at release may be either superheated, dry or satu- rated, or wet. The second of these cases is represented in the figure. CHAPTER XII. THE MEASUREMENT OF LIQUIDS, GASES, AND VAPORS. 186. General Considerations. — The number of methods of meas- uring fluids is large. The choice of one or the other for any given case depends generally, first, upon the quantity of liquid to be meas- ured, and second, upon the relative accuracy of the several methods that are available. The methods in common use are by most authorities classed under two heads: positive and inferential. A positive method is one in which all of the liquid concerned in any given transaction is subjected to measurement, while by an inferential method only a certain part of the total quantity is measured. The proportion that this part bears to the whole must of course be known. Examples of positive methods are very common. To the class of inferential methods belong the method of Brauer for measuring water (see p. 367) and the use of so-called proportional gas meters for large capacities. Generally speaking, positive methods are more accurate than in- ferential, because they obviate the error involved in determining the proportionality of the part subjected to measurement. Such methods should therefore be preferred; unfortunately, however, the size of the apparatus or appliances required in many cases limits their applicability. Another distinction that can be made between the various methods of measuring fluids is to class them as direct and indirect. The difference lies in the fact that in some cases it is possible to determine the entire quantity of any flowing fluid by direct measurement (weighing or volume determination). In other cases, since quantity is a function of velocity of flow and of stream cross section, total quantity may be found indirectly by determining each of these fac- tors separately. In the majority of cases direct methods are more accurate than indirect, but, again, their field of application is limited to comparatively small rates of flow. 356 MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 3 57 METHODS OF MEASURING WATER oR OTHER LIQUIDS. 187. Classification of Available Methods. — The various methods for measuring water may be enumerated in greater detail as follows: I. Actual weighing. May be positive or inferential. When used positively this is the most accurate method known. II. Measurement by means of orifices, such as weirs, nozzles, Venturi tubes, etc. The accuracy of these methods may be made almost anything by the care taken in arranging and calibrating the orifice. May be positive or inferential but generally used positively. III. Measurement by volume displacement. IV. Measurement by volume displacement in mechanical meters which are practically always hydraulic engines of some kind, being moved by all or a fraction of the liquid flowing through them. The motion is recorded automatically and the instrument is generally arranged to read cubic feet or pounds. Meters of different types have very different degrees of accuracy and even those of the same make and type often vary considerably among themselves and differ from time to time. Where great accuracy is required this method is only permissible when all precautions have been taken to deter- mine the accuracy and constancy of the meter, or other vessel used to obtain volumes. V. Measurement by determining the average velocity of flow in a channel or pipe of known cross section. This method is essen- tially inferential because it is impossible to obtain the velocity of all the material flowing, measurements being taken at different points in the section and averaged. It is often the only possible method, as in the measurement of the flow of large rivers, and for such work it must be considered satisfactory. The devices used for determining the velocity are floats, tachometers, Pitot tubes, hydrometric pen- dulums, current meters, etc. I. MEASUREMENT BY WEIGHING. 188. Methods Used. — As already pointed out, ‘weighing on cali- brated scales is the most accurate method known for determining quantity of water. Its application is frequently limited by the failure of sufficient scale capacity. Where the quantities are greater than can be handled by the scales directly, recourse may be had to au 358 EXPERIMENTAL ENGINEERING indirect method of weighing by means of calibrated tanks. Such tanks, besides having the usual outlet in or near the bottom, should be furnished with an overflow pipe near the top to insure that the top level shall in all cases come the same. The best way to construct such an overflow pipe is to put the pipe through the walls of the tank, reaching to about the center, and to place an elbow on the end, which of course should turn up. This method of construction will make the top level come to the same height very quickly in all cases. Be- fore use, the tanks are calibrated by weighing into them smaller quantities of water until they are filled to the top level. This method is to be preferred to computing capacity by the dimensions. During use it is then merely necessary to keep a record of the number of times each tank is filled and emptied. Since this method is funda- mentally one of measurement by volume displacement it becomes necessary to record the éemperature of the water used for calibration and of that used during a test, in order to make the necessary correc- tions for change of weight per unit volume should the two tempera- tures not be the same. In computing the size and number of tanks required to handle any given flow of water, we must consider the capacity of the supply main and the shape, location, and size of the outlet opening. The supply main capacity, together with the size of the tank, determines the time required for filling, while the time of emptying depends upon the size of the tank and the conditions at the outlet. The usual proceeding is to fix upon the approximate size of the tank, since that is often determined by questions of room, of manu- facturing facilities, etc., and then to determine the necessary number of them by considering inlet and outlet conditions. In some cases of preparing for a test, tanks will be already on hand, and it then merely becomes a question of deciding whether they are large enough. The question of determining the necessary size of supply main for a given desired capacity will be taken up in Art. 218. The time allowance (for weighing, opening, and closing valves, etc.) that should be made over and above the actual time required for filling from a given main, depends altogether upon the kind of tank instal- lation, quality of help employed, etc., and its estimation must be left to the engineer. It might, however, be stated that it is not usu- MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 359 ally the filling but the emptying operation in which trouble may be encountered where large quantities of water are concerned. The time of emptying any prismatic tank (usual case) may be computed from the formula: 2234 eee (V9, =v5,) seconds. (9) CF V2 ¢ This applies to cases where the outlet is in the bottom, but can be applied with sufficient accuracy for approximate estimation in other cases. A = the uniform cross section of the tank in square feet. y,= water level at the beginning, and y, = water level at the end of the emptying operation. Both distances are measured in feet above a certain datum line, taken at the center of the outlet orifice, if that should be located in the side, or at the bottom of the tank if the outlet is located in the bottom. In any practical case the tank is usually emptied as completely as the location of the orifice permits, in which case y, = 0. C = the coefficient of discharge of the outlet orifice. F = the area of the orifice in square feet, and & = 32.2. The only factor in the above equation requiring judgment in assuming it properly is the coefficient C. Its value can be affected in a multiplicity of ways. Usually there will be a short nipple lead- ing out of the tank, the outlet being controlled by a globe or gate valve. The nipple may be flush with the walls of the tank or pro- ject to a certain extent. Type of valve, length of pipe, and inside projection are all factors which affect C. Its value may be anything from about .s5 to .97 or .98, depending mainly upon conditions at the entrance. For details see Art. 191. In general, a well-rounded (bell-mouth) orifice, flush with the inside walls and with a short tube leading to the valve, gives the most favorable conditions. A certain reduction, upon which there is, however, no definite data, should be made for the coeffictent C that would normally apply to a given orifice for the effect due to valves. A gate valve is in this respect preferable to a globe valve, as it offers much less resistance to the flow. 360 EXPERIMENTAL ENGINEERING Allowing the outlet pipe to project beyond the inside walls of the tank causes a decrease in the value of C. Sometimes, however, especially in the use of calibrated tanks, it is found desirable to locate the lower level quickly or very accurately, and it will be found that an elbow secured to the inner end of the outlet pipe, and turned either up or down, helps matters in this respect very much. Of course the value of C experiences a still further decrease by this proceeding. The arrangement of tanks of course varies with the conditions of use. For the specific case of boiler supply it will in general be found best to have the weighing or calibrated tanks discharge into a tank on a lower level, from which the feed pump draws. Aconvenient arrangement for more than two tanks is to place them in MED an arc of acircle around the supply pipe and to have a single swing pipe which can be brought over each tank in turn. For small work a convenient form of calibrated tank used at Sibley College ~is illustrated in Fig. 269. The round tank is divided by a partition which has an overflow notch near the top. As one side fills the other side is emptied and EG. 209. the valve on that side closed. When the overflow begins, the swing supply pipe is shifted to the empty side, time is given for the overflow to cease, and the first side can then be emptied and made ready. 189. Sources of Error in Weighing. — For accurate work the scales should be calibrated. All valves, connections, and vessels should be free from leaks on the delivery side, as a considerable quantity of liquid can escape from what seems to be an insignificant opening. Evaporation sometimes causes errors of considerable magnitude. With water at ordinary temperatures it may be neglected, but at a temperature above 150° F. it is best to keep all vessels covered. Some of the oils and alcohol may cause trouble in this way at ordi- nary temperatures and this possible source of error should always be recognized and guarded against when necessary. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 361 II. MEASUREMENT BY USE OF ORIFICES.- The general term “ orifices” is in this case intended to cover sub- merged orifices, nozzles, weirs, and Venturi tubes. 190. Submerged Orifices. — These orifices are in nearly all cases circular in cross section, and circular orifices will be the only ones here considered. In the flow of water or other liquids the particles are urged on- ward by gravity, or an equivalent force, and move with the same velocity as bodies falling through a height equal to the head of liquid exerting the pressure. If this head in feet be represented by h, Fig. 270, and the corresponding veloc- ity in feet per second by V, we have, neglecting friction losses, V =~V2 gh. (2) If we denote the area in square feet of the discharge orifice by F, the quantity discharged in cu- bic feet per second by Q, then, theoretically, ae Q=VF=FV2 gh. (3) Fic. 270. It is found, however, in the actual discharge of liquid, that, except in rare cases: 1. the actual velocity of discharge is less than the theoretical; 2. the area of the stream discharged is different from the area of the orifice through which it passes (f different from F). These losses are corrected by introducing coefficients. The coefficient of velocity is the ratio of the actual to the theoretical velocity, and is represented by Cy. The coefficient of contraction is the ratio of the least area of cross section of the discharged stream to the area of orifice of discharge, and is denoted by C,. The coefficient of efflux or discharge is the product of these two quantities, and is represented by C. The theoretical velocity V is attained most nearly at the minimum section of the stream in contact with air and the formulas are based upon the assumption that the maximum velocity is at- tained in this section. Hence the necessity of the contraction 362 EXPERIMENTAL ENGINEERING coefficient. The coefficient of velocity is very nearly unity for any smooth orifice and becomes of importance only when the liquid flows for a considerable distance over rough surfaces. The actual discharge, then, becomes Q, = CQ =CVF = CF V2 gh cu. ft. per sec. (4) If V, denotes the actual velocity of discharge, we shall have Vz = Cy V2 gh. (s) The coefficient C, may be determined by experiment; it is nearly constant.for different heads with well-formed simple orifices. 191. Value of the Coefficient C. — In practice it becomes necessary to determine the coefficient C by actual experiment, unless a standard calibrated orifice is available, according to which another for use can be made. For accurate work it is doubtful if even this pro- ceeding is justified on account of the difficulty of duplication. Where the head under which the flow takes place varies widely, it further becomes necessary to determine C for various values of h, as the constant may vary slightly with the head for the same orifice. As already pointed out, C for various orifices varies over a rather wide range, depending mainly upon conditions at entrance. The following figures show what values may be expected under the different conditions likely to be en- countered. The constants for the orifice in thin plates (under a) are those compiled by F. Van Winkle in an article in Power,* while those under (b) are taken from Hiitte and are originally due to Weis- bach. (a) Orifices in thin plates, sharp edges. By this is meant either an orifice in a thin plate, or, if the wall is thicker, that the inner edges are so sharpened that no other part of the wall interferes in the stream filaments (see Fig. 271). This is probably the best type of standard orifice for water as long as the edges are unim- * Power, Aug. 25, 1908. 7? Zs INL LLL EZ Fic. 271. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 363 paired, because any wall effect is eliminated. The constants in the following tables apply to cases where there is complete contraction, and they may also be used for orifices in the bottom of vessels. COEFFICIENTS OF DISCHARGE FOR ROUND VERTICAL ORIFICES IN THIN PLATE. Head in Diameter of Orifice in Feet. Feet. v.02 0.04 0.07 o.I0 v.2 v.6 a.u 0.6 0.65 0.63 v.62 v.61 0.60 0.8 0.65 0.63 v.62 v.61 0.60 0.59 1.0 0.64 o. 62 0.61 0.61 0.60 0.59 2.0 0.63 0.61 0.61 0.60 0.60 0.60 | 0.60 4.0 0.62 0.61 0.60 0.60 0.60 0.60 0.60 6.0 0.62 0.61 0.60 v.60 0.60 0.60 0.60 20.0 0.60 0.60 0.60 v.60 0.60 0.60 0.59 100.0 0.59 °.59 0.59 0.59 0.59 0.59 0.59 COEFFICIENTS OF DISCHARGE FOR SQUARE VERTICAL OPENINGS IN THIN PLATE, Head in Side of Square in Feet. Feet. 0.02 0.04 0.07 o.r 0.2 0.6 I.o0 ve v.66 v.64 us 62 0.62 0.61 0.8 v.65 v.63 v.62 0.62 0.61 v.60 I.0 0.65 0.63 o. 62 v.61 0.61 v.60 v.60 2.8 0.64 0.62 0.61 0.61 0.61 0.60 0.60 4.0 0.63 0.61 0.61 0.61 0.61 0.60 0.60 6.0 0.62 0.61 0.61 0.61 0.60 0.60 0.60 20.0 0.61 0.60 0.60 v.60 v.60 0.60 0.60 100.0 0.60 0.60 0.60 0.60 v.60 0.60 v.60 COEFFICIENTS OF DISCHARGE FOR RECTANGULAR VERTICAL ORIFICES ONE FOOT WIDE IN THIN PLATE, Head in Depth of Orifice in Feet. Feet. v.125 v.25 v.50 v.75 Tae Tacs 2.0 0.6 0.63 0.63 o. 62 v.61 0.8 0.63 0.63 0.62 0.61 0.61 I.0 0.63 0.63 0.62 0.61 0.61 0.63 2.0 0.63 v.63 0.62 0.61 0.61 0.62 0.63 4.0 0.62 v.62 v.61 0.61 0.61 0.61 0.62 6.0 0.62 o. 62 0.61 0.60 0.60 0.61 0.61 I0.0 0.61 0.60 0.60 0.60 v.60 0.60 0.60 0.60 v.60 v.60 0.60 364 EXPERIMENTAL ENGINEERING (b) External mouthpieces or ajutages, perpendicular to walls. Area F in formula always that corresponding to diameter d in the figures. Fic. 272. Shape of Fig. 272: Angled = 0° 53° 113° 223° 45° 674° go° Edge a strongly chamfered, C= .07 05 .02 .88 .75 .68 .63 G=3a) Edge @ sharp, C = 83.94.92 85 (d = 2.6 d) Shape of Fig. 273: = 1 23 12d Edge @ sharp, C = 88 .82 77 Edge a slightly rounded, 1=3d, C=.90. Edge a strongly rounded (bell mouth), L=3d, C =.097. Shape of Fig. 272, except that flow is in opposite direction: Angle} = © go5° 45° 672° 90° C=.54 55 -58 .60 .63 @=3¢4) Fic. 275. Shape of Fig. 274 (bell-mouth orifice): For] = .6 d, C = -96 — 1.00, depending upon smoothness of walls. Shape of Fig. 275: Depending upon length of piece and velocity of efflux, C may be from .96 to 1.5, referred to smallest cross section. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 365 192. Method of Calibrating an Orifice. — The method of deter- mining the constant C is a very simple operation. Means must be provided for weighing the liquid, while the rest of the work consists principally of determining the head h. The orifice must be care- fully measured in order to determine F accurately. Runs should be made under various heads, and curves drawn between coefficient C and head #, to properly exhibit the relation. Since accurate scales are a necessity for calibration, the ques- tion sometimes arises as to whether it would not be better to use scales throughout and to discard the orifice. The advantages of the use of an orifice over weighing are, however, manifold. An orifice, when properly cared for, needs to be calibrated only once, and the relation of constant C to head / can be used with con- fidence at any time thereafter. The labor involved in making measurements is much less than with weighing, since only one reading, that of the head, is required for each determination. Further, it is much easier to transport an orifice from place to place than it is to handle scales or meters. Finally, there is the possibility, by duplicating orifices and operating them in par- allel, of measuring quantities of liquid far beyond ordinary scale capacity. Regarding the latter point, care should be had to note that the several orifices are not too close together, since they may influence one another. The head over an orifice should be such that the sur- face of the water is not affected by the flow and there should be room around each orifice equivalent to at least the square of ten times the orifice diameter to prevent mutual interference. The head on an orifice is measured to the center of the section of least area of orifice. ‘The head # is always expressed in feet, since g in formula (4) is in feet. It may be measured directly, or, where the heads are high, it may be determined by means of a gauge or other:manometer. In the latter case, pounds pressure per square inch or inches of mercury must be transposed to equivalent head in feet of water for substituting in the formula. For quick con- version, the following table may be of service: 366 EXPERIMENTAL ENGINEERING TABLE SHOWING RELATION BETWEEN PRESSURE EXPRESSED IN POUNDS, AND THAT EXPRESSED IN INCHES OF MERCURY OR FEET OF WATER, 70° F. Pressure in Pounds per Seen siicia aetna Feet of Water. | Inches of Water. cury. I 2.0378 2.307 27.68 2 4.0756 4.014 55-36 3 6.1134 6.921 83.04 4 8.0512 9.23 110.72 5 10.1890 II.54 138.40 6 12.2268 13.85 166.08 7 14.2646 16.15 193.76 8 16.3024 18.46 221.44 9 18.3402 20.76 249.12 Io 20.3781 23.07 276.80 Where any other liquid than water is concerned, and h is measured directly, equation (4) will give the correct result in cubic feet dis- charged per second. To convert this into weight requires a knowl- sdge of the specific gravity of the liquid at the temperature of test. When the head is measured by means of a pressure gauge, the head hk to be used in the formula must be the height in feet of a column of the liquid concerned which will exert the pressure per square inch shown by the gauge. Most liquids other than water change specific gravity (weight per cubic foot) considerably with temperature, so that the influence of the temperature factor cannot always be left out of account. Even the specific gravity of water, contrary to a general assumption, varies enough to cause considerable error in some cases if temperature differences are neglected. Thus, water at 4o degrees weighs 62.42 pounds per cubic foot; at 150 degrees its weight has decreased to 61.18 pounds per cubic foot. (See Kent, p. 688.) 193. Use of Orifices for Measuring Continuous Flow. — In prac- tical work, orifices are not as much used for measuring continuous flow as the simplicity of the method would seem to warrant. The reason probably is that in one respect at least this simplicity is more MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 367 apparent than real, that is, with reference to determining the head A. For widely varying rates of flow the determination of the average value of Vh is not easy, unless a device recording the variations _ continuously be employed. This fact at once restricts the use of the method to cases in which h is fairly constant. The proper arrangement of baffle plates to obtain still water around the orifice is impor- tant. (See Fig. 276.) There is a method of orifice measurement, due to Brauer,* which avoids the necessity of noting the head /, and which is capable of being used for large capacities and varying rates of flow. Suppose that the vessel is fitted with two orifices of exactly the same proportions but of different diameters. Then the quantities of water flowing will be directly in the ratios of the areas of the two openings. This assumes that the constant C is the same for the two orifices for the same heads, which is true within the other errors of measurement. It then becomes necessary merely to weigh or otherwise determine the quantity of liquid flowing through the small opening, when the quantity flowing through the other is found by simply multiply- ing by the ratio of the areas. This scheme is capable of easy expansion of capacity by using several large orifices in parallel, the quantity of liquid subject to actual weighing remaining the same in all cases. The accuracy of the scheme depends directly upon the degree of accuracy with which the diameter of the small orifice is determined. The error made here can easily exceed allowable limits. Thus, if the small orifice is called .25 inch in diameter and is really only .24 inch, the area of the small orifice will be brought into the com- putation about 8 per cent too large, making the multiplier to obtain the quantity flowing from the orifice too small by about the same Fic. 276. * Zeitschrift des Vereins deutscher Ingenieure, 1892, p. 1493, 368 EXPERIMENTAL ENGINEERING percentage. Errors of this magnitude are not usually permissible and the computation points out the necessity of accurately deter- mining the diameter of the small orifice. 194. Measurement by Means of Nozzles. — The term 1o022Ie usually refers to a conically convergent mouthpiece of the type shown in Fig. 272, screwed to the end of a hose or pipe. In the majority of cases, however, the length of the nozzle is greater than two to three times the smallest diameter, for which proportions the constants ac- companying Fig. 272 are given. In other cases the nozzle may come within these proportions, and even an orifice in thin plate, when fastened by means of a cap to the end of a pipe, is commonly termed nozzle. From the foregoing it will be seen that the quantity of liquid discharged by a nozzle can be computed by equation (4); that is, oa OQ =CFW2 gh. (6) The area F is the smallest cross section of the nozzle, in the ordi- nary type located at the extreme end. The head / is determined by a pressure gauge, the read- ing of the gauge being re- duced to feet. Note that the head must be meas- ured to the level of the smallest cross section of the nozzle. Thus, in Fig. 277 a, the distance h’ is to be added to the head shown by the gauge, while in Fig. 277, the distance 2 h’ should be subtracted to Fic. 277. get the true head. The coefficient of discharge C is again the product of the velocity coefficient C, and the contraction coefficient C,. In nozzles of some length as compared with the diameter at the end, the constant is likely to be considerably affected by the conditions of the walls. Since the constant also varies considerably with the angle of con- vergence, no general figures for the constant for such nozzles can be given and the only accurate method is to calibrate. The general Becca > ss Sree se MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 369 directions given on page 365 for calibrating an orifice also apply in this case. 195. The Venturi Tube or Venturi Meter for Measuring Water or Other Liquid. — The Venturi tube is in principle nothing but an orifice placed in a pipe and through which the liquid to be measured is forced. The contracted passage increases the velocity of the liquid and causes a pressure loss, converted into velocity. This pressure loss may be measured, and since it is a function of the velocity, we are enabled to compute velocity and thus to compute the rate of flow through the pipe. The Venturi tube as now built is shown in cross section in Fig. 278. It consists in reality of two convergent nozzles placed end to end with the smaller ends joined. The end through which the water enters is usually called the “upstream end,” the other is desig- nated the “downstream — end,” while the section of smallest diameter is known as the “throat.” For measuring water it is desirable to have the throat area of sucha size that the velocity through it shall be between the limits of 15 and 35 feet per second. The upstream end and the throat section are surrounded by pressure chambers, with which the respective sections communicate by means of a number of small openings, as shown. Gauges or other manometers connected to these chambers will then indicate the pressure heads at the sections, or by connecting the chambers to the two ends of a U-tube manom- eter, the reading of the latter will indicate the loss of pressure head between the upstream section and the throat. The equation for the tube is best developed on the basis of Ber- nouilli’s theorem, which states that the total energy of a steadily flow- ing stream remains constant except for friction losses. In Fig. 279, let the pressure heads shown by the manometers at the up- and downstream section be H, and H,, above a certain hori- zontal plane, as indicated. The downstream section is usually made equal to that upstream, so that H, will only differ from H, by the friction in passing through the tube, assuming the latter hori- Fic. 278. — VENTURI TUBE. 1 370 EXPERIMENTAL ENGINEERING zontal. The pressure at the throat may be anything, depending mainly upon the relation between the upstream and throat areas. If positive, it will be represented by some pressure head H,; if nega- tive (that is, if a vacuum), it will sustain a water column h,. In that case the value of H, becomes H— h,, in which H is measured as shown in Fig. 279. Let the velocity in feet per second upstream be V,, that at the throat be V,, then according to the theorem cited, equating total If Negative si If Positive LOU La Up Stream Section Down Stream Section Datum Plane Fic. 279. energies, we can write for the upstream and throat sections, assum- ing the tube horizontal, and the datum plane to coincide with the axis of the tube, so that H =0, ve 2§ 2 Hy + = Hy + + Hy (7) ‘ oe . : In this equation soe the velocity head equivalent to a velocity V, while H, is the head lost by friction between the up- stream and throat sections. Note that all terms of the equation are expressed in feet, and that if the pressure heads are measured either by gauge or by mercury manometer the readings must be reduced to feet of water. Herschel, in his experiments, showed that the loss of head H,, due to friction, is very small in a properly made tube, and can be taken care of in the final formula by a coefficient. For the present, there- MEASURE-MENT OF LIQUIDS, GASES, AND VAPORS 371 fore, H, can bé neglected. Further, if F, = the area in square feet of the upstre’am section, and F, the area of the throat section, we must have from which \ Substituting this in equation (7) an 2 main mel or, solving for the throat velocity, ere VF, — F2 Equation (8) is then = by a coefficient (C) to adapt it to actual conditions. The flow through the pipe may then be directly computed from CFF, ~ “VP — Fy} ; In practice the pressure pipes leading from the two pressure chambers are connected to the two legs of a manometer, thus de- termining (H, — H,) directly. Note that the measuring liquid in the manometer must be heavier than water. Mercury is the liquid best adapted, but where small-pressure differences must be deter- mined, either some multiplying form of manometer must be used, or a liquid only a little heavier than water, but which will not mix with water, can be employed. Note also that the connections leading to the manometer must be free from trapped air. Herschel’s experiments to determine the constant C gave values varying from .94 to 1.04. Out of fifty-five experiments, only four gave a value greater than 1.01, and only two a value less than .96. The tube experimented with had an upstream diameter of close to 1 foot, while the throat diameter was close to 4 inches. It seems from this that for ordinary work the coefficient C may be taken = 1.0. For more accurate work, of course, the tube requires calibration. The tube diameters should be carefully measured, as errors made with regard to them affect the result in the square. V,= -V2 g (H, — H,) ft. per sec. (8) Q =CFV, FY? g (Hi, — H,) cu. ft. per sec. (9) 372 EXPERIMENTAL ENGINEERING , C = 1.00 exactly if 4(H, — H,) is deducted from (H, — H,), so accounting for the friction head H; between upstream and throat sections. This form of meter is very satisfactory and car, be built to fit any commercial size of pipe. It is not subject to appreciable wear and cannot be easily damaged by any foreign substances carried by the liquid. For best results the liquid must be free from mechanically en- trained gas and must have fairly constant temperatures. It is possible to meter the liquids at widely differing temperatures by making allowance for changes in size of meter and density of liquid. For comparatively brief tests and where the flow does not differ widely, the difference (H, — H,) may be noted at stated intervals. Where the pressure differences vary considerably it will be more accurate to find the average of the square roots of (H, — H,) than to find the square root of the average difference. 196. The Flow of Water over Weirs. — A weir, or weir notch, is primarily a dam or obstruction over which the water (or other liquid) is made to pass. The head of water producing the flow is the verti- cal distance to the surface of still water from the center of pressure of the issuing stream. The depth of water over the weir is measured vertically from the surface of still water upstream to the level of the bottom or sill of the notch. It should be noted that this depth is usually referred to as the head on the weir and is the factor generally de- signated by h or H in most weir » formulas. Rectangular Weir. Theoretical Equation. — Any small particle of water at a distance y, Fig. 280, below the surface of the stream has imparted to it a velocity V = V2gy. This is the velocity possessed by the narrow vertical plane of height dy and of length b, where 6 is the width of the weir notch. Hence the volume of water discharged through the infinitesimal orifice bdy will be Fic. 280. Q = bdyV = bdy V 2gy. (10) MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 373 Integrating between the limits y = o and y = h, we will have h Q=bv El, yidy = 2) V2gh'cu. ft. per sec. (11) Note that in equation (11) 6 and /# must be measured in feet. Now it has been found that, due to various causes, the actual quantity of water discharged by a weir of given proportions is less than that found by equation (11). Hence the introduction of a coefficient C, and the practical form of the equation is then Q =2Cb V2 gh cu. ft. per sec. (12) This coefficient for small and accurate work should always be determined by calibration, but for larger work this proves in many cases impossible, and it will then have to be assumed upon the basis of other experiments. This makes it important to look into the causes influencing the value of C. The causes operating to make C I “ less than unity are primarily the : following: i The depth of water (y) over the crest is less than the head /, meas- ured to still water, see Fig. 281. Contraction also takes place on the under side of the stream at a, if the stream is free (aired) under- neath. If weir measurements are -to be accurate and consistent, care should always be taken to see that the stream is free under- neath after passing the notch, and does not in any way adhere. Contraction of the stream sidewise (side or end contraction) may Fic. 281. PLAN VIEW PLAN VIEW Fic. 282. —SHowrnc SWE or END Fic. 283. — WEIR WITH SIDE OR END CONTRACTION IN WEIRS. CONTRACTION SUPPRESSED. also occur, Fig. 282, which further decreases the actual flow, unless these contractions are suppressed, as in Fig. 283. 374 EXPERIMENTAL ENGINEERING Another factor strongly influencing the value of C is the velocity of approach. If the water has considerable velocity as it approaches the weir, C will be increased. This effect is connected with the relation between the total depth of the channel H and the head h, Fig. 281. While the suppressing of end contraction may increase the value of C, it should also be remembered that for small weirs this sup- pression may bring the side walls so close that the friction of the water against them begins to affect the discharge. It must be evi- dent from the foregoing that there is rather wide latitude in the choice of the value of C, and that all conditions of use of the notch must be definitely known before an intelligent choice can be made, if no calibration is possible. From experiments made at Lowell, Mass., J. B. Francis concluded that the effect of end contraction could be taken into account by subtracting from 0, the width of the crest, an amount equal to one- tenth of the head / over the weir. If # = the number of end con- tractions, his formula reads, Q =2C (6 — .1 nh) V2gh? cu. ft. per sec. (13) For the ordinary rectangular notch, since 7 = 2, this reduces to Q=2C (b—.2h) Vagh® = 5.3 C (6 — .2 h) hb (14) Francis found the value of C in his experiments close to .62. If there is considerable velocity of approach, it must be corrected for. This can be done on the consideration that the velocity head ee / Ye (15) where V’=velocity of approach in ft. per sec., the value of which can be approximately determined at first by dividing the flow, as com- puted by ordinary formula, by the cross section of the weir channel. Church (“Mechanics of Engineering,” Art. 501) shows that taking into account the velocity of approach, but disregarding the con- tractions, the equation for the rectangular weir becomes 0 =2CbV2gl(ht+ h’)® — h’3)cu. ft. per sec. (16) With the oe correction for contraction, the final form of the equation then is, MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 375 Q=2CV2¢ (b—.1 mh) [(h +H)? — he?) cu. ft. persec. (17) This complete equation is little used; instead equation (14) is used, and changes are made in C to account for the effect of veloc- ity of approach. See the discussion below regarding the value of C. The variation of C has been studied by a number of experimenters, and the results of these made by Costel, Poncelet, Lesbros, Francis, Ftely-Stearns and by Frese were collaborated by the latter in the Zeitschrift des Vereins deutscher Ingenieure, 1890. Later work by Hansen has confirmed Frese’s conclusions.* These were as follows: For weirs without end contraction, — .0021 0.00064 | i(mctasy oo eek This constant C, may be used directly in connection with equation (12). Where the velocity of approach is considerable, however, (say for small weir greater than 4 ft. per sec.), C, must be multiplied by another factor ¢ > 1, to allow for the increased discharge. Frese found this factor to be Thy €=.iIt+ “55 (&) so that C=Ce. For the significance of # and H, see Fig. 281. C, = .615 + Example: In a weir without end contraction, suppose = .50 feet and H = 2.5 feet. Find C to be used in formula (12). Then so 0.5\" C, = .615 + —— = .616, ande = 1+ .55 a2 = 1.022, So that the coefficient C ate = .616 X 1.022 = .629. Weirs with Full Contraction. —This case is more complicated than the other because the degree of side contraction depends upon the relation between width of notch and total width of canal. Wher- ever possible it is therefore best, on the score of accuracy, to suppress the end contractions. Where this cannot be done, have the canal of such a size that both the velocity of approach and the influence * Another paper containing an extended discussion of weir formulas is contained in “‘ Water Supply and Irrigation ” Paper No. 200, U. S. Geol. Survey (R. E. Horton). This touches upon the most important investigations, with the exception apparently of those of Frese. 376 EXPERIMENTAL ENGINEERING of the side walls upon the contraction can be neglected. For such conditions Frese gives _ .O17 az 075 C, = .576 + h (meters) + .18 6 (meters) + 1.2 = sie 0.0052 0.0023. h (feet) +0.59 5 (feet) + 3.9 This value of C, again applies to equation (12). For the case where the canal has a width B and a depth H and neither the velocity of approach nor the effect of the walls can be neglected, the above coefficient C, must again be multiplied by a factor = | 4 + ¢ (=) os 25 (5) | H 0375 h ) aif oar 302 (i The coefficient for equation (12) will then again be C=Ce Example: Assume h = 1 foot, b = 5 feet, H = 4 feet, and B = 10 feet. Find C. in which e = 025 + Gs, Sak 4, 9,00§2_ 0.0023 _ ag a 57 t+ 0.59 5 + 3.9 5°4 Ls 0.0375 en a (4)? + 0.02 Ponte 5\2 r\2 €=i+ [-25( 5 + 79 | (:) = 1.034 C= Cy = .584 X 1.034 = .604. Weir notches having shapes other than the rectangular have some- times been employed. The principal ones among these are the triangular notch and the trapezoidal (Cippoletti) notch. Triangular Weir Notch. —The triangular weir has the advan- tage that the cross section of the stream is geometrically similar in form whatever the value of h. Hence the discharge coefficient is very regular in its variation and is more nearly constant than for other forms of weir. It has been found * that C for a triangular n weir varies with h by the function C = m + Was and ” depend- * Strickland, London Engineer, Oct. 28, 1910, p. 598. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 377 ing upon the angle of the notch and upon conditions of approach. The triangular weir with an acute angle of opening is peculiarly well fitted for the measurement of small flows. For large values of 0 (see Fig. 284), say about 135 degrees, researches on the value of C are as yet lacking. In Fig. 284, @ is the angle of opening, b the width of the crest for any head h. As in the case of the rectangular weir, the velocity that any small particle of water has at a distance y below the sur- face is ey 1 1 le- — ——~-—---f------- - - - -> V=~2 gy ft. per sec. (18) Fic. 284. If 0’ represents the width of the notch at the head # — y, and dy the thickness of the filament of water at h — y, the quantity dis- charged will be Q = bldyV2 gy cu. ft. per sec. (19) But 7 2 ia. from which 6 =h 2 tans, and similarly > v= (hy) 2 tan’. Hence 6 — of Q= 2 tan = (h — y) by V2 gy =2 tan (h — y) V2 gy dy 0 = C /2 g tan yee cu. ft. per sec. (20) For practical use this equation is of course again adapted by intro- ducing the coefficient C, so that Q=C = V2 g tan a cu. ft. per sec. (21) If the angle at the apex = 60 degrees, tan 30° = .5773, and Q = 2.46 Chi cu. ft. per sec. (22) If the angle = go degrees, tan 45° = 1.00, and Q = 4.28 Chi cu. ft. per sec. (23) Trapezoidal Notch. —To avoid the corrections for end contrac- tion, Cippoletti in 1886 proposed the use of a trapezoidal notch of 378 EXPERIMENTAL ENGINEERING such dimensions that the area of the stream flowing through the triangular portion at the sides should be just sufficient to correct for the contraction of the stream in a rectangular weir. The proportions of such a weir, in terms of the length at bottom of the notch, are as follows: height equal to six-tenths the bottom length, width of top equal to the bottom plus one-fourth the height, added to each side; the tangent of the angle of inclination of the sides equal to 0.25. It is asserted that such a weir will give the discharge with an error less than one-half of one per cent. The formula for the use of such a notch would be simply Q = 3 Cbh V2 gh = 3.33 bn}, (24) assuming that C = .62, and that the opening of the sides does truly compensate for variation of C. 197. Methods of Measuring the Head over Weirs. — The head in all cases is to be measured at a distance sufficiently back from the weir to insure a surface which is unaffected by the flow. The channel ‘above the weir must be of sufficient depth and width to secure com- paratively still water. The addition of baffle-plates, some near the surface and some near the bottom, under or over which the water must flow, or the introduction of screens of wire netting, serves to check the current to a great extent. Such an arrangement is some- times called a tumbling-bay. The object of the baffle-plates is to secure still water for the ac- curate measurement of the height of the surface above the sill of the weir. The same object can be accomplished by connecting a box or vessel to the water above the weir by a small pipe entering near the bottom of the vessel; the water will stand in this vessel at the same height as that above the weir, and will be disturbed but little by waves of eddies in the main channel. The height of water is then obtained from that in the vessel. Professor I. P. Church has the connecting-pipe pass over the top of the vessel and arranged so as to act as a siphon. The accurate measurement of the head is of the greatest impor- tance in weir measurements and careful work is necessary in all cases. The Hook-gauge. —'This consists of a sharp-pointed hook at- tached to a vernier scale, as shown in Fig. 285, in sucha manner that the amount it is raised or lowered can be accufately measured. To MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 379 use it, the hook is submerged, then slowly raised to break the sur- face. The correct height is the reading the instant the hook pierces the surface. To obtain the head of water flowing over the weir, set the point of the hook at the same level as the sill of the weir. The reading taken in this posi- tion will correspond to the zero-head, and is to be subtracted from all other readings to give the head of the water flowing over the weir. In some forms of the hook-gauge the zero of the main scale can be adjusted to correspond to the zero- head, or level of the sill of the weir. A type of hook-gauge used by Professor Frese has three points instead of one, all three being arranged in aright line. The instrument is so constructed and so set that two of the points pierce the water surface from below, as in the ordinary type, while the third (middle) one must touch the surface from above. Floats. —Floats are sometimes used. They are made of hollow metallic vessels, or painted blocks of wood or cork, and carry a vertical stem; on the stem is an index-hand or pointer that moves over a fixed graduated scale. 198. Conditions Affecting the Accuracy of Weirs. — 1. The weir should be preceded by a straight channel of constant cross section, with its axis passing through the middle of the weir and perpendicular to it, of sufficient length to secure uniform velocity without internal agitation or eddies. 2. The opening itself must have a sharp edge on the upstream face, and the walls cut away so that the thickness shall not exceed one-tenth the depth of the overflow. 3. For complete contraction, the distance of the sill or bottom of the weir from the bottom of the canal should be at least three times the depth on the weir, and the ends of the sill should be at least twice the depth on the weir from the sides of the canal. 4. The length of the weir perpendicular to the current should be about three or four times the depth of the water. 5. The velocity of approach should be small; for small weirs Fic. 285. HOOK-GAUGE. 380 EXPERIMENTAL ENGINEERING it should be less than 6 inches per second. Where this condition does not obtain, proper correction should be made. 6. The layer of falling water should be perfectly free from the walls below the weir, in order that air may freely circulate underneath. 7. The head on the weir should be measured with accuracy, at a point back from the weir unaffected by the suction of the flow and by the action of waves or winds. 8. The sill should be horizontal, the plane of the notch vertical. 199. Effect of Disturbing Causes and Error in Weir Measure- ments. — 1. Incorrect measurement of head. This may imcrease or decrease the computed flow, as the error is a positive or negative quantity. 2. Obliquity of weir; the effect of this or of eddies is to retard the flow. 3: Velocity of approach too great, sides and bottom too near the crest, contraction incomplete, crest not perfectly sharp, or water clinging to the outside of the weir, tend in each case to increase the discharge. The causes tending to increase the discharge evidently outnumber those decreasing it, and are, all things being taken into account, more difficult to overcome. 200. Directions for Calibrating Weirs, Nozzles, and Venturi Meter. — This experiment combines the determination of the constant used in the flow formula for the three appliances mentioned. The water is sent through a Venturi meter to a horizontal header pipe of considerable capacity, into the bottom of which are several nozzles or orifices of varying construction, from each of which the water may be turned on or off as desired. The water discharges into a tumble- bay and flows over a weir without end contraction. As arranged in Sibley College, the water next reaches another tumble-bay at a lower level and is finally discharged over a rectangular notch with full contraction into tanks on scales. The following are the directions: Apparatus: Tanks and scales, hook-gauges for weirs, pressure gauge for nozzles, pressure gauges and manometer for Venturi tube. 1. Accurately level the sills of the weirs and see that the notches are in vertical planes. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 381 2. Take the zero reading of the hook-gauges, by setting the point of the hook with a spirit level or other means at the level of the sill. 3. Turn off all of the cocks at the gauges; open valve above Venturi tube very slowly; open cocks at gauges; open valve to nozzle to be tested slowly until it is wide open. In making a run, put a tare weight of pounds on the scales, then adjust the hook-gauges so the points just pierce the surface of the water. When the flow is steady (the level at the hook-gauge remaining constant), close the discharge valve of the weighing tank. Note the time to nearest second when the beam floats; then put—— pounds on the scale and note the time when the beam again floats.* The difference in time gives the number of seconds for the flow of —— pounds. At each different pressure on the Venturi meter the following observations are to be made: a, Pressure at entrance to Venturi tube. b. Pressure at throat of Venturi tube. c. Pressure in receiver at nozzles. d. Hook-gauge readings for each weir. e. Weight of water discharged. f. Time to nearest second. In addition to the above runs at a sided series of pressures, the following runs are to be made: g. Fully open all of the valves controlling the flow through the nozzles, then slowly open the valve at the entrance to the Venturi tube until a maximum difference is obtained between the Venturi tube gauges. Make a run of approximately pounds net of water, taking the same observations as before. This run is a maxi- mum discharge through the Venturi. h. For a maximum discharge over the weirs, in addition to all the nozzle valves being wide open, feed from a secondary supply pipe. Now very slowly open the valve at the Venturi tube until the water fills the weir notch; the water must not touch the upper edge of the notch. Makea run of pounds net, taking the usual observations. The. forms used for recording the observations and computed quantities follow. * Entrance of water to weighing system must be horizontal or nearly so for this method of weighing to be correct. EXPERIMENTAL ENGINEERING 382 SIBLEY COLLEGE, CORNELL UNIVERSITY. —DEPARTMENT EXPERIMENTAL ENGINEERING. CALIBRATION OF NOZZLES. Date...... Observers . Diametés:. oc 5csccsias ca apeaiaee acess CYOSS SOCUOR, 204 dance eae hetsw evade ne een Venturi Readings. ‘adieyo -sIq_ jo quaroyyaog (a)-(v) linquaA UO pray ul goudtoyiqd [e10OL *(worq08g payoesqu0g) q 493 -9uIOUrY JO asney (‘aoursjuq) Vv 4} -9uIOUR IO adney Nozzle Coefficient. sasleyosiq “APOOTIA, “uolqpoeIJUOD ‘vag Jed “4g ‘Jef Jo ApO0TAA “298g god “3g ng ‘asreyosiq : 4 ° . wo 4 3 *ssO1n) 2 Ee ‘ore | 5 2 Jayeyy JO 2097 b2 o a g ‘uy ‘bg tad spunog *spuoseg Ul UOlyeIng ‘uny jo ‘oN SIBLEY COLLEGE, CORNELL UNIVERSITY. — DEPARTMENT EXPERIMENTAL ENGINEERING. CALIBRATION OF WEIRS. FORM siya ais gp atdurwaia ke we HN aNSe. Sy wiogy Daten is4 ea cules Menno hel oan ace Observyers...¢¢25504% Geena be eee’ Wengthi | oe Nh Po « ii aor BX A HESS atc si SMaIOg Xog 10}uMO, . | eS \ aryoeg YIOD ay tun] cr may 9 [aed Soug—prp Eos = aaa xog 197009 —_— zayaN0g: 3 IOMOTOT xog JUNG xog s9}UN0N, pry xog sayahop 396 EXPERIMENTAL ENGINEERING quite severe on the meter, and it pays in general to install hot-water meters in a by-pass to prevent delays in the operation of a plant due to meter troubles. 205. The Calibration of Water Meters. — It should be taken as fundamental that no water meter of whatever make should be used without calibration, and not without frequent calibration if the work is of any importance. It is essential that the method of calibration should reproduce the conditions of use. It is consequently necessary in all cases where meters are used to note (a) the pressure, (0) the temperature, and (c) the rate of flow, in order to be able to reproduce these conditions when desired. The temperature reading is also -- necessary for the reduction of the meter readings, which are in cubic feet, to pounds. In any test in which a meter is used it is usually best to install the meter in a by-pass. This is done for the double purpose of avoiding serious interruptions (as in boiler trials, for instance) and also to be able to calibrate the meter on the spot. For the method of doing this, see the meter connections recommended in the Code for Boiler Testing, Chapter XVII. As a general rule, applicable to all meter calibrations, it may be stated that the greater the quantity of water drawn and weighed at the proper rate of flow, the better. The upper limit in this respect is generally soon reached on account of the limitations of tanks and scales, but for large meters it is almost necessary to provide capacity for not less than 20 to 30 cubic feet. It is generally more accurate not to draw a certain weight of water, but to operate the meter while the pointer on the first dial of the register moves from one definite mark on the dial to another definite mark. This avoids the estima- tion of fractional values on the dial between marks. It sometimes happens that a meter is used on the same test under widely varying rates of flow and that the meter constant also varies greatly with the rate of flow. In that case a single calibration at the average rate of flow will not give the true correction factor, and it will be necessary for accuracy to determine the law of variation and to apply individual correction factors to various parts of the meter record. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 397 V. MEASUREMENT OF THE QUANTITY OF LIQUID BY MEASUREMENT OF THE AVERAGE VELOCITY OF FLOW. 206. Measurements of this kind are made in closed pipes or con- duits and in open channels. They are generally confined to cases where the flow of liquid to be measured is too great to be determined by the other methods so far discussed. The principle in each case is to determine the volume as the product of its two factors — cross section of stream and velocity of flow. Determination of the last factor only need here be considered. 207. Measurement of Average Velocity in Open Channels and Streams. — The instruments and appliances used for this purpose come under three or four heads: floating bodies, or floats for short; pressure plates, hydro-dynamometers or hydrometric pendulums; tachometers or current meters; and the Pitot tube. 208. Floats. — For a complete discussion concerning the use of floats for measuring average stream velocity the reader is referred to almost any book treating on water-power development. The method is so little used in purely experimental engineering practice, being hardly accurate enough for efficiency computations, for in- stance, that it will suffice here briefly to point out the method. The floating body should be small and have adensity approximately that of water. Any small piece of wood or other material which will float and which can be observed from the banks may be used. If the stream is a natural one, as distinguished from the symmetrical channels often used for head or tai] races in water-power plants, it is essential that the part of the stream chosen for the trial shall be fairly straight and as nearly as possible uniform in width and depth. The course may be from 50 to 200 feet long, a base line being laid off on the bank. At each end of the base line stretch a cord across the stream at right angles to the base line. These are the so-called transit lines. The transit lines are divided into any convenient number of equal divisions by means of tags fastened to the lines. Measuring the depth at each tag provides a means of drawing a profile of the stream for the up- and down-stream sections, thus de- termining mean cross section. The floats are released, one by one, some distance above the upper transit line, and time and spot of crossing the line are observed, the former by stop watch. The down- 398 EXPERIMENTAL ENGINEERING stream observer similarly notes the place of crossing the lower transit line, and at the instant the float crosses gives a signal to the up- stream observer to note the time. In this way a number of velocities can be obtained across the width of the stream. If the stream is so wide that no cords can be stretched across, the method becomes more elaborate. In that case a theodolite is stationed at each end of the base line. When a float is started, the upper observer sights his instrument on the imaginary transit line and signals the time when the float passes. At the same time the lower observer focuses on the float and when the up-stream observer gives the signal, he reads the angle which locates the float as it crosses the upper transit line. Next the functions of the observers are reversed, the upper one fol- lowing the float and noting the angle as it crosses the lower transit, the instant of which is signaled by the lower observer with his in- strument clamped on the lower transit line. The time of transit has in the meantime been taken with a stop watch by a third observer. Floats are of two kinds, — surface or single floats and sub-surface or submerged or double floats. ‘The use of the latter is based on the consideration that a body simply floating on the surface of a stream may give a fairly accurate indication of the surface velocity, but tells nothing of the mean velocity over the entire cross section, which is certainly less than the surface velocity. Submerged floats are made by fastening a body capable of sinking to a surface float able to sustain the former by means of a light cord or wire. The latter is made of the proper length to maintain the bottom float where wanted, say about mid-depth. With these double floats it is assumed that the top float indicates much more nearly the average stream velocity. For very regular channels, rod floats reaching nearly to the bottom of the channel have often been used. They generally consist of a wood rod, weighted at the lower end so as to float nearly vertical. The method of using them is the same as in the other cases. For a discussion of the limits of accuracy of any of the float measurements, the reader is referred to Frizell’s “ Water Power” and Mead’s “ Water Power Engineering.” The latest development of measurement by means of floats is perhaps that reported in the Zeitschrift des Vereins deutscher In- genieure for April 20, 1907. The method can be applied only in MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 399 regular, artificial channels, but has been found to give very accurate results when used in the tail race of a turbine installation for deter- mining the amount of water used. It consists of an “apron,” con- structed of a very light framework, over which varnished cloth is stretched. This apron e is supported on a carriage c-c (see Fig. 297), which runs on a track a—a the length of the canal. Accurate con- struction makes the force required to move the carriage very small. In the installation described, the canal had a width of about 10 feet, the depth of water was about 4.5 feet, while the length was 72 feet. Fics. 297 AND 298. —Apron MeEtHop OF DETERMINING VELOCITY IN A CHANNEL. The carriage and apron weighed 88 pounds, but a force of only .88 pounds was required to move it. The. method of using the apron is shown in Fig. 298. From the position I, at the left, the apron is released, and as the lower edge enters the flowing stream, the carriage is drawn forward. After a few feet of travel the apron hangs verti- cal, and is latched in this position by a special arrangement located at fon the carriage. The apron enters the water without shock and does not disturb the flow conditions appreciably. The measured course along the canal was 32.8 feet, and since this was passed through in some cases in about 12 seconds, it became necessary to use elec- trical instruments for recording time, distances, etc. The apparatus 400 EXPERIMENTAL ENGINEERING used is fully described in the article referred to. Fig. 298 shows the apron at position JI as it is during the test. As soon as the end of the course is passed, the latch arrangement f is unhooked by con- tact with a rigid member, and the apron is then brought by the current into the inclined position shown at position III, which stops the carriage. An analysis of this method of measurement shows that it is in principle identical with the ordinary float measurement except that it gives the average velocity over the entire cross section at a single trial. The writer of the above article showed that it could give very accurate results, even for very low speeds, down to.or foot per second. But its application is likely to be restricted by the fact that straight channels of the requisite length are rarely available. It is also necessary that the containing walls shall be smooth and straight in order to allow of a close fit of the apron, to minimize the error due to water passing around the edges of the apron. For permanent ~ testing flumes, the method probably de- serves and will receive extended con- sideration. 209. Hydro-dynamometers and Hydro- metric Pendulums. — The difficulty of obtaining satisfactory conditions for float measurements has led to the development of apparatus by which it is possible to obtain the mean stream velocity at a single well-defined section.* In pressure plates, or hydro-dynamometers, the cur- rent is made to impinge upon a plate, and the magnitude of the force or pres- sure exerted by the stream is then meas- * ured in various ways. To illustrate one His; 299. Farnopm Hypro- type of this class, Fig, 209 gives an idea oa of the construction of the Perrodil hydro- dynamometer as shown by Van Winkle. The pressure plate P is carried by the framework ABCD, which is supported at K by the * See an article by F. Van Winkle on “Stream Flow at a Single Cross- Section,” in Power for Aug. 30, 1910. The two books named in Article 208 also contain discus- sions on current meters and similar instruments. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 401 standard MN, as shown. UJ is a torsion rod suspended at K on the upper end and fastened to the frame ABCD between B and C,asshown. EF is a graduated horizontal circle over which moves a pointer H which is rigidly fastened to the torsion rod. The in- strument is used as follows: by loosening set screw S, the plate and framework are allowed to swing into the current like a loose rudder until the position of P is parallel to the current and the pointer in- dicates the zero on the scale EF. Next the pointer H is forced around, twisting the rod UJ until the plate P is perpendicular to the current. S is then fastened and the angle of torsion, which is a function of the pressure on the plate, may then be read. The principle of the hydrometric pendulum is similar. This instrument consists of a ball, two or three inches in diameter, at- tached to a string. The ball is suspended in the water and carried downward by the current; the angle of deviation from a vertical may be measured by a graduated arc supported so that the initial or zero- point is in a vertical line through the point of suspension. If the current is less than 4 feet per second an ivory ball can be used, but for greater velocities an iron ball will be required. The instrument cannot give accurate determinations, because of the fluctuations of the ball and consequent variations in the angle. The formule for use are as follows: Let G equal the weight of the ball, D equal the weight of an equal volume of water; then G — D is the resultant vertical force. Let F equal area of cross section of the ball, v the velocity of the current, ¢ a coefficient to be determined by experi- ment; then we have the horizontal force P = cFv’. Let angle of deviation be 6; then a= P = cv? “Gap G=D from which _./(G—D) tand v= / cF 2 (25) The best results with this instrument will be only approximations. The one advantage that this instrument and the hydro-dyna- mometer have over current meters lies perhaps in the fact that the former can be used for lower velocities of flow than the latter. On 402 EXPERIMENTAL ENGINEERING the other hand, fluctuating velocity of current makes the determina- tion of the mean reading very difficult with hydro-dynamometers. 210. Tachometers or Current Meters. — These instruments con- sist of light fan or propeller wheels, mounted either horizontally or vertically, and geared to a registering mechanism which indicates the number of turns made by the wheel in a given time, actuated by the current. The registering mechanism may be simply the ordi- nary type of revolution counter directly driven from the wheel shaft by worm and gear. The counter can be worked by lever and cord. The disadvantage of this scheme is that the counter is exposed to the grit and dirt that the water may carry, and further, that the instru- ment has to be bodily removed from the water to obtain its reading. Fic. 300. — ERTEL CURRENT METER. Attempts to avoid this have been made by gearing the wheel shaft to a light vertical shaft and having this drive the register above water. This scheme is generally bad, as it increases the friction seriously and thus raises the lower velocity limit below which the instrument will not record. The best solution of the problem is perhaps the electric recorder. In that case the friction loss is reduced to a mini- mum, since the wheel shaft is simply required to make and break electric contact. Another advantage of this arrangement is that the recorder may be located at any convenient distance from the point of observation. Another good scheme for. reducing friction is to use the so-called acoustic method of recording. In this scheme parts of the wheel shaft are arranged so as to give a distinct click at every turn. The MEASUREMENT OF LIQUIDS, GASES, AND VAPORS = 403 sound may be transmitted to the operator by means of flexible tubing connected to the tubing supporting the current meter and through a simple form of receiver. Current meters are generally provided with rudders to keep them parallel to the current, and, if readings at considerable depth must be taken, are also weighted so as to keep taut the rope by which they are suspended in the stream. For shallow channels rigid rod sus- pensions are preferred. Fig. 300 shows Ertel’s current meter * of the type first discussed. The instrument is supported by the rod FE. A is the wheel and Z the counter. B-C is the cord and lever mechanism fastened to the top of the rod. Raising lever B re- leases the catch D and starts thecounter. Pressing against C releases B and the flat spring on D then forces the catch back into position. The next illustration, Fig. 301, shows the so-called Woltman mill, a type of current meter very largely employed. In this case the revolutions are recorded electrically. | Instruments built on this principle are made by several manufac- turers, differing in wheel construction and in method of recording. BLECTRIC REGISTER Fic. 301.— WottTMAN Mri. Finally, Fig. 302+ shows one type of acoustic meter, T being the flexible transmitting tube and RK the receiver. * Gramberg, Technische Messungen, p. 65. { F. Van Winkle in Power, Aug. 30, 19T0. See also Water Supply and Irrigation Paper, Nos. 94 and 95, U. S. Geological Survey, for further information regarding stream measurements and the meters used. 404 EXPERIMENTAL ENGINEERING 211. Calibration of Current Meters and Methods of Determining Average Velocity in Cross Sections. — This class of instruments is capable of giving very accurate results, but it requires rating or calibration. This may be done either by moving the instrument through still water at a definite velocity or by comparing the readings or the instrument with those of a standard instrument run alongside. The former method is perhaps the best, but not many testing flumes are available for the work of calibration. Theoretically considered, the equa- tion for a current meter should be V= an, where V = velocity in unit time, = number of revolutions in the same time, and a = a constant peculiar to the particular type of wheel used. In prac- tice, however, there is a certain current velocity, 6, below which the wheel will not revolve on account of friction, and the real equation therefore is V = an +b. This is a straight-line law and the numerical constants of the equation may therefore be found from any two calibration tests made at different speeds. The manufacturers will ordi- narily furnish calibration tables, giving n and V in parallel columns, but it is Fic. 302.—Acoustic Current needless to say that for important work MerrErR. with an instrument that has been in use, recalibration is required. Concerning the method of obtaining mean velocity over a given section, Van Winkle gives the following ways in which the current meter may be used: The mean velocity may be obtained either by taking the mean of averages of velocities at equally spaced points in this section; or by taking the mean velocity of the averages of velocities taken along equally spaced vertical lines; or by taking a MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 405 single reading from the movement of the instrument uniformly over the section. The first and second methods are most appropriate for taking measurements with an instrument which is supported by a pole resting on the bottom of the stream, but for employment of instruments capable of being suspended, the last mentioned method has advantage in greater convenience and saving of time. 212. The Pitot Tube. — In its simplest form this is a bent tube held in the water in such a manner that the lower part is horizontal and opposed to the motion of the current in an open channel. By Fic. 303. — FUNDAMENTAL Form oF Fic. 304. —Piror TuBE ror OPEN Piror Tuse. CHANNEL Work. the impulse of the current a column of the water will be forced into the tube and held above the level of the water in the stream; this rise DE (see Fig. 303) depends upon the velocity of the water. If the height DE in feet above the surface of the water equal /# and the velocity of the water equal V feet per second, we have V=Cv2 gh (26) in which C is a coefficient to be determined by experiment. Con- cerning the value of C, see Art. 214. The Pitot tube, as ordinarily used for open channel work, consists of two tubes, one, AB, bent, as in Fig. 304, the other, CD, vertical. 406 EXPERIMENTAL ENGINEERING The mouth-pieces of both tubes are slightly convergent, to prevent rapid fluctuation in the tubes. These tubes are so arranged that both can be closed at any instant by pulling on the cord ss leading to the cock R. Between the glass tubes dD and 0B is a scale which can be read closely by means of the sliding verniers m and m. The tubes are connected at the top, and a rubber tube with a mouth- piece O is attached. In using the instrument it is fastened to a stake or post by the thumb-screws EF; the bent tube is placed to oppose the current of water, the cocks K and R opened. The difference in height of the water in the tubes will be that due to the velocity of the current. The water in the column dD will not rise above the sur- face of the surrounding water, and the instrument may be inconvenient to read. In that case some of the air may be sucked out at the mouth- piece O, and the cock K closed; .this will raise the water in both columns with- out changing the difference of level, so that the readings can be taken in a more con- venient position ; or by closing Fic. 305.—Prirot TUBE FoR CLoszD CONDUIT. -, 7 the cock R, by pulling on the strings ss, the instrument may be withdrawn, and the readings taken at any convenient place. 213. Measurement of Average Velocity in Closed Pipes and Con- duits. — The instrument best adapted to this purpose is a modi- fication of the Pitot tube (see Fig. 305). Here P is the impact open- ing facing the current, while D is the static opening at right angles to the flow. Both tubes are connected by flexible hose to the differ- ential manometer 7M’. Since the opening P registers both the static and the velocity head, while D registers the static head only, the static head cancels out and MM’ shows only the velocity head h, ‘rom which V = C V2 gh, as before. Hence the reading of the MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 407 manometer is independent of the static pressure in the pipe, but for accurate work it is absolutely essential that D register the static head properly. 214. Conditions Affecting the Value of the Constant C in the Best Form of Pitot Tube.— There has been considerable controversy con- cerning the equation of the Pitot tube, and some authorities have given the theoretical equation V = Vgh instead of V = V2 gh. The work of later experimenters, however, has shown that the latter formula is the correct one, and also that with proper construction of tube and proper handling the constant C may with confidence be assumed = 1.0. For a complete discussion of this matter see the following papers: Vol. XXII, Trans. A.S.M.E., p. 284; Mr. W. M. White, in the Journal of the Association of Engineering Societies, August, 1901; Prof. W. B. Gregory, Vol. XXV, Trans. A.S.M.E., p. 184; Prof. W. B. Gregory and E, W. Schoder, Vol. XXX, Trans. A.S.M.E., p. 351. CoRN BEE It would appear that where the constant: C is not practically 1.0 in the equation, the trouble may be found either at the impact or at the static opening. To get a true impact indication seems, how- ever, to be a simple matter, it being apparently merely necessary to have a small hole, say not over 4 inch, and better smaller, facing accurately against the current, and to have the shape of the tube in the immediate vicinity of the hole such that the presence of the tube in the stream will not affect the stream filaments in front of the impact opening. Note the shape of the tube around the impact opening in Figs. 306 and 307. Both of these tubes will give excellent service. To get a true static reading is apparently more difficult. The reason for this becomes apparent when we consider that if the static tube, which should be at right angles to the stream flow, is inclined slightly against the current, we will get too high a static reading because the true reading is increased by impact, while if the tube faces slightly down the stream, the static reading will be less than the true reading because it is affected by suction. Any irregularity in the flow of the individual water filaments in the pipe, owing to eddies, etc., will produce similar effects. Further, in some designs of Pitot tube the static tube is so placed with reference to the impact tube that the latter cannot help but disturb the stream 408 EXPERIMENTAL ENGINEERING conditions around the former, and inaccurate static readings are the result. This is no doubt why many Pitot tube measurements have proven unsatisfactory. Pitot Tube No. 8 U nA Te Fic. 306.— Pitot TusE (GREGORY). Professor Gregory, in the paper above mentioned, shows the con- struction of a number of tubes and discusses the results obtained Vag thick — Yaz hol& Fic. 307.— Prror Tuse (Taytor). with them. The shape of the tube finally settled upon as giving a value of C = 1.0; as proved by test, is shown in Fig. 306. Here, as will be seen, the inner tube is the impact tube. The static pressure MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 409 is measured through small openings in the side of the outer tube. The handle at the top is used to set the tube parallel with the sides of the pipe or conduit. Another tube of similar construction is shown in Fig. 307, except that the static openings are two or three narrow slots well back from the impact opening, as shown. Besides thus determining the proper form of tube, Professor Gregory has introduced a further simplification for tubes to be used in a straight pipe. He has shown that the static pressure, except for gravity, does not change over the cross section of a pipe or con- duit. Consequently, since the static pressure can just as well be measured at the walls as anywhere else, it becomes unnecessary to have the static tube follow the impact tube when making a traverse. This means that only the impact tube need be introduced, and if the tube is of the right shape the only openings necessary in any conduit will be, say, a 13 inch opening for the impact tube and two } inch or 4 inch openings 90 degrees from the former and located at the ends of a diameter for the static reading. Into the latter are screwed } inch valves, but care should be taken first to round off the inner edges of these holes with a rat-tail file and the valves should not be screwed through the thickness of the wall. This prevents suction or impact at these openings. The Pitot tube itself is pushed through a packing gland in a plug which is provided with ordinary pipe thread. The tube is provided witha handle, by means of which it is raised or lowered and also aligned with the pipe. The con- nections are then as shown in Fig. 308, Fig. 309 showing the lower end of the tube on a largerscale. The form of differential manom- eter shown is also very convenient. At A there may be connected a force pump by means of which the position of the water levels in the manometer may be controlled. 215. Calibration of Pitot Tubes.— The only methods of cali- brating Pitot tubes are the same as those available for current meters; that is, they must either be dragged through still water at a definite rate or they may be placed in streams the velocity of which is known. The experimental work done, however, has shown that where the best form of tube is used with care, the constant may be assumed equal to 1.0. The error involved in this assumption is almost sure to be not greater than + 1 per cent. ‘410 EXPERIMENTAL ENGINEERING Fic. 308. TL LL SLL OT Fics. 308 AND 309.—Moprriep Form or Pitot TuBE (GREGORY). MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 411 216. Method of Making a Traverse and Obtaining the Average or Mean Velocity. —It has been shown by a number of tests that the velocity of water going through a pipe is greatest at the center and least at the walls, and that the ratio of these two velocities approxi- mates two to one. The variation of the velocities may be repre- sented by a solid of revolution whose axial cross section consists of a rectangular part ABDE, Fig. 310, with a semi-elliptical end BCD. The rectangle has for its length one-half the center Diam, of Pipe in Inches Velocity of Flow in Ft,/Sec, Fic. 310. DISTRIBUTION OF VELOCITIES IN A PIPE. velocity FC’, while the other dimension is the diameter of the pipe AE. The semi-ellipse has for its minor axis the diameter of the pipe and for half its major axis CC’, one-half of the center of velocity FC’. How closely the ellipse is approximated is well shown in Fig. 310. For the purpose of determining the complete shape of the cross section ABC’DE, the pipe must be traversed. This may be done by taking readings at stations equally spaced along a diameter, in which case the curve must be plotted and the mean velocity determined by finding by integration the mean ordinate of the solid of revolution. Or certain definite stations may be chosen so 412 EXPERIMENTAL ENGINEERING that the velocity readings may be averaged straight without going through the process of drawing the velocity curve. The last method is the quicker and fully as accurate as the former. Any number of stations may be chosen along a given diameter, but it has been shown that ten stations give an average sufficiently close. Hence this method of determining average velocity is sometimes known as the ro-point method. In Fig. 311 the cross section of the pipe is divided into five equal concentric areas indicated by the dotted circles. Each area is then divided into two equal areas indi- cated by the short circular arcs, resulting in “Stations” -1 to 10 (marked by heavier dots) along the diameter AB. The reading at each one of the stations 1-5 will give the mean velocity for the concentric area in which it is located. - Stations 6-10 simply duplicate the readings taken in the upper half of the pipe, so ‘that if a complete traverse is made, two velocity head readings will be taken ineach area. Since the areas are equal, the sum of all the velocities for any one traverse is simply divided by 1o to obtain the average velocity. Note that the center velocity, while it should be read on the traverse, does not enter this computation. Fig. 311 shows how the stations may be determined. In practice a scale may be laid off on the Pitot tube itself so that the adjustments may be made quickly. 217. Relation between Center Velocity and Mean Velocity. — Assuming that the velocity traverse curve is a true ellipse, the mean velocity would be .833 X the center velocity. Gregory and others have in actual cases found this factor to be about .84. In any case this ratio gives a very quick means of approximately determining flow from a single Pitot tube reading of the center velocity, but it should be noted that the error may be + 3 per cent. 218. The Flow of Water in Pipes. — Many of the factors govern- ing the flow of water in pipes are as yet not definitely determined, Fic. 311. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 413 and the computations are therefore to a certain extent approximate. For a full discussion of this matter see any book on Hydraulics or on Mechanics containing chapters on Hydromechanics. In general, if / is the total head in feet available to produce flow, and V is the velocity of the issuing stream from the pipe (not nozzle) in feet per second, we may write y? h---=h+h, +h, +h, ~ (27) 2g in which the right-hand member of the equation expresses the sum of all the losses of head. Here h, = the loss of head at entrance. h, = the loss due to skin friction in the pipe. h, = the loss of head due to curves and bends. h, = the loss of head due to other causes, such as obstructions, valves, etc. I 2 Each one of the losses may be expressed by a term equal tom 2 multiplied by some correction factor ¢, except the loss due to skin 2 friction, a general expression for which is h, = 4f - ; where 7 is the length and d the diameter of the pipe in feet, and f may be considered as a coefficient of friction. Hence sae (27) oe be written: b- ag 4f where V is in every case - velocity in feet per second at that place in the pipe for which the loss is being computed. Where the pipe is made up of lengths of different diameters, or where bends of vari- ous curvatures are used, or where several kinds of valves are em- ployed, each one of the factors h,, h, and h, stands for the sum of all the individual losses coming under that particular classification. Value of ¢,. — This may be taken equal to .5 for a pipe at right angles to the reservoir or source of supply and flush with the inside wall, and where the entrance edges are sharp. These are about the conditions that exist when a pipe is screwed into a tee in the main pipe. Where the pipe projects inside, ¢, may be as high as .g3, while if the entrance is bell-mouth, ¢, may be almost = o. Vy? Igthetee, 68) 414 _ EXPERIMENTAL ENGINEERING Value of f. —For values of the coefficient of friction f, see the curves in Fig. 312.* These figures are for clean pipe. Note that they vary with the size of the pipe and the velocity V. For rough 6 a _| a 13 TA Nn A Tn Te & C8 ee ee TT HNN TTT i) i A 2 2 Ss Ss Ss a g gs S 3 s s 012 003 002 001 000 or foul pipe the value of f should be increased. The amount of increase varies with the kind of pipe and is not definitely known. For a slightly rough pipe an increase of 30 per cent, while for a very * Adapted from a table given in Merriman’s “ Hydraulics.” MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 41 5 foul pipe one of roo per cent may serve the purpose, although the matter must be left to the judgment of the engineer. Value of ¢,. — For this factor various authorities also give infor- mation somewhat at variance. Weisbach found gb, = .0457 sin’ + 2.047 — where @ is the exterior angle (ABC, Fig. 313). From this, when ° @ = 223° 45° go gb, = .038 .181 .984 These are experimental figures found for 1} inch pipe. For smaller pipe the values in- Pic: 314: crease. Thus Weisbach found for a 3 inch pipe a coefficient of 1.53 for a 9o-degree elbow. On the other hand, for larger pipe the values for ¢, may be expected to be less than those given. / = In long bends, instead of elbows, the friction loss is much less, R _ Ratio of curvature radius of pipe loss. Thus for go-degree fee Weisbach found, if fe 10 5 24 I r $y = 0.131 138 -206 O77 1.978 Some authorities content themselves by simply adding for each elbow in a pipe line a certain number of extra feet to the length J of the line to allow for the extra friction. Thus Latta gives the fol- lowing allowances: and the greater the Tatio ~ » the smaller the I RIK Nominal Diam. of Pipe, inches, I I Allowance in ft. for each elbow, 2 2 5 | O Ir 33 26 bole vo dS die w Ww NiH a uL Such allowances are of course empirical, since they do not take into account the velocity of the water. Value of $,.— Perhaps least is known about the value of this coefficient. Weisbach gives figures for gate valves, plug cocks, and 416 EXPERIMENTAL ENGINEERING butterfly valves, but not for the globe valve so much used in this country. For a gate valve the figures are as follows (see Fig. 314): / Ratio =o t i g 3 8 : $ f,=0 07 .26 BL 2.1 5.5 17 98 No definite figures for globe valves appear to be available. Some writers assume the resistance of such a valve, when open, at about 1.5 times that of \ a go-degree elbow. q In practice the case encountered in the great majority of instances is that of a pipe of uniform ~ diameter. For this case the velocity V in all the terms of equation (28) may be taken the same and the equations may be solved for V, the mean velocity in the pipe. We will then have SS Fic. 314. 2 gh ee eres ft. per sec. (29) DP, haf ae ey + Oy The relative importance of the terms varies with the length / of the pipe, as the following example will show. In many cases all l but f 7 and perhaps ¢, may be neglected. Example 1. Compute the discharge through a 3-inch wrought-iron pipe slightly in- crusted. The pipe is rooo feet long in all, has 6 right-angled turns (ordinary elbows) with a globe valve at the end. The pressure of water at the main is 30 pounds by gauge and the discharge end of the pipe is 10 feet below the point of connection to the main. Here the total head h = 2.3 X 30 ++ 10 = 79 feet. The value of ¢; may be taken equal to .5. Since equation (29) involves the inter-related factors V and f, it must be solved by trial, and for a first approximation put f = .0o6, for which V =6 feet per second (see Fig. 312). The length / = 1000 feet, and d = 3 inches = .25 feet. , may be taken equal to .984, and since there are six elbows, the total loss will be 6 X .984 = 5.90. For the globe valve put $4 = 1.5 X .984 = 1.5. Then v=4/- 2X 32.2 X 79 r+ .§+.006 X 4 + 5.9 + Ls 08 e 5087 6x Bess koe ae ae .9 feet per second. This is in close enough agreement with our assumption for all practical purposes. Since the internal area of a 3-inch pipe is .0513 square feet, the cubic feet discharged will be 6.9 X .0513 = .35 per second. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS = 417 An analysis of the above example will show that approximately go per cent of the loss of head is accounted for in skin friction and about 5.5 per cent is accounted for in the loss through the six elbows. Neglecting all losses except that due to skin friction, the result would have been V = 7.2 feet per second, which is within 5 per cent of the former result. Hence for very long pipe it is only necessary to take skin friction into account and all other losses may be neglected, provided the number of curves or bends is not excessive. Case of Short Pipes. — A pipe is regarded as short when its length is less than 500 times the diameter and very short when it is less than sodiameters. In such a case with high heads, V is apt to be so great that little is known about the value of f. It also becomes necessary to determine ¢, as closely as possible. For the conditions existing and where the pipe is very short, a length equal to three diameters should be subtracted from the length /, since that part of the length is accounted for in the value of ¢,. Example 2. Conditions same as in Example 1 except that the pipe is only 50 feet long. The statement then becomes, assuming for the moment that f remains the same, v=4/ 2X 32.2 X 79 1+ .§ + .006 X 452+ 59+ 1-5 = | ft er sec Vat +48 +594 25 Ho P ; Now the curves, Fig. 312, for this case indicate that the value of f for this velocity is probably much nearer .oo5. With this value we get V= pier OED Lae =109.9 ft. per sec TVrtst4t5qotags 7 Note that in this case the head lost in friction is smaller than the head lost in the elbows and that none of the losses can be neglected. MEASUREMENT OF GASES. 219. As in the case of liquids, the methods of measuring gas may be positive or inferential. In all cases positive methods should be used where possible, on account of greater guarantee of accuracy. The various possible methods available may be grouped as follows: ‘418 EXPERIMENTAL ENGINEERING I. Chemical Methods. Used positively for the measurement of small quantities of gas. Used also inferentially in boiler and pro- ducer testing. In either of the last two applications only a small part of the flue or producer gas is analyzed, and from this with the aid of other factors the total quantity of gas concerned in a given operation may be determined. The reader is referred to Chapters XIII and XXI for discussion of these analyses. II. Measurement by means of orifices, such as openings in flat plates, nozzles, etc. These methods are equally applicable to large and small volumes and among them are some of the best available. III. Measurement by volume displacement, as in gasometers or gas meters in general. IV. Measurement by determining the average velocity of flow in a pipe of known cross section by means of anemometers, Pitot tubes, Venturi meters, etc. V. Measurement by calorimetry, or by steam and electric heaters. In measuring gases there are several things which must be con- stantly borne in mind. They are: i. Volume means-nothing unless temperature and pressure at which the volume is measured are determined and recorded. 2. Pressure measurement means nothing unless the degree of sat- uration of the gas with water vapor is known. All gases as handled by the engineer are more or less nearly saturated with water vapor and the pressure exerted by such a mixture is the sum of that due to the gas and that due to the water vapor. In making refined calculations the pressure due to the water vapor must be subtracted from that of the mixture giving the “partial pressure”’ due to the gas; and the pressure of water vapor in question is no¢ that given in the steam tables as corresponding to the temperature, but some fraction of that, the fraction being the “percentage humidity.” This cor- rected partial pressure is then used in the ordinary gas formulas. 3. Methods of measurement in which the gas to be measured comes in contact with water or similar liquid are always subject to error, due to the solubility of the different gases in the liquid. Any liquid to be used in this way should be saturated with the gas or gases in question by allowing them to bubble through it for a considerable length of time before measurements are begun. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS = 419 Where the quantity of liquid is relatively small, as in a wet gas meter, it soon becomes saturated with the gas and its effect may thereafter be disregarded unless there are considerable changes of temperature. The following table gives the cubic feet of gas measured at 60° F. and 14.7 pounds per square inch which are soluble in one cubic foot of water at 14.7 pounds pressure and different temperatures. Temp., Deg. F. 32° 68° 212° 32° 68° 212° Alfesng ves cies ©.027/0.0185]...... Carbon monoxide. ..] 0.037] 0.025] .... Nitrogen....... 0.026/0.017 |o.o105| Carbon dioxide...... 1.96 | v.98 | 0.26 Oxygen.......- 0.053|0.034 ]o.o185| Ammonia.......... L250 | FOO |ewwee- Hydrogen...... 0©.023/0.020 |o.o18 Il. THE MEASUREMENT OF GAS BY MEANS OF ORIFICES. 220. Theoretical Velocity and Weight Discharged. — The flow is assumed adiabatic. Where the work must be so close that friction effects must be allowed for, this is generally done by applying experi- mentally determined coefficients to the results obtained by adiabatic computations. a. Following the methods of Peabody,* suppose the vessel A, Fig. 315, contains a frictionless piston B and the connecting tube C a friction- less piston D. Let the absolute pressure on B be P, pounds and the pressure on D be P, pounds per square foot. As B moves to the right, each pound of gas has done upon it the work P,v,, while each pound of gas entering C does the work P,v,, v, and v, being the specific volumes in cubic feet of the gas —— for the respective absolute pres- A sures P, or P, per square foot. If {oo the velocity of the gas in A=V,, = LQ and the velocity in the orifice : C = VJ, the kinetic energies pos- sessed by one pound of the fluid Fic. 315. 2 2 will be i and Na respectively. Let the intrinsic energy in A be 28 * Thermodynamics of the Steam Engine, p. 424. 420 EXPERIMENTAL ENGINEERING E, and that in C be EZ, Then it follows, from the assumption of adiabatic flow, that V? Ve E, + Py, + a =E,+ Pv,+ zi o (30) With well-insulated nozzles or pipes the condition of adiabatic flow is very nearly realized, even if the pipe is of considerable length. In practice it is customary, where orifices are used for measure- ment, to so proportion the size of A to the size of the orifice that V, shall be very small as compared with V,. Hence the terms depend- ing upon the former can usually be neglected, and solving for V, we may write, V,=V2g(E, — £, + Pv, — P,v,) ft. per sec. (31) Now it can be shown that all the intrinsic energy in a gas is avail- able for outside work in an adiabatic change and that in general Pu 7-1 Making the substitution in (31) we then have Vi=V20(2% - 722 + Po, - Py) fe jou. I I =Y2 | Pm me h :) — Pv, (- aes + 1)| ft. persec. (32) From the adiabatic law we may derive y-1 Pon as Ps, (2) : 1 and substituting this value of P)v, in (32) we obtain B= WEE = r P\7 Vi= (/ 2 gP,v, ae if — a | ft. per sec. (33) Since temperatures are quite readily determined, it is more con- venient to substitute for P,v, in the above equation the equivalent RT,, where R is the gas constant and T, the absolute temperature in the reservoir. Hence we will finally have the theoretical velocity vat = i P,\? Vea) 2 ene = if — @ ft. per sec. (34) MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 421 With the aid of formula (34) it becomes easy to find the equations for theoretical discharge. If F is the area of the orifice in square feet, the theoretical discharge in cubic feet will be y-l Q=FV,=Fy/ 2gRT, I- (2) "Tou. ft. per sec., (35) 1 x and further, if 6 is the density of the gas, in pounds per cubic foot, under the condition for which V, is determined, the weight theoreti- cally discharged will be yok r P,\ 7 W = Foé,/ 2 gRT, 1—{=*) _Jlbs. per sec. (36) r—i P, In practice, equation (36) must be multiplied by a coefficient of: discharge C, which depends upon the kind of orifice and for which values will be given later. 221. Value of the Pressure P,.— So far nothing has been said of the value of the pressure to which the gases expand in the nozzle or orifice. It has been tacitly assumed that P, is always the pressure in the discharge space beyond the orifice. Experiment, however, has shown that the flow under some conditions follows laws which do not correspond with this assumption.. An examination of equation (36) will bring out the error of such a supposition also on theoretical grounds. Assume in one case that the pressure in the discharge space is equal to P,. Then equation (36) will give W = 0, and that is a logical result, for there is then no pressure difference. Next assume that the pressure in the outside space is 0, that is, that there is a perfect vacuum. But if P, could drop to that value, equation (36) would again give W = 0, because 0 would then be equal to o. This conclusion is absurd, because under these conditions we should rather expect maximum discharge. Hence P,, the pressure in the orifice, does not in all cases fall to the pressure in the outside space. It can be shown that there is an increase in the flow as P, de- creases below P, until a certain maximum discharge is reached. 422 EXPERIMENTAL ENGINEERING It can also be shown mathematically that this condition is obtained when ¥Y ae (; : Jv ee G2) The value of P, obtained from this expression, for a given P,, is we L 58 . called the critical pressure, and the ratio Pp the critical ratio. Its 1 theoretical value for air and some other gases, for which 7 is near 1.4, ise = .527. Should the pressure in the dis- = charge space drop below the critical yf value of P,, the latter shows no fur- / ther decrease but retains its value { .§27 P,. Graphically this condi- tion of things may be represented 0 Bel 10 as in Fig. 316, in which ABC Values of "/r, represents the curve of discharge. Fic. 316. From C to B, as P, decreases, the rate of discharge increases until Values of W =.527. Theoretically, W should then again decrease to o =o, as shown by the branch BO. Instead of this, P, becomes independent of the outside pressure and W becomes sensi- bly constant, as shown by the line BA. In any practical case the method of computation is then as follows: Pressure in discharge space Pressure in reservoir * (b) If this is equal to or greater than .527, substitute in equations (34), (35) and (36) for P, the value of the pressure in the discharge space. (c) If the ratio is less than .527, substitute in the equations for P, a value equal to .527 of the reservoir pressure. 222. Formulas for the Flow of Air. — Fixing upon the kind of gas, air in this case, allows of the substitution in equations (34), (35) (a) Determine the ratio of MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 423 and (36) for the constants g = 32.2, R = 53.3and 7 = 1.405.* The equations then become V, = 109.1 C, V rf — € i ft. per sec. (38) Q = 109.1CF rx — ( ) Jew ft. persec. (39) +29 and W = 109.1 CFOV r,t ~ @ | Ibs. per sec. (40) 1 webs" ryt = in which C, and C are the coefficients of velocity and of discharge respectively. Within the assumptions made, these formulas are exact and must be used whenever there is any considerable change of density in passing from P, to P,. When the change of density is small, that is, when the ratio oi is, say, not less than .g, there P, are certain substitutions that may be made which simplify the numerical work involved without introducing great errors. But judgment must be exercised in the use of such approximate equations. In this connection see papers by S. A. Moss in Power for Sept. 20 and 27, 1906, and by R. J. Durley, Trans. A.S.M.E., 1905. Note particularly that P, is the pressure in the discharge space only as long as the latter is not less than .527 P,. For the condition of lower pressures than this in the discharge space, P, remains at the critical value, and the area F is that cross section of orifice or nozzle at which P, is established. Further, 0 is the density accord- ing to the pressure P, and the temperature 7,. Unless P, is also the pressure in the discharge space, T, is hard to determine, and should be substituted for in terms of P,, T, and R. This can be done as follows: From a combination of the adiabatic law and of the equation of state for gas, we may write co 222 (By P, (Ey v, U,\P, RT,\P, * y change with temperature, see Chapter XXI under “ Specific Heat.” 424 EXPERIMENTAL ENGINEERING Substituting this in the general theoretical equation (36) and in the special equation (40), we obtain 2 ra = 25 ie (2) ‘ W= FP, /2 Cs Ie P. Ibs. per sec. (41) I P. 1.42 P. 1-71 and W-=2.047 CFP, Tr (2) — (7) | Ibs. persec. (42) 1 1 1 Equations (41) and (42) are probably the most serviceable, the former giving the theoretical discharge for any. gas, the latter the actual discharge for air and other gases for which 7 = about 1.405. The following table gives values of 7 for some of the more common gases, for ordinary conditions of pressure and temperature. For air, y = 1.402 oxygen, y = 1.400 atmospheric nitrogen, 7 = 1.408 hydrogen; y = 1.420 CoO, 7 = 1.408 CO,, 7 = 1.296 223. Value of the Coefficient of Discharge C. —. No definite in- formation seems to be available concerning the value of C for high- pressure work. For low pressures the following figures may be used. For high-pressure work, and indeed for all accurate work, each orifice should be specially calibrated. The scheme mentioned in Art. 224 may sometimes be used when it is desired to avoid cali- bration in connection with high pressures. For the purpose of measurement it seems best, judging from the ‘data now available, to choose a bell-mouth orifice. This becomes apparent upon examination of the values given below for the con- stant C. A well-rounded orifice has a constant close to .95 and, above all, this figure does not change materially with a variation in a 2 : ‘ the ratio Pp’ Both Hirn and Rateau have shown this, the former 1 for air and the latter for steam. For an orifice in a thin plate or for short cylindrical mouth-pieces with sharp edges, the discharge con- stant varies with the pressure ratio. It may be near .6 for pressure ratios in the neighborhood of .9 or above and may rise to .8 for MEASUREMENT OF LIQUIDS, GASES, AND VAPORS = 425 pressure ratios near .5. The work of Hirn and Rateau confirm this, and Weisbach also found this, as indicated below. Weisbach determined the following values of C for air: Conoidal mouth-piece of the form of the contracted vein, with effective pressures of 0.23 to 1.1 at- MOSpheres p13 Aya ds a ee ea ea 0.97 to 0.99 Circular sharp-edged orifices.......0............ 0.503 to 0.788 Short cylindrical mouth-pieces ........... ...... 0.81 too.84 The same rounded at the inner end....... ... 2. 0.92 to 0.93 Conical converging mouth-pieces... .... .... 0.90 to 0.99 Moss * found the coefficient of discharge C to be on the average .942 for moderate pressures, say up to 8 pounds above the atmos- phere, and for a well-rounded orifice 1 inch in diameter, the straight portion having a length of about 13 inches. Prof. R. J. Durley, in the paper above mentioned, gives coefficients of discharge for circular orifices in thin plates up to 4.5 inches diameter for pressures up to 5 inches water. (See table.) The thick- Pressure in Inches Water. Diameter of Orifice, Inches. I 2 3 4 5 Sa A acts ey RiedN Sally C=! 603 .606 610 613 616 cist isec Can cae losses Se Aoepiesee 602 605 608 .610 -613 De ea tob eran Se muitats .601 603 605 -606 -607 Tg 3 ideo dun atebceat te ease ake the .601 601 .602 603 603 dase tah "sok av ier cera .600 .600 -600 -600 .600 Oe ct eu pranageeeene eae -599 +599 +599 -598 -598 3 tates use teeth ak wait 599 -598 +597 -596 -596 Be as Vise asin Seka RoR He -599 -597 -596 595 504 ib ssi ta gs o gies duds cAc dich ie lengaboe -598 -597 +595 +594 593 NaNO Dad ker nee 598 596 594 593 592 ness of the orifice plates was .o57 inch. The orifices were placed in the end wall of a long box of considerably greater cross section, so that the initial velocity could be neglected. For consistent results it was found that the cross section of the box should be at least 20 times that of the orifice. Pressure and temperature were measured about 5 feet back from the orifice, the manometer connection * S.A. Moss, Power, Aug. I0, 1905. 426 . EXPERIMENTAL ENGINEERING being carried through the wall so as to be flush with the inner surface. The older work of Hirn* on the flow of air through orifices and nozzles showed that for a properly designed nozzle the discharge coefficient C varied but slightly with pressure ratios varying from a = .52 to .gg, and found C = .966 to .985 for a nozzle with 9 1 degrees convergence, and C = .980 to .gog1 for a nozzle with 13 degrees convergence. For an orifice in a thin plate he found the following results: ty i = .95 9 8 7 6 5 4 1 = .627 -640 674 708 -741 773 -799 ty This series is recomputed from the values given by Hirn, and repre- sents the ratio of the discharge volume of the thin-plate orifice to the theoretical discharge volume of a bell- -mouth orifice (not to the discharge volume of a convergent nozzle, as Hirn gives it). One of the most recent investigations on this subject is that made by A. O. Miiller and reported in the Zeitschrift des Vereins <—;— deutscher Ingenieure, Feb. 22, 1908. The paper describes the testing apparatus and the equations applying to each case in Ate detail. The pressure differences being small, Miiller neglected differences of density in the gas on the two sides of the orifices and used the simplified formulas V =CF V2 gh or V=KF V2 gh (see below), in which V is volume in cubic feet per second and h is the pressure difference expressed in feet of gas column at the density corresponding to the reservoir pressure. It should therefore be remembered that the coefficients quoted below apply to low-pressure work only. The dimensions of the orifice used are given in Fig. 317. Four cases were investigated : 8 = o Fic. 317. * Annales de Chimie et de Physique, March, 1886. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 427 (1) Flow from the receiver through the orifice direct into the atmosphere. ——— . (2) Flow from the receiver through the orifice-into a tube having an internal diameter of 3.22 inches. (3) Flow through-an orifice, placed at the end of a tube having an internal diameter of 3.22 inches, into the atmosphere. (4) Flow through an orifice placed across a pipe having an internal diameter of 3.22 inches. The conditions of flow are indicated in Figs. 318 to 321. In cases (2), (3) and (4) the flow is affected by the varying ratios of the area of orifice F to the tube area F,. This ratio = in the following tables 1 is indicated by m. The, pressure differences used in this work did not exceed about 4 inches water. ‘The results obtained by Miiller for case (1) agree very well with those found by Durley. In the other three cases the constant is largely affected by the conditions, that is, by the ratio m and, the friction in the length of the tube /, the latter being measured as shown. The constant is in the latter cases radically different from the constant C applying to the thin- plate orifice alone, and has been designated therefore by the letter K. There is a _ certain relation between C and K by \t means of which in any given case, after C a, P, is determined from experimental data avail- z Se able, K may be computed, taking into account the ratio m and the friction loss in the length 7. For the derivation of this relation see the paper mentioned. Below the equation is given for each P, case. Fic. 318. Case (1) Diameter of orifice, inches, +92 1973 2.44 Range of pressures above atm., in. H,O, .37-2.32 .29-1.45 .21-.96 Mean coefficient C, 597-598-596 428 EXPERIMENTAL ENGINEERING Fic. 319. Case (2) z7VG + fl) m+ (E- m) where / is expressed in feet, f may be taken equal to .124. Diameter of orifice, inches, 92 E93 2.44 Range of pressures above atm., in. H,O, .19-2.2 .21-2.2 .04-2.8 F 3 —=m= .082 .287 578 F, K (determined), -632 685 -764 C (computed), 602 2585 -583 _—— Be P, Case (3) K aaa eae Vi-a-fl) wC i and f same as in case (2). Diameter of orifice, inches, 92 1.73 2.44 Range of pressures above atm., in. H,O, .12-4.2 163.8 .12-4.0 . =m = 082 287.578 K (determined), 603 644 755 C (computed), .602 633 .691 MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 429 Case (4) i and f same as in case (2). Diameter of orifice, inches, 92 1.73 2.44 Range of pressures above atm., in. HO, .20-3.4 .12-3.5 .07-2.5 F [=m = .082 287 578 F, K (determined), 641 750 1.084 C (computed), 609 621 -697 224. Necessary Precautions in Orifice Methods. — Great care must be taken in measuring air by means of orifices that flow may take place and observations may be made in the same way as in the original experiment for the determination of the constant. It is best, when possible, to consult the original report in order to be able to correctly reproduce the conditions. In general, attention must be given to the following points: (1) The orifices must be carefully and accurately made and cor- rectly measured. ; (2) The velocity of approach must be reduced to a negligible value. (3) The pressure must be measured in such a way as to get least disturbance of flowing gas. The common method is to connect the manometer to a tube which passes perpendicularly through the walls of the reservoir or pipe just ahead of the orifice. The inner end of the tube must be flush with the inner surface of the wall. (4) Leakage must be prevented or its value determined and cor- rections made. (5) All changes of section immediately preceding the orifice should 430 EXPERIMENTAL ENGINEERING be avoided when possible, and if absolutely necessary should be gradual and rounded. (6) Steady conditions of flow must, if possinle,| be secured during measurements. ; With proper precautions this method is ant of giving results accurate to I or 2 per cent, and with extreme care‘an accuracy well within 1 per cent can be obtained. _ For measurement by means of orifices when the pressure differ- ences are greater than those for which reliable values of the constants are available, it is only necessary to reduce the high reservoir pressure by throttling into another vessel from which the flow to the orifice takes place. Care should then be taken to insure against distur- bances caused by throttling the discharge. This can always be done by allowing sufficient dis- tance between the orifice and the point at which throttling takes place. III. MEASUREMENT BY MEANS OF VOL- UME DISPLACEMENT; GAS METERS, ETC. 225. The Gasometer.— The simplest form of gas meter is the well-known gas holder, or so- called gasometer. This apparatus consists essentially of a tank 4, Fig. 322, containing water or other liquid into which dips an inverted tank B called the bell. The piping may be arranged as in Fig. 322, or separate inlet and outlet pipes may be used. The bell is either entirely or partly counterbalanced by a weight F, depending upon the gas pressure desired. This method of counter- balancing, if used alone, would result in a pressure change in the gas as the bell ascends or descends on account of different degrees of immersion of the bell. To allow for thisa compensating weight F’ Fic. 322. —GASOMETER. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS acting on a changing arm is used where accurate work is essential. To definitely determine weight or volume of gas with this instrument, three observations are necessary: Pressure, tem- perature and movement of bell in a given time. Any suitable instrument may be employed for the former, although since the pressure is usually but a few inches above atmosphere the ordinary water manometer is mostly used, see M, Fig. 322. To determine temperature accurately it is essential that the tem- perature of the gasometer liquid should not be far different from that of the gas. The movement of the bell can usually be read directly by méans of a suitable scale S fastened to the bell, while the tank supports a pointer or sighting ar- Tangement V. This measurement is suscep- tible of great refinement by electrical means, if that should be required. Where the bell is not __I Fic. 323. —METER PRoveER. 431 432 EXPERIMENTAL ENGINEERING large and accurately guided, a reading of the movement of the bell at a single station may be sufficient, otherwise simultaneous readings at not less than three stations are recommended. Gasometers may be calibrated either by computation or by actual experiment. The former method should be used only where the bell is comparatively small, so that the diameter can be accurately measured, and where it is accurately cylindrical. Where the second method of calibration can be applied it should always be used in preference to the first. Gasometers are used in two ways,—to measure gas from a pro-. ducer or to a consumer, and largely also to calibrate other types of meters, in which case they are usually called meter provers. The former method of service needs no further explanation. It is intermittent unless two gasometers are used in parallel, one empty- ing while the other is filling. Meter provers are simply accurately constructed and carefully calibrated gasometers. A type of one of these in elevation is shown in Fig. 323. 226. Gas Meters. — It was stated above that a single gasometer cannot be used for continuous measurement. Gas meters are usu- ally simply adaptations of the: gas- ometer principle modified so as to act continuously. They are of two dis- tinct classes, wet and dry. Wet Meters. —The method of operation of a meter of this type is best explained ‘by the conventional sketch, Fig. 324,* which shows a cross section. ‘The meter consists of a horizontal drum which rotates in Fic. 324.—Stpre Form or WeT 4 stationary drum and is divided Gas Meter. . into four compartments, A, B, C, D. The lower part of the rotating drum dips into water which opens and closes the slots or ports abcd, by which the gas coming through the central pipe E enters the respective compartments, and also controls the outlet ports a’'b’c'd’ through which the gas * See Gramberg, Technische Messungen, p. 121. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS = 433 leaves the compartments and reaches the discharge side of the meter at F. With the rotation of the drum as shown by the arrow, it will be seen that B is filling with gas, while the filling of C just starts. A is discharging, while the discharge of D is just about completed. No gas can go through the meter without registration, because in no compartment will the in- and outlet ports be open at the same time. Rotation is produced by the fact that on account of the slightly greater pressure at the inlet, the water level will be slightly higher on the right side of the meter. Hence this half is continuously heavier than the left side and descends. Such a meter is not used much in practice, because it is not easy to make the ports at the center and in the side wall of the drum of sufficient size. In many constructions, there- fore, the ports are placed in the end walls, the inlet ports at one end, the outlet ports at the other. The com- partment walls are spirally twisted, because it is necessary to offset the ports about the same as in Fig. 324. The gas then passes nearly axially in- stead of radially through the meter. A study of Fig. 325, in which the cylindrical side wall of the drum has been removed, may make the construction clear. The accurate indication of wet meters depends upon the height of the water level in the chambers, since the capacity of the latter varies with a drop or rise in the water level. It is therefore essential that this be checked from time to time, because the gas passing will tend to saturate itself and lower the level. Meters constructed for experimental purposes are usually furnished with a fill- and an over- flow opening. Through the former water is fed into the housing until it shows at the latter opening. The meter is then allowed to drain out until the flow of water through the overflow ceases, and both openings are then closed. Large meters, such as station meters, are often furnished with continuous water circulation to maintain the proper level. Any wet meter to be used for accurate work Fic. 325.— ORDINARY CONSTRUCTION or Wer Gas METER Drum. 434 EXPERIMENTAL ENGINEERING should be supplied with spirit level, or levels, so that it may be set true every time it is used. As in the case of gasometers, the observations required, besides the movement of the drum, which is usually mechanically recorded on dials suitably graduated, are pressure and temperature. The pres- sure determination should be made in the filling chamber near the end of the filling operation, while the temperature should be that of the gas near the outlet. It is desirable to have gas and water temperature as close together as possible, and to have the water saturated with the gas. Dry Gas Meters. —The dry gas meter possesses the advantages of not being affected by frost nor of increasing the amount of moisture in the gas. It is made in various forms, and generally con- sists of two chambers separated from each other by partitions. Each chamber is divided into two parts by a flexible partition which moves backwards and forwards, and actuates the recording mechanism as the gas flows in or out. This motion is regulated by slide valves somewhat similar to those of a steam engine. A type example of such. a meter is illustrated in Figs. 326 to 328.* The meter casing is divided into two exterior measuring chambers PP by a vertical partition. On each side of this partition there are located two in- terior measuring chambers QQ, which consist of two movable disks DD and flexible shells. In Fig. 328, the left-hand side shows the interior measuring chamber exhausted, while at the right the chamber Q is filled. Gas is admitted from the inlet pipe A to the measuring chambers on the same side of the central partition, that is, to P and O alternately, by means of simple slide valves V. As Q fills, a corre- sponding quantity of gas is displaced out of P, flows through the center port of valve V and finds its way into passages E and into the discharge pipe B. Guides HH are provided to preserve parallel motion of the disks D. The motion of the latter is transmitted through G and rods R to the crank mechanism KKN, which turns a short vertical spindle. The length of the crank, in order to regulate the disk travel, may be changed by adjusting the position of the pin N in the slot shown. The motion of the spindle is transmitted to the * Webber, Town Gas and its Uses. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS = 435 CUBIC FEET pb rl ea Fic. 327. Fic. 328. Fics. 326-328. — Type oF Dry Gas METER. index by wheel and shaft S. The crank O, see Fig. 327, operates the slide valves. 227. Dry Meters of Large Capacity. — The ordinary gas meter, whether wet or dry, soon reaches great proportions when it is at- tempted to handle large quantities of gas. To obtain large capacity 436 EXPERIMENTAL ENGINEERING with moderate size, several modifications of the dry meter have been brought out. Fig. 329 shows a rotary or turbine meter, the operation of which is plain from the cut. This type of meter has a minimum limit, like the water meter of similar construction, in that it requires a certain velocity of flow to overcome the frictional resistance of the Z| Outlet Inlet Ls Fic. 329. —RoTaRY OR TURBINE GAS METER. mechanism. Such a meter gives nearly unrestricted passage and is consequently of large capacity. Another method of reaching the same end is to use the shunt principle, that is, to actually meter only a definite proportional part of the total quantity flowing. Such a construction really consists of two distinct parts; a meter, either wet or dry, but usually the latter, is placed in the smaller shunt pipe, while the main pipe con- MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 437 tains a pressure regulating mechanism which is designed to main- tain a definite proportion between the volumes passing the two pipes for widely varying inlet pressures. The accuracy of the meter depends directly upon how well the regulating mechanism performs its functions of maintaining proportionality. 228. Calibration of Meters and the Relative Accuracy of Wet and Dry Meters. — It should be made a general rule that no meter be used for experimental work unless it be calibrated. This holds espe- cially for dry meters, as this class is usually inferior to wet meters as far as accuracy is concerned. The only way to calibrate is to send or draw through the meter a definite volume of gas for which the pressure and temperature are known. In every case a calibration curve covering a range of rates of flow should be determined, and to prevent unnecessary computations it is well to construct this curve for standard conditions, which for gas work are fast becoming fixed at 60° F. and 14.7 pounds pressure. For small meters, such as the Junker gas calorimeter meter, a bottle holding several liters may be conveniently used for calibration, the air or gas being displaced and sent through the meter at different rates by water displacement. For larger meters the meter prover will have to be used. 229. Gas-meter Capacities. — Gas meters are often rated accord- ing to the number of gas burners they will supply, a burner being rated at somewhat over 5 cubic feet of gas per hour. Thus, a r1o- light meter is good for a normal capacity of about 50 cubic feet per hour, a 200-light meter will have a capacity of about 1000 cubic feet per hour. A dry meter of the latter capacity would call for about a 2-inch pipe connection. Meters of the rotary type are made in capacities from about 1500 to 100,000 cubic feet per hour. For the latter meter, the pipe con- nection would be about 30 inches, for the former about 3 inches. Proportional meters can be had with capacities up to 200,000 cubic feet per hour. 230. Reservoir Method of Measuring Air or Other Gases. — This method is somewhat similar to the gasometer method except that the volume instead of the pressure is kept constant. It is sometimes used in measuring the discharge of air compressors. For this pur- 438 EXPERIMENTAL ENGINEERING pose the compressor is made to deliver against any desired pressure, which is kept constant by a regulating valve, into a tank or receiver until the pressure in the tank approaches the desired delivery pressure. The readings necessary are the following: , and ¢, in the tank at the beginning of a trial, p, and ¢, at the end of the trial and time required to pump from the pressure #, to the pressure p,. A relief valve is provided between tank and regulating valve which serves to again reduce the pressure in the tank and through which the com- pressor may also discharge between trials. Concerning the pressure determination, it is well to state that if a gauge is used p, should be taken at some pressure above the atmosphere, as the gauge indi- cations are generally very uncertain near the zero of the scale. The bad feature of the receiver method of measuring air consists in the determination of the average air temperature. The temperature is not likely to remain constant during a given trial, but changes, due to the different temperature of the incoming air, to the heat developed by compression in the receiver itself, and to the loss by radiation. If possible, the higher pressure should be maintained in the tank until the final temperature is determined, which is not particularly easy where the volume is large. If the latter method is adopted, a tight tank is an absolute requirement. As far as the computations are concerned, the result will be ex- pressed in weight of air, since the volume V of the tank in cubic feet isaconstant. For the condition at the beginning, the tank contains a weight of air equal to VP, 53:3 53-3 being the value of the constant R for air and P the absolute pressure in pounds per square foot. For the end condition we have similarly 1 pounds, 1 W,= pa eciarg: 53-3 T, The weight added in the given time is therefore ae ees W=W,-W,= ae ounds. OES NE, as) This weight of air can then easily be converted to cubic feet of MEASUREMENT OF LIQUIDS, GASES, AND VAPORS = 439 compressor discharge when the pressure and temperature conditions are given. In case the gas consumption of any given machine or apparatus, as for instance a gas engine, is desired, the above described receiver method may be inverted; that is, the tank is pumped up to a high pressure and the gas is then throttled to the desired pressure. The measurements and computations are the same as above. The method is likely to give better results because the temperature determination can be made in the outlet pipe with more certainty of obtaining an average. IV. MEASUREMENT OF GAS BY DETERMINATION OF AVERAGE VELOCITY. The principal instruments used for this purpose are anemometers, Pitot tubes, and Venturi meters. 231. Anemometers, as far as the principle of their action is con- cerned, are very similar to current meters, see Art. 210, p. 402, and what is stated there concern- ing accuracy applies equally well to these instruments. Anemometer wheels are of course built as light as pos- sible consistent with stiffness, mounted in bearings that can be nicely adjusted, and are very carefully balanced. A form shown in Fig. 330 with flat vanes, and with the dial arranged in the center as shown, or on top of the case in various positions, is much used as a portable instrument. The dial mechanism of the anemometer can be started or stopped by a trip arranged convenient to the operator; in some instances the dial mechanism is operated by an electric current similar to that described in connection with the current meter. They can also be made self-recording by Fic. 330. — ANEMOMETER. 440 EXPERIMENTAL ENGINEERING attaching clockwork carrying an endless paper strip which is moved under a pencil operated by the anemometer mechanism. Robinson's anemometer, which consists of hemispherical cups revolving around a vertical axis, is much used for meteorological observations. This type of instrument can be used for higher velocities than the other; it is good for about 200 ft. per sec., while the other often fails at about 100 ft. per sec. Calibration of Anemometers. —Anemometers are calibrated by moving them at a constant velocity through still air and noting the readings on the dials for various rates of movement. This is usually done by mounting the anemometer rigidly on a long horizontal arm which can be rotated about a vertical axis at a constant speed. The distance moved by the anemometer in a given time is computed from the known distance to the axis and the number of revolutions per minute; from these data the velocity is computed. In performing this experiment care must be taken that the axis of the anemometer is at right angles to the rotating arm. Readings should be taken at various speeds, since the correction is seldom either a constant quantity or one directly dependent on the velocity. Anemometers can also be calibrated by measuring the quantity of air flowing through a conduit with some other apparatus and com- paring the anemometer reading in the same conduit with the velocity thus determined. The test should be made with different quanti- ties so as to calibrate the anemometer over its entire range. Some- times such a test is made by placing the anemometer in a pipe which tightly fits the casing, thus causing all of the air measured to pass through it, computing the actual velocity from volume and cross section. It will in general be found, on comparing the result with that obtained for the same actual velocity when swinging the ane- mometer through still air, that the results do not check, but that the velocity shown in the latter case, where the air may pass around the outside of the anemometer case, is less than that given by the former method. The difference may amount to 20 per cent, and it becomes a question to decide which one of the calibration results is the one to use. Evidently the conditions of calibration are not the same. That being the case, it is next evident that the conditions under which the anemometer is used should determine the method MEASUREMENT OF LIQUIDS, GASES, AND VAPORS = 441 of calibration. If, for instance, the velocity of the wind is to be found, the anemometer should be calibrated by swinging it. On the other hand, if the cross section of the pipe or duct in which gas velocity is measured is not very great as compared with the size of the anemometer, evidently the second method of calibration is to be preferred. But between these extremes there are a variety of intermediate cases, and this fact is what makes the anemometer in some instances an unreliable instrument. 232. Precautions Necessary in the Use of Anemometers. — These instruments possess upper and lower velocity limits beyond which they should not be used. When the velocity is very low the friction of the instrument is relatively so great as to make it unreliable or totally inoperative, as is the case with current meters. When the velocity is very high an anemometer built for ordinary service is apt to be bent out of shape, due to its light construction, and the friction loss is often considerably increased. Due to the delicate construction of most of these instruments they require careful handling, and they should be frequently calibrated to guard against changes of the calibration constants due to bending of the vanes, wear of parts, etc. 233. Measurement of Gas by Means of Pitot Tubes. — The device described in Arts. 213 to 215 for use with water may also be used for measuring the velocity of gases, and the statements there made con- cerning accuracy, etc., apply in general also to this case. The velocity may be computed from the formula V>OVe ge (44) in which C is an experimentally determined constant and H is the velocity head. H depends upon the gas used, and care must be taken to compute it properly from the velocity head as measured. If water is used as the manometer liquid, let # = the velocity head in water inches. Then H = hr, where 7 is the number of feet of gas which will give the same pressure as 1 inch of water. In general, for any manometer liquid H = kh’r, where 7 is as above, h’ = velocity head as measured in inches, and & is the density of the manometer liquid as compared with water. C should be close to 1.0, if all conditions are properly adjusted. For a temperature of 60° F. and a barometric pressure of 29.92 442 EXPERIMENTAL ENGINEERING inches Hg, 1 inch of water column will balance 68 feet of dry air, or 7 = 68. It should be noted that for ordinary gas velocities the actual manometer reading may be very small, so that it is very difficult to guard against appreciable errors in the calculated velocities. The best that can be done is to use some form of differential manometer so as to make the manometer reading as reliable as possible; see Art. 91, p. 174. The density of gas increases directly with the absolute pressure and inversely as the absolute temperature; it varies also with moisture, so that corrections are required for pressure, temperature, and the amount of moisture. . When the precautions and directions laid down for the use of the Pitot tube with water are observed, the instrument will give satis- factory results also for gases. A thorough discussion of the use of the Pitot tube for the measurement of gases flowing in pipes is given by R. Threlfall in a paper before the British Institution of Mechani- cal Engineers in 1904. 234. Measurement of Gas by Venturi Meter. — Recent experi- ments show the Venturi meter to be a satisfactory instrument for the measurement of gases.* For the theory for this instrument see Art. 195, p. 369. The formula for velocity in the throat of such a meter is y-1\3 P mY =? P\t [22 . = (2) v.=c(F ee SS (45) 2 = (Fy (By F,/ \P, in which Subscripts 1 refer to the upstream end of meter, Subscripts 2 refer to the throat of meter, P is the pressure in pounds per square foot, d is the density of the gas being metered, pounds per cubic foot, F is the area in square feet, * See paper “The Flow of Fluids in a Venturi Tube,” by E. P. Coleman, Trans. A.S.M. E., Vol. 28, p. 483. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS = 443 7 is the ratio of specific heats, re , and C is an experimentally determined constant. The value of C is not as yet well determined for widely differing conditions, but it seems to be practically constant over a wide range of throat velocities and to be near unity. In any case, a meter once calibrated over a sufficient range can be used without sensible error over the same range with little danger of the constant changing, unless the gas carries foreign matter such as dust or tar in suspen- sion. In such cases periodic cleaning must be resorted to. V. MEASUREMENT OF GAS BY CALORIMETRY. 235. Methods Used. — This method offers a very convenient and comparatively simple means of measuring gas. It is applicable to the measurement of both large and small quantities, but is apt to give erratic results when the quantities become so small that radia- tion may cause an appreciable error. For large quantities it is one of the best. In principle it is simple: a measured quantity of heat is added to the gas flowing through a conduit and the rise of temperature is measured; then . H —r=WC, (T’ -T), (46) in which H = heat supplied, in a given time, ry = radiation loss in same time, W = weight of gas passed in same time, C, = specific heat of gas at constant pressure, T’ = final temperature of gas, T = initial temperature of gas. From this H-yr nS C,(T’ — T) and if radiation be neglected pes PEt A method of making the measurements above outlined is illus- trated in Fig. 331, in which the gas enters the pipe or channel at A 444 oo 2s EXPERIMENTAL ENGINEERING and is discharged at D. Means for heating, which may be either a steam or electric radiator, is to be supplied. If a steam radiator is used, the heat discharged is computed from measurements of the weight and temperature of the condensed steam, the heat entering from measurements of pres- sure, quality, and weight by methods already explained. The heat taken up by the air is the difference of that enter- ing and discharged. If an electric heater is used, the elec. tric energy disappearing is measured and reduced by computation to heat-units. The means for heating should be of such form as to heat the air uniformly. The temperature of the entering and discharged air should be taken at sufficiently numerous points in the cross section to make the aver- age results accurate, and the thermometers should be protected from radiant heat. The average temperature should also be measured at the section where the velocity is to be computed. It may be de- sirable, in case extreme accuracy is required, to compute the weight of moisture in the air from observations with the dry- and wet-bulb thermometer. Very satisfactory results are obtained by the use of resistance thermometers, because the wire forming the resistances can be strung on frames or insulators in such a way as to be well distributed over the entire section of the channel, giving a good average temperature reading. An electric meter constructed on these principles is now in the market.* As the actual rise of temperature in practical cases is small, radia- tion may in general be disregarded. In case it is desirable to allow for it an approximate value may be obtained by stopping the flow of gas and measuring the heat input necessary to maintain the heating chambers at a temperature about halfway between the values of entering and leaving temperatures when the gas is flowing. Fic. 331. — CALORIMETRIC METHOD OF Measurine Gases (Steam Heater). * See an article on the Thomas electric gas meter in Machinery for March, IQII.-- MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 445 MEASUREMENT OF VAPORS. 236. General Considerations. — In general, vapors may be meas- ured by any of the means used in the measurement of gases, but when dealing with vapors wet, dry and saturated, or only slightly superheated, many of these methods give very questionable results. The laws of vapors slightly superheated, that is relatively near the dry, saturated condition, are not as yet well known. During the past few years much work has been done in this region in the case of water vapor, but even here considerable doubt still exists. The more the vapor is superheated, that is, the further it is removed from the condition of saturation, the more nearly does it obey the laws of perfect gases and therefore the more accurate do the methods of gas measurement become. For vapors which are near the saturated condition, or are actually saturated, it is best, when possible, to base all measurements upon the weight or volume of the liquid before vaporization or after con- densation. This is the most common method of measuring steam and is undoubtedly the best. The various methods in more or less common use for the measure- ment of vapors may be grouped as follows: I. Determination of the volume or weight of liquid before vapori- zation or after condensation. II. Measurement by means of orifices. III. Measurement of the average velocity of flow in a pipe or conduit. IV. Calorimetric measurement. I. DETERMINATION OF WEIGHT OF LIQUID. 237. Methods Used. — For this purpose any of the methods given for the measurement of liquid may be used. The most common methods are direct weighing or the use of a calibrated meter. In engineering the vapor to be measured is generally steam, and it is customary to measure either the boiler feed water or the liquid resulting from condensation in some apparatus. It should be ob- served that in either case there are possibilities of considerable leak- age, and unless these are guarded against or the leakage actually measured, errors of unknown magnitude may occur. 446 EXPERIMENTAL ENGINEERING Il. MEASUREMENT BY MEANS OF ORIFICES. 238. General Case. Theoretical Velocity Attained. — If it is again assumed that the flow is adiabatic, and that there is no friction, a brief consideration will show that the kinetic energy that the vapor has gained in passing the orifice must be exactly equal to the differ- ence in the heat content of the vapor under the initial and final con- ditions.* Case of Saturated Vapor. The equation for velocity can be developed by making the proper substitution for the intrinsic energy in equation (31), p. 420. Fora mixture of a liquid and its vapor the intrinsic energy generally is E= 7 (xe +49); in which A =>) 778 quality of the vapor mixture, internal latent heat, ie = heat of the liquid. As in the case of gases, we then obtain Ve 2 2g =5 (410. + 91 — %0,— 9.) + Py, — Pv, (47) Now in general, Il x v = xu + (1 — x)o, in which v = specific volume of the mixture of liquid and vapor, “ = increase in volume during vaporization, o = specific volume of the liquid. The factor (1 — x)o is so small that for ordinary engineering work it may be neglected, and substituting for v, and v, in equation (47), we shall have AV? ae = %10, — % — %0, — 9, + AP xu, — APU, (48) To simplify this equation, write r = @ + APu, whence AV? ae 1+ — Not, — Gs (48a) from which finally \ /2 Vi= a (x17, + G — “, — 9) ft. per sec. (49) * Strictly, this statement is not accurate on account of the fact that the A Pu values are not the same for the initial and final conditions. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 447 In this formula the terms 7, and g, are known from the steam table for the pressure P,, and x, can easily be found by calorimeter. The terms 7, and g, become known as soon as the final pressure P, in the orifice or nozzle (which is not necessarily that of the atmosphere into which the vapor may be discharging) is determined (see Art. 221). x,, the quality at the pressure P,, may then be found from the entropy equation xP, a — 6 — 22 T, + 1 . + 6, ) (50) xr T of the liquid. P,, P,, and x, being known, all the terms of this equa- tion except x, may be obtained from steam tables (see Appendix). Case of Vapor Initially Superheated. (a) Vapor wet in final condition. Usual case. The simplest way of taking care of this is to add some term to equation (48a) to allow for the heat represented by the degree of superheat. Thus equation (48a) may be modified to read in which the term — represents the entropy of the vapor and @ that eV [reat ++ — X fy — I (51) 2§ th Here, as in the case of saturated steam, the value of «, must be found, which can be done from Colog. zt + zt + % =F + (52) where T, = absolute temperature of the superheated vapor, T, and T, are the saturation temperatures of the vapor at pressures P, and P, respectively, and Cp is the mean specific heat at constant pressure of the super- heated vapor in the temperature interval T, — T,. (6) Vapor remaining superheated throughout. ‘This case is not of much practical importance. The equations applying to it may be easily developed in case of necessity from equations (50) and (5 1) by certain modifications. 239. Method of Determining Theoretical Velocity for Steam from the Heat Chart, Fig. 245.—A quick method of determining V, is available by the use of the diagram Fig. 245. From the 448 EXPERIMENTAL ENGINEERING point on the diagram corresponding to the initial condition of the steam move down a vertical (isentropic) line to a point of inter- section with the pressure P,, existing in the smallest section F in the nozzle or other orifice. This corresponds to the adiabatic change. The first point on the diagram gives the heat content of the steam in the beginning, the last the heat content after expansion in the nozzle. Calling the difference B, we may compute the velocity from = = 2 ft. per sec. (53) 240. Value of the Pressure P,. — As in the case of the gases the value of the pressure P, is not necessarily that of the pressure in the discharge space, there being critical pressures and critical ratios which appear to change slightly with the shape of the orifice and with the condition of the vapor as to quality. None of the equations so far given for steam will serve to bring out this critical data, as none of them involve the pressure ratios. Equations exactly similar to those for gases have, however, been developed by Zeuner and others. Zeuner gives the following ex- pression for the theoretical velocity: yal PN v= i SEK L ; i = a) | ft. per sec. (54) This value for V, becomes a maximum when the pressure in the nozzle is y hepa i: (55) 2 c ae 1° 55 For saturated steam, with x not less than .7, we may write y = 1.035 + .1 4, so that for B= io, 7 = nag and for ¥=.7, 7 = 1.105. This about covers the field of saturated steam as commercially used, and for these values of 7, P, = .578 P, in the case of the higher quality, and = .583 P, in the case of the lower. Evidently the criti- cal value P, = P, = .58 P, fits every ordinary case of saturated steam. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS = 449 For superheated steam y = approximately 1.29, for which P, would be = .55 P,. But in the ordinary case the superheated steam expanding becomes wet and changes its value of 7 to near those first quoted. The case is complicated, the value of P, then being some- where between .55 and .58 P,. To apply equations (49) and (51) in any practical case, it there- fore again becomes necessary, as A. Nozzle 1049 Nm. Diam. at 16°C. for a gas, to check the pressure ee Pressure in Discharge Space Pressure in Reservoir If this is greater than .58 (or .55 for superheated steam), 7, and q, apply to the pressure in the dis- charge space, and x, may then be found from equations (50) or (52). If, on the other hand, the ratio is less than .58 (or .55), the pressure for which 7, and q, (and also x,) are found will be for the critical pressure = .58 (or .55) Py. 241. Weight of Vapor Dis- charged. —If F is the area in sq. ft. of the section of the nozzle at which V, and P, are established (in convergent nozzles and bell-mouth orifices the smallest section), and d is the density (pounds per cubic foot of the mixture of liquid and vapor, or vapor alone if superheated), the theoretical discharge weight will be Orifice in Thin aia ratio W = FOV, lbs. per sec. (56) In any actual case this is modified by a coefficient of discharge C, for which values are given below, so that W = CFOV, lbs. per sec.. (57) 242. Value of the Coefficient of Discharge C. — Comparatively few experiments have been made on orifices or nozzles properly 450 EXPERIMENTAL ENGINEERING shaped to give the maximum discharge. Perhaps the most exten- sive ones made on steam are those of Rateau¥ and Gutermuth.t The dimensions of the orifices and nozzles used by Rateau are given in Fig. 332. These have been left in millimeters, from which they may be easily reduced to inches by dividing by 25.4. The results ob- tained plotted as the ratio of the discharge W actually obtained to the £10 2 ° = 0 2S 3 2 o> 2 2 Ee) i 2 ts 7 an Ratio of Observed Discharge W to Max, Discharge W So m ° 1,0 0,95 0,9 0,85 0,8 0,75 0,7 0,65 0,6 0,55 0,5 0,45 0,£ Ratio of Back Pressure P, to Initial Pressure P; Fic. 333. — VALUES oF DiscHarcE COEFFICIENT C For FLow oF STEAM THROUGH NOZZLES. Curve A-B is the theoretical discharge, curve C-D the average actual discharge for the three nozzles A, B, and C, Fig. 332. The discharge coefficient C is then the ordinate of C-D re ordinate of A-B” theoretical maximum discharge W,,, are given in the curves, Fig. 333. The initial pressures used went up to about 145 pounds per square inch for nozzles A and B, to about 85 pounds for nozzle C, and to 75 pounds for the thin-plate orifice. The curves show that for a properly designed mouth-piece or convergent nozzle, the constant C is again slightly below 1.0, as for air. The curve A—B is the curve of theoretical discharge, while C-D is the average of the figures * Experimental Researches on the Flow of Steam through Nozzles and Orifices, A. Rateau, translated from the French by H. B. Brydon. t Gutermuth, Experiments on the Flow of Steam through Orifices, Zeitschrift d. V.d.I., Jan. 16, 1904. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS = 451 obtained for all three nozzles. Taking the ratio of the ordinates of these curves gives the coefficient C. This increases from .94 at F 1 = about .96 to .967 at? = .8, to .974 at = .7, and has practi- 1 1 cally the value 1.0 when the critical ratio : = .57 is reached. 1 The results for the thin-plate orifice are shown in curve E-F. In this case, again taking the constant equal to the ratio of ordinates of E-F to ordinates of A-B, the variation is shown by the practically straight line G-H. ‘The coefficient starts with a value of .622 at 22 L ‘ P. ‘ ‘ = .g and increases to .770 at P. = .6. It still seems to increase: 1 after the critical ratio = = .58 is passed. 1 A close analysis of Rateau’s work will show that it is subject to several cumulative errors, especially for pressure ratios around the critical, so that the values of C may be as much as 2 per cent too high. The inaccuracies are partly due to new steam-table data which was not available at the time the work was done. Gutermuth’s work was done with a view to determining the conditions controlling the flow of steam through valve ports of steam engines, and to that end, besides investigating cir- cular, sharp-edged, and_bell-mouth orifices, he also tested rectangular ori- fices with curved extensions approxi- mating the shape of valve ports. Only the results on the circular ori- fices are of interest here. Big. 334: Fig. 334 shows the dimensions, estimated from the original cuts, of the circular orifices used. Form II gave a constant C very close to 1.0, as might be expected. This orifice practically gave the theoretical discharge as computed by Zenner’s equation and equation (57), taking y = 1.135. Form I, 452 EXPERIMENTAL ENGINEERING not a true thin-plate orifice, gave the following results, the initial pressure being about 130 pounds per square inch absolute. For - =.977. -944 .888 .777 .666 612 .577 1 C=.705 «78 05 .846 .855 .868 .88 These values are throughout greater than those found by Rateau for a thin-plate orifice, as might be expected. In applying the orifice method of measuring steam it therefore seems better to use a well-rounded orifice than an orifice in a thin plate, on account of the greater certainty in the coefficient and its smaller variation. 243. Approximate Formule for the Flow of Steam through _Orifices. — If in equation (54) we substitute g = 32.2, 7 = 1.135, and a = .58, and P, = 144 p,, we obtain 1 V, = 70 V p,y, ft. per sec., (58) and in theory this velocity will be constant as long as the pressure in the discharge space is less than .58 P,. Now for saturated steam pv," = constant = approx. 485, (59) where p, is pounds per square inch, and v, = specific volume in cubic feet. From this = ee ae and substituting this value in equation (58), we have V, = 1274 Vp, ft. per. sec. (60) The weight discharged will then = W =CF 0 V, = 1274 CF 3 Vp,™ Ibs. per sec. (61) 3 is the density of the vapor at the lower pressure P,, and assuming that the vapor is still saturated at that pressure, we may write el a +939 _ (58 p)™ py" UV, 332-6 332.6 Substitute this value of 0 in equation (61) and we obtain W = 2.3 CF,” lbs. per sec. (62) For an orifice with well-rounded entrance, put C = 1.0, and if F is expressed in square inches instead of square feet, we will finally have for such an orifice W = .o16 Fp,” lbs. per sec. (63) MEASUREMENT OF LIQUIDS, GASES, AND VAPORS = 453 This is Grashof’s formula, and the dimensions of the equation are: W, in pounds per second; F, in square inches of smallest area; and p,, the initial pressure in pounds per square inch. Grashof’s equation may be written W= pi Ibs. per sec. (64) 62.5 An equation of very similar form was developed by Rankine upon the basis of work done by R. D. Napier. He gives _ Fh > a" (65) and this equation is known as Napier’s formula. When the pressure P, is greater than .58 P,, the flow, according to Rankine, may be approximately expressed by W = phe 3th — pb) Ibs. per sec. (66) 42 2 p, Note that the pressures in equation (66) are in pounds per square inch. . The error of either one of the approximate equations is likely to be + 2 per cent. Ill. MEASUREMENT OF VAPOR BY DETERMINING AVERAGE VELOCITY. STEAM METERS. 244. The instruments which may be used for this purpose are mainly Pitot and Venturi tubes. The method of applying these to gases has been outlined in Arts. 233 and 234. The laws are practi- cally the same for vapors. 245. Steam Meters. — When the readings of either one of the above instruments are made continuous in some manner, we have what is known asasteam meter. There are, however, several other fundamental types of steam meters,* and for the purpose of explain- ing their principle they may be generally classified as (2) Meters employing the Pitot tube principle. (6) Meters employing the Venturi tube principle. (c) Orifice meters. (d) Float meters. * Probably the most extensive treatise on steam meters is that given by F. Bendemann in the Zeitschrift des Vereins deutscher Ingenieure, Jan. 2 and 23, 1909. To this treatise several of the following cuts are due. 454 EXPERIMENTAL ENGINEERING Some of the oldest steam meters employed a wheel and were con- structed much like the present-day turbine water meter, but that design has apparently been given up. The number of steam meters on the market to-day is considerable. Their accuracy depends upon how well the various factors entering the problem are taken care of. The makers of the best of them will guarantee an accuracy of + 3-5 percent on steady flow. None of these are apparently quite satisfactory on intermittent or pulsating flow. In any case where they must be used with such flow, a special calibration after installation is necessary. What may be called the “operating” part of most of the steam meters is very simple; the “recording’’ apparatus is, on the other Self-Adjusting Water Column Velocity Steam Fic. 335. — Burnaam STEAM METER. hand, in many cases quite complex, especially if compensations for pressure and temperature variations are made. The quantity of steam flowing through any given main depends upon the function Vp, — p, and upon the density 0, which for prac- tical purposes may be expressed by V py A meter to be accurate must therefore account for both of these factors, and if the steam should at any time be superheated, a temperature correction also enters. Apparently only one of the commercial meters corrects for temperature, and even in that case the adjustment is made by hand and not automatically, MEASUREMENT OF LIQUIDS, GASES, AND VAPORS = 455 (a) Pitot Tube Meters. The simplest form of this meter is appar- ently that designed by Burnham, Fig. 335. The height of the water column in the glass is a function of the velocity. The position of the impact opening with reference to the cross section of the pipe is evi- dently of importance. It should in theory be placed at the point of average velocity, but the determination of this position in practice is not so easy and would in any case require traversing with various velocities of current. The density factor is apparently not taken care of in the instrument and will have to enter into the computation for weight. A much more elaborate meter based on this principle is that made by the General Electric Company. Here the static and impact tubes, combined in what is called the nozzle plug, Fig. 336, extend nearly Fic. 336.— Nozze Pruc, G. E. Co’s Steam METER. across the diameter of the pipe in which the flow is to be measured. The two tubes leading from this plug are connected to the two unions shown near the top of Fig. 337, which illustrates the recorder used. This consists essentially of two vertical tubes partly filled with mer- cury, connected across near the bottom by another tube, so that the whole practically forms a U-tube manometer. The entire arrange- ment is balanced on knife-edges as shown. The nozzle plug tubes are connected to the manometer by flexible tubing, one to each branch of the tube. The excess of pressure on one side causes a part of the mercury to flow over to the side of least pressure, causing the beam to move about the knife-edge until balance is again established. The movement of the beam, which is multiplied by levers, is thus a direct function of the difference in pressure, i.e. of the velocity of the cur- rent of steam through the pipe. The rest of the instrument is a clock arrangement for recording the movement of the beam on paper, which is graduated so that the flow can be read directly in pounds per hour. Compensating devices for pressure and temperature are fur- 456 EXPERIMENTAL ENGINEERING nished. Pressure variation is corrected for automatically. A tube of the Bourdon type, influenced by the static pressure at the point where the velocity is being measured, causes a small “correction” weight to shift so as to correct the pencil travel. Temperature is compensated for by hand adjustment of the same weight, according to a special calibration curve sent out for each meter. This meter is also made in two other forms, as a recording meter without the compensating device, for installations where neither pressure nor To Nozzle Plug Pressure Correction Balancing Weight Spring Flexible Steel T; Pressure and Temp. Weight Clock Fic. 337——Recorpinc Apparatus, G. E. Co’s SteaAM METER. temperature vary to any great extent, or as a simple indicating meter where no continuous record of flow is necessary. (0) Venturi Steam Meter. The only meter of this type so far brought out is that made by J. C. Eckardt, Stuttgart-Cannstatt, and is shown in Fig. 338. The Venturi tube is combined with a steam separator, which, by the way, is always good practice in connection with any steam meter. The tube R, leads to the high-pressure space, MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 457 while the pressure existing at the throat is measured by means of the small tube / and the larger tube R. Both pressures are autographi- cally recorded, the strip of paper showing the pressure difference continuously. The average pressure difference may from this be found by the planimeter. The steam flow is then read off directly from tables furnished with the instrument. The weak point of the Fic. 338.— Eckarpt STEAM METER. meter seems to be the recording apparatus. In the first place the two recording manometers must maintain a fixed adjustment with relation to each other. In the second place, while the distance be- tween the two pressure curves may be 1.5 or 2 inches for maximum flow, as it is in the instrument illustrated, this distance rapidly de- 458 EXPERIMENTAL ENGINEERING creases, so that it is only a few hundredths when the flow is Io per cent of the normal. Under these conditions the error of planimetra- tion may be quite serious. (c) Orifice Meters. The principle upon which these meters oper- ate is well shown by Figs. 339 and 340, illustrating the meter made by Hallwachs & Co.* The method of measuring the pressures existing Fic. 339. — HALLWAcHS’ STEAM METER. ahead of and behind the orifice is shown in Fig. 340. The indicat- ing apparatus, Fig. 339, consists of a simple form of differential mul- tiplying mercury manometer. The spiral coils in each pressure pipe are put in for the purpose of maintaining the same height of water column on the mercury on each side irrespective of pressure variation. For a constant steam pressure, that is for constant 0, the steam flow- * Malstatt St.-Johann an der Saar. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 459 ing may be computed from the head H. To obtain the results directly for different steam pressures, various flow scales are some- times placed on a cylinder which is pivoted next to the manometer, and the flow may be read off directly by bringing the proper scale Fic. 340. — OriricE, HALLWaAcus’ STEAM METER. into position. This instrument has been made recording by electri- cal means by fusing into the manometer tube metallic contacts at proper intervals. As the mercury reaches each contact in turn, an ’ L\ Te Pi a HS i) FIG. 341. — CONVENTIONAL SKETCH SHOWING PRINCIPLE OF GEHRE RECORDING APPARATUS FOR STEAM METER. electric circuit is closed and a line proportional in length to the square root of H! is recorded. From this diagram the average VH may then be directly found. The density factor Vp, is apparently not accounted for. This type of meter is otherwise quite reliable and many of them are in use on the continent. 460 EXPERIMENTAL ENGINEERING Several other designs of orifice meters, differing in their recording apparatus, are on the market. One of the most recent and one of the most accurate is that brought out by M. Gehre,* who has turned out several designs within the past few years. The recording appara- tus of the last Gehre meter is quite complicated, but the principle underlying it may be explained from Fig. 341. The higher pressure p, acts on the surface of the mercury in the stationary vessel A. This vessel is so shaped that the weight of mercury forced over into the vessel B, which is fastened to one arm of a balance, is proportional to the square root of the differences in level. The pointer P then moves distances proportional to Vp, — p,. By ingenious modifica- tion of this idea, which is old, and additional adjustments to auto- matically allow also for density variations, Gehre has produced an apparently satisfactory commercial instrument. The flow may be read directly from an integrating attachment, which is of advantage, or it may be autographically recorded, or both methods may be used in the same instrument. N) The accuracy is guaran- teed to within + 5 per cent. 1 (d) Float. Meters are of two classes: those in which the float moves against a constant resistance but in which the free passage for steam increases with the magnitude of the move- ment and those in which the movement takes place against an increasing re- sistance but the free pas- sage remains constant. Fic. 342. — Diacrammatic SKETCH OF FLOAT Srram Meter. Nearly all true float meters are of the first type. The diagrammatic sketch, Fig. 342, shows the principle. The seat of the float A is extended in the direction of the current. Ifa * Gehre Dampfmesser Gesellschaft, Berlin. See the above-mentioned articles by Bendemann. MEASUREMENT OF LIQUIDS, GASES, AND VAPORS 461 simple conical form is used the effective cross section of free passage is only approximately proportional to the movement of the float, but the degree of approximation is sufficiently close for most purposes. The force required to lift the float, and consequently also the pressure difference (drop of pressure), remains constant. This pressure dif- ference is kept so small that the effect on the density of the steam may be neglected and the formula for flow of liquids, W=CFVb#, — p, may be employed. Since Vp, — P, is constant, but F varies in 7 o i] is = a rh | i Fic. 343. — Cross SECTION oF St. Fic. 344. — GENERAL VIEW, ST. Joun Steam Meter. Joun Steam METER. direct proportion to the lift of the float, the quantity W is practically a linear function of the lift. This principle is in this country applied commercially in the St. John and in the Sargent steam meters. Fig. 343 shows a cross section of the former. The construction differs from that of Fig. 342 in that the float itself is made conical. This destroys the simple relation of proportionality between lift and quantity of flow, because 462 EXPERIMENTAL ENGINEERING the effective area of the float changes. Correction for this is appar- ently made in the construction of the registering apparatus which is connected as shown in Fig. 344. The record may be directly planimetered. Variation of density with pressure is not taken into account automatically by this meter. The Sargent indicating steam meter is of later origin. It was first CD SWZ) QMQ’NRHS Ss Ui Eh =) mn Hh CH aE SS op ranean aren gee ae a) Ce Ss 2? CEES 2 N g Fics. 345 AND 346.— SARGENT STEAM METER. described by its inventor in the Transactions of the American So- ciety of Mechanical Engineers, 1905, but since that time has appar- ently undergone considerable changes in construction. Figs. 345 and 346 are reproduced from Bendemann’s discussion. ‘The valve A isa conical float fitting over a conical seat and closing the passage com- pletely with its lower edge when at rest. During operation the steam lifts the float proportional to the quantity passing. The valve spindle B is prolonged downward into the space C, which is open to the ‘atmosphere. At the lower end the spindle carries a Bourdon tube, see G in Fig. 346, to which the pressure is transmitted through a hole ‘in the spindle. The Bourdon tube carries a pointer D which moves MEASUREMENT OF LIQUIDS, GASES, AND VAPORS = 463 over.achart E, Fig. 346. The pointer has therefore a double motion, up or down, depending upon the lift of the valve, and in a horizontal plane, depending upon the steam pressure. The correction for den- sity is therefore automatic. As far as a comparison between orifice and float meters is concerned it might be said that they are probably not far apart on the score of accuracy. Where the steam main is inaccessible, as may sometimes be the case, the orifice meter is probably better, because its register- ing mechanism may be placed at some distance from the orifice and may be better taken care of. IV. CALORIMETRIC MEASUREMENT OF VAPORS. 246. Methods Used. — The two calorimetric methods described in connection with the methods of measuring gases can be used for the measurement of vapors. The heat added either vaporizes en- trained moisture or superheats the vapor. If the apparatus be so constructed that the vapor is slightly superheated before entrance, the determinations are generally fairly accurate. One method of calorimetric determination which is applicable to vapors but not to gases is of interest. If vapor at a known tempera- ture and pressure and with a known quality be condensed in a known weight of liquid, the weight of vapor condensed can be found from the temperature rise of the liquid. This method is used in connec- tion with condensing calorimeters where the equations applying to the case may be looked up, see Chap. XIV. 247. The Flow of Steam in Pipes. — This problem is mentioned here merely with a view to indicating approximately what the flow of steam through any given pipe may be expected to be under given conditions. An approximate formula may be derived by assuming that the velocity of the steam is not to exceed 6000 feet per minute. If we let W = the steam flowing in pounds per minute, 0 the density of the steam in pounds per cubic foot, and d = diameter of the pipe in inches, we will have with the above assumption of velocity W = 33 0@ lbs. per min. (67) This formula is considered good for pipe sizes between 4 and 8 inches and for lengths under too feet. For smaller sizes than 4 inches the 464 EXPERIMENTAL ENGINEERING discharge will be less, and for the small sizes of pipe, especially if they are of considerable length, the formula is probably useless. G. F. Gebhardt, in his “Steam Power Plant Engineering,” has examined a number of formule established by various authorities for the flow of steam in pipes. He shows that in general they are all based upon the loss of head H expressed by * v L af — «4-31 oS eG which is the same expression also used in the flow of water, see Art.218. For general practice, Gebhardt recommends the following formula: 5 1 W = 87 es * Ibs. per min. (68) L € F 3) W = weight of steam in pounds per minute. Od = mean density in pounds per cubic foot. P = drop in pressure. Assumed at the figure desirable in any given case. d = diameter of pipe in inches. L = length of pipe in feet. in which This strictly applies to well-lagged pipe only. As in the case of the flow of water the length Z is not only the actual length, but the added friction of fittings should be taken care of by adding a cer- tain equivalent length for each fitting. But few experiments have been made on the friction of fittings, and those give anything but concordant results. Until more satisfactory figures are available, those given by Briggs (Warming Buildings by Steam) and quoted by Gebhardt will have to serve. For a standard go-degree elbow or for a tee, the allowance should be about L’= ee feet. Late an The resistance offered by a gate valve when wide open may be neg- lected, while the allowance for a globe valve will be about 3 times that for an elbow. * Power, June, 1907. CHAPTER XIII. COMBUSTION AND FUELS. 248. Combustion. — Combustion or burning is any kind of chem- ical combination evolving heat. The only kind of combustion used to produce heat for engineering purposes is the combination of various kinds of fuels with oxygen. In the ordinary sense the word combustible implies a capacity for combining rapidly with oxygen to produce heat. 249. Weight and Volume Relations. — The study of chemistry shows that when chemical reactions occur between elements or compounds there are involved definite weight relations characteristic of the particular elements acting and definite volume changes corresponding to the number of gaseous molecules reacting and produced. The reaction is a rearrangement of the atoms of the chemical elements into a new set of molecules. The volume of solids is in general negligible in comparison with that of gases of the same weight. For example, take the reaction Cy, +2 Oz = 2 CO, t Ib. Cy +-2.664 lbs. Oo 3.664 lbs. CO2 0.0071 cu. ft. C2 + 29.85 cu.ft. O2 = 29.85 cu. ft. CQ. (solid) (gaseous) (gaseous) The gas volumes above are under standard conditions, i.e. 32° F. and 14.7 pounds pressure per square inch. Air is a mixture (not a chemical compound) of the gases nitrogen (N2) and oxygen (Oz), and slight amounts of moisture (H20), carbon dioxide (COz), argon, and other inert gases. Considering the inert gases as nitrogen, the analysis of dry air is: ; By Volume By Weight Noitescseee eindrsntees 79.00 70.74 COS sales eee eer 0.04 0.06 Otis avheteesee ss 20.96 23.20 466 EXPERIMENTAL ENGINEERING For engineering purposes the Nz and CO. may be added together and considered as No. gas with a molecular weight of 28.94 (based on Oz It is sometimes convenient to treat air as a 32.00). The following table gives weights and volumes of the principal substances concerned in the combustion of ordinary fuels: Weight in Pounds Chemical Symbol and Weight of per Cu. Ft. at 32° F. and 14.7, Lbs. per Substance. Sq. In. (One At- mosphere) Pressure Se Molenule, (Standard Condi- tions).* Carbon s « sa) saga tataumdarse tess C2T2OT wd pouialelcmaleras 145 (Solid) Sulphiir.: : .¢4d0« dsiiiagesiee cae nee S=323707 srs xradodanenss m5“ OXY BOD is suai ee ind btseowauainaacsncla eye 8 O=16.00 QO, = 32.00 0.08922 (Gas) NiGPO SET. eo2 es decd Bakaanneseis 23 Sake N=14.04T N2= 28.08 f | 0.07830 “ Hydrogen... . 0.2.0... 000 cee eee H= 1.008 Hp. =2.015 0.00562 “ Marsh gas, or methane..........].........05- CHy= 16.03 0.0447 fe INA Te asass cede oh eta ta a eA AE heck a lls dh $date a (28.94) 0.08071“ Carbon dioxide.......... 0.00.0 c hese cece eee CO, = 44.01 0.12268 “ Carbon. monoxide: . . vcscieac cas cpa eiews eee mane CO =28.01 0.07807.“ Wa tet reg 36s ctor on nlaittaendiaietelleumes cAmeeiEES H,O= 18.02 (See steam ta- bles) Vapor Sulphur dioxides oj ss caecsaxavecelhs 4 aes SO2= 64.07 0.1786 (Gas) * With sufficient accuracy the weight in pounds per cubic foot of a non-associated dry gas, at stand- ard conditions, is 0.002789 times the molecular weight of the gas. + The “nitrogen” of the above table is “atmospheric” nitrogen, differing from chemically pure nitrogen in being mixed with a slight amount of the inert gas argon. weight slightly under 14.01. Chemical nitrogen has an atomic 250. Heat of Combustion or Calorific Power. — The value of a fuel for heat production is the number of British thermal units of heat which may be generated by the complete combustion of one pound of the fuel, or in the metric system the number of large calories generated by one kilogram. This number of heat units, which is a constant for any given fuel irrespective of the manner in which the combustion is carried on, as long as it is complete, is known as the heating value, or calorific power, of that particular fuel. The relation of B.t.u. per pound to calories per kilogram is 9:5 or 18:1. 251. Combustion of Elementary Fuels. — The following table gives the heating values of the principal elements occurring in fuels, and data on the combustion of these elements: COMBUSTION AND FUELS 467 Heating Value. Oxygen, Product of Com- Fuel of which Unit Weight is Burned. ee Required | bustion and Weight ories, 3 B.t.u./Lb. ietngrana Weight. of Same. Hydrogen, Hy................0-. 61,950* | 34,400 7.94 H20, 8.94 Carbon, burned to CO........... | 4,380 2,430 1.332 CO, 2.332 Carbon, burned to COQz........... 14,540 8,080 2.604 CO2, 3.664 CO burned to CO: .............. 4,380 2,430 0.571 CO, 1.571 Sulphur, 5, burned to SQz......... 4,020 2,230 ©.999 SQ, 1.999 Sulphur, S, burned to SO3........ 5,940 3,300 1.447 SO3, 2.447 Tron, Fe, burned to FeO.......... 2,430 1,350 0. 286 FeO, 1.286 * Higher Heating Value. 252. Combustion of Hydrogen or of Fuels Containing Hydro- gen. Higher and Lower Heating Value of Fuels. — When a fuel contains hydrogen a complication occurs, due to the fact that the water formed by the union of hydrogen and oxygen may or may not be condensed. If such water vapor is completely condensed, the heating value of the fuel is the so-called higher heating value; if the water vapor is not condensed, but passes off as steam, we obtain the lower heating value. The difference between the two heating values is the total heat of the steam as it escapes, less the sensible heat of the same weight of water at the temperature of the fuel and oxygen before combustion (room temperature). The total heat above 32° in one pound of steam, in the form of ‘‘ humidity ” in air or gases of combustion, is (1058.7 + 0.455 4) B.t.u.,* 4 being the temperature of the air or gases of combustion. If room temperature be taken as 4° F., the sensible heat of one pound of the steam condensed is (t, — 32) B.t.u. One pound of steam escaping uncondensed in the products of combustion, at temperature 4° F., will then take away (1058.7 + 0.455 f — te + 32.0) or (1090.7 + 0.455 fh — fe) B.t.u. One pound of hydrogen burns to 8.94 pounds of water; hence per pound of hydrogen the loss is 8.94 (1090.7 + 0.455 4 — #2) B.t.u. Assuming f, room temperature, at 60° F. (standard practice), the difference between the higher and the lower heating values of hydro- * This equation is the result of plotting the total heat in superheated steam of low pressure (less than 3 lbs. absolute, as even that is beyond the partial absolute pres- sure of water vapor occurring in flue gases or exhaust gases) against temperature. The expression is therefore in a sense empirical, but holds good for flue or exhaust gas computations. 468 EXPERIMENTAL ENGINEERING gen shows the following values for various temperatures of escaping steam: n° F., Temp. of | Difference of Heat- n° F., Temp. of Difference of Heat- Escaping Steam. ing Values, B.t.u. Escaping Steam. ing Values, B.t.u. 60° 9,450 700° 12,060 300° 10,430 I000° 13,280 500° 11,240 1500° 15,320 The experimental higher heating value of hydrogen is 61,950 B.t.u.; if the products of combustion are brought back to 60° F., but uncondensed, the lower heating value is 61,950 — 9450 = 52,500 B.t.u. The difference is 15 per cent of the higher, 18 per cent of the lower heating value. So large a difference is not negligible; we must decide whether we are to charge a furnace with the higher or the lower heating value of a fuel containing hydrogen. The German custom is to use the lower heating value; the American tendency is to use the higher. No actual furnace or engine does cool the products of combustion so as to condense the steam in them. Calorimeters, which are used to find experimentally the heating value of fuels, generally condense only a part of the steam, and consequently give neither the higher nor the lower heating value directly. Theoretically perfect absorp- tion of heat after combustion would condense all moisture formed from hydrogen. Ji seems right to charge against a furnace or an engine what a theoretically perfect apparatus would do. The volume of the products of combustion may be different from the volume of the combustibles, or the gases entering the combustion may not be saturated with “ humidity,” so that a larger amount of moisture might remain at room temperature as “‘ humidity ” in the burned than in the unburned gases. The correction for humidity is very small if the air supplied to a furnace is satu- rated or nearly so; but in the case of ordinary coal burning, with the air supplied about 50 per cent saturated, over one-fourth of the moisture formed from hydrogen combustion would remain uncondensed if the products of combus- tion were cooled back to room temperature. 253. Temperatures Obtained in Combustion. — The calculation of the temperatures obtainable in combustion is made from the amount of available heat and the amount and specific heat of the COMBUSTION AND FUELS 469 products of combustion. Specific heats are not constant, but in- crease with temperature. The values in the last column of the table below, intended for use in ordinary combustion calculations, are nearly correct for a temperature of 600° F., a common temperature for flue gases.* MEAN SPECIFIC HEATS AT CONSTANT PRESSURE, FOR COMBUSTION AT ATMOSPHERIC PRESSURE. | Specific Heat Substance. At Room Tem- Ordinary Flue- ° as Temperature perature 60° F. 600° F Albis Vaden ccts e's Sod eee See ENE SAESes as 0.237 0.243 Oxygen ibe, dea eitlergstnanage ae ar ghd doe le Silene eres AUS Gy LS Sea as 0.217 0.220 INIETOZERS. s aieeoudla ac Stains Ra miQeetand oO ANGE ARES 0.243 vu. 249 AYydrPOgetiin. cncnciaecekance tates ir bonecemeds 3.380 3.54 Carbon monoxide............. 0 cece eee eee eee 0.243 0.249 Carbon dioxidés-o. scciccaccdaanaioataist anaes oO. 201 0.222 Steam, in form of “humidity”................. 0.455 0.462 Sulphur dioxide oycc.cdenses eas cede csaa wees 0.154 v.17 ASH tenia tuicbews saat eeeres Henmameusy aay aeeees 0.2-6 0.24 COPPER oicncciudeet teva ss Meee Teeeeess 93003.) cla cabdauduean adorns TOM. iaussenentusuioionsa ho saves Gardener tay Sauer eed OAT lesan iennns IB LASS sncya bsiar Vena wer daimauniiagrsasipuiua ied Leelee hae 6.693, letamatainek aes CaS a 3 certs i atencht neers’ OG ROAR eG Ls Peet Reet fet Ok: Neg antareeanectan ayers ZANG) A: crtst, eee aaa a eae Re ANS Sinema OVOOBS) lee gceiamnen ns WO Od ivircre si aitesisrartcsyine 2 Gaae a mei dogmicuns a Rota se cacent OVO) fe ygengiaedls op ee The last six items are added to this table, as this data is some- times required for calorimetric work. To take an actual case, suppose we desire to compute the maxi- mum possible temperature attainable by the combustion of carbon. Burning carbon in pure oxygen, the heat evolved from one pound of carbon is 14,600 B.t.u., and there are formed 3.664 pounds of COs. Taking the specific heat of CO: as 0.222 (it would really be higher at high temperatures), the temperature should be 14,600 + (0.222 X 3.664) = 18,000° F. Actually, however, the combustion cannot be made to go on rapidly enough to reach this theoretical tempera- ture; heat will be lost too rapidly by radiation, and it is impossible * These values were obtained from comparison of numerous sources, greater credence being given to recent determinations at the Reichanstalt. For an extended discussion of the variations of specific heat see Chap. XXI. 470 EXPERIMENTAL ENGINEERING to avoid heating surrounding materials as well as the products of combustion. If hydrogen be taken as the fuel, the available heat for raising the temperature of the products of combustion above 60° F. is the lower heating value for 60° F., 52,500 B.t.u. per pound. For combustion in oxygen the theoretical temperature is then 52,500 + (0.462 8.94) = 12,500° F. Despite this lower theoretical temperature, we actu- ally obtain higher temperatures of combustion from hydrogen than from carbon, for in practice the problem becomes one of maximum energy development in a given space. The principal reason for the low temperatures obtained in actual combustion is the dilution of the products of combustion with inert material. Every pound of O, in air carries with it 76.8/23.2 = 3.31 pounds of Nz. Taking this into account for the combustion of car- bon, using only the air necessary to supply the oxygen needed, we get 14,540 + (0.222 X 3.664 + 0.249 X 2.664 X 3.31) = 4900° F. If we used 1.5 times as much air as was needed to supply Os» for the combustion of carbon, the theoretical rise of temperature during combustion would become 3360 degrees; with 2.0 times the needed air, 2550 degrees. By comparing these values with the 18,000 de- grees for combustion in pure oxygen we see how large is the effect of dilution. Roughly, the theoretical temperature of combustion of carbon with air is 5000° F., divided by the “dilution coefficient,” or ratio of air actually used to that necessary to supply oxygen to the carbon. For some years past it was thought that the reason we cannot, in practice, realize the high theoretical combustion temperatures indicated above, was a dissociation of the CO, or H:0; that is, the chemical compounds of C or H with O were supposed to break down spontaneously into their elements when the temperature became high. It is now known that dissociation of either CO, or H;O occurs only to a very slight extent (less than 1 per cent) even at 3000° F. (1600° C.). Dissociation therefore plays little part in any com- mercial case of combustion. 254. Calorimetry. — A calorimeter, broadly speaking, is any de- vice for measuring heat or heating value. A fuel calorimeter is a device in which a fuel sample may be completely burned, while the heat it produces is absorbed and measured. The combustion of the fuel must be complete. All the heat produced must be absorbed and COMBUSTION AND FUELS 471 measured. Heat from other sources should, as far as possible, be excluded, and allowance made for that which cannot be excluded. These requirements apply to all types of calorimeters. In operation, calorimeters fall into two classes, the discontinuous and the continuous types. Solid fuels are nearly aways tested in calorimeters of the discontinuous type, burning a weighed sample in a calorimeter using a fixed amount of heat-absorbing body. Liquid fuels are occasionally tested in the same way. Liquid fuels are usually, and gaseous fuels practically always, tested in continu- ous or constant flow calorimeters, both fuel sample and heat-absorb- ing body being under flow at measured rates. It may be said that both theoretically and practically the continuous-flow calorimeter is superior to the discontinuous, because of greater ease of handling and freedom from extraneous heat losses of the “ radiation type.” The discontinuous calorimeters will be discussed first. The parts of such a calorimeter are in general as follows: (1) Crucible for holding sample of fuel. (2) Igniter for firing the sample. (3) Combustion chamber. (4) Apparatus for supplying oxygen for combustion, for only in oxygen can complete combustion be assured in these calorimeters. (5) Heat-absorbing body surrounding the combustion chamber. (6) Thermometer or other device for measuring temperature changes in the heat-absorbing body, and thus measuring the heat absorbed. i“ (7) Jacket for excluding extraneous heat. The general problems of discontinuous calorimetry will be dis- cussed under the description of the bomb calorimeter, which is the most accurate, reliable, and also the most expensive of the calo- rimeters for solid fuels. 255. The Bomb Calorimeter. — There are a number of forms of this calorimeter now on the market, nearly all of them modifications of the original Berthelot type. The essential parts in every case are: (a) a strong steel vessel, usually lined with some non-corroding substance like platinum, gold, porcelain, or nickel, serving as a com- bustion chamber; (5) a small crucible, usually of platinum, inside of the vessel, to hold the sample; (c) valves or connections for 472 EXPERIMENTAL ENGINEERING A, containing vessel serving as water jacket; B, bomb; C platinum tray; D, calorimeter vessel; LKS, stirring apparatus; T, thermometer; O, tank containing high pressure oxygen; P, igniter battery. Fic. 347.— Mauer Fuet CALORIMETER. is | i are oe | CHER s[ ==: = Cail) il ll | , a MIE — Sm poo ee a 3 a OE OP OP PP PELE SG 6 EP a z= STITT \ II Onc COMBUSTION AND FUELS 473 charging the bomb with oxygen; (d) means for igniting the fuel; (e) a calorimeter vessel filled with water into which the bomb is placed; (f) a second vessel to serve as a jacket for the calorimeter vessel to reduce heat losses; (g) thermometers to measure tempera- ture; and (i) stirring apparatus to maintain uniform temperature in the water. These parts will be recognized in the following cuts, in which Fig. 347 represents the Mahler, Fig. 348 the Hempel, Fig. 349 the Atwater, and Fig. 350 the Emerson calorimeter. CLL $ YY Y; “7 Fic. 348. — HEmpet’s FUEL CALORIMETER WITH ENLARGED CHARGING PivG. The “bomb” is a heavy-walled combustion chamber in which the oxygen for the combustion is held under a pressure of 125 to 300 pounds to thesquare inch. By using the high pressure, aconsiderable amount of gaseous oxygen can be put into a small space, surrounding the fuel to be burned; more oxygen, of course, being put in than is needed for complete combustion of the fuel. The oxygen may be obtained either by chemical reaction between certain substances (as, for instance, manganese dioxide and chlorate of potash, equal parts) or by electrolysis, or by purchasing it in steel vessels compressed to about 20 atmospheres.. In the latter shape it may be obtained from any wholesale chemical house, which is 474 EXPERIMENTAL ENGINEERING perhaps the simplest and best way of obtaining this necessary gas. The method first mentioned may be carried out as shown in Fig. 351, in which the crucible C contains the mixture of chemicals. The latter is heated and the oxygen gas generated flows through dcb into the calorimeter. A gauge B indicates the pressure attained. The Tic. 349. ATWATER BomsB CALORIMETER. vessel E is filled with water to cool the gas. Any chlorine gas coming over may be removed by first passing the gas through a close roll of brass-wire gauze. Ignition of the fuel is generally electrical, and is accomplished either by fusing and burning a piece of fine iron wire in contact with the fuel, or by heating to redness a platinum wire dipping into the COMBUSTION AND FUELS 475 fuel. Heat from the igniting device is added to that given out in the combustion of the fuel, and correction must be made for this extra heat from the igniter. This igniter heat may easily amount to 0.3 to 0.5 of one per cent of the heat developed in the calorimeter. The bomb is immersed in a small body of liquid, usually water. Fic. 350.— EMERSON BomB CALORIMETER. The heat from the combustion raises the temperature of the bomb and of this liquid and its containing vessel. This rise of tempera- ture of the bomb, water, and containing vessel, when corrected for radiation and similar heat exchanges, measures the heat evolved in the bomb. In practice the absorption of heat by the bomb and the containing vessel is equivalent to having a certain extra amount of 476 EXPERIMENTAL ENGINEERING water present to absorb heat; hence the term water equivalent for the summation of the products mass times specific heat for each of the metallic parts of the calorimeter which run through the same temperature changes as the water. In the most accurate work it should not be forgotten that the specific heats of both the water and the metallic parts change with temperature. The magnitude of this change is not likely to exceed 0.3 of one per cent. It is uniformly neglected in commercial work. The temperature of the water, bomb, and containing vessel is measured by a mercury thermometer or some equivalent device, Fic. 351.— APPARATUS FOR PREPARING OXYGEN. such as a spiral wire of which the electrical resistance is measured. To make sure that the temperature reading (usually a measurement taken at one spot only) represents the temperature of the entire instrument, stirring of the water is necessary. If the instrument could be thermally isolated from its surround- ings, it would be necessary only to measure the temperature before _ ignition and the temperature after complete combustion, calculating the heat evolved from the temperature range and mass and specific heats of the calorimeter parts absorbing heat. Such thermal isola- tion is impossible; the calorimeter is continually exchanging heat with its surroundings by (1) direct radiation, (2) convection cur- rents of air, (3) evaporation of water from the calorimeter to the atmosphere, which is practically never saturated with moisture. COMBUSTION AND FUELS 477 To reduce these heat exchanges — usually classed as “radiation,” al- though real radiation loss is the smallest of the exchanges mentioned — to their lowest terms, it is customary to surround the containing vessel of the calorimeter with a “jacket”? and to cover the calo- rimeter so as to prevent access of air and consequent convection cur- rents. The containing vessel of the calorimeter is made of polished metal to diminish radiation. The jacket is a double-walled vessel, polished at least on the inside, with the space between its walls filled with water or other liquid, so as to keep the jacket fairly con- stant in temperature. It is usually assumed that for a jacketed calorimeter the “ radiation rate,” or rate of loss or gain of heat by the calorimeter in exchange with its sur- roundings, is proportional to the difference of temperature between calorimeter and jacket. Analysis shows that this assumption is not justified. True radiation between calorimeter and jacket is closely enough a straight-line function of the temperature difference between them. Convection transfer of heat between calorimeter and jacket is also probably given nearly enough as a straight-line function of the same temperature difference. These heat exchanges reverse in direction and amount when the temperature difference between calorimeter and jacket changes sign. But there is also a slight amount of convection loss of heat from calorimeter to the outer atmosphere, or room, when the calorimeter is hotter than the room —a heat exchange outside of the control of the jacket. This exchange is not reversed when the calorimeter is colder than the room, for the space between jacket and calorimeter then fills with dead air, colder than the room, and the exchange ceases. Frequently the most important of all these extraneous heat effects, on the calorimeter, is the heat loss by evaporation of water into the unsaturated atmosphere of the room. This heat loss depends on the temperature of the calorimeter, increas- ing in rate as the temperature of the calorimeter rises, and on the relative “humidity ” of the air inthe room. This effect is always a loss and is inde- pendent of the jacket. Summing up all of these heat exchanges between the calorimeter and its surroundings, it will be seen that the “ radiation rate” is dependent on so many different things that it must, for accuracy, be determined for the beginning and end of each run of the calorim- eter. The best simple assumption as to variation of the “radia- tion rate? between the two end conditions of the run is that the radiation rate varies directly with the temperature of the calorimeter. This is better than to assume straight-line variation with tempera- 478 EXPERIMENTAL ENGINEERING ture difference between calorimeter and jacket, because this tem- perature difference controls only part of the various heat exchanges, while the calorimeter temperature enters as a controlling factor into all. The common assumption that “radiation” is zero or negli- gible, when the initial calorimeter temperature is just as much below the jacket temperature (or room temperature) as the final calorim- eter temperature is above the same, is quite unjustified. 256. Method of Operating a Bomb Calorimeter. — The conduct of a determination may now be considered. The calorimeter and accessory apparatus are assumed to be clean and in working order. The first thing to be done is to find the “ water equivalent” of the calorimeter, unless this is already known. This may be done in one of three ways: (a) Calculation. — Weigh separately each of those parts of the instrument that go through the same temperature range as the water. Multiply each weight by the specific heat of the material of which the part is made. The summation of these products is the water equivalent. Allowance must be made for the poor con- ductivity of wood or glass, which generally acts so that only a sur- face layer of such material is thermally active during the running of the calorimeter; in a less degree such an allowance should be made for neutral parts projecting markedly above the surface of the water. (b) Method of Mixtures. — Partly fill the calorimeter vessel with a known mass of water. Allow all parts to come to thermal equi- librium, then determine temperature and radiation rate. Add a known mass of water (completing the filling of the calorimeter), of a known temperature considerably higher or lower than that of the water already in the calorimeter. Stir to equilibrium, taking read- ings of temperature, and finish with a determination of the final radiation rate. After correction for radiation the discrepancy in the heat balance is the product of the water equivalent and the observed temperature range. Make several determinations and average the results. (c) Method of Adding a Known Amount of Heat Inside the Bomb.— This may be done by (1) burning a sample of fuel the value of which is already well known; (2) inserting an electrical resistance heater inside the bomb and measuring the input to the heater with an COMBUSTION AND FUELS - 479 accurate wattmeter. Runs are made as with an unknown fuel, and the calculations worked backward to find the water equivalent. Methods (0) and (c) are to be preferred to method (a) for accuracy. The water equivalent of a calorimeter is usually determined once for all. There is no reason why it should change with time, but it does change slightly with temperature, because of change of the specific heat of the parts. Knowing the water equivalent, the regular run proceeds as follows: Weigh out into the crucible of the calorimeter a proper amount of sample, usually from half a gram to two grams, depend- ing on the make and size of the calorimeter. The sample, if of coal, should be in a finely divided condition, about fine enough to pass a too-mesh sieve. It should preferably be somewhat moist, as moderately moist coal burns less explosively than dry coal, particu- larly if the sample is of the bituminous or lignite variety. Hence the calorimeter sample may best be made up from the coal “ as received.” (See later directions for coal analysis.) Put the crucible with the weighed sample into the bomb and arrange the igniter for operation. Put a few drops of water into the bomb. This insures an initially saturated atmosphere in the bomb, and hence the find- ing of “ higher heating value” from any hydrogen. Screw the top onto the bomb and charge the bomb with oxygen gas to the correct pressure. Close the charging cock, and put the charged bomb into position in the calorimeter vessel. Fill the calorimeter vessel with a weighed amount of water. Weighing is more accurate than measuring. Arrange stirrers, thermometers, etc., ready for opera- tion. The calorimeter liquid should not be over a degree or two colder or hotter than the jacket, and neither ought to be more than five degrees different from room temperature, although this is less important. Let the calorimeter stand a few minutes, watching the temperature and occasionally stirring, until the parts are in a settled condition. Then determine the initial radiation rate by tempera- ture observations at one-minute intervals extending over five or more minutes, stirring between readings. When the readings have shown a satisfactory constant rate of change of temperature (so- called “‘ radiation rate’’), start the igniter on some even minute. Thereafter take readings every half minute until combustion is over 480 EXPERIMENTAL ENGINEERING and the calorimeter settles to a second radiation period. Stir thoroughly between readings. Finish with a determination of final radiation rate similar to the initial. Remove the bomb from the calorimeter. Open the charging cock carefully to let out the gases. Then unfasten the cover and inspect the crucible and the interior of the bomb to make sure of complete combustion. Clean up for the next run. The observations taken during a commercial test, and the method of working them up, are as follows: SAMPLE CALCULATIONS FOR BOMB CALORIMETER. Weight of coal sample, grams. ........00... 0... e cece eee eee es 1.2794 Weight of iron igniter wire burned, grams...................0005 0.0022 Weight of calorimeter water, grams................ 00... eee eee 1408 Water equivalent of calorimeter, grams..............-..-..00 eee 345 Water + water equivalent, grams................ 00s eee eee eee ee 1753 Pressure of oxygen charge in bomb............... 250 lbs. per square inch. Observations of Run. Calculated Values (see below). i Cor- oe Mean .(-Radiation Radiation | Total Ra- | rected : ‘emp. in Temp. Rate for ee Time. Calo- of In. | the Inter: for the In- diation Cor-| Tem- seme: tanya. gall terval. rection. pera- ture. CP. T3253) Bec26> W. . PeeSencleouis di utalas yeaa +o.1222/23.322 14] 23.22 Initial 23.21] —0.0137; —0.0274| +0.0948)23.315 16} 23.25 radia- 23.23) —0.0136) —0.0272} +0.0676)23.318 18} 23.28 tion 23.26) —0.0136, —0.0272} +0.0404' 23.320) 23.318 20} 23.30 rate. | 23.29] —0.0135| —0.0270; +0.0134]23.313 21] 23.32 Ignition. 23.31] —0.0134) —0.0134) 0.0000)23.320) 22} 27.20 25.26] —0.0079| —0.0079| —0.0079|27.192 23} 28.45 27.92| —0.0004] —0.0004| —0.0083)28.442 24) 28.68 28.57| +0.0015| +0.0015| —0.0068)/28.673 a 25 28.74 28.71] +0.0019| +0.0019] —0.0040|28.735 3226} 28.77 28.76} +0.0021| +0.0021] —0.0028]28.767 M127, 28.78+ 28.78) +0.0021) +0.0021] —o.0007/28.784 28} 28.79 28.79] +0.0021] +0.0021) +0.0014/28.791 29} 28.79 28.79| +0.0021| +0.0021| +0.0035|28.794' 30] 28.79 28.79| +0.0021] +0.0021] +0.0056/28.706 32} 28.79 28.79] +0.0021] +0.0042} +0.0098/28 . 800 34] 28.79 |). 28.79] +0.0021| +0.0042} +0.0140|28. 804 36], 28.78+ Final 28.79| +0.0021] +0.0042} +0.0182 28 .803 38} 28.78 radia- 28.78! +0.0021| +0.0042} +0.0224/28.802 4o| 28.77+| / tion 28.78) +0.0021| +0.0042| +0.0266|28. 802] ¢28- 803 42) 28.77 | rate. 28.77) +0.0021| +0.0042] +0.0308]28. 801 44, 28.77 28.77| 0.0021} +0.0042/ +0.0350|28. 805 ‘ The first calculation is for the “ radiation correction.” The readings of the initial and final radiation-rate determinations should be plotted to an open COMBUSTION AND FUELS 481 2 Fic. 352. 482 EXPERIMENTAL ENGINEERING temperature scale, as in Figs. 352a and 352b, and the slopes of the straight lines accurately determined, with the mean temperatures at which each rate is found. Then plot Fig. 352c, radiation rate against temperature in calorimeter, drawing a straight line through the two points determined. 1. Long Method for Radiation Correction. — Average the readings of the test in pairs successively, to give the column “ mean temperature of interval.” For each mean temperature of interval pick off from the curve, Fig. 352c, the “radiation rate for the interval.’”’ Multiply the radiation rate by the time length of the interval in minutes, getting the ‘‘ radiation for the interval.” Assume zero radiation correction at any arbitrary reading (in this case the reading at ignition). Then the “total radiation correction” at any other reading of the test is the summation of the values of “radiation for the interval”? between this reading and the reading at which the radiation is assumed zero. The continued summation of the column “ radiation for the interval” gives the column “ total radiation correction.” Total radiation correction added to the observed temperatures gives “corrected temperatures.” If the radiation correction has been properly made, the corrected tempera- tures for the radiation runs at the beginning and end of the test should be constant within the error of reading. This is very nearly realized, the average being 23.318° for the initial and 28.803° for the final radiation runs. Inspec- tion of the column of “ corrected temperatures,” in comparison with that of “observed temperatures,” will show that the observed temperatures reached a constant value for some time before the corrected temperatures did. This means that there was still going on in the calorimeter a slight evolution of heat which was practically balanced by radiation loss. The run proper on the calorimeter must not be considered complete until a constant rate of change of calorimeter temperatures against time has been established. The corrected rise of temperature in the example here given is the differ- ence of the average corrected temperatures for the final and initial radiation periods, or 28.803 — 23.318 = 5.485° C. 2. Shorter Method for Radiation Correction. — Plot Fig. 352a and Fig. 352b as before. Find, by the trapezoidal or Durand’s tule, the time average tem- perature of the run proper, that is, from 12:21 to 12:34 inclusive in the example. The average temperature is 28.42° C. In Fig. 352c find that the radiation rate corresponding to this average temperature is --o,0011 degree per minute. The time is 13 minutes. Hence, 13 X 0.0011 = +0.0143, the radiation cor- rection for the run. The corrected temperature rise is then 28.79 + 0.014 — 23.32 = 5.484°. This method of calculation is exactly equivalent to the long method above, but avoids practically all of the work. If, however, one took the run as lasting from 12:21 to 12:28, as might be done, Judging from observed temperatures only, this short method would not show that the chosen length of run was in error, while the longer method does reveal such errors. 3. A bproximate Short Method for Radiation Correction. — This assumes that the initial radiation rate applies until the time when a temperature is reached COMBUSTION AND FUELS 483 midway between the initial and final temperatures, and after that time the final radiation rate applies. In the example given here, the average of initial and final temperatures is (28.79 + 23.32) + 2 = 26.06. This temperature is reached in three-quarters of a minute from the start, as found by plotting a rough curve of temperature against time for the run. Hence we have: Initial radiation rate for 3 min., 2 X (— .0136) = —.o102. Final radiation rate for 124 min., 124 X (+ .0021) =+ .0257. Total radiation correction, + .0257 — .o10o2 =+ .o155. Corrected rise, 28.79 + .o15 — 23.32 = 5.485°. This result agrees exactly with that of Method 1, but this agreement is only accidental. 4. The method of calculating radiation correction for the run by applying the algebraic mean of the initial and final radiation rates to the entire time is incorrect; a little thought shows it to be irrational. It seems, however, to be quite commonly used. 5. Calculations of Heat Evolved.— The heat, in calories, evolved in the calorimeter is the product of the water + water equivalent in grams, multi- plied by the corrected temperature rise in degrees C. In the example it is 1753 X §.485 = 9615 calories. The combustion of the iron wire in igniting gave 1350 X .0022 = 3.0 calories. As much or more again was due to the electric current used to heat up the iron wire. Hence, we may say that 9615 — 6 = 9609 calories came from the coal burned. Since B.t.u. per pound = 1.8 times calories per gram, and weight of coal was 1.2794 grams, the heating power of the coal was 9609 X 1.8 1.2794 This calculation assumes the specific heat of water = 1.0000; the real specific heat for the mean temperature of the run is 0.9972. Remembering that the correction for this specific heat applies only to the 1408 grams of water out of the 1753 of (water -+ water equivalent), the corrected and final value for the heating power is 13,820 — 30 = 13,780 B.t.u. per pound. In commercial work the corrections for heat from the igniter wire and for variation of the specific heat of water from unity are not ordinarily made. = 13,820 B.t.u. per pound. Other Forms of Fuel Calorimeters. 257. Favre and Silbermann Fuel Calorimeter. — This apparatus, as shown in Fig. 353, consisted of a combustion chamber A formed of thin copper, gilt internally, and fitted with a cover through which solid combustibles could be introduced into the cage C. The cover was traversed by a tube E, connected by means of a suitable pipe to a reservoir of the gas to be used in combustion, and by a seconG 484 EXPERIMENTAL ENGINEERING tube D, the lower end of which was closed with alum and glass, transparent but adiathermic substances which permitted a view of the process of combustion without any loss of heat. For convenience of observation a small inclined mirror was placed above the peep-tube D. The products of combustion were carried N =4 Sf S on se & as 4 eS = ESS = Be F = Ss a Ly se | H H |S ee = LU 7 J s ee | SF She iat ls TGS A afin § EMI ae UT a A |e inch. Fic. 353.— FAVRE AND ‘SILBERMANN FUEL CALORIMETER. off by a pipe F, the lower portion of which constituted a thin copper coil, and the upper part was connected to the apparatus in which the non-condensible products were collected and examined. The whole of this portion of the calorimeter was plunged into a thin copper vessel, G, silvered internally and filled with water, which was kept thoroughly mixed by means of agitators, H. The second vessel stood on wooden blocks inside a third one, I, the sides and bottom of which were covered with swanskins with the down on and the whole was immersed in a fourth vessel, J, filled with water COMBUSTION AND FUELS 485 kept at the average temperature of the laboratory. Thermometers KK of great delicacy were used to measure the increase of tempera- ture in the water surrounding the combustion chamber. The quantity of heat developed by the combustion of a known weight of fuel was determined by the increase of temperature of the water contained in the vessel G. For finding the calorific value of gases only, the cage C was removed and a compound jet, NO, substituted for the single gas pipe, ignition being produced by an electric spark or by some spongy platinum fixed at the end of the jet. Combustion is slower than in the bomb, and radiation thus becomes more important, and introduces larger uncertainties into the results. Favre and Silbermann calorimeters will not be found in commercial work. 258. Carpenter Calorimeter. — The Carpenter calorimeter, Figs. 354 and 355, introduces a novelty in that it makes the calo- rimeter liquid do its own thermometry. For this purpose the calorimeter vessel is closed at the top, and is completely filled by the calorimeter liquid (usually water). The calorimeter vessel thus becomes practically the bulb of a huge thermometer. The general appearance of the instrument is shown in Fig. 354; a sectional view of the interior part is shown in Fig. 355, from which it is seen that in principle the instrument is a large thermometer, in the bulb of which combustion takes place, the heat being absorbed by the liquid which is within the bulb. The rise in temperature is denoted by the height to which a column of liquid rises in the attached glass tube. In construction, Fig. 355, the instrument consists of a chamber, 15, which has a removable bottom, shown in section. The chamber is supplied with oxygen for combustion through tube 24, 25, the products of combustion being discharged through a spiral tube 28, 29, 30. Surrounding the combustion chamber is a larger closed chamber, , filled with water and connecting with an open glass tube 9 and to. ‘ Above the water chamber 1 is a diaphragm 12, which can be changed in position by screw 14 so as to adjust the zero level in the open glass tube at any desired point. A glass for observing the process of combustion is inserted at 33, in the top of the combustion chamber, 486 EXPERIMENTAL ENGINEERING and also at 34, in the top of the water chamber, and at 36 in the top of the outer case. This instrument readily slips into an outside case, which is nickel- plated and polished on the inside, so as to reduce radiation as much as possible. The instrument is supported on strips of felting, 5 and Petit |l z avai fm PD aA tid y HLA Hn Hid ‘f y i HIYA i) } 4 i HII 4 Y 4 Y 4 A SS ——— Fic. 355. CARPENTER FUEL CALORIMETER. 6, Fig. 355. A funnel for filling i is provided at 37, which can also be used for emptying if desired. The plug which stops up the bottom of the combustion chamber carries a dish, 22, into which the fuel for combustion is placed; also two wires passing through tubes of vulcanized fiber, which are ad- justable in a vertical direction, and connected with a thin platinum COMBUSTION AND FUELS 487 wire at the ends. These wires are connected to a source of electric current and used for firing the fuel. On the top part of the plug is placed a silver mirror, 38, to deflect any radiant heat. Through the center of this plug passes a tube, 25, through which the oxygen passes to supply combustion. The plug is made with alternate layers of rubber and asbestos fiber, the outside only being of metal, which, being in contact with the wall of the water chamber, can transfer little or no heat to the outside. The discharge gases pass through a long coil of copper pipe, and are discharged through a very fine orifice in a cap at 30 in Fig. 355, or at C in Fig. 354. . The effect of the combustion is to expand the water and thus raise the outer level in the tube 10. The theory is that this expan- sion is a direct function of the amount of heat added to the water. In practice the rise in the tube must be corrected not only for radia- tion but also for the fact that the coefficient of expansion of water varies rapidly with the temperature. In the directions furnished with the earlier instruments the latter fact was not taken into account and radiation was accounted for simply by letting the calorimeter stand, after the combustion was completed, for the same length of time as was taken up by the combustion, noting the drop in the water level in the tube. This drop was then added to the rise obtained during combustion, on the assumption that radiation kept the rise down by the amount noted. This method is not rational. It will be appreciated that the heat interchanges controlling the rise in the tube are rather complex, and the best way to obtain a- standardization of the instrument is to calibrate by means of burn- ing a certain quantity of a fuel of known heating value. The “cali- bration constant ’”’ will be a function of the temperature of the calorimeter liquid (on account of the change of coefficient of ex- pansion with temperature), and a thermometer should therefore be provided. In the commercial form of this calorimeter as described ‘this may be done by inserting a thermometer cup in place of the filler plug or funnel 37. Adjustment of the height of liquid in the expansion tube is some- times necessary. To make this adjustment, cut in between the 488 EXPERIMENTAL ENGINEERING stuffing box at the top of the calorimeter and the expansion tube a glass tee with a ground cock in the side branch, making connection by a rubber tube to a reservoir hung behind the scale and expansion tube. Adjustment of scale reading is made by opening the glass cock, moving the reservoir up or down, and closing the cock. When the calorimeter is not in use the cock should be open, so that as the calorimeter cools off the liquid may not contract so far as to draw air into the top of the calorimeter. No stirring is done. The argument is that if one part of the liquid becomes hotter than the rest, it expands correspondingly, and hence changes the scale reading. As the scale shows the total ex- pansion of the entire body of liquid, it indicates accurately the mean temperature of the liquid. Temperature differences in different parts of the liquid cannot become large, for convection currents would then be set up which would tend to restore equilibrium. To make a run with the Carpenter calorimeter proceed as follows: See that the calorimeter is correctly set up inside its jacket, that thermometer and plug are in place, etc. Adjust the water level in the scaled expansion tube to be just above the zero of the scale. Weigh out a fuel sample (about one gram), preparing the sample as in the directions above for the bomb, by grinding some of the “‘coal as received’ to about the fineness of a 100-mesh sieve. Remove the charging plug from the calorimeter, adjust the loaded crucible upon the stand, and set the igniter ready for operation. Screw the plug back into place. Connect up the igniter wires and the oxygen tube. Turn on the oxygen, adjusting the supply until it flows through under an entering pressure of about 3 inches of water, as indicated by a manometer connected on the line. Let the arrange- ment stand with oxygen on for about five minutes to become steady. Then take a reading of the scale and the thermometer. Five minutes later repeat these readings. These establish the initial “radiation rate.” At the instant of this second set of readings operate the igniter to start the combustion, watching through the windows provided for that purpose. If the coal flames up consider- ably, choke the oxygen supply until the flame quiets. Take read- ings of the scale at least every five minutes, exactly on the minute, dating from the time of ignition. It is better to take readings COMBUSTION AND FUELS 489 rather more frequently, say every two or three minutes, while the combustion goes on. Combustion continues from ten to fifteen minutes. After combustion ceases it takes from ten to fifteen min- utes longer for the calorimeter to steady on to the second radia- tion rate. Continue readings at five-minute intervals until a main- tained steady change from reading to reading shows that the final radiation rate has been found. With the last scale readings observe also the temperature by the thermometer of the liquid in the calo- rimeter. Shut off the oxygen; remove the plug. Weigh the crucible and ash, after drying, to determine the ash content of the coal. The combustion in this calorimeter is so quiet that the calorimeter sample serves for the ash determination. 259. Calculations with the Carpenter Calorimeter. — The calcu- lations and observations for this test are like those of the bomb calorimeter, with the substitution of calorimeter scale reading for calorimeter temperature. Radiation rates, rise, corrected readings, etc., are figured on the scale readings. Then, adding the actual observed temperatures of calorimeter liquid at beginning and end of run, and dividing by 2, find the actual mean temperature of the run. With this enter the calibration curve (of calorimeter constant against mean temperature of run), and find the particular value of the constant applying to the run. The calorimeter constant times the corrected scale rise gives the B.t.u. (or calories) produced by the burning of the sample. From there on the calculations are again like those of the bomb calorimeter. It has been mentioned that calibration of this calorimeter must be made. A “known” fuel may be prepared very easily by either burning, coking, and grinding. granulated sugar or by coking and grinding any good grade of soft coal. The coking should be done at white heat under exclusion of air. The coke thus made should be ground to pass a 5o-mesh sieve, and should be used dry — that is, just previous to use it should have been dried by heating for an hour or more at 250° F. or higher. The combustible portion of the material so made may safely be assumed to be pure carbon, of a heating power of 14,540 B.t.u. per pound, equivalent to 32.20 B.t.u. per gram. The difference in weight of crucible + sample before the run and dried crucible + ash after the run gives the weight of 490 EXPERIMENTAL ENGINEERING carbon burned. For calibration, runs should be made with this known fuel exactly as with an unknown; then by calculating back- wards the calorimeter constant for the mean temperature of each run is found. A calibration curve of calorimeter constant against mean temperature of run should then be plotted. It will be noted that nothing has been said about the heat from the igniter. This should be controlled so as to be the same from run to run. Further, such a weight of sample should be taken as to make the total heat evolved in the calorimeter practically the same in every run. When these conditions are met no attention need be paid to the heat from the igniter, as it will form the same propor- tionate part of runs upon both known and unknown fuels; and the “constants” found in the runs on known fuels will apply to runs upon unknown fuels. If these conditions are not met the calo- rimeter will not give satisfactory results. The actual run during which calorimeter readings are being taken lasts about half an hour with the Carpenter calorimeter. On account of this long time radiation mounts up, so that the radiation correction may become as much as 10 per cent of the total corrected scale reading. As the certainty of radiation calculations is of the order of + 10 per cent, this introduces a possible error of + 1 per cent, and better work than this should not be attempted with the Carpenter calorimeter. This accuracy is, however, good enough for most engineering work. 260. The Parr Calorimeter.— The Parr calorimeter, Fig. 356, in its general operation, method of run, etc., is essentially similar to the bomb calorimeters. It differs from them in that, instead of using compressed gaseous oxygen surrounding the fuel, it gets oxy- gen from a chemical powder (sodium peroxide) mixed with the powdered fuel. The reactions in this case, however, are not those of simple combustion. The products of combustion, COs, H2O, SOs, or SOs, etc., further react with some of the NazO». or NasO to form Na2CO;, NaOH, NazSOsz, or NapSOy, etc., and these products are therefore chemically bound and do not escape. These by- reactions also evolve heat, the quantity of which depends upon the proportion of the mixture used. In a way this is an advantage, in that it increases the amount of heat to be measured in the calo- COMBUSTION AND FUELS A4gI rimeter for a given weight of fuel sample. The excess of heat may amount to from 30 to 4o per cent of that from the combustion proper, and is corrected for by multiplying the heating value of the combustion as determined by a percentage factor. Fig. 356 shows the general rela- tion of the parts of this calorimeter, while Figs. 357 and 358 give the de- tails of the so-called cartridge D. In this cartridge there is placed the prepared coal together with the proper amount of the ‘chemical used for the generation of the necessary oxygen, the charge be- ing inclosed gas tight. The mix- ing is done by shaking. After filling, the cartridge is placed in the calorimeter vessel, the covers are put on, and the fuel is lighted. Stirring is done by continuous ro- tations by means of the pulley P, Fig. 356, the water being agitated by the small blades shown at the sides of the cartridge. The casing E in the same figure is open top and bottom to promote water cir- culation. Ignition is produced in two ways, depending upon the construction of the cartridge. In Fig. 357, depressing the cap O against the spring NW opens the valve M, and ignition may then be effected by dropping a piece of red-hot wire down the central hole. Fig. 358 shows a modification in which an electric current is used to fuse the wire G. Contact is made through K and the stem B. In either case the heat of ignition must be corrected for. The observations taken during a run are the same as for the ordi- nary bomb and the computations are made in the same way. The calorimeter allows of very quick determinations. There are, how- Fic. 356.— Parr FUEL CALORIMETER. EXPERIMENTAL ENGINEERING 492 ever, several things tending to impair accuracy that should be mentioned. (2) The sodium peroxide combines violently with water, even in the form of moisture; it is hard material to handle, and it is likely to deteriorate in keeping. K Li PPPS SSS Uh SSS ANN DENI” oOo DODO Kyu Jd .[ 1 LAA xy [IIIT ITI OLE SASS SS Ss-sS SSS _ WN GW =MW®] rrjE AAA I, Sie a Sq I! ss UIE LA WS errr VO Fic. 358. OOOO KK WF S Fic. 357. DETAILS OF CARTRIDGE, PARR CALORIMETER. WUD Ua (b) When the Na2O, has aged, partially changing to NaOH, the character of the by-reactions and the heat evolution from them change. (c) The excess heat from the by-reactions does not have exactly the same ratio for C, H, and S; hence a change in the composition COMBUSTION AND FUELS 493 of the fuel tested involves a change in the ratio between true heat of combustion and heat evolved in the calorimeter. (d) It is hard to get complete combustion. The fused coke re- maining in the “ bomb” after a run frequently contains unburned material. Despite these disadvantages, the Parr calorimeter is accurate enough for most commercial work, and when checked occasionally Fic. 359.— JUNKER GAS CALORIMETER. against a good bomb calorimeter it is quite satisfactory. This checking enables the operator to make corrections for the errors above, as they are occurring in his own work. Of the discontinuous calorimeters, the “bomb” and the Favre and Silbermann may be called “ primary” instruments, being of sufficient accuracy for scientific as well as commercial work; the Carpenter, Parr, and others like them, are “secondary” instru- 494 EXPERIMENTAL ENGINEERING ments, good enough for most commercial work and quite accurate provided they are occasionally checked against a primary instrument. 261. Continuous Calorimeters. — Continuous calorimeters may be typified by the one most important in engineering, the Junker cal- orimeter, Fig. 359 and Figs. 360a and 36ob. Fig. 359 shows the parts belonging to a complete outfit. At the left there is a delicate wet gas meter (inlet at g). The gas flows Overflow aa Fic. 360a. Fic. 360b. through a pressure regulator and is then supplied to a burner located centrally in the calorimeter. Water is supplied at a (b being an overflow), regulated at e, and escapes atc. fisadrain cock. The water is measured, either in a graduated cylinder as shown, or by some other means. The water of condensation is caught and measured at d. COMBUSTION AND FUELS 495 The cross section of Fig. 360a makes the construction of the calo- rimeter clear. The rate of supply of water is regulated by means of the plug cock 9, and the pointer and scale 11, Fig. 360b. Tempera- ture of the inlet water is taken at 13. The water rises in the jacket around tubes (see cross section) through which the products of combustion formed in the space 28 pass downward. The warm water passes plates 38, having staggered holes to promote thorough mixing, and flows out through 18, 20, and 21 either to the measuring apparatus or to waste. Temperature of outlet water is measured by thermometer 43. The gas from the regulator is furnished to the burner at 22. Orifice 24 can be exchanged to suit the kind of gas. Slide 23 serves to regulate the air supply. The gases of combustion formed in 28 rise to 29, pass down through 30, and escape through 31 and 32. The damper 33 serves to control the rate of escape. The pipe 32 is furnished with a thermometer to indicate the tem- perature of the outlet gases. The degree of cooling is thorough enough to partially condense the water vapor in the gases, the condensation flowing out through 35. The entire calorimeter body is surrounded by a polished metal jacket 36 forming an air space 39. This instrument is adapted for either gaseous or liquid fuels, a special attachment (weighing balance) being furnished for the latter. By the device of maintaining a constant head upon an orifice the rates of flow of heat-absorbing liquid (water) and fuel (gas or liquid) are kept very closely constant. The products of combustion flow counter to the water, so that they are thoroughly cooled. By con- trolling the rates of flow of gas and of water as described above, the observer should be able to get simultaneously: (1) discharge gases of the same temperature as the atmosphere or the entering gases; (2) a sufficient range of temperature of the water between intake and outlet to give accuracy in the heat calculations. The observations are: (x) Rate of flow of water. (2) Temperature of water entering the calorimeter. (3) Temperature of water leaving the calorimeter. (4) Rate of flow of fuel. (5) Temperature of fuel. 496 EXPERIMENTAL ENGINEERING (6) Temperature of room. (7) Temperature of discharge gases. (8) Amount of water of condensation. (6) and (7) enter only into the regulation of the instrument. (1), (2), (3), (4), and (8) are used in the calorimetric calculations. (x) is measured by observing, with a stop watch, the time re- quired to fill a large graduate (2000 c.c., for example) with discharge water from the calorimeter. By suitable means of measuring water the operation of the calorimeter may be continued for a considerable time. By the use of an accurate scale of considerable capacity it is easy to make runs lasting several hours, and long-time trials on pro- ducer gas plants, for instance, may thus be covered by an almost continuous heating value determination of the gas. The tempera- ture of this water is known (measurement 3), so correction can be made for its density and specific heat. (2) and (3) are the averages of frequent readings of the water thermometers during the progress of the run. (4) If gases are being burned, the rate of flow of gas may be measured either by the fall of a gasometer or, more commonly, by the use of a special gas meter. In either case the temperature and pressure of the gas must be taken at the point where its volume is measured. With the gas meter one has to calibrate the meter care- fully — the ultimate recourse must be the gasometer. To measure the rate of flow of liquid fuels, an ingenious device is furnished with the calorimeter, consisting of a pressure tank, holding the fuel and supplying the burner, this tank being suspended from one knife- edge of a balance. The rate of flow is found by taking with a stop watch the time between throws of the balance beam when a known weight has been taken from the opposite pan of the balance between the throws. To find the heating value of the fuel, multiply the volume of water flowing per unit of time (the time unit is arbitrary) by the density and specific heat of water at the discharge temperature, and by the temperature range of the water between intake and dis- charge; divide by the volume or weight of fuel flowing in the same unit time. The result is approximately the higher heating value of the fuel. COMBUSTION AND FUELS 497 Radiation is small and is neglected. There is no water equivalent of the calorimeter to consider. If the temperature of the discharge gases differs from room temperature the results will be in error, but the amount of correction is uncertain and cannot be computed. The volume of a gaseous fuel must be corrected to whatever condi- tions have been determined upon as standard. In most industrial reports this standard condition must be the condition at the gas meters according to the measurements of which charges are made for gas. The results should also be given calculated to the scientific standard conditions of 32° F. and 29.92 inches of mercury pressure in order to be comparable with measurements made in other places. The Junker calorimeter measures nearly the higher heating value of the fuel. It does not quite do so, because moisture escapes un- condensed as “humidity” in the exhaust gases. If the air and gas supplied to the calorimeter be both saturated with moisture, then the calorimeter will truly give the higher heating value of the fuel, for it will condense all moisture found from the combustion of hydrogen. The lower heating value of the fuel can be readily found under any conditions from the instrument as it is run ordinarily. The condensed moisture can be caught and measured as it drips from the instrument. Find the rate of this drip, and calculate by the methods given above, page 467, in the discussion of the difference of higher and lower heating values, the corresponding heat; sub- tract this from the heat measured, and the lower heating value of the fuel will be accurately determined. If the hydrogen content of the fuel be known, the higher heating value can be easily calcu- lated from the lower. The true higher heating value of the fuel will be found to be considerably above the value measured by the calorimeter under the ordinary running conditions. For ordinary gases the Junker calorimeter uses a form of Bunsen burner. Gases of low heating value, such as producer gas, can be mixed with air and burned in a simple metal tube. In burning liquid fuels, such as gasoline, kerosene, or heavier oils, a regenera- tive burner may be used. Air pressure forces the liquid through a coil of metal tubing which lies above the flame and is heated by it. In this coil the liquid is gasified. It then passes downward, turns upward again, and escapes through a tiny orifice in a gaseous jet, 498 EXPERIMENTAL ENGINEERING which burns much after the fashion of a Bunsen flame. In dealing with heavy oils the regenerator coil must be artificially heated before the burner can be started. Care must be used not to choke the orifice of the burner. Commercial Fuels. 262. Composition of Fuels. — Fuels are classified as solid, liquid, and gaseous. By far the most important of all fuels is coal, the vari- ous grades of which are again classified, usually in three main classes: anthracite or hard coal, bituminous or soft coal, and lignite. Next to coal in properties come peat and wood, and vegetable and animal wastes, such as bagasse, garbage, etc. The most important liquid fuels are petroleum or petroleum products. The gaseous fuels are natural gas and various forms of artificial gases, such as illuminat- ing gas, water gas, producer gas, blast-furnace gas, etc. Wood and similar vegetable materials consist of cellulose, starch, water, and secondary amounts of various carbohydrates other than cellulose and starch. When decomposed by heat, out of contact with air, wood yields acetic acid, methy] alcohol, and small amounts of CHy, He, COz, CO, C2He, etc. Acetic acid and methyl alcohol are both hydroxyl derivatives of methane, CH; When vegetable matter is deposited in damp places, such as swamps and marshes, and slowly decomposes, it gives off CH4, which is commonly known as ‘‘marsh gas.”’ Peat is the result of decomposition of vegetable matter under water. When dried it acts as a combustible inter- mediate in grade between wood and coal. Coals are the result of long-continued slow decomposition of vegetable matter deposited in marshy places, followed by long periods of high pressure, and in some cases of quite high temperature while buried underground. Nearly all of the moisture of the peat has been driven out by pressure, and both pressure and temperature have assisted in the decomposi- tion of the carbohydrates of the original vegetable matter. Coals consist of elementary carbon, together with hydrocarbons and car- bohydrates, mostly of the methane or “paraffin” series, moisture, and such clay and sand as were deposited in the original vegetable matter, and now make the “ash” of the coal. Where the coal during its formation geologically has been highly heated, little of COMBUSTION AND FUELS 499 the hydrocarbons or carbohydrates are left, and in extreme cases the elementary carbon has been partially transformed into graphite. Classification of coals is difficult because of the variety of the original vegetable materials, of differences in the geologic ages, and of the variations in pressures and temperatures which have played parts in determining the final result. There is hardly a definite break in the series from wood to graphite. Roughly, the parts of the series run as follows: 1. Wood. — Fresh vegetable material, cellulose, starch, and water; needs usually to be dried for satisfactory use. 2. Peat. — Vegetable matter more or less decomposed under water. Must be dried either by weathering or by pressure, or both, before use. 3. Brown lignite. — Carbon, complex paraffin hydrocarbons and carbohydrates, water. Loses large amounts of “ hygroscopic” water by weathering (20 to 30 per cent by weight of the lignite as mined). 4. Black lignite. — Like the brown lignite, but with more ele- mentary carbon and less water. 5. Semi-bituminous coal. — Intermediate in grade between black lignite and bituminous proper. 6. Bituminous coal.— Carbon, complex hydrocarbons with some carbohydrates, and no hygroscopic water. 7. Semi-anthracite coal. — More elementary carbon than 6, and no carbohydrates, less of hydrocarbons, and these simpler. 8. Anthracite coal.— Elementary carbon and simple hydro- carbons (CH,). 9. Graphitic anthracite. — Very little hydrocarbons left, and some of the elementary carbon transformed to graphite by heat. 10. Graphite. — Final result of long-continued heat. From peat downward through the series to graphite, moisture and ash (mineral matter) are of course present. The amounts of moisture and ash are almost entirely accidental, and have nothing to do with the above classification, which deals with the combustible portion of the fuels. Liquid fuels, or oils, are either petroleum or petroleum derivatives. American petroleum of the eastern fields is largely a mixture of 500 EXPERIMENTAL ENGINEERING liquid hydrocarbons of the methane or paraffin series, of the general formula C,Hend2. The first member of this series, methane, CHu, is a gas prominent in natural gas. The heavier members of the series are liquids. By distillation these different hydrocarbons may be more or less completely separated from each other. Simulta- neously with the distillation more or less chemical break down goes on, and towards the end of the distillation this chemical break- down of the heavier hydrocarbons is the most important part of the process. The Texas petroleum contains both paraffins and olefins, the latter hydrocarbons of the general formula C,H2,. The presence of the olefins makes the Texas petroleums less valuable as a base for the making of gasoline or kerosene, and causes the Texas oil to be used more largely in the crude state. California petroleum has an asphaltum base, and is largely used in the crude state as well as in the refined. Russian petroleum is composed mostly of olefins and therefore refines differently from the Eastern American petroleum. Natural gas has considerable use as a fuel and illuminant in those localities favored by its occurrence. Artificial gaseous fuels are made by the distillation or partial combustion of coals. Coal gas or illu- minating gas is a distillation product. Water gas combines distilla- tion with partial combustion in the presence of steam. Producer gas is made by a partial combustion process in the presence of a mixture of air and steam. The characteristics of the various gases are illustrated in the following table: Volumetric Analysis. Per Standard Cubic Foot. Gas Variety. CHi+ Weight, B.t.u. CoH, | Be |< | ° Ms | HA | poids, | (Higher), Natural.......... 93 2 0.5 Orgel 48S besoin 0.45 II00 Coals cectn ss patina 44 46 6 OS!) 5) Beg.) “Oxs2 730 Water. cc .ciecunen 2 45 45 0.5 BO 1.5 0.45 325 Producer......... 2 12 27 0.3 Be Nene gs 0.65 I40 Analysis of Fuels. The analysis of fuels is commercially necessary as a basis of de- termining the market value of the fuel, or its relative value for a particular case. In the following we shall consider almost entirely COMBUSTION AND FUELS 501 the analysis of coals, bringing in the oil and gas analyses incidentally in other sections of this chapter. See also Chap. XXI. 263. Coal Analysis. — There are two methods of coal analysis in common use. The chemical or ultimate analysis determines the percentages by weight of carbon, hydrogen, nitrogen, oxygen, sulphur, and ash (and generally the moisture). This kind of anal- ysis is rather costly and is not necessary for ordinary engineering work, unless close determinations of the efficiency of the apparatus using the fuel must be made. The engineering or proximate analysis (not approximate, but quite as definite an analysis as the chemical) breaks the coal up into parts in the same way as it acts in the fur- nace, determining moisture, volatile combustible, non-volatile com- bustible (called fixed carbon), and ash, and also determining heating power. An incidental determination of coking power is always made. The pertinence of the proximate analysis to engineering work is obvious. It tells at a glance how the fuel will act in the furnace. If the volatile combustible percentage is high, a large combustion chamber is necessary in the furnace, with provision for oxygen supply to mix with the volatile matter and burn it. If a furnace has a relatively small combustion chamber it must, within limits, to be efficient, burn a coal with low volatile, i-e., an anthra- cite. 264. Sampling. — The first step toward the analysis of a coal is to obtain a truly representative sample. In sampling a carload or a pile of coal, a shovelful of coal should be taken from each of 10 or 15 places in the heap, choosing each shovelful to be representative of the material in its vicinity. In sampling the coal used in a test, of a boiler for instance, a shovelful of coal should be set aside at short intervals throughout the test from the lots of coal just before they are weighed out to be fired. In one or the other of the above ways there will be obtained a fairly representative sample of from 100 to 200 pounds’ weight. This sample should be protected always from gain or loss of moisture, and from gain of foreign matter, such as dirt. This first sample is too large for laboratory use. All lumps should be broken down, until the large sample is uniformly chestnut size or smaller. Then thoroughly mix the sample and quarter it. Again crush the coal, this time to about pea size, mix 502 EXPERIMENTAL ENGINEERING thoroughly, and from this material take out the laboratory samples, immediately sealing them air and water tight in glass jars. Ordinary fruit jars are very convenient for this purpose. The best practice would take duplicate samples. These samples are to remain sealed air and water tight until opened in the laboratory for analysis. In the laboratory the first act is a further grinding and mixing of the sample. A large coffee mill is a convenient machine for this. First mix the sample, then put through the mill a small part of the sample, and throw away what comes from the mill. This thoroughly cleans the mill. Grind, mix, and regrind the sample, until it is reduced to about the fineness of granulated sugar. The finer the grinding and more thorough the mixing at this stage of the process, the easier and more satisfactory will be the determinations to follow. 265. Moisture is determined by a drying process. A sample of ten or twelve grams’ weight is taken, carefully weighed, then dried for an hour or so at 105° C. or 220° F._ The temperature must be as high as this for thorough drying, and must not go much higher on account of the danger of driving out volatile hydrocarbons as well as moisture.* Commercially the loss of weight at the end of an hour’s drying at 220° F. is called the moisture. Accurately, weights should be taken at intervals, to determine the end point of the moisture loss. The samples should be cooled in a desiccator before weighing on the chemical balance; if weighed hot, air currents in the balance chamber will vitiate the weighings. Determinations of moisture should always be made in duplicate, and should check within one-half of one per cent. The drying cabinet may be of the simplest construction, — merely a metal box heated externally by a Bunsen burner, and provided with a thermometer by which to watch the temperature. If anal- yses are to be made more than occasionally, it is economical to have a more elaborate apparatus, with a thermostat to control the temperature automatically. 266. Volatile Matter is determined in a manner similar to the moisture determination, but with the temperature at red to white * With American anthracite and bituminous coals the temperature may go up to 300° F. without serious danger of loss of “ volatile,” but trouble will be met from slow oxidation of the coal being dried. COMBUSTION AND FUELS 503 heat, and with careful exclusion of air in order to prevent any burn- ing of the sample. The determination really made is (moisture + volatile), both being expelled by the process. The volatile is then found by difference, since the moisture is already known from the preceding test. A convenient method is as follows: Weigh out accurately on a chemical balance 10 to 12 grams of sample. Put it into a porcelain or fire-clay (Hessian) crucible of a capacity two or three times the volume of the sample. If the coal is not very moist, wet it slightly after putting it into the crucible. The extra moisture so introduced serves to expel air from the crucible and prevent all oxidation of the sample. Take a piece of asbestos paper somewhat larger than the top of the crucible; wet it, put the wet paper between the edge of the crucible and the lid, and weight down the lid. This gives a tight lid, which will act as a safety valve, allowing the escape of moisture or volatile from within the crucible, but preventing the ingress of air. Heat the crucible with a blast lamp capable of taking the temperature well up toward a white heat. Heat slowly for the first five minutes, while expelling the moisture; then heat to the limit of the apparatus for the balance of a half hour. Cool with the lid on. When cool, remove the lid and inspect the contents of the crucible as to coking power of the coal, noting whether the coal has coked into a single spongy mass or is still granular. Carefully remove all the residue from the crucible and - weigh the residue; the loss from the original weight of sample taken is moisture + volatile matter. Run the determination in dupli- cate; the results should check to within one per cent. Find the volatile by difference of the result of this and the moisture deter- mination. As variations on the above method the weights might be taken of crucible, crucible + sample, and crucible + residue; and special crucibles for these determinations may replace the common porce- lain or fire-clay laboratory crucible. Fire-clay crucibles change their weight when first used in this test, absorbing volatile matter and decomposing it with a deposition of carbon in the crucible walls. In case the crucible is weighed, a new fire-clay crucible should there- fore be saturated by a blank run before using it for an actual determination. The special crucibles which can be had for this 504 EXPERIMENTAL ENGINEERING determination have clamp lids and allow the recovery and analysis of the volatile matter and moisture driven off from the coal. This. latter analysis is not of much importance commercially, save where the coal is to be used for making gas. 267. Determination of Fixed Carbon, or non-volatile combustible, is by difference. Above have been given the determination of moisture and volatile; with ash and fixed carbon added, the sum is too per cent. The fixed carbon is found by subtracting from 100 per cent the sum of moisture, volatile, and ash. An explanation should be given of the relationship between the “volatile” and the ‘‘fixed carbon ”’ found in this method of testing. The volatile represents only a portion of the hydrocarbons or car- bohydrates of the coal. The heating of the coal, either in the actual furnace or in the crucible in the volatile determination, decomposes the hydrocarbons partially and the carbohydrates almost completely, leaving carbon from them to add to the elementary carbon already present in the coal, increasing the fixed carbon, and giving off as volatile simpler hydrocarbons and those in smaller quantities than the hydrocarbons contained in the coal. It is because of this de- composition of the hydrocarbons and the carbohydrates that the analysis of the volatile does not give the composition of the hydro- gen-carbon-oxygen compounds in the coal. The volatile also includes sulphur from either S or FeS2 in the coal, CO, from the decomposition by heat of carbonates in the coal, and N.O; from the decomposition of organic nitrates. The smaller the quantities of hydrocarbons or carbohydrates present, the higher is the temperature required to begin their destructive distillation. In the hardest anthracites even CH, is decomposed and the volatile obtained is largely hydrogen, together with sulphur and oxygen and nitrogen from the decomposition of organic nitrates. Up to 20 per cent volatile in total combustible, the CH, probably makes up all of the hydrocarbon volatile in the coal. Beyond 20 per cent volatile in the combustible, that is, with bituminous coals and lignites, heavier hydrocarbons are present. Carbohydrates characterize the lignites. In the case of lignites and semi-bituminous coals, even heating to drive out moisture may drive out some volatile combustible. COMBUSTION AND FUELS 505 268. The Ash Determination is best made by the quiet burning of a weighed sample in an atmosphere of oxygen at low pressure. Under high oxygen pressure the burning is too nearly explosive and ash or combustible may be blown out of the crucible. Burning in air is too slow and too liable to be incomplete for a satisfactory commercial method. In finding ash by burning in air, the sample must be heated nearly white hot in an open crucible for some hours. The burning in oxygen is complete in ten or fifteen minutes. The weights are: (1) crucible; (2) crucible + sample; (3) crucible + ash. The crucible and ash should be heated to dry them and then cooled in a desiccator before weighing. The ratio of ash weight to sample weight gives the percentage of ash. Duplicate determina- tions should be made and should agree to within one per cent. Oxygen is necessary for the calorimetric determination of the heat- ing value of coal. It is very easy to rig up a small oven or com- bustion chamber with an igniter, for the making of combustions in an oxygen atmosphere for the ash determination. All drafts across the crucible must be avoided. The oxygen supply must be under control so as to regulate the rapidity of combustion. Coals with high volatile must be made to burn slowly. The combustion chamber should have a window through which the burning can be watched. The ash of a coal is not identical with the mineral matter in the coal. Coals carry sulphur and iron as FeS, (pyrites); sulphur as S; and frequently mineral matter as carbonates. The ash consists mostly of oxides and silicates, and is in part at least a product of the combustion of the coal. Combustion makes 5 into SO2; FeS, into Fe.0; and SO.; carbonates into CO: and oxides. The CO: from carbonates and S from FeS, or S appear as volatile in the volatile test. It is therefore not scientifically correct to figure true coal by subtraction of moisture and ash from coal as received; although in general this computation is good enough as a first approximation. 269. Determination of Heating Value.— The last determination of the proximate analysis is that of the heating value. For most calorimeters, except the Parr, which requires absolutely dry fuel, it is best to use either coal as received or an air-dried sample of which the moisture loss from coal as received is known. To prepare the 506 EXPERIMENTAL ENGINEERING coal for the calorimeter, grind the coal with a mortar and pestle or equivalent device to about the fineness of flour, so that half or more is fine enough to pass a t0o-mesh sieve. Do not, however, take that part of the coal which passes the sieve, rejecting that which does not. The sample so obtained would not be a fair one. Mix up well all of the ground material, whether it passes the sieve or not. Bottle and cork this finely ground coal immediately after it is prepared, for if left exposed in the room it will rapidly change its moisture content. (For the operation of the calorimeter and the computation of heat- ing power, see the preceding part of this chapter.) Results of the proximate analysis are reported in the following form, on which the items usually observed are indicated by a star, the rest being calculated. “Coal as received”’ means the sample as it came to the laboratory. “Dry coal” is coal as received less the moisture, expanding the remaining items to sum up to roo per cent. “Combustible” is coal as received less both moisture and ash; it expands the two items “ volatile’ and “ fixed carbon” to sum up to 100 per cent. FORM FOR REPORTING THE PROXIMATE ANALYSIS OF COAL. As Received, 100%. | Dry Coal, 100%. | Combustible, 100%. IND OIS HUT Gi) s ue tig tnd Siete Saul was Ges EAE | Maer PARAS Cee DROS Saas Volatile-ma ther: acer eves owns “Pec naeagee aes) sa see oka eel ewate teehee ee Birced Ween Doria giariao0 6 xassas wise ease eek Beka | aw a tans eaianes Tee ees GoloriotMsh 4s iry vite cs ataindd Seine nds baatomae es = Cokitig Qualities vccoeranss Gang end nega nee ee neers, General remarks: The method of calculating across from coal as received to the other columns is obviously the division of the items in the coal ‘“‘as received ”’ column by the percentages of dry coal or combustible in COMBUSTION AND FUELS 507 coal as received. It should be remembered that the calorimeters generally find the higher heating value of the coal. 270. The Chemical Analysis of a coal is one to be made only by a chemist. It determines the percentages by weight of C, H, O,N,S, and adds frequently determinations, like those of the proximate analysis, of moisture and ash. This analysis is necessary whenever definite heat balances must be established for any test. In this connection the most impor- tant item not found by the proximate analysis is hydrogen. Hap- pily, Prof. L. S. Marks has shown* that the hydrogen not in moisture can be found very accurately from the results of the proximate analysis. The writer has fitted equations to Professor Marks’ curves, allowing the computation of the chemical analysis of a coal to be made from its proximate analysis with sufficient accuracy for most work. In the proximate analysis the combustible is the summation of the items “volatile matter” and “‘fixed carbon,” or it is equal to coal as received less moisture and ash. Let V = the weight per cent of volatile matter in combustible, H = the weight per cent of hydrogen in combustible, C = the weight per cent of volatile carbon in combustible, N = the weight per cent of nitrogen in combustible. Then the following equations express the Marks’ curves: +35 H= Wes = 13) This gives the hydrogen not in moisture for all American coals, to an accuracy of about + 0.2 of one per cent. For volatile carbon (carbon occurring in the volatile matter), with an accuracy of + 2 per cent approximately: C =,0.02 V? or C =0.9(V — 10) for anthracite and semi-anthracite, C =0.9 (V — 14) for bituminous and semi-bituminous, C =0.9 (V — 18) for lignites. Sulphur in the coal directly increases the value of V; hence the calculated value of C here will be too high practically by the S con- tent of the combustible. * Power, Vol. 29, p. 928, Dec., 1908. 508 EXPERIMENTAL ENGINEERING For nitrogen (nitrogen comes off in the volatile matter), with an accuracy of + 0.5 of one per cent: N =0.07V for anthracite and semi-anthracite, N = 2.10 — 0.012 V for bituminous and lignite. Oxygen and sulphur are too widely variant to allow of any calcu- lation; their amounts are more or less accidental. A chemical analysis sufficient for the purposes of the engineer can be obtained from the proximate analysis by the use of the above equations, as the following example will show: Example. — The following are the proximate and chemical analyses given by the U. S. Geological Survey for a certain sample of Illinois coal: HO Vol. Matter Fixed C Ash Proximate Analysis, per cent, 12.91 31.9 43-55 11.64 H TotaC N oO s Ash Chemical Analysis, per cent, 5.43 60.74 I.15 19.72 1.32 11.64 Evidently since the ash content of these two analyses is the same, the percentages of H and O given in the chemical analysis must include the per- centages of these gases in the 12.91 per cent of H.O given in the proximate analysis. Restating this analysis so as to have the water appear, we will have: H Total C N oO Ss Ash H:20 Chemical Analysis, per cent, 4.00 60.74 1.15 8.24 1.32 11.64 12.91 The problem is to see how closely this chemical analysis can be checked by starting with the proximate analysis above. , Computing the proximate analysis to the basis of combustible by dividing by (1.0 — .1291 — .1164) = .7545, we will have: Vol. Matter Fixed C 40.95 59.05 Substituting in the equations given above (V = 40.95) we then obtain H = 40.05 (85 _ 13) = 5.38 per cent, Vol. C = .9 (40.95 — 14) = 24.30 per cent, and N = 2.10 — .o12 X 40.95 = 1.61 per cent. The analysis of the combustible will now read as follows: Vol. i H ol £ mee € N Rest Total 5.38 83.45 1.61 9.56 = 100 Recomputed to the basis of coal as received by multiplying by .7545 we will have: H Total C N Rest (O) Ash Water 4.06 63.0 1.22 7.22 11.64 12.91 COMBUSTION AND FUELS 509 Comparing these figures with those given by the chemical analysis above it will appear that the agreement is fairly close with the exception of that for total carbon. As pointed out above, this is largely due to the fact that in this method of computation the sulphur content is practically all added to the total carbon, and if the sulphur content of the coal be known, as it is in this case (1.32 per cent), correction can be made so that the computed chemical analysis will finally show. H Total C N Oo s Ash #0 4.06 61.68 1.22 7.22 1.32 11.64 12.91 271. Sulphur Determination. A determination of sulphur is occasionally of interest, and in some cases necessary, as, for example, in coals used to make illuminating gas and for the fuel for gas producers, cupolas, or blast furnaces. High sulphur will make its presence known without special analysis. In ordinary boiler work sulphur is fairly harmless. In economizer installations, where the flue gases are cooled considerably, the SO. and SO; formed from combustion of S combine with moisture to form H2SO3 or H,SO, (sulphurous or sulphuric acid), which corrode the joints of the economizer. Similar trouble may occur in ordinary boiler work, but there the temperature of the flue gases is usually too high to allow the formation of much of the acids. The American Chemical Society directions for sulphur analysis are as follows: Mix thoroughly one gram of finely powdered coal* with one gram of magnesium oxide and one-half gram of dry sodium carbonate in a thin platinum dish having a capacity of 75 to roo c.c. A crucible may be used, but a dish is preferred. The magnesium oxide should be light and porous, not a compact, heavy variety. The dish is heated in a triangle over an alcohol lamp, held in the hand at first. Gas must not be used, because of the sulphur that it contains. The mixture is frequently stirred with a platinum wire and the heat raised very slowly, especially with soft coals. The flame is kept in motion and /barely touching the dish, at first, till strong glowing has ceased, and is then increased gradually till, in fifteen minutes, the bottom of the dish is at a low, red heat. When the carbon is burned, transfer the mass to a beaker and rinse * With coals high in moisture a correction may be necessary on account of the loss of water in powdering the coal. (See above, under Moisture.) 510 EXPERIMENTAL ENGINEERING the dish, using about 5oc.c. water. Addrs c.c. of saturated bromine water and boil for five minutes. Allow to settle, decant through a filter, boil a second and third time with 30 c.c. of water, and wash till the filtrate gives only a slight opalescence with silver nitrate and nitric acid. The volume of the filtrate should be about 200 c.c. Add one and a half cubic centimeters of concentrated hydro- chloric acid, or a corresponding amount of dilute acid (8 c.c. of an acid of 8 per cent). Boil till the bromine is expelled, and add to the hot solution, drop by drop, especially at first, and with con- stant stirring, 10 c.c. of a 10 per cent solution of barium chloride. Digest on the water-bath, or over a low flame, with occasional stirring, till the precipitate settles clear quickly. Filter and wash, using either a Gooch crucible or a paper filter. The latter may be ignited moist in a platinum crucible, using a low flame, till the carbon is burned. Weigh as barium sulphate and calculate sulphur. In the case of coals containing much pyrites or calcium sulphate, the residue of magnesium oxide should be dissolved in hydrochloric acid and the solution tested for sulphuric acid. 272. Methods of Computing the Heating Value of Fuels. — The chemical or ultimate analysis of coal has been much used for a computation of the heating value of the coal, after the Dulong formula. If C represents the weight percentage of carbon in the coal, H that of hydrogen, O that of oxygen, S that of sulphur, the Dulong formula gives the following heating power: 52,500 O B.t.u. per pound = 14,540C +4 or (a - - + 40208. 61,950 The coefficients are the heating powers of the separate chemical elements, with that of hydrogen giving either the lower or the higher heating value according to the coefficient used. The term ( _ 2) is supposed to contain a correction for hydrogen already combined with oxygen in the coal as moisture.’ The formula is in a sense rational, but the following points should be noted: The carbon and sulphur are the only elements present in the coal in a free state, and only a portion of them is elementary. Part of the elementary carbon may be, and in some anthracites certainly is, graphite. Graphite has a decidedly lower heating value than amorphous carbon (about 14,300 instead COMBUSTION AND FUELS 51L of 14,540). Part of the sulphur is present as FeS. (pyrites). The sulphur may burn to either SO2 or SO;; and depending on its initial condition and the com- pound formed in burning, the heating power varies widely. Combined carbon and hydrogen in hydrocarbons have not the same heating power as if they existed separately side by side; the heat of formation or dissociation of the hydrocarbon must be considered. This makes the heating powers for part of the carbon and all of the hydrogen wrong. The amount of error depends on the particular set of hydrocarbons present in the coal; in some cases it may amount to 20 per cent of the Dulong formula value for the heating value of a hydrocarbon. ‘The term (a = 3) does not contain a proper correction for the hydrogen contained in moisture, for not all of the oxygen in the coal is combined with hydrogen. Part of the oxygen is probably combined with nitrogen in organic nitrates and part may be present in carbonates in mineral matter caught in the coal. Taking these facts into consideration, it is not surprising to find the differen between the Dulong formula values of heating power and the values detet- mined experimentally in a calorimeter to be frequently as high as 10 per cent. Usually the formula comes within 5 per cent in the cases of anthracite coals. The error of the formula, with the coefficients given above, is usually an error of excess. Empirical formulas, of the same type as the Dulong, but with coefficients worked out by comparison of chemical analyses with experimentally determined heating powers, give better results, but are still too widely and irregularly in error to be allowable in modern engineering work. One such formula, of fairly wide use, is that of the Verein Deutscher Ingenieure. It gives the Jower heating value of a coal, with W = per cent of moisture, and other symbols as above. Calories per kilogram = 8000 C + 29,000 (2 - ) +2500S—600W. B.t.u. per pound = 14,400 C + 52,000(H7 — 4 +4500 S — 1100 W. The only way to get the heating value of a fuel reliably and accurately is to determine it experimentally with a calorimeter. Such a calo- rimeter determination forms a part of the proximate analysis of a coal. Similar empirical formulas have also been established for com- puting the heating value of hydrocarbon combinations, either solid, liquid, or gaseous. It will not do simply to proceed on the Dulong principle and to multiply the percentages of C and H 512 EXPERIMENTAL ENGINEERING contained by the heating value of these elements, for reasons pointed out above. For gaseous hydrocarbons like CHy, C,H», C2H,, etc., the following empirical formula, due to Slaby, gives satisfactory results: Lower heating value = (112 + 18,880 y) B.t.u. per standard cubic foot, in which y = the weight of a standard cubic foot of the gas in pounds. Thus for CHz, y = .04464, so that the heating value is (112 + 18,880 X .04464) = 952 B.t.u. The heating value of commercial gases, like producer gas or illuminating gas, can of course be directly determined from its percentage composition as soon as the heating value of the individ- ual combustible gases it contains is known. 273. Buying Coal by Analysis. — The increasing use of coal analyses as a basis for determining coal values, and the growing practice of buying by analysis, make it desirable to indicate how business firms not fully equipped for the making of analyses may keep check on the quality of the coal they are buying or selling. As a general thing, coals coming from the same mine at different times, or even from different points of the same coal field, do not vary greatly in the composition or value of their combustible portions. The variations are in the ash and moisture content. By sending samples at intervals to some laboratory, complete analyses of the coal may be obtained, which will give the nature and value of the combustible part of the coal. Then the firm may make frequent checks, upon every large delivery, say, of ash and moisture. These latter determinations can be made by working with fairly large weights of samples, with no more elaborate ap- paratus than a fairly accurate bench scale, some tin pans, a drying oven, a thermometer, two or three Bunsen burners, and a few Hessian or porcelain crucibles, which equipment should not cost more than $20.00. 274. Flue Gas Analysis and Combustion Calculations. — The gases analyzed in engineering work are those resulting from com- bustion, commonly called “flue gases.”* They consist of varying * For the analysis of producer gas, see the chapter on the testing of gas engines and producers. COMBUSTION AND FUELS 513 mixtures of nitrogen, oxygen, and carbon dioxide, with lesser amounts of carbon monoxide, hydrogen, water vapor, and sulphur dioxide. The analysis is useful as a basis from which to judge of the efficiency of combustion. The methods to be e nployed must be such as any engineer can fully comprehend aff the apparatus portable and convenient. The degree of accuracy sought need not be such as would be required in a chemical laboratory where every convenience for accurate work is to be found. Indeed, considering the approximations to be made in its application, it is very doubtful if determinations nearer than one per cent in volume are required, or even of any value. Such determinations are obtained readily with simple instruments, and serve to show the approximate condition of the gaseous products of combustion. The student is referred to ‘‘ Handbook of Technical Gas Analysis,” by Clemens Winkler (London, John Van Voorst), and to “‘ Methods of Gas Analysis,” by Dr. W. Hempel, translated by L. M. Dennis (Macmillan Company); also to a paper on tests of a hot-blast apparatus by J. C. Hoadley, Vol. VI, ‘‘ Transactions of the American Society of Mechanical Engineers.” 275. Sampling. — The first step in the analysis is the obtaining of a representative sample. In the flues the mixture of the gases may be far from homogeneous. Hence the sampling apparatus must either provide for mixing the gases before taking the sample at one point, or must take the sample at so many points, and points so distributed, as to get a fair average. Allowance should be made in the latter case for variation in the velocity of flow of gases in different parts of the flue. It is easy to provide baffles to cause eddy currents in the flue, and so bring about a good mixing of the gases. Then a single sampling point near the center of the flue is sufficient. The simplest collecting arrangement is a j-inch pipe of such length as to reach nearly across the flue. This pipe is perforated with a number of small holes spaced along its length, the end of the pipe being plugged up. This scheme is very often used in practice, and where the mixture of the gases may be assumed to be fairly uniform it is probably satisfactory. It is open to the objection that probably a greater proportion of gas is drawn into the tube through the holes near the aspirator than through the openings farther away. 514 EXPERIMENTAL ENGINEERING A more elaborate scheme (see “Trans. Am. Soc. Mech. Eng.,” Vol. VI) consists in running a number of collecting tubes, open simply at the end, to various parts of the flue and connecting all the outside ends of these tubes to a common mixing box into which an aspirator then draws the gas and from which the sample is taken. Even this scheme may not give a uniform mixture, because with the same suction on all the tubes, the shorter tubes will certainly supply more gas to the mixing box than the longer ones. The material for the collecting tube or tubes is preferably porce- Fic. 361. — ASPIRATOR. lain or glass, but iron has no specially selective or absorptive action upon any of the gases, and iron pipe is therefore often employed. Use as little rubber tubing as possible. The gas should always be collected as closely as possible to the furnace, after combustion is sure to be as complete as it will become in the apparatus under test. At any distance away in the flue there is apt to be dilution due to inleakage of air. If the sample must be ‘taken some distance away, the flue must be examined for leakage and the leaks stopped. As the pressure in the flue is generally below atmospheric, it is COMBUSTION AND FUELS 515 necessary to have some form of aspirator to draw out the sample. The aspirator should either work continuously or should be worked for such a time before taking a sample as to secure a thorough flush- ing out of the system of piping used in the sampling device. The aspirating apparatus may take several different forms. The most common type consists of two bottles with double outlets and connected as shown in Fig. 361. The operation of this apparatus is of course intermittent, and since the bottles are usually not very large, the time during which any given sample is taken is comparatively short, which means that many of them are neces- sary thoroughly to cover a test. A modification of the simple bottle aspi- rator by means of which it is possible to take a time sample is illustrated in Fig. 362. Two cans, E and S, are mounted as shown about the shaft V. In the position shown, £ is connected with the sampling tube through the connections R, L, N. The water, with which £ was originally filled to the top, is allowed to drain out of EF into S through the connecting pipe M, the rate of transfer being controlled by the setting of the cock, 7. As the water recedes, F fills with gas. The water level is continuously indicated on the glass H. Inthe meantime the gas, which it is as- sumed was collected in S when this was in the top position, is displaced out of S through connection A and is either taken to the analyzing apparatus or wasted. When all the water is transferred, the position of the vessels is reversed and the apparatus is ready for a new sample. The cut is defective in that no stopcocks are indicated in the out- lets near the conical heads of the vessels. The transfer liquid used in collecting apparatus of the type de- scribed is usually water. It will be pointed out below that water has a certain influence upon the composition of flue gases with which it comes in contact, and it is consequently better to collect Fic. 362. 516 EXPERIMENTAL ENGINEERING without contact with water if possible. One method of doing this, is indicated in Fig. 363. This apparatus consists of a glass sam- pling tube furnished with glass stopcocks. These tubes can be bought from any chemical dealer. At one end the tube is con- ——> Gas ] ; | Sampling Tube Fic. 363. ASPIRATING AND COLLECTING APPARATUS FOR FLUE Gas. nected to the flue, at the other to a rubber aspirator bulb. By alternately squeezing and releasing this bulb, gas will be drawn into the tube. Enough must be drawn through to replace the air or old gas in the tube. The proceeding is therefore rather laborious, but the sample obtained will not be disturbed by contact with water. These tubes are also the best means of collecting and storing gas, if the analysis cannot be performed on the spot. The stop- cocks should be greased with vaseline from time to time, both to prevent their sticking and to make them gas-tight. To cut down the labor of filling the tube with fresh gas, an ejector is a handy instru- ment, where water or steam of sufficient pres- sure to operate one is available. Fig. 364 shows the construction and operation of one 3 2 Oui Fic. 364.—EyEcTOR FOR type. Asprration or Gas Water is a solvent for all of the flue gases. SAMPLE. For oxygen and nitrogen, tap water is al- ready saturated; but it will absorb considerable quantities of COz, CO, He, and SO;. Hence it is necessary to draw a gas sample into the sampling bottle, shake liquid and gas sample together, reject that sample, draw another, and repeat, until the water in COMBUSTION AND FUELS 517 the sampling bottle is saturated with the particular gas mixture which is being sampled. It is desirable not to use new water each time in the sampling bottles, but to keep and use the same liquid over and over again. This reduces the possible error from failure to saturate the water with the gases. H,O vapor in the flue gas of course disappears partly at this stage of the sampling process. SO: probably does the same, and it is unlikely that SO, would be found in the gas in the sampling bottle. If it were it would be shown in the subsequent analysis as CO». The solubility of the gases in the collecting liquid may be limited. The scientific method is the collection of the gas sample over mercury instead of water. The addition of glycerine to the water gives a liquid in which the solubility of the gases is less than with water alone. The addition of a slight amount of some strong acid, as H2SQ,, will keep CO: from going into solu- tion. The collection of samples is made more rapid, and analysis more accurate, by the addition of glycerine and H2SQ, to the sampling water. 276. Analysis of Flue Gas. — The analysis ordinarily employed is volumetric. A definite portion of the sample, usually roo c.c., is taken and submitted in turn to reagents capable of absorbing the various component gases. After each absorption the volume of the remaining gas is measured. The decrease of volume from the preceding measurement shows the volume percentage of the gas taken up by the last absorbent. The absorbents used, their order of use, and method of action, are as follows: 1. KOH (potassium hydroxide, caustic potash) in solution in water is used to absorb CO:. It will not absorb Ne, O2, CO, or H:, but it will absorb SO, if any be present in the sample. As large a surface of the KOH solution as possible should come in contact with the gases. Hence the gases should either be made to bubble through the solution or the absorption bulb should be filled with glass beads or iron wire gauze, which will expose to the gases a large surface wet with the KOH solution. The strength of the solution is ordinarily one part by weight of KOH to two parts of water. 518 EXPERIMENTAL ENGINEERING 2. Oxygen may be absorbed by one or the other of two reagents. Neither of these reagents absorbs CO, Ne, or He. They are: (a) an alkaline solution of pyrogallic acid; (6) phosphorus. (a) To make the pyrogallic acid solution, dissolve 5 grams of pyro- gallic acid in 15 c.c. of water, and 120 grams of KOH (stick form) in 80 c.c. of water, and mix the two solutions. The alkaline solution so made will absorb CO, or SO; hence these must have been removed by the KOH solution before the absorption and determina- tion of Og is attempted. The use of the pyrogallic acid solution is similar to that of the KOH solution, save that it is advisable to protect the pyrogallic solution from light. (0) Phosphorus for oxygen absorption should be in stick form. It is kept under water. When the gas sample to be analyzed is taken into the phosphorus reagent bulb, it displaces this water; the O. reacts with the P, forming white clouds of fumes of P,0;. These clouds soon settle and dissolve in the water. The phosphorus bulb should be pro- tected against light. To form the phosphorus sticks, melt the phosphorus under water in a beaker set in a water-bath. Heat very gently. After melting, take a glass tube having an internal diameter of the size of the sticks desired. Push this into the melted phosphorus. Place the finger over the upper end of the tube and quickly transfer the tube with the phosphorus it contains to a beaker containing cold water. If the tube has been cut off square at the lower end and is not of too large diameter, this operation can be carried out without any danger whatever. After cooling, push the stick out of the tube into cold water by means of a glass rod. The strict rule to be observed is that phosphorus should never be handled except under water or oil. The reagent tubes for the absorption of oxygen must be so constructed that they remain air-tight. 3. Carbon monoxide is absorbed in an ammoniacal copper chloride solution. The solution does not absorb No» or Hz, but does absorb CO2, SO: or Oz. Hence it must follow the KOH and P (or pyrogallic acid) absorptions. This copper chloride solution is hard to make, does not keep well, and has a comparatively limited absorbing power. Hence the determination of CO is often omitted in ordinary flue gas analysis, although this is never advisable. COMBUSTION AND FUELS 519 To make the solution, dissolve 10 grams of copper oxide (CuO) in 100 to 200 c.c. of concentrated hydrochloric acid (HCI), and allow the solution to stand in a stoppered flask filled with copper wire until it becomes colorless, that is, has become cuprous chloride. This clear solution is poured into a beaker containing 14 to 2 liters of water. The cuprous chloride will be precipitated. Pour off the liquid above the precipitate, add 100 to 150 c.c. of distilled water, and add ammonia until the liquid takes a pale blue color. The solution should be used fresh. It is preserved, and its capacity for CO increased, by immersing in it spirals of fine clean copper wire. 4. Hydrogen may be absorbed and measured by (a) combustion; (b) by taking it up in palladium. (a) After removal of CO from the sample, H2 is the only combustible left. Hence an amount of air, about equal to the remaining gas sample, may be taken into the measuring tube, measured, and this new gas mixture may then be passed into a combustion tube where a succession of electrical sparks, or an electrically heated wire, will cause the burning of the hydrogen, with the oxygen of the air just added. The water formed has a relatively negligible volume; therefore remeasurement gives the volume of the hydrogen and oxygen consumed. As the volu- metric reaction is 2H, + O, = 2H.O, two-thirds of the volume diminution by the combustion is the volume of the hydrogen. (b) Palladium foil has the peculiar property of absorbing hydrogen gas in large amounts at ordinary temperatures, although it does not absorb other gases. The hydrogen may be driven out of the palladium by heat, and the palladium is then ready to use again. This method of absorbing hydrogen is more suited to commercial use than the combustion method. It requires, besides the ab- sorbing tube containing the palladium foil, a small alcohol lamp or other device for heating the palladium. 5. Moisture (H.O vapor) in flue gases can be found by drawing the gases through a calcium chloride tube, obtaining the increase of weight of the tube, and comparing this weight of H,O with the weight of the gas drawn through, figured from volume and density. This measurement of H,0 is rarely made, as it is possible to calculate the H,O from the analyses of the coal and of the flue 520 EXPERIMENTAL ENGINEERING gases. If it is made it must of course be done before the gas has come in contact with water. 277. Absorbing Power of the Reagents. — This is stated in cubic centimeters of the particular gas which one cubic centimeter of the reagent concerned will absorb. The following table, however, gives the cubic centimeter of gas that may be absorbed before the reagent ceases to act with a fair degree of rapidity. a aon Reagent. Absorbing Power. CO, KOH solution 4o oO j Potassium pyrogallate 2.25 2 Phosphorus Practically unlimited if protected properly. co Ammoniacal copper chlo- ride solution 4.0 The full absorbing power can be obtained approximately by multi- plying the factors given by 4. 278. General Forms of Flue Gas Analysis Apparatus and Method of Operation. — The apparatus employed for volumetric gas analysis consists of a measuring tube, in which the volume of gas can be drawn and accurately measured at a given pressure, and a treating tube into which the gases are introduced and then brought in con- tact with the various reagents already described. The apparatus employed may be divided into two classes: (1) those in which there is but one treating tube, the different reagents being successively introduced into the same tube; (2) those in which there are as many treating tubes as there are reagents to be employed, the reagents being used in a concentrated form, and the gases brought into con- tact with the required reagent by passing them into the special treating tube. In either case the steps are as explained in Article 276. (a) Ob- tain 100 c.c. in the measuring tube; (6) transfer to CO» treating tube and absorb CO:. Transfer back to measuring tube and note the reduction in volume. Repeat the operation until there is no further reduction. If the reagent is in good shape, the absorption should be complete after two transfers. If the reduction is measured in cubic centimeters, the reading is per cent CO, direct. (c) Trans- COMBUSTION AND FUELS 521 fer remainder of gas to treating tube for O2 and repeat the opera- tions under (6). The total reduction in volume will now be the sum of CO2.+O:. (d) Transfer to all the other reagent tubes in their proper succession in the same manner. The following form is convenient for the recording of data, and also shows the principal items of computation based upon the analysis. MECHANICAL LABORATORY, SIBLEY COLLEGE, CORNELL UNIVERSITY. FLUE GAS ANALYSIS. Location of Plant........... 0. DOIG aiid ts arcia osts ethos 19 OWES sce ROS ini Ne EARNS RG ecg ncn ef DY gpa R nee etre tcl hore ated eet EN PC Of BOUTS ci camiea tein Recep 6 eb dbeianeddnemanmmannes he aa owe Nuniber of Botlersss.ces. cists x.cnninneescavomem ne watiee — stabadha a kiana eh arena ain @ haa Character 0f Droits ccsx einaas teaser emer | aerate erswassaldingiee yes eee Determination Number. I | 2 | 3 | 4 | 5 6 Time cOf SAM pCbg 5-5 dua uaquocs wimeeseves sista dagiaellheniud dden|tenctemst Wie [adaediene | sis @iguel| Suasaleng ll Gunn eck Draft palige; ACHES WALER, «cos scnena calls ad dslbevoneece fe Salon | ameaanatel Ioana as | as toa ‘Temperature: of fle, deg? Bis. ccpeg asia |aiw cameace wa a| soir s el naval] ann aini dived ave Temperature of boiler room, deg. F.... J... 0. fo... cfee eee ebe eee fee eee fee eee D5 icc segs (aia a eanann it chtapleeteseca gs corer de cata ee Wetter elon caracacseee | a renee eter Goin ll haeeeias B g (D5 SOs sav slaps Siw arate teghls pla iea renga cea fae IG dramesey | mab eal xfsein ce all aueveveeans 2s) | Frée OXVell-«. +o. 1244 seeewnesbestedes saleayver|sesaed|sesedile weree|aeeece 851 Oo COs+ COsscasss niewars erleasgaviewery . 543 544 EXPERIMENTAL ENGINEERING Now from the above definitions of quality for wet and dry satu- -rated steam it appears that quality may be expressed as the quotient of the heat remaining in a given weight of steam after the heat of the liquid is subtracted from the total, divided by the latent heat r at the given pressure. Following out the analogy in the case of superheated steam, we then will have Quality « = ie CoP This expression is of course always greater than 1.0. The result, however, is meaningless unless the pressure is stated at the same time, and in commercial practice it is usual to transpose it to degrees of superheat D, thus: pat (7 — 1) Cy 289. Importance of Quality Determinations. —The importance of correctly determining the quality of steam is great, because the per- centage of water carried over in the steam in the form of vapor or drops of water may be large, and this water is an inert quantity so far as its power of doing work is concerned, even if not a positive detriment to the engine. Any tests for the efficiency of engine or boiler not accompanied with determinations of the amount of water carried over in the steam would be defective in essential particulars, and might lead to erroneous results. On the other hand, the greatest precautions should always be taken to insure an average sample of steam for quality determina- tion. Carelessness in this respect may easily lead to errors larger than would be the case if the quality determination had been omitted altogether. 290. Methods of Determining the Quality. — The methods of measuring the amount of moisture contained in steam may be considered under three heads: first, Calorimetry proper, in which the method is based on some process of comparing the heat actually existing in a pound of the sample with that known to exist in a pound of dry and saturated steam at the same pressure; second, Mechanical Separation of the water from the steam, involving the processes of separation and of weighing; third, Chemical Methods, in which case a soluble salt is introduced into the water of the boiler. DETERMINING AMOUNT OF MOISTURE IN STEAM 545 All methods for determining the quality of steam are included under the head of calorimetry, and instruments for determining the quality are termed calorimeters. 291. Classification of Calorimeters. — The following classification of different forms of calorimeters is convenient and comprehensive: Jeticxnowacns joe or Tank, Condensing...... Continuous. Surface..... Hoadley Calorimeter, Barrus — Continuous, . External — Barrus Superheating. Calorimeters. . }Superheating. .. }Internal — Peabody Throttling. Electric Superheating — Thomas. Directly determining moisture........ seme [peparaton: Chemical. Universal or Combination. ..............5. Ellyson, In what follows, the construction and method of use of a repre- sentative type of each kind of calorimeter will be briefly discussed, and errors will be pointed out wherever their possible occurrence is likely to affect the results seriously. 292. Use of Steam-tables. — In reducing calorimetric experiments steam-tables will be required. The explanation of the terms used will be found in Article 180, page 335, and tables will be found in the Appendix of this book. Students will please notice that the pressures referred to in the steam-tables are absolute not gauge pressures, and that gauge pressures must be reduced to absolute pressures by adding the barometer reading reduced to pounds per square inch, before using the tables. The following symbols will be employed to represent the different properties of steam: TABLE OF SYMBOLS. Properties of Steam. Symbol. Properties of Steam. Symbol. Pressure, pounds per sq. in..... p Total heat, B.tu....... -...| AorH Pressure, pounds per sq. ft..... P Weight of cu.ft. of steam, lbs. 6 Temperature, degrees Fahr...... t Vol. of 1 lb. steam, cu. ft... v Temperature, absolute......... T Vol. of r lb. water, cu. ft.... o Heat of the liquid............. gorS ||Change in volume v — co... u Internal latent heat............ porl ||Quality of steam.......... x External latent heat........... APu or E||Per cent of moisture.......] 1 — 2 Total latent heat..........-... ror L’ ||Degree of superheat....... D 546 | EXPERIMENTAL ENGINEERING 293. Method of Obtaining a Sample of Steam. — It has already been pointed out that the obtaining of.a representative sample of steam is of the utmost importance in steam calorimetry. It is usually necessary to so arrange the apparatus that only a small percentage of the total steam passing can be examined in a calo- rimeter. Unfortunately there are certain practical conditions which make the taking of an average sample anything but certain. From experiments made by the author, it is quite certain that the quality varies greatly in different portions of the same pipe, and that it differs more in horizontal than in vertical pipes. Steam drawn from the surface of the pipe is likely to contain more than the average amount of moisture; that from the-center of the pipe to contain less. Perhaps the best method: for obtaining a sample of steam is to cut a long-threaded nipple into which a series of holes 34 Pipe = Pipe es Fic. 373. © ck Fic. 374. is drilled, and screw this well into the pipe. Half-inch pipe is gener- ally used for calorimeter connections, and it may be screwed into the main pipe one-half or three-quarters of the distance to the center, with the end left open and without side perforations, as shown in Fig. 373, or screwed three-quarters of the distance across the pipe, a series of holes drilled through the sides, and the end left open or stopped, as shown in Fig. 374. A lock nut on the nipple, which can be screwed against the pipe when the nipple is in place, will serve to make a tight joint. The best form of nipple is not definitely determined, although many experiments have been’ made for this purpose; a form extending nearly across the pipe and provided with a slit or with numerous holes is probably preferable. When the current of steam is ascending in a vertical pipe, the water seems to be more uniformly mixed than when descending in a vertical pipe or when moving in a horizontal one. There is, however, consider- DETERMINING AMOUNT OF MOISTURE IN STEAM 547 -able variation for this condition, especially if the steam contains more than 3 per cent of water. .« 294. Method of Inserting Thermometers. — In the use of calorim- eters it is frequently necessary to insert thermometers into the steam in order to correctly measure the temperature, a matter scarcely less important than the proper taking of the- sample. For this purpose thermometers can be had mounted in a brass case, as shown in Fig. 375, which will screw into a threaded opening in the main pipe. | The author prefers to use instead a thermometer cup of the form shown in Fig. 376, which is screwed into a tapped opening in the pipe. Cylinder oil or mercury is then poured into the cup, and a ther- mometer inserted with graduations cut on the glass. The thermometer cups are usually made of a solid brass casting, the outside being turned down to the proper dimensions and threaded to fita -inch pipe fitting. The inside hole is drilled 4 inch in diameter, and the walls are left ps inch thick. It should be noted that mercury cannot ~ be used with a brass cup on account of amalgamation. In such cases iron or steel will have to be used. The total length of the cups may vary from 2 to 6 inches, depending on the place where they are to be used. In any case it is essential that the thermometer be inserted deep =F into the current of steam or water, and that no Fic. 376.—Tuermom- air pocket forms around the bulb of the ther- 78 Cur or Wet. mometer. The thermometer should be nearly vertical, and as much of the stem as possible should be protected from radiating influence. If the thermometer is to be inserted into steam of very little pressure, the stem of the thermometer can be crowded into a ‘hole | | ( 548 EXPERIMENTAL ENGINEERING cut in a rubber cork which fits the opening in the pipe. In case the thermometer cannot be inserted in the pipe it is sometimes ‘bound on the outside, being well protected from radiation by hair felting; but this practice cannot be recommended, as the reading is often much less than is shown by a thermometer inserted in the current of flowing steam. 295. Condensing Calorimeters. — Condensing calorimeters are of two general classes: 1. The jet of steam is received by the con- densing water, and the condensed steam intermingles directly with the condensing water. 2. The jet of steam is condensed in a coil or pipe arranged as in a surface condenser, and the condensed steam is maintained separate from the condensing water. The principle of action of both of these calorimeters is essentially the same; the first class is, however, probably more often used than the second. The equations involved are as follows: Let W = weight of condensing water. w = weight of condensed steam. t, = temperature of condensing water, cold. i, = temperature of condensing water, warm. t, = temperature of condensed steam. = water equivalent of calorimeter (see next article). Now the heat gained by the calorimeter upon condensing one pound of steam will be equal to Wek @ 4h Sia. (1) The heat in one pound of the sample steam above 32°F., as taken from the steam-table, for the pressure of the original sample, may be expressed by xr + q. The condensed steam is, however, not cooled to 32°F., but to some temperature fs usually higher than 32° Then the net amount of heat per pound of steam condensed will be axr+q — (t,— 32) B.tu. (2) The loss of heat by radiation must either be determined and added to equation (x) or it must be compensated for by so conducting the trial that ¢, is as much below the temperature of the room at the DETERMINING AMOUNT OF MOISTURE IN STEAM 549 start as ¢, is above that temperature at the end of the test. Assuming that this method is used, we then have W+tk Gn 4) =br+q- és oS 32); (3) from which : W+K (Gh gi ge x= Bg (4) r In the case of calorimeters of the first class, ¢, = ¢, and equation (4) becomes W+K mre t)-@q + t,— 32 x= = . (5) r If « turns out to be greater than 1.0, compute the degree of super- heat D from the equation oe oe, (6) 296. Determination of the Water Equivalent of the Calorimeter. — The calorimeters exert some effect on the heating of the liquid contained in them, since the substance of the calorimeter must also be heated. This effect is best expressed by considering the calorimeter as equivalent to a certain number of pounds of water producing the same result. This number is termed the water equivalent of the calorimeter. The water equivalent, K, can be found in three ways*: 1. By computation from the known weight and specific heat of the materials composing the calorimeter. Thus, let C be the specific heat, W. the weight; then K = CW. 2. By drawing into the calorimeter, when it is cooled down to a low temperature, a weighed quantity of water of higher tem- perature and observing the resulting temperature. Thus, let W equal the weight of water, ¢, the first and ¢, the final temperatures, * See also the discussion on the same subject in Chapter XIII, p. 478. 550 EXPERIMENTAL ENGINEERING and K the water equivalent sought. Since the heat before and after this operation is the same, (W+ K)t,= Wi; from which re WG 4). ty Radiation, however, affects the accuracy of the determination and must be corrected for. 3. By condensing a quantity of steam known to be dry saturated. Then, + = 1.0, and the equation of the previous article may then be used to determine K. 297., Forms of Condensing Calorimeters. — Barrel or Tank Calo- rvimeter. — The barrel calorimeter belongs to that class of condensing Fic. 377. — BARREL CALORIMETER. calorimeters in which a jet of steam intermingles directly with the water of condensation. It is made in various ways; in some instances the walls are made double and packed with a non-condensing sub- stance, as down or hair felting, to prevent radiation, and the instru- ment is provided with an agitator consisting of paddles fastened to a vertical axis that can be revolved and the water thoroughly mixed; but it usually consists of an ordinary wooden tank or barrel resting on a pair of scales, as shown in Fig. 377. DETERMINING AMOUNT OF MOISTURE IN STEAM 551 A sample of steam is drawn from the main steam pipe by con- nections, as explained in Article 293, and conveyed by hose, or partly by iron pipe and partly by hose, to the calorimeter. In the use of the instrument, water is first admitted to the barrel and the weight accurately determined. The pipe is then heated by permitting steam to blow through it into the air; steam is then shut off, the end of the:pipe is submerged in the water of the calo- rimeter, and steam turned on until the temperature of the condensing water is about 110° F. The pipe is then removed, the water vigor- ously stirred, the temperature and the final weight taken. A tee screwed crosswise of the pipe, as shown in Fig. 377, forms an efficient agitator, provided the temperature be taken immediately after the steam is turned off. The pipe may remain in the calorimeter during the final weighing if supported externally and if air be admitted so that it will not keep full of water; in such a case, however, it should also be in the barrel during the first weighing, or else the final weight must be corrected for displacement of water by the pipe. The effect of displacement is readily determined by weighing with and without the pipe in the water of the calorimeter. The determination of the water equivalent of the barrel calorim- eter will be found very difficult in practice, and it is usually cus- ‘tomary to heat the barrel. previous to using it, and then neglect any effect of the calorimeter. The accuracy of this instrument depends principally on the accuracy with which the temperature and the weight of the condensed steam are obtained. The conditions for obtaining the temperature of the water accurately are seldom favorable, as it is nearly impossible to secure a uniform mixture of ‘the hot and cold water; the result is that determinations made with this instrument on the same quality of steam often vary from 3 to 6 percent. From an extended use in comparison with more accurate calorimeters, the author would place the average error resulting from the use of the barrel calorimeter at from 2 to 4 per cent. Example. — Temperature of condensing water, cold, t1, is 52.8° F.; warm, ¢2, t09.6° F, Steam pressure by gauge, 79.7; absolute, 94.4. Entering steam, normal temperature, from steam-table, ¢, 323.7° F. Latent heat, 7, 891.2 B.t.u., g = 294 B.t.u. Weight of condensing water, cold, W, 360 pounds; warm, 552 EXPERIMENTAL ENGINEERING W +w, 379.1 pounds; wet steam, w, 19.1 pounds. Calorimeter equivalent eliminated by heating. The quality 3 te, (z09.6 — 52.8) —294 + 109.6 — 32 Q-I x= = 891.2 oa = 95.9 per cent. oo 298. Directions for Use of the Barrel Calorimeter. — A pparatus.— Thermometer reading to 4 degree F., range 32° to 212°; scales reading to s'5 of a pound; barrel provided with means of filling with water and emptying; proper steam connections; steam gauge or thermometer in main steam pipe. 1. Calibrate all apparatus. 2. Fill barrel with 360 pounds of water, and heat to 130 degrees by steam; waste this and make no determinations for moisture. This is to warm up the barrel. 3. Empty the barrel, take its weight, add quickly 360 pounds of water, and take its temperature. 4. Remove steam pipe from barrel; blow steam through it to warm and dry it; hang on bracket so as not to be in contact with barrel; turn on steam, and leave it on until temperature of resulting water rises to 110° F. Turn off steam; open air cock at steam pipe. 5. Take the final weights with pipe in barrel, in same position as in previous weighings; also take weights with the pipe removed: calculate from this the displacement due to pipe, and correct for same. Alternative for fourth and fifth operations. — Supply steam through a hose, which is removed as soon as water rises to a temperature of 110° F. Weigh with the hose removed from the barrel. Stir the water while taking temperatures. 6. Take five determinations, and compute results as explained. Fill out and file blank containing data and results. 7. Compute the value of the water equivalent, K, in pounds by comparing the different sets of observations. 299. The Continuous Jet Condensing Calorimeter. — A calorim- eter may be made by condensing the jet of steam in a stream of water passing through a small injector or an equivalent instrument. The method is well shown in Fig. 378. A tank of cold water, B, placed upon the scales R, is connected to the small injector by the DETERMINING AMOUNT OF MOISTURE IN STEAM 553 pipe C; the injector is sup- plied withsteam by the pipe S, the pressure of which is taken by the gauge P; the temperature of the cold water is taken at e, that of the warm water at g. Water is discharged into the weighing tank A. The amount taken from the tank B is the weight of cold water W; the differ- ence in the respective weights of the water in Fic. 378. — Continuous JET CONDENSING CALORIMETER. tank A and that taken from B is the weight of the steam w. The quality is computed exactly as for the barrel calorimeter. i) ee Fic. 379. — Mrxinc DEvICE FOR CONDENSING CALORIMETER. In case a regular injector is used, as shown in Fig. 378, the tank B is not needed: water can be raised by suction from the tank A 554 EXPERIMENTAL ENGINEERING through the pipe d. The original weight of A will be that of the cold water; the final weight will be that of steam added to the cold water. In case an injector is not available, and the water is supplied under a small head, a very satisfactory substitute can be made of pipe fittings, as shown in Fig. 379. In this case, steam of known pressure and temperature is supplied by the pipe A, cold water is received at S’, and the warm water is discharged at S. The tem- perature of the entering water is taken by a thermometer in the thermometer cup 7’, that of the discharge by a thermometer at 7. The steam is condensed in front of the nozzle C. This class of instruments presents much better opportunities for measuring the temperatures accurately than the barrel calorimeter, and the results are somewhat more reliable. Fic. 380. — HoapLey Steam CALORIMETER. 300. The Hoadley Calorimeter. — This instrument belongs to the class of non-continuous surface calorimeters. It was described in DETERMINING AMOUNT OF MOISTURE IN STEAM sg. “Transactions of the American Society of Mechanical Engineers,” Vol. VI, and consists of a condensing coil for the steam, situated in the bottom of a tank calorimeter, very carefully made to pre- vent radiation losses. (Fig. 380). The dimensions were 17 inches diameter by 32 inches deep, with a capacity of about 200 pounds of water. The calorimeter was made of three concentric vessels of galvanized iron, the spaces being filled with hair felt and eider- down. The condenser consisted of a drum through which passed a large number of half-inch copper tubes, the steam being on the ° ° Fic. 381. — HoapLEy CALORIMETER. outside, the water on the inside, of these tubes, the agitator con- sisting of a propeller wheel attached to an axis that could be rotated by turning the external crank K, effectually stirring the water. The thermometer for measuring the temperature was inserted in the axis of the agitator at T. In the hands of Mr. Hoadley the instrument gave accurate determinations. In practice the instrument was arranged as in Fig. 381; the calorim- eter E was placed on the scales F and supplied with cold water from the elevated barrel A. The temperature of the entering water was taken at C. Steam was admitted to the condensing coil until the temperature of the condensing water reached, say, 110° F. The 556 EXPERIMENTAL ENGINEERING weights before and after adding steam were taken by the scales F; the temperature of the warm condensing water was taken by a ther- mometer, G, inserted in the axis of the agitator. The water equivalent was determined as explained in article 296, and the quality computed by equation (4). The rate of cooling was deter- mined, and an equivalent amount added as a correction for any loss of heat by radiation. 301. The Barrus Continuous Calorimeter. — This calorimeter is shown in Fig. 382. It consists of a steam pipe, aJ, surrounded by a tub or bucket, O, into which cold water flows; the condensing water is received as it enters the bucket in a brass tube, %, surrounding the pipe a, and is conveyed over and under baffle plates, m, so as to be thoroughly mixed with the water in the vessel, and is finally dis- charged atc. Thermometers are placed at f and at g to take the temperature of the water as it enters and leaves, and finally the condensing water is caught from the overflow and weighed. The condensed steam falls below the calorimeter; by means of the water-gauge glass at ¢ it may be seen and kept at a constant height. The tem- perature of the condensed steam while it is still under pressure is shown by a thermometer at #. In order to use the calorimeter it is necessary to weigh the condensed steam; this cannot be done without further cooling, as it would be converted into steam were the pressure removed. For this purpose it is passed through a coil of pipe immersed in a bucket filled with water. The water | —__D <——Cold Water b Condensed Steam Fic. 382. —Barrus Continuous CALORIMETER, ‘DETERMINING AMOUNT OF MOISTURE IN STEAM 557 used in the cooling bucket has no effect on the quality of the steam and is not considered in the results; it is allowed to waste, but the condensed steam is caught and weighed. The method of computing the quality of the steam from the observed data should be clear from previous articles. The following form for recording readings and results obtained with this calorimeter will be found convenient: SIBLEY COLLEGE— DEPARTMENT OF EXPERIMENTAL ENGINEERING. DETERMINATION OF MOISTURE IN STEAM BY CONDENSING CALORIMETER. MADE BY Tthacay, Nig Wajid e:5: ds dunnecaaomeeinncdeeie IgI.. Type of Calorimeter.................. Barometer vcs ve Po sesasic es inches Hg. Room Temp.............. beeit hee Duration of run — min... PRCSCUPES oo ain $5 5 Ra wae GAM BCs nceenie ecg in hes Absolute............. Weight of barrel........ Weight of water......... Warercacadansesars as MATE: covztarahne cose eigeabe LOtAl , svaimaraeercelaa ieee 5 Temperatures........... Condensing water — Tinh all acy its joes fn tag 2d Condensing water — finals siccmawerae cast Steam — initial........ Steam (condensed) — finalveccnaninerasarnas Weight of water — lbs.... Weight of steam — Ibs... Water equivalent of Calorimeter......... Ratio of water to steam. . Latent heat of steam at initial pressure...... Quality — per cent...... Moisture — per cent..... Total heat in Ib. steam _as determined ...... 558 EXPERIMENTAL ENGINEERING 302. Superheating Calorimeters. — These are of two forms, the external and the internal. The former is typified by the Barrus superheating calorimeter, the latter by the throttling calorimeter, of which the Peabody is the original example. Steam to be tested 34" Pipe Steam for Superbeater F x4!" Pipe A G Superheater i p = Fic. 383. —BARRUS SUPERHEATING CALORIMETER, 303. The Barrus Superheating Calorimeter js shown in Fig. 383. The pipe carrying the sample steam separates into two branches, DETERMINING AMOUNT OF. MOISTURE IN STEAM 559 of equal size, one, H, carrying steam to be tested, the other, EZ, supplying the superheater G. R is a heater for superheating the steam passing through G. From G the now superheated steam passes through Q and J down through the jacket J, and out to the atmosphere through the orifice M. The test sample passes through the central pipe in J and out to the orifice N. M and WN are of the same size. Conditions must be such that in passing through J the sample steam shall first be dried and then superheated by taking heat from the superheated steam surrounding it, and the latter must still be superheated when it reaches the orifice M. Temperatures are taken at A, B,and C, and either the pressure or the temperature of the sample steam must be accurately found. Theory of the Instrument. —The accuracy of the instrument depends in the first place upon the condition that equal weights of steam must flow out of the orifices N and M in a given time. If this is not maintained the weights of the two quantities of steam must be considered. This can of course be done by condensing and weighing. Let W = weight of steam in a stated time from orifice N. W, act ” ” ” Md Hd. ” uy: » a} M. T = saturation temperature of steam in main. T, = temperature at A. T. T | temperature at B. 3 — temperature at C. = radiation loss in B.t.u. in the stated time. quality of sample steam. amount of moisture carried by each pound of steam. C, = mean specific heat at constant pressure in the range T, to T,. Cy = mean specific heat at constant pressure in the range. T to T,. | We may then equate the amount.of heat lost by the steam escaping through M to the amount of heat gained by that flowing out through N, or us WC, (T,— T) —R=W,[r (a — *)+ Cy (YT, — T)] (7) The usual assumption is that W = W,. The mean specific heat Cy, for the range T to 7’, can be obtained directly from Fig. 244, R&P Il 560 EXPERIMENTAL ENGINEERING while 7 is taken from the steam-table for the absolute pressure of the sample steam. The factor Cp in the first member of the equation cannot be found directly from Fig. 244; it can, however, be determined in two steps, as follows: Let Cz, be the mean specific heat in the range T' to T,, and Cy, be the mean specific heat in the range T' to T,. Both of these can be read directly from Fig. 244. We may then write WC, (T,- T,)— R= WIC», (T, — T) — Cy (ZT, — DI-R, 8) and the final form of the equation for this calorimeter is, putting W=W,, €,,(TeT) =n G-T— Rar G8 te ©) The radiation loss, R, is some function of T,, and can be determined by calibration. The following form shows the scheme used at Sibley College for recording the observations made with the super- heating calorimeter: SIBLEY COLLEGE, CORNELL UNIVERSITY — DEPARTMENT OF EXPERIMENTAL ENGINEERING. LOG OF TESTS WITH SUPERHEATING CALORIMETER. Bytes sce ead aa He eh aay eae ge SRR Ee SEE eee Dat. vexss a aratnsisn hes tas Keane 3 Places cick eis se he cerne He aimee wh ones aoe Barometer.............. ches Hg. Temperature. Steam Absolute Satura- Moisture . No. | Time. | Pressure} Steam tion Jacket | Jacket | Sample in Quality Main. Préscuré: Temp. | Steam | Steam | Steam | Steam x of Steam|Entering|Leaving,|Leaving,| 1 x in Main,}| Ty. T.. Ts. Ee ‘ 304. The Throttling Calorimeter. — This instrument was designed in 1888 by Professor C. H. Peabody of Boston, and represents a greater advance than any previously made in practical calorimetry. DETERMINING AMOUNT OF MOISTURE IN STEAM 561 The equations for its use and limitations of the same were given by Professor Peabody in Vol. IX, ‘“ Transactions of the American Society of Mechanical Engineers.” The form of calorimeter at present used in Sibley College was patented by the writer in 1893. Fig. 384 shows the essential details. The sample steam from the main passes through a valve and a throttling orifice into the interior of the calorimeter. Here the low- pressure or exhaust steam completely surrounds a thermometer | | Thermometer Lee Exhaust Steam Main Steam Pipe 5 Manometer rT vida uibddgasiida YL ——— Fic. 384. — THROTTLING CALORIMETER. cup before passing out of the calorimeter through the bottom opening. In many instances a gauge or thermometer cup is in- serted between the valve and the throttling orifice in order to deter- mine the pressure of the sample steam as accurately as possible. The pressure of the steam in the calorimeter is obtained by means of a manometer or low- -reading gauge, connected as shown. Where the exit from the calorimeter is comparatively free, that is, not obstructed by long pipes, bends, or valves, the so-called back pressure in the calorimeter should not be more than 3?” mercury, and a manometer is therefore the best instrument with which to 562 EXPERIMENTAL ENGINEERING determine it. The throttling orifice has a diameter of about .08”. The calorimeter itself is about 3” in diameter by 6” long. For the purpose of cutting down radiation the body is nickel-plated, but it is nevertheless advisable thoroughly to cover the instrument with some non-conducting material after installation. The sample pipe leading to the calorimeter should be as short as possible, and should also be thoroughly covered. If the instruments determining the pres- sure of the sample are inserted between the valve and the throttling orifice, it is essential that the valve be opened wide during a trial. Theory of the Instrument. —It is assumed in the operation of the throttling calorimeter that there is exactly as much heat in one pound of steam ahead of the throttling orifice as there is’ in the same weight of steam after throttling; that is, no heat is lost in radiation and no work is done in the expansion process in the orifice. There is,. however, less total heat in saturated steam at the lower pressure than there is at the higher, and the excess heat thus liberated in'the expansion through the orifice will first evaporate any moisture that the sample contains and will next superheat the dry steam, if any heat is left after the drying process is completed. Hence, provided enough heat has been liberated, the steam in the calorimeter will be superheated. As a matter of fact, this must be the case or the instrument cannot be used, for if the thermometer shows the saturation temperature of the steam in the calorimeter, there is ho guarantee that even the original moisture in the sample has been evaporated. The heat in one pound of the high-pressure steam may be ex- pressed by («7 + g) B.t.u.; that in low-pressure steam by 4+ C, (T, — T,) B.tu., where T, is the temperature indicated by the thermometer and 7, is the saturation temperature of the steam at the absolute pressure existing in the calorimeter. As pointed out, T’, must be greater than T,. By the theory above outlined we may then write art q=2+Cp(T,— Ty, (10) from which A+ Co (Ff, -— T,)-— = ok ; ) g (11) C, may be closely estimated from Fig. 244. DETERMINING AMOUNT OF MOISTURE IN STEAM 563 Example.— Pressure in ask main steam pipe is 150 lbs. by gauge, back pressure in the calorimeter. 4” ME TEUTYs barometer pressure 29.9' mercury, temperature in the calorimeter 92° EF. Here we have absolute pressure of sample steam = 150 + 14.7 = 164.7 lbs., absolute pressure in the calorimeter = 29.9 + 4 = 33.9’ "He. = 16:6 lbs. The saturation temperature, T 1) for the latter pressure, by interpolation from the steam-table, = 218°. The degree of superheat i is, therefore, T, — Ty = 292 — 218 = 74°. For this range, C, = .47 from Fig. 244. The total heat d for 16.6 Ibs. = 1152.6 B.t.u. Further, for dba, 7 lbs., 7 = 857.9 B.t.u. and g = 338 B.t.u. Finally, by substitution in the above formula, _ 1152.64 .47 (292 — 218) — 338 _ 840.4 = 857.9 857-9 In case the result for x is greater than 1.0, it indicates that the sample steam was originally superheated, and the degree of super- heat should next be determined as shown in Example 3, page 338. The following form is now used at Sibley College for recording the throttling calorimeter observations taken and the results: = 99 per cent. SIBLEY COLLEGE, CORNELL UNIVERSITY —DEPARTMENT OF EXPERIMENTAL ENGINEERING. LOG OF TESTS WITH THROTTLING CALORIMETER. Bypeiadneys day abn debs Qoneeelein ses yal aid aes Aaa aise be ease eae aan DAO sautdimenm ment Soe Shek + oe Geko AE Wee ae ed ILA Gates ke a a hes Bec dance ae Mean Boiling Temp. in Calorimeter................ Barometer........ inches Hg, e ae ; g ‘ o ga 2 a g2. oo eb : 3 e ahw! af |= 8 s ; g o oe] g SEM! pt | HB yg be a 3 oa-3 Ga eS o 2 §& o 2 : g i |B i |*s od) pa | eee] BE 2 2 | a | de lgie| e208) oo [G88] 28] 2 oO aa es SS 3 # | 3 |4ac| $2 |888| 28 |sdA| 8a | 8 a & a < a. -Q ° a a a 305. Graphical Solutions for Throttling Calorimeter Computations. — The Mollier diagram, Fig. 245, offers a very quick means of arriving at the final result for percentage of moisture as based 564 EXPERIMENTAL ENGINEERING upon throttling calorimeter observations. Thus, in the case of the example above computed, follow the 16.6 lbs. pressure line until it crosses the line of 74° superheat. From this point follow a line parallel to the entropy axis until it cuts the 164.7 lbs. absolute pressure line. This operation assumes a constant heat content of the steam, as laid down in the theory of the calorimeter. The last point of intersection will be found to indicate 99 per cent quality. This diagram is universal, that is, it takes into account the varia- tion of C, with pressure and temperature and is therefore applicable to any case. 306. Limits of the Throttling Calorimeter.— When in equation (11) T, becomes equal to T,, there will be no superheat in the calorim- eter, and all of the heat liberated in the throttling process has been used to dry the moisture in the original steam. This condition then marks the minimum value of x, that is, the highest percentage of moisture that the calorimeter can indicate under the conditions of initial and final pressure. The following table, which may be computed by substitution in equation (11), assuming T, = T,, or may be constructed by means of the entropy heat chart, Fig. 245, shows what the lower limit of the calorimeter is for a series of pressures, taking the pressure in the calorimeter at 15 lbs. absolute. There is, of course, no upper limit, that is, no limit to the degree of superheat in the sample steam that the calorimeter can indicate. LIMITS OF THE THROTTLING CALORIMETER. Pressure, pounds per sq.’ in. ‘ i Maximum fer} Quality of Gauge (Ba- | cent of Mois-| the Steam, Absolute. rometer as- ture. per cent. sumed, 29.9””) 300 285.3 6.7 93-3 250 235-3 6.2 93.8 200 185.3 5.6 04.4 175 160.3 53 94-7 150 135-3 4-9 95-1 125 110.3. 4.6 95-4 100 85.3 4.0 96.0 75 60.3 3-3 96.7 5° 35-3 3-5 97-5 It should be noted, however, that it is not safe to trust the readings from a throttling calorimeter when T,= T,, for there is no definite DETERMINING AMOUNT OF MOISTURE IN STEAM 565 indication under such conditions that the original moisture in the steam has all been evaporated. Further, when T, is close to Ty, the readings should be accepted only with caution, and should in fact be accepted only when the thermometer used is known to be correct or when the error is known and allowed for. In the former case some other form of calorimeter must be used, in the latter case the writer would recommend a change if the margin between T,and T, is less than, say, 10 degrees. In this connection proper lagging of the calorimeter and stem correction for the emerging film of the thermometer are often of importance. 307. Throttling Calorimeter Constructed from Pipe Fittings. — It is possible to construct a very satisfactory throttling calorimeter ! Fic. 385.— THROTTLING CALORIMETER MADE FROM Pipe FITTINGS. from pipe fittings, as shown in Fig. 385. Connection is made to the main steam pipe, as explained already elsewhere. The calorimeter is made of 3-inch fittings arranged as shown; the steam pipe W is of Z-inch pipe, and the throttling orifice is made by forcing a taper plug into the end of the pipe, in which is drilled a hole 3 or ys inch in diameter. A thermometer cup, Fig. 376, is screwed into the top, and a pet cock inserted opposite the supply of steam... A manometer, 566 EXPERIMENTAL ENGINEERING B, for measuring the pressure is attached by a piece of rubber tubing, as shown. The exhaust steam is discharged at Z. The back pressure on the calorimeter can be increased any desired amount by a valve on the exhaust pipe; when no valve is used the pressure is so nearly atmospheric that a manometer is seldom required. 308. The Thomas Electric Superheating Calorimeter.— Figure 386 shows a sectional view and Fig. 387 a general view of this instrument.* It consists practically of an elec- tric heater which is constructed by passing a continuous coil of German-silver wire up and down through holes in a soapstone cyl- inder. Connections to the source | oO ESSY EE (heezzrrerrare oh 78 7a aaa aa aaa aaa eB Ww SES > SPP " Si COE LEO ff | SS SSS Fic, 386.— Section, Toomas ELecrric Fic. 387.— GENERAL View, THomas CALORIMETER. CALORIMETER. of electric supply are made as shown. The steam passes in at A, Fig. 386, is.dried, and in some cases superheated-in passing the coil, and leaves through the opening C. The branch pipe-C contains a section of glass tubing, as shown in Fig. 387. This serves as a * Full description in Power, November, 1907. . DETERMINING AMOUNT OF MOISTURE IN STEAM 567 watch glass to indicate whether the steam is wet or superheated, A thermometer is introduced at B, Fig. 386, to indicate the tempera- ture of the steam passing out. Arrangements are made to accurately measure the watts input into the heating coil. The current used is ordinarily 110 volts, about 10 amperes being required. Operation. — After steady flow is obtained, turn on current and first dry steam, as shown by fog disappearing from watch glass and by thermometer reading. Then superheat to some temperature T. Call input after this temperature has become constant Ey watts. Next, decrease current until steam is just dry. Call input then E, watts. Then Ep — E,= E,= watts required to superheat T degrees. It can be shown that the heat required to dry one pound of the steam is then equal to H=K— ms B.t.u., (22) E, = where K is a constant for any one steam pressure and for a given degree of superheat. This factor has been experimentally deter- mined (see Fig. 388). Next, if 7 is the heat of vaporization of the steam at the pressure used, then _ - 1-H ae x= (13) - Example.—Suppose the steam pressure is 165 lbs. absolute, and that to maintain the temperature of the steam at 460° requires 650 watts = Er. When the steam is just dry, as shown by the watch glass, suppose the input = 260 watts = E;. Then EF, = 650 — 260 = 390 watts. The critical tem- perature at 165 Ibs. abs. = 366°, while = 856.8 B.t.u. Hence, the degree of superheat = 460 — 366 = 94°. For this degree of superheat and for 165 lbs. pressure; Fig. 388 shows a value of K = 59. Hence 260 H= eee 59 X Fog 7 30d and the quality is _ = $56:8 — 30.4 856.8 309. Methods of Direct Determination of Moisture in Steam. The Separating ,Calorimeter.— The separating calorimeter is an instrument which removes all water from the sample of steam ‘by = 95.4 per cent. 568 EXPERIMENTAL ENGINEERING some process of mechanical separation, and provides a method of determining the amount of water so removed and also the weight of the sample. This process is dependent upon the greater density of water as compared with that of steam. Thus, for instance, steam at 100 lbs. absolute pressure is more than 260 times lighter than water - at the same temperature, and if the sample of steam when moving with considerable velocity can be made to change its direction of motion abruptly, the water will be deposited by the action of inertia. The accuracy of this instrument depends on the possibility of completely separating the water from the steam by mechanical methods. To determine this, a series of tests were conducted for the author by Messrs. Brill and Meeker with steam of varying degrees of quality. The range in moisture was from 33 to I per cent, yet in every case the throttling calorimeter attached to the ex- haust gave dry steam within limits of error of observation. The following were the results of this examination: SEPARATING CALORIMETER. Examination of Ex- Observations on Entering Steam. paaprnicaia ie Calorimeter. T 2 Ww w x t x 4 a 9° Calo- 2 Pounds Pounds é * OF : Duration} Gauge Quality | Temp. in uality | $ rimeter.| “pin, | Pressure, Separated | Condensed Sten || Galois Ein af 8 e minutes. | pounds Water in.| .Steamin per cent eter Exhaust S : ‘ : Run. - Run. : , : : Aue 25 81.5 1.15 4-45 79.46 281 99-95 6 b 25 78.2 0.15 5-20 97.2 281.3 | 100.00] 6 As 25 80.8 0.525 4.25 89.005 286.5 100.00 | 6 B 25 79.5 0.150 4-75 96.94 281.8 99.95 | 6 a. 25 78.5 0.300 5.000 94.34 282.8 100.00 | 6 B 25 77.0 -150 5-45 97-32 282.3 | 100.00] 6 2 24 79-5 1.8 4.55 71.65 280.1 99.94 | 6 B 24 78.5 1.4 4.90 77-77 279.5 99-9 6 1 20 83.5 2.15 4.1 77.67 286.5 100.00 | § B 20 81.6 1.70 4-75 73.04 282.7 99-98 | 5 20 74.8 0.65 3-95 85.87 283.7 | 100.05 | 5 20 82.0 0.85 3-95 82.29 286.8 | roo.05 | 5 20 82.6 0.35 4.15 92.22 285.6 | 100.0 5 20 81.5 0.20 3-95 95-15 285.2 | 100.05 | 5 a 20 81.4 2.20 4.325 66.28 283.1 | 100.0 5 B 20 80.3 0.30 4.55 93.81 282.8 | 100.0 5 a 20 82.0 0.20 4.65 95.8 282.8 99.98 | 5 B 20 Sr. v.20 4.40 95.7 284.0 | 100.0 5 ’ Average of 18 trials, involving 98 observations .................00. 99.998 DETERMINING AMOUNT OF MOISTURE IN STEAM 569 “ggf “old “Bq yeoyrodng sso1soqg. OG 08S OCS OFS 00S OGT OST OLT OT OST OFT OST OCT OTT OOT 06 O08 oo of OF OF OF OF O 0 3898 & # 22 8 3 y JO SOnTeA So a aa cL W3nor7y wrv943 9713 yeay.edns 07 S340 <1 9 yeoqaedns 0 puv SurMog uresys 0g} L1p 07 poonporjzur sey = +y eq} USn01g} TAO wrH4s oT} Ap 07 paonposqUr 9398 AA — Ty ‘wivaye Jo punod T 41p 0} perjddns eq 03 Arvsse0ou n°" —7 *1OJPOUILIOTO OY} Ul GrnyerIaduI94 [BUTTLIO 07 Sutpuodso1100(s0[qB} Wee84s Wor) MOIjwz1I0dvA_JO OH] — A}Y * =A = fAyeae wree4ys Jo £qrpenb =zn-0n -* = x H YSaLIWIYOTVO SVWOHL AHL HLIM WV3LS SO ALITVND SHL ONININYS.L30 NI ASN YOS YM LNAIOISSIOO AHL JO SAN IVA ONIMOHS S3ANND oor 57° EXPERIMENTAL ENGINEERING This experiment indicates that the complete separation of moisture from steam is possible by mechanical means. Any radiation in the instrument will increase the apparent moisture in the steam, and must also receive consideration, especially if it be sufficient in amount to sensibly affect the results. The earliest form of separating calofimeter used in experimental work, in the Sibley College laboratory, consisted of a vessel with an interior nozzle, extending below the outlet and so arranged that the current of steam would abruptly change direction and deposit the moisture into the bottom portion of the vessel. The dry steam was allowed to escape near the top. This instrument, even when covered with hair felt, gave off sufficient amount of heat to sensibly affect the results, and a correction for.radiation was essential. The amount of radiation was determined by using two instruments of the same kind and size, arranged so that the discharge from one was the supply to the other. The second instrument receives perfectly dry steam from the first, the water deposited is due to the radiation loss, which, being the same in both instruments, provides a method of determining its amount. In figuring the percentage of moisture, the amount thrown down by radiation in the second instrument is to be de- ducted from the total amount caught in the first calorimeter. In later forms of the instrument the amount of radiating surface has been made so small as to render the correction for radiation, in all ordinary cases, negligible, by constructing the instrument in such a manner as to be jacketed by steam of the same pressure and temperature as in the sample. The form of this instrument is shown in a more or less conventional sketch in Fig. 389, in which the steam is supplied through the pipe D, the moisture being re- ceived in the interior vessel E, the discharge steam passing out of the chamber E at the top, into the jacket F, and thence out of the instrument through a small opening at L, the opening at L being made sufficiently small to maintain the pressure in the jacket the same as that in the sample. The discharged steam is then con- densed inacan, J. This can is provided with a small top in which is set a gauge glass with attached scale, graduated so as to read to pounds and tenths of pounds of water. A gauge glass N attached DETERMINING AMOUNT OF MOISTURE IN STEAM 571 to the calorimeter is provided with index, mn, arranged to move over a graduated scale, S, which shows the weight of water in the vessel E in pounds and hundredths. In using this instrument the condensing can J is filled with water to the zero point of the scale. The amount of condensed steam is read on the scale of the can, J; ——— ————}. [=] |IlIIp B WwW | 1 K R HORA OC A F 8 ie N a n ©) S) L P R Y \ Fic. 389. — SEPARATING CALORIMETER. the amount of water in the sample of steam for the same time is read on the scale S. The percentage of moisture, in case radiation is neglected, is the quotient of the reading of the calorimeter scale S divided by the sum of the readings on both scales. The latest form of the instrument is shown complete with all accessories.in Fig. 390, and is a great improvement over the earlier forms in points of portability and convenience. It differs from the 572 EXPERIMENTAL ENGINEERING form last described principally in the construction of the steam- separating device, which has been increased in efficiency, and in the substitution of a so-called flow gauge attached to the outer jacket, which regis- ters the total flow of steam through the instrument ‘in ten minutes of time. The flow of steam through a given orifice is proportional to the absolute steam pres- sure, by Napier’s law* (see page 453), which has been proved correct for pressures above 25 pounds absolute; and hence it is possible to calibrate by trial a pressure gauge in such a manner that the graduations will show the flow of steam in a given time. The only error which is produced in this graduation is that due to changes in barometric pressure, which is never suf- ficient to sensibly affect the results obtained in the use of the instrument. Much, how- ever, depends also upon the proper con- struction of the orifice. Unless this is a well-rounded (bell-mouth), smooth opening, the actual discharge of steam will be considerably less than that computed. The quality will therefore appear better than it really is, since w (see next article) will be assumed too large. Should any doubt arise, the accuracy of the readings of the gauge are easily verified by con- densing the discharged steam for a given period of time. This should be done occasionally to test the graduations. 310. Formula for Use with the Separating Calorimeter.— Let w equal the weight of dry steam discharged at the exhaust orifice, W. the water drawn from the separator, R the water thrown down during the run by radiation. Then the quality of the steam is CALORIMETER, eae Ww (14) * See “Transactions American Society Mechanical Engineers,” Vol. XI., 1887, paper by Prof. C. H. Peabody. DETERMINING AMOUNT OF MOISTURE IN STEAM 573 the amount of moisture Wek Wt+w To reduce the radiation loss as much as possible the instrument should be thoroughly covered with hair felt to the thickness of 4 to inch. In this case the total loss by radiation will be about 0.4 B.t.u.* per square foot per hour for each degree difference of tem- perature between the steam and the surrounding air. This will amount to about 220 B.t.u. per square foot per hour, or about $ of a pound of steam under usual conditions of pressure and tempera- ture. In the instrument described the actual exposed surface amounts to about ry sq. ft., so that the condensation loss may be considered as from 5 to os of a pound of steam per hour. The total flow of steam through the instrument usually varies from 40 to 60 lbs. of steam per hour, so that if the instrument is covered, the radiation loss would be less than 245 of one per cent. If the instrument be not covered, the loss would be about five times this amount, or under usual conditions about } of one per cent. The radiation loss can in every case be determined by using steam of known quality, as determined by the throttling calorim- eter, or better still by arranging two separating calorimeters of exactly the same size in series, so that the steam exhausted from the first is used as a supply to the second in a manner already explained. 311. The Limits of the Separating Calorimeter. — The instru- ment will give correct determinations with any amount of moisture that the sample of steam may contain. With steam containing a very small amount of moisture, the radiation loss will have more effect than with steam containing a greater amount. When the fact is considered, however, that a sample of steam cannot probably be obtained but what differs more than } per cent from the average, the futility of making this correction becomes at once apparent. It is, of course, almost superfluous to note that the instrument cannot indicate superheat in the original sample, as the throttling calorim- eter is able to do. But the separating calorimeter can be used (15) I-%x * See numerous experiments, Carpenter’s ‘Heating and Ventilation” (N. Y., J. Wiley & Sons), Chapter IV. 574 EXPERIMENTAL ENGINEERING for degrees of moisture for which the throttling calorimeter fails, and these two instruments together, therefore, cover all of the quality conditions of steam. 312. General Method of Using the Separating Calorimeter. — The general method of using is given only for the instrument last shown, which is briefly as follows: First, attach the instrument to a pipe leading to the main steam pipe, as already explained, so as to obtain the fairest sample of steam. Second, wrap the instrument and connections thoroughly with hair felt, to prevent loss of heat by radiation, leaving only the scales visible. Third, permit the steam to blow through the instrument until it is thoroughly heated, before making any determinations. Fourth, take the initial and final readings on the scale 12 Fig. 390, at beginning and end of a period of ten minutes of time and note the average position of the hand on the gauge dial during this time. The pressure should be kept as nearly constant as possible dur- ing the period of discharge, in which case this hand will remain constant. Fifth, compute the percentage of moisture as explained by dividing the reading on the scale 12, Fig. 390, by the sum of the readings on scale 12 and the gauge dial. Attention is again called to the difficulty of obtaining an average sample of steam for the calorimetric determination. The principal cause of this difficulty is due to the great difference in specific gravity of water and steam, as, for example, at a pressure of 100 pounds absolute per square inch a cubic foot of steam weighs 0.23 pound; a cubic foot of water at the corresponding temperature weighs about 56 pounds, or more than 225 times as much. _ If any great amount of water is contained in the steam, it is likely, if moving in a horizontal pipe, to be concentrated on the bottom; if moving downward in a vertical pipe, to fall under the influence of gravity and inertia; if moving upward in a vertical pipe, it tends to remain at the bottom until absorbed or taken up by the current of steam. The amount of water by weight that will be absorbed as a mist or fog and carried by the steam is not ‘definitely known, but it depends in a large measure on the velocity of flow. DETERMINING AMOUNT OF MOISTURE IN STEAM 575 Because of the great difference in weight of water and steam nearly all the water can be deposited from a current of steam, in a vessel or reservoir conveniently connected to the steam pipe, by action of gravity or inertia. Such a device is known com- mercially as a steam separator. The water is removed from the separator either by an automatically controlled pump or trap or by hand. In the determination of quality it is desirable to remove the free water by a steam separator before making the connection to obtain the sample, as in that case the sample is more likely to be an average one. See papers on this subject in the “ Transactions of the Ameri- can Society of Mechanical Engineers,” Vol. XIII, by Prof. D. S. Jacobus, and Vol. XII, by the author. The following is a convenient form for recording observations and results: MECHANICAL LABORATORY, SIBLEY COLLEGE, CORNELL UNIVERSITY. PRIMING TEST WITH SEPARATING CALORIMETER. Made: bys siceseneiensiasesye ot te oP te Teens ees eee a er eebewses Qeeaes ee gees IQI ROSESOEs rigscetaticgo trea tetcauetssanih erecer rd ees EAE HEARS SOaWleves Meee vases <4 BREAST REE A A Darevepauceepsiashatedeacun reptstyeeeabutuste tub Sotnastenanes IN, WY. D 7 G. Rysest Pounds of Water. . No. | Time. uration auge bsolute Mois- of Run. | Pressure. | Pressure. |Condensing Can . ture. Calorimeter. or Flow Gauge. Quality 313. The Chemical Calorimeter. — This instrument depends on the fact that certain soluble salts will not be absorbed by dry steam, but will be carried over by water, so that if the salt appears in the steam its presence indicates water. 576. EXPERIMENTAL ENGINEERING Various salts have been used, but common salt, chloride of sodium, gives as good results as any. The proportion that the salt in a given weight of condensed steam bears to that in a given weight of water drawn from the boiler, is the percentage of moisture in the steam. The method of analysis is a volumetric one, and is as follows: Add three or four ounces of common salt to the water in the boiler; after it is dissolved, draw from the boiler a small amount of water and condense an equal weight of steam, which are to be kept in separate vessels. Add to each of them a few drops of neutral chromate of potash, but in each case an equal quantity, which amount may be measured by a pipette; the same amount should also be added to a vessel containing an equal weight of distilled water, in order to obtain a standard or zero point for the scale used in the analysis. By means of a graduated pipette a standardized solution of nitrate of silver is permitted to flow, a single drop at a time, into each of the three solutions. The effect is to cause the formation of the chloride of silver, and until that formation completely takes place the resulting liquid will be whitish or milky; but because of the presence of the chromate, the instant the chloride has all been precipitated the liquid turns red. The amount of nitrate of silver required is meas- ured by the graduated pipette, and gives the information regarding the salt present. The detailed directions for the test are as follows: Take in each case 100 cubic centimeters of liquid containing a few drops of neutral chromate of potassium, and use a standard solution holding 10.8 grams of silver to the liter; the following data were obtained in a test: AMOUNT OF NITRATE OF SILVER REQUIRED TO TURN too c.c, RED 100 c.c, of First Trial. | Second Trial. | Third Trial. Condensed steam.......... Oud Cie 0.05 C.c, OT CC, a Water from the boiler......} 13.6 c.c. 14:0 €.C, 13-35 C.c. b Distilled water............ 0.05 CG; 0.05 C.c. 0.05 C.c. c DETERMINING AMOUNT OF MOISTURE IN STEAM 577 Let the results with these three samples be denoted by a, 6, and ¢ respectively, and the amount of moisture by 1 — x, we then have - a =6 I-x= . 16 b-e¢ ve This gives the following results: First Trial. Second Trial. Third Trial. Amount moisture........ oe 08 5037 9:05 S105). | OST 0:05: 00375 13.6—.05 14.0-0.05 13.35 0.05 Average = 0.0025. Instead of common salt, sulphate of soda may be used, and the percentage of moisture determined by the percentage of sul- phuric acid present in the steam as compared with that in water from the boiler. It will be noted that this method of determining moisture is rather complicated, and, on account of their evident limitations, none of the chemical methods are used. 314. Universal or Combination Calorimeters. — It sometimes happens that a throttling calorimeter fails during a test on account of excessive moisture in the steam, and that recourse must be had to some other form, like the separating. If proper arrangements are made it is usually possible to quickly make the change from one to the other, but sometimes this cannot be done. Further, there are cases in which nothing is definitely known about the quality of the steam to be tested, and in such cases the use of a so-called universal calorimeter may simplify matters considerably. ‘These calorimeters are practically the combination of a throttling with a separating calorimeter, these two being used in that order. The best known of these is perhaps the Ellyson, illustrated in Fig. 391.* No extended description is required. If the throttling at the en- trance of the chamber is sufficient to dry and superheat the steam, we have the ordinary throttling calorimeter. If, on the other hand, the steam after passing the opening is still wet, the amount of * Power, Oct. 27, 1908. 578 “EXPERIMENTAL ENGINEERING moisture remaining in it is determined in the lower chamber as in a separating calorimeter. Designating the items connected with the steam in the chamber by the subscript 2, and those for the original sample of steam by the subscript 1, we may write UN + N= Ml2+ (17) ll SORIA ERR Fic. 391. — ELLYSON UNIVERSAL STEAM CALORIMETER. In this equation, since x, is determined in the separating attach- ment to the apparatus, all the quantities but «, are known, and this may therefore be computed. 315. Comparative Value of Calorimeters. — These instruments, arranged in order of accuracy, are no doubt as follows: throttling; separating; Barrus superheating; Hoadley; continuous condensing; chemical; and lastly the barrel. DETERMINING AMOUNT OF MOISTURE IN STEAM 579 The ease with which the throttling and separating instruments can be used, their small bulk, and great accuracy, render them of chief practical importance. The throttling calorimeter can be used only for steam with com- paratively small amounts of moisture, as-explained in Article 306; but the separating instrument is not limited by the amount of moisture entrained in the steam. It is not, however, adapted for superheated steam, nor can the results be determined as quickly as with the throttling instrument; when carefully handled the accu- racy is, however, substantially the same. CHAPTER XV. THE ENGINE INDICATOR. 316. Uses of the Indicator. — The indicator is an instrument for drawing a diagram on paper which shall accurately represent the various changes of pressure on one side of the piston of an engine during both the forward and the return stroke. The general form of the indicator-diagram for a non-condensing steam engine is shown in Fig. 392; the ordinates of the diagram, * \B Fic. 392.—-Dracram FRoM NoN-coNDENSING STEAM ENGINE. measured from the line GG, are proportional to the pressure per square inch above the atmosphere; measured from the line HH, are proportional to the absolute pressure per square inch acting on the piston. The abscissa corresponding to any ordinate is proportional to the distance moved by the piston. BCDG is the line drawn during the forward stroke of the engine, GEFAB that drawn during the return stroke. The ordinates to the line BCDG represent the pressures acting to move the piston forward; those to the line GFB represent the pressures acting to retard or stop the motion of the piston on its back stroke. The ordinates intercepted 580 THE ENGINE INDICATOR 581 between the lines represent the effective pressure acting to urge the piston forward. Since the abscissas of the diagram are propor- tional to the space passed through by the piston, and: the inter- cepted ordinate to the effective pressure acting on the piston, the area of the diagram must be proportional to the work done by the steam on one side of the piston, acting on a unit of area and during both forward and return stroke. From an indicator-diagram taken from a steam engine can be obtained, by processes to be explained later: 1. The quantity of power developed in the cylinder, and the quantity lost in various ways, —by wire-drawing, by back pressure, by premature release, by mal-adjustment of valves, leakage, etc. 2. The redistribution of piston pressures at the crank-pin, through the momentum and inertia of the reciprocating parts, and the angular distribution of the tangential component of the piston pres- sure; in other words, the rotative effect around the path of the crank. : 3. Taken in combination with measurements of feed-water or of the exhaust steam, with the amount and temperatures of condens- ing water, the indicator furnishes opportunities for measuring the heat losses which occur at different points during the stroke. 4. The indicator-diagram also shows the position of the piston at times when the valve-motion opens or closes the steam and exhaust ports of the engine. It also furnishes information regard- ing the general condition of the engine, and the arrangement of the valves, the adequacy of the ports and passages, and of the steam or the exhaust pipes. 317. Indicated and Dynamometric Power. — The engine indicator is used in most engine tests to measure the force of the working medium acting on a unit of area of the piston. A dynamometer of the absorbing or transmission type (see Chap. X) is used to measure the work delivered by the engine. The work is usually expressed in horse power, one horse power being equivalent to 33,000 foot-pounds per minute. The work shown by the in- dicator-diagram is termed the Indicated Horse Power (I.H.P.); that shown by the dynamometer, Dynamometric or Developed Horse Power (D.H.P.), or Brake Horse Power (B.H.P.). 582 EXPERIMENTAL _ENGINEERING The mean effective pressure (M.E.P.) per unit of area acting on the piston during one complete cycle is obtained from the indicator- diagram. This quantity, multiplied by the area of.the piston in square inches and by the distance traveled by the piston per stroke in feet, will give the work done by-the working substance per cycle in foot-pounds. Multiplying by the number of complete working cycles per minute and dividing by 33,000 will give the work done by the working substance in horse power, that is, the L.H.P. hs Thus, let p equal the mean effective pressure in pounds per square inch, J the length of stroke of the engine in feet, a the area of the piston face in square inches, and » the number of cycles per cylinder end per minute. Then the work done per minute by the working substance acting on one side of the piston is plan_ 33,000 LH.P. = (1) The numerical difference between the I.H.P. and the B.H.P. of an engine must give the power lost in friction, so that 1.H.P. — B.H.P. = Friction loss, (2) and B.H.P. ‘ : LHP. Mechanical Efficiency. (3) 318. Early Forms of the Steam-engine Indicator.— Waitt and McNaught —'The steam-engine indicator. was invented by James Watt, and was extensively used. by him in perfecting his engine. ~The indicator of Watt,* as used in 1814, consisted of a small steam- cylinder AA, as shown in Fig. 393, in which a piston was moved by the steam-pressure, against the resistance of a spring FC. The end of the piston-rod carried a pencil, which was made to press against a sheet of paper DD," moved backward and forward in conformity to the motion of the piston. By this method a diagram was produced similar to that shown in Fig. 393. McNaught’s indicator, which succeeded that of Watt and was in general use until about 1860, differed from the form used by Watt * See Thurston’s Engine and Boiler Trials, page 130. THE ENGINE INDICATOR 583. principally in the use of a vertical cylinder, instead of thetsliding panel, which was turned backward and forward on a vertical s| axis, in conformity to the motion of the piston. 319. The Richards Indicator.* The Rich- ards indicator was invented by Professor C. B. Richards about 1860; it contains every essen- tial constructive feature found in recent indi- cators, and may be considered the prototype from which all other indicators differ simply in details of workmanship, form, and size of parts. SZ SS SS KS Fic. 393. — Wart’s InDICATOR. The construction of this in- dicator is well shown in Fig. 394, from which it is seen to consist of a steam-cylinder AA, in which is a piston B, connected by a rigid rod with the cap F. The movement of the piston is resisted by the spring CD in such a man- ner that its motion in either direction is proportional -to the pressure. The motion of the piston-rod is transferred to a pencil at K, by links which are so arranged that the pencil moves parallel to the Fic. 394. — Ricaarps INDICATOR. * See the Richards Indicator, by C. B. Porter; New York, D. Van Nostrand. 584 EXPERIMENTAL ENGINEERING piston B, but through a considerably greater range. The indi- cator-spring can be taken out by unscrewing the cap EZ, removing the top of the instrument and unscrewing the piston B, and another spring of a different strength can be substituted. The drum OR is made of light metal, mounted on a vertical axis, and provided with a spring arranged to resist rotation. The drum is connected to the cross-head or a reducing motion by a cord, and is given a motion in one direction by the tension transmitted through the cord and in a reverse direction by the indicator drum-spring. The paper on which the diagram is to be drawn is wrapped smoothly around the drum OQ, being held an, place by the clips PQ. The indicator is connected to the~ steam. “cylinder by a pipe leading to the clearance-space of the engine, a cock, T, being screwed into this pipe, and the indicator connected to the cock by the coupling U. Pat l 7 us | | = hs Et ! Ps Cn Fic. 395. — THompson INDICATOR, Fic. 396. — SEction, THOMPSON InpDIcaTor. 320. The Thompson Indicator. — This indicator is shown in Figs. 395 and 396. It differs from the Richards indicator principally in the form of the parallel motion, form of indicator-spring, and details of workmanship. The parts of the instrument are much lighter, and it is better adapted for use on high-speed engines. The construction is essentially the same as the Richards;. the THE ENGINE INDICATOR 585 method of changing springs should be thoroughly understood, and is as follows: Unscrew the milled edged cap at the top of the steam- cylinder; then take out piston, with:arm and connections; disconnect pencil-lever and piston by unscrewing the small milled-headed screw which connects them; unscrew the spring from the cap and from the piston, substitute the one desired, and put together in same manner, being careful, of course, to screw the spring up firmly against cap and down to the piston-head. The method of chang- ing springs is simple, easy, and convenient, and does not require the use of any wrench or pin of any kind. The position of the atmospheric line on the drum may in this indi- cator be changed by regulating the position of the small screwed head A, Fig. 396, on the piston-rod. 321. The Tabor Indicator. — The Tabor indicator, shown in Figs. 397 and 3098, differs from other indicators principally in producing Teena are ee S Fic. 397.— TABOR INDICATOR. Fic. 398.—SEcTION, TaBor INDICATOR. the parallel motion of the pencil by a pin moving in a peculiarly shaped slot. It also differs in details of construction and in form of the indicator-spring. The method of changing springs in the Tabor indicator is as. follows: Remove the cover of the cylinder, remove the screw be- neath the piston, unscrew the piston from the spring and the spring from the cover and replace with the spring desired. When the 586 EXPERIMENTAL ENGINEERING lower end of the piston-rod is introduced into the square hole in the center of the piston, care must be taken that it sets fairly in the hole before the screw is applied. Unless such care is observed, the comers may catch and cause derangement. The tension on the drum-spring may be varied by removing the paper drum, loosening the thumbscrew which encircles the ceritral shaft, lifting the drum- carriage so as to clear the stop, and then winding the carriage in the direction desired. 322. The Crosby Indicator. — The Crosby indicator is shown in Figs. 399 and 4oo. It differs from those already described in the Le TL 4 Q Ny, 2d" Te oneal) z HS, t alll ial q D at Wht Fic. 399. — Crossy INDICATOR. form of piston and drum-springs and in the arrangement for pro- ducing accurate parallel motion., The special directions for this instrument are given by the manu- facturers as follows: To remove the piston, spring, etc., unscrew the cap, then, by the sleeve, lift all the connected parts free. This gives full access to the parts to clean and oil them. THE ENGINE INDICATOR 587 To detach the Spring, unscrew the cap from spring-head, then unscrew piston-rod from swivel-head, then with the hollow slotted wrench unscrew the piston-rod from the piston. To insert a spring, simply reverse this process. Before setting the foot of the spring unscrew G slightly, then, after the piston-rod has been firmly screwed down to its shoulder, set G up firmly against the bead, and thereby take up all lost motion. ee Ss 4 Ke LY SSS HOH mo Wii SING Ha boy HoH bob V2 VED Vee) Unit VB KY] IN WV) SASIA VASA KW ik W CWS KS SEK Fic. 400. — SECTION, CrosBy INDICATOR. It is often desirable to change the position of the atmospheric line on the paper. This can easily be done by unscrewing the cap from the cylinder and raising the sleeve BB which carries the pencil- movement. Then turn the cap to the right or left, and the piston- rod will be screwed off or on the swivel E, and the position of the atmospheric line will be raised or lowered. 588 EXPERIMENTAL ENGINEERING Never remove the pins or screws from the joints K, J, L, M, but keep them well oiled with refined porpoise-jaw oil, which is furnished with each instrument. The tension on the drum-spring should be increased or dimin- ished according to the speed at which the instrument is used, by means of the thumb-nut on top of-the drum-spindle. 323. Indicators with External Springs. — It will be pointed out later more in detail that the varying temperature to which indi- cator-springs are heated in actual service has a certain effect in changing the scale of spring. This fact has of late years become of greater importance on account of the high temperatures encoun- tered in case highly superheated steam is used and on account of the highly heated products of combustion in gas engines. Pro- vision can be made for cooling the ordinary form of spring, either by using a water-cooled indicator cock or by water-jacketing the spring barrel, but in the past few years indicators with external springs have found their way into the market. There are two main types of such external spring indicators. In the one the spring is flat, is fixed at the end away from the piston barrel of the indicator and is flexed over a fulcrum whose position along the spring can be regulated. This type is illustrated by the Bachelder indicator (see Fig. gor). The ad- vantage of this construction, is that the spring is kept cool, and that two or three springs at most can be made to cover the entire range of ordinary pressures, since, by change of fulcrum, one spring may serve Fic. 401. Bacwetper Inpicator, for a number of different scales. The main objection to the indicator would seem to be the chances of error involved in setting the fulcrum to the proper point. This of course could be taken care of by calibration. It should be stated that this indicator was on the market some time before the second type about to be described was developed. THE ENGINE INDICATOR 589 In the second type the spring is of the ordinary form; in fact, American manufacturers have developed this indicator so that the springs of the ordinary instrument may be used interchangeably. Fic. 402. — Various Types of EXTERNAL SPRING INDICATORS. This indicator has for the past six or eight years gone through a course of development during which it assumed a variety of forms, some of which are shown in sketch in Fig. 4o2.* The problem * Haeder, Der Indicator, p. 13. 590 EXPERIMENTAL ENGINEERING seemed to be mostly one of reducing the weight of the moving parts without sacrificing strength and necessary rigidity. To-day the springs are used either in tension or compression, and each type of spring has its advocates. It is claimed for the tension spring that it will not buckle over and bind the piston, but it is pointed out also that in the tension spring the force on the piston is trans- (2) Fic. 403. — TaBor INDICATOR WITH EXTERNAL SPRING. Hi 2 mitted to the Ye} | ua outer end of the : 2 = spring through | a rather long — = = and slender /} ll i= rod, which, n being under compression, may itself show signs of buck- ling. Figs. 403 and 404 illustrate aS two indicators having thecom- pression form of indicator spring. The first one is a Tabor, the second an American Thompson. Fig. 405 shows several views of a Star indicator having the tension form of spring. Another indicator Fic. 404. — AMERICAN THOMPSON EXTERNAL SpRING INDICATOR. THE ENGINE INDICATOR 591 [TT i} OOH aN Gara) IW eS) ex KES i A ASS SOON 7 Fic. 405.— Star INDICATOR WITH EXTERNAL SPRING. é roi RT a_i th I i rd i I Li i 1 iy i vai lit ' 1M i ii Hd il A Mf | : tM fl : 1 | Hy ey sl ‘ye — a I rai I? i! Hs a x all | | Fic. 406. — Crospy Continuous InpIcaToR wITH EXTERNAL SpRING. "592 EXPERIMENTAL ENGINEERING with the same type of spring is the Crosby continuous (see Fig. 406). 324. Indicators for Ammonia Machines. — The indicators manu- factured for use with the steam and the gas engine are made of brass or similar material containing copper, and are hence unsuited for use with ammonia or other vapor which attack this metal. For use in testing refrigerating and similar machinery, most of the manufacturers make an all iron or steel indicator, and care should be taken to see that such instruments are used in these tests. In all the types so far described, the piston must be compara- tively loosely fitted in the cylinder to prevent excessive friction and binding at high temperatures, and as a result there is always more or less leakage to the upper side of the piston and from thence into the atmosphere. This is practically nonpreventable in this form, as the upper side of the piston must be freely open to the atmosphere in order that the atmospheric line may be correctly traced and that the piston and spring may operate properly. The leakage of ammonia vapor is naturally not desirable, and to pre- vent such leakage various forms of indicator have from time to time been produced. The most common among these is the dia- phragm indicator, in which a diaphragm takes the place of the ordinary piston spring or piston and spring. This enables com- plete isolation of the cylinder from the atmosphere, but has the disadvantages that the scale of the spring is not uniform, deflec- tions decreasing as the pressure rises, and that the amount of motion obtainable is so small as to necessitate excessive multipli- cation in order to obtain a diagram of reasonable height. This process is apt to introduce serious errors if carried out by mechan- ical linkages in the ordinary way. In one of the optical indicators described below, it is effected in such a way as to introduce only negligible errors. 325. Small Piston Indicators. — The spring which would be re- quired if the ordinary indicator were to be used with very high pressures, such as those attained in gas engines and hydraulic accumulators, might be so bulky that it could not well be fitted into the space available for it. This would mean either the manu- facture of special indicators for use with such high pressures, or THE ENGINE INDICATOR 593 the making of the ordinary indicator in such a way that springs of usual size could be used with it. Either method means addi- tional expense, in the purchase of two indicators or in the pur- chase of a number of springs of widely different strengths. To make the ordinary indicator with the ordinary supply of springs available for use over wide pressure ranges, many of the manufacturers furnish what are known as small piston indicators. In these the indicator cylinder bore is continued downward with a diameter of such size as to accommodate a piston with one-half or one-quarter the area of the ordinary piston. By using the small piston instead of the full-sized one, the ordinary springs can be used for the measurement of much higher pressures. The use of a half-size piston amounts to doubling the scale of the spring; the use of a quarter-size piston is the same as quadrupling the scale. 326. Large and Small Indicators. — In the early days of the indicator the speeds of rotation of engines and the pressures used were both low, but during recent years both have been materially raised. As will be shown below, the errors of indicators increase very rapidly with the speed and with the pressure because of inertia effects, which cause the various parts to over- and under-travel and run ahead or behind their proper positions. These errors can be materially reduced by decreasing the weights and the travel of the moving parts, and most of the makers of indicators now pro- duce a large size for ordinary speeds and pressures and a small size for high speeds and pressures. The small size naturally gives a smaller diagram than the other, but it is found that these small diagrams give results with smaller errors than result from the attempt to get larger ones. 327. The Continuous Indicator. — In some types of engines the successive working cycles traced through a given period of opera- tion vary so radically in amount of energy developed that an aver- age determination of power, obtained by evaluating a series of diagrams taken one at a time and at stated intervals, may be very far from a true mean value. In some cases, as, for instance, in rolling-mill engines, the time of operation is so short that even this procedure is not possible. To take a series of diagrams over one 594 EXPERIMENTAL ENGINEERING another on the same card is not a satisfactory method on account of the difficulty of integrating all the cards or of locating the mean card. Conditions found in indicating gas engines which govern on the hit-and-miss principle are somewhat similar, although the cycles traced between two miss periods are usually not so numerous or as varying in size as in the case ofa rolling mill or hoisting en- gine. For obtaining the average power developed in such engines with a fair degree of accuracy, the so-called continuous indicator does good service. This is, in principle, just like the ordinary indicator, except that provision is made for moving the paper a certain small distance around the indicator-drum every time the latter oscillates. The means for doing this are various. Some- times two drums are used, the roll of paper being wound from one onto the other. In most cases, however, two small spools are located inside of the indicator-drum, the paper passing from one spool around the outside of the drum, winding up on the second spool. A modification of this idea is used in the Crosby con- tinuous indicator, Fig. 406.* The small roll seen near the slot in the main’ drum holds the supply of paper, which after passing around the main drum is wound on a concentric drum inside. The travel of the paper may in this indicator be adjusted so that from 6 to 100 diagrams may be obtained per foot of paper. Fig. 407 shows an example of the work done, the series being taken from a plate-mill engine, starting with the friction load, showing the pass, and ending again with the friction load. The points of admission and of release are marked with the same numbers for each diagram. 328. The Errors of the Piston Indicator.— There has always been a tendency on the part of engineers to regard the indicator as an instrument of great precision, and the fact is that it can be made one of the most precise of any used by the engineer by great care in its selection and operation. As ordinarily handled it gives results which may be in error anywhere from five to as much as ten per cent, and it is doubtful if it ever gives results closer than two per cent, except in the hands of an expert in its use. As used for the measurement of power, the drum of the indicator should move in synchronism with the piston of the engine, follow- * Power, Nov. 23, 1909. THE ENGINE INDICATOR ing its changing speed accurately, and the pencil point should move up and down in a vertical line in exact phase with the varying pressure within the cylinder. With modern constructions the pencil motion is theoretically suf- ficiently accurate to allow one to assume that the pencil point moves vertically and that it multiplies the motion of the indicator-piston by ex- actly the same amount at every point of its motion. It is never safe, how- ever, in the ordinary case, to arbitrarily assume that the motion of the drum is correct (that is, that the reducing motion is accurate), or that the vertical distances traveled by the pencil point give the pressures within the cylinder correctly (that is, that the scale of the spring is correct). The principal sources of error are: (a) Inaccurate springs, that is, springs’ in which the deflection per unit increase of load is not the same for the entire range of the spring, and springs in which the deflection per unit of load is not what it is assumed to be and what is stamped on the spring. To these errors, which can be more or less closely determined by spring calibration, see Art. 329, must be added that introduced by the uncertainty as to the real action of the spring under the varying temperatures to which it is subjected. (6). Weak springs, that is, springs which are too weak to quickly damp 10 11- 12 21 28 746 68 57,2 35.4 —10.8 -9.6 595 11 12 Fic. 407. DIAGRAMS TAKEN FROM A PLATE Mitt ENGINE By A Continuous INDICATOR. 596 EXPERIMENTAL ENGINEERING out vibrations produced by the inertia effects of the attached parts. (c) Poorly fitted and guided pistons, making the pressure actu- ally applied to the spring something different from that existing in the cylinder below the piston. (d) Improper connections to the ‘cylinder of the engine under test, resulting in the application of pressures below the indicator- piston different from those existing in the engine cylinder. (ec) Lost motion in the piston connections and in the joints of the pencil mechanism. (f) Non-parallelism between the indicator-piston travel and the axis of rotation of the paper drum. (g). Inertia effects of indicator-piston, piston connections, and writing mechanism, causing late starting and stopping of vertical motions. (h) Excessive pressure applied to the pencil point when tracing the diagram, resulting in distortion due to the friction of the point on the paper of the drum. (i) Inaccuracies and lost motion in the reducing mechanism used to transmit the travel of the crosshead or other reciprocating part of the engine to the indicator-drum in reduced magnitude. (7) Inertia effects in this reducing mechanism, causing it to lag behind the phase of the engine’s motion. (k) Stretch in the string or other material used to connect the reducing mechanism or motion with the drum of the indi- cator. (2) Inertia effects of the drum and connected parts, causing the moving parts to lag behind the phase of the reduced motion trans- mitted to it. All of the sources of error enumerated exist in the application of every piston type of indicator, and it is only by reducing the effect of each to the minimum possible amount that a fair degree of accu- racy can be attained. The use of small indicators of light weight and fitted with strong springs is the only satisfactory means of reducing inertia effects, and even these fail at excessively high speeds of rotation, say above five hundred revolutions per minute in the average case. The methods of calibrating for and guard- THE ENGINE INDICATOR 507 ing against the other principal errors are given in the following paragraphs. 329. Calibration of Indicator-Springs. — The Indicator-spring is usually a helical spring; when in use it has one end screwed to the upper head of the cylinder, and the other screwed to the piston, except in the case of the Crosby spring (see below). To insure accu- rate results the spring must’be accurate, and there must be no play or lost motion between the piston and the cylinder-head, and the spring must receive and deliver the force axially. /The number of pounds pressure on the square inch required to move the pencil one inch is stamped on the spring, and the springs are designated by that number, which is called the scale of the springs It is essential to know the error, if any, in the scale. A spring can be readily removed and another substituted when desired; probably the maximum compression should not exceed one-third of an inch. With the usual multiplication of 6 to 1, this would mean a pencil travel equal to 6 X 4 = 2 inches, so ‘that the allowable maximum pressure in the case of say an 80-pound spring would be 160 pounds. A rule given by one of the manufacturers is to multiply the scale by 23 and then to subtract 15 pounds to get the allowable maxi- mum pressure. For the 80-pound spring this would give 185 pounds. The spring is in many respects the most important part of the indicator, as the form of the diagram is directly affected by any error. The following cuts, Figs 408 to 410, show some of the princi- pal forms adopted by a few of the makers, and it may perhaps be sufficient to state that within the range of action of the indicator any of these forms can be made practically perfect. The best method of calibrating an indicator spring is still a mooted question. It is admitted by all that the conditions during calibration should as nearly as possible duplicate those during use, but so far no calibrating device which will do this has been pro- duced. Roughly all the methods so far used divide naturally into two classes: (a) Dead-weight calibration, and (b) Fluid-pressure calibration. Either method may be used with the spring hot or cold. 598 EXPERIMENTAL ENGINEERING The term dead-weight calibration is here used -to designate any method in which the pressure is applied to the piston or spring mechanically and the reaction of the spring measured by suitable weighing apparatus. A convenient and simple apparatus for this purpose is that devised by Professor Cooley of Ann Arbor. In this case the indicator con- taining the spring to be tested is supported on a bracket above the platform of a platform scale or balance. Force is applied to the indicator-piston by means of a rod which can be lengthened or a — oe Fic. 408. — THoMPSON ‘Fic. 409. — TABOR Fic. 410. — CRosBY SPRING. SPRING. SPRING. shortened by turning a hand-wheel. This rod terminates above in a cap nicely fitted to the underside of the indicator piston, while the lowér end rests on a pedestal standing on the platform of the balance. Any force applied to compress the spring is registered on the scale beam. The reading of the scale beam is that of the force acting on the face of the piston, which is usually some even fraction of a square inch in area, one-half in the ordinary indicator. The spring is made to deflect a certain distance by such a force, but its scale is set in terms of pressure per square inch. Thus, a fifty-pound spring is one which moves the indicator-pencil one inch to indicate THE ENGINE INDICATOR 599 a pressure of fifty pounds per square inch, but in an ordinary indi- cator with a piston having an area of one-half square inch this spring will cause a movement of one inch when an actual load of twenty-five pounds is applied to the face of the piston. It thus: follows that the reading of the platform scale would in this case have to be multiplied by two to give a value comparable with the indication of the spring. In general, the reading of the balance must be multiplied by the reciprocal of the area of the indicator- piston in square inches to obtain the load on the piston in pounds per square inch. Fic. 411. — SAMPLE INDICATOR-SPRING CALIBRATION D1acRaMs. The spring is calibrated by raising the pressure in even incre- .ments, generally such as will give pencil positions about a fifth of an inch apart, and rotating the indicator-drum when each desired value is reached, obtaining a line upon the paper on the drum in- dicating the pencil position for each pressure. After the highest desired pressure is reached the pressure is decreased by similar amounts, marks being made at each value as before. It will generally be found that the two marks obtained for the same pressure value do not correspond (see Fig. 411), those obtained when reducing the pressure being above those obtained when 600 EXPERIMENTAL ENGINEERING raising the pressure. This is due to friction and similar retard- ing forces. The average between every two corresponding lines is to be taken as the reading for that pressure. It is very impor- tant never to overrun a setting going up or down and then back up to it, as it is evident that the retarding forces will then be acting in the wrong direction. Another dead-weight tester, a modification of the platform-scale idea, has been lately brought out and patented by Mr. A. B. Calkins.* Fig. 412 shows that this apparatus consists essentially of a heavy vertical standard, S, supporting a compound lever system, L, L,, L,. The lower lever L, is so arranged that steel scales F may be inserted according to the scale of indicator-spring to be tested. Certain weights, G, are placed on the poise EZ, also according to the scale of the spring. The weight of the counterpoise H is constant. The apparatus is furnished with leveling screws K in the base and should be erected on a solid foundation and carefully leveled up. The indicator to be tested is attached to the connection J’. The piston J fits against the underside of the indicator-piston. The rod of piston J is so constructed that its length may be varied by turning the knurled heads JJ’. The lower end of the piston-rod rests against the lever L. The method of testing the indicator- spring is as follows: Insert proper scale F and place proper weights G on the poise £, as shown by a card of directions furnished. Place the vernier C on the zero of the scale F. Attach the indicator to J’ and adjust the length of the piston-rod so that J is just in contact with the indicator-piston. The proper balance of the apparatus will then be shown by the pointer B coinciding with the stationary hair line A. In this position draw the atmospheric line. Next run the poise — along the scale F to any desired position. This will put the apparatus out of balance and throw the pointer B to the left of the line A. Restore the balance by adjusting by means of I and J’. Draw a second line on the indicator-drum which will represent the pressure as indicated on the scale F. A series of lines at definite pressure intervals going up and down may thus be obtained, as in the apparatus previously described. * See Power for Aug. 10, 1909. THE ENGINE INDICATOR 6or _ t { ° 1 "0 [wT oes TIT TTP TTT TTT TTT TTT TTT TTT PTT AT LJ og te came ' 1 ' 2.4 tbo Fic. 412. — CALKINS INDICATOR-SpRING TESTING APPARATUS. 602, EXPERIMENTAL. ENGINEERING Neither of the above types of dead-weight apparatus is easily adapted for use with steam should it be desired to test springs hot. This can be done in the apparatus shown in Fig. 413, which is of German origin.* In the left-hand figure the indicator is shown loaded by dead weight as if under steam pressure, while the right- hand shows the method of attachment: and of loading for vacuum springs. Steam is admitted_for heating only, through -a lateral connection A (see plan view), the method of confining it being shown in the detail figure B. Fluid-pressure calibrating devices _nearly always employ steam to load the piston and deflect the spring... Water is not a suitable medium, because it is difficult to maintain any given pressure owing to leakage past the piston. To make the piston sufficiently tight to prevent this would introduce excessive friction and probably make the indicator useless. In general, some dead-weight or equivalent apparatus, as, for instance, a mercury column, is used for measuring the pressure exerted on the piston, because the determination of this pressure by means of a gauge would not give values accurate enough and would, moreover, give values depending upon the accuracy and the calibration of the gauge. A very accurate arrangement for laboratory use consists of a closed vessel into which steam can be introduced at various con- trolled pressures and to which can be attached the indicator and a long mercury column. By varying the pressure by convenient increments and determining the value of that pressure from the reading of the mercury column, very consistent and accurate’ results can be attained. The apparatus has the disadvantage that the mercury column must generally be, very long and unwieldy. A simple device is shown in Fig. 414, consisting of a cylinder, A, supported on a bracket above a pair of scales and fitted with a piston having an area of cross-section exactly the same.as the indicator-piston. A rod from this piston extends downward onto a platform scale, as shown in the figure. The indicator is con- nected by suitable piping to the upper end of the cylinder. The steam for the purpose of calibration is adjusted in pressure by a * Roser, Priifung der Indicatorfedern, Zeitschrift d. V. Di Then euiies 1902, P- 1575. . THE ENGINE INDICATOR _.. Spribgs fh ‘i Fic. 413. | Testing | |.Vacuum | ~ 603 604 EXPERIMENTAL ENGINEERING valve, E, before it enters the drum, B. The pressure of the steam in the drum is shown on the attached gauge. This steam pressure 1 exerts an upward pressure on the indicator-piston and a downward pressure on the piston in the cylinder, A, which latter, corrected for dead weight, is measured on the weighing-scales shown. A modification of this ap- paratus is shown in Fig. 415, which consists of a vessel, A, into which steam can be ad- mitted at any desired pressure. The pressure in the vessel acts on the piston, K, which is one-half square inch in area, and it may be measured by Fic. 414. —Inpicator-Sprinc Testinc the attached scale-beam. The APPARATUS. same pressure acts on the indicator-piston. By taking simultaneous readings of the pressure ZZ LN “ pak I M N > fe: Fi K CT u a” poly ®) D E E E Fic. 415.— INDICATOR-SPRING TESTING APPARATUS. on the piston, K, and on the indicator-piston, the calibration may be performed substantially as described. This apparatus has proved satisfactory after an extensive use. THE ENGINE INDICATOR 605 330. Comparison of Dead-Weight and Fluid-Pressure Methods of Calibration, and Hot vs. Cold Calibration.* The advantages of the dead-weight methods may be outlined as follows: (a) Comparatively low cost of apparatus. (b) Possibility of placing apparatus in any desirable place. (c) Easy and quick manipulation. Opposed to these are the following disadvantages: (a) The axis of the indicator-piston must be set accurately vertical. © (b) The rod transmitting the pressure must be centered accu- rately on the piston. If either of these items is neglected, eccentric load may introduce excessive piston friction. (c) It is in general not easy to control spring temperature, if the springs are to be tested hot. (d) The scale of the spring depends upon the accurate: determina- tion of the diameter of indicator-piston. Fluid-pressure calibration, unless compressed air is used, gener- ally means the employment of steam, that is, it is practically- hot calibration. The great advantage of this method is undoubtedly that the condition of the indicator, pistons and spring approximates more closely to the actual condition of use than if the spring were tested cold. One or two disadvantages of the method may, how- ever, be cited. The first is generally greater cost of apparatus, less quick and easy manipulation, and less choice of location of the apparatus. Further, the temperature which an indicator and its spring attains during use is generally an unknown quantity. It is probably certain that the spring and piston get hotter during calibration than they were during most tests, especially if the appa- ratus is not quick in its regulation of steam pressure. ‘Tests on spring temperatures have been made, but they do not fully agree, the results showing temperatures anywhere from 20 to 120 degrees less than the temperature of the steam. It should be pointed out here that the fit of the piston has 4 good deal to do with the tem- perature of spring and of spring chamber. It has been pointed out, however, that the error introduced by having the spring * For detailed information on these points, see the above mentioned article by Roser in the Zeitschrift. 606 EXPERIMENTAL ENGINEERING temperature not quite what it was on the test is generally so small that it comes within the error due to the other imperfec- tions, as, for instance, lost motion, inaccurate straight-line | motion of pencil, etc. As far as -present practice is concerned, American engineers still prefer hot calibration under fluid pressure, i.e., with the use of steam. German engineers, in the adoption of a‘code, under date of May s, 1906,* have gone on record in favor of dead weight. calibration. The provisions of this code are in brief as follows: 1. Every indicator whose spring -is to be calibrated should first be examined with reference to piston friction, fit of piston; and lost motion in the pencil mechanism. - ‘2. Springs are to be tested by dead-weight calibration. 3. Springs should be tested in the indicator to which they belong. 4. Every spring which during use attains temperatures higher than ordinary, should in general be tested both hot and cold, at room temperature and at about 212° F. 5. Springs should be tested at several pressure intervals, at least 5 above the atmosphere and at least 3 below the atmosphere. The report should show the detail results for each interval. 6. The diameter of the indicator piston should be determined at room temperature. With reference to paragraph 3, the code points out that to test the spring in the indicator to which it belongs is the best way to correct for inaccuracies in the pencil mechanism. While in use, indicators are subject to more or less jar, which serves to reduce the effects of piston friction, and it is consequently advocated to slightly jar the indicator when on the testing stand just before drawing the line for any given pressure interval. The second calibration advocated under paragraph 4 may be avoided by calibrating cold and then using a temperature correc- tion factor. For accurate work, however, this method can hardly be recommended because the factor is by no means a constant for all springs. ‘The formula that may be used for this computation is : Pr = Pu [r— af, — 4)] * See Zeitschrift des Vers Deutscher Ingénieure under that date. - 607 THE. ENGINE. INDICATOR. ze ‘uve | -umoq] “dq ‘ut “bs 4 eee “Ue | ‘umoq) ‘dq “ul ‘bs " “xorg | “soyouy ! “IOI “sayout ‘ . ! ‘UOjs!q-IOPeOIpUy uO “u0ysiq-107yto1puy uo “SayeUIpIC, ainssald [enjoy *Saqyeulpio, ainssaig [enjoy opesssres ss oar Busddg crc Butads fo aypag eC ON sutads rs Suds fo aqv9g soyvoypuy fo ayoyy Diet ee tee eee eee e eee eee se esse sss gam uostanguos Kg rc A01DILDUT fo ay yqim uostang mor Kg eee cece eee Ste eaRan nee map Aap Enema ‘Burad g-soponepuy fo uoyvaquog “ONTYUAANIONG IVLNAWIVAdXA AO LNAIWLUVdAd — “ADATION ATAIS 608 EXPERIMENTAL ENGINEERING Ps, = scale of spring at room temperature ¢,, scale of spring at some higher temperature ¢,, = I @ =a constant varying from .ooo1g to .00038, with an average of .00023. This equation clearly brings out the fact that heating the spring weakens it. The provision of paragraph 6 is based on the ground that the change of diameter of piston with temperature is not sufficient to appreciably affect the determination of the spring scale. 331. Determination of Scale of Spring and the Evaluation of Diagrams taken with Faulty Springs. —It is always desirable to test springs before they are used on important work. This gives opportunity for rejecting at the outset springs which show serious lack of proportionality. In most cases commercial springs can be had which show but little variation from their nominal scales, and in such cases it is sufficiently accurate to proceed as follows: From the data obtained (see preceding form for recording) a cali- bration curve may be constructed with the mean ordinates as determined from test as the ordinates of the curve and the true pressure readings as abscissas. Fig. 416 shows such a curve as constructed from actual test of a 100-pound spring used with a teduced piston (4 size) in the indicator and tested cold. To use this curve, determine the mean ordinate from each indicator-dia- gram taken on an engine test. The mean effective pressure cor- responding to this ordinate may then be read directly from the curve. The above method results in negligible errors only when the springs are not very far wrong, and above all, when they show satisfactory proportionality, as is the case with the spring for which the data is given in Fig. 416. When the latter is not the case and much depends upon the results of the tests, there are several methods that may be used to correct the results, all of which are, however, more or less laborious. THE ENGINE INDICATOR 609 To illustrate the procedure, take the data contained in the table, page 610, obtained on a calibration test of a nominally 100o-pound spring tested hot. og § Zz a z a oe a P og ow N 2 il wu a Bz g Fa 2 Aw ° 4 a a Q< 200 180 160 100 120 8140 True Pressure-Lbs. per Sq. In, 80 Fic. 416. — CALIBRATION CURVE FoR INDICATOR-SPRINGS. 60 40 20 7 = = @ 8 & @ © @ & & = = = SS 7 “MOWMBIQITeD Wo; SoYSUIPIO UBOPT This spring shows a decided lack of uniformity, as the scales computed for the individual pressure intervals clearly show. There is not much use in computing the mean spring scale, as is some- ‘times done, because in this case results varying from 97 to 107 610 EXPERIMENTAL ENGINEERING pounds per square inch will be obtained, depending upon the method used. Further, on account of the decided variations in the pencil travels for the same pressure increment, it would be difficult to draw a_just mean curve among all of the points. Height of Ordinate | Scale of Spring No. of True Pressure | Above Atmospheric _| for the Suecessive Reading in Ibs. per Line, Mean of Up Intervals. “ “| sq. in. = p. | and Down Readings _? a 6, rectus = ; s= h a “15 rat 8186. = 83.4 2 30 320 93-7 3 45. -465 96.7 4 60 .610 98.2 2 75 *77° 97-4 6 “90 -QI0 98.9 7 105 1.050 100.0 8 120 1.175 102.1 9 135 u2g15 : 102.6 Io 150 1.445 103.7 In such a case it is best to proceed as follows. Integrate the cards obtained on-a test and determine the mean effective pressure for each, assuming the spring correct,'l.e., 100 pounds to the inch of pencil travel. Then determine the mean M.E.P. of all the cards and pick. out the card nearest the mean. To this card apply the correction following. If the cards do not all’ show approximately the same size, but if they differ materially, divide them into classes of approximately the same area, and apply the correction method to the mean of each class. This will give in either case a correction factor by which the M.E.P. of each card, as determined on the assumption of a correct spring, can be recti- fied. The reason for choosing mean cards at all is because it would be too much labor to apply the method to each of a prob- ably large number of cards. : Suppose the diagram, Fig. 417, represents the mean diagram of a set. From the atmospheric line lay off vertically the successive pencil travels which correspond to equal pressure increments, as per table above. Next divide the diagram by lines parallel to the atmospheric line into a number of horizontal strips, as shown. THE ENGINE INDICATOR 611 For each strip determine the mean ordinate in the usual way by planimeter and find the M.E.P. corresponding by multiplying by the spring scale belonging to the particular pressure interval. ‘Thus, for the partial area III, for which the pressure interval is from 105 to 120 pounds, the scale of the spring is, from the table, equal to io2.1 pounds. Finally, tHe total mean ordinate of the diagram is he sum of the partial mean ordinates of the various strips, and his total mean ordinate divided by. the mean ordinate obtained on the assumption that the spring is correct, will give the correction factor to be applied to all of the other diagrams. Be, 417. — METHOD oF Finpinc Correct MEAN EFFECTIVE PRESSURE. Another method of correction is to completely redraw the mean diagram chosen from the lot and from this determine the proper average M.E.P. To redraw the diagram, extend atmospheric line (Fig. 418), to left, and along OA lay off the successive pencil travels from the table, p. 610. Along OB lay off the intervals on the assumption that the spring is a correct 100-pound spring. Determine the line OC. Then for any point on, the diagram whose ordinate is X, we can find, as shown,- the, corrected ordinate X,, which determines one point, D, on the redrawn diagrarh. This same operation must be repeated until a sufficient number of points have been found to locate a new diagram accurately. From this the correct mean M.E.P. is then found in the usual way. “os GBEe Gear” It should be pointed out with respect to both an the correction methods above explained, that the work must -be very: carefully 612 EXPERIMENTAL ENGINEERING done or else it is worse than useless. It would seem that the last method is open to greater objection on this score than the first. Fic. 418. — MrEtHop oF FINDING Correct MEAN EFFECTIVE PRESSURE. 332. Other Errors in Indicators and Methods of Determining Their Magnitude. —Inertia Effects Due to Piston and Pencil Motions. — In theory, the pressure exerted by the spring should at all in- stants balance the pressure exerted by the working fluid on the piston. In practice, this may or may not be the case, because of the inertia of the indicator-piston and of the pencil mechanism. a b v Fic. 419. Suppose that the pressure of the working medium has been con- stant for some little time and that it then steadily decreases accord- ing to the law of the line abc, Fig. 419. THE ENGINE INDICATOR 613 The pencil has followed the line ad, fluid pressure and spring force balancing. Now, however, the pencil refuses to follow bc, because a certain drop in pressure is necessary to overcome the piston inertia, even if we assume that the indicator is without friction. Hence the pencil.draws line 4 b’ until the pressure differ- ence is some value AP. ° The piston now commences to move downward, but, although at d the piston may drop as fast as the pressure, at that point the pressure difference is greater than AP, and hence the piston receives an acceleration downward. At e the forces apparently again balance, but owing to its momentum the Fic. 420. — Diacram SHowine Inertia EFFECTS. indicator-piston then overshoots the mark, repeating the same thing below the actual pressure line along efg. Friction. of the piston, not excessive but ordinary, modifies this action in that it acts as a dampener, and in most cases soon reduces the vibrations to zero. This action may often be observed in indicating a gas engine, because the range of pressure is high and the pressures rise and fall with great rapidity (see Fig. 420). A change to a stiffer spring is sometimes of benefit in toning down the amplitude of these vibra- tions, but unless these are excessive, their occurrence should rather be taken as a sign of a free working instrument. 614 EXPERIMENTAL ENGINEERING Effect of Excessive Friction or. Sticking of Piston, or-Siriking of the Pencil Mechanism. —The effects produced by some of these faults are in some cases very similar to inertia effects, and the two Fic. 421.— Diacram SHowine Excessive Priston FRICTION. may sometimes be confused. ‘Thus, the waves in the expansion line of the diagram in Fig. 421 were most likely due to sticking of Fic. 422. Errecr or Excessive PENCIL FRICTION. Normat Dracram 1s Furr Line. the indicator-piston rather than due to inertia, especially since there is no such effect noticeable at the beginning of admission at a. To help distinguish between the two effects, it may be said THE ENGINE INDICATOR ~ 615 that excessive friction or sticking of an indicator-piston sonietimes affects the compression as well as the expansion line, while inertia effects only rarely show in the compression line. Further, inertia effects should be nearly harmonic vibrations, and if the wavy lines are redrawn to abscissas representing equal intervals of time, the curve obtained should be of the nature of a.sine curve.* Effect of Excessive Pencil Friction. — Pressing the pencil too strongly against the paper gives a faulty diagram, the main effect being to make all events late, (see Fig, 422). Effect of Drum Striking the Stops. —This occurs usually at the inner stop, when the string is too long; too short a string may me | Fic. 423. — Errect-or DRuM STRIKING THE STOPS. simply pull in two. The effect is to cut a piece off the end of the card, as shown by the shaded areas in Figs. 423 and 424. In some cases this effect may be hardly noticeable and may escape observa- tion. It is best in every case, after an indicator has been applied and set in motion, to put one finger lightly on the top of the drum, when any striking of the drum will at once manifest itself by a distinct jar. : Test for Parallelism of the Pencil-movement with respect to the Axis of the Drum. — Parallelism between movement of pencil and axis of drum may be tested for by removing the spring from the indicator, rotating the drum, and drawing a horizontal line; then holding the. drum stationary in various positions press the piston * See article by Thomas Hall, Power, August, 1906. 616 EXPERIMENTAL ENGINEERING of the indicator upward throughout its full stroke, while the pencil is in contact with the paper. The lines thus drawn should be parallel to each other and perpendicular to the horizontal line. Tests of Drum-Motion and Adjustment of Drum-Spring. — The accuracy of the drum-motion depends on the form of the drum- spring, the mass moved, the length of the diagram, and the action of the connecting cord. Indicator-drums would revolve in a harmonic motion if the in- ertia of the mass could be neglected. The speed of rotation is X 2 ee Fic. 424. Errecr oF Drum STRIKING THE STOPS. greatest near the half-stroke of the piston; therefore, if the drum- spring tension can be adjusted so as to exactly counterbalance the effect of the inertia of the moving parts, the theoretical harmonic motion will be nearly realized. In most indicator drum-springs the tension increases directly in proportion to the extension. Since the speed of the drum is greatest at half-stroke, at this point the drum will run ahead of its theoretic motion if the spring tension is not sufficient to counteract the effect of the inertia of the moving parts. Therefore if the ten- sion of the drum-spring is adjusted to exactly balance the effect of inertia at half-stroke, the card should be as nearly as possible theoretically correct. To obtain the value of this tension is not a THE ENGINE INDICATOR 617 simple matter. It depends upon the speed of rotation, the mass of the rotary parts, the initial drum-spring tension, the weight and stretch of the connecting cord, and the friction of the mechanism. The initial spring tension must of course be such that on the return stroke the spring can accelerate the drum at least as fast as the engine piston returns. Otherwise the string will at some part of the travel become slack, which leads to non-permissible errors. Concerning the stretch of the cord, care should of course be taken either to use connections as short as possible, or to use a material, like very fine piano wire, which will not stretch. The objection to such materials in general is their excessive weight. If the length of the cord, or its quality with regard to stretch, is such that the error is not serious, and if the tension on the cord does not vary a great deal, it can further be shown that the action of the deformation existing is such as not to disturb the propor- tionality between the motion of the piston and that of the drum, except for the action of friction that may exist. Hence in many cases the effect of the error introduced by stretch of cord becomes negligible. It must be evident that a mathematical determination of proper drum-spring tension becomes practically useless on account of factors in the problem which are peculiar to each individual case. It is better, therefore, where it becomes necessary, to know something about the error introduced in the diagram by inertia of moving parts and by varying tension in the cord, to rely upon actual tests. The total error introduced by inertia can be determined as fol- lows: Attaching the indicator to an engine, permit it to run suffi- ciently long to harden the cord and the knots, then stop the engine, turn it over by hand, and find the length of the diagram with the speed so small as to eliminate the inertia; leaving the cords connected, run the engine at full speed: any inertia effect will be shown by an increase in the length of the diagram. This increase in length may be due partly to stretch in the indicator-cord caused by inertia of the rotating parts, and even with the best tension on the springs it may be sensibly lessened by the use of wire. A simple arrange- ment, consisting of a pin and connecting-rod leading to the face- plate of a lathe, the tool-rest being utilized as a guide, may be used 618 EXPERIMENTAL ENGINEERING instead of’an engine for obtaining complete determination of this error. The amount of error caused by over-travel of the drum has ae ; | | dq Tro rise in o fea if r= see : U oe - myo rth | | been found by experiment to be from o.5 to 1.5 per cent at 250 revolutions, with the best tension on the drum-spring. . To Indicator A To Indieato Fic. 425. — APPARATUS FOR TESTING DruM-SPRING TENSION. | __d . THE ENGINE INDICATOR ._.. 619 It is often important to~ determine whether the drum-spring maintains a uniform tension on the cord, or whether it alternately exerts a greater or less stress. This may be determined by the instrument shown in Fig. 425. The apparatus consists of a wooden plate, A, on one end of which is fastened the brass frame, BB, carrying the slide, C, with its crosshead, D. The head of the. spring, R, is screwed to the crosshead, while the other end is con- nected with the bent lever, G, carrying a pencil P. The connecting- rod, E, which moves the slide, C, receives its motion from a crank not shown in the figure. The swinging leaf F holds the paper on which the diagram is to be taken. The indicator to be tested is Indicator. 250 Revolutions Indicator. 250 Revolutions A B Indicator, 400 Revolutions Indicator. 400 Revolutions Cc D Fic. 426. — DiaAcRAMS SHOWING VARIATION IN DRUM-SPRING TENSION. clamped to one end of the plate A, and the drum-cord connected with the free end of the spring. The crank is made to move at the speed at which it is desired to test the drum-spring. The paper is then pressed up to the pencil and the diagram taken. i the tension on the cord is constant, the lines which represent the forward and return strokes will be parallel to the motion of the slide; but if the stress is not constant, the pencil will rise and fall as the stress is greater or less. The line drawn when the cord has been detached from the indicator (Fig. 426) is the line of no stress.. In the diagram, horizontal distance represents the position of the drum, and vertical distance represents strain on the cord. The perfect diagram would be two lines near together and parallel to the line of no®stress, and would represent a constant stress, and conse- quently a constant stretch of the cord. 620 EXPERIMENTAL ENGINEERING When the length of the cord and the amount it will stretch under varying stresses are known, the errors in the diagram due to stretch of cord caused by irregular stresses applied by the drum-spring can be calculated. 333. Method of Attaching the Indicator to the Cylinder. — Holes for the indicator are drilled in the clearance-spaces at the ends of the cylinders in such a position that they are not even par- tially choked by any motion of the piston. -These holes are fitted for connection to half-inch pipe: they are located in horizontal cylinders preferably at the top of the cylinder; but if the clear- ance-spaces are not sufficiently great they may be drilled in the heads of the cylinder, and connections to the indicators made by elbows. The holes for the indicator-cocks are usually drilled by the makers of the engine, but in case they have to be drilled great care must be exercised that no drill-chips get into the cylinder. This may be entirely prevented by blocking the piston and admit- ting twenty to thirty pounds of steam pressure to the cylinder. The connections for the indicator are to be made as short and direct as possible. Usually the indicator-cock can be screwed directly into the holes in the cylinder, and an indicator attached at each end. In case a single indicator is used to take diagrams from both ends of the cylinder, half-inch piping with as easy bends as possible is carried to a three-way cock, to which the indicator is attached. The cock is located as nearly as possible equidistant from the two ends of the cylinder. The form of the three-way cock is shown in Figs. 427 and 428 and the method of connecting in Fig. 442. In connecting piping for indicators, use lead or oil and graphite on the threads as sparingly as possible, as an excess of these mate- rials is likely to get into the indicator and prevent the free motion of the piston. ° For accurate work an indicator should be used at each end of a double-acting cylinder rather than the pipe connections and three- way cock described. Further, all connections must be of practi- cally uniform bore, as short as possible, and free from sharp bends. Indicators seem to work just as well in a horizontal as in a vertical position, so that it is sometimes advisable to place the indicator THE ENGINE INDICATOR 621 horizontally rather than to use an elbow or bend. Care must be taken to see that the connections used are sufficiently rigid to pre- vent oscillatory motions of the instrument under the action of the rapidly changing forces brought into play. Such motion would of course vary the relative position of the indicator and engine crosshead and would correspond to the use of a string of varying length. Errors of such magnitude as to cause an error of five per cent in the area of the diagram are easily introduced by improper con- nections, and tests have shown that by sharp bends, long pipes, SSSSSSSSSSSESSG Wan Kl SSSI F Fics. 427 & 428.— THREE-way Cock For InpIcatoR CONNECTIONS. and restrictions of bore, errors of as much as twenty per cent can be introduced. 334. Reducing-motions for Indicators. — The maximum motion of the indicator-drum is usually less than four inches; consequently it can seldom be connected directly to the crosshead or other re- ciprocating part of the engine, but must be connected to some apparatus which has a motion less in amplitude but corresponding exactly in all its phases to that of"the engine piston. This appa- ratus is termed a reducing-motion. Since the horizontal components of the indicator-diagram, and consequently its area and form, de- pend pon the motion of the piston, it is evident that the accuracy of the diagram depends upon the accuracy of the reducing-motion. Various combinations of levers and pulleys have been used for 622 EXPERIMENTAL ENGINEERING reducing-motions, a few of which will be described. Several simple forms of reducing-motion are given here as suggestions, but it is expected that the student will devise other motions if required, and ascertain the amount of error, if any, in the motion used. There are two main types of reducing-motions to be considered, — pendulums (including pantographs) and reducing wheels. In the case of pendulum reducing-motions, it is of special im- portance to see that the angle made by the cord as it passes over the indicator guide pulley at one end and as it leaves its point of ~ S--—- - 7 —--f----- ‘ 6 “Sal p@ a7 Py ‘\ 1 \ I \ | x | AN I \ | \ La | - I \ i in tt ee ee ne Le 5 \ A 1c B t Fic. 429. fastening at the reducing-motion at the other end, does not change its magnitude during the entire range of motion. Just what this means is perhaps best illustrated by a diagram, Fig. 420. Here A-B represents the line of travel of any reciprocating part of the engine which travels in tnison with the piston. To lead a cord directly from a pin D on the pendulum to the pulley C’ on the indicator would give an incorrect motion because the angle changes from D C’ C” at midstroke to D’ C’ C”’ at one end and to D’” C’ C” at the other end of the stroke. It must be obvious that the paper travels a much greater distance while the piston moves from C to. B THE ENGINE INDICATOR 623 than when it moves from A to C. The conditions are purposely exaggerated to. make this clear. To minimize the error in this construction the string should lead off in the direction D D’” and a guide pulley should: be placed somewhere along this line as far from D as possible. : . The correct remedy for the trouble outlined in Fig: 429 is to use a sector grooved on the edge, which must be fastened to the lever so as to have its center of. rotation at the lever pivot, and the arc must be of such length that at all times the cord will be tangential to the sector. Fig. 430 shows conventional sketches of pendulum motions with the sector in. three different positions. ° Sometimes, instead of FIG. 430. _ the sector a circular disk is used, which may “either be turned to any position and fastened with a lock nut, or which may be so made that the cord may be fastened at any one of a number of points around the circumference. Concerning the rest of the construction of pendulum motions, the lower end of the lever may be fastened to the operating pin by an intermediate link, as is indi¢dated in Fig. 431, or the lower end may be slotted, as shown in, Fig. 432. In the latter type the stand- ard supporting the lever- pivot must be mounted exactly over the middle of the travel of the pin working in‘the slot. The former type has the advantage in that it can be mounted to one side of the-centet of travel, and hence in the case of long- -stroke engines this: type allows the use of shorter cords. In this case, the follow- 624 EXPERIMENTAL ENGINEERING ing precautions should, however, be observed. The link 1’—1 (see Fig. 433) must be of such a length that the lever 1-6 hangs vertical S | fo Se @ 2 O = e@ {] ; O O si a Fic. 431.— PENDULUM ReEpucinG MoTION witH INTERMEDIATE LINK. when the piston is at the middle of the stroke. Further, the length of lever 1-6 should be such that, in connection with the length of LTA | Fic. 432.— PENDULUM REpUcING Motion wits SLoTTED Matn LEVER. link 1-1’, the travel on both sides of the line 1-6 shall be equal, that is, the distance 1-2 should equal distance 1-3. If this is not THE ENGINE INDICATOR 625 approximately observed, large errors may result. Thus, in case of too short a lever 1-6, the respective travels are 1-2” and 1’/-3”, which differ in length by the distance 3’-4’’, the former being the longer. Or, in case of too long a lever, 1’”’—6, the travels are 1/’”—2’” and 1/’-3’”, differing by the distances 4’”’-3’””, in this case the latter being the longer. Ne” 7 a rail 2s ™~ a“ Tine 4” 3 3” go SS ae ae ae 407 2 ie - - - Sseionmce aa ae ae 3 isc SS == aN a a ~ HOS CL 2 eee CF 1 ~. ' NN St b—e—_——_*s-Stroke————»—_ > a ' stro SN ~. ~ ~. “S. N A N N ™~. SS Re Sp "Dag — Fu Meseno ta tran Fic. 455. separate computation and the results averaged. This can be readily done for each engine by computing a table made up of the products of the average value of ” by length of stroke / and area of piston a, and for different values of M.E.P. Take from this table the values corresponding to the given M.E.P., and increase or diminish this as required by the per cent of change of speed from the average. A very convenient table for this purpose, entitled ‘‘ Horse Power per Pound Mean Pressure,” is given in the Appendix to this work, arranged with reference to diameter of cylinder in inches and piston-speed in feet per minute. Piston-speed in feet per min- ute is the product of length of stroke in feet by revolutions per minute = In. - 344. Form of the Indicator-diagram. — The form of the indicator- diagram has been carefully worked out for the ideal case by Rankine 648 EXPERIMENTAL ENGINEERING and Cotterell.* In the ideal case the steam works in a non-con- ducting cylinder, and all loss of heat is due to transformation into work, the expansion in such a case being adiabatic. In the actual case the problem is much more complicated, since a large portion of the heat is utilized in heating the cylinder, and is returned to the steam at or near the time of exhaust, doing little work. It is found, however, in the best engines working with quick-acting valve-gear, that the steam and back-pressure lines are straight and parallel to the atmospheric line, and that the expansion and compression lines are very nearly hyperbole, asymptotic to the clearance line and to the vacuum line. If we denote by p the pressure measured from the vacuum line, and by v the volume corresponding to a distance measured from the clearance line, so that pv shall be the codrdinates of any point, we shall have as characteristic of the hyperbola pv = constant. (x) This is the same as Boyle’s law for the expansion of non-con- densible gases, since, according to that law, the pressure varies inversely as the volume. Rankine found by examination of a great many actual cases that the expression pv! = constant agrees very nearly with the ideal. case of adiabatic (isentropic) expansion.| The variation from the ideal expansion line in any given case may be considerable, and the hyperbola drawn from the same origin is considered as good a reference line as any that can conveniently be used. The student should therefore become familiar with the best methods of con- structing it. 345. Methods of Drawing an Hyperbola.— The methods of drawing an hyperbola, the clearance and vacuum lines being given, are as follows: First Method. (See Fig. 456.) — CB, the clearance line, and CD, the vacuum line, being given, draw a line parallel to the atmospheric line through B; find by producing expansion line the point of cut- * Steam Engine, by James H. Cotterell. } For more detailed information see under “ Adiabatic (Isentropic) Change for Steam ” in Chapter XI. THE INDICATOR-DIAGRAM 649 off, c. Draw a series of radiating lines from the point C to the points EZ, F,G, H, and A, taken at random, and a line cb inter- secting these lines, drawn from c parallel to BC. From the points of the intersection of cb with these radiating lines draw horizontal lines to meet vertical] lines drawn from the points FE, F, G, H, and A; the intersections of these lines at e, f, g, #, and a are points in the hyperbola passing through the point c. If it is desired to pro- duce the hyperbola from a.upward, the same method is used, but B c 3 F 3 H A > Fic. 456. —Mrtuop or Drawinc HypersBo.ta. the line AB is drawn through the point a, and the vertical lines are extended above AB instead of below. Second Method. (See Fig. 457.) — The hyperbola may be drawn by a method founded on the principle that the intercepts made by a straight line intersecting an hyperbola and its asymptotes are equal. Thus if abcd represents an hyperbola, BC and CD its asymptotes, then the intercepts aa’ and 6b’ made by the straight line a’b’ are equal. To draw the hyperbola: Beginning at any point, as a, draw the straight line a’b’, and lay off from the line CD, b’b equal to a’a; then will 6 be one point on the hyperbola. Draw a similar line c’d’ 650 EXPERIMENTAL ENGINEERING through b, making d’c equal c’b; then will c be another point on the hyperbola. This process can be repeated until a suitable number of points is found; the hyperbola is to be drawn through these points. A similar method can be used to draw the hyperbola EF. Fic. 457. —MetHop oF DRAWING HYPERBOLA. 346. Construction of Saturation and Isentropic* Curves for Steam. — The Saturation Curve is the curve which results if the specific volumes of dry and saturated steam are plotted against correspond- ing absolute pressures. No doubt the easiest way to construct such a curve is to take the volumes from the steam-tables corresponding to given pressures and set them off along the volume axis; lay off the corresponding pressures as ordinates; then a curve drawn through the extremities of the ordinates will be the saturation curve, which does not differ greatly from an hyperbola. It has been stated that the saturation curve for steam follows the general law, prt = pv! — constant. (2) As a matter of fact, this exponent changes with the pressure range as computations by means of a steam-table will show. The curve obtained by the use of m = 1.064 is, however, probably close enough to the real curve to serve all practical purposes. * This curve is in general practice called an adiabatic curve. See note, p. 344. THE INDICATOR-DIAGRAM 651 The equation of the isentropic curve for saturated steam (see equation (59), p. 346) is, for all qualities between .7 and 1.0, goers = constant. (3) For initially dry and saturated steam (% = 1.0) this reduces to » pol = constant. (4) s 8 8 8 ra y — Abs. Press. Lbs. per sq. inch 6 8s & np o 2 6 jo 12 14 16 18) (20 (22 Volume, Cubic Ft. Fic. 458. The exponent of the equilateral hyperbola is m =1, and this curve, together with the saturation curve and the isentropic curve for ini- tially dry steam, is plotted in Fig. 458 to show the mutual relation. AB is the hyperbola, AC the saturation curve, and AD the isen- tropic line. It is to be noticed that the saturation curve corresponds to a uni- form quality of steam, the isentropic curve to a condition in which the moisture is increasing, and the hyperbolic curve to a condition in which the moisture is decreasing. "652 EXPERIMENTAL ENGINEERING 347. Clearance Determined from the Diagram. — The clearance is usually to be determined by actual measurement of the volume of the spaces not swept through by the piston, and comparing this result with the volume of piston-displacement. Since the expan- sion and compression lines of the diagram are nearly hyperbole, the position of clearance line can be determined by a method nearly the reverse of that used in constructing an hyperbola (Article 345). In this case proceed as follows: Lay off the vacuum line CD (Fig. 459) parallel to the atmospheric line FT, and at a distance B Ke | fl i corresponding to the atmospheric pressure. The position of the clearance line can be determined by two methods, corresponding to those used in drawing the hyperbola. First method: Take two points, a and 0 in the expansion curve and ¢ and d in the compression line, and draw horizontal and vertical lines through these points, forming rectangles aa’bb’ and cc'dd’. Draw the diagonal of either rectangle, as a’b’, to meet the vacuum line CD; the point of inter- section C will be a point in the clearance line CB, and the clearance will equal CN + FT. Second method: Draw a straight line through either curve, as mn through the compression curve or ef through the expansion curve, and extend it in both directions. On the line THE INDICATOR-DIAGRAM 653 m'n’ lay off nn’ equal to mm’, or on the line e’f’ lay off ee’ equal to ff’; then will either of the points e’ or n’ be in the clearance line, and the line drawn perpendicular to the vacuum line through one of these points should pass through the other. In an engine working with much compression the clearance will be given more accurately from the compression curve than from the expansion curve, since it is more nearly an hyperbola. 348. Weight of Steam Accounted for by the Indicator-diagram. The Diagram Water-rate. — The diagram shows by direct measure- ment the pressure and volume at any point in the stroke of the piston; the weight of steam per cubic foot for any given pressure may be taken directly from a steam-table. The method, then, of finding the weight of steam for any point in the stroke is to find the volume in cubic feet, including the clearance and piston-displace- ment to the given point, which must be taken at cut-off or later, and multiply this by the weight per cubic foot corresponding to the pressure at the given point as measured on the diagram. This will give the weight of steam in the cylinder accounted for by the indicator-diagram, per stroke. In an engine working with com- pression, the weight of steam filling the clearance-space is not ex- hausted; this weight, computed for a volume equal to clearance and with weight per cubic foot corresponding to compression pressure, should be subtracted from the above. The result may be reduced to pounds of steam per I.H.P. per hour, by multiplying by the number of strokes made per hour and dividing by the I.H.P. de- veloped. It should be noted in this computation that the steam caught in clearance is assumed dry at the end of compression. An alternative method, often used for computing the weight of steam caught in clearance, is to assume the steam dry at the point of exhaust closure and to determine the weight from the cylinder volume up to that point and from the back pressure. The method of computing would then be: Find, from a steam- table, the weight of steam per cubic foot corresponding to the absolute pressure at the given point, multiply this by the corre- sponding volume in cubic feet, including clearance, and this by the number of strokes per hour. Correct this for the steam imprisoned in the clearance-space. Divide this by the horse power developed 654 EXPERIMENTAL ENGINEERING and we shall have the consumption in pounds of dry steam per I.H.P. as shown by the diagram. Thus let A = area of piston in square feet; a= “c ce e ce ce inches; N = number of strokes per hour; n= « 73 6c 6c minute: 2 w = weight of cubic foot of steam for the pressure at the point under consideration; ‘ = weight of cubic foot of steam for the pressure at end of compression; : 1 = total length of stroke in feet; 1, = length of stroke in feet to point under consideration; ¢ = per cent of clearance; l’ =1, + cl = equivalent length of stroke to point under con- sideration (including clearance) ; J I if Tr Then the total volume up to the point under consideration will be = (, + cd)A =IA cu. ft., and the corresponding weight of dry steam is /’Aw pounds. The volume of steam caught in the clearance space is clA cu. ft., and its weight will be clAw’ pounds. Hence the net weight of steam supplied, as shown by the indicator, will be (’'Aw — clAw’) pounds per stroke. From this it follows that the steam consumption from the diagram in pounds per I.H.P. hour, or the diagram water-rate, is cae LEP. 6 = [!’Aw — clAw"] pounds v = walt w— cw’ | pounds =THP. (bw — cw’) pounds a 1 (bw —-o#’) oe lan Pounds 33,000 _ 13,750 (bw — cw" = 131 “ 2 amnall (5) THE INDICATOR-DIAGRAM 655 Example. — Compute the steam consumption as shown at £ and at release point F, in the diagram of Fig. 453. The absolute pressures shown by the diagram are as follows: At cut-off, 97 pounds; at release, 37 pounds; at end of compression, 60 pounds. The mean effective pressure, p= 50 pounds; length of stroke, J = 3 feet; distance up to cut-off, J, = .75 foot; distance up to release, J, = 2.78 feet. Per cent of clearance, c = 3.2 per cent; ’ =1,+ cl = .754+ .032 X 3 = .845 - foot at cut-off, and 2.78 + .032 X 3 = 2.876 feet at release. Hence d = = 45 3 2.876 = .282 at cut-off, and= = .958 at release. w at cut-off = .2193 pound per cubic foot; at release = .o886 pound per cubic foot, and w’ at end of compression = .1394 pound per cubic foot. Steam consumption at cut-off: 5 = 131750 (.282 X .2193 — .032 X .1304) 50 15.78 lbs. per I.H.P. hr. Steam consumption at release: S = 131750 (.958 X .0886 — .032 X .1394) 50 = 22.10 lbs. per .H.P. hr. This, it should be noticed, is not the actual weight of steam used per horse power by the engine, but is that part which corresponds to the amount of dry steam remaining in the cylinder at the points under consideration. The amount is usually less when computed at cut-off than at the end of the stroke, since some of the steam which was condensed when the steam first entered the cylinder is restored by re-evaporation during the latter portion of the period of expansion. 349. The Diagram Water-rate for Multicylinder Engines. — The equations of the previous article apply only to simple engines. To compute the diagram water-rate for a compound or triple engine, proceed in exactly the same way for any given point on the expan- sion line of the cards from any of the cylinders, but after determining the steam accounted for per stroke, multiply by the number of strokes made per hour and divide bythe sum of the horse powers of all the cylinders. This gives tlfe-steam credit for all the work it either has already done since entering the high-pressure cylinder or will do before leaving the low-pressure. This computation is equivalent to substituting for p in equation (5) what is known as the “ equivalent mean effective pressure.” Thus, if the computation is being made 656 EXPERIMENTAL ENGINEERING for the H.P. cylinder of a compound engine, the quantities above the line in equation (5) are chosen from the high-pressure card, while the Equiv. M.E.P: = p’ + rp” where p = M.E-P. of H.-P. card, p” = M.ELP. of L.P. card, and Vol. L.P. Piston-Displacement Vol. H.P. Piston-Displacement r =ratio Similarly, if the computation is being made for the low-pressure card, the Equiv. M.E.P. = . apg 350. Approximate Formulas for the Diagram Water-rate. — If we put J, = /, and further neglect alJl considerations of clearance, the final form of equation (5) would be S= 13,7505) ; (6) in which p = the M.E.P. of the diagram, and w the weight of steam per cubic foot corresponding to terminal pressure. Several authori- ties have computed tables for this equation as follows: Thompson’s tables (see Appendix) give values of 13,750 w, and the tabular values must be divided by the M.E.P. to give the steam-consumption per I.H.P. per hour. Tabor’s tables give values of 43:75°, and the tabular values must be multiplied by the weight of a pound of steam corresponding to the terminal pressure, to give the steam-consumption. Williams’s tables, published in the Crosby catalogue, give values (2 425-43 32.32 w to give the steam-consumption. A graphical correction may in all cases be made for the steam caught in clearance by drawing a horizontal line through the ter- minal pressure to compression line of diagram, and multiplying the result computed from the table by the ratio between the portion of » and the results in each case have to be multiplied by THE INDICATOR-DIAGRAM 657 of this line intercepted between the terminal point and the com- pression line, to the whole stroke. 351. Re-evaporation and Cylinder Condensation. — By con- sidering the hyperbolic curve as a standard, an idea can be obtained of the restoration by re-evaporation and the loss by cylinder con- densation. Thus in Fig. 457, suppose that a is the point of cut-off at boiler-pressure. Construct an hyperbola as explained; in the example considered it is seen to lie above the expansion line for a short distance after cut-off, then to cross the line at 0, and remain below it nearly to the end of the stroke. The amount by which the expansion line rises above the hyperbola may be considered as due to re-evaporation. The area of the diagram lying above would represent the work added by heat returned to the steam from the cylinder walls. The methods for determining the cylinder condensation are simi- lar to this process, except that the hyperbola is usually drawn up- ward from the point correspond- ing to the terminal pressure, to meet a horizontal line drawn to represent the boiler-pressure, as shown by the dotted lines in the diagrams in Fig. 460. The area | of the figure enclosed by the dotted lines, compared with that Fic. 460. of the diagram, is the ratio that the ideal diagram bears to the real; the difference is the loss by cylinder condensation. The student should understand that both these methods are approximations which may vary much from the truth. 352. Various Forms of Actual Indicator-diagrams. — The form of the indicator-card often reveals certain defects in steam distribu- tion, due in most cases to improper valve setting. As a matter of fact, the main purpose of applying an indicator to an engine is in many cases merely to discover such defects in order to be able to eliminate them. A great variety of causes will affect the lines of the diagram and typical examples might be multiplied indefinitely. In many cases the cause of certain defects is easily located; in other 658 EXPERIMENTAL ENGINEERING cases, several causes may be at work and a certain amount of skill and experience may be necessary to interpret correctly. If a card shows unusual features, the causes for them may be sought for in at least three directions: (a) faulty working of the indi- cator and faulty indicator connections, (6) errors in the setting of the valves, and (c) effects due to bad steam connections, leaky valves and pistons, etc. (a) Errors Due to Indicator and Faulty Indicator Connections.— Some of these have already been discussed in the previous chapter under reducing motion, pencil motion, indicator pipe con- nections, etc. (See Chap. XV, Art. 332.) Wavy lines in the expansion line, Fig. 461, may indicate spring vibration due to inertia effects or due to water in the piston and connections. The latter is the more likely cause, unless inertia effects also appear in other parts of the diagram. The effect of faulty indicator connections usually manifests itself by throttling; see Fig. 462, where the broken line shows the Fic. 461. — D1acram SHowINnG EFFECTS OF Water IN INDICATOR CONNECTIONS. a Fic. 462.— DiaGram RESULTING FRoM FAULTY AnpicaTor CONNECTIONS. normal diagram and the full line one which may result from too small or too long connections. The net result of this may be to make the diagram larger in area than it should be. (0) Errors Due to Valve Setting. — Probably the great majority of unusual conditions in the lines of steam-engine cards is due to THE INDICATOR-DIAGRAM 659 lela a : b , Lead too Great, Admission too Early. Lead too Small, Admission too Late. d Not Enough Compression. e f Late Admission of Steam. Admission of Live Steam after Cut-off, Leaky Valves. h § Same as (f). May Occur in Valve Too Early Release. Gears with Riding Cut-off. Fic. 463. (a to h.) 660 EXPERIMENTAL ENGINEERING Too Late Release. Loop Diagram due to Light Loads on Automatic Cut-off Engines. k Drop in Compression Line, most likely due to Leaky Pistons and Valves. Held in some cases to be due to condensation. Fic. 463. (7 to k.) incorrect valve setting. There are many different valve gears, each likely to have its own peculiarities, but it will suffice to point out a few of the more usual abnormal conditions that may occur. In some of the following cases, Fig. 463, a to k, what may be con- sidered the normal diagram is shown in dotted line, the actual diagram in full line. (c) Effects Due to Bad Steam Connections, Leaky Valves and Pistons. — Steam connections which are too small produce excessive wire drawing, (see Fig. 464). A somewhat similar effect is produced in the use of valves which open and close too slowly. Some of the effects of leaky pistons and valves have already been shown (Fig. 463, f and k). Ifa diagram shows an expansion line Boiler Pressure Ss | Wire Drawing Loss Mol Fic. 464. THE INDICATOR-DIAGRAM 661 lying markedly below the hyperbola, Fig. 465, the effect may be due to serious leakage, steam leaking from the working to the exhaust side. If this loss is very serious it also appears in the compres- sion line. 353. The Combining of Dia- grams from Multicylinder En- gines.— The methods used will be shown for the case of the compound engine, from which it is easy to generalize for triple or Fic. 465. — Diacram SHow1ne Erect or . 5 SERIOUS PisTON AND VALVE LEAKAGE. quadruple expansion engines. There are two methods in use for combining indicator-cards. In the one the diagrams are each offset from the line of zero volumes in the combined diagram by a distance corresponding to the clear- ance volumes in the respective cylinders. In general, conditions will be such that the amount of steam expanding in the cylinder (which is in all cases equal to the sum of the weights of the steam taken into the engine per stroke plus the weight of steam caught in clearance) will not be the same in the two cylinders on account of the fact that the weight of clearance steam is not generally the same in the two cylinders. Hence it will not be possible to start with the H.P. cylinder and draw a single saturation curve for both cylinders, but such a curve must be drawn for each cylinder sepa- rately. The second method of drawing the combined card is to eliminate the clearance steam and to set off from the line of zero volumes only the volumes of the steam taken into the engine per stroke. The method of doing this will be explained more fully later. In this construction a single saturation curve (or, for approximate work, an hyperbola) may be drawn for both cylinders, and some idea may thus be gained of how nearly the ideal work area represented under the saturation curve is realized by the actual area shown by the cards. But no quality computations can be made on such a diagram, and, for general usefulness, construction according to the method first outlined is generally preferred. Where the steam distribution in the two ends of the cylinder is fairly equal, it is EXPERIMENTAL ENGINEERING 662 usually satisfactory to average the two cards from the head and crank ends of the cylinder and to draw the combined diagrams ‘INIONY SSITHOD ,9f Ad ,9I Ad ,6 V WOMd SauVD TovaTAY —"99P ‘OLA ee _ oury av ourT TV A x 09 08 2S eee 1 MvaIg “19 Joy aang soe at ¢or7 Shoes +00T 3 0¢T 1 ---| OFL 1 “sy ‘Sq'T from the average cards only. Where this cannot be done, it may be necessary to draw combined cards for the head and crank ends separately. THE INDICATOR-DIAGRAM 663 Figure 466 represents a set of cards taken from a cross-compound Corliss engine whose dimensions are as follows: Dia. Ay Pr Cyl. soca aatiaenimaseannage Se page ees eS 9 ins. Dias LP C ye iin sg okies wae tAWicd Anes akan me take 16 ins. Length of stroke.) e..c ps csucdes kes awycuuyeeiebaes 36 ins. Dia, piston: tod, HP; Gyles oog see carder ceanewar pas 21% ins. Dia. piston rod, H.P. cyl... 2. eee 2ié ins. Piston displacement, average: Head end and crank end, H.P. cyl............... 1.28 cu. ft. Piston displacement, average: Head end and crank end, L.P. cyl................ 4.15 cu. ft. Average clearance, H.P. cyl., per cent............... 7.59 Average clearance vol., H.P. cyl................0005 .096 cu. ft. Average clearance, L.P. cyl., per cent................ 8.93 Average clearance vol., L.P. cyl...............0.... .372 cu. ft. Scale of indicator-spring, H.P. cyl.................. 80 lbs. Scale of indicator-spring, L.P. cyl................... 20 lbs. Barometer, 28.75 in. Hg = ...............0..000. 1s Iq. lbs. CONSTRUCTION OF COMBINED Carp, METHop I.—In Fig. 467 lay off on the X-axis a scale of volumes, and on the Y-axis a scale of absolute pressures as shown. Draw in the atmospheric line. Divide the length of each indicator-card, or the average card, into any convenient number of equal parts, say ten, and erect per- pendiculars at the points of division, prolonging them downward until they reach the line of zero pressures in each case. In Fig. 467 lay off first the L.P. clearance volume (.372 cubic foot) and the volume of the L.P. cylinder (4.15 cubic feet), making a total of 4.522 cubic feet; divide the distance corresponding to 4.15 cubic feet also into ten equal parts, and erect ordinates. From the average L.P. card, Fig. 466, determine the pressure existing at the points of intersection of the ordinates for both forward and back pressure lines, measured above the line of zero pressure and using the proper spring scale. Lay in these pressures along the ordinates of Fig. 467, connect the points determined, and the result will be the L.P. diagram transferred to the new volume and pressure scales chosen. Next, from the line of zero volume, Fig. 467, lay off the clearance volume of the H.P. cylinder (.096 cubic foot) and then the volume 664 EXPERIMENTAL ENGINEERING be 1.0 15 2.0 2.5 3.0 3.5 4.0 45 Volume, Cb. Ft. Fic. 467. —ComBINED DIAGRAM FOR CoMPOUND STEAM ENGINE. . THE INDICATOR-DIAGRAM 665 of the H.P. cylinder (1.28 cubic feet), making a total volume of 1.376 cubic feet; divide the distance corresponding to 1.28 cubic feet into ten equal parts and erect ordinates. Then proceed to determine the pressures from the average H.P. card, Fig. 466, measured above the line of zero pressure as a line of reference, and transfer these pressures to the ordinates of Fig. 467, as in the case of the L.P. card. Connecting the points will give the H.P. card. If in any given case the lines of the original diagrams show more irregular variations than the sample cards chosen, it may be neces- sary to determine a greater number of pressure points by dividing the card lengths into a greater number of parts. The Saturation Curves.— The next operation i to draw in the saturation curves. The steam taken into the engine per stroke for the test and the cards under consideration was .103 pound, as computed from water consumption and number of strokes. The weight of steam caught in the clearance spaces may be com- puted from the pressure either at the beginning or end of the com- pression line, the corresponding volumes in the cylinder, and the specific volumes corresponding to the pressures, on the assumption that the steam is dry and saturated. There is some uncertainty regarding the quality of the steam along the compression line. Most authori- ties agree to call it dry and saturated at the beginning of compres- sion. Hence the steam caught in clearance will in this case be found as follows for the H.P. cylinder: Average absolute pressure at beginning of compression.. 21.82 Ibs. Beginning of compression, per cent of back stroke...... 88.3 Piston displacement during comp. = (1.00 — .883) 1.28 = -15 cu. ft. Clearance volume... 0.2.0... .096 cu. ft. Total volume remaining at beginning of compression... . . 246 cu. ft. Sp. vol. per pound of steam at 21.82 Ibs. (fromsteam-table) 18.52 cu. ft. Weight of steam caught in clearance = =. ee .o13 lb. The total weight of steam in the H.P. cylinder at the beginning of expansion is therefore = .103 + .o13 = .116 pound. The satura- tion curve can now be determined by finding the volume that this weight of steam, assuming it to remain dry, will occupy at different pressures, as shown in Article 346. For example, at 100 pounds 666 EXPERIMENTAL ENGINEERING absolute pressure, the specific volume of steam is 4.429 cubic feet; hence .116 pound of steam will occupy a volume of .514 cubic foot. This determines one point, marked A, on the saturation curve, Fig. 467. The computations for the saturation curve for the L.P. cylinder are exactly similar. The engine steam per stroke is the same as before, = .103 pound. The weight of steam caught in the clearance is, however, in the L.P. cylinder only .oo6 pound as compared with .o13 pound in the H.P. cylinder. The total weight of steam ex- panding is therefore = .109g pound. For this weight the volumes occupied at a series of different pressures are then found from the steam-table as before. The Quality Curves. — The location of the saturation curve with reference to the expansion line shows the quality of the steam as the expansion progresses. In the case of the example in hand, the satu- ration curve for the H.P. cylinder lies entirely outside of the diagram and shows that the steam is wet throughout expansion. Since, at any given absolute pressure, the volume up to the expansion line shows the volume occupied by the steam in the mixture of steam and water contained in the cylinder, while the volume up to the saturation curve shows the volume that the weight of wet steam in the cylinder would have if it were just dry, it follows that the ratio of the total volume (including clearance) up to the expansion line to the total volume up to the saturation curve is a measure of the quality of the steam at the pressure chosen. Thus at the point of release in the H.P. cylinder, the pressure is 30.02 pounds and the volume is 1.325 cubic feet. At the same pressure, the saturation curve indicates a volume of 1.55 cubic feet. The quality at release a = 85.5 per cent. To get this result it is not at is therefore all necessary to determine these volumes; the ratio of the actual distances to the points on the two curves, measured say in hun- dredths of an inch, will give the same result. Making this computation for a number of points along the expansion line allows of the construction of a quality curve showing the vari- ation of quality continuously. In this example this curve shows that the quality was 72 per cent at cut-off and increased grad- THE INDICATOR-DIAGRAM 667 ually to 85 per cent at release, indicating a considerable amount of re-evaporation. In the case of the L.P. diagram, the saturation curve lies entirely within the diagram, showing that the steam was superheated along the entire expansion line, due to the action of steam jackets which were not in use on the H.P. cylinder. The quality of the steam (i.e., the degree of superheat) can now no longer be determined by the simple ratio of volumes, because this relation no longer holds. The relation that may be used to find the temperature of the steam is the Tumlirz equation (Article 184): T v = 85.85 — — .256 5 a6 where v = specific volume of superheated steam in cubic feet, T = absolute temperature, p = absolute pressure in pounds per square foot. To apply this to one point on the expansion line of the L.P. cylinder, take the volume at 17.5 pounds pressure. This equals 2.51 cubic feet for .109 pound of steam, so that the specific volume 2.51 : =~ = 23. feet. v 966 23.03 cubic feet Therefore T 23.03 = OOO as Soa = .256, from which T = 685° F. abs. = 225° F. The steam-table shows that the critical temperature for 17.5 pounds is 220°. In this case the steam is therefore superheated only 5 degrees. This amount of superheat is practically negligible and is of course subject to the error of the measurements taken from the combined diagram and to the error of the Tumlirz equation which in itself is + .8 per cent. It is therefore accurate enough to conclude in this case that the steam is dry and saturated along the expansion line, and therefore no quality curve for the L.P. cylinder need be drawn. In case superheat is shown to a greater extent, a quality curve with volumes as abscisse and degrees of superheat as ordinates can be con- structed similar to the quality curve for the H.P. cylinder. 668 EXPERIMENTAL ENGINEERING CONSTRUCTION OF COMBINED Carb, MeErtuop II.— The first step in the process is to draw through the points of exhaust closure on each card a saturation curve for the weight of steam caught in the clearance. Then divide each diagram, that is an average for the H.P. cylinder and an average for the L.P. cylinder, into any convenient number of equally spaced horizontal strips, starting in each case from the line of zero pressures. Next on cross-section paper lay off scales of volumes and of pressures as for Method I. Lay in the atmospheric line and divide the field into as many horizontal strips as there are on the original diagrams, drawing the horizontal dividing lines at the proper pressure intervals by taking into account the scales of the springs. In Fig. 466 the H.P. head end card shows the saturation curve drawn in for the clearance steam and also the method of horizontal subdivision. The next step is to determine the volumes along any horizontal line such as AB, Fig. 466, and to transfer them to the combined card. To do this by computation is rather cumber- some. Thus in the actual diagram, the length AC was .12 inch and the length AD was .g2 inch. Since the actual full length of the card was 3.91 inches (which represented 1.28 cubic feet cylinder volume), the corresponding cylinder volumes are for AC .o4 cubic foot and for AD .30 cubic foot. The line AB repre- sents a pressure of 100 pounds absolute in this case. To transfer volumes AC and AD to the combined diagram, Fig. 468, lay off along the roo pound pressure line the volumes .o4 and .30 cubic foot, which determines the location of points C and D respectively, the clearance steam being eliminated. To apply this method of computation to a number of pressure intervals, as would be necessary to obtain sufficient points to con- struct the diagram, is, as stated, very cumbersome, and for that reason a graphical method, given by Professor Heck, is preferable. In Fig. 469, lay off MN equal to the actual length of the H.P. diagram. Make WO equal to the actual distance on the combined diagram corresponding to 1.28 cubic feet (the volume of the H.P. cylinder). Draw OM. Then if we take any abcissa, as AD in the case of the H.P. head end card, Fig. 466, and transfer this to Fig. 469 (distance MN’), then will the distance N’N” give the THE INDICATOR-DIAGRAM 669 0 5 1.0 15 2.0 2.5 3.0 35 £0 4.5 Cyl. Vol. Cb. ft. Fic. 468. — METHOD oF CoMBINING INDICATOR CARDS, ELIMINATING CLEARANCE STEAM. 670 EXPERIMENTAL ENGINEERING proper distance to be set off on the combined card for the volume AD. A similar construction figure may be drawn for the L.P. cylinder; in that case MW will repre- sent the actual length of the L.P. card and NO the distance on the combined chart corresponding to 4.15 cubic feet, the volume of the L.P. cylinder. The final result of the construction of the combined card is shown in Fig. 468. To complete the diagram, draw in the saturation curve EF; in this case with a weight of steam equal to .103 pound, the engine steam. In case the combined diagram ac- cording to Method I has already been drawn, the work of obtaining the diagram according to Method II is very much simplified, as it is merely necessary to draw in on the first combined card the saturation curves for the compression lines, starting with the point of exhaust closure (see curve RS in the L.P. card, Fig. 467), and then to set off from the line of zero volumes in Fig. 468 the volumes as measured from these saturation curves considered as lines of zero volume. 354. The Actual Entropy Diagram for a Steam Engine. — This diagram is sometimes used in the study of heat interchanges in the cylinder. It is, however, of doubtful utility for this purpose because we have definite information about the condition of the steam only along the expansion line. For every other line of the P-V diagram certain assumptions are ordinarily made which, de- pending upon conditions, may or may not be seriously wrong, and we obtain corresponding lines in the T-¢ field subject to errors of the same uncertain magnitude. In effect, the usual method of transferring a diagram from the P—V to the T-@ field consists in determining the quality of the steam from a number of points around the P-V diagram, on the assumption: (a) That the total weight of steam (engine + clearance) re- mains the same throughout the cycle, and (0) that the quality of N Oo N’ Fic. 469. THE INDICATOR-DIAGRAM 671 this weight of steam for any point may be found by comparing the volume which it does actually occupy with that which it should occupy at the same pressure if it were dry and saturated In other words, all condensing and evaporation processes are assumed to take place in the cylinder. Quality, pressure, or tem- perature are all that is required to determine entropy, and the transfer is thus very simple. But condition (a) only holds for the expansion line and is not true for all the other lines of the P-V diagram, although the assumptions made give lines in the T-¢ field which show the heat changes with fair approximation, except for the compression line, for which the real conditions are certainly far different from those assumed. Whenever assumption (a) is incorrect it of course affects assumption (8) in like manner. The principle upon which the J-¢ diagram in general rests has already been explained in Article 183. The method of transferring an actual card will be illustrated in connection with Fig. 470. This represents a diagram taken from a single-cylinder throttling engine. The data required are as follows: Diameter of cylinder..................000...0.0.00.... 6 ins. DETOK Eau scect canada nmuantdaht sh make ee Hee tae ae 8 ins. Clearance, average...... 0.6 ce ccc cece cence 12 per cent Revolutions per minute...................000000.. 186 ScaleOf SPHip so cugsew even ceedes is Hap ee ella ct sewers 40 lbs. Pressure, absolute, steam pipe...................... 129 lbs. Pressure, absolute, steam chest..................... 85 lbs. BETOMC LR oct sco, pga ceremseivan eats He Sp RAG Ge hence Waa 5 14.5 lbs. Quality of steam, steam chest. ..............0.0 98.8 per cent Steam used per hour, from test................200-. 351 lbs. Length ofcard).4.;0aadannesceepig 4¢4aylates eaaes 3.41 ins, Derived quantities: Cylinder volume.......0.0000 000 ccc cece eee eee .131 Cu. ft. Clearance volume.......0.0.. 0000 ccc cece eee e cess .o16 cu. ft. LGtal VOLUME 3 sired» ossorgadiaeeg eee Gorgs aes Whee 2 .147 cu. ft. Weight of engine steam per stroke................ 0157 lb. Weight of clearance steam per stroke .......... 0020 |b. Total weight per stroke (engine + clearance)...... .0177 lb. The preliminary work consists in laying in the zero pressure line in Fig. 470 and dividing the card into horizontal strips at definite pressure intervals with zero pressure as the reference line. The EXPERIMENTAL ENGINEERING 672 intersections of the horizontal lines with the lines of the diagram Where the changes of volume and pressure are rapid, as around the toe of the card, give a number of definite points of reference. “ANIONY ONITLLOYH], UAANITAD-TIONIS V Woe WVAOVIG — ‘olb ‘olq | —— “sa'n9 Ter" aerial oury “TT intermediate reference points may be chosen. In this particular This In such cases case there are twenty such reference points (see Fig. 470). card shows inertia waves in the admission line. it is common to draw in the average pressure line as shown. THE INDICATOR-DIAGRAM 673 Next construct a table (see below) with the columns headed as shown. Columns 1 and 2 are self-explanatory; the data for 3, 5, 8, and ro are read directly from the steam-table. Column 4 is obtained by measurement from the indicator-card. For point 5, for example, the distance from the line of zero volumes is 2.64 inches. The total length of the card itself is 3.41 inches, which equals .131 cubic foot. Hence volume to point 5 = ve X .131 = .t015 cubic foot. Column 6 is obtained by dividing the volumes in column 4 by .0177, the total weight of steam, the result being the volume that this mixture of steam and water would occupy per pound. Column 7, the dryness fraction, is obtained by dividing column 6 by column 5. The method of finding column g is obvious, while column 11 is the sum of columns g and ro. I 2 3 4 5 6 7 8 9 Io Ir z a ~ z By lb pes ; ey a a Ql a I | 80 | 312 | .o160] 5.47 -QI -167 |r.1665| .1912] .4535 644 2 70 303 | .0575! 6.20 3-25 -524 |1.1896; .6280) .4411] 1.069 3 | 62 295 | .0853] 6.95 4.77 -688 |1.2104] .8320] .4302] 1.262 4 | 60 203 | .0877| 7.17 4.95 -690 |1.2160] .8370] .4272] 1.264 5 50 281 | .r0rs} 8.51 5-73 -675 {1.2468} .8410] .4113] 1.252 6 40 267 | .1323/10.49 7.48 -713 |1.2841] .9170] .3920] 1.309 7 38 264 | .1420/1I.01 8.05 +730 |1.2950] .9470] .3877| 1.335 8 | 30 250 | .1460/13.74 | 8.24 -600 |1.3311| .7960} .3680] 1.164 9 25 240 | .1470|16.30 8.31 +510 |1.3604} .6930] .3532| 1.046 10 20 228 | .1470/20.08 8.31 -413 |1.3965} .5780] .3355| .913 Ir 18 222 | .1300/22.16 35 +331 |I.4127| .4690]} .3273] .796 I2 16.5 218 | .0890/24.00 5.03 .209 |1.4261| .2980] .3208] .618 13 16.5 218 | .0470|24.00 2.76 .IT5 |1.4261] .1640] .3208] .484 14 |} 20 228 | .0418/20.08 2.36 -II7 |1.3965| .1640] .3355] .499 15 30 250 | .0271|13.74 1.53 -II2 |1.3311] .1480) .3680) .516 16 40 267 | .o182|10.49 £205 .098 |r.2841} .1255| .3920] .517 17 46 276 | .o160} 9.18 -QF -099 |1.2607) .1247| .4040] .531 18 50 281 | .o160) 8.51 -OI -107 |/1.2468) .1334] .4113] .544 Ig | 60 293 | .o160) 7.17 -OI -127 |I.2160| .1548] .4272] .582 20 70 303 | .o160| 6.20 -Qr -147 |1.1896) .1745] .4411] .615 The last step consists in plotting the results in columns 3 and. 11 (see Fig. 471). Choose any convenient scale for ¢ and ¢. The water 674 EXPERIMENTAL ENGINEERING line AB and the steam line CD are drawn directly by aid of steam- table data. Plotting the values in columns 3 and 11 gives the closed diagram shown, in which the points are marked with their proper reference number. This makes it easy to identify the lines with those on the P-V diagram. 1 2 8 4 5 6 8 9 10 11 12 13 14 15 16 L7 18 19 2.0 Entropy Fic. 471. — Entropy DiaGRAM FOR CARD SHOWN IN Fic. 470. To get some idea of the use of such a diagram, plot next what may be considered the theoretical (Rankine) diagram, assuming that the steam reaches cut-off under steam-chest conditions, that it then expands adiabatically to the end of the stroke, that next we have constant-volume exhaust to back pressure, and finally constant- pressure exhaust to the end of the stroke without compression. This diagram is marked I-IJ-III-IV-V on the P-V card, Fig. 470. The steam-chest pressure is 85 pounds, the quality 98.8 per cent, so THE INDICATOR-DIAGRAM 675 that .or77 pound of this steam would locate the point IJ. These conditions in the steam chest also determine ¢ = 316 degrees and total entropy = 1.1561 X .988 + .4590 = 1.602, by means of which point IT on the entropy diagram, Fig. 471, may be fixed. The rest of the theoretical diagram on the entropy chart is drawn by the method already explained for the real card. In the real engine the steam in the steam chest, whose condition is defined by the point I, Fig. 471, due to wire drawing or passing through the valves and to initial condensation, changes its condition until at cut-off it is defined by point 3. The exact location of the line along which this change takes place is uncertain because of the lack of necessary data. It must be obvious from this and from the statements made above, that the exact itemizing of the heat losses and heat interchanges is hardly possible by means of such a diagram. Generally the interpretation is as follows: The loss represented by the area 1-3-3’-1’, Fig. 471, is attributed to wire drawing. The shape of the expansion line shows that heat is lost to the cylinder walls from 3 to 5, and that re-evaporation takes place from -5 to7. The areas below 3-5 and 5-7 to the ¢-axis (zero of absolute temperature) represent the amounts of the respective heat inter- changes. The area 3/-II-II’-3” represents the loss due to initial con- densation. The loss due to early release is shown by the area 7—10-12—7’ for the real card and IIJ-IV-II’ for the Rankine diagram. The line 13-14 . . . . 20-1 shows a gain of entropy from the begin- ning, but no dependence should be placed in what this line seems to indicate on account of the arbitrary assumption made in obtain- ing it. 355- Steam-chest and Steam-pipe Diagrams. — These diagrams are sometimes taken in order to determine the pressure variations in steam chests and pipes. They are occasionally useful in bringing out wire drawing and other losses that may be due to insufficient pipe capacity. The method of taking them is exactly the same as for the cylinder diagram. Fig. 472 shows a steam-pipe and Fig. 473 a steam-chest diagram taken directly above the cylinder diagram 676 EXPERIMENTAL ENGINEERING from a 30 inch X 60 inch Bass Corliss engine.* Concerning the last diagram, Barrus makes the point that since the wire-drawing loss in the cylinder card is accompanied by about the same loss of => Fic. 472. — STEAM-PreE D1acRAM IN CONNECTION WITH INDICATOR CARD. pressure in the chest, the trouble is not due to the valve but to some cause between the steam chest and the boiler. The steam- pipe diagram would indicate that the pipe is too small, although as a matter of fact the loss of pressure is not at all excessive. SS ee Fic. 473. —StEAM-CuEest DiacRAm IN CONNECTION wiTH INDICATOR CARD. 356. Displaced Diagrams and Time Diagrams. — The ordinary diagram is drawn with an harmonic motion, the speed being a * Reproduced from Barrus, The Star Improved Indicator. THE INDICATOR-DIAGRAM 677 maximum near the middle of the stroke, while near each end the speed is much less and is zero at the end of the stroke. This in a sense disguises the pressure variations occurring at the ends of the stroke. For certain purposes of study (explosion actions in gas engines, valve gear actions in steam engines, etc.), the pressure variations at the ends of the card are of the greatest importance, and in this connection displaced or distorted diagrams and time diagrams are of service. Atmos. Line Suction Fic. 474. — DispLacep D1acRAM FROM A GAS ENGINE. In the case of displaced diagrams, the reducing motion is simply so constructed as to lag behind or lead the engine crank by a certain definite angle. If, for instance, the angle is made go degrees in the case of the gas engine, the diagram obtained will be somewhat of the shape of Fig. 474. The pressure variations during compression and explosions may from such a diagram be studied with much greater accuracy than from the regular type. m oO Pu | = Z Fic. 475. — CRANK SHAFT DIAGRAM FROM A STEAM ENGINE. The motion for an indicator may of course be taken from any moving part of the engine and occasionally crank-shaft diagrams, Fig. 475, are taken for the purpose of studying valve gear action. In such a case the distances moved by the drum are made proportional to the travel of the crank-pin, not to that of the piston. In the figure, line AB is the exhaust, BC compression, CDE admission, and EA expansion. Marks FF indicate the travel for one stroke (180 degrees). 678 EXPERIMENTAL ENGINEERING In the time diagram, the oscillating motion of the drum is replaced by continuous uniform motion, by means of special apparatus (chronograph). For a gas engine a time diagram would look as indicated in Fig. 476. Fic. 476.— Time Diacram From A Gas ENGINE. It need hardly be mentioned that none of the displaced or time diagrams can be used for the determination of power without trans- position. II. Gas-ENGINE D1AGRAMS 357. Theoretical and Normal Diagrams. — The lines of the theoretical gas-engine diagrams and the efficiency formulas for these diagrams have already been discussed in Art. 185, Chap. XI. In that connection only the lines of the actual power diagram were considered. In practice, however, normal diagrams show also suction and exhaust lines, at least in the case of 4-cycle engines, while in 2-cycle engines there must always be a“‘pump” diagram sep- arate from the power cylinder card. The suction and exhaust lines of a 4-cycle diagram also enclose an area, known as the lower-loop diagram, and this diagram, or the pump diagram of the 2-cycle engine, represents the work required for scavenging and charging the power cylinder. The term “ fluid ” friction is sometimes used to designate the work so expended. It is of course not available for useful purposes, lowers the brake horse power developed, and is in that sense a loss. In the normal 4-cycle gas-engine diagram, either from a constant- volume (Otto) engine or from a constant-pressure (Diesel) engine, the lower-loop diagram is not sufficiently clear to allow of integra- tion for the purpose of determining the fluid friction loss, on account of the stiffness of indicator spring necessary to obtain the rest of the THE INDICATOR-DIAGRAM 679 diagram. See Figs. 477 and 478. The former of these is from a 6- H.P. Hornsby-Akroyd oil engine, the latter from a 114 inch X 18 inch Struthers-Wells natural-gas engine. The latter diagram shows the loop well. As might be expected, the Diesel engine card, Fig. Fic. 477. Normat Diacram, 4-CycLE O1t ENGINE. 479, shows no indication of a lower loop on account of the extremely stiff spring that had to be used to stand the maximum pressure (over 500 pounds per square inch). To determine accurately the horse power lost in fluid friction, it becomes necessary to take lower-loop diagrams. This is done by Fic. 478. —Normat DiAcGRAM, 4-CYCLE GAS ENGINE. using a weak spring and putting a “ stop” on the piston-rod of the indicator piston, to prevent wrecking the spring. A good example of this kind of diagram, taken from a 7 inch X 9 inch Fairbanks gasoline engine, is shown in Fig. 480. The arrows show which way the lines. were traced and the lines themselves are marked. 680 EXPERIMENTAL ENGINEERING Abnormal features may occur in gas-engine diagrams due to a variety of causes whose number is probably even greater than in the case of steam-engine cards. What has been said under steam- engine diagrams concerning the faults due to indicator, reducing motion and connections, applies with generally equal force also to Fic. 479. —Normat Diacram, DieseL ENGINE. gas-engine diagrams. Besides faulty valve timing, which is analo- gous to wrong valve setting in the steam engine, we have in the case of the gas engine also chances of error in wrong spark-timing, bad proportion of mixture, non-uniformity of mixture, etc. What can be accomplished by proper or improper control of mixture and —> Suction Fic. 480.— Lower Loop Diacrau, FArRBANKS GASOLENE ENGINE. spark is well shown in the series of cards, Fig. 481, a to f, which were taken from a 7 inch X 9 inch Fairbanks gasoline engine. Figs. 482, a, b, and c were taken from a 6-H.P. Hornsby-Akroyd oil engine. This engine ignites by compression, so that there is no spark control. The most valuable aid to determine whether the valves are of proper size, or whether the valve timing is right, is the lower-loop diagram. Fig. 480 in this connection shows a normal lower loop. Figs. 483, a, b, and c were obtained from a Hornsby-Akroyd engine. Compare the magnitude of the loss in 6 and c with that ina. A THE INDICATOR-DIAGRAM 681 a. Mixture normal. Spark normal. Mixture lean. Spark changed from what would be normal for normal mixture ms in order a, b, ¢, d. to advanced position. Diagra: c normal for normal mixture. Mixture changed normal to rich. Spark Cards in order a, 4, ¢. Fic. 481. (a to c.) 682 EXPERIMENTAL ENGINEERING d. Mixture changed normal to lean. Spark normal for normal mixture. Cards in order a, 0, c. é. Mixture normal. Spark too far advanced. Card a, normal spark. Card 6, advanced spark. fs Mixture normal. Spark too late. Card a, normal spark. Card 5, retarded spark. Fic. 481. (d to f.) THE INDICATOR-DIAGRAM 683 a. Normal Card. b. Air Supply gradually throttled. Cards in order a, 8, c. Oil Supply normal. C. Case of Pre-ignition. Compression too high. Fic. 482. (a, 6, ¢.) 684 EXPERIMENTAL ENGINEERING good example of the complexity of the actions that may take place during exhaust and suction with high speeds is shown in Fig. 484. COR ‘D, xa ee — > Suction a. Valve Setting about normal. —_—S b. Admission Valve opens too late. — C. Exhaust Valve closes too early. Fic. 483. (a, b, c.) Inertia effects are shown on most of the cards in the series, Figs. 481, ato f. An extreme case of this is shown in Fig. 485. This Fic. 484. points directly to a bad choice of spring (generally too weak), although there is some controversy among authorities as to whether THE INDICATOR-DIAGRAM 685 some indications of this kind are not due to a series of explosion waves correctly recorded by the indicator. Fic. 485.— ExTREME CASE OF INERTIA EFFECT. A typical 2-cycle diagram from the power cylinder is shown in Fig. 486. The exhaust port or valve opens at ¢ and the pressure drops very quickly to nearly atmosphere. The new charge then Lbs. per 0” 355 WO ¢G b Fic. 486. — Type oF 2-cyCLE DIAGRAM. Atm. Qe enters, charging is complete by the time 0 is reached, when the exhaust and inlet valves close and compression begins. For further details see Chapter XXI on gas engines. 358. The Actual Entropy Diagram for a Gas or a Mixture of Gases. — The entropy diagram for a gas engine is even more approximate than that for a steam engine, because in the present state of our knowledge we do not possess the means for a definite computation of heat quantities around the cycle. This is due to 686 EXPERIMENTAL ENGINEERING the fact that, although the laws of variation of the specific heats C, and C, with temperature are now fairly well known for the lower temperatures occurring in a gas engine cycle, considerable uncertainty still exists for temperatures over 2000° F. (See Chap. XXI.) The problem is further complicated by the complex actions along the combustion line, which, according to recent re- searches, make it probable that during this period the quantities of heat existing cannot be computed in the ordinary way by aid of values of C, and C, determined by experiments on mixtures of the same composition and corresponding temperatures, but unac- companied by the energy (chemical) interchanges that occur along the combustion line. It is usual, in present practice, to avoid all these difficulties by computing C, and C, for the mixture as it enters the cylinder, and then to assume that these remain constant throughout the cycle. An improvement upon this method is to analyze the exhaust gases (or to compute the analysis approxi- mately from the ratio of fuel to air used) and to compute C, and C, for the burned gases as well as for the fresh mixture from the specific heats of the component gases. Either method is an ap- proximation only. Further approximations result from the fact that in the 4-cycle engine diagram the lower loop is generally neglected, and, in the case of the Diesel engine, the charge weight is not constant. The simplest method™ of transferring a P-V diagram for a gas engine to the T—@ field is the following. To take a concrete case, Fig. 487 represents a card from a 7-H.P. 4-cycle illuminating gas engine. This is the actual card transferred to cross-section paper because this transfer makes all measurements of pressure and volume direct. The lower loop (shaded area) is neglected. * Draw a line g-a to close the diagram. From the engine test obtain the following data: (a) Clearance and stroke volumes (.28 and .46 cubic foot). (b) The ratio of air to fuel (13.8 by weight). * For a more elaborate method, see Carpenter & Diederichs Internal Combustion Engines, Chapter V. + This card shows very low compression and explosion pressures, but will serve the purpose of showing the method of transfer as well as any other. THE INDICATOR-DIAGRAM 687 (c) The temperature at point a. If this is not known, it will have to be assumed. (739 degrees abs.). (d) The values of C, and C, for the mixture at point a. These are assumed constant for the entire cycle (C, = .265, C= i): YI | 1 N Abs{Pr,#/0” 280 t 1 °F Abs. 260 3370— i ; \ 2404 4 i \ ' \ 220! 2850 45+ \ \ 1 2005 = ! \ \ \ V4 1805 2335 x ‘ VN , vf 160} 2 x x I | I vo\ 6) 140; 1815-8 APN ! Novy 120} \ a | VINE NOS I ‘ \ \ \ \Q 100 | 129542» N a . je el Se I \ \ . 4 > 80; 4 \ \y ~\ N I any Sy ral 5 al Pe ss Sol Ne | So SS | ‘I we “RO Pees SS | ‘ s ~ ~~ Sad 40! Be Oh, [Pa eg |e ~ ee, Pes | = t ~IN eel otc 20\— Sabon! pe a g I! Cia Ve Oboe cIMs lente J = = x 08 16 24 82 40 48 56 64 «72 Cyl. Vol. Cb. Ft. Fic. 487. Draw in the line of zero pressure OX and the line of zero volume OY. At any convenient volume division, V,, draw a vertical. MN. 688 EXPERIMENTAL ENGINEERING Through the point a, for which the temperature is known, draw an isothermal line (PV = const., with OX and OY as axes) to cut the line MN in point 1. Choose any other number of convenient pressure intervals along the line WN, as 2, 3, 4, etc., and through them draw isothermal lines. Each one of these cut the card in two points. Thus the isothermal drawn through the point 6 (260 pounds) cuts the card in 6’ and 6”. Temperatures along the line MN can be computed (since tem- : ? oo. ee he Pe be perature at point 1 is known) from the relation Tt Be Fr etc. (Note that all temperatures are absolute). This at once determines the temperatures for a number of points around the card, for Ts = Ty = To. To draw the entropy diagram for one pound of the mixture choose convenient scales of T and ¢, see Fig. 488. The general equation for a change of entropy in gases is = Ts = Vo. be ?1 =e C, log. Ti, + cae Cy) log. V1 The line MN is a constant-volume line, hence Z ‘= 1, and the 1 second term of the right hand member in the above equation is o. Also, if we assume arbitrarily that the entropy for 32 degrees is zero, the equation for any point, as 6, on the line MN becomes os = C, log... 492 Compute a sufficient number of values for other points from this equation to locate the line MN, Fig. 488. Next compute the entropy for a number of points on the diagram. To explain the method, take point 6’ as an example. For the change from 6 to 6’, the first term of the general equation __ above becomes 0, since T; = Ty, and the equation becomes i bmia Vien V. Lay off the entropies thus computed from the line MN. Com- pute for sufficient points to locate the diagram, Fig. 488. The THE INDICATOR-DIAGRAM 228 82 34 86) 688 640 42d Entropy Fic. 488. — Entropy Diacram ror Gas ENGINE. 46 48 689 690 EXPERIMENTAL ENGINEERING resulting diagram is abcd, the points marked being those indicated by the same letters in Fig. 487. To interpret this diagram it will be necessary to draw in the ideal Otto cycle diagram for the heat content of a pound of the mixture used, see Fig. 254, p. 349. This is indicated in Fig. 488 by the area ab‘c'd’a. Then the various areas may be taken .to represent the following heat quantities: Area 1’ b ¢ 3’ 1’ heat received along combustion line. Area 3’ ¢ f 5’ 3’ heat received during expansion. Area 4’ df 5’ 4’ heat lost to cylinder walls during expansion. Area 2’ ada’ 2’ heat lost in exhaust. Area 2’ a b 1’ 2’ heat lost in compression. Area 4’ d fcc’ d’ 6’ 4’ heat lost in radiation and conduction (jacket loss, etc.). The last loss is very approximate only, since the assumption of constant specific heats affects this loss area very largely. CHAPTER XVII. THE TESTING OF STEAM BOILERS. 359. Methods of Testing Steam Boilers. — In 1884 the American Society of Mechanical Engineers adopted a code for the testing of steam boilers which was published in Vol. VI of the Transactions. This code was revised in 1899, the full text, together with a number of appendices, being published in Vol. XXI. The Code is repro- duced in full in the following pages. In the forty-one appendices attached to the Code in the Transactions the various members of the code committee express their views on certain provisions in greater detail, offer more detailed suggestions concerning certain operations, discuss instruments, apparatus, etc. To quote all of this material in full would occupy too much space, especially since many of the subjects mentioned have already been discussed in other parts of this book. But many of the remaining suggestions are valuable and to the point, and for that reason it is thought best to abstract these and to offer them as a sort of comment on the rules of the Code. The Code has now been established some ten years. In that time there has been obtained more accurate information regard- ing some subjects, as, for instance, the heat content of steam. Further, the practice of many testing engineers differs somewhat, although in no important detail, from some of the rules. It was thought best, therefore, in commenting upon the rules, also to take into account these developments and varying view- points. Whenever a rule has been thus annotated, the page reference to the note is given in every case. The notes themselves give chapter or page reference if the subject matter of the rule to which the note refers is treated in other parts of this book. 691 692 EXPERIMENTAL ENGINEERING RULES FOR CONDUCTING BOILER TRIALS. CoDE oF 1899. I. Determine at the outset the specific object of the proposed trial, whether it be to ascertain the capacity of the boiler, its efficiency as a steam generator, its efficiency and its defects under usual working conditions, the economy of some particular kind of fuel, or the effect of changes of design, proportion, or operation; and prepare for the trial accordingly (see note, p. 710). II. Examine the boiler, both outside and inside; ascertain the dimensions of grates, heating surfaces, and all important parts; and make a full record, describing the same, and illustrating special features by sketches. The area of heating surface is to be computed from the surfaces of shells, tubes, furnaces, and fire-boxes in contact with the fire or hot gases. The outside diameter of water-tubes and the inside diameter of fire-tubes are to be used in the computa- tion. All surfaces below the mean water level which have water on one side and products of combustion on the other are to be considered as water-heating surface, and all surfaces above the mean water level which have steam on one side and products of combustion on the other are to be considered as super- heating surface (see note, p. 710). III. Notice the general condition of the boiler and its equipment, and record such facts in relation thereto as bear upon the objects in view. If the object of the trial is to ascertain the maximum economy or capacity of the boiler as a steam generator, the boiler and all its appurtenances should be put in first-class condition. Clean the heating surface inside and outside, reniove clinkers from the grates and from the sides of the furnace. Remove all dust, soot, and ashes from the chambers, smoke connections, and flues. Close air leaks in the masonry and poorly fitted cleaning doors. See that the damper will open wide and close tight. Test for air leaks by firing a few shovels of smoky fuel and immediately closing the damper, observing the escape of smoke through the crevices, or by passing the flame of a candle over cracks in the brickwork. : IV. Determine the character of the coal to be used. For tests of the efficiency or capacity of the boiler for comparison with other boilers the coal should, if possible, be of some kind which is commercially regarded as a standard. For New England and that portion of the country east of the Allegheny Mountains, good anthracite egg coal, containing not over 10 per cent of ash, and semi- bituminous Clearfield (Pa.), Cumberland (Md.), and Pocahontas (Va.) coals are thus regarded. West of the Allegheny Mountains, Pocahontas (Va.) and New River (W. Va.) semi-bituminous, and Youghiogheny or Pittsburg bitu- minous coals are recognized as standards.* There is no special grade of coal * These coals are selected because they are about the only coals which possess the essentials of excellence of quality, adaptability to various kinds of furnaces, grates, boilers, and methods of firing, and wide distribution and general accessibility in the markets. See various appendices in Vol. XXI, Transactions A. S. M. E. THE TESTING OF STEAM BOILERS 693 mined in the Western States which is widely recognized as of superior quality or considered as a standard coal for boiler testing. Big Muddy lump, and Illinois coal mined in Jackson County, IIl., is suggested as being of sufficiently high grade to answer these requirements in districts where it is more con- veniently obtainable than the other coals mentioned above. For tests made to determine the performance of a boiler with a particular kind of coal, such as may be specified in a contract for the sale of a boiler, the coal used should not be higher in ash and in moisture than that specified, since increase in ash and moisture above a stated amount is apt to cause a falling off of both capacity and economy in greater proportion than the proportion of such increase (see note, p. 711). V. Establish the correctness of all apparatus used in the test for weighing and measuring. These are: 1. Scales for weighing coal, ashes, and water. 2. Tanks, or water meters, for measuring water. Water meters, as a rule, should only be used as a check on other measurements. For accurate work, the water should be weighed or measured in a tank. (See Chapter XII.) 3. Thermometers and pyrometers for taking temperatures of air, steam, feed-water, waste gases, etc. (Chapter VII.) 4. Pressure-gauges, draught-gauges, etc. (Chapter VI.) The kind and location of the various pieces of testing apparatus must be left to the judgment of the person conducting the test; always keeping in mind the main object, i.e., to obtain authentic data. (See note, p. 711.) VI. See that the boiler is thoroughly heated before the trial to its usual working temperature. If the boiler is new and of a form provided with a brick setting, it should be in regular use at least a week before the trial, so as to dry and heat the walls. If it has been laid off and has become cold, it should be worked before the trial until the walls are well heated. VII. The boiler and connections should be proved to be free from leaks before beginning a test, and all water connections, including blow and extra feed pipes, should be disconnected, stopped with blank flanges, or bled through special openings beyond the valves, except the particular pipe through which water is to be fed to the boiler during the trial. During the test the blow-off and feed pipes should remain exposed to view. (See note, p. 711.) If an injector is used, it should receive steam directly through a felted pipe from the boiler being tested.* * In feeding a boiler undergoing test with an injector taking steam from another boiler, or from the main steam pipe from several boilers, the evaporative results may be modified by a difference in the quality of the steam from such soutte compared with that supplied by the boiler being tested, and in some cases the connection to the injector may act as a drip for the main steam pipe. If it is known that the steam from the main pipe is of the same pressure and quality as that furnished by the boiler undergoing the test, the steam may be taken from such main pipe. 604. EXPERIMENTAL ENGINEERING If the water is metered after it passes the injector, its temperature should be taken at the point where it leaves the injector. If the quantity is deter- mined before it goes to the injector the temperature should be determined on the suction side of the injector, and if no change of temperature occurs, other than that due to the injector, the temperature thus determined is properly that of the feed-water. When the temperature changes between the injector and the boiler, as by the use of a heater or by radiation, the temperature at which the water enters and leaves the injector and that at which it enters the boiler should all be taken. In that case the weight to be used is that of the water leaving the injector, computed from the heat units if not directly measured, and the temperature, that of the water entering the boiler. Let w = weight of water entering the injector. Si “ steam 7 - * Jy = heat units per pound of water entering injector. hy = cc iT ce “ce “c steam “et ce hye “eo “ «© water leaving ey Then, w + # = weight of water leaving injector. hs — In a Oi =e Bi, See that the steam main is so arranged that water of condensation cannot run back into the boiler. VIII. Duration of the Test. — For tests made to ascertain either the maxi- mum economy or the maximum capacity of a boiler, irrespective of the par- ticular class of service for which it is regularly used, the duration should be at least ro hours of continuous running. If the rate of combustion exceeds 25 pounds of coal per square foot of grate surface per hour, it may be stopped when a total of 250 pounds of coal has been burned per square foot of grate. In cases where the service requires continuous running for the whole 24 hours of the day, with shifts of firemen a number of times during that period, it is well to continue the test for at least 24 hours. When it is desired to ascertain the performance under the working conditions of practical running, whether the boiler be regularly in use 24 hours a day or only a certain number of hours out of each 24, the fires being banked the balance of the time, the duration should not be less than 24 hours. IX. Starting and Stopping a Test. — The conditions of the boiler and furnace in all respects should be, as nearly as possible, the same at the end as at the beginning of the test. The steam pressure should be the same; the water level the same; the fire upon the grates should be the same in quantity and condition; and the walls, flues, etc., should be of the same temperature. Two methods of obtaining the desired equality of conditions of the fire may be used, viz.: those which were called in the Code of 1885 ‘* the standard method ” and “ the THE TESTING OF STEAM BOILERS 695 alternate method,” the latter being employed where it is inconvenient to make use of the standard method.* (See note, p. 713.) X. Standard Method of Starting and Stopping a Test. — Steam being raised to the working pressure, remove rapidly all the fire from the grate, close the damper, clean the ash pit, and as quickly as possible start a new fire with weighed wood and coal, noting the time and the water levelt while the water is in a quiescent state, just before lighting the fire. At the end of the test remove the whole fire, which has been burned low, clean the grates and ash pit, and note the water level when the water is in a quiescent state. and record the time of hauling the fire. The water level should be as nearly as possible the same as at the beginning of the test. If it is not the same, a correction should be made by computation, and not by operating the pump after the test is completed. XI. Alternate Method of Starting and Stopping a Test. — The boiler being thoroughly heated by a preliminary run, the fires are to be burned low and well cleaned. Note the amount of coal left on the grate as nearly as it can be estimated; note the pressure of steam and the water leve!. Note the time, and record it as the starting time. Fresh coal which has been weighed should now be fired. The ash pits should be thoroughly cleaned at once after starting. Before the end of the test the fires should be burned low, just as before the start, and the fires cleaned in such a manner as to leave a bed of coal on the grates of the same depth, and in the same condition, as at the start. When this stage is reached, note the time and record it as the stopping time. The water level and steam pressures should previously be brought as nearly as possible to the same point as at the start. If the water level is not the sam€as at the start, a correction should be made by computation, and not by operating the pump after the test is completed. XII. Uniformity of Conditions. —In all trials made to ascertain maximum economy or capacity, the conditions should be maintained uniformly constant. Arrangements should be made to dispose of the steam so that the rate of evaporation may be kept the same from beginning to end. This may be accom- plished in a single boiler by carrying the steam through a waste steam pipe, the discharge from which can be regulated as desired. In a battery of boilers, in which only one is tested, the draft may be regulated on the remaining boilers, leaving the test boiler to work under a constant rate of production. * The Committee concludes that it is best to retain the designations “ stand- ard” and “ alternate,” since they have become widely known and established in the minds of engineers and in the reprints of the Code of 1885. Many engineers prefer the “ alternate ” ‘to the “ standard ”’ method on account of it being less liable to error due to cooling of the boiler at the beginning and end of a test. { The gauge-glass should not be blown out within an hour before the water level is taken at the beginning and end of a test, otherwise an error in the reading of the water level may be caused by a change in the temperature and density of the water in the pipe leading from the bottom of the glass into the boiler. ae 696 EXPERIMENTAL ENGINEERING Uniformity of conditions should prevail as to the pressure of steam, the height of water, the rate of evaporation, the thickness of fire, the times of firing and quantity of coal fired at one time, and as to the intervals between the times of cleaning the fires. The method of firing to be carried on in such tests should be dictated by the expert or person in responsible charge of the test, and the method adopted should be adhered to by the fireman throughout the test. XIII. Keeping the Records. — Take note of every event connected with the progress of the trial, however unimportant it may appear. Record the time of every occurrence and the time of taking every weight and every observation. The coal should be weighed and delivered to the fireman in equal propor- tions, each sufficient for not more than one hour’s run, and a fresh portion should not be delivered until the previous one has all been fired. The time required to consume each portion should be noted, the time being recorded at the instant of firing the last of each portion. It is desirable that at the same time the amount of water fed into the boiler should be accurately noted and recorded, including the height of the water in the boiler, and the average pressure of steam and temperature of feed during the time. By thus recording the amount of water evaporated by successive portions of coal, the test may be divided into several periods if desired, and the degree of uniformity of com- bustion, evaporation, and economy analyzed for each period. In addition to these records of the coal and the feed-water, half-hourly observations should be made of the temperature of the feed-water, of the flue gases, of the external air in the boiler-room, of the temperature of the furnace when a furnace pyrom- - eter is used, also of the pressure of steam, and of the readings of the instru- ments for determining the moisture in the steam. A log should be kept on properly prepared blanks containing columns for record of the various observa- tions. (See note, p. 714, also p. 716.) When the “‘ standard method ” of starting and stopping the test is used, the hourly rate of combustion and of evaporation and the horse power should be computed from the records taken during the time when the fires are in active condition. This time is somewhat less than the actual time which elapses between the beginning and end of the run. The loss of time due to kindling the fire at the beginning and burning it out at the end makes this course necessary. XIV. Quality of Steam. — The percentage of moisture in the steam should be determined by the use of either a throttling or a separating steam calorimeter. The sampling nozzle should be placed in the vertical steam pipe rising from the boiler. It should be made of }-inch pipe, and should extend across the diam- eter of the steam pipe to within half an inch of the opposite side, being closed at the end and perforated with not less than twenty 3-inch holes equally dis- tributed along and around its cylindrical surface, but none of these holes should be nearer than } inch to the inner side of the steam pipe. The calorimeter and the pipe leading to it should be well covered with felting. Whenever the THE TESTING OF STEAM BOILERS 6907 indications of the throttling or separating calorimeter show that the percentage of moisture is irregular, or occasionally in excess of three per cent, the results should be checked by a steam separator placed in the steam pipe as close to the boiler as convenient, with a calorimeter in the steam pipe just beyond the out- let from the separator. The drip from the separator should be caught and weighed, and the percentage of moisture computed therefrom added to that shown by the calorimeter. Superheating should be determined by means of a thermometer placed in a mercury well inserted in the steam pipe. The degree of superheating should be taken as the difference between the reading of the thermometer for super- heated steam and the readings of the same thermometer for saturated steam at the same pressure as determined by a special experiment, and not by reference to steam tables. (See note, p. 717.) XV. Sampling the Coal and Determining its Moisture. — As each barrow load or fresh portion of coal is taken from the coal pile, a representative shovel- ful is selected from it and placed in a barrel or box in a cool place and kept until the end of the trial. The samples are then mixed and broken into pieces not exceeding one inch in diameter, and reduced by the process of repeated quartering and crushing until a final sample weighing about five pounds is obtained, and the size of the larger pieces is such that they will pass through a sieve with }-inch meshes. From this sample two one-quart, air-tight glass preserving jars, or other air-tight vessels which will prevent the escape of moisture from the sample, are to be promptly filled, and these samples are to be kept for subsequent determinations of moisture and of heating value and for chemical analyses. During the process of quartering, when the sample has been reduced to about 100 pounds, a quarter to a half of it may be taken for an approximate determination of moisture. This may be made by placing it ina shallow iron pan, not over three inches deep, carefully weighing it, and setting the pan in the hottest place that can be found on the brickwork of the boiler setting or flues, keeping it there for at least 12 hours, and then weighing it. The determination of moisture thus made is believed to be approximately accurate for anthracite and semi-bituminous coals, and also for Pittsburg or Youghiogheny coal; but it cannot be relied upon for coals mined west of Pitts- burg, or for other coals containing inherent moisture. For these latter coals it is important that a more accurate method be adopted. The method recom- mended by the Committee for all accurate tests, whatever the character of the coal, is described as follows: Take one of the samples contained in the glass jars, and subject it to a thorough air-drying, by spreading it in a thin layer and exposing it for several hours to the atmosphere of a warm room, weighing it before and after, thereby determining the quantity of surface moisture it contains. Then crush the whole of it by running it through an ordinary coffee mill adjusted so as to pro- duce somewhat coarse grains (less than rs-inch), thoroughly mix the crushed sample, select from it a portion of from 10 to 50 grams, weigh it in a balance 698 ; EXPERIMENTAL ENGINEERING which will easily show a variation as small as 1 part in 1000, and dry it in an air or sand bath at a temperature between 240 and 280 degrees Fahr. for one hour. Weigh it and record the loss, then heat and weigh it again repeatedly, at in- tervals of an hour or less, until the minimum weight has been reached and the weight begins to increase by oxidation of a portion of the coal. The difference between the original and the minimum weight is taken as the moisture in the air-dried coal. This moisture test should preferably be made on duplicate samples, and the results should agree within 0.3 to 0.4 of one per cent, the mean of the two determinations being taken as the correct result. The sum of the percentage of moisture thus found and the percentage of surface moisture previously determined is the total moisture. (See note, p. 717.) XVI. Treatment of Ashes and Refuse. — The ashes and refuse are to be weighed in a dry state. If it is found desirable to show the principal charac- teristics of the ash, a sample should be subjected to a proximate analysis and the actual amount of incombustible material determined. For elaborate trials a complete analysis of the ash and refuse should be made. (See note, p. 718.) XVII. Calorific Tests and Analysis of Coal. — The quality of the fuel should be determined either by heat test or by analysis, or by both. The rational method of determining the total heat of combustion is to burn the sample of coal in an atmosphere of oxygen gas, the coal to be sampled as directed in Article XV of this code. (See Chapter XIII.) The chemical analysis of the coal should be made only by an expert chemist. The total heat of combustion computed from the results of the ultimate analysis may be obtained by the use of Dulong’s formula (with constants modified by recent determinations), viz.: 14,540 C+ 61,950 (4 - e)+ 4000 5S, in which C, H, O, and S refer to the proportions of carbon, hydrogen, oxygen, and sul- phur respectively, as determined by the ultimate analysis.* (See note, p. 710.) It is desirable that a proximate analysis should be made, thereby deter- mining the relative proportions of volatile matter and fixed carbon. These proportions furnish an indication of the leading characteristics of the fuel, and serve to fix the class to which it belongs. As an additional indication of the characteristics of the fuel, the specific gravity should be determined. XVIII. Analysis of Flue Gases. — The analysis of the flue gases is an espe- cially valuable method of determining the relative value of different methods of firing, or of different kinds of furnaces. In making these analyses great care should be taken to procure average samples — since the composition is apt to vary at different points of the flue. The composition is also apt to‘vary from minute to minute, and for this reason the drawings of gas should last a con- siderable period of time. Where complete determinations are desired, the _ * Favre and Silberman give 14,544 B.t.u. per pound carbon; Berthelot, 14,647 B.t.u. Favre and Silberman give 62,032 B.t.u. per pound hydrogen; Thomson, 61,816 B.t.u. THE TESTING OF STEAM BOILERS 699 analyses should be intrusted to an expert chemist. For approximate deter- minations the Orsat* or the Hempel} apparatus may be used by the engineer. (See Chapter XIII for treatment of methods, computations, etc.) For the continuous indication of the amount of carbonic acid present in the flue gases, an instrument may be employed which shows the weight of the sample of gas passing through it. XIX. Smoke Observations. —It is desirable to have a uniform system of determining and recording the quantity of smoke produced where bituminous coal is used. The‘system commonly employed is to express the degree of smokiness by means of percentages dependent upon the judgment of the observer. The Committee does not place much value upon a percentage method, because it depends so largely upon the personal element, but if this method is used, it is desirable that, so far as possible, a definition be given in explicit terms as to the basis and method employed in arriving at the percent- age. The actual measurement of a sample of soot and smoke by some form of meter is to be preferred. (See Chapter XIII, under smoke determination.) XX. Miscellaneous. —In tests for purposes of scientific research, in which the determination of all the variables entering into the test is desired, certain observations should be made which are in general unnecessary for ordinary tests. These are the measurement of the air supply, the determination of its contained moisture, the determination of the amount of heat lost by radiation, of the amount of infiltration of air through the setting, and (by condensation of all the steam made by the boiler) of the total heat imparted to the water. (See note, p. 719.) As these determinations are rarely undertaken, it is not deemed advisable to give directions for making them. XXI. Calculations of Efficiency. — Two methods of defining and calculating the efficiency of a boiler are recommended. They are: Heat absorbed per lb. combustible _ Calorific value of 1 lb. combustible Heat absorbed per Ib. coal _ Calorific value of 1 lb. coal 1. Efficiency of the boiler = 2. Efficiency of the boiler and grate = The first of these is sometimes called the efficiency based on combustible, and the second the efficiency based on coal. The first is recommended as a standard of comparison for all tests, and this is the one which is understood to be referred to when the word “ efficiency ” alone is used without qualification. The second, however, should be included in a report of a test, together with the first, whenever the object of the test is to determine the efficiency of the boiler and furnace together with the grate (or mechanical stoker), or to compare different furnaces, grates, fuels, or methods of firing. The heat absorbed per pound of combustible (or per pound of coal) is to be * See R. S. Hale’s paper on ‘‘ Flue Gas Analysis,” Transactions, Vol. XVIII, p. gor. t See Hempel’s ‘Methods of Gas Analysis,’ translated by L. M. Dennis (Macmillan & Co.). 700 EXPERIMENTAL ENGINEERING calculated by multiplying the equivalent evaporation from and at 212 degrees per pound combustible (or coal) by 965.7. (See note, p. 719, concerning this rule, the following rule, and the Tables below.) XXII. The Heat Balance. — An approximate “ heat balance,” or statement of the distribution of the heating value of the coal among the several items of heat utilized and heat lost, may be included in the report of a test when analyses of the fuel and of the chimney gases have been made. It should be reported in the following form: HEAT BALANCE, OR DISTRIBUTION OF THE HEATING VALUE OF THE COMBUSTIBLE. Total Heat value of 1 lb. of combustible... ..............0022008- B.t.u. B.t.u. | Per Cent. 1. Heat absorbed by the boiler = evaporation from and at 212 degrees per pound of combustible X 965.7. 2. Loss due to moisture in coal = per cent of moisture referred to combustible + too X [(212 — 4) + 966 + 0.48 (T — 212)] (¢ = temperature of air in the boiler-room, T = that of the flue gases). 3. Loss due to moisture formed by the burning of hydrogen = per cent of hydrogen to combustible + 100 X 9 X [(212— 1?) + 966 + 0.48 (I — 212)]. 4." Loss due to heat carried away in the dry chimney gases = weight of gas per pound of combustible X 0.24 X (T — 2). 5.¢ Loss due to incomplete combustion of carbon CO, + CO x per cent C in combustible 100 © 6 Loss due to unconsumed hydrogen and hydrocarbons, to heat- ing the moisture in the air, to radiation, and unaccounted for. (Some of these losses may be separately itemized if data are obtained from which they may be calculated.) Totals X I0,150. plein ak saectaed dp agusenegsaas endo as gedeeee es a gu Roe OIE! Wee agenda Bra NEMA OKI Ole te 100.00 * The weight of gas per pound of carbon burned may be calculated from the gas analyses as follows: 1 CO» Dry gas per pound carbon = cet OO » in which CO», CO, O, and N are the percentages by volume of the several gases. As the sampling and analyses ‘of the gases in the present state of the art are liable to considerable errors, the result of this calculation is usually only an approxi- mate one. The beat balance itself is also only approximate for this reason, as well as for the fact that it is not possible to determine accurately the percentage of unburned hydrogen or hydrocarbons in the flue gases. The weight of dry gas per pound of combustible is found by multiplying the dry gas per pound of carbon by the percentage of carbon in the combustible, and dividing by roo. + CO, and CO are respectively the percentage by volume of carbonic acid and carbonic oxide in the flue gases. The quantity of 10,150 = Number of heat units generated by burning to carbonic acid one pound of carbon contained in carbonic oxide. THE TESTING OF STEAM BOILERS 7O1 XXIII, Report of the Trial. — The data and results should be reported in the manner given in either one of the two following tables, omitting lines where the tests have not been made as elaborately as provided for in such tables.* Additional lines may be added for data relating to the specific object of the test. The extra lines should be classified under the headings provided in the tables, and numbered as per preceding line, with subletters a, b, etc. The Short Form of Report, Table No. 2, is recommended for commercial tests and as a convenient form of abridging the longer form for publication when saving of space is desirable.t For elaborate trials, it is recommended that the full log of the trial be shown graphically, by means of a chart. TABLE NO. t. DaTA AND RESULTS OF EVAPORATIVE TEST. Arranged in accordance with the Complete Form advised by the Boiler Test Committee of the American Society of Mechanical Engineers. Code of 1890. UIDs OF FUEL ia 8 3 cil cls ch cde ce Hecate terres eet Meany fin ate Ne Buty ob ed PRR TASS KANG Of JU NOCE eg 5b 5 Bier S sg teh 58 eS te Se SccesSpe heat ints A Go REE Ta SE ets RE BOS State of the weather Method of starting and stopping the test (‘‘standard”’ or “alternate,” Art. X and XI, Code, and note, p. 713) Dit DIGUESOf EPGOE seco op Sele seh irc ten tap ehehes ahah Saat ggen pis d ANTS ESR BE Oe BOGE Biv DUPGiON Of WAGs soa iene eh RARE SOLER La EI NS hours. Dimensions and Proportions. A complete description of the boiler, and drawings of the same if of unusual type, should be given, on an annexed sheet. 3. Grate surface........ width....... length...... aread...... sq. ft. 4. Height: of f0rMace, 2.2. esr dewenaadcwinnn an adced oe Laeens ins. 5. Approximate width of air spaces in grate................ in. 6. Proportion of air space to whole grate surface * The items printed in italics correspond to the items in the “ Short Form of Code.” + See Forms for recording the observations, pages 708 and 709. 702 EXPERIMENTAL ENGINEERING 7. Water-heating surface......... Tre SR esa ke hea deat ee sq. ft. Bi SUPCRNEGINS SUP {ECE iso s6 aed werk dG HDS Me RA eh Bi s 9. Ratio of water-heating surface to grate surface........... — tor. to. Ratio of minimum draft area to grate surface. .......... 1 to — Average Pressures. 11. Steam pressure DY BQUZE. 6. ccc eee Ibs. per sq. in. 12. Force of draft between damper and boiler i... es ee ins. of water. 13. Force of draft in furnace. ...............0 000 eee eee es " 14. Force of draft or blast in ashpit....... .........-e.0400- eS e Average Temperatures. Tes Oh external vary 4 cay woe dae Mis a Ata Sea eek eres deg. LO. Of HTELOOMI< ok. aden pha ails Panes ag Heels ive ms TOL Steamy ys ovis Sedat yee res woe Ghee essed aner evar dices o 18. Of feed water entering heater....................00000. ss 19. Of feed water entering economizer...................... a 20. Of feed water entering boiler... 0... eee eee ee ee 21. Of escaping gases from boiler 6 eee of 22. Of escaping gases from economizer..................... a Fuel. 23%» SIZE AMG. CONGLION ty si sncaia ye a's vimtelducs Wee en ee eesee oa ae Shand 24. Weight of wood used in lighting fire.................... lbs. 25. Weight of coal as fired * 2... ccc eee es 26. Percentage of moisture in coal}... 6... 06.0000 eee per cent. 27. Total weight of dry coal consumed. — ... eee lbs. 28. Total ash and refuse. cece eee . 29g. Quality of ash and refuse..........0.....000000 02 e eee 30. Total combustible consumed..............0.0..00.00 0004 lbs. 31. Percentage of ash and refuse in dry coadl.. ............... per cent. * Including equivalent of wood used in lighting the fire, not including unburnt coal withdrawn from furnace at times of cleaning and at end of test. One pound of wood is taken to be equal to 0.4 pound of coal, or, in case greater accuracy is desired, as having a heat value equivalent to the evaporation of 6 pounds of water from anid at 212 degrees per pound. (6 X 970.4 = 5822 B.t.u.) The term “as fired” means in its actual condition, including moisture. + This is the total moisture in the coal as found by drying it artificially, as described in Art. XV of Code. (Note, p. 717.) THE TESTING OF STEAM BOILERS 703 Proximate Analysis of Coal. Of Coal. Of Combustible. 39, Bixed carbonsiis a cccaws esa urea va dew edie es s per cent. per cent. 93. Volatile-mattet, sj pseswuwesesesetace var s ef G4, MOISture.....24 3. iG Losec nan danas wee basen Se - — Bs NSH eas a cose cosa PRS AREA A SO eS — 100 per cent. 100 per cent. 36. Sulphur, separately determined............. per cent. per cent. Ultimate Analysis of Dry Coal. (Art. XVII, Code.) Of Coal. Of Combustible. ah. Carbon: (CG). 224 nent ences poised rhea Whe per cent. per cent. 38. Hydrogen (H).... 0.0.2.0... cece eee eee 6 Ke 208 Oxyeen (O)n.. in boca ay ba Qecdactnears mare a ef 40. Nitrogén. GN). «0 .cceceecaeacesiedeavasde eas dvs Sulphur (S$). ¢c2s6 Mee eea hus este eee a “ AaAshia ae agcpacae necdnieee RAMOS aes Cod « = Ioo per cent. 100 percent. 43. Moisture in sample of coal as received....... per cent. per cent. Analysis of Ash and Refuse. 4a. “Carbone s secuvsa die ie eather pi os Oo el ae Se eS RO aS per cent. 450 Barthy wMiatten es ciicg ahs fin bd divin dla be eee de duh sasuke baad tore 7 Fuel per Hour. 46. Dry coal consumed per hour... 0.00600 o ccc ee lbs. 47. Combustible consumed per hour. . .........---0055 oe 48. Dry coal per square foot of grate surface per hour.......... : 49. Combustible persquare foot of water-heating surface per hour - Calorific Value of Fuel. (Art. XVII, Code.) 50. Calorific value by oxygen calorimeter, per lb. of dry coal. ... B.t.u. 51. Calorific value by oxygen calorimeter, per lb. of combustible... ny 52. Calorific value by analysis, per lb..of dry coal* . ..... : 53. Calorific value by analysis, per lb. of combustible........ roe Quality of Steam 54. Percentage of moisture im steam... 6... cece cee per cent. 55. Number of degrees of swperheating....... 0.00. e eee eens deg. 56. Quality of steam (dry steam = unity)...............-.. * See formula for calorific value under Article XVII of Code, and note, p. 710. 704 EXPERIMENTAL ENGINEERING Water. 57. Total weight of water fed to boiler® ..... cece cece eres Ibs. 58. Equivalent water fed to boiler from and at 212 degrees... . so. Water actually evaporated, corrected for quality of steam..... 6o. Factor of evaporation }.. 0.06... cee eee eee eee 61. Equivalent water evaporated into dry steam from and at Ibs. 212 degrees.t (Item 59 X Item 60.)..............-.-- Water per Hour. 62. Water evaporated per hour, corrected for quality of steam..... 63. Equivalent evaporation per hour from and at 212 degrees .. 64. Equivalent evaporation per hour from and at 212 degrees ber square foot.of water-heating surfacet........ .......005 Horse Power. 65. Horse power developed. (34% lbs. of water evaporated per hour into dry steam from and at 212 degrees, equals one horse POWET)S oon vine a's AS Soee oe he DEERE OS SLSR PEE RE ERE ELP. 66. Builders’ rated horse power... 1.0.6... eee “ 67. Percentage of builders’ rated horse power developed.......... per cent. Economic Results. 68. Water apparently evaporated under actual conditions per pound of coal as fired. (Item 57 + Item 25.)........... 00004. lbs. 69. Equivalent evaporation from and at 212 degrees per pound of coal as fired.{ (Item 61 + Item 25.).................. ae 70. Equivalent evaporation from and at 212 degrees per pound of dry coal.t (Item 61 + Item 27.)... 2.2.0.0 002 ee s 71. Equivalent evaporation from and at 212 degrees per pound of combustible.t (Item 61 + Item 30.)....... 000000000008 Bs (If the equivalent evaporation, Items 69, 70, and 71, is not corrected for the quality of steam, the fact should be stated.) * Corrected for inequality of water level and of steam pressure at beginning and end of test. { Factor of evaporation = a = in which H and h are respectively the total heat in steam of the average observed pressure, and in water of the average observed temperature of the feed. (See note, p. 722, for a discussion of Items 60 and 61.) { The symbol “ U.E.,” meaning “ Units of Evaporation,” may be conveniently sub- stituted for the expression “ Equivalent water evaporated into dry steam from and at 212 degrees,” its definition being given in a footnote. § Held to be the equivalent of 30 pounds of water per hour evaporated from too° F. into dry steam at 70 pounds gauge pressure. 72. 73+ 74: 75. 76. 77° 78. 79- 80. 81. 82. 83. 84. 85. 86. 87. 88. THE TESTING OF STEAM BOILERS 705 Efficiency. (Art. X2XI, Code, and note, p. 719.) Efficiency of the boiler; heat absorbed by the boiler per pound of combustible divided by the heat value of one pound of com- DUSTED es Se Ga cose Set sae Rad. aya Seas Gk Ghusta see dene pes Seka per cent. Efficiency of boiler, including the grate; heat absorbed by the boiler, per pound of dry coal, divided by the heat value of one PoUnd.Of GP COD. do dcitewcuadsnte tte s@osena se sanea ye Cost of Evaporation. Cost of coal per ton of —— pounds delivered in boiler-room. . $ Cost of fuel for evaporating 1000 lbs. of water under observed CONMIMONS is oaasresacineass pe bad are wee nae mek wea $ Cost of fuel for evaporating 1000 lbs. of water from and at 212 GO BPCOS ani ne wevin Cardi Gage AEH wits te Re te hoe. Hee ste oR $ Smoke Observations. Percentage of smoke as observed.................-00055 per cent. Weight of soot per hour obtained from smoke meter. ..... ounces. Volume of soot per hour obtained from smoke meter...... cub. in. Methods of Firing. Kind of firing (spreading, alternate, or coking)........... Average thickness of fire... 2.0.0.0... ccc eee eee eee eee Average intervals between firings for each furnace during time when fires are in normal condition................ Average interval between times of levelling or breaking up. Analyses of the Dry Gases. Carbon dioxide (CO2). 2.0... 00... per cent. Oxy pen (O) ness. sas ober Acta ssi da ausan eae Aanaearah atone es Carbonsmonoxidé: (CO) siscie ons aera were akees Yok wa ee oS es Hydrogen and hydrocarbons..... ha adivnh insur ee uae Nitrogen (by difference) (N)..............00 00000 eee eee a Ioo per cent. * In all cases where the word combustible is used, it means the coal without mois- ture and ash, but including all other constituents. It is the same as what is called in Europe “coal dry and free from ash.” 706 EXPERIMENTAL ENGINEERING TABLE NO. 2. DaTA AND RESULTS OF EVAPORATIVE TEST. Arranged in accordance with the Short Form advised by the Boiler Test Com- mittee of the American Society of Mechanical Engineers. Code of 1899. Method of starting and stopping the test (‘‘standard” or “alternate,” Art. X and XI, Code) Grate surface................05- Pda gS ana ee NR ne 4 sq. it. Watet-heating Suriaceninseyiaded ey weed edek eee es Bios abe = Supéetheating surface... 2.2 cc.cc ca eescvavew gucdee ses ceceue ae sf a: Dateof tial: ccas chcdterereaamdeeeqad aad abate topes a Duration, OF thal ssc Gage? ola de aeaeeeee yas | oe hours. 3. Weight of coal as:fired* .jacis erase cad sped edtaeeege Ibs. 4. Percentage of moisture in coal*................02200004 per cent. 5. Total weight of dry coal consumed...................-- Ibs. 6. Total:ash-and refuse s+ 6.4245. 644 ¢455 Beare tie eguoie cae - 7. Percentage of ash and refuse in say COal. 4> Sawa le tet xele per cent. 8. Total weight of water fed to the boiler *................. lbs. 9. Water actually evaporated, corrected for moisture or super- HeatsimStearn si hachoce'ey wine yeaa qa 4 wi eae avalae Wale Ae “ to. Equivalent water evaporated into dry steam from and at 212 ER TCESS Hacc an Seceieaid a easier ae what Meee me Moe ee Hourly Quantities. 11. Dry coal consumed per hour........... 0.000.000 euee Ibs. 12. Dry coal per square foot of grate surface per hour........ ae 13. Water evaporated per hour corrected for quality of steam . “f 14. Equivalent evaporation per hour from and at 212 degrees * « 15. Equivalent evaporation per hour from and at 212 degrees per square foot of water-heating surface *... ........, ee * See footnotes of Complete Form. 16. 17. 18. 19. 20. 2i. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33- THE TESTING OF STEAM BOILERS 707 Average Pressures, Temperatures, etc. Steam pressure by gauge............ 0.00 ccc cece eee Ibs. per sq. in. Temperature of feed water entering boiler. ............. deg. Temperature of escaping gases from boiler............... o Force of draft between damper and boiler................ ins. of water. Percentage of moisture in steam, or number of degrees of Superheating cic aie ies cadcs owes Gabe aupasglaaewlabes per cent or deg. Horse Power. Horse power developed. (Item 14 + 343.) *............. ELP. Builders’ rated horse power........... 0.0.2.0 cee eeee eee a Percentage of builders’ rated horse power developed...... per cent. Economic Results. Water apparently evaporated under actual conditions per pound of coal as fired. (Item 8 + Item 3.)............ lbs. Equivalent evaporation from and at 212 degrees per pound of coal as fired.* (Item 10 + Item 3.)................ Equivalent evaporation from and at 212 degrees per pound “ of dry coal.* (Item 10 + Item §.)..................4. a Equivalent evaporation from and at 212 degrees per pound of combustible.* [Item 10 + (Item 5 — Item 6.)]...... a (If Items 25, 26, and 27 are not corrected for quality of steam, the fact should be stated.) Efficiency. Calorific value of the dry coal per pound................ B.t.u. Calorific value of the combustible per pound............. “ Efficiency of boiler (based on combustible) *............. per cent. Efficiency of boiler, including grate (based on dry coal).... “ Cost of Evaporation. Cost of coal per ton of —— lbs. delivered in boiler-room . . $ Cost of coal required for evaporating 1000 pounds of water from and at 212 degrees........... 0... ese e eee eee eee $ * See footnotes of Compiete Forms. EXPERIMENTAL ENGINEERING 708 PN ‘arey, | *ss015 ‘yN | carey | ‘ssorg ‘2ON ‘amey, | “ssois caaned | “omy, | “UOHIpuoD | “suIL ‘ou, “om, * ouany, "SitEog “74310. “14310 “Wq3REM *[aAay IVA ‘ay ‘asnjayy ‘yang “aye pray ALORS S GS Ce Tse hE SSE me) *asnfay PSST Sse FRCS TEL D TS SSSI S94) HES Ee SESSA SPOS 6 OHS T & Gee eee ee ee “490g fo uoulpuory ES FS © we een wier en hie Ya ee ee 4940 A CRS ee eS Hee Sw Buidig fo uo’tpUuoD ee ee ee ee ee ee ee ee a ee ee a | 4a]10g fo pury a oe ee ee ee ee ee ee ee ee Jans] ee ee ee ee ee pang fo pury TROT Oe Le ee ee a ee he en a ae ee Ne Sa fo aqDq :SUTAUASAO ‘ISHL UATION JO ODOT UALVM ANV TVOD ‘ADATION AXTAIS — ONIAAANIONG IVLNAWIAAdxXd JO LNAWLYAVdad THE TESTING OF STEAM BOILERS 709 DEPARTMENT OF EXPERIMENTAL ENGINEERING —SIBLEY COLLEGE, LOG OF BOILER TEST. Io. Il. 12. 20. ai. 22. Rand Of BOW 2 sas Risse oS ccanense setae a eindase Mfg. by Pressures. Temperatures. Water Gauge. Air Boiler- EB Alico8ls, eeealexane 4 aemale gas shag set se ale os aceles Kells ied elpecemone eee Sal eee Se Thiel pjcle dlp docs lege] pace eye calle saa cdetdiga tfleces ale cage ys ieee aces | at baal sae a £5) | oes) ocr laashalneawe el ase tele eeleedy oie es Helse rata pmage fates reese 16. D7 Aa oe salle, cee dhe asaial ents) apa'| goaremia Paiccranelpa etc # ect a fanace gs] FER Meee pal] eases he ; 18, Tile cwashasereiience| ia Sacleis4 eee Hb 061 84 Cal ees el eae ahS a as peek eps EPS BRE 2 accor klisasmyaall cckecina cal leve-cyovealead oan ae sctees SES A ht ep de ocean snip oats 9 Bk Nae a. aN? 710 EXPERIMENTAL ENGINEERING 360. Notes on the Rules. — Rule I. Appendix II states the possible objects of the test at greater length, and is quoted in full. In preparing for and conducting trials of steam boilers, the special object of the proposed trial should be clearly defined and steadily kept in view. 1. If it be to determine the efficiency of a given style of boiler or of boiler setting under normal conditions, the boiler, brickwork, grates, dampers, flues, pipes, in short, the whole apparatus, should be carefully examined and accurately described, and any variation from a normal condition should be remedied if possible, and if irremediable, clearly described and pointed out. 2. Ifit be to ascertain the condition of a given boiler or set of boilers with a view to the improvement of whatever may be faulty, the conditions actually existing should be accurately observed and clearly described. 3. If the object be to determine the relative value of two or more kinds of coal, or the actual value of any kind, exact equality of conditions should be maintained if possible, or, where that is not practicable, all variations should be duly allowed for. 4. Only one variable should be allowed to enter into the problem; or, since the entire exclusion of disturbing variations cannot usually be effected, they should be kept as closely as possible within narrow limits, and allowed for with all possible accuracy. Rule IIT. Appendix X specifies in detail the dimensions and data that should be taken and is quoted in full. The report should include a complete description of the boiler, which, for special boilers, should be written out at length, but generally can conveniently be presented in tabular form substantially as follows: Type of boiler. Diameter.of shell. Length of shell. Number of tubes. Diameter of tubes. Length of tubes. Diameter of steam drum. Width of furnace. Length of furnace. Kind of grate bars. Width of air spaces (in grate bars). Ratio of area of grate to area of air spaces. Area of chimney. Height of chimney. Length of flues connecting to chimney. THE TESTING OF STEAM BOILERS WII Area of flues connecting to chimney. Grate surface. { Water Heating surface < Steam UTotal Area of draft through or between tubes. Ratio grate to heating surface. Ratio draft area to grate. Ratio draft area to total heating surface. Water space. Steam space. Ratio grate to water space. Ratio grate to steam space. Rule IV.. It is an easy matter to test, with the same kind of coal, different boilers which are to be compared in regard to efficiency or capacity. All that would appear to be necessary to specify the coal is that it should be a good grade of its kind. To attempt to say what is ‘‘ commercially standard” coal might lead to difficulties. In most practical cases a buyer of boilers would naturally desire to use the coal most common in his neighborhood, that being the kind which he can obtain at least cost, and will certainly call for guarantees of efficiency or capacity based upon this coal. This fact at once disposes of the matter of choice of coal. In order to prevent misunderstandings and possible litigation, the kind of coal should be specified, and if possible the proximate analysis, including the heat value of the coal, should be distinctly specified in every boiler guarantee. Rule V.—For details concerning measurement of water and calibration of apparatus, see Chapters VI, VII, and XII. Rule VII. The provision requiring the disconnecting or blank flanging of all water connections and blow-off pipes, except the pipe through which the boiler receives its feed water, should be followed to the letter whenever possible. There are now and then cases in practice, however, where, under the circumstances existing, this is not possible. There are also cases in which it is desired to test a boiler plant in the then existing conditions and where the deter- mination of the losses through leaky blow-off cocks, leaky tubes, etc., is a part of the test. In such cases the amount of such loss can be 712 EXPERIMENTAL ENGINEERING determined by making what is called a “ leakage test ” at the end of the main test. To make this test, proceed as follows: Previous to the test, fasten behind each gauge glass a scale which can be read to at least .o5 inch. Just after the main test is completed, close all of the outlets from the boiler or battery through feed water and steam connections, and have the pressure maintained constant at the working pressure by proper manipulation of the drafts. Ob- serve the water level for at least an hour, taking the readings Gage Glass Reading H Fic. 489. — DETERMINATION OF BoILER LEAKAGE. at first, say every minute and later on every two or three minutes, depending upon how rapidly the water level sinks. Plot a curve between scale reading and time. This will usually be of the form shown in Fig. 489, the rapid drop from a to 6 being in part due to the natural shrinking of the volume of water as active ebullition ceases. The more nearly straight part be represents true leakage. The leakage in the time represented by b’c will then be equal to 6b’ inches. Or cb’ may be prolonged back to a’, in which case a’a” represents the inches of leakage per hour. What this amounts to in pounds depends upon the size of the steam drum and upon the THE TESTING OF STEAM BOILERS 713 location of the gauge glass with reference to the center line of the drum. In computing the leakage in pounds, the temperature correction should not be forgotten, since the volume of water leaking out is at the temperature corresponding to the steam pressure. In guarantee tests the leakage correction should not amount to more than one or two per cent of the total water evaporated. If it does, one should either be absolutely certain of this correction, or the boiler should be put in proper shape and retested. Rules IX, X, and XI. The “ standard” method of starting and stopping a test, although defended by some engineers, is strongly criticized by the majority, and the “‘alternate ’’ method is to-day the one most used. Professor Wm. Kent, in Appendix XXXVI to the Code, briefly compares the two methods and also warns against some possible errors in the use of the alternate method, both with regard to the condition of the fire and the in- fluence of the latter upon the movements of the apparent water level. Of the two methods of starting and stopping a test, the so-called ‘* stand- ard’ method and the “ alternate’’ method, the writer prefers the latter, believing that the errors in the estimation of the quantity and condition of the small amount of coal left on the grate after cleaning are less than the errors of the “standard ” method, which are due first, to cooling of the boiler at the beginning and end of the test; second, to the imperfect combustion of the fuel at the beginning; and third, to excessive air supply through the thin fire while burning down before the end of the test. A special caution is needed against a modification of the “alternate ” method, which has been adopted by some testing engineers within the past few years. It consists in taking the starting and the stopping times each at a time subsequent to the cleaning, say after 400 pounds of coal has been fired since the cleaning. There are two sources of serious error in this method, one causing an incorrect measurement of the coal, the other an incorrect measurement of the water. Suppose 200 pounds of hot coke are left on the grate at the end of cleaning and 400 pounds of fresh coal are added by the end of, say, half an hour after cleaning. If the coal left at the end of the cleaning, and the boiler walls also, are very hot, and the coal is highly volatile and dry, and the pieces of such size as not to choke the air supply, the fire mav burn so briskly that at the end of the half hour the fuel value of the partly burned coal left out of the total 600 pounds is equivalent only to 200 pounds of coal. If, on the contrary, the hot coke on the grates at the end of the cleaning, and the boiler walls, are cc 714 EXPERIMENTAL ENGINEERING considerably cooled, if the fresh coal fired is moist and of small size, such as the slack of run-of-mine bituminous coal, which is often found in one portion of a pile in greater quantity than in another, the fire during the half hour may burn so sluggishly that the coal and coke on the grate at the end of the half hour may have a fuel value equal to 400 pounds of coal. If, in this case, it is assumed that the quantity and condition of the coal at the end of the half hour after cleaning are the same at the starting and stopping time, and if the fire burned briskly during the half hour before starting and slowly during the half hour before stopping, the boiler will be charged with more coal than was actually burned. If, on the contrary, the coal burns away more slowly during the half hour after the cleaning before the starting time and more rapidly during the half hour before the end of the test, the boiler is not charged with as much coal as was actually burned. The error in water measurement is due to the fact that the condition of the fire, and especially the quantity of flaming gases arising from it, influences the height of the water level. A bright, hot fire, or a fire with an abundance of burning gas proceeding from it, causes the water level to rise; while anything that cools the furnace, such as freshly fired coal, an open fire door, or a check to the draft, causes the water level to fall. A rise or a fall of several inches in a few seconds frequently occurs when bituminous coal is used. If the water level is noted at the starting of the test, when it is raised by a bright fire, and at the end of the test, when it is depressed by the stoppage of violent ebullition or of rapid circulation, due to the cooling of the fire, the boiler will be credited with more water than was really evaporated, and vice versa. The only correct times to be noted as the starting and the stopping times are when the smallest amount of fuel is on the grate and when it is in the most burned-out condition; that is, just before firing fresh coal after cleaning, and when the water level is inits most quiet condition and the least raised by ebulli- tion; that is, after the furnace door has been kept open for some time for clean- ing and the furnace therefore is in its coolest state. This condition of fire and of water level can be duplicated immediately after cleaning the fire; but there is no certainty of duplication of any condition when there is a bright fire and consequent rapid steaming. ‘ Rule XIII. In keeping the record and in presenting the results, it is sometimes of benefit to construct what is known as a log chart. Such a chart shows at a glance the conditions that obtained for the entire period of the test. An example of such a log is shown in Fig. 490, which is a reproduction of the one given by Mr. G. H. Barrus, in Appendix XX XVIII of the Code. Concerning the methods of tallying, the number of assistants required, etc., Appendix IV, written by Mr. C. E. Emery, gives some valuable points. THE TESTING OF STEAM BOILERS 715 It should be steadily kept in mind that the principal observations to be made are the quantities of coal consumed and of water evaporated. If these quanti- ties are ascertained accurately, and the conditions made the same at the beginning and end of test, the most important requisites of a boiler trial will be secured. Other observations have their value both for scientific and practical purposes, but are in most cases subsidiary. Boiler tests are often undertaken with insufficient apparatus and assistance. It is possible for a single person to test one boiler, or even several in a battery, but it requires a great deal of labor to do so, and in many cases such persons would be so fatigued as to be liable to make a simple error vitiating the results. He would, moreover, at no time be able to give proper oversight to the test Lbs, CHART SHOWING LOG OF BOILER TEST 170,000 160,000 150,000 140,000 130,000 120,000 ,_ 110,000 & 100,000 90,000 80,000 70,000 60,000 18,000 16,000 3 14,0002 °o 12,000 Scale of W: 50,000 10,000 40,000 8,000 30,000 6,000 20,000 4,000 ° 10,00 2,000 0 os 910112123 4667 8 9 1011 AM. P.M. AM. Fic. 490. so as to prevent accidental or unauthorized interferences. It is very desirable, in fact almost indispensable, that an assistant be detailed to weigh the coal, and another to weigh or measure the water; if calorimeter tests are to be under- taken, still another assistant should be provided. The engineer in charge is then left free to oversee the work of all, and relieve either teniporarily when necessary. Engineers are frequently called upon to make boiler trials in connection with parties whose interests are antagonistic to a fair test, and frequently the voluntary assistance of busybodies is likely to produce errors in the results. It is therefore essential to have trustworthy assistants, and those of sufficient caliber not to be confused by interested parties, who will frequently endeavor in the most plausible manner to make out that a certain measure of coal has already been tallied, or that a certain tank of water has not been tallied. ; In the first engine trials at the American Institute Exhibition (1869), in the 716 EXPERIMENTAL ENGINEERING Centennial trials (1876), and since in private trials respecting performance of boilers as between the contractor and purchaser, the writer has arranged for both interests to take the data at the same moment, with instructions, if agreement could not be had, that the difference be at once referred to him. In weighing the coal, the barrow or vessel used should be balanced on a scale and then filled to a certain definite weight. The laborer will soon learn to fill a vessel to the same weight within a few pounds by counting the number of shovels thrown in, when the change of a lump or two to or from a small box alongside the scale will balance it. [Mr. Emery next discusses methods of measuring water.] A simple tally should never be trusted. Nothing seems more reliable to an inexperienced observer than to mark 1, 2, 3, 4 with a diagonal cross mark for 5; but when there are waits of several minutes between the marks, and several operations performed after the tally is made, there will be confusion in the mind whether or not the tally has actually been made. The tallies both of weights of coal and of tanks of water should be written on separate lines, the time noted opposite each, and the records always made at the beginning or termination of some particular operation; for instance, in weighing coal only at the time when barrel or bucket is dumped on the fire-room floor. It is desirable to have a number of coincident records of coal and water throughout the trial, so that in case of accident it may be held to have ended at one of such times. The uniformity of the operations may also be tested in this way from time to time. For this reason it will be found convenient to fire from a wheel- barrow set on a scale and to have a float or water-gauge connected with the tank from which the water is pumped; by which means the coal and water used may, in an evident way, be ascertained for any desired interval. Rules [X, X, XI, XII, and XIII. If uniformity of operation of the boiler and furnace is secured, as it should be (Rule XII), it is obvious that the curves of “ total water” and “ total coal” against time (curves marked “water” and “coal” in Fig. 490) will be straight lines. The slopes of these lines are the rates of evapora- tion of water and supply of fuel. The real object of a boiler test is to obtain the ratio of these rates. It is evident that these rates may be obtained without regard to the end conditions of the tests. It appears then that there is a third method of “ starting and stopping ” a boiler test, a method more scientific and more accurate than either the “standard” or the “alternate”? methods. This third method requires merely that the boiler be brought to, and kept at, uniform operation for the length of time over which the test is to continue. During this time observations should be THE TESTING OF STEAM BOILERS 717 made of the amounts of water and coal supplied during every ten or fifteen minute interval, and of the amount of refuse coming through the grates every half hour. The curves of “ total water,” “total coal,” and “ total refuse”? against time are then to be plotted. The rates are to be found from the slopes of these curves, using those portions which are straight lines, and leaving out the curved end portions where the boiler was heating up or cooling off. In working up the test the other observations, as steam pressure, quality, feed temperature, flue temperature, etc., are to be averaged and used only for that period of time within which the coal, water, and refuse curves are straight lines. The ‘‘ end conditions ” need not be considered; their effects are eliminated by the determination of rates. Rule XIV. For a discussion of the methods of determining moisture in steam, see Chapter XIV. The specific heat of superheated steam has now been determined with sufficient accuracy to allow of satisfactory determination of the total heat of superheated steam, see Chapter XI. It is advo- cated in the Code and in Appendix XIX to determine the range of superheat by finding the normal or saturation temperature of the steam by a special experiment, taking a reading of the thermom- eter when the fires are dull and superheat has disappeared. This method certainly has the advantage of doing away with the cali- bration of the thermometer with its attendant difficulty of dupli- cating the conditions of immersion of bulb and stem, surrounding air temperature, etc. The average steam pressure, however, must be exactly duplicated and maintained during the experiment, which may not be an easy matter. With the error of the steam gauges known, direct reference to the steam table for the saturation tem- perature is now probably of sufficient accuracy. Rule XV. Of the two methods given for the determination of moisture in coal, the first must be held distinctly unreliable and in most cases useless. In the first place, an approximate deter- mination is not what is wanted. In the second place, considering the sources of error involved and the usual lack of facilities in boiler houses for making close weighings, grave doubt must usually exist concerning the degree of approximation. 718 EXPERIMENTAL ENGINEERING Regarding the second method of determination, see Chapter XIII. Rule XVI. It is perhaps not superfluous to point out that the correct determination of the “ ash” (total ash and refuse in the tables below) made during the test is not so simple a matter as it would appear at first sight, especially if the alternate method of starting and stopping is used. The entire matter of course rests on the correct estimation of the condition of the fire at beginning and end of test, and this in turn is largely a matter of experience. The accurate determination of the ash weight is of particular importance where the efficiency of the furnace, which may be of special type, is at issue, or where a heat balance as nearly correct as possible must be established. The coal analysis of course shows the absolute minimum of ash that can be obtained on a test. But since no grate is perfect, there should, in most cases, be more “ash” than the analysis shows, due to unburned carbon dropping through. It may, however, happen that the coal is of such a nature that, under the draft conditions existing, a part of it or of its ash may be carried along with the gases for some distance and deposited in the passes or in the com- bustion chamber. If this action is suspected, provision should be made for determining the weight and composition of material so carried over. In establishing the heat balance it becomes necessary to deter- mine the combustible still remaining in the ash. The best way of doing this is by analysis. The scheme sometimes used of sub- tracting the percentage of true ash shown by the coal on analysis from the percentage of ash and refuse in the tests and calling the difference the carbon lost in “‘ash,”’ may or may not be correct, depending upon how accurately the “ash”? was determined on the test. Provided the latter is correct, the results of the two methods for carbon in “‘ash” should be the same, and in that sense the carbon in “‘ash” as found from the analysis may be used as an indication of the degree of accuracy of the ‘“‘ash” determination on test. Assuming that the combustible part of the refuse is carbon, there are two ways of determining this combustible. Either a chemical determination of the carbon is made by one of the usual THE TESTING OF STEAM BOILERS 719 methods, or the carbon may be burned out in the calorimeter, when the heat developed divided by the heating value of carbon should give the amount of carbon the sample contained. It may be difficult to keep the sample burning in the calorimeter, even in an atmosphere of oxygen, in which case the expedient of mixing the ash with a certain proportion of some known combustible may be used. Rule XVII. The applicability of Du Long’s or any similar formula to all grades of coal without any differentiation is a dis- puted question. It seems certain, however, that the method of computing heating values from analyses should be used only with great caution in the case of bituminous or semi-bituminous coals. See Chapter XIII for more detailed discussion of this matter, and of the making of coal analyses in general. Rule XX. Condensation of the steam is not in this case an accurate method of obtaining the total heat imparted to the water. Rules XXI, XXII, and the Tables. The subject matter of these rules is closely connected with the interpretation of the meaning of some of the items in the tables. It will therefore be best to consider them together. The value 965.7 B.t.u. given in the Code (Rule XXI) for the heat of vaporization per pound of water from and at 212° F., has been changed to 970.4 B.t.u. by recent accurate researches, and this is the figure that should be employed. The formula for ‘‘ Efficiency of Boiler and Grate ”’ in the same rule does not state whether coal as fired or dry coal is used as the basis of the computation. It is however shown, by Item 73 of Table No. 1, and Item 31 of Table No. 2, that the computation is to be based on dry coal. Appendix XX of the Code states: “When the object of a boiler test is to determine its efficiency as an ab- sorber of heat, or to compare it with other boilers, the efficiency based on com- bustible is the one which should be used; but when the object of the test is to determine the efficiency of the combination of the boiler, the furnace, and the grate, the efficiency based on coal must necessarily be used.” ” Every engineer will in general agree with the distinction made in this statement, but some disagreement of opinion exists whether 720 EXPERIMENTAL ENGINEERING dry coal or coal as fired should be used as the basis of computation for boiler and grate efficiency. If it is desired by this efficiency to characterize the performance of the boiler as a whole under the conditions of operation, it is certainly hard to see why dry coal should be used as a basis, since the coal is in general not dry and the assumption does not therefore conform to actual conditions, and, further, it is easily conceivable that the performance of the boiler and grate might have been quite different had dry coal been actually used. The efficiency based on combustible may serve as a basis of comparison for different boilers, but the efficiency of boiler and grate, the real efficiency of the apparatus, applies only to the particular boiler for which the computation is made, and there would therefore seem to be little reason for making an arbi- trary assumption concerning any test condition. The method of computing the boiler efficiency is not clearly enough defined. As the formula given is ordinarily applied, the term ‘‘ combustible ” does not represent quite the same basis above and below the line. The heat absorbed per pound of combustible would most certainly be computed from the equivalent evaporation per pound of combustible by multiplying the latter by 970.4 B.t.u. (Item 71 of Table No. 1.) But the “ combustible ” used in the derivation of Item 71 (Item 30) is computed from (coal as fired — refuse — moisture). The heating value of the combustible, on the other hand, is usually determined from calorimeter observations, taking ‘‘ combustible ” equal to (coal as burned — calorimeter ash — moisture). The difference lies in the fact that “refuse” and ‘calorimeter ash” are not the same, if fuel is lost through the grate, as it usually is to some extent. The heating value of each pound of combustible as determined under Item 30 is likely to be somewhat less than that given to the combustible on the basis of calorimeter computations, on account of the carbon lost, and the boiler efficiency is therefore generally stated too small, although the difference may not be great in most cases. The footnote to Item 72, defining combustible, is misleading if strictly interpreted as to “ash,” because the equivalent evaporation per pound of combustible is not computed that way. In some reports of tests, a third efficiency, that of the furnace, THE TESTING OF STEAM BOILERS 721 is separately computed. Unless some attempt is made to deter- mine the distribution of the radiation losses between furnace and boiler proper, the furnace efficiency may be expressed as the ratio of boiler and grate efficiency to boiler efficiency. The Code itself calls the Heat Balance given in Rule XXII ‘‘ approximate,” and this is certainly true concerning several of the items, notably Item 4. The heat balance given is based upon combustible, but it is much more common to base it upon the coal as fired, because the method gives a much clearer insight into what becomes of the heat in thecoal supplied to theboiler. Further, such a heat balance is more rational in that it considers the boiler as a whole and thus analyzes the performance not only of the steam generator itself but also of the furnace, which is naturally what is desired in most cases. A complete heat balance should state the following items: 1. Heat loss through incomplete combustion. (a) Loss of fuel through grate and over bridge wall. (b) Loss of combustible in chimney gases. 2. Loss in sensible heat in the flue gas, except that due to moisture. 3. Heat loss due to moisture in the flue gas. (a) Moisture in coal as fired. (b) Moisture formed from combustion of hydrogen in fuel. (c) Moisture as humidity in air used. 4. Heat losses due to radiation and other losses unaccounted for. 5. Heat absorbed in steam. For a complete discussion of the method of computing the heat quantities for Items 1 to 3 inclusive, see pp. 531 to 538, Chapter XIII. Item 4 is obtained by the difference between the heating value. of the fuel as fired and the sum of the rest of the items. Item 5 must be accurately computed, and is in all cases equal to (ar + q¢ — q of feed) B.t.u. times the number of pounds of water evaporated per pound of fuel as fired. The items of Table No. 1 are in most cases self-explanatory in the light of the provisions of the Code. But certain of them call for explanation or comment. 722 EXPERIMENTAL ENGINEERING Items 30, 51, and 53. It has already been pointed out that the “combustible” under 30 is somewhat different in its nature from that determined in either the proximate or chemical analyses, on account of the loss of fuel in refuse, and that the heating values given under 51 and 53 do not therefore strictly apply to the combustible as determined under 30. Item 59 is obtained from 57 by multiplying the latter by the ‘quality of steam (Item 54). This therefore represents the actual weight of dry and saturated steam generated. Item 60. The formula given for the ‘‘ Factor of Evaporation ” is not thermally exact, irrespective of the fact that the denominator should be 970.4. The form given is pe 970.4 (I) in which H (= 2) is the total heat above 32 degrees in dry and saturated steam at the observed pressure, and # = the heat in the feed water above 32 degrees = ¢ — 32, where ¢ is the feed-water temperature. This form neglects the heat carried away from the boiler in the moisture in steam and gives the boiler credit only for the heat that can actually be accounted for in the dry and saturated steam. This method of computation may be satisfactory if the boiler is considered merely as an instrument for generating dry and saturated steam, but considered as an apparatus transferring heat, the basis of computation is not correct. The thermally correct method would lead to a different result for the ‘‘ Equivalent Evaporation from and at 212°.” It is not contended that the method of computation used in the Code is not satisfactory, considering the boiler merely from the standpoint of its ability to generate dry steam, but it should be made clear that the method does not account for all the heat absorbed by the boiler shell. The true factor of evaporation is Ug t-E 32 ar an u THE TESTING OF STEAM BOILERS 723 where the numerator expresses the heat above feed-water tempera- ture in a pound of steam as actually made. 970.4 is the expendi- ture of heat that would have been necessary to generate one pound of dry steam if the feed-water temperature had been 212 degrees and the temperature of the steam made finally also 212 degrees (hence the term “‘ from and at 212 degrees’’). Hence the factor expresses the number of pounds of steam that could have been made from and at 212 degrees with the expenditure of heat applied to a pound of the boiler steam as actually made. It will be seen that the use of such a factor established a common basis (a heat unit of large size) for all evaporative tests and that we are therefore able directly to compare coals as to their evaporative qualities. Item 61. It was pointed out above that a different result may be obtained for this item, depending upon which factor of evapora- tion isemployed. To show the difference between the two methods on a heat basis, let W = weight of water apparently evaporated (Item 57). x = quality of steam (Item 54). EF, = factor of evaporation, form I, given in Code. E, = factor of evaporation, form I above. Then, as per Code, A— t+ 32 Soir. Equivalent Evaporation = W X E, = W X 970.4 The thermally exact method would give Equivalent Evaporation = W ees 970-4 The difference in the results is perhaps best illustrated by an average example. For an absolute steam pressure of 150 pounds, a feed-water temperature of 70 degrees and a quality of steam equal to 98 per cent, the second formula gives a result 3 per cent higher than the first, and consequently all of the ‘‘ Economic Results”’ and the “ Efficiencies” of the table will be higher by the same amount. For greater moisture in the steam the difference will be greater; thus if x = .94, with the same steam pressure and feed- water temperature, the difference is 1.6 per cent. For dry and saturated steam the formulas of course give identical results, 724 EXPERIMENTAL ENGINEERING For superheated steam the second form of the equation for factor of evaporation will read, By = MC (Ta = Ty) = t+ 32 979-4 temperature of the superheated steam temperature of the saturated steam at the same pressure, and mean specific heat in the range from 7; to T>. ? in which Ty T; I Cp CHAPTER XVIII. THE TESTING OF STEAM ENGINES, PUMPING ENGINES, AND LOCOMOTIVES. Tue American Society of Mechanical Engineers has established and adopted codes for the testing of steam engines, pumping en- gines, and locomotives. For the full wording of these codes the reader is referred to the Transactions of the Society.* These codes in general not only discuss the objects of the various tests, and the methods of making the tests, but also go into the matter of instruments to be used, their choice, application, calibra- tion, etc., besides giving methods of computing and presenting the results. In many instances these things have been thoroughly covered, sometimes at greater length, in previous chapters of this book, and to repeat these parts of the code text would therefore lead to unnecessary repetition. Wherever possible such parts have therefore been omitted and proper page references to other parts of the book are given. Additional comment upon some of the provisions is given in footnotes. 361. The Testing of Steam Engines. General Considerations and Definitions. — The Code concerns itself very largely with direc- tions for complete plant tests. The testing of an engine alone is a comparatively simple matter. The test may be made to determine: (a) Economy. (b) Capacity. (c) Mechanical Efficiency. (d) Regulation. * Final Report of the Committee appointed to Standardize a System of Testing Steam Engines, Vol. XXIV, 1903. Report of Committee on a Standard Method of Conducting Duty Trials of Pump- ing Engines, Vol. XI, 1890. Report of the Committee on a Standard Method of Conducting Locomotive Tests, Vol. XIV, 1893 725 726 EXPERIMENTAL ENGINEERING The simple economy test based on I.H.P. requires nothing further than the determination of the amount of steam used, the quality of the steam, the taking of indicator cards, and the recording of the average speed. In such a test it is immaterial by what means the engine is loaded, as long as any given load remains constant for a sufficient length of time. The steam consumption may be determined either from the boiler end or by means of the surface condenser, as the Code provides. The latter method is preferred because of greater accuracy. _ Economy guarantees are sometimes made for other than the rated capacity. Thus many guarantees cover the steam consump- tion at 4 load, full load, and at some overload, as may be agreed upon. In the majority of these cases the guarantees are based upon developed, and not upon indicated, horse power in order to eliminate the mechanical efficiency of the engine. At the same time, separate agreements are made concerning the mechanical efficiency at the different loads. This kind of test requires means for loading the engine, such as brakes, generators, etc. In case electric generators are used to produce the load, it becomes neces- sary to correct for the efficiency of these machines in order to deter- mine the net shaft (developed) horse power, unless the guarantees should happen to be based upon electrical horse power at the switchboard. An economy test for a series of loads, as above described, is really also a test for capacity and for mechanical efficiency. During the progress of such a test a curve should be plotted between horse power and total steam used per hour. It will be found, if the work is accurate, that this curve is usually a straight line up to heavy overloads on an engine. This line is a graphical expression of Willan’s law and is known as Willan’s line. It serves as a check upon the accuracy of the test results as the test proceeds, and the tests may be considered completed if the highest load in a series gives-a total steam consumption which is markedly off the line of the previous results. The report on an economy test should include three curves: Willan’s line, the relation between load and steam consumption per L.H.P. or per D.H.P. per hour (water-rate), and the relation TESTING STEAM ENGINES AND LOCOMOTIVES 7297 between load and mechanical efficiency. Figure 491 shows a typical example of these curves for an automatic engine. Regulation tests are usually not a part of the regular economy test. It is true that testing an engine under a series of loads will usually reveal that there is a certain amount of change in the aver- age speed from load to load, the engine running a few turns per minute faster under low than under high loads, but that is no certain indication of the regulation. ‘To obtain a reliable test for regulation, means should be provided to record the speed continuously. The : Economy Test of a 15x Automatic Engine. Steam Press. Ay. R.P.M. 220. 5 a : a 8 4000 3 90 5 a oO Oo q % q s 80 3 a we E 3000 70 8 3 4 4 60 & 3 E 2000 40 50 3 & 30 1000 20 4 4 1 14 Load 20 40 60 80 100 120 140 160 LEP. Fic. 491. — WATER-RATE AND MECHANICAL EFFICIENCY CURVES FOR A Steam ENGINE. test is then made by suddenly throwing load on or off. Figure 492 shows the results obtained on a regulation test of a 12’ X 18” X 10” tandem compound engine, the load variation being 125 H.P. Time and revolution records were taken by means of a chronograph. The curve shows that the engine was running at 280.5 R.P.M. under a load of 125 H.P. and at 283.5 R.P.M. at no load. The mean speed is 282 R.P.M., the speed variation is 3 R.P.M. The percentage of total variation, based on mean speed, is therefore : AeR M@rorS = = 2 Be 508 ts Se os en cae ts 4 7 * ‘Boiler Pressure dey \ \ x \ \ ° \ \ \ \ \] \l \ gh a Bo ee o. 1 2 | c Fic. 497. fe Pressure Cc g | \ | eee K = 1S Atmos. Line 7 | | Mi-———— ———— — +--+ dJ Line of Zero Pressure” Fic, 498. ‘Boiler Pressure N po eee \ \ \ CN is determined in the same way as RS in Fig. 497 t I 1 t i 1 { { ! ! SSS 3H ti y Atmos, Line \ Weve ed Se eee SSS SS SS iS Ke emerald x Line of Condenser Presure! * Line of Zero Pressure FIG. 499. 1oe 752 EXPERIMENTAL ENGINEERING Boiler Pressure N ~ I | I ! 1 I I ! I I ! 1 NC is determined for the high-pressure diagram in the same way as RS in Fig. 497. | ! i I ! 1 ' ' 1 ! ! ! ! ! 1 1 I | | ! | | / I I i I / t t i i I f I ne ee ua J % Zero Line of Pressure Naive of Pressure in Condenser FIG. 500. TESTING STEAM ENGINES AND LOCOMOTIVES 753 the distance CV is found ina similar way. In Fig. 500 the distance CN for the high-pressure cylinder is found in the same manner as in the case of a simple engine. The mean effective pressure of the ideal diagram can readily be obtained from the formula AC + Hyp. Log. R.) — p. (z) where P is the absolute pressure of the steam in the boiler, R the ratio Mn and the pressure of the atmosphere or in the condenser. XCXI. STANDARDS OF Economy AND EFFIciENcy. — The hourly consump- tion of heat, determined by employing the actual temperature of the feed water to the boiler, as pointed out in Article IX of the Code, divided by the indicated and brake horse power, that is, the number of heat units consumed per indicated and per brake horse power per hour, are the standards of engine efficiency recommended by the Committee. The consumption per hour is chosen rather than the consumption per minute, so as to con- form with the designation of time applied to the more familiar units of coal and water measurement, which have heretofore been used. The Brit- ish standard, where the temperature of the feed water is taken as that corresponding to the temperature of the back-pressure steam, allowance being made for any drips from jackets or reheaters, is also included in the tables. It is useful in this connection to express the efficiency in its more scientific form, or what is called the ‘‘thermal efficiency ratio.” The thermal eff- ciency ratio is the proportion which the heat equivalent of the power devel- oped bears to the total amount of heat actually consumed, as determined by test. The heat converted into work represented by one horse power is 1,980,000 foot-pounds per hour, and this divided by 778 equals 2545 B.t.u. Consequently, the thermal efficiency ratio is expressed by the fraction 5A B.t.u. per H.P. per hour MEMORANDA REGARDING THE BRITISH STANDARD. — The principal objec- tion which the Committee has to the use of the British standard of engine economy for the leading place is as follows: The practical utility of an engine depends almost wholly upon the fact that it is used for some form of industrial work, and, in combination with a boiler and various appurtenances, it is a part of a complete power plant. Were it not for the unreliable character of coal and other fuels, the proper standard of economy for such an engine, with a boiler of given efficiency, would be the fuel consumed, because fuel is, in reality, the source of the power, and this is the most important thing to be supplied in operating the engine. The use of a standard of heat units in place of fuel meets the objection- able characteristics of coal due to its heat variability, and in doing this it 754 EXPERIMENTAL ENGINEERING makes no change in the conditions under which the standard should be employed. These are the actual conditions of use, and not the ideal conditions. The British method furnishes a means of determining and stating the ideal performance of an engine working under assumed condi- tions. It does not give the performance of the entire engine plant under the actual conditions as affected by the efficiency of the heaters and auxili- aries, and the performance under such conditions is usually of the greatest importance. The advantages in favor of the British standard are as follows: 1. It expresses the economy of the engine as an independent machine, unaffected by the failings of the feed-water heater or condenser. 2. In this form it is useful for expressing the economy of an engine in the testing shop of an engine builder, or in the mechanical laboratory of a college, where it forms no part of a power plant. 3. A comparison of the British standard with the economy of an ideal engine working between the same limits of temperature reveals those losses going on which are due to the engine alone, and this furnishes information not otherwise obtained. The arrangement of the various forms used in stating the efficiency, as proposed by the Committee, gives due weight to both of these standards, placing the one in the lead which is regarded as the most important. XXII. Heat Anatysis. — For certain scientific investigations it is useful to make a heat analysis of the diagram, to show the interchange of heat from steam to cylinder walls, etc., which is going on within the cylinder. This is unnecessary for commercial tests. For details of the method of carrying out such heat analysis, see Art. 365, p. 799 of this book. XXIII. TemMprerature-Entropy Diacram. — For method of drawing such a diagram and explanation of what it shows, see Art. 354, p. 670. XXIV. Ratio oF Economy oF AN ENGINE TO THAT OF AN IDEAL ENGINE. — The ideal engine recommended for obtaining this ratio is that which was adopted by the Committee appointed by the Civil Engineers of London to consider and report a standard thermal efficiency for steam engines. This engine is one which follows the Rankine cycle, where steam at a constant pressure is admitted into the cylinder with no clearance, and, after the point of cut-off, is expanded adiabatically to the back pressure. In obtaining the economy of this engine the feed water is assumed to be returned to the boiler at the exhaust temperature. Such a cycle is preferable to the Carnot for the purpose at hand, because the Carnot cycle is theoretically impossible for an engine using superheated steam produced at a constant pressure, and the gain in efficiency for superheated steam corresponding to the Carnot efficiency will be much greater than that possible for the actual. cycle. The ratio of the economy of an engine to that of the ideal engine is obtained TESTING STEAM ENGINES AND LOCOMOTIVES 755 by dividing the heat consumption per indicated horse power per minute for the ideal engine by that of the actual engine.* XXV. MisceLLaneous. — In the case of tests of combined engines and boiler plants, where the full data of the boiler performance is to be deter- mined, reference should be made to the directions given by the Boiler Test Committee of the Society, Code of 1899. (See Chap. XVII of this book.) In tests made for scientific research, and in those made on special forms of engines, the line of procedure must be varied according to the special objects in view, and it has been deemed unnecessary to go into particulars applying to such tests. In testing steam pumping engines and locomotives in accordance with the standard methods of conducting such tests, recommended by the committees of the Society, reference should be made to the reports of those committees in the ‘‘ Transactions.”’ (See also pages following). XXVI. Report or Test. — The data and results of the test should be reported in the manner and in the order outlined in one of the following tables, the first of which gives, it is hoped, a complete summary of all the data and results as applied not only to the standard heat-unit test, but also to tests of combined engine and boiler for determining all questions of performance, whatever the class of service; the second refers to a short form of report giving the necessary data and results for the standard heat test; and the third to a * The Code gives means of computing the heat consumption of the ideal cycle described, reproducing a set of curves from the Minutes of the Proceedings of the Civil Engineers of London. It is not thought necessary to reproduce this here, espe- cially since the Mollier Diagram, Fig. 245, gives practically the same information, based upon later data. To show the method of using the Mollier chart, take the following examples: Steam pressure 135 lbs. abs.; back pressure 15 lbs. abs. Assume steam dry and saturated at cut-off. The chart shows that the heat content of the steam at the higher pressure is 1193 B.t-u. After adiabatic (isentropic) expansion to 15 lbs., the heat content is 1031 B.t.u. Out of each pound of steam, 1193 — 1031 = 162 B.t.u. are therefore converted into work. The number of pounds of steam required per 1.H.P. hour, when operating on the ideal cycle, will then be 4’? = 15.71 lbs., and the heat consumption of the ideal engine per I.H.P. hour will then be 1193 X 15.71 = 18,742 B.t.u. If the steam at 135 Ibs. abs. pressure had been superheated to 500° (= 150° of superheat), and expanded to 15 lbs. abs., as before, the figures would have been: Heat content at 135 lbs. and 500° = 1273 B.t.u.; heat content at 15 lbs. abs. = 1093 B.t.u.; heat converted into work per pound of steam = 180 B.t.u.; steam consump- tion of ideal engine = 754? = 14.14 pounds; heat consumption of ideal engine = 14.14 X 1273 = 18,000 B.t.u. per hour. The ideal cycle above outlined is by many authorities called the Clausius instead of the Rankine cycle. The latter is then defined as the cycle in which isentropic expansion is not carried to back pressure as in the Clausius, but stops at some terminal pressure higher than the back pressure. See the discussion on theoretical cycles, in Chap. XI of this book. 756 EXPERIMENTAL ENGINEERING short form of report for a feed-water test. It is the intention that the tables should be full enough to apply to any type of engine, but where not so, or where special data and results are determined, additional results may be inserted under the appropriate headings. Although these forms are arranged so as to be used for expressing the principal data and results of tests of pump- ing engines and locomotives, as well as for all other classes of steam engines, it is not the intention that they shall supplant the forms recommended by the committees on Duty Trials and Locomotives, in cases where the full report of a test of such engines is desired. _ It is recommended that any report be supplemented by a chart in which the data of the test is graphically presented. TABLE NO. I. Data AND RESULTS OF STEAM-ENGINE TEST. Arranged according to the Complete Form advised by the Engine Test Com- mittee of the American Society of Mechanical Engineers. Code of 1902. 5 MD ALENOL CRIA 1. + isucnAcwa na pine o udden aieeeioedas gacanets dues 2 Zev gungedanewinwndawiraniaes ein Type of engine (simple, compound, or other multiple expansion; condens- Ing OF NOM=CONdENSING):, «<2. av edocs gages wh ek Re ORES Cade eH RR Class of engine (mill, marine, locomotive, pumping, electric, or other). ... Ratéd. powerOf €ngine:...5.cce0 cased a see eee aue eee Ra ee dee a Name Or builders. esjase chien ie a8 acne bm see SSpN Re ode Liao tonutata wes Number and arrangement of cylinders of engine; how lagged; type of con- CBSE. Gia 4 iade seh he Ne aed ERE see EEE aaa were enihee e Ss EV POiGE VALVES). cio kati Sarat ake tataw aduad GME ohne ls hme Sede aeale aaa 6; Ly pero bollétissajemeve ves oars wien ee Ye ox eae eR ESR aT ee teas to. Kind and type of auxiliaries (air, circulating, main, and feed pumps; Jackets: Heaters Etsy aaa Me aaheles ana beak} olan aoa doa cunt aay eA wir Be COP % ; ; : 1st Cyl. 2d Cyl. 3d Cyl. 11. Dimensions of engine............... 0.000 c eee (a) Single or double acting................. (b) Cylinder dimensions: NBOLE 2253 ses. sudl wie ard GS kote ucsee gael in SITOK Gs a4. uticckaes ot ane 2 Gay adie yo Sake ft Diameter of piston rod............. in. Diameter of tail rod................ in. TESTING STEAM ENGINES AND LOCOMOTIVES 757 ast Cyl. 2d Cyl. 3d Cyl. (c) Clearance in per cent of volume displaced by piston per stroke: Head 6nd sists Ge a8 sana awe s.nnn Sawn AVETARE 4 a. oes taved oan ete eee ee Ha (d) Surface in square feet (average)......... Barrel of cylinder...........0.0.0.... Cylinder heads: suc cusesasee oh ee kes Clearance and ports.................. Ends of piston....................... (e) Jacket surfaces or internal surfaces of cyl- inder heated by jackets, in square feet: Barrel of cylinder.................... Cylindé’ headsss eersuscnavteda canes Clearance and ports.................. Receiver jackets..................... (f) Ratio of volume of each cylinder to volume of high-pressure cylinder. (g) Horse-power constant for one pound mean effective pressure, and one revolution Per MiNUt. oe cecaeeeeeee Re 12. Dimensions of boilers: (a) Num bet sate setts Yak doa ae ekg dean hae wad (6) Total grate surface.............0000000.00 00000 q. ft (c) Total water-heating surface (external)............ (d) Total steam-heating surface (external)............ 13. Dimension of auxiliaries: (a) Air pulm pia ks Gaines dha hWe kaon Lee Ae deleee eacusnte ede oes 15. Size, length, and number of turns in main steam BIS leading from the boiler ‘to: thesengine® r,s ead cage sae va he caee eerie de Beaeas 16. Give description of main features of plant, and illustrate with drawings to be given on an appended sheet. 758 EXPERIMENTAL ENGINEERING Total Quantities, Time, Etc. 17, -Dutation of testes secs eveyone kee ge sate dsed hese ee hs hours. 18. Length of time engine was in motion with throttle open. . 19. Length of time engine was running at normal speed...... 20. Water fed to boilers from main source of supply......... lbs. 21. Water fed from auxiliary supplies: (ONE eee Ue aR Sahar aOtuman aah satiate eataemens a (OD) SA Shee sa so ag eee Bee Se eee ele e oi CO) as naa er teas catia watebe Meieeg te eer aunts ae AO od as * 22. Total water fed to boilers from all sources.............. . 23. Moisture in steam or superheating near throttle......... per cent or deg. 24. Factor of correction for quality of steam, dry steam being UNLEY Sch git ee bag OWA oo wie watnadeeWwa ata MiNi: 25. Total dry steam consumed for all purposes *............ Ibs. 26.. Total: coal asfired Fs secon ive cace gets s ateaavien cue sacle 29; Moisturésin;-coal, wicuarsses a taude tetas are eee ees per cent. 28. Total dry coal consumed..............0.000000000000 Ibs. 20, INSWvand telUus@e.2 Find oe ae aceciimatie we a dieeedeeae ae ee 2 30. Percentage of ash and refuse to dry coal................ per cent. 31. Calorific value of coal by calorimeter test per pound of dry coal, determined by............... calorimeter....... B.t.u. 32. Cost of coal per ton of 2240 Ibs...................00000, $ Hourly Quantities. 33. Water fed from main source of supply.................. lbs. 34. Water fed from auxiliary supplies: OY gates hat foe nt Nes Atolls hse Gok tacacst aon ghia aed dha aay et CD) Pca ted Ane a eal dst Siy isehd Goda patente setae eaten Oe e CO) san eipelseg'e dis ate arse wat eed Bh Seuie Da Akg ea Asa s wae eh a 35. Total water fed to boilers per hour.................... - 36. Total dry steam consumed per hour. ............... s 37. Loss of steam and water per hour due to drips from main steam pipes and to leakage of plant.................. Hs 38. Net dry steam consumed per hour by engine and auxiliaries ee 39. Dry steam consumed per hour: (a) Main cylinders... 2.0.0... cece cee eee oe (b) Jackets and reheaters...............-..00-0.-00, ae (6) CATR UTD) eaisee haces suede Seno seea s Hise tee pce ok * In case of superheated steam engines, determine, if practicable, the tempera- ture of the steam in each cylinder. + Where an independent superheater is used, this includes coal bummed in the superheater. 40. 41. 42. 43. 45. 46. 47. 48. 49. 50. SI. 52. 53- 54. 55: 56. 57: 58. 59. 60. 61. 62. 63. TESTING STEAM ENGINES AND LOCOMOTIVES 759 (d) Circulating pump..........0.00.00.0 00. c cece eee ee Ibs. (e) Feed-water pump...........0.. 0000 cece eee ees Hs (f) Other auxiliaries..... 20.0... ‘ Dry coal consumed per hour: (a) During running period.......................... me (6) During banking period. ........................ te Covi Total eyes coniak tie hola Cay anereaet etisalat «ane all . Injection or circulating water supplied condenser per hour. cu. ft. Pressures and Temperatures (Corrected). Steam pressure at boiler by gauge..................... Ibs. per sq. in. Steam-pipe pressure near throttle, by gauge............. « Barometric pressure of atmosphere in inches of mercury. . ins. Pressure in first receiver by gauge..................... Ibs. per sq. in. Pressure in second receiver by gauge..................5 o Vacuum in condenser: (a) In inches of mercury. .........0.00 000.0 0c eee eee ins. (0) Corresponding total pressure............ eee Ibs. per sq. in. Pressure in steam jacket by gauge................ 00005 “ Pressure in reheater by gauge............... 000 cee eee Moisture in steam or superheating at boilers............ p. c. or deg. F. Superheating of steam in first receiver................. deg. Fahr. Superheating of steam in second receiver............... eS Temperature of main supply of feed water to boilers..... Temperature of auxiliary supplies of feed water: ce COV a sia Decay aatgahyata ah wea eS am eae PRPs ele Gd " (CD) sere wlareta date Setar are area Laos Seana geet eee i (OES Gk a Se epatssad en heel oe esi Gown ities KEE a #5 Ideal feed-water temperature corresponding to the pressure of the steam in the exhaust pipe, allowance being made for heat derived from jacket or reheater drips......... " Temperature of injection or circulating water entering con- Temperature of injection or circulating water leaving con- Mapes er uk ndanamonaeenataade ans Temperature of chimney gases entering economizer....... Temperature of chimney gases leaving economizer....... Temperature of water entering economizer.............. Temperature of water leaving economizer............... Temperature of airin boiler room. .................. Temperature of air in engine room..................005 760 EXPERIMENTAL ENGINEERING Data Relating to Heat Measurements. 64. Heat units per pound of feed water, main supply........ B.t.u. 65. Heat units per pound of feed water, auxiliary supply: CD) chai Race aac AN Sanh ois Geta gat eran Mae erg ap treaties eS (B)) are Ue cicatgieg ak tea nwa De ga DON Soames mane BRE ee EES UG)" osesciatnainanres Cos Me SOaN GA Wasnt e nena cad neatane “s 66. Heat units consumed per hour, main supply............ : 67. Heat units consumed per hour, auxiliary supplies: CG): 1k ct yaheecencitona Mere ete oeneie te Rca alirage Enea ethene “ MOD cre hee oben Mietincgmles aeatelnk Wale Atal, BUh AUN dtlek wats a8 ee UG) SRG G BAe OS eae ORO a REDE 68. Total heat units consumed per hour for all purposes... ot 69. Loss ef heat per hour due to leakage of plant, drips, etc.. = 70. Heat units consumed per hour: (a) By engine alone <5 cia sea Gee sevagi ooten eevee as QO) By auxiliaries: cc cqegsucoheaciaeeragas ovens hs 71. Heat units consumed per hour by the engine alone, reck- oned from temperature given in line 55..,,,,.....500- ee Indicator Diagrams. 1st Cyl. 2d Cyl. 3d Cyl. 72. Commercial cut-off in per cent of stroke........ 73. Initial pressure in lbs. per sq. in. above atmos- PHETEr sg ca2nit suelidal sane nian veo sae ian 44. Back-pressure at mid-stroke above or below atmosphere in lbs. per sq. in... 6... 0.0002. 45. Mean effective pressure in lbs. per sq. in........ 76. Equivalent mean effective pressure in lbs. per sq. in.: (a) Referred to first cylinder................ (b) Referred to second cylinder............. (c) Referred to third cylinder.. . ......... 77. Pressures and percentages used in computing the steam accounted for by the indicator dia- grams, measured to points on the expansion and compression CUIVeS............0....00. Pressure above zero in lbs. per sq. in.: (a) Near cut-off (by: Near release si: sins eencue es on dshawe ean (c) Near beginning of compression........... 78. 79: 80. 81. 82. 83. 84. 85. 87. 88. 89. go. ol. 92. 93- TESTING STEAM ENGINES AND LOCOMOTIVES 761 ast. Cyl. 2d Cyl. 3d Cyl. Percentage of stroke at points where pressures are measured: Co) Near satelins sdhiteicorasia ecu eee (b) Nedr-veleast.c.cu os cidise Se peeked at as s (c) Near beginning of compression.......... Aggregate M.E.P. in lbs. per sq. in. referred to each cylinder given in heading.............. Mean back-pressure above zero, lbs. per sq. in... Steam accounted for in lbs. per indicated horse power per hour: (@) NGAP CULO His us .cmacanss Woraw ds dame hdc (8): Near release: 26 oop Gana ee hee es Ratio. of Expansion ec ug.c4 ee cut eas sede ee eee wean’ Mean effective pressure of ideal diagram................ Ibs. per sq. in. Diaeranit TACO ti nadwd enesewicike ays based Phin deeb aoe yore os per cent. Speed Revolutions per minute. ................. 000 cee eee rev. Piston speed per minute................ 00000-0200 ft; . Variation of speed between no load and full load........ rev. Fluctuation of speed on suddenly changing from full load to no load, measured by the increase in the revolutions divewta the change. see ewe de sjee bas whtwasdae ios Power. Indicated horse power developed by main-engine cylinders: First) cylinders evan pvases duiedaree hem eee daeree iss HP Second Cylinders seeded edge een ace We baiehiadan mae as Mite Gy lind etic icc Wi eu oanaeas AAD Law Aes aes a Total ouc5 eatin s 3 hoe let es BISSAU new e eed aw SES OR EAL s “ Brake H.P., electric H.P., pump H.P., or dynamo H_P., according to the class of engine. .... .............. # Friction I.H.P. by diagrams, no load on engine, computed for average speed ssc vos4 ckyeshie kt Gcaekate es peak eee - Difference between indicated H.P. and brake H.P........ se Percentage of indicated H.P. of main engine lost in friction. _ per cent. Power developed by auxiliaries: OV) we pled ts emtedt antigen Dae ana ncdatweetochs cell coupe Mn ae HLP. (CD)S: Aaceia eats Btu eR ay B.caeeiat Ascent: anes pence Rae eae Cea AS - O) ac csiecctninte ig Syd heap eens ean Pd Sees a PIE A AS es 762 EXPERIMENTAL ENGINEERING Standard Efficiency Results. Heat units consumed by engine and auxiliaries per hour: (a) Per indicated horse power..................0005 B.t.u. (b) ‘Per brake horse powe.s..0..ccucaverdver oes pads « a 95. Equivalent standard coal consumed by engine and auxil- jaries per hour, assuming calorific value such that 10,000 B.t.u. are imparted to the boiler per lb.: (a) Per indicated horse power....................0.- ‘Tbs. (b) Per brake horse power..................0000000- 96. Heat units consumed per minute: (a) Per indicated horse power....................... B.t.u. (6) Per brake horse power..................0 0000s 97. Heat units consumed by engine per hour corresponding to ideal maximum temperature of feed water given in line 55, British standard: (a) Per indicated horse power....................04. (0) Per brake horse power.....................0000. Efficiency Ratios. 98. Thermal efficiency ratio: (a) Per indicated horse power...................000. per cent. (b) Per brake horse power...................0000004 = (c) Ratio of efficiency of engine to that of an ideal en- gine working with the Rankine cycle........... “ Miscellaneous Efficiency Results.* 99. Dry steam consumed per indicated H.P. per hour: (a) Main cylinder, including jackets................ Ibs. (b) Auxiliary cylinders, etc.........0..00...000. 2000. es (c) Engine and auxiliaries................0..0.000, 100. Dry steam consumed per brake H.P. per hour: (a) Main cylinders, including jackets............... lbs. (0) Auxiliary cylinders, etc... .......00.0..0 0. eee es (c) Engine and auxiliaries......................... ror. Percentage of steam used by main-engine cylinders ac- counted for by indicator diagrams: (a) Near cut-off....0...000.0000..00...... me? Seep (b) Near release.................000.000., * The horse power on which the above efficiency results (items 94 to 103) are based is that of the main engine, exclusive of auxiliaries. TESTING STEAM ENGINES AND LOCOMOTIVES 763 102. Dry coal consumed by combined engine and boiler plant per I.H.P. per hour: (a) During running period........................ Ibs. (6) During banking period... ..........0..0.00-00. a NG) BUSCA ies a earn wenn anin anna aypshibaeN aoo ec 103. Dry coal consumed by combined engine and boiler plant per brake H.P. per hour: (@) During running period.............0..00..000... (6) During banking period................0..00... Cys ORAS vou cinch tion dedi at peat enh ee a ee 104. Water evaporated under actual conditions per pound of Oty Coal cakes Geaiiae tone ees oe ee ee aes dis Ibs 105. Equivalent evaporation from and at 212° F. per pound of Uy COAL a cota iaa: AG Re RAMS She Laces neers 5 a 106. Efficiency of boilers based on dry coal................. per cent. 107. Combined efficiency of boiler and engine plant. ...... Additional Calculations Recommended for Special Classes of Steam Engines. Water-pumping Engines. 108. Duty per 1,000,000 heat units imparted to the boiler... . ft.-lbs. tog. Duty per 1000 pounds of dry steam................... es 110. Duty per 100 pounds of actual coal consumed by plant.. 6c 111. Number of gallons of water pumped in 24 hours........ gals. Locomotives. 112. Dynamometric horse power................00000 0000s HP. 113. “Standard Coal” of 12,500 B.t.u. value consumed, per dynamometric H.P. per hour..... .............04. Ibs. Electric-light Engines and those Driving Generators for Electric Railways. Tide CUCM ES fy o'5.0 ekei cha cana eae age MSc ew hip we ee oaths amperes, Ers.. Electro-motive forces 42 2:4.n2voae vi eevee ere se ced volts. 116. Electrical power generated in watts................... watts. 117. Electrical horse power generated...................... H.P. 118. Efficiency of generator. .............00.02 2000 per cent. 119. Heat units consumed per electrical horse power per hour B.t.u. 120. Dry steam consumed per electrical horse power per hour lbs. 121. Dry coal consumed per electrical horse power per hour: (a) During running period....................004. Ibs. (6) During banking period....................00.. “co 764 EXPERIMENTAL ENGINEERING Additional Data. Add any additional data bearing on the particular objects of the test or relating to the special class of service for which the engine is used. Also give copies of indicator diagrams nearest the mean and the corresponding scales. TABLE NO. II. DaTA AND RESULTS OF STANDARD HEAT TEST OF STEAM ENGINE. Arranged according to the Short Form advised by the Engine Test Committee of the American Society of Mechanical Engineers. Code of 1902. w 5 ce 0 ® 2 =I Q Cy © wn wn ° e @ DB gg . 3 a @ a ° ° ph ° ° = Qa @ 5 wn o a ; 2 ; : tst Cyl. 2d Cyl. 3d Cyl. 4. Dimension of main engine: (a) Diameter of cylinder................. in. (6) Stroke of pistotes <2 26 ah: 805 ad eee aun ft. (c) Diameter of piston rod............... in. (d) Average clearance................... p.c. (e) Ratio of volume of cylinder to high-pres- Sureevlinder. G44. oan eee ae ae (f) Horse-power constant for one pound mean effective pressure and one revolution per ATUL LES si lac ch ae irre trata sete Bae RS ce 6. Diration Of testis occ oss cai acavevnnsaansocaevanenees hours. 7. Total water fed to boilers from main source of supply.... lbs. 8. Total water fed from auxiliary supplies: (Oil paieiag chee a th atin maw Daten Meo eee ty Sat Mess s (D)e crural anla alee ha soe i ae Googe eel ee “a MOMs rch dhncaitaun ney eercog eas Di ct SR Oe Mar as, dente al ef 9. Total water fed to boilers from all sources.............. to. Moisture in steam or superheating near throttle......... p. c. or deg. 11. Factor of correction for quality of steam................ 12. Total dry steam consumed for all purposes............. lbs. 13. 14. ts. 16. 17. 18. IQ. 20. ois 22s 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33- 34. TESTING STEAM ENGINES AND LOCOMOTIVES 705 Hourly Quantities. Water fed from main source of supply.................. lbs. Water fed from auxiliary supplies: (O) | wissiicete santas aes Sa tae acess BS Sas da ee aS e CO) eines Seka eb WN pita ett Spee coh SER GALE IED Re a 1g aS CGY) asad en a a tee agli en age ea ad a Total water fed to boilers per hour.................... - Total dry steam consumed per hour. ................ x Loss of steam and water per hour due to drips from main steam pipes and to leakage of plant.................. a Net dry steam consumed per hour by engine and auxiliaries a Pressures and Temperatures (Corrected). Pressure in steam pipe near throttle by gauge........... Ibs. per sq. in. Barometric pressure of atmosphere in inches of mercury. . ins. Pressure in receivers by gauge..............0..00 0000 ee lbs. per sq. in. Vacuum in condenser in inches of mercury.............. ins. Pressure in jackets and reheaters by gauge.............. Ibs. per sq. in. Temperature of main supply of feed water.............. deg. Fahr. Temperature of auxiliary supplies of feed water: UO ihe ates Se aun sow eter w ie i aie a ah iell is . KD). uosouin ea deh Soak oh ones osama ne em eee gees es # UG) Sor Septhrea ween eh nee Ye ane ae BOs ee Ee Se see aE o Ideal feed-water temperature corresponding to pressure of steam in the exhaust pipe, allowance being made for heat derived from jacket or reheater drips........ Data Relating to Heat Measurement. Heat units per pound of feed water, main supply........ B.t.u. Heat units per pound of feed water, auxiliary supplies: (GY mace: ner anciiee bdo t punked Ghar wh 3g eRe aie ts (OV psoas se BES GRR eRe elie haa wan Maire Geg er (ONS cha ask ks eae ea ken Gey RSE eee eee ss Heat units consumed per hour, main supply............ Heat units consumed per hour, auxiliary supplies: "EY a cheasiesk Miaiaden SER Boerne aa he mee core i (DY ee lloiny shi dieses a crate manfa ald ease AMO ie es a : (6 ee ee ee Total heat units consumed per hour for all purposes...... Loss of heat per hour due to leakage of plant, drips, etc. Net heat units consumed per hour: (a) By engine alone... ...... 2.02.0 eee eee eee es (B) By auxiliaries, 00. Heat units consumed per hour by engine alone, reckoned from temperature given in line 26.............-.-.-- 766 EXPERIMENTAL ENGINEERING Indicator Diagrams. ast Cyl. 2d Cyl. 3d Cyl. 35. Commercial cut-off in per cent of stroke........ 36. Initial pressure in pounds per square inch above atMOSPHEre ne cuss uae ne wba deaminase 37. Back pressure at mid-stroke, above or below at- mosphere in pounds per square inch......... 38. Mean effective pressure in Ibs. per sq. in........ 39. Equivalent mean effective pressure in lbs. per SQV TU iss ny dincadcuednne Maat dengue wees (a) Referred to first cylinder............... (b) Referred ro second cylinder............. (c) Referred to third cylinder............... 4o. Pressures and percentages used in computing the steam accounted for by the indicator dia- grams, measured to points on the expansion and compression curves. Pressure above zero in lbs. per sq. in.: (a) Near cut-off..... 00. CD) Near release): oo. aceite a. cos partie 'g abdehboe ais eae (c) Near beginning of compression. ........ Percentage of stroke at points where pressures are measured: (@) Nearcut-Offen: cos ss be Hea eae ees (8) Near release........ 000. c cece ccc e eee (c) Near beginning of compression.......... 41. Steam accounted for by indicator in pounds per I.H.P. per hour: (@) NGAP CU+OM ocean een poeta das meaurnees (0) Near release.........00.0.0-0....00 00000 42. Ratio of expansion......................000. 43. Revolutions ver minute...................0.,. rev. Power. 44. Indicated horse power developed by main-engine cylinders: Pirst-Cylindets es civsu ee kates egal oad aeaden keene ned H.P. Second cylinder..........0000.00000.0000.0.0..20. : “s Third cylinder, 00.0... eee a RObAL sais sawcinesaeiehead Gen Sinsad Maee a teed mn Oe eaneat a 45. Brake horse power developed by engine................ TESTING STEAM ENGINES AND LOCOMOTIVES 767 Standard Efficiency and other Results.* 46. Heat units consumed by engine auxiliaries per hour: (a) Per indicated horse power..............0.c0c00ee B.t.u. (b) per brake horse power.............0. 0.0. ccc aeus 7 47. Equivalent standard coal in Ibs. per hour: (a) Per indicated horse power................00..00. Ibs. (b) Per brake horse power................00.000c eee - 48. Heat units consumed by main engine per hour correspond- ing to ideal maximum temperature of feed water given in line 26, British standard: (a) Per indicated horse power.............00000 0000s B.t.u. (b) Per brake horse power............0..00 cece eevee 49. Dry steam consumed per indicated horse power per hour: (a) Main cylinders including jackets...............-. Ibs. (0) Auxiliary cylinders.........0.0.0. 00.00. c eee ees " (c) Engine and auxiliaries............0.00. 0c e eee 50.. Dry steam consumed per brake horse power per hour: (a) Main cylinders including jackets...............-. (b) Auxiliary cylinders............000 0000.0 cee eees (c) Engines and auxiliaries................-..00 000s 51. Percentage of steam used by main-engine cylinders ac- counted for by indicator diagrams, near cut-off of high- Pressure Cylinders 255 psd p endo Somer elke eeu eCnne per cent. Additional Data. Add any additional data bearing on the particular objects of the test or relating to the special class of service for which the engine is used. Also give copies of indicator diagrams nearest the mean, and the corresponding scales. TABLE NO. III. Data AND RESULTS OF FEED-WATER TEST OF STEAM ENGINE. Arranged according to the Short Form advised by the Engine Test Committee of the American Society of Mechanical Engineers. Code of 1902. * The horse power referred to above (items 46-50) is that of the main engine, exclusive of auxiliaries. 768 EXPERIMENTAL ENGINEERING 5d, Datierol tialaca paccdhgeow sid aa Mewk eae NET STORE GaN eens Sole eee 3. Type of engine (simple, compound, or other multiple expansion; condens- ing or non-condensing)... 01-6. 66-66 e eee ee eet eee ees Class of engine (mill, marine, locomotive, pumping, electric, or other).... Rated power of enging.....cncsep vena ntnuias G8 cet henna neues Name OF builders. yun cera ge tao isda edd pa aie Reo es eee BE eRe Number and arrangement of cylinders of engine; how lagged; type of walvessand of Condensers. oo... ¢25c¢e 0 ces e eee news he este aoe eas sagas 8. Dimensions oféngines a4 vesneeses jane de (a) Single or double acting. ......-......-- (b) Cylinder dimensions: BOLE sad ta wean e MOM ome thaws in. S tGkenieh oa ie sald wie een Meee ft, Diameter of piston rod............. in. Diameter of tail rod................ in. (c) Clearance in per cent of volume displaced by piston per stroke: FLEA ONG ee aidegc cd Aas See Gees Cram Cd ects coven duis esi hanna nc RoR eos ANELABC csccdeucde de pee ee Ria ee ha tes (d) Ratio of volume of each cylinder to volume of high-pressure cylinder.............. (e) Horse-power constant for one pound mean effective pressure, and one revolution PSl MINUEs . sie spain Hele eae ew ails GO. Duration-of teste y.ccceucee 2vaupeyarsiapenaeengees hours. to. Water fed to boilers from main source of supply......... lbs. 11. Water fed from auxiliary supplies: (Cage dd Sok enivern pale reshe aaghrey Wants ane aores hPa oe e CONS dy Bcc te Bie het Rote Buh ee be shah cha phn n aleaia hea cece ms a CG). iy eetemyl nd wigawe Ge aay aes han be St AMORA Sie arta 7 12. Total water fed from all sources..................22055 “ 13. Moisture in steam or superheating near throttle *........ p. c. or deg. 14. Factor of correction for quality of steam. ........... 15. Total dry steam consumed for all purposes. ........... lbs. * Tn case of superheated steam engines, determine, if practicable, the temperature of the steam in each cylinder. 16. 17. 18. 19. 20. 2i. 22. 23. 24. Dis 26. 27. 28. 20. 30. aq, 32. 33- 34. 35: 30. TESTING STEAM ENGINES AND LOCOMOTIVES 769 Hourly Quantities. Water fed from main source of supply................. lbs. Water fed from auxiliary supplies: (GY ic had Rissa Ee CS ERG hale Pea OTN ECR SS e ED) sien insti ys hee door le ite ee ed Sa tale Rin Rl ee Be (Cae aes sate rete teh ohh oa ny Mase Ry iene Read tat rae ae Total water fed to boilers per hour. =. ...... 00... “ Total dry steam consumed per hour................... i Loss of steam and water per hour due to leakage of plant, GH pSs Cte id ein oven PL caw eu Heke eee ry Net dry steam consumed per hour by engine and auxiliaries re Dry steam consumed per hour: (a): Main-evlindets:~ 2cc3d or 2. rie CA oe ee ees ss (6) Jackets and reheaters. =... ss ee eee a Pressures and Temperatures (C orrected). Steam-pipe pressure near throttle, by gauge............. Ibs. per sq. in. Barometric pressure of atmosphere in inches of mercury. . ins. Pressure in first receiver by gauge...................-. Ibs. per sq. in. Pressure in second receiver by gauge................... 7 Vacuum in condenser: (a) In inches of mercury............... 0000 ce eevee ins. (6) Corresponding total pressure.................... Ibs. per sq. in. 6c Pressure in steam jackets by gauge. ................. Pressure in reheater by gauge.......................-. Superheating of steam in first receiver.................. deg. Fahr Superheating’ of steam in second receiver. ............. Indicator Diagrams. ast Cyl. 2d Cyl. 3d Cyl. Commercial cut-off in per cent of stroke........ Initial pressure in lbs. per sq. in. above atmos- Back-pressure at mid-stroke above or below at- mosphere in lbs. per sq. in.................. Mean effective pressure in Ibs. per sq. in........ Equivalent mean effective pressure in lbs. per sq. in. per indicated H.P: | (a) Referred to first cylinder................ (6) Referred to second cylinder............. (c) Referred to third cylinder.... .......... 77° EXPERIMENTAL ENGINEERING 1st Cyl. 2d Cyl. 3d Cyl. 37. Pressures and percentages used in computing the steam accounted for by the indicator dia- grams, measured to points on the expansion and compression curves...............4. Pressures above zero in lbs. per sq. in.: (Gy NG@AFICUtOR: ics ny A caches pe pa wees (6) Near release..... 0... eee ees (c) Near beginning of compression.......... Percentage of stroke at points where pressures are measured: (a): Near cut-offinns seks sean cakes gaan eee (b) Near release.........0 00.20 e cece eee es (c) Near beginning of compression........... 38. Aggregate M.E.P. in lbs. per sq. in. referred to each cylinder given in heading............-. 39. Mean back-pressure above zero, lbs. per sq. in... 40. Steam accounted for in lbs. per indicated horse power per hour: (6) NGariCitsOf sco 22828 Bene da en ghee hale (6) Near releases sce ck a eG eae 41. Ratio of expansion: (@) -Commeéttialy, c0nsnan tose nooks eee Pet be cansnae (O) GGA sis A ptylare ad wdlehocg anes ERAN Aciba Daa anthe Suaduits Speed 42. Revolutions per minute... ........ 00.0.0... 22000000. rev. 43. Piston speed per minute................0.........005. ft. Power. 44. Indicated horse power developed by main engine cylinders: Pirsticylinder; exes heer i ed eeme pax eves dad conned’ H.P. Second cylinder..............5..0000 0000 cc cece ee % Thirdseylinders ex .ssveves useweds Bhs SRE eee ewan s Total pg aac sae Seah Gee Roe eeeieate ey Bees Bee Efficiency Results. 4s. Dry steam consumed per indicated H.P. per hour: (a) Main cylinder, including jackets................. Ibs. (6) Auxiliary cylinders, etc...............0.000.000. “ (c) Engine and auxiliaries...............0...0..008. fe TESTING STEAM ENGINES AND LOCOMOTIVES 771 46. Percentage of steam used by main engine cylinders ac- counted for by indicator diagrams: 1st Cyl. 2d Cyl. 3d Cyl. (a) Near cut-off....... 0... eee eee (6) Near release. .wuv sien ey Saves SY aN Saws Sample Diagrams. Copies of indicator diagrams, nearest the mean, with corresponding scales, should be given in connection with table. DEPARTMENT OF EXPERIMENTAL ENGINEERING, SIBLEY COLLEGE. JACKET STEAM, DATA AND RESULT Dest of Engine Dat 09) wicisce-sastolaless sch 8.8 Batteses Oars aan eka Eien Ge ROLES RENTED TESTE GE isto dats shad tae Sag EE TRO OS Sage Ns Bs Daher 2s schetecesiiheg is eeee Cu. Ft. 7 Wt. Per | Weight Per Hr, | T&™P: |cy Ft. | Per Hr.| Measurements made by High-pressure Cylinder...) 0.0... .)o ccc cece elec cee fee ee ce cece eee enneeees Intermediate OE” setdS Ne estire 2 | ataenas|wawae alae Engine tested by Low- pressure eo ‘Mies oa cee jceriau’| oeaives laouaags [ae sarees Sete tad cts Put Ree cee s vc Alsen eal cecah alee he BALAY 4 «SoM AG 44 beRoudse Pe ion ekee eae SCCOND RECEIVER: ocd ekc tea AG alles arena Shao Saale Galas [uae A Savane eee tae! He DOWD oe He as avant 8 8 ne ee | Ge aed alee ee ea H. P. Cylinder First Receiver. Int. Cylinder. Second Receiver. L. P. Cylinder. 3 s re : o » | 3 a] & @ a] & 3 cu 2 3 a. a 3g a | & # g = £ g a g g s & E 3 & g s Bye l/o|;/ea&lae};o};ai{a 3 a |e o &]/a]o EXPERIMENTAL ENGINEERING 772 *IaputyAo ‘dH Jo ysneqxa uy , eee nee ee . < we ae we . eee eee epee ef eee epee Lee fee ew lee owe OBRIIAY cides a evened | Ssenaredlts Saeed ort | Ska foe rn se Re aainec | eicee hau Mestad ae a ell eae + ee wee ele eee . ee . oe oe ae ea pace pee eae ee bee es fem af eh eww fe 6 fe eee eno . ee Zz woh | eens ye sana ache ef Leahey el nara te Ne ledgetetel| A eee eve ecadleane dae ofl p Hl Oo tb Hw |a ioe] H |W a wm 4 of {| F|e)e | 2] 2 le B loflele| g Sil es ee| @ | ee te g 5 |S * . ee a . a3 coe ae B eslele| & | 8 | 2 |B Sle cele a | 212 Gir £15 ies F : Be alee S/S] 8 | 2 | 8 Bx|@|8 | & oi hy 8 |h8 = a gs s a gi] 7 4 4 g #9 a ie jels| @ |" 1 Og mile 5 os - : s+|o 2 BF & sg ' g 4 B r a + [°Q Suyeiedag | ureajg pasuapuog AmoiajY SoyIaT] aFnvy Aq “sy SLHOITM SHUNLIVATINaA T, saunssay SNOILONTOATY “+ JajyawWoIeg | é ...po you carey ** “ssors: ‘peor ayeig)* ‘jou’ are} ‘°*ssoiB {peo ayeig]"* Ras : "* "aay ‘---gso13 pro] ayeig “ts -qoaq ‘wae ayRIq 9 Soe *qooy ‘wae oyraq a ape * Jooy ‘ue ayRIq" » SENS yeoy ‘gyorys Jo WySuaT] so "3004 ‘gyorqs Jo yysuay| te *y09y ‘Qyor}s Jo qsuaT : : “sayout ‘por is seis ee *SOYSUE "POR gy gg. PPR RAE sayout ‘por : Sta) oe oes, Seq our ‘uoysid jo IG ESSENSE Sap ee Save “qo ysid jo wd CE SEN aiar ae soyoul ‘uoysid jo eI SSdicinwha hose eae ER ELS SERIES “SULIAS JO S[VIG|* PFT TERE epee ee *“BUIS JOvaTBIG HPs ey Seas ee suds jo 2(29S . eae OREO eee ERS ’ ees ” yuers ”? : ” yuvIo ” ot » YueIS ” - yUtao Jad ‘pua pray ‘sourvivatD|° = ques Jod ‘pua proy ‘aouvivafa]*-* + “qu90 Jod * pua prey ‘oouerea|) UIGNITAD AANSSAAd- MOT UAGNITAD ALVIGANATLNT . 1 YAINITAD TAASSAad-HOT “4D pajsay BEB Atak ei earl eA . “iq WING ‘auisusy tee fo yaz’ ‘ALISUHAINA TIANYOO ‘“AOATION AATAIS ‘AUOLVUOIVT TVOINVHOAN 773 TESTING STEAM ENGINES AND LOCOMOTIVES a nH 2 : g 1 a t 0 2 ® fl re fi 4 t R 8 Ele l|e) 8 lgele ls] 2 | & ei & |a2|"[e] 6 x8 32 89 x x Be n B n wn B ei 5 3 oO o x e e ‘ammssolg oynjosqy es a amnssoig aynjosqy ‘aNG] HNVED ‘aNg ava 5,200 anes Sarai a® Saciunee asnapayy Baca fade Bis arsiegse cee ore flo-uncy apna xapa Al MBIBONEE May 77 to ns hitmen a Eee OSA RHA EN TO ERS 84 Dann fo oI Ye ea day Cadac eh tc AL ty AOR ic Rode Ses RSET SS ST CASE EEG GP VBL AR ED A NIOR Set TE A Gch aS OEE Te &q poyo4.) Sigs geile ds: ThavaiGha sepene reve stars eyes eke hq pando synsay ss tr octets eres eects eee ssescses sess sess sss sf pagmataquy Savy Boe ails so esinlmuasternaren a Ba Res aw ares Bagh ot oe she aenieh Se TREES AT EMRMaN Gy pre en sews eet R EERE Seees 8 spp dpm inne fo BOAT ied korea Oheiie eS 4 accinmea eR singe ta ertmemen AE Renna RoRNNRNE NYT NaeH> Cosmutiokw eG nner tema hones Sg pagea Sawa med aeeek ete exe adatesadeaers en nn ere oe re 3 ogee andenttena tate ec ear aN &q qing aui3uq wosf span “KLISUAAINN TIANYOD ‘ADATION AATAIS 774 EXPERIMENTAL ENGINEERING 363. The Testing of Pumping Engines (Steam Pumps). — Con- sidering a pumping engine merely as a steam engine, in which the useful work is represented by the water pumped against certain re- sistances, it will be seen that there should be no great difference between the methods of testing employed for the two types of engine, at least as far as the steam end of the plant is concerned. To deter- mine the useful performance of the pump, certain measurements in connection with the pump cylinders become necessary. These should include the taking of indicator cards, to determine the water horse power, the measurement of the water pumped, and of the suction and discharge heads, and the determination of slip or leakage of plungers and valves. The method of taking indicator cards from the pump cylinders is the same as for steam cylinders (see Chapter XV), and the water horse power is determined by the same method of computation. The ratio between the water horse power and the I.H.P. of the steam cylinders may be considered as representing the mechanical efficiency of the pump. The total head #4 pumped against is equal to the sum of the following heads: ve = VD, h=\hy—h, th + feet, 28 in which ha = discharge head. This is usually measured by connecting a gauge to the discharge main close to the pump. h, = suction head. Usually measured by connecting a gauge or mercury manometer to the suction main close to the pump. The usual case is to have the pump lift the liquid. In that case #, must be considered negative and this factor in the equa- tion then becomes —(—h,) = +h,. the vertical distance in feet between the discharge and suction gauges, or between the center of the discharge gauge and the point of attachment of the mercury manometer. hy TESTING STEAM ENGINES AND LOCOMOTIVES 775 vgandv, are the velocities in feet per second in the discharge and suction mains respectively at the points of gauge connection. If the suction and discharge mains are of the same size, this factor | of course cancels out. The total head pumped against in connection with the weight of water pumped, determines the foot-pounds of useful work done by the pump. The determination of the actual amount of water pumped (pump delivery *) can rarely be done by direct weighing, on account of the quantity usually involved, but must in nearly all cases be done by some indirect means. For this purpose weirs, nozzles, and Venturi meters have all been proposed and used. The Committee, however, recommends the method of using the plunger displace- ment corrected for leakage (slip) of plungers and valves, on the ground that the use of the other schemes mentioned involves the assumption of coefficients which may make them no more accu- rate than the method recommended. The latter certainly has the advantage of great simplicity. For directions concerning the determination of leakage, see the provisions of the Code. The term duty is often used as an efficiency standard in con- nection with pumping machinery. It refers to the number of foot-pounds of work done by a pump for a certain energy quantity supplied to the machine. Thus we speak of duty per 100 pounds of coal, or duty per 1000 pounds of steam, or duty per 1,000,000 B.t.u. The Committee recommends the use of the term duty in connection with the heat-unit basis stated in preference to the first two definitions given, for the reason that 100 pounds of coal may mean very different quantities of heat supply for different parts of the country, and 1oco pounds of steam will represent dif- ferent heat quantities, depending upon the conditions of the steam. The 1,000,000 B.t.u. basis, on the other hand, is a fixed basis. How the total heat supply to the engine is to be computed is shown in the following formulas, which show the method of computation for the principal results for a steam-pump test. These are quoted directly from the Code. * A distinction should be made here between capacity and delivery. The former is always based on plunger displacement. 776 EXPERIMENTAL ENGINEERING Dee Foot-pounds of work done a Total number of heat units consumed _A(Pept+s) XLXN XX 1,000,000 X 1,000,000 (foot-pounds). yo4 2. Percentage of leakage = aa x 100 (per cent). ‘ AXLXWN 3. Capacity = number of gallons of water discharged in 24 hours _AXLXN X 7.4805 X 24 DX 144 —~AXLXN X 1.24675 x X 1.24675 (gallons). 4. Percentage of total frictions fk gee = — X 100 LHP. = [1 - de setae A,XMEP.XL,XN5 or, in the usual case, where the length of the stroke and number of strokes of the plunger are the same as that of the steam-piston, this last formula becomes: A(P+p+ts) A, X M.E.P. In these formulas the letters refer to the following quantities: A = Area, in square inches, of pump plunger or piston, corrected for area of piston-rod. (When one rod is used at one end only, the correc- tion is one-half the area of the rod. If there is more than one rod, the correction is multiplied accordingly.) P = Pressure, in pounds per square inch, indicated by the gauge on the force main. p = Pressure, in pounds per square inch, corresponding to indication of the vacuum gauge on suction main (or pressure gauge, if the suction pipe is under a head). The indication of the vacuum gauge, in inches of mercury, may be converted into pounds by dividing it by 2.035. 5 = Pressure, in pounds per square inch, corresponding to distance be- tween the centers of the two gauges. The computation for this pressure is made by multiplying the distance, expressed in feet, by the weight of one cubic foot of water at the temperature of the pump well, and dividing the product by 144. L = Average length of stroke of pump plunger, in feet. N = Total number of single strokes of pump plunger made during the trial. xX I00 (per cent); Percentage of total frictions = E _ | X 100 (per cent). TESTING STEAM ENGINES AND LOCOMOTIVES wae A, = Area of steam cylinder, in square inches, corrected for area of piston-rod. The quantity 4, x M.E.P. inan engine having more than one cylinder is the sum of the various quantities relating to the respective cylinders. L, = Average length of stroke of steam piston, in feet. N; = Total number of single strokes of steam piston during trial. M.E.P. = Average mean effective pressure, in pounds per square inch, meas- ured from the indicator-diagrams taken from the steam cylinder. I.H.P. = Indicated horse power developed by the steam cylinder. C =Total number of cubic feet of water which leaked by the pump plunger during the trial, estimated from the results of the leakage test. D = Duration of trial, in hours. H = Total number of heat units [B.t.u.] consumed by engine = weight of water supplied to boiler by main feed-pump total heat of steam of boiler pressure reckoned from temperature of main feed-water + weight of water supplied by jacket-pump X total heat of steam of boiler pressure reckoned from temperature of jacket-water + weight of any other water supplied x total heat of steam reckoned: from its temperature of supply. The total heat of the steam is corrected for the moisture or superheat which the steam may contain. For moisture the correction is subtracted, and is found by multiplying the latent heat of the steam by the percentage of moisture, and dividing the product by 100. For superheat, the correction is added, and is found by multiplying the number of degrees of superheating (i.e., the excess of the temperature of the steam above the normal tem- perature of saturated steam) by the specific heat. No allow- ance is made for heat added to the feed-water, which is derived from any source, except the engine or some accessory of the en- gine. Heat added to the water by the use of a fluc heater at the boiler is not to be deducted. Should heat be abstracted from the flue by means of a steam reheater connected with the interme- diate receiver of the engine, this heat must be included in the total quantity supplied by the boiler. STANDARD METHOD OF CONDUCTING DUTY TRIALS OF PUMPING ENGINES. t. Test OF FEED-WATER TEMPERATURES. The plant is subjected to a preliminary run, under the conditions deter- mined upon for the test, for a period of three hours, or such a time as is neces- sary to find the temperature of the feed-water (or the several temperatures, if 778 EXPERIMENTAL ENGINEERING there is more than one supply) for use in the calculation of the duty. During this test observations of the temperature are made every fifteen minutes. Frequent observations are also made of the speed, length of stroke, indication of water-pressure gauges, and other instruments, so as to have a record of the general conditions under which this test is made DIRECTIONS FOR OBTAINING FEED-WATER TEMPERATURES. When the feed-water is all supplied by one feeding instrument, the tempera- ture to be found is that of the water in the feed-pipe near the point where it enters the boiler. If the water is fed by an injector this temperature is to be corrected for the heat added to the water by the injector, and for this purpose the temperatures of the water entering and of that leaving the injector are both observed. If the water does not pass through a heater on its way to the boiler (that is, that form of heater which depends upon the rejected heat of the engine, such as that contained in the exhaust steam either of the main cylinders or of the auxiliary pumps) it is sufficient, for practical purposes, to take the temperature of the water at the source of supply, whether the feeding instrument is a pump or an injector. When there are two independent sources of feed-water supply, one the main supply from the hot well, or from some other source, and the other an auxiliary supply derived from the water condensed in the jackets of the main engine and in the live-steam reheater, if one be used, they are to be treated inde- pendently. The remarks already made apply to the first, or main, supply. The temperature of the auxiliary supply, if carried by an independent pipe either direct to the boiler or to the main feed-pipe near the boiler, is to be taken at a convenient point in the independent pipe. When a separator is used in the main steam-pipe, arranged so as to dis- charge the entrained water back into the boiler by gravity, no account need be made of the temperature of the water thus returned. Should it discharge either into the atmosphere to waste, to the hot well, or to the jacket tank, its temperature is to be determined at the point where the water leaves the sepa- rator before its pressure is reduced. When a separator is used, and it drains by gravity into the jacket tank, this tank being subjected to boiler pressure, the temperatures of the separator water and jacket water are each to be taken before their entrance to the tank. Should there be any other independent supply of water, the temperature of that is also to be taken on this preliminary test. DIRECTIONS FOR MEASUREMENT OF FEED-WATER. As soon as the feed-water temperatures have been obtained the engine is stopped, and the necessary apparatus arranged for determining the weight of the feed-water consumed, or of the various supplies of feed-water, if there is more than one. : TESTING STEAM ENGINES AND LOCOMOTIVES 779 In order that the main supply of feed-water may be measured, it will gen- erally be found desirable to draw it from the cold-water service main. The best form of apparatus for weighing the water consists of two tanks, one of which rests upon a platform scale supported by staging, while the other is placed underneath. The water is drawn from the service main into the upper tank, where it is weighed, and it is then emptied into the lower tank. The lower tank serves as a reservoir, and to this the suction-pipe of the feeding apparatus is connected. The jacket water may be measured by using a pair of small barrels, one being filled while the other is being weighed and emptied. This water, after being measured, may be thrown away, the loss being made up by the main feed-pump. To prevent evaporation from the water, and consequent loss on account of its highly heated condition, each barrel should be partially filled with cold water previous to using it for collecting the jacket water, and the weight of this water treated as tare. When the jacket water drains back by gravity to the boiler, waste of live steam during the weighing should be prevented by providing a small vertical chamber, and conducting the water into this receptacle before its escape. A glass water-gauge is attached so as to show the height of water inside the chamber, and this serves as a guide in regu- lating the discharge valve. The chamber may be made of piping in the manner shown in the appended figure (sor) . When the jacket water is returned to the boiler by means of a pump, the discharge valve should be throttled during the test, so that the pump may work against its usual pressure; that is, the boiler pressure as nearly as may be, a gauge being attached to the discharge pipe for this purpose. When a separator is used and the entrained water discharges either to waste, to the hot well, or to the jacket tank, the weight of this water is to be determined, the water being drawn into barrels in the manner pointed out for measuring the jacket water. Except in the case where the separator discharges into the jacket tank, the entrained water thus found is treated, in the calculations, in the same manner as moisture shown by the calorimeter test. When it discharges into the jacket tank, its weight is simply subtracted from the total weight of water fed, and allowance made for heat of this water lost by radiation between separator and tank. When the jackets are drained by a trap, and the condensed water goes either to waste or to the hot well, the determination of the quantity used is not necessary to the main object of the duty trial, because the main feed- pump in such cases supplies all the feed-water. For the sake of having com- plete data, however it is desirable that this water be measured, whatever the use to which it is applied. 780 EXPERIMENTAL ENGINEERING Should live steam be used for reheating the steam in the intermediate receiver, it is desirable to separate this from the jacket steam, if it drains into the same tank, and measure it independently. This, likewise, is not essential to the main object of the duty trial, though useful for purposes of information. The remarks as to the manner of preventing losses of live steam and of evaporation, in the measurement of jacket water, apply to the measurement of any other hot water under pressure which may be used for feed-water. Should there be any other independent supply of water to the boiler besides those named, its quantity is to be determined independently, apparatus for all these measurements being set up during the interval between the prelim- inary run and the main trial, when the plant is idle. 2. THE Main Duty TRIAL. The duty trial is here assumed to apply to a complete plant, embracing a test of the performance of the boiler as well as that of the engine. The test of the two will go on simultaneously after both are started, but the boiler test will begin a short time in advance of the beginning of the engine test, and continue a short time after the engine test is finished. The mode of procedure is as follows: The plant having been worked for a suitable time under normal conditions, the fire is burned down to a low point and the engine brought to rest. The fire remaining on the grate is then quickly hauled, the furnace cleaned, and the refuse withdrawn from the ash pit. The boiler test is now started, and this test is made in accordance with the rules for a standard method recommended by the Committee on Boiler Tests of the American Society of Mechanical Engineers.* This method, briefly described, consists in starting the test with a new fire lighted with wood, the boiler having previously been heated to its normal working degree; operating the boiler in accordance with the conditions deter- mined upon; weighing coal, ashes, and feed-water; observing the draught, temperatures of feed-water and escaping gases, and such other data as may be incidentally desired; determining the quantity of moisture in the coal and in the steam; and at the close of the test hauling the fire, and deducting from the weight of coal fired whatever unburned coal is contained in the refuse with- drawn from the furnace, the quantity of water in the boiler and the steam pressure being the same as at the time of lighting the fire at the beginning of the test. Previous to the close of the test it is desirable that the fire should be burned down to a low point, so that the unburned coal withdrawn may be in a nearly consumed state. The temperature of the feed-water is observed at the point where the water leaves the engine heater, if this be used, or at the point where it enters the flue heater, if that apparatus be employed. Where an injector * Vol. VI, p. 267, Transactions A. S. M. E., 1885. (See also Chap. XVII.) TESTING STEAM ENGINES AND LOCOMOTIVES 781 is used for supplying the water, a deduction is to be made in either case for the increased temperature of the water derived from the steam which it consumes. As soon after the beginning of the boiler test as practicable the engine is started and preparations are made for the beginning of the engine test. The formal beginning of this test is delayed till the plant is again in normal work- ing condition, which should not be over one hour after the time of lighting the fire. When the time for beginning arrives the feed-water is momentarily shut off, and the water in the lower tank is brought to a mark. Obser- vations are then made of the number of tanks of water thus far supplied, the height of water in the gauge-glass of the boiler, the indication of the counter on the engine, and the time of day, after which the supply of feed-water is renewed, and the regular observations of the test, including the measurement of the auxiliary supplies of feed-water, are begun. The engine test is to continue at least ten hours. At its expiration the feed-pump is again momen- | a tarily stopped, care having been taken to have the water slightly higher than at the start, and the water in the lower tank is brought to the mark. When the water in the gauge-glass has settled to the point which it occupied at the beginning, the time of day and the indication of the counter are observed, together with the number of tanks of water thus far supplied, and the engine test is held to be finished. The engine continues to run after this time till the fire reaches a condition for 3 hauling, and completing the boiler test. It is then stopped, and the final observations relating & to the boiler test are taken. The observations to be made and data ob- tained for the purposes of the engine test, or duty F1¢. 502.— Metuop or Os- trial proper, embrace the weight of feed-water TATNING Boonen (eaves : 3 i READINGS. supplied by the main feeding apparatus, that of the water drained from the jackets, and any other water which is ordinarily supplied to the boiler, determined in the manner pointed out. They also embrace the number of hours duration, and number of single strokes of the pump during the test; and, in direct-acting engines, the length of the stroke; together with the indications of the gauges attached to the force and suction mains, and indicator-diagrams from the steam cylinders. It is desirable that pump diagrams also be obtained. Observations of the length of stroke, in the case of direct-acting engines, should be made every five minutes; observations of the water-pressure gauges every fifteen minutes; observations of the remaining instruments, such as steam gauge, vacuum gauge, thermometer in pump well, thermometer in 782 EXPERIMENTAL ENGINEERING feed-pipe, thermometer showing temperature of engine room, boiler room, and outside air, thermometer in flue, thermometer in steam pipe, if the boiler has steam-heating surface, barometer, and other instruments which may be used, every half-hour. Indicator-diagrams should be taken every half-hour. When the duty trial embraces simply a test of the engine, apart from the boiler, the course of procedure will be the same as that described, excepting that the fires will not be hauled, and the special observations relating to the performance of the boiler will not be taken. DIRECTIONS REGARDING ARRANGEMENT AND USE OF INSTRUMENTS, AND OTHER PROVISIONS FOR THE TEST. The gauge attached to the force main is liable to a considerable amount of fluctuation unless the gauge-cock is nearly closed. The practice of choking the cock is objectionable. The difficulty may be satisfactorily overcome, and a nearly steady indication secured, with cock wide open, if a small reservoir having an air-chamber is interposed between the gauge and the force main, in the manner shown in the appended figure (soz). By means of a gauge-glass on the side of the chamber and an air-valve, the average water-level may be adjusted to the height of the center of the gauge, and correction for this element of variation is avoided. If not thus adjusted, the reading is to be referred to the level shown, whatever this may be. To determine the length of stroke in the case of direct-acting engines, a scale should be securely fastened to the frame which connects the steam and water cylinders, in a position parallel to the piston-rod, and a pointer attached to the rod so as to move back and forth over the graduations on the scale. The marks on the scale, which the pointer reaches at the two ends of the stroke, are thus readily observed, and the distance moved over computed. If the length of the stroke can be determined by the use of some form of regis- tering apparatus, such a method of measurement is preferred. The personal errors in observing the exact marks, which are liable to creep in, may thereby be avoided. The form of calorimeter to be used for testing the quality of the steam is left to the decision of the person who conducts the trial. It is preferred that some form of continuous calorimeter be used, which acts directly on the mois- ture tested. If either the superheating calorimeter * or the wire-drawing + instrument be employed, the steam which it discharges is to be measured either by numerous short trials, made by condensing it in a barrel of water previously weighed, thereby obtaining the rate by which it is discharged, or by passing it through a surface condenser of some simple construction, and * Vol. VII, p. 178, 1886, Trans. A. S. M. E. + Vol. XI, p. 791, 1890, Transactions A. S.M.E. (Paper on “A Universal Calo- rimeter,” May, 1890.) (See Chap. XIV.) TESTING STEAM ENGINES AND LOCOMOTIVES 783 measuring the whole quantity consumed. When neither of these instruments is at hand, and dependence must be placed upon the barrel calorimeter, scales should be used which are sensitive to a change in weight of a small frac- tion of a pound, and thermometers which may be read to tenths of a degree. The pipe which supplies the calorimeter should be thoroughly warmed and drained just previous to each test. In making the calculations the specific heat of the material of the barrel or tank should be taken into account, whether this be of metal or of wood. If the steam is superheated, or if the boiler is provided with steam-heating surface, the temperature of the steam is to be taken by means of a high-grade thermometer resting in a cup holding oil or mercury, which is screwed into the steam pipe so as to be surrounded by the current of steam. The temperature of the feed-water is preferably taken by means of a cup screwed into the feed- pipe in the same manner. Indicator pipes and connections used for the water cylinders should be of ample size, and, as far as possible, free from bends. Three-quarter-inch pipes are preferred, and the indicators should be attached one at each end of the cylinder. It should be remembered that indicator springs which are correct under steam heat are erroneous when used for cold water. When such springs are used, the actual scale should be determined, if calculations are made of the indicated work done in the water cylinders. The scale of steam springs should be determined by a comparison, under steam pressure, with an accurate steam gauge at the time of the trial, and that of water springs by cold dead- weight test. The accuracy of all the gauges should be carefully verified by comparison with a reliable mercury column.* Similar verification should be made of the . thermometers, and if no standard is at hand, they should be tested in boiling water and melting ice. To avoid errors in conducting the test, due to leakage of stop-valves either on the steam pipes, feed-water pipes, or blow-off pipes, all these pipes not concerned in the operation of the plant under test should be disconnected. 3. LEAKAGE Test oF Pump. As soon as practicable after the completion of the main trial (or at some time immediately preceding the trial), the engine is brought to rest, and the rate determined at which leakage takes place through the plunger and valves of the pump, when these are subjected to the full pressure of the force main. The leakage of an inside plunger [the only type which requires testing] is most satisfactorily determined by making the test with the cylinder head * AutHor’s Nore. See the chapter on the Measurement of Pressure for other apparatus fully as accurate and easier to operate. 784 EXPERIMENTAL ENGINEERING removed, A wide board or plank may be temporarily bolted to the lower part of the end of the cylinder, so as to hold back the water in the manner of a dam, and an opening made in the temporary head thus provided for the reception of an overflow pipe. The plunger is blocked at some intermediate point in the stroke (or, if this position is not practicable, at the end of the stroke), and the water from the force main is admitted at full pressure behind it. The leakage escapes through the overflow pipe, and it is collected in barrels and measured. Should the escape of the water into the engine room be objectionable, a spout may be constructed to carry it out of the building. Where the leakage is too great to be readily measured in barrels, or where other objections arise, resort may be had to weir or orifice measurement, the weir or orifice taking the place of the overflow pipe in the wooden head. The apparatus may be constructed, if desired, in a somewhat rude manner, and yet be sufficiently accurate for practical requirements. The test should be made, if possible, with the plunger in various positions. In the case of a pump so planned that it is difficult to remove the cylinder head, it may be desirable to take the leakage from one of the openings which are provided for the inspection of the suction valves, the head being allowed to remain in place. It is here assumed that there is a practical absence of valve leakage, a con- dition of things which ought to be attained in all well-constructed pumps. Examination for such leakage should be made first of all, and if it occurs and is found to be due to disordered valves, it should be remedied before making the plunger test. Leakage of the discharge valves will be shown by water passing down into the empty cylinder at either end when they are under pressure. Leakage of the suction valves will be shown by the disappearance of water which covers them. Tf valve leakage is found which cannot be remedied, the quantity of water thus lost should also be tested. The determination of the quantity which leaks through the suction valves, where there is no gate in the suction pipe, must be made by indirect means. One method is to measure the amount of water required to maintain a certain pressure in the pump cylinder when this is introduced through a pipe temporarily erected, no water being allowed to enter through the discharge valves of the pump. The exact methods to be followed in any particular case, in determining ‘leakage, must be left to the judgment and ingenuity of the person conducting the test. 4. TABLE oF Data anp RESULTS. In order that uniformity may be secured, it is suggested that the data and results, worked out in accordance with the standard method, be tabulated in the manner indicated in the following scheme: Co Or an fw NH HHH No H O 13. I4. IS. 16. 17. 18, 19. 20. 2i. 22. 23. 24. 25. 26. 27. 28. 29. TESTING STEAM ENGINES AND LOCOMOTIVES 785 DUTY TRIAL OF ENGINE. Dimensions. Number of steam cylinders........................... . Diameter of steam cylinders.......................... . Diameter of piston-rods of steam cylinders.............. . Nominal stroke of steam-pistons....................... . Number of water-plungers........000.0.00.0 000.0000 0000. . Diameter of plungers... 0.0.00. 22. . Diameter of piston-rods of water cylinders.............. . Nominal stroke of plungers.............00000..0000000% . Neb area of pHIngets! ..2.0.c2ccaeasvaas depewewe vee kes . Net area of steam pistons... 0... eee . Average length of stroke of steam pistons during trial... . . Average length of stroke of plungers during trial......... (Give also complete description of plant.) Temperatures. Temperature of water in pump well.................... Temperature of water supplied to boiler by main feed- Temperature of water supplied to boiler from various OLNEE SOULCES icin eieniap e.a Gneeieane Soo eoe aN een nem ney Feed-water. Weight of water supplied to boiler by main feed-pump... Weight of water supplied to boiler from various other SOURCES ys beth in duc sakes dtd ae tev vAE se Agua ayy ade nme die ahs Pressures. Boiler pressure indicated by gauge. Ss... ss eee Pressure indicated by gauge on force main.............. Vacuum indicated by gauge on suction main............ Pressure corresponding to vacuum given in preceding line. Vertical distance between the centers of the two gauges. . Pressure equivalent to distance between the two gauges. . Miscellaneous Data. Duration of trial, ..c.ssaseuebekee odes aney Bee eee Total number of siagle stzokes during trial............. Percentage of moisture in steam supplied to engine, or num- ber of degrees of superheating....................... Total leakage of pump during trial, determined from re- sults of leakage test..........00 00000000 cece eens Mean effective pressure, measured from diagrams taken from steam cylinders............ 00.0... c cece ee eee ins. oe ft. ins. ce ft. sq. ins. “ch ft. ce ins. Ibs. ins. lbs. hrs. p. c. or deg. Ibs. 786 EXPERIMENTAL ENGINEERING Principal Results. 20,. DULY: oo sdinipca snk oideies BYGE RU ee BAU e eee ews Pelee ft.-lbs. 31. Percentage of leakage.........--. 0s cece eee eee eee per cent. 39..' CAPACLEYS a xastera na sieee os se PRE DHS Beet BREET HTS gals. 33. Percentage of total frictions................-....00-085 per cent. Additional Results.* 34. Number of double strokes of steam piston per minute... . 35. Indicated horse power developed by the various steam GyMINGerSisca tei Seegeeadeeea tata eenea th ealtA wh ae 1.H.P. 36. Feed-water consumed by the plant per hour............ Ibs. 37. Feed-water consumed by the plant per indicated horse power per hour, corrected for moisture in steam....... 38. Number of heat units consumed per indicated horse power per Hour). voseaess peri rea deere eee eeedey hs B.t.u. 39. Number of heat units consumed per indicated horse power Per MIM tes oa eanddas aioe ver sMaURe Hae ehh eF4 - 4o. Steam accounted for by indicator at cut-off and release in the various steam cylinders..............-.2.2200000- Ibs. 41. Proportion which steam accounted for by indicator bears to the feed-water consumption.................00e 2000 Sample Diagrams Taken From Steam Cylinders. [Also, if possible, full measurements of the diagrams, embracing pressures at the initial point, cut-off, release, and compression; also back pressure, and the proportions of the stroke completed at the various points noted.] 42. Number of double strokes of pump per minute......... 43. Mean effective pressure, measured from pump diagrams. . M.E.P. 44. Indicated horse power exerted in pump cylinders........ L.H.P. 45. Work done (or duty) per 100 lbs. of coal............... ft.-lbs. Sample Diagrams Taken From Pump Cylinders. DaTA AND Resutts oF BOILER TEST. For the items of this table see the Boiler Code, Chap. XVII, of this book. 364. The Testing of Locomotives.—Tests on locomotives are divided into shop tests and road tests. In the former the engine is supported, so that, although it may be operated at full speed as far as revolution of drivers is concerned, the locomotiveas a whole has no * These are not necessary to the main object, but it is desirable to give them. TESTING STEAM ENGINES AND LOCOMOTIVES 787 motion. The equipment required for such a test is rather elaborate and quite costly, and hence out of reach of the ordinary testing laboratory. Several of such testing stands are, however, found in one or two of the colleges and in the shops of some of the important railroads. The road tests, as the name implies, are made with the locomotive in actual service drawing a train over the road. The advantage of shop tests over road tests consists in the fact that it is possible to make measurements with probably somewhat greater accuracy and that all conditions can be maintained constant. This is important when it is desired to study one particular feature of operation. The road tests, on the other hand, exhibit actual operat- ing results and therefore furnish a valuable complement to the shop test. When engine performance alone, as compared with that of other engines, is the matter under investigation, it is desirable to make the road test of considerable length, say not under too miles, and to have each engine draw the same train, which should be a special rather than a regular train, in order to be independent as far as number of stops is concerned. The Committee recommends that a dynamometer car be used in all road tests in order to determine accurately the useful work done. The Code gives several figures illustrating the arrangement of apparatus in a dynamometer car, but, since no description is given, these figures are of doubtful value for the purpose of this book. The student is therefore referred to articles dealing with the operation of dynamometer cars as well as with the construction of the testing stands for shop tests which have appeared from time to time in various technical railway journals. The Committee also recommends the adoption of an efficiency standard for locomotives, defining it as the number of pounds of “standard coal’? consumed per dynamometer horse power per hour. Standard coal is defined as one which will, when tested in the oxygen calorimeter, show a heating value of 12,500 B.t.u_ per pound. To convert the actual amount of coal used into the equiv- alent weight of ‘ standard coal,” the weight of coal burned per dynamometer horse power per hour is multiplied by its heating value and divided by 12,500. 788 EXPERIMENTAL ENGINEERING STANDARD METHOD OF CONDUCTING EFFICIENCY TESTS OF LOCOMOTIVES. 1. PREPARATIONS FOR TEST, AND LocaTION oF INSTRUMENTS.* A. The locomotive should be put in good condition preparatory to the test. The boiler and tubes should be tight, and both the interior and exterior surfaces should be clean, and, if possible, free from scale. There should be no lost motion in the valve gear, and the valves should be set properly. No change in the engines should be allowed during the progress of a series of tests, unless so ordered for the purposes of the trial. A glass water-gauge should be fitted to the boiler, if not already provided. A rod should be attached to the reversing lever and carried forward to the front end of the boiler, where a graduated scale is provided and suitably marked, so that the position of the reversing lever can be seen at a glance by the person taking indicator-diagrams. The throttle-valve lever should be provided with a scale, to show the degree of opening of the throttle. B. The valves and pistons should be tested for leakage with the engine at rest. The steam valve can be tried by setting the engine so that the valve on one side will be at the center of its throw, in which position both ports are usually covered, and pulling open the throttle valve, blocking the drivers if there is a tendency for the engine to be set in motion. Leakage of the valve, if any occurs, will show itself by escaping at the smokestack, or at the open drain-cocks. The tightness of the piston may be tested by setting the engine so that it takes steam, blocking th drivers and opening the throttle valve. This should be tried first on one cylinder and then on the other, and, if desired, it may be tried with the pistons at various points in the stroke. The leakage, if any occurs, will be shown either at the top of the smokestack or at the open drain-cock. C. The following instruments should be verified, or calibrated: steam gauges, draft gauge, pyrometer, thermometers for calorimeter and feed-water, water meter, tank, revolution counter, indicator springs, dynamometer springs, and dynamometer recording mechanism. The radiation loss on the steam calorimeter should be determined, or the normal readings ascertained; t and the quantity of steam which passes through the instrument in a given time should be measured. , D. The quantities of steam consumed by the air-pump, the blower, and the whistle, under conditions of common use, should be determined, thereby obtain- ing data by which to correct for the steam thus used. This can best be de- termined for each one by observing the fall of water in the gauge glass when no steam is drawn from the boiler for any other purpose; the quantity being com- * The directions here given apply largely to both shop and road tests, but espe- cially to the latter. {Transactions A. S. M. E., Vol. XI, p. 793. TESTING STEAM ENGINES AND LOCOMOTIVES 789 puted from the data thus found, and the dimensions of the boiler. The leak- age of the boiler should also be found, using the same method. E. To facilitate the measurement of coal and the determination of the quantity used during any desired period of the run, it is desirable to provide a sufficient number of sacks of a size holding a weight of, say roo lbs., and weigh the coal into these sacks preparatory to starting on the test. If desired, the sacks may be numbered, to facilitate the accuracy of record. F. The instruments and other apparatus that should be provided, and their locations, are as follows: To facilitate the work of operating the indicators and reading the instru- ments at the front end, the smoke box should be surrounded with a wooden fence, or “pilot box,” as it may be called, resting on the top of the cow-catcher and extending back far enough to inclose also the sides of the cylinders. This box is floored over, and the inclosure thus provided forms a convenient place for the accommodation of the assistants at this end of the locomotive, and it affords them some measure of protection against wind and rain, as also the jolting and vibrations due to rapid travel. A special steam gauge with a long siphon is to be used for registering the boiler pressure. It can best be located on the left-hand side of the cab. The indicator apparatus which is most suitable consists of a three-way cock * for the attachment of the indicators, and some form of pantograph motion for the driving rig. The pipes leading from the cock to the cylinder should be three-fourths inch diameter inside, and they should connect into the side of the cylinder rather than into the two heads. The indicator should also be piped so that a steam chest diagram can be drawn by it. Sharp bends in the pipe should be avoided, and they should be well covered, to intercept radiation. The three-way cock should be provided with a clamp rigidly secured to the cylinder, and thus overcome any tendency of the indicators to move longitudinally with reference o the driving rig. Absolute rigidity is highly essential in this particular. (For forms of driving rig for the indicators, see Chap. XV of this book.) A draft gauge consisting of a U tube containing water, properly graduated in inches, should be connected to the smoke box and attached to the side of the pilot box. A pyrometer for showing the temperature of the escaping gases should be used in a position below the tip of the exhaust nozzles. The calorimeter should be attached either to the steam dome at a point close to the throttle opening, or to the steam passage in the saddle casting on one side, according as it is desired to obtain the character of the steam at one point or the other. The former locationis preferred by the Committee. A perforated half-inch pipe should be used for sampling and conveying the steam to the calorimeter pipe. For descriptions of various forms of calorimeter * AutHor’s Notre. The use of a three-way indicator cock is not countenanced by many engineers under any circumstances. 790 EXPERIMENTAL ENGINEERING which are adapted to locomotive use see Transactions A. S. M. E., Vol. X, p. 327; Vol. XII, p. 825. The water meter should be attached to the suction pipe of the injector, and located at a point where it can be conveniently read when the locomotive is running. It should be provided with a check valve to prevent hot water from flowing back through it from the injector, and a strainer to intercept foreign material. To measure the depth of the water in the tank, a metallic float should be used, carrying a vertical tube which slides upon a graduate rod, the lower end of which rests upon the bottom of the tank. This should be placed at the center of gravity of the water space. If the desired location cannot be used, provision should be made for ascertaining the level or inclination of the tank. The best device for this purpose is a plumbline of a certain length provided at the bottom with a double horizontal scale having one set of divisions par- allel to the side of the tank, and the other set at right angles to it. From the readings on these scales referred to the length of the line, the level of the tank in both directions can be ascertained. A similar device should be attached to the boiler to correct for the variation in its inclination. The plumbline may be conveniently attached for this purpose at some point near the front end. The revolution counter should be placed near the front end of the engine in plain view from the pilot box. It is operated through a belt from the driver shaft. This recommendation applies to that form of counter which shows at a glance the exact speed in revolutions per minute. A stroke counter should be provided for showing the number of strokes made by the air-pump. Electric connection should be made between the dynamometer car and the pilot box, so that dynamometer records and indicator-diagrams may be taken simultaneously. Another desirable provision is a speaking tube leading from the dynamometer car to the locomotive cab, and one also to the pilot box. G. It is needless, except for a complete record of directions for preparatory work, to call attention to the desirability of having the test, and especially the road test, made under the supervision of a competent person, who is not only familiar with the details of testing, but also with the proper method of firing and the mechanical operation of the locomotive. This is a most important factor, for it is only the clear-headed and able experimenter who is likely to obtain satisfactory work in this most difficult department of engineering tests. In the matter of assistants, the conductor of the test is best able to judge as to the number required, the various duties of the different men, and the manner of taking records. A good test can be made with eight (8) assistants, distributed in the manner indicated in the following list, which gives their duties: Two (2) cab assistants, who read the steam gauge, the position of the throttle-valve and reversing lever, the water meter, the height of water in the tank, the height of water in the glass water-gauge, the level of the tank, TESTING STEAM ENGINES AND LOCOMOTIVES 791 the number of times the whistle is blown, the length of time the safety-valve blows, the length of time the blower is in action, the reading of the air-pump counter, the temperature of the feed-water in the tank, the time of starting and stopping the injector, the time of opening and closing the throttle-valve, and the number of sacks of coal used. These two observers have previously checked the weights of coal placed in the sacks. Three (3) pilot-box assistants, one of whom reads the pyrometer, the draft-gauge, the steam-chest gauge, the revolution counter, and marks on the indicator diagrams the time, position of reversing lever, steam-chest pres- sure, and revolutions per minute. He also takes the levels of the boiler at stopping places. The other two observers are stationed at the cylinders and manipulate the indicators, one being employed on each side. One (1) calorimeter assistant, who reads the calorimeter thermometers, and the gauges connected with the instrument, if these are employed. Two (2) dynamometer car assistants, who record time of each start and stop, time of passing each station and each mile-post, time of taking each indicator diagram as obtained from signals of the indicator men, and all these readings are marked so far as possible on the dynamometer paper. One of these men also assists the cab observer in reading the tank depth and its levels at stopping places. These men also keep a record of the direction and force of the wind, and the temperature of the atmosphere. An additional assistant is required if the gases are sampled and analyzed. H. It is of paramount importance, after the complete preparatory work has been accomplished, that the locomotive be subjected to a preliminary run, of sufficient duration to make a fair trial of the testing apparatus, and to give the various assistants an opportunity to become trained in their duties. I. SHOP TEST. A. Preparation and Location of Instruments. In preparing for a shop test the preparations described in Section I should be followed so far as the nature of the test requires. When run as a stationary engine the locomotive is not circumscribed by the conditions of road service, and many provisions required on the road are unnecessary. It is unnecessary to determine the quantity of steam consumed by the whistle and air-pump, for these are not brought into use on the shop test; and no occasion exists for finding the quantity lost at the safety valve, for on the continuous shop run the steam pressure can be maintained at a uniform point, and blowing off readily prevented. It is unnecessary to use sacks for the convenient measure of coal, because the coal can be readily weighed up in lots as fast as needed for the test. It is unnecessary to provide a “pilot box,” and no fixed location of the instruments is required, as on the road test. The feed-water may be weighed before it is supplied to the tank, and the tank may be used in this case as a reservoir, the float showing its depth. The meter would thus be un- necessary as the principal instrument of measurement, but a meter is in all 792 EXPERIMENTAL ENGINEERING cases useful as a check upon this most important element in the data. The long indicator pipes required on the road test may be dispensed with, and one indicator applied close to each end of the cylinder —a practice much to be preferred to the use of a three-way cock and the single indicator. The dyna- mometer car is not required, but its equivalent should be provided, consisting of a dynamometer which registers the pull on the draw-bar, in the same manner as the device used on the road. The number of assistants required on a shop test is less than that needed for a road test. A good test can be made with four (4) assistants, distributed as follows: One (1) assistant for operating indicators. One (1) assistant for measuring water. Two (2) assistants for general observations and coal measurement. If the gases are sampled and analyzed, one more assistant is required. B. Conditions of Test. The test should be continued for a run of at least two (2) hours from the time normal conditions have been established. At the close of the test the water height in the boiler, and the height of water in the tank, should be the same as at the beginning, or proper correc- tions made for any differences which may exist. The fire-box and ash-pit are then cleaned, and such unburnt coal as may be contained in the refuse is separated, weighed, and deducted from the total weight of coal fired. The balance of the refuse is weighed, as also the cinders removed from the smoke box. During the progress of the test samples of the various charges of coal should be obtained, and at its close a final sample of these should be selected, dried, and subjected to chemical analysis and calorimeter test. The weight of the sample is taken before and after drying, to ascertain the amount of moisture contained in the fuel. . C. The Data and Results. The data and results of the shop test can best be arranged in the manner indicated in Table No. 1. So far as these are in common with the data and results obtained on the road test, the forms used on both kinds of test are identical. TABLE NO. I. Data AND Resutts or SHoP TEST ON...... ENGINE, MADE.......... 1Q.. General dimensions, etc. (to be accompanied by a complete description, with drawings and full dimensions). te, Windsof Ene: s5 sui ha aaras mak Jie @mareatlneuaw Ketek th Dee Size and clearance of cylinders. Area of heating surface Area of grate surface np wn TESTING STEAM ENGINES AND LOCOMOTIVES 793 Whole Run. 13. 14. 15. 16. 17. 18. 19. 20. at. 22. 23. 24. 25. 26. 27. 28. 20. 30. 3I. 32: . Equivalent weight of water evaporated per hour with feed- 34- 35+ 36. 37. Wei . Weight of “standard coal” consumed per dynamometer . Weight of cinders from smoke box.................... . Percentage of ash, as found by calorimeter test. ...per cent. . Total heat of combustion per pound coal as found by calo- TOTAL QUANTITIES. PUPA TOM & ad se aisign Siseaig aie Phinda daneewehan pad wes Ae ents hrs. Weight of dry coal burned, including .4 weight of wood. . . lbs. Weight of water evaporated corrected for moisture in the SLOATNS fit pete Ra Ee ee S Bertie a Ga te Me alee Rua ea at as lbs. Weight of ashes and refuse from ash pan. ........... is PIMELET- LES bs, 2,20 a wree hacia na vio kine Aa Bath bats eal B.t.u. POWER DATA. Mean effective pressure, high-pressure cylinders........ lbs. Mean effective pressure, low-pressure cylinders......... - Average revolutions per minute...................... rev. Indicated horse power, high-pressure cylinders. ...... H.P. Indicated horse power, low-pressure cylinders......... Indicated horse power, whole engine................. Pullsonsdra ws bars ces oncnes vorniig Meas ae Boeee a ReneS Rees Ibs. AVERAGES OF OBSERVATIONS. Average boiler pressure......0000 000.00. Ibs. Average steam-chest pressure............0..-.. 00000008 es Average temperature of smoke box... .............45 deg. Average draft suction... 0... 0c eee in. Average temperature of feed-water................... deg. Average temperature of atmosphere..................- Average percentage of moisture in the steam....... per cent. Maximum percentage of moisture in the steam. ...per cent. HOURLY QUANTITIES. Weight of dry coal burned per hour................--- lbs. Weight of dry coal burned per hour per square foot of grate SUE CO aes ndaiae ceech eoh ae le sa BR ede Me At lbs. Weight of coal burned per hour per square foot of heating SUMACE cu vary Ahsan Nye wn alae ee metered Se lbs. Weight of water evaporated per hour................- o water at 100° and pressure at 70 Ibs...............-- Ibs. Equivalent weight of water from 100° at 70 lbs. evaporated per square foot of heating surface.................55 lbs. PRINCIPAL RESULTS, COMPLETE ENGINE AND BOILER. Coal consumed per I.H.P. per hour.. .. ..........-.- Ibs. Coal consumed per dynamometer horse power per hour.. Weight of ‘standard coal” consumed per I.H.P. per hour. ce horse power per hour... 0.0.0... 0. cece eee lbs. 794 EXPERIMENTAL ENGINEERING Whole Run. BOILER RESULTS. 39. Water evaporated per pound of coal.............+-++. MOS. aside ee Boedgie 40. Equivalent evaporation per pound of coal from andatiere? "ogee pees 4t. Equivalent evaporation per pound of combustible from and AU BID: « ioc cndus shanna 6 Rye oO age See pate IDSaica kegs veaes CYLINDER DATA. 42. Mean initial pressure above atmosphere. ..............-.0 20s ees lbs. H. P. Cyl L. P. Cyl 43. Cut-off pressure above zero...........--.. IDS!) saves weasel os Week Bees 44. Release pressure above zero.............5 FEU Eed oh n aBte. smanhiel| ene ucr ss we 45. Compression pressure above zero.......... Se ae cceinee deed lee aeGudlaeraneh eet 46. Lowest back pressure above or below atmos- PHELEY Se oinarau-sdy Chasen Ree eae eae IbSiies. deatetcal pear ose ake 47. Proportion of forward stroke completed at cut- OM aus ne eee Cane Gah Veni maion eta wen hie due ae TbS8leciwa teed fas len sews cesses 48. Proportion of forward stroke completed at re- VOASER rea egg aerial a escape eM A IDSs euSe cates ede 49. Proportion of return stroke uncompleted at com- PIESSIONs esas etnies Goal wa eiar em nainws IDS: eve oie dena lees ded aay CYLINDER RESULTS. so. Total water consumed per indicated horse power per hour corrected for MOISturean StEATM,. 2.22. Gee Saha eese Sh Ad eee eRe ESOT E BAe lbs. gr. Water consumed per I.H.P. per hour by cylinders alone (from line 51 less allwmeasured NOSséS) nites as avn aqnes whine de tau Reh ewes wp mina eRe Ibs. H. P. Cyl L. P. Cyl. 52. Steam accounted for by indicators at cut-off.Ibs.)...........J.....000005 53.” Steam accounted for by indicators at release. “ |...........)...-..200005 54. Proportion of feed-water used by cylinders (line 52) accounted for at cut-off............. MDS eerste feeds A GaAaiee ES aie 55. Proportion of feed-water used by cylinders ac- counted for at release.................. lbs Reports should give copy of a set of sample indicator-diagrams, also com- bined diagram (in case of multi-expansion engine) and a chart showing graph- ically the principal data. TESTING STEAM ENGINES AND LOCOMOTIVES 795 Tl. THE ROAD TEST. A. Preparation and Location of Instruments. The preparations required for the road test, and the proper location of instruments for the purpose, are fully described in Section I, and repetition is unnecessary. B. The Dynamometer Car. With a suitable dynamometer car the force required to move the train, or the pull upon the draw-bar, is registered upon a strip of paper traveling at a definite rate per mile. The scale upon which this diagram is drawn should be as large as is possible within reasonable limits; a scale of + inch per 1000 lbs. pull being suitable, as the maximum registered pull rarely exceeds 30,000 lbs. The height of the diagram should be measured from a base line drawn upon the paper by a stationary pen, so located that when no force is exerted upon the draw-bar the base line should coincide with zero pull. The apparatus should be arranged to make a record of time marks in con- nection with the curve showing the pull. A chronometer should be provided, having an electric circuit breaker, by means of which a mark is made on the dynamometer paper every five (5) seconds. A better apparatus may be used in which a continuous speed curve is traced upon the paper, parallel to the curve of pull. The ordinates of this curve, measured from a base line, give the speeds desired. The location of mile-posts and other points along the route should be fixed upon the dynamometer paper by employing an additional pen, and operating it by means of electric press buttons, which are placed at convenient points in the car. As already noted, a similar device should be provided for marking upon the dynamometer paper the time of taking indicator diagrams. The rate of travel of the paper per mile should be such that one inch measured upon the diagrams represents 100 feet for short-distance work, and for long-distance work 4 inch or 1 inch should be used to represent 100 feet of track. The driving mechanism for the paper should be so arranged that it can be changed to give these three proportions. It is necessary to have all the registering pens located upon the same transverse line at a right angle with the direction of the movement of the paper, in order that simultaneous data may be recorded. C. Method of Conducting the Road Test. The locomotive having been brought to the train, the steam pressure being at or near the working point, the fire being clean and in good condition though not over 4 to 6 inches thick, the ash-pan being also clean; observations are taken, say five (5) minutes before starting time, of the thickness and condition of the fire, the height of water in the boiler, the depth in the tank, the levels, 796 EXPERIMENTAL ENGINEERING the water meter, and the air-pump counter; and thereafter the regular obser- vations are carried forward, and coal is fired from the weighed sacks. Indicator diagrams should be taken as frequently as possible, the intervals between them being not over two minutes. Other regular observations should be taken at close intervals. Calorim- eter readings, when taken, should be continued for at least five (5) minutes at one-minute intervals. At water stations careful records should be obtained of water heights and levels of boiler and tank. As the end of the route is approached, the fire should be burned down so as to leave the same amount and the same condition as at the start. When the end is finally reached, the fire should be raked, and its condition carefully noted. If it differs from that which obtained at the beginning, an estimated allowance must be made for such difference. At the close of the test the height of water in the boiler should be the same as at the beginning, or, if not, the difference, corrected for inclination of the boiler, should be allowed for. During the process of weighing the coal into the sacks numerous samples should be obtained, and a final sample of these selected. This is to be dried and subjected to chemical analysis and calorimeter test. The sample is weighed before and after drying, and data obtained for determining the weight of dry coal used during the test. The duration of the road test is the length of time which the throttle-valve is open. D. The Data and Results. The data and results of the road test may be tabulated in the form given in Table No. 2. This form corresponds in general with that recommended for the shop test; viz., Table No. 1. TABLE NO. II. Data AND ResuLts OF Roap TEST ON........ ENGINE, MADE........ I9.. General dimensions, etc. (to be accompanied by a complete description of engine with drawings and dimensions, also of train and route). iy Wind OfMengin@iaxtc ccd mi we «He elninee pind aan ted taeda cis Bi. SIZENOL CYNNAELS je 1. cen ng gles tase a eee Gane edemaranmctae BS wea 3. Clearance of -cylindersis..¢ sch eoac.y dase ncaa tedles wba: per cent. as. Agee of heating SuriaGe.ce.uavecuawese eo iae aw dec es sq. ft. §. direa of grate surface... occ ca.iueaade sin ueaweeeues ove “ 6. Size of exhaust nozzles..........0..0..00.00000 cc cece ee ins. 7. Average weight of locomotive and tender (including water) tons. 8: INUMBER OR CATS cen oon eee powered rw me ewes Woe Oe Oe. Weight Of- Caisiy..! vad Rath owlsinddnntonn bata tienen tees tons. TESTING STEAM ENGINES AND LOCOMOTIVES 797 to. Length of route... 00... eee eee eee miles. tz. Number of ton miles of train load..................... ton miles. 12. Number of ton miles of total load..................... ss 13. Schedule time of trips....... lid guia bab abe A Shoah eas ab ectaile TOTAL QUANTITIES. 14. Duration or time throttle-valve is open................. hours. 15. Weight of dry coal burned.......................0.0. Ibs. 16. Weight of water evaporated corrected for moisture in the steam and loss at injector *.....................00., as 17. Weight of ashes and refuse from ash pan............... i 18. Weight of cinders from smoke box..................-04 1g. Percentage of ash as found by coal calorimeter test...... per cent. 20. Total heat’of combustion as found by calorimeter test.... B.t.u. 21. Results of chemical analysis of coal POWER DATA. 22. Mean effective pressure, H.P. cyls..................... lbs. 23. Mean effective pressure, L.P. cyls...................... i 24. Average revolutions per minute....................... rev. 25. Indicated horse power, H.P. cyls....................... H.P. 26. Indicated horse power, L.P. cyls................0000055 “ 27. Indicated horse power, whole engine................... oe 28... Pulloncdraw-Datyss. 2 nasesacid ee tek apes bo oaaye gues Ibs. 29. Dynamometer horse power..............000.000 cece eee H.P. AVERAGES OF OBSERVATIONS OF INSTRUMENTS. 30. Average boiler pressure.........0... 000. e cece eee eee Ibs. 31. Average steam-chest pressure...............000 00 ee eee . 32. Average temperature of smoke box..................... deg. 33. Average draft suction...........0.0000 00000 cece eee ins. 34. Average temperature of feed-water...................4. deg. 35. Average temperature of atmosphere.................... i 36. Average percentage of moisture in the steam............ per cent. 37. Maximum percentage of moisture in the steam.......... Bs 38. Weather, wind, etc OTHER DATA. 39. Average position of throttle................0 0.0.0 cease 40. Average position of reversing lever..................... * Should be corrected for steam used by calorimeter, air pump, blower, safety valve, and whistle, to find cylinder results — line 56. 798 4I. 42. 43- 44. 45: 46. 47- 48. 49- 50. 51. 52: 53: 54- 55: 56. 57- . Coal consumed per dynamometer horse power per hour... 59- 60. 61. 62. 63. 64. 65. 66. 67. EXPERIMENTAL ENGINEERING Average speed in miles per hour....................455 Maximum speed in miles per hour.................044- Number of st0pSivici ~ AA " ~-MRnWaY pa] 5 “Yea ~MRAAr A -Yoe SBBVBMaS Mae Boiler —~P/ AVA SWAy —Boiler_“ >| Le Pressure He => | =F be H § 8 On Le ee aog Condenser g 2 or a Dn Exhaust Pressure Lost y Velocity Gy Fic. 512. — Mutti-Stacr TURBINE Fic. 513. — Curtis TURBINE. (Five PRESSURE STAGES). pressure and increases the velocity. This set of nozzles is followed in the same stage by sets of movable blades and of guide blades, in this case three of the former and two of the latter. In passing through the movable blades the velocity is reduced, while in passing through the guide blades it is kept practically constant. On leaving the last set of movable blades in this stage, the pressure is practically the same as it was after leaving the nozzles A. The steam next encounters a second set of stationary nozzles A; in which the pres- * French, ‘Steam Turbines,” p. 114. 814 EXPERIMENTAL ENGINEERING Steam Chest DYDD yyy)yp yy) Kec C Cd C ee p>Dydybyddddyydyy)D Moving Blades KG ¢ COE (CCC «d Stotionary Blades DDDDDDWDDLYYDDDHDDD DDD Moving Blades ¥ ¥ + ~~ worse nore | IDPDDPYLDYYDYYLPHPPPDY) CCG “ats” KCC Nozzle Diaphragm Blades reine Dasa SSSPPPYPDPDWD} ele COCKE (@ Moving Blades ee bpp 7 » Dy t v v Fic. 514. — Two Pressure StaceEs or a CurTIS TURBINE. Velocity Pressure Exhaust Fic. 515. — Mutti-Stace REACTION TURBINE. STEAM TURBINES 815 sure is again reduced with a gain in velocity, and the second velocity stage then follows. 371. The Multi-stage Reaction Turbine. — See Figs. 5152 to d, concerning the principles of operation. There are no special noz- zles, the steam from the steam chest entering at once the first set of stationary guide blades A. In these, expansions take place and the pressure drops a certain amount with a gain in velocity (see Figs. 515c and d). In the movable set of blades B further expansion takes place and the pressure drops, but owing to the work done the net result is a loss of velocity. In the second set of guide blades A, the velocity is again increased by a further pressure drop, and thus the velocity is alternately increased in the stationary blades and decreased in the movable blades, by pressure drop in each case, until exhaust pressure is reached. One of the most important commercial examples of this type of turbine is the Parsons, built by the Westinghouse Machine Co. To Condenser Fic. 516. — WESTINGHOUSE-PARSONS STEAM TURBINE. Fig. 516 shows the construction of one of these machines. Another type built by the same company is a double-flow turbine designed to avoid the end thrust present in the ordinary construction. This machine is, however, really compounded, in that it has a set of nozzles with two velocity stages, one intermediate section, and two low-pressure sections of Parsons blading.* * Moyer, “The Steam Turbine,” p, 173. &16 EXPERIMENTAL ENGINEERING The Allis-Chalmers turbine is of the Parsons type, the main differences being in mechanical details of construction. 372. Turbines of the Pelton Type (Open-vane or Bucket Tur- bines). — Turbines of this type were developed by Rateau in Paris Fic. 517. ~ WHEEL AND CASING. OF STURTEVANT TURBINE. and by Riedler and Stumpf in Berlin. Riedler-Stumpf turbines of considerable size were built and are in operation. In this country these turbines are built by Stur- tevant, by Kerr, by Terry, and others. The general construc- tion of the wheels used is very well shown in Fig. 517,* which illustrates a Sturtevant wheel. The similarity to the ordinary Pelton water-wheel is striking. Figure 518 | shows a section of a Kerr turbine having five com- partments and wheels. The po- sition of the nozzles with reference to the wheel is well shown in Fig. 519.7 [ay ft SS SLI, tr} oy Poa. int Cay SY eG exit, TSN Fic. 518. — KERR TURBINE. * Moyer, “Steam Turbine,” p. 208. ft Ibid., p. 213. STEAM TURBINES 817 373- The Testing of Steam Turbines. -— Commercial testing of steam turbines is a comparatively simple matter. There is no direct way of determining the actual work done by the steam in the rotating ¢ parts of the turbine; that is, there is no test quantity analogous to the ‘Indicated Horse Power” of reciprocating engines. For an economy, efficiency, or capacity test, therefore, the measurements made are the amount of steam used, the condition of the steam at inlet (and in exhaust if possible), and the power output. The arrangements for the measurement of steam used are the same as for the reciprocating engines. For the purpose of obtain- ing the best economy, the great majority of turbines are operated condensing,* and the usual type of condenser is the jet. This means that in most cases measurement of feed water to the boilers will have to be resorted to. Depending upon whether the turbine operates upon superheated or saturated steam, either a thermometer is inserted or a calorim- eter is attached to the steam pipe near the main throttle. For the precautions necessary to observe, see Chap. XIV. It has been found that the effect of superheated steam upon economy is more marked in the case of turbines than in that of reciprocating engines, and many turbines operate on superheated steam. That simplifies the determination of steam quality. Concerning the determina- tion of quality of steam in exhaust, this is desirable as a matter of scientific data. If the steam was originally sufficiently super- heated, it may happen that the steam is still superheated in exhaust, in which case the quality determination consists merely in deter- mining the pressure and temperature. Where this is not the case, the determination of quality in exhaust becomes difficult in con- densing turbines. The ordinary calorimeter is practically useless on account of the difficulty of inducing flow. The shunting of a * For discussions of the effect of different vacuums upon economy, see any of the works above mentioned. t Mainly on account of decreased friction due to elimination of water particles in the steam. See works mentioned. Fic. 519.—WHEEL AND Noz- ZLE OF Kerr TURBINE. 818 EXPERIMENTAL ENGINEERING part of the exhaust steam through an electric calorimeter, of the type of the Thomas, for instance (see Chap. XIV), may solve the problem, but while the use of such an instrument is possible in a laboratory, it is generally out of question in testing in the field. DEPARTMENT OF EXPERIMENTAL ENGINEERING, SIBLEY COLLEGE. REPORT OF STEAM-TURBINE TEST. i. Dutation Ob testy... .venueny sthesensc al lee torliowas Sales ccalleoeas mhrewaas 2. Baromeéteriing He. ess aadeoe’S tocanedslorete dese ge dese relates aloes Bo POOR 5: Pe is, dee wsaia.c. 3 aeaniesnisas 58d araed ened Aial|hwrsiens ss [Sera oie eR d | eats a Hl eeltiness 4. Steam pressure, WSs AUG Sis a.nd dice duets: dell auergr'g eh | Seis lal enoawias a eiebsGae oleate dt oS IDS, ADS: caciictieet ptaae aoa a gepecale Gcaeaoetsl scenes al bee pihag | dings 6 7 8 6“ . ve MSs aD Sisaicses ssa Ri cprns anes] aueitieen a |acanecesene |laebedetcd| amdesmuese | meebaranm Oo, Superheatiol steam, deg. Fahr: 3.5 sac0epe-p)scacie:|sacuea|onee ssfewec ed |s sec sen’ to; Quality: of steam‘per centedry:.+.n».yseccs lei A saee os (ddeneel eae els uate 11. Condensed steam per hour, Ibs...........).....- fe... 00) e. eee fee eee fee eee Te VOltSin ence hanel so hs 2a AeheS Reta yeee #4 eleedelcs scans oeeks leeewte |e ates P35. AUT PET OS 5 MING cs Seger aiearnngaeareie wicehewe OG, etkcodis oil cahaduind |Memusbne di) a Ske wie [aoeeaeias - field 15. ts COCA] soi dt, tute nighal vidi aeasia cis ieee Pmalaes |'Aeaeee a [Wealatel aa becton wae | gestae 16. Power output of generator, K.W.......... J... 0. .[e cece fee cece fe eee fen eee 17. Efficiency of generator, per cent..........).....-[e..2 0 Jee ee ee fee eee efeeeeee a8, “Generator losses, Ke Wie. niscitna untae accg arias lr neeliedl olneuereee Irmusejesie a aiewn auare| migucbeverc 1g. Power input to generator, K.W., or B.H.P. |......)......)......)...0.-fe 0000s 20. Power output of steam turbine, internal ai. Steam consumption POE Fe Wests. Ste cid |incdeoe easel oral ardent Vadelaum are -adduaatiecieataiies 22): © Untermal HOP AHQUE |ecswes fers easlonnass {ses aas|raenen 23: Bz t. u. supplied per K. Wish. DER: oo a4.5. 4) neers ede wane feoaaena| seanes | araeays 24. 2 Steen al EL .PeSWOUR ccces bspcasta eal ena iad | dasha lammneeneg | ncaa 25. B.t.u. available per lb. steam. Clausius , CYCLE inn aiaigerraooma nian oe Mid acs 4 wea Saracen 26. Theoretical water rate. Clausius cycle....J......)....../.0..0.[e.0. cc fee eens 27. B. t. u. utilized per, Upsteains . Setare, eqs oo leet elle. Cel Wecdara Sac 8 lagen 8 ceed henge 28. 5s Trtemnal FP laciw veloc une alea cea cde seca aleewuws 29. Potential efficiency ayer alls 5 of5 ascciides det ladeutinisce ("esteest 2 arma al beau toll dealeossnss 30. i based on internal H.P.|......)..... 0)... 00. fe cece efew eee 31. Temp. injection water, deg. Fahr. 32. Temp. discharge water, ‘i ie 33- Temp. condensed steam, ‘ 8 34. Condensing water per hr. “Ibs. HEAT BALANCE. 35. Heat supplied, B.t.u 36. “ utilized a Sos Lee SGISCHAT BOO EY pareve ta cunastc lien case nin ae a pad tare ental ois Soe Laseenriae (tah roe 38. “lost by radiation, leakage, etc., B.t.u.. STEAM TURBINES 819 The question of determining the power output of turbines is generally easily solved, because most of them are used for the genera- tion of electric current. The switchboard readings, therefore, de- termine the output. This corrected for generator efficiency, which can be separately determined or computed but is best obtained from the builders of the machine, gives the actual mechanical work delivered by the turbine to the generator. It occasionally happens that the power developed is used in some other way. In sucha case a fluid friction brake (see Chap. X) is best on account of the high speed, especially if the power to be absorbed is considerable. The power developed by marine steam turbines is best measured by means of some type of torsion meter. The preceding form is convenient for recording the data from a turbine test and also points out the principal results to be computed. 374. Computations in Connection with Steam-turbine Tests. — If the turbine is tested for economy at a series of loads, Willan’s line (see p. 726) should be plotted during the tests as a check upon the work, as in the case of a reciprocating engine. The final report should show economy curves drawn between steam consumption per horse power and kilowatt-hour and output (see Chap. XVII). Internal Horse Power. — Where the turbine is driving a gen- erator, the output will be determined in kilowatts. This is transposed to electrical horse power by multiplying by <—— = 1.34. 740 Dividing the electrical horse power next by the efficiency of the generator gives what is the equivalent of brake or shaft horse power in a reciprocating steam engine. It has already been pointed out that there is no indicated horse power in the case of steam tur- bines, but in order to make the results of steam turbine tests com- parable with those of reciprocating engines, the term internal horse power is invented. This is obtained from the brake horse power by taking into account the mechanical efficiency of a reciprocating engine of the same capacity and operated at the same load. The assumption of this efficiency is, of course, largely a matter of esti- mation based on the results of available tests. For instance, in a test quoted by Moyer, the brake horse power of a 400-K.W. tur- 820 EXPERIMENTAL ENGINEERING bine was found to be 660. From available data it was assumed that the mechanical efficiency of a reciprocating engine would be 93-3 per cent when operated at the same load and under the same . 660 conditions. The internal horse power, therefore, ca = 708.* Thermal Efficiency. — As in the case of reciprocating engines, this is defined as the ratio of the heat equivalent of the work done ina given time divided by the heat supplied the turbine in the same time. For the mathematical expression of this ratio, see Chap. XVIII. BetleP sihsais 2etiespendhnen anes 594.9 | Heat in dry and satu- rated steam, per lb.. 1195.4 B.t.u. Internal H.P. (efficiency = Heat in superheat, per (oy eer Re nema enti 632.5 Wisse oi au Huet. 62.0 “ Total steam per hour, Ibs... 7384 Total heat per Ib. of steam above 32° F.. 1257.4 “ Steam per internal H.P. per Heat in condensed hour WSs se geste Bion 11.67 SECAM 4. ca e4ac aw eos $2.3, 8 Absolute steam pressure, lbs. 170.0 | Heat in steam per lb. above temp. of con- densed steam...... 1205.1 Superheat, degrees......... 109.0 | Thermal efficiency based on total heat in steam above 32° Spee A at 11.67 X 1257.4 17-37 Temp. condensed steam.... 95.8 | Thermal efficiency : based on total heat in steam above temp. of condensed steam = ——2545__ 18.1% 11.67 X 1205.1 There appears to be some difference in practice as far as comput- ing the heat supplied in a given time is concerned. In all cases the total heat in the steam supplied is computed above 32 degrees. Most authorities subtract from this the heat of the liquid left in * It may be stated that “internal horse power” is based upon arbitrary defini- tion, and that for the purpose of getting an equitable basis upon which to base sci- entific comparisons it is much better to express the steam or heat consumption of either engines or turbines upon the brake horse power. STEAM TURBINES 821 the condensed steam. This introduces a factor into the computa- tion which is peculiar to the individual plant, depending upon the operation of the condensing plant, irrespective of the pressure in the exhaust. It is hard to see why, in the computation of a crite- rion by which the performance of the turbine itself is to be judged, any factors independent of the turbine should be considered. It is true, of course, that this matter is largely one of definition, and, as stated above, the subtraction of the heat of the liquid in the condensed steam is usually made. To show the difference that occurs in the results when this allowance is made and when it is not made, the figures on p. 820 are quoted from French*: Potential (Clausius) or Cylinder Efficiency. — The theoretical cycle of the steam turbine is the Clausius, in which there is assumed to be adiabatic expansion of steam from boiler pressure and initial quality conditions to exhaust pressure. (See Art. 185, Chap. XI.) It is a simple matter, for any given condition, to compute the heat units that such a cycle renders available per pound of steam assumed to be operating, and if the quantity 2545 B.t.u. (which is the heat equivalent of 33,000 foot-pounds = 1 horse-power hour) is divided by the heat transformed into work per pound of steam, we evidently obtain the number of pounds of steam required by the turbine per horse-power hour if it were operating on the theoretical cycle. If, further, this theoretical water rate is then divided by the actual water rate of the turbine as determined from tests, we obtain an efficiency ratio which has been called potential or Clausius efficiency, and is analogous to the cylinder efficiency in reciprocating engines. Let H = the heat units transformed into work per pound of steam operating on the theoretical Clausius cycle, and W = the actual water rate of the turbine in pounds per s horse-power hour. Then the Clausius efficiency = oe H may be computed but is most easily determined by means of the Mollier diagram, Fig. 245. * These figures are slightly changed from the original, Marks’ and Davis’ Steam Tables being used. 822 EXPERIMENTAL ENGINEERING Example.—In the above test figures, quoted from French, the condenser pressure is not given, but assume that the exhaust pressure was 1 pound absolute. For 170 pounds absolute pressure and 109 degrees of superheat, the diagram gives 1257 B.t.u. per pound of steam, as closely as it can be read. From the point in this diagram denoting this condition of steam, drop verti- cally downward (adiabatic or isentropic change) until the 1-pound absolute- pressure line is reached. The quality of the steam has dropped to 80.2 per cent, while the heat content is now 896 B.t.u. per pound. Thus the theoretical cycle renders available H = 1257 — 896 = 361 B.t.u. The theoretical water- rate is therefore oe = 7.05 pounds per horse-power hour. Since the actual Ir water-rate based on the internal horse power was 11.67 pounds, the correspond- 7:05 11.67 375. Separation and Estimation of Steam-turbine Losses. — The losses occurring in steam turbines may be classified as follows: 1. Losses in nozzles and blades, owing to imperfect action of the steam in its passage. The greater part of this loss is in the blades, the nozzle efficiency being in most cases over 95 per cent. 2. Disk and blade friction, due to the rotation in the steam. Also windage losses in electric generator. (Together called rotation losses.) 3. Leakage of steam through clearance spaces without doing work. 4. Bearing and stuffing-box friction losses. 5. Loss due to radiation. The sum total of these losses is measured by the difference be- tween roo per cent and the Clausius efficiency, based upon the brake horse power, ot the internal horse power. Thus, in the figures . ; : : B.H.P. above given, the equivalent mechanical efficiency Internal ELP. is assumed = 94 per cent. Hence, based upon the brake horse power, the Clausius efficiency in the above example would have been 94 X 60.4 = 56.7 per cent. The sum of the five losses above enumerated is, then, 100 — 56.7 = 43.3 per cent. A first attempt at separating the individual losses may be made on the basis of Willan’s line. In Fig. 520, let 4B be the curve of total steam consumption per hour. Compute the data for the ing Clausius efficiency is = 60.4 per cent. STEAM TURBINES 823 line OC, which is the line of total steam consumption for the turbine operating on the theoretical Clausius cycle. Since there are no losses, this line will pass through the origin O for no load. Through O draw also the line OB’ parallel to AB. Prolong the line BA to D. A! ak 6! CH r 7 Pa eae a Le Total Steam per Hour hy, \ ‘NY \ LZ) oe 7 7] 7, x A 7 Pi Pe fo DO Y % 4 ”A 14 14% Load Fic. 520. — DETERMINATION OF TURBINE LossES. The line AB shows that there is a certain quantity of steam, represented by OA, used per hour when the turbine is delivering no power and simply turning over against its own resistances. The power thus expended and lost is measured by the distance OD, and is represented by losses 2, 4, and 5, enumerated above. These losses are fairly constant and independent of the load. Hence they can be eliminated by drawing in the line OB’. The rest of the losses may be considered varying with the load, and are repre- sented in the diagram by the widening distances between lines OB’ and OC as the load increases. To determine the percentage of the losses at any given load, say B, draw through B the line A’C. Distance A’C shows the power that the steam used should have produced had there been no losses. Distance A’B is the power actually produced. Hence, y ag = the Clausius efficiency. The distance BC represents total 824 EXPERIMENTAL ENGINEERING power lost. Of this the part BB’ is due to the constant losses and B’C to the variable losses. The further subdivision of the two classes of losses is not a simple matter and the reader is referred to steam-turbine treatises for detailed information. 376. Method of Correcting the Results of Steam-Turbine Tests for Standard or Guarantee Conditions. — Contract guarantees generally state that a steam turbine will operate on not to exceed a certain steam consumption per K.W.- or B.H.P.-hour for a certain absolute steam pressure at the inlet, a certain quality of steam (usually superheat), and acertain vacuum. It occasionally happens that on an acceptance test one or the other of the conditions speci- fied cannot be exactly met, and the question then arises as to what allowances shall be made mutually satisfactory to manufacturer and purchaser. The same question also comes up when it is desired to compare turbines of the same size but of different types with respect to steam economy, if the test figures available were not obtained under the same conditions of pressure, superheat, and vacuum. The method of correcting is in both cases the same. In the for- mer case the test figures are corrected to the guarantee conditions, while in the latter case some standard set of conditions (usually about the average of two sets of actual conditions) is assumed and all the results are computed to this standard. In either case it is of course necessary to obtain certain data on the change of economy with a change of any of the three conditions named. Such data can, in nearly all cases, be obtained from the manufacturers. In contract guarantees it is common for the manufacturers to give tables showing the allowances to be made in specific cases. How the corrections are computed for full load is perhaps best shown by a concrete example. The figures are quoted from Moyer, “Steam Turbines,” Chap. VI. Fig. 521 shows the three correction curves for full load furnished by the manufacturer for a 125-K.W. turbine. This turbine, with 175 pounds absolute admission pressure, 27.5 inches vacuum, and 50 degrees of superheat, showed a steam consumption at full load of 24.5 pounds per kilowatt-hour. It is desired to recompute this to the STEAM TURBINES 825 basis of 165 pounds absolute pressure, 28 inches vacuum, and o degrees super- heat. Curve I, Fig. 521, between 27 and 28 inches vacuum, shows a gain of 1.0 pound in steam consumption, hence the correction should be a subtraction of .§ pound from the observed steam consumption, since the new basis shows an increase of 4 inch vacuum. Curve II shows a gain of 2 pounds in the steam consumption for an increase in superheat from o to 100 degrees. The correction should therefore be an 35 ee — | 30 . pe | - 1 q oS [pe A = : I 4 a a a [11 2 td IL g S 20 3 nD oD a = 15 20 21 22 23 24 2 26 27 28 Vac!’ He. Curve I for Changes in Vac.(0'F. Superheat; 165* abs. Pressure.) P 0 20 40 60 80 100, 120 140 160° Serer Curve IT for Changes in Superheat. (28 Vac. 165* abs. Pressure.) 100 no = 120 180 140 150 160 170 180. ts At Press. Curve III for Changes in Abs. Press (28” Vac. 0 F. Superheat.) Fic. 521. — CURVES SHOWING VARIATION OF TURBINE ECoNoMY. addition of 1 pound to the observed steam consumption, because the new basis shows a loss of 50 degrees of superheat. Finally, Curve III shows a gain of 4 pounds in the steam consumption for an increase of 80 pounds in the admission pressure. Hence the correction should be an addition of .5 pound to the observed water-rate, since the new basis shows a loss of 10 pounds admission pressure. The corrected steam consumption therefore is 24.5 — .5 + 1.0 + .5 = 25.5 pounds per kilowatt-hour. Correction for fractional loads (1 load to 14 load) may be made in a similar manner by a “ratio” or “percentage”? method, on the assumption that the percentage correction found at full load applies also at any other load. This is very nearly true for any but the very low loads. 826 EXPERIMENTAL ENGINEERING To explain the method, it will be found from Curve I that the consumption for 27.5 inches vacuum is 25.6 pounds, while for 28 inches vacuum it is 25 pounds per kilowatt-hour. Obviously the percentage correction, from the 27.5 inches 250 — 25 = — 2.34 percent. This correction is nega- 25. tive (that is, a subtraction) because the new basis of computation shows a better vacuum and hence better economy, as already stated. Similar per- centage factors may, from Curves II and III, also be computed for changes of superheat and of admission pressure, keeping in mind always to designate the factors by a minus sign if the change from the actual to the assumed basis is a gain of economy, and using the plus sign if the change is accompanied by an increase in the steam consumption. For this particular case the following table shows the final result: to the 28 inches basis, is Test Conditions. | Assumed Conditions. Correction Correction ae a) ies a Ratio. Percentage. K.W.-hr. K.W.-br. 6x Vacuum, inches....... 27.5 25.6 | 28.0 25.0 are aie —2.34 Superheat, deg. F...... 50.0 24.0 0.0 25.0 50x +4.17 Abs. press. adm........|175.0 24.3 |165.0 24.8 a6 2S +2.06 24.3 pease ee Net correction... 3.89 Finally, the following table shows the results obtained for this turbine at fractional loads and the percentage correction applied to them: ri] a | @ fro] a Steam consumption from tests, Ibs. per K.W.-hr.) 31.2 | 26.9 | 25.2 | 24.5 | 23.6 Net correction, +3.89%...............000.. 12 Ta E,0 | <0 | Ox9 Corrected steam consumption, Ibs. per K.W.-hr.| 32.4 | 28.0 | 26.2 | 25.5 | 24.5 CHAPTER XX. THE TESTING OF INJECTORS. 377. General Theory of the Instrument.— An injector is an appa- ratus in which a jet of vapor from a nozzle strikes upon, and is con- densed by, a mass of liquid, with the result that the combined mass of liquid and condensed vapor gains kinetic energy comparable with that which a similar liquid mass would gain by discharge through a nozzle under the same pressure as that driving the vapor jet. The underlying principle which makes the injector possible is that the velocity of discharge of a gas or vapor from a nozzle, under a certain difference of pressures through the nozzle, is con- siderably greater than the corresponding velocity for a liquid under the same pressure conditions. The greater velocity for the gas or vapor arises from a transformation of part of the heat energy content of the gas or vapor into mass-velocity energy, a trans- formation that either does not occur at all, or only in slight amounts, for liquids. This extra velocity energy of the vapor then becomes available to force both the condensed vapor and some additional condensing liquid from the lower to the higher pressure. The vapor jet and the condensing liquid may be different substances; in practice, however, the vapor is steam and the condensing liquid water. The necessary parts of an injector are three: the steam nozzle, the combining tube, and the delivery tube. See Fig. 522. The steam nozzle should so control the flow of the steam supplied, that in dropping the pressure from the supply pressure to the pressure of the combining space, the steam should gain the maxi- mum possible velocity; that is, the nozzle expansion should be isentropic. The pressure in the combining space, the lower of the two pres- sures between which the nozzle works, cannot be lower than, and for perfect action should be as low as, the vapor pressure determined 827 828 EXPERIMENTAL ENGINEERING by the temperature of the suction water entering the combining space. This definition of the theoretical pressure in the combin- ing space is of the utmost importance in the determination both of the efficiency and of the limits of operation of the injector. In the combining tube, the energy exchange of velocities between water and steamis by impact. Hence the flows of water and steam, as they come together, should be as nearly as possible in the same direction; any cross velocities result in loss of efficiency of impact. Low efficiency of impact means that the kinetic energy of the steam is spent in heating the water rather than in giving it kinetic energy. The further function of the combining tube is the con- densation of the steam in the water. The steam, in the usual case of being initially nearly dry and saturated, decreases in quality during the isentropic expansion in the steam nozzle, coming from the nozzle some Io or 15 per cent wet. The condensation is not completely finished in the combining tube. It cannot be complete until sufficient velocity head of flow is changed to pressure head that the pressure equals or exceeds the boiling pressure corre- sponding to the temperature of the fluid. The maximum velocity of flow, and hence the lowest pressure head, occurs at the end of the combining tube and beginning of the delivery tube; the pressure necessary for complete condensation of the steam is therefore not attained until the fluid mass is part way through the delivery tube. The function of the delivery tube is to change velocity head to pressure head. The fluid enters the delivery tube with very low pressure and very high velocity (see the pressure and velocity dia- grams in Fig. 522); it leaves the tube with pressure equal to the discharge pressure and almost negligible velocity. In the delivery tube, as in the steam nozzle, the first condition for highest me- chanical efficiency (lowest friction loss) is that the change of section area along the length of the tube shall be such as to give uniform acceleration to the fluid handled. The second condition is that the tube shall be as short as possible with avoidance of eddy currents in the stream; this reduces skin friction to a min- imum. As explained above, the completion of condensation of the steam occurs in the delivery tube. THE TESTING OF INJECTORS 829 aeea | | \ | PRESSURES | AN \ | | PAT ' \ Atmospheric Pressure _ _ _-— === | Uz oars . S = CS SS Z- DISCHARGE = a = ( Water+Condensed Tipe TS an Cm SS sill e Combining Tube Delivery Tube Suction WSS I Water / WSs | / | \ oe VELOCITIES I | | I u u Fic. 522.— DIAGRAM OF INJECTOR. 378. Practical Construction and Operation. — A distinction may be made between injectors proper, which are intended to discharge against a pressure equal to or greater than the steam pressure, and ejectors, discharging against a lower pressure than that of the steam. Injectors proper handle correspondingly smaller amounts of water than do ejectors. Injectors now on the market may be classified as: ta. Automatic or restarting, when the mere opening of the steam valve is all the handling necessary to bring the instrument into operation. 1b. Nonautomatic, when manipulation of steam, water, and overflow valves is necessary each time the injector is started. 2a and 2b. Single tube or double tube, depending upon whether the instrument has between the suction and discharge ends one single set of steam nozzle, combining tube, and delivery tube, or two such sets in series with each other. Each type may be auto- matic (2a) or nonautomatic (20). - 3a and 30. Lifting or nonlifting, according as the instrument can, in starting, pick up its supply water through an appreciable 830 EXPERIMENTAL ENGINEERING suction head, or requires that the supply water be received at the instrument under some pressure. Each type may again be auto- matic (3a) or nonautomatic (30). 4a. Live steam injectors draw their steam directly from the boiler. 4b. Exhaust steam injectors operate on exhaust steam from some steam user such as an engine or pump. Exhaust steam injectors usually require auxiliary live steam supply. sa and 50. Compensating or noncompensating, depending upon whether the relative positions or sizes of the various nozzles and tubes may be adjusted to best suit various operating conditions, or whether these parts are fixed in size and position. Compensation may or may not be automatic. ta. Automatic starting is secured by using some form of divided combining tube. When steam is turned on it flows through the 4 YS oseom es Fic. 523.—SINGLE-TuBe Automatic Lrrrinc INJECTOR (PENBERTHY). steam nozzle and the first part of the combining tube, then escapes into the overflow space, and from this space into the air through a large and easily moved check valve. Flowing in this way, the steam rapidly sucks the air from the suction water line, and draws water into the instrument. As soon as enough water enters to THE TESTING OF INJECTORS 831 thoroughly condense the steam, the combined mass flows through the delivery tube and passes the delivery check valve. The pres- sure in-the overflow space then drops to less than atmospheric, and pressure relations along the combining and delivery tubes are used to cause an automatic closing together of the hitherto divided parts of the combining tube. An automatic injector will restart itself after any temporary interruption of action, provided the steam is left on. 1b. Nonautomatic injectors generally start by manipulation of the size and position of the steam nozzle. The overflow valve may or may not be automatic. 2. Double-tube injectors use one set of tubes for lifting and one Te 7 m1 Fic. 524.—Dovusie-Tuse NonavutomatTic Lirtinc INJECTOR (ScHUTTE-K OERTING ) for forcing. They have, in general, a wider operating range than single-tube injectors. 3. The sizes, forms, and relative positions of steam nozzle and combining tube determine whether an injector is lifting or non- lifting. 4. Exhaust steam injectors are usually double-tube injectors, using exhaust steam in the lifting set of tubes, and exhaust steam with or without auxiliary live steam in the forcing set of tubes. Whether or not live steam is necessary is determined by the pres- 832 EXPERIMENTAL ENGINEERING Ta To Boiler > INTERIOR VIEW Fic. 526.— Automatic Lirtinc EJECTOR. sure of the exhaust steam and the pressure against which the dis- charge must go. 5. Nonautomatic injectors are generally more or less compen- sating, through possible changes in relative positions of parts. Double-tube injectors are partially compensating because of the differentiation of functions. THE TESTING OF INJECTORS 833 Figs. 523, 524, 525 and 526 illustrate various forms of injectors. Fig. 525, by the omission of the ejector nozzle A and valve J and their connecting passages, becomes a nonlifting injector. 379. Efficiency of Injectors. — The injector may be considered in two ways: as a mechanical pump, and as a device for supplying hot feed water. Viewing the injector merely as a pump, the energy input is measured by the weight of steam supplied in unit time multiplied by the heat energy in one pound of steam above 32° F., under the observed conditions. The output is measured by the weight of discharge water multiplied by the total head through which it is lifted. In this view of its operation the injector is analogous to a piston steam pump which condenses its exhaust steam in its suction water, and discharges the combined mass of suction water and condensed steam. No credit is here given the injector for the fact that the water is heated as well as moved. When used as a boiler-feeding device, or as a pump where the heating of the water handled is an object, the injector must be credited with both the pump work done and the heating effected. The only loss is then the so-called “ radiation loss”’ of heat from the injector and its piping, as all friction losses in the flow of steam or water reappear as heat in the discharge. As this “ radiation” is quite negligible in comparison with the heat quantities in the steam, the heat efficiency of the injector is very nearly 100 per cent. Let w = pounds of steam supplied per unit of time. H = the “ total heat ” per pound of such steam as supplied =sr+qorrx+C,D. v = velocity of the steam, ft. per sec., at the point where H is determined. h, = distance from injector to center of steam gauge. See Fig. 527. J = the mechanical equivalent of heat = 777.5. Then the total energy supplied to the injector in steam in unit time is ‘ : why , WwW wH + oe =f er (1) 834 EXPERIMENTAL ENGINEERING wr or wHI + wh, + age (2) Let W = the pounds of suction water in unit time. p. = the absolute vapor pressure in lbs. per sq. in. corre- sponding to the suction water temperature. 4 = the discharge pressure, lbs. per sq. in. abs. ha = the head in ft., down to the injector, from the center of the discharge gauge. See Fig. 527. p, = the suction pressure, lbs. per sq. in. abs. h, = the head in ft., from injector down to the center of the suction gauge. See Fig. 527. V = the discharge velocity, ft. per sec., at point where p, is measured. 6 = the density of the discharge water in lbs. per cu. ft. Then useful work done in lifting suction water is “Al (hit jpg = + bei 144) ft-dbe, in unit time, @) and useful work done in lifting condensed steam is Ww (i 4. - + P= Pe, 144) ft-lbs. in unit time. (4) Note that in these equations 4, p,, and p, are expressed in pounds per square inch absolute. The pump efficiency of the injector is the sum of (3) and (4) divided by (2), or WY, ha +H + Ha b)f +w Via 4 a= Pa) 2g 6 2¢ 6 - (5) 2 wHJ +why+— 28 Let g, = the sensible heat of water at the suction temperature. ga = the sensible heat of water at the discharge temperature. Then the heat accounted for already in the suction water is Wa} the heat accounted for in discharge is (W + w) ga. The differ- ence is (W + w) q,—Wgq,. Note that this heat increase includes all the mechanical friction losses, such as friction head losses in suc- tion and discharge, and impact losses in the injector. If the in- THE TESTING OF INJECTORS 835 jector be credited with this heat gain as well as with the useful me- chanical work done, we have as the heat efficiency of the injector 2 — = Whe thaty +A PER P)} tab ig +E PE P9| 74 7 4 w)ga—Wesh wHI-+ihy + In the above equations, as circumstances change, various quan- tities may become negligibly small. The one quantity which will almost always be negligible is the term wh, in the denominators of Eqs. (5) and (6). Equation (6) should give practically 100 per cent. The magnitude of the “ radiation ” loss from an injector and its piping should be of the order of 0.1 to 0.5 of one per cent of the heat supplied in the steam. 380. Testing of Injectors.—One type of testing apparatus isshown in diagram in Fig. 527. It is based upon one designed and described Air Separating and Level. Tank J Cooling Outlet Weighing Tank M Make-up Feed Water Valve Venturi Meter Must be tight Fic. 527. APPARATUS FOR TESTING INJECTORS. by Schrauff in the Zeitschrift des Vereines deutchser I ngenicure, some modifications being made. The idea is to have continuous 836 EXPERIMENTAL ENGINEERING flow in a closed circuit. In passing through the injector, the water experiences both a pressure and a temperature increase. The tem- perature is again brought back to the initial by means of the cooling tank A, while the pressure is reduced and controlled by a valve B in the suction pipe to the injector. The discharge pressure is controlled by valve C. The steam pressure on the injector is regulated by valve D. The quality of the steam below valve D must be determined. Four gauges, E, F,G, and H, of which G should be a compound gauge, serve to measure the main steam pressure, the steam pressure on the injector, the suction pressure, and the discharge pressure, respectively. The quantity of water flowing through pipe J consists, of course, of the sum of suction water plus condensed steam. ‘This flows into a tank J which serves both as an air-separating tank and as a “ steam-level”’ tank. The air which separates goes to the top of the tank and may be allowed to escape through the air valve K. Temperatures are read at L (steam), M (suction water), N (dis- charge water), and O (in level tank). To make a run, start the injector and adjust valves D, B, C, cooling water control valve P, and condensed steam control valve Q, so that the desired pressure and temperature conditions are estab- lished, and so that the water level in tank J remains at one point as noted_on the gauge glass. When constant conditions are estab- lished, the run may be started and continued as long as desired. The actual quantity of suction water handled may be determined by any good meter. In the diagram, a Venturi meter R is indicated. The condensed steam is caught and weighed in tank S. To make certain that there is no loss at this point from vaporization, it is well to have both the condensed steam and the air pipe dip into cold water. Rough testing of an injector may be done with a pair of similar tanks on scales, drawing suction water from one tank and discharg- ing into the other. The suction and discharge piping running down into the tanks must then be of the same size, and end fittings the same, to avoid displacement errors in weights. The suction tank readings give the rate W; the discharge gives (W + w). The values of w so obtained are subject to large errors. It is perhaps better THE TESTING OF INJECTORS 837 to compute w from the observed value of W by means of Eq. (6), on the assumption that heat efficiency = 100 per cent. The independent variables entering into the injector operation are: (x) Steam pressure and heat content of steam. (2) Suction pressure. (3) Suction temperature. (4) Discharge pressure. When an injector is used as a boiler feeder (1) and (4) are equal; more precisely, (4) just exceeds (1). An injector test should include the following runs: 1. With suction pressure and temperature constant at average values, take a series of steam pressures and for éach steam pressure vary the discharge pressure from the lowest to the’ highest under which the injector will operate. Between the lowest and highest discharge pressure for each steam pressure, choose three or four other discharge pressures in a series in order to obtain five or six points for a curve. 2. With steam and discharge pressures adjusted at any desired points (usually taken as the pressures of regular ordinary operation), and fot an ‘average suction lift or pressure, make runs with a series of temperatures of suction water, continuing to increase the temperature until the injector “ breaks,” that is, refuses to operate, the discharge either going out of the overflow or the steam blow- ing down the suction pipe. Make sufficient runs to determine a curve. 3. With-the same steam and discharge pressures as. under 2, and with an average suction temperature, make a series of runs with varying suction lifts or pressures, increasing the lift until the injector breaks. Of the following forms, the first may be used for recording the observations, the second shows the principal data that should be reported, together with the items to be obtained by computation. The best method to show the limits of operation of the injector, efficiency, etc., is to plot certain curves. The most useful of these are the following: 838 EXPERIMENTAL ENGINEERING (2) For the suction pressure and temperature under (1) above, plot as abscisse steam pressures, and as ordinates 1. Values of w. 2. Values of W, maximum and minimum, or w x as 3. Values of —, maximum and minimum, also 4. Values of maximum discharge pressure, and 5. Values of minimum discharge pressure. DEPARTMENT OF EXPERIMENTAL ENGINEERING, SIBLEY COLLEGE. TOS Ofiec oe eeaeas soa iwues eenes 745 HES Injector MOGs i cnniaiaiesaiesareietire te 19 Dia. Suction Pipe......... Dia. Discharge Pipe...... BY 's es aeidaees see eee Dia. Steam Orifice. ........ Did. Water OPfiCC 6 5 aoce eacncacsrnels teenie Fee MiOee wee ee nad Gauges, Lbs. Temperatures, Degrees F. g g g F ; Bel 3 2 8 B : BR g ee | oo ee ee ee lee) Se eee 3 4 dg % 2 | 3 g a | 3 ict 8 4 3 a a fa ce) a a a a a oO “4 Hy 4 THE TESTING OF INJECTORS 839 MECHANICAL LABORATORY, SIBLEY COLLEGE, CORNELL UNIVERSITY. DATA AND RESULTS OF INJECTOR TEST. Lest Of she adiiniWuivervsreacua sulouegiaran ees Injector Date............. IQl.... Vertical Distance from Injector to Center Made by... . cece eee of Steam gauge = hw Pisceasene- «a iowah oRartlooduaa Vertical Distance from Injector to Center a eee ee eee of Discharge gauge = ha fist waa Moi Barometer Reading....... Vertical Distance from Injector to Center of Suction Gauge = he ere Run No. I 2 3 4 5 6 Duration of test; minutésie cde de ness | eescel ss Sicallescnsallensagall pees ealecea oa Boiler pressure, by gauge.............. Steam pressure on injector, by gauge.... Steam pressure on injector, absolute. ... Suction pressure, by gauge............. Suction pressure, absolute, =ps ......./... cc cfeeece fee eee [eee e selec ee eefen een Discharge pressure, by gauge. .....--- 0)... ccfece eee few eee fee eealeceeeefee ees Discharge pressure, absolute, = pd... -..J......[ec cree [ere ce [ewes eeleceeeefeeeeee Pressure corresponding to suction water temp; absolute, —=Peraskcsis sca creo as |aguwew|sensd | tee] soos shes aues Total discharge Heal ae 1 cobs: yes eaianasasl oncag al -pemasel-caueaahevsieuelienwendbees sac Total suction head in feet. .i.4 scxauess[ocvavelevsansle sane s|evnsndfereuen [ans sa Steam supplied per hour=w..........- feces ee fee eee efor eee fee eee lene ee epee ees Suction water per hour =W 20sec wera vallees sau hsees os lhewes.wsdlaeeiawe' ine we at RECON WE Sie seer ccntraresRogs: 3 OG IEA Feechl aare draval| io see eedouanas 2s laid. 'e lsat adel eee ierd Velocity of steam at point where pres- sure is measured, ft., per sec., =O...-[o.. es. feces e fees eee feceee fence efor eee. Velocity of discharge at point where pres- sure is measured, ft., per sec., = V....]. 0... feccce fees eee lec eee elece ee efe re aes Density of discharge water, Ibs. per cu. fe Siccs caadaoiaiarttigise ties selveaeas| $e tens | Peaawe| teeeeeleeeae eke ys Quality of steam, moisture, or superheat |......]....../......)e.eee [eee e fees Sensible heat of water at suction temp., Bible, SGas a vies vesonevie wees mee fewliaioad oorddine | seems | 6 4 etna [ey wneeal eles Sensible heat of water at discharge temp., Bitty Sage sc ekatih oan nce es erkactws lpameus ly eeead |e maxed] Pasewna | Poaemeleenaian Total heat per pound of steam supplied, Bits, Hie ws cactdsadaneds ve acta cs esate syecen|peassh po denales a mewlaseees Total energy supplied to injector per HOUR, Bet Wisin scp aceden ys soe te GEA S ele call Sete s aloe] ba saa Gils ccna llerenaiecas Total energy supplied to injector per Ovirg FEMS isc ices epee se Se onc us| echoes alte Bue aaa de Ascent toh Soa Sika. adie avai oeeaanaees Useful work done in lifting suction water, Bites. 2g cisah vn saa ete enna a $ ae sts soptalanaeal| doccargcnn) | a\craysre) spies a | a a marsala Useful work done in lifting suction water, fEA1BS: coches eee ah be adsodeuiee to IOS | aaleetall wadechis eesell oe seunlereaigiapMedues Useful work done in lifting cond. steam, Useful gore done in Witing cond. steam,) ==} 3 3=| 3 3o|) 3 326) READS: |. ks Sechaee Mates aah ye seree et lente | Vata! ae eet finally dllhe tudtuess Tlayeemseale Pump efficiency of injector, per cent....J.....-f.. 02. fee ee efee eee eee eee efe cece Heat efficiency of injector, per cent.....).....-Je..---feeeee fees eee fence epee eens 840 EXPERIMENTAL ENGINEERING (0) With steam and suction pressures constant at the probable working values, plot as abscisse suction temperatures, ordinates same as under (a). (c) With steam pressure and suction temperature constant at the probable working values, plot as abscissee suction pressures, ordinates same as under (a). If all of the curves listed above should be determined and plotted, they would show the operation of the instrument in so complete a fashion as to answer any of the questions which would be likely to arise in any commercial practice. An injector is peculiarly sensitive to variation of suction temper- ature. This sensitiveness will be explained by considering the heat energy available in isentropic drop from the initial condition of the steam to the vapor pressure corresponding to the temperature of the suction water. It will be found that the available heat energy falls very rapidly as the suction temperature rises. CHAPTER XXI. GAS ENGINES AND GAS PRODUCERS. 381. Types of Gas Engines. — All gas engines belong to the class of internal combustion engines. (See introductory paragraph, Chap. XXII.) Without reference to any types that may have been tried and abandoned during the past, we, at the present day, dis- tinguish only two fundamentally different types of internal com- bustion engines. The distinction is based upon how the combus- tion proceeds, whether at constant volume or at constant pressure, and we therefore have, as a primary classification, constant volume and constant pressure engines. . In engines operating upon the constant volume cycle, the com- bustible charge is compressed and then exploded at the inner dead center position of the piston. This results in practically constant volume combustion. The cycle is completed by the expansion {Vee ee == _ Atm. Line 1 Fic. 528. —TyPIcAL 4-CYCLE DIAGRAM. stroke following, the burned gases being discharged after the open- ing of the exhaust valve, largely at constant volume. This is the theoretical cycle, which, from the inventor who first applied it successfully in commerce, is also called the Otto cycle. For the 841 842 EXPERIMENTAL ENGINEERING Suction == Fic. 529.— OPERATION OF 4-CYCLE ENGINE. efficiency computations on the basis of this theoretical cycle see P- 349. In practice, engines operating upon the constant volume or Otto cycle are divided into two classes, depending upon the method GAS ENGINES AND GAS PRODUCERS 843 of charging and discharging the cylinder. We distinguish accord- ingly 4-cycle and 2-cycle engines. The terms four-stroke cycle and two-stroke cycle engines would be more strictly correct, but are too cumbersome, hence the shorter designation. In 4-cycle engines, the charging and discharging actions are carried on by the engine cylinder itself, the latter acting as a pump for two strokes. Fig. 528 shows a conventional 4-cycle indicator diagram, the lower part of the diagram, the so-called lower loop, being some- what exaggerated for the sake of clearness. The strokes are marked in order. Stroke 1 is the suction stroke, the piston on its outstroke drawing in the new charge behind it. Stroke 2 is the compression stroke. At the end of this instroke the charge is exploded, the pressure increasing at constant volume. Stroke 3 is the expansion stroke. Near the end of this stroke the exhaust valve opens and on the next instroke, the exhaust stroke, the piston drives the burned gases out ahead of itself, after which stroke 1 is repeated. The corresponding valve movement may be studied by aid of Fig. 5209. In a 2-cycle engine, the suction and exhaust strokes of the 4-cycle engine are eliminated, the cylinder being charged with fresh mixture and cleared of burned gases by agencies other than the action of the power piston of the engine. The power cycle is complete b Fic. 530.— TyPIcAL 2-CcYcLE DIAGRAM. in two strokes and there is no lower loop to the diagram, the work of charging and discharging represented by the loop area being done in an outside pump of one type or another. Fig. 530 shows the typical 2-cycle diagram. The mixture, compressed by the instroke 844 EXPERIMENTAL ENGINEERING of the piston, is ignited at point a. Expansion takes place from b toc. At the exhaust ports open and the pressure drops rapidly to nearly atmosphere. Soon after point c is passed, the inlet valve opens and fresh mixture is forced in by the outside pump. At d the piston starts to return, and at e the exhaust port and inlet valve close; compression then begins. The charging and discharging Charging Pump Inlet Vv / sz roe oS ON i Me oe Transfer © V: Tnlet Valve Exhaust Port. Charging Pi Inlet Valve Transfer Valve Exhaust we ‘ort. Fic. 531. OPERATION OF 2-CYCLE ENGINE. actions evidently take place while the power piston is moving from c around d to e. The burned gases escape partly by their own expansion while the rest is forced out by the fresh mixture coming in. It is evident that the exhaust ports must close, whatever design of inlet and exhaust ports is used, before the combustible mixture reaches the exhaust ports. Otherwise there will be a serious loss of fuel. A conventional sketch of a type example of such an engine is shown in Fig. 531. It consists of a power cylinder with separate » GAS ENGINES AND GAS PRODUCERS 845 charging pump, whose crank leads the main crank by a certain amount (in this case about go degrees). In the upper sketch the mixture is just being exploded and the piston starts on the outstroke (point a, Fig. 530). In the meantime the charging pump is drawing in the next charge. In the lower sketch the power piston has opened the exhaust ports (point c in Fig. 530), the hot gases have largely escaped, and the charging pump piston, being now on its instroke, is forcing a new charge into the power cylinder under some slight compression. When the power piston, on its return, closes the exhaust ports and the inlet valve to the cylinder also closes, compression begins (point e in Fig. 530). In practice, nearly all medium or large sized 2-cycle engines are built with separate pumps as described. In some cases, to cheapen the construction, or to make it more compact, the front end of the power cylinder is enclosed, thus converting that end into a charging pump. A large variety of small, vertical, 2-cycle engines are built in which the entire crank mechanism together with the lower end of the cylinder are enclosed, and this space is used as a charging pump. Most small 2-cycle marine engines are constructed in this way. In both of the latter modifications the power piston also acts as the pump piston, but not in the power end of the cylinder. The only commercial example of the constant-somme engine is the Diesel. Its operation is very similar to that described above for the constant volume type. The difference is that only air is compressed and that to the maximum pressure existing in the cycle. Then at or near the inner dead center, the liquid fuel, which is always used, is injected into this body of air, highly heated by compression. The result is combustion at practically constant pressure until the fuel valve cuts off. Then follow expansion and exhaust in the regular manner. The student is referred to Chap. XVI, for type examples of actual indicator diagrams from gas and oil engines. Gas engines may be made single or double acting. In a double- acting gas engine, each cylinder end is used for power development, the engine being built with piston rod, crosshead, and connecting rod, as in a steam engine. In this design, a 2-cycle engine will receive an impulse every stroke, just like a steam engine. 846 EXPERIMENTAL ENGINEERING As far as cylinder arrangement is concerned, we distinguish the following: Tandem. — All the cylinders are in line acting on the same crank. Not more than two cylinders are usually employed, and these may be either single or double acting. Double, two-cylinder, three-cylinder engines, etc., according to the number. The cylinders are placed side by side, usually acting on as many cranks as there are cylinders. May be single or double acting. Double-tandem. — Usually four cylinders, two each in tandem, acting on two cranks. May be single or double acting. Opposed Arrangement. — Two or four cylinders opposed to each other, in the latter case in pairs. Any two opposed cylinders may act on the same crank, or each cylinder may have its own crank. Usually built single acting. 382. Gas Engine Fuels. —The combustible charge in a gas engine cylinder at the moment of explosion always consists of a mixture of a gas or of an oil vapor with certain quantities of air. The explosibility of these mixtures, as well as their characteristics in general, depend upon the proportion of fuel to air present. Fora discussion of this matter, the student is referred to books on gas engines. It is desired to point out here merely the fact that the combustible part of a charge is always a gas or a vapor, irrespective of the original state of the fuel. All three classes of commercial fuels, that is, the solid, the liquid, and the gas fuels, are used, but only the gas fuels can be used directly in anengine. The liquid fuels must first be vaporized or atomized in carburetors, vaporizers, or spray nozzles, while the solid fuels must be converted into producer gas in special apparatus called producers or generators. The gas fuels most used in gas engine practice are: illuminating gas, natural gas, blast furnace gas, and producer gas. Any of these gases are fixed or permanent gases, and it is merely necessary to furnish the engine with suitable mixing valves to maintain the proper proportion between gas and air. The liquid fuels are generally divided into two classes: the light or volatile liquids, and the heavy liquids. To the former belongs GAS ENGINES AND GAS PRODUCERS 847 gasoline, while kerosene, the so-called distillates, and crude oils belong to the latter class. Alcohol holds a somewhat intermediate position. The distinction between the two classes is not very sharply defined. Generally it is stated that the light liquids can be successfully converted into fuel gas or vapor without the agency of heat, while the class of heavy liquid fuels usually requires heat. The use or nonuse of heat is apparently also the distinguishing mark between carburetors and vaporizers. Thus the apparatus used for the formation of the fuel gas in the case of gasoline is called a carburetor, the air merely passing through and taking up a sufficient quantity of the volatile liquid. In the case of alcohol, kerosene, or crude oil, this simple scheme is not applicable, these liquids not being sufficiently volatile at ordinary temperatures to form a combustible mixture with the air passing through the appa- ratus. It is necessary to apply heat to hasten volatilization (vapor- ization) and the apparatus used is then known as a vaporizer. It is true that in some engines any of the liquids above mentioned are atomized or sprayed directly into the engine cylinder without first going through the process of volatilizing or vaporizing. It will generally be found upon examination, however, that (except perhaps in the case of the constant-pressure engines, like the Diesel) the fuel is sprayed into the cylinder at such a part of the cycle that sufficient time is available for the finely-divided oil “ fog ” floating in the charge of air to vaporize largely before ignition takes place. The solid fuels, such as wood, peat, lignite, coke, and the various classes of coal, are gasified in producers, as has been already men- tioned. The manufacture of producer gas has grown to be of great economic importance, so that the principles underlying the process merit some detailed discussion. 383. Producer Gas. — Producer gas is a composite gas consisting mainly of CO, Hz, CO2z, Ne, and certain other gases resulting from the distillation of the green fuel used. The producer-gas process is essentially a combination of the air- and water-gas processes. In the former, a fuel column is supplied with air alone under certain conditions of control, and the resulting gas consists of CO, COs, and Nz. In the water-gas process, water vapor (steam) alone is forced through a fuel column which has been previously made incandes- 848 EXPERIMENTAL ENGINEERING cent by blowing air through it. The result is a gas consisting of CO, CO, and Hy. The reactions occurring during the time that water gas is being made absorb heat, and the process is combined with a continual cooling of the generator contents. The process of making water gas is consequently intermittent, a blowing period (with air, making air gas), alternating with a period of water gas make (blowing with steam). Combining these two periods, that is, blowing with a mixture of air and water vapor, makes the process continuous, and constitutes our modern producer-gas process. The chemical reactions involved in the making of producer gas and the thermal relations existing are outlined by Fischer,* as follows. The quantities of heat given in each equation assume that one pound of carbon enters the reaction instead of stating the heat on the molecular weight basis, as is generally done in scientific works. The algebraic sign preceding the quantity of heat states whether heat is developed (plus sign) or absorbed (minus sign), that is, whether the reaction is exothermic or endothermic. The first reaction occurring in the producer is probably the formation of CO, frora the C in the fuel and the free oxygen of the air, according to the equation Cy + 20, = 2 CO, + 14,540 B.t.u. (1) The development of heat indicated in (1) serves to render the fuel incandescent, so that with water vapor we next obtain the reactions C. + 4H,O = 2 CO, + 4 Hy — 2848 B.t.u., (2) and Cy + 2 CO, = 4 CO — 5780 B.t.u. (3) Both of these reactions are endothermic and require a temperature of about 1500°F. Equations (1) and (3) result in the indirect formation of CO. Combining these equations by addition to obtain a direct expression for this end result, we may write C. + QO. = 2CO + 4380 B.t.u. (4) Similarly, a combination of equations (2) and (3) gives C. + 2H2O = 2 Hp + 2 CO — 4316 B.t.u. (5) * Fischer, Kraftgas, Seine Herstellung & Beurteilung. GAS ENGINES AND GAS PRODUCERS 849 If there were no losses of heat, the ideal producer-gas process would then be a combination of equation (4) (ideal air-gas process) and equation (5) (ideal water-gas process), which may be written 2C,+0O:,+2H,0 =4CO+ 2m). (1) Since the oxygen in (4) is obtained from air, a certain amount of nitrogen (Ne) will also appear in both sides of equation (I). The composition, volume, and weight of the resulting gas per pound of C consumed is shown in the following table. To obtain volumes, the weights of the various gases per cubic foot at 14.7 pounds and 32° F. have been used. Weights Involved in Eq. I. iti eights Involved in Eq. Sip Ppa ices Composition of Gas. Gas, Cu. Ft. per Deeaeh Be Gay Z ‘ a Lb. of C. er Cent by er Cent by Left Side. Right Side. 9 Weight. Raine Coeencaeades LOO.” ¢ yas be cecin mrad. dal tealed erat ce neon | aaah asa, te aval hectic de anepeadelus Diecast exer SNOOP Hl hccuecantedh tare Sak a eweahis Wg iht-eot ar. apa teiootas en ese ea acnoeaeho aan esata Nos eciceondtet 2.23 2.230 28.4 48.0 38.9 H,O........ BUG Meters sre ne oe | adhe aie aleienal imnaedcenehe dean hal hgeareeia yamine COs erase [eet amine 2.330 29.8 50.2 41.0 His Seated ee edge ha oe 083 14.8 £8 20.1 4.643 73.0 100.0 100.0 In practice, however, a large part of the sensible heat developed by equation (4) is lost instead of being used to make up the deficiency shown in equation (5). Hence, if any given temperature level is to be maintained in the producer, the reaction represented by equa- tion (4) must occur several times as rapidly in the same time as the one represented by equation (5). Assuming, for instance, that only 1500 B.t.u. of the 4380 in equation (4) are actually utilized, it is evident that (4) must occur about three times as often as (5) in the same time. The producer-gas process can then be represented by the equations C, + 2H,O = 2 H+ 2CO — 4316 B.t.u. 3 Ce +3 0,= 6CO + 13,140 B.t.u. or 4C, +302. +220 =8CO + 2 FR + 8824 B.t.u. (II) If it is next assumed that the decomposition of the water vapor takes place solely according to equation (2), then, again assuming that only 1500 B.t.u. of the heat developed in equation (4) is utilized, 850 EXPERIMENTAL ENGINEERING the latter reaction would have to occur about twice as often in the same time as equation (2) to make up for the deficit of 2848 B.t.u. This condition can be represented by the equations C, +4H,0O = 2 CO, + 4 He — 2848 B.t.u. 2C, +20, = 4CO + 8760 B.t.u. or 3C2 +20.+4H,0 = 2CO,+4CO+ 4H + 5912 B.t.u. (II) In practice, gasification according to equations (II) and (III) is likely to go on simultaneously, so that in any given case the actual gas made will show a composition intermediate between those given for these two equations in the following table. The higher the temperatures, the more nearly will equation (II) be realized. Weights Involved in Vol. - Prod. Composition of Gas. as, Cu. Ft. per Lb. Weight, Per Volume, Per Eq. II. Eq. III. of C. Cent. Geat. Left Right Left Right . Side. Side. Side. Side. Eq. II. | Eq. III.} Eq. II. | Eq. IL.| Eq. II. | Eq. III. oe ete tate t lsyeces L100" |Wa vas slewod dale ces ends Sl eane corel ln: ence alee Ope sa. ssnanaiees Mop. Meret 89 Brees 95 Si A adaec take: ve. ieee esatydy ay Pataca tam ve Reyrerg Sh bile Gaig.ve abatadlne doses Is Nasa seats 3-35 | 3-35 | 2-97 | 2-97 | 42.8 | 37-9 | 58.6 | 50.6 | 53.4 | 43.3 H.O...... BIS) orice s TiOO: |aseeten gis Reee adr] Vives pin| haat ace [leumtaceom oil wesgecise at lheuatatiantss CO isos aliases BAB. We ceeae 1.56 | 29.8 | 20.0 | 40.7 | 26.6 | 37.2 | 22.8 Riess auallewendellegcae eliveenee P28 omen atu TO [esewes CUO naka Il.4 Fg: os seeds fesse (oy. bo] ae Imm] 7.5 | 19.7 7 1.8 9.4 | 22.5 6 v922 5.871| 80.1 | 87.6 |100.0 |100.0 |100.0 |100.0 384. Types of Gas Producers. — The simplest type of a gas pro- ducer is shown in Fig. 532. The fuel bed is divided into different zones showing where the reactions above outlined occur. The composition of the gas is, of course, changed from that computed by whatever gases or vapors are added to it in passing through the distillation zone. It is obviously immaterial, as far as the gasification process is concerned, whether the air-steam mixture is forced through the fuel column by maintaining a slight pressure above atmosphere in the ash pit, or whether the mixture is drawn through by producing, by some means or other, a vacuum at the outlet of the producer, which vacuum, of course, causes a pressure difference between gas outlet and ash pit and hence produces flow. These two methods of pro- GAS ENGINES AND GAS PRODUCERS 851 ducing gas flow, however, distinguish the two main types of pro- ducer-gas plant, the former being called a pressure-gas, the latter a suction-gas installation. A pressure-gas plant requires a closed ash pit, and the gas is forced through an economizer, or preheater, and through a washing appa- Actions, Airs ‘Water Vapor Fic. 532.—Smere Type or GAS PRopucer. ratus into a gas holder. The pressure is produced in various ways, generally by means of a steam blower. The essential parts of such a plant are shown in Fig. 533.* B is the generator with the filling hopper C. The air under some pressure, furnished by the blower V, reaches the ash pit by first passing through vaporizer (or econ- omizer) EZ. The proper quantity of water is supplied to this vaporizer through the funnel Ff. The heat of the producer gas made, entering E through n, vaporizes the water and the vapor is picked up by the air passing on its way to the ash pit. The partly- cooled gas reaches the scrubber G through W, passing upward * This and the next three figures are due to Fischer, Kraftgas. 852 EXPERIMENTAL ENGINEERING Widitddietbittlttl Fic. 533.— PRESSURE-GAS PLANT. l = y : PTOI, % WihiiVG @ Hi , * UW vi tlhiiithisbeny Peartainlil . Fic. 534. — SUcCTION-GAS PLANT. GAS ENGINES AND GAS PRODUCERS 853 through a coke column. The washing is done in G by water sprays passing downward against the ascending gas column. A is a purge pipe through which the poor gas made while the producer is being put into service is allowed to escape. The gas receives a final cleaning and drying in the purifier S, the trays of which carry either sawdust or excelsior, before being sent to the gas holder through HZ. The main parts of a suction-gas plant are shown in Fig. 534. Here 6 is the producer with its filling hopper a. The vaporizer c is a hollow casting surrounding the top of the producer. As the piston of the engine cylinder makes an outward (suction) stroke, it creates a vacuum of several inches in the small receiver m. This causes a flow of gas toward the engine through seal-box /, scrubber k, ‘and pipe g, and the difference of pressure thus produced between g and ash pit f causes a rush of air-steam mixture through the fuel column. The air enters the vaporizer through the regulating valve d’, saturates itself in passing through c, and finds its way through d into f; eis an auxiliary air-supply valve to regulate the proportion of air to water vapor; # is the purge pipe and 7 a double-throw valve; is a “ wire brush ” cleaning box which serves to remove the last traces of tar that the gas may carry. In gas-engine practice, the suction-gas plant has largely sup- planted the pressure-gas installation, the main reasons being the smaller cost of installation, on account of the absence of the gas holder, and the fact that the regulation of the gas made in the suc- tion-gas plant is automatic, the quantity made varying directly with the demands of the engine. There are so-called ‘‘combination” plants. If, for instance, in Fig. 533 the blower V were removed and an exhauster had been in- stalled at H, between the purifier and the gas holder, the installa- tion up to the exhauster would evidently be of the suction type, while the gas beyond the exhauster would be under some pressure. Producers are also classified according to the kind of fuel burned, and among the gases made we have anthracite-producer gas, bitu- minous-producer gas, peat gas, wood gas, oil gas, etc. Of course, for any given fuel, the plant may be either a pressure, a suction, or a combination gas plant, but in some cases the producers 854 EXPERIMENTAL ENGINEERING themselves show radical differences in design, depending upon the fuel used. These differences in design are necessitated by the fact that some of the fuels produce tar-forming gases to such an extent that the ordinary scrubbing apparatus is not capable of properly cleaning the gas for engine service. The types of producers above described will do very well for anthracite coal, a fuel which carries very little tar-forming gas (mostly hydrocarbons); and the gases of distillation escaping from the green fuel and which add themselves to the rest of the producer gas, therefore cause little trouble. The same is not true, however, of bituminous coal, and in that case special precautions must be taken to get a satisfactory gas. The way usually chosen is to collect the gases of distillation from the green fuel and to “ fix” these gases, that is, to render them per- manent in some manner. This has led to the design of “ down- draft ” and “ double-zone ”’ and “ ring ”’ (series) producers. The principle involved is perhaps best understood by studying the series producer, Fig. 535. Two producers, G; and Gz, are con- Fic. 535.— SERIES PRopucERs. nected as shown. In G the fuel used is bituminous coal, in G it is anthracite or coke. The gas in the connecting pipe y carries the tarry gases resulting from the distillation in G,, and the entire body of gas is made to pass upward through the column of incan- descent coke in G;. An auxiliary air supply is furnished through GAS ENGINES AND GAS PRODUCERS 855 In. The tarry gases are either, burned to H,O and CQ, near the base of the column, or certain reactions take place, the final prod- ucts being Hz, and CO. These are, of course, permanent gases and the trouble of tar deposit is avoided. In the down-draft producer the operation is very similar to that above described except that only one producer is used. The air- steam mixture is sent in at the top, under the filling hopper and moves downward through the fuel bed, carrying with it the gases of distillation from the green fuel in the upper layers. These gases are fixed, as before, in passing through the incandescent layers of fuel on their way to the bottom. The double-zone principle is illustrated in Fig. 536, which rep- resents a suction-gas producer. The green fuel is charged at the top and the fire near the top is maintained by an air supply through the cover. The vacuum ZZ. VILLE produced at ¢ draws the gases BO of distillation downward through the upper fire zone, fixing them. At the same time air enters at a, saturates itself in passing through the vaporizer, and finds its way through 0 to the ash pit, maintaining a second fire zone over the grate. The gas made passes out at c. The lower fuel supply is maintained by coked fuel which passes by the opening ¢ unconsumed in the upper zone. There are many modifications of the design described, for which the reader must be referred to special books on the subject. 385. Data Relating to Gases, Fuels, etc., Generally Used in Efficiency Computations on Gas Producers and Gas Engines. (a) Atomic Weight, Density, Specific Weight and Volume. Stand- ard Conditions. — The density A of a gas is generally referred to air as a standard, and is defined as the weight of a certain volume of a given gas divided by the weight of an equal volume of pure, dry Fic. 536.— DovuBLe-zONE PRODUCER. 856 EXPERIMENTAL ENGINEERING air, the temperature and pressure conditions, of course, being the same. The weight of a cubic foot of any gas is designated by 4, and, if the conditions are standard (14.7° pressure per sq. in. and 32° F.), is called the specific weight 6). Since one cubic foot of dry air under these conditions weighs 0.08071 pound, we have the following relation between specific weight and density. 6p = 0.08071 A. (6) The specific volume, v, of any gas, that is, the number of : i I ‘ re cubic feet per pound, is, of course, = 3 and if the conditions are standard I Vo = 55 (7) The table below gives the values of 59 and v for a series of gases, but they may also be computed from the following relations. From the general gas law Pv = RT, we have RT = P . (8) Now for standard conditions, T=459.6+32=491.6°, and P=2117 pounds per square foot. Hence iI 492R R v, =e oS oS i © 8 -217—«4.306 anak (9) v= O!lH We may also derive from Avogadro’s law that m 59 = —— lbs. per cu. ft. toa ee (10) where m = the molecular weight of the gas. Example. — The molecular weight of CO, = 44. Hence 44 6 = =. . Oe 1229 lb. per cu. ft., iL I - : and 0% = ec a = 8.14 cubic feet. Or, since R = 34.89 for this gas (see table below), we will also have V = R = 34:89 = 8.10 cu. ft. 4.300 4.306 The agreement is close enough for all practical purposes. GAS ENGINES AND GAS PRODUCERS 857 Since the volume of any given weight of gas is a function of both pressure and temperature, all gas volumes should be reduced to some standard set of conditions, in order to obtain a comparable basis. The conditions usually assumed are 14.7 pounds pressure per square inch and 32° F., although in view of the fact that 32° is an unusual temperature, some authorities have proposed to use 60° F. Volume varies inversely with absolute pressure and directly with absolute temperature. Consequently if V is the volume of gas under an absolute pressure of P pounds per square inch and an absolute temperature of T degrees F., the volume Vo under standard conditions will be Vom Vi AOE — 35.485 V cu ft. (11) Where engine guarantees are based upon cubic feet of gas used, the matter of reaching an understanding as to pressure and temper- ature is of importance. The latter evidently control the weight of the number of cubic feet of gas guaranteed. Engine performance is a function of charge weight, not charge volume, and of heat content of the charge, and these factors are largely controlled by pressure and temperature. ‘ Pe a} a a s B/2 |22|/ Fit jae | 3 | g @ Bales 8 & og 3 Ry = uw 2 & & m, etc. This quan- tity is little used in engineering work. Practically all of the experimental work in connection with spe- cific heats has been done with the Centigrade scale of temperature. Hence this scale is retained in all the equations, the transposition being made only in the curves. It can be shown that if C,, the instantaneous specific heat at any temperature, ¢, is represented by the function Cry =eth+c+dh +ef#+ (16) the mean specific heat in the range from o to the same temperature, t, can be represented by b Cc d e Cu See ee + ee ee, I (0-1) r 3 a 5 (17) These relations will serve for the conversion of mean into instan- taneous specific heats or vice versa. Note that the mean specific heats are computed above o° C, Concerning the inter-relation of C,; and C,,;, Boynton has shown that for Nz, Or, Hz, CO, CO2, H20, SO2, and NHs3, we may write BmC,;(y — 1) =3; or mC,;(y —1) = 2.00. (18) : Cor igs 3 g Since y = a. this expression may also be written vt m (Cys a, Cy.) =2; or Cos Py Cys a = (19) How closely this equation is actually fulfilled, as judged from GAS ENGINES AND GAS PRODUCERS 865 the basis of existing experimental results, may be seen from the following: 8 For co Air H:0 He mC yp; — MC, = 2.017 1.960 2.020 1.955 The theoretical value for y is the same for all monatomic gases (= 1.667); for all diatomic gases (=1.400); for all triatomic gases (= 1.286) etc., assuming no association or dissociation to occur. Consequently Gs ; and C,; should be the same for all gases of the same atom ember in the molecule. Experimental data show that this condition is not quite met (see the curves below), but how far this is due to errors involved in the investigations is, of course, problematical. The following equations represent the final results of Professor Upton’s investigation, except for the case of He, for which Langen’s equation is used. (Temperatures are in degrees C.) Mean specific heat................ eo = 0.216 + 0.000014 f Oxygen Com = 0.153 + 0.000014 t (0.) Instantaneous specific heat...:.... Ci = 0.216 + 0.000028 t aa Cy; = 0.153 + 0.000028 ¢ itrogen = (N.) and | Mean specific heat ............... ae Bai por meee Cahn Com = 0.171 + 0.000019 F monoxide | Instantaneous specific heat........ Cys = 0.243 + 0.000038 f (CO) vg = 0.171 + 0.000038 f Com = 0.237 + 0.000019 ¢ Mean specific heat............... Cin: = Orn68 60000086 E ‘ Cpoi = 0.237 + 0.000038 £ He HEA. y.en esd P* Instantaneous spec: e lon Si eae ‘pm =-200+75 X10 °t—21 X10 Ph +2.2X10 "FB Pas Mean sp- Bt le m=.I55-+75 X10 °t—-21 X10 ° 2+2.2X10 VF (COs ick eet C,. =.200+150X10-°t—65 X10 °° #+9.1 X10 7 (COs cr lon ng =-155+150X10-° ¢—-65 X10 #+09.1 X10 7 F Com = -452+7-4 X10 *t+92.6 X 10°! — 20.6 X10 PF Wate Meese al =.340+7.4 X107 %+92.6 X10 °f — 20.6 X 10-1 Lecter Tass ep. ht a =.452+14.8 X10 °f+278 X10 °F —82 X10? a ae Cy, =.340+14.8 X10 *t+4+278 X10 °F —82 X10- PB. For hydrogen (Hz) the following may be used: Com = 3-369 + 0.00055 ¢ Mean sp. heat. ......... ie a ea ecca Cpt = 3-369 + 0,0011¢ Coz = 2.369 + 0.0011 ¢ Hydrogen (Hs) Inst. sp. heat............ 866 EXPERIMENTAL ENGINEERING The information on CH, with regard to specific heats is very meager. The writer has been able to find only one equation, that given by Richards in his Metallurgical Calculations, Part I, p. 110. The equation there given, computed to the ordinary basis, shows the following: Mean sp. heat........... Com = «532 + .00031 Methane Com = .407 + .0003 t (CH,) Coir = -532 +-00068 Inst. sp. heat............ Nene ats Cy; = .407 + .c006t To save the labor of solving these equations for any ordinary case, the curve sheet, Fig. 537, gives a graphical solution of them up To Obtain Mean Specific at Constant Vol. Subtract L110] - from (Cpm)the following OQ, Ny Air CO, HyQ CO He CH 1.05} : .063 .072 .069 .045, 112 .072 1.00 1.00 0 200 400 600 600 700 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 Temperature Deg. C 32 212 392 572 762 932 1112 1202 1472 1652 1832 2912 21922372 2552 2732 2912 3092 3272 Temperature Deg. F Fic. 537. to 1800° C. (3272° F.). It should be stated that beyond 1000° C. the results are somewhat uncertain and that in consequence depend- ence can be placed in only the first two significant figures in the decimal. The curves give the mean specific heat at constant pressure (C,,,) between 0° C. (or 32° F.) and any other given tem- perature 7. From this the value of C,,, may be derived, as shown on the sheet. GAS ENGINES AND GAS PRODUCERS 867 1.42 1.40 1.38 1.16 114 1.12 400 500 600 700 Temperature Deg. C 82 212 392 572 752 932 11121292 1472 1652 1832 2012 2192 2372 2552 2732 2912 3092 3272 Temperature Deg. F 1200 1300 1400 1600 1700 1800 Fic. 538. The second curve sheet, Fig. 538, gives values of y = Cos, as the change in this figure is large enough to be of importance in some cases. It happens quite often that the quantity of heat gained or lost between some temperature #’ (not o° C. or 32° F.) and a temperature tis desired. This case occurs, for instance, when it is desired to compute the heat loss in a gas from a temperature of ¢ degrees to room temperature at ¢’/ degrees. The most obvious way of solving this problem is to compute the heat in the gas at ¢ degrees by use of Com (oto) and to subtract from this the heat still in the gas at t’ degrees by use of Com (o to v). But it can be shown mathematically that if mean specific heat can be expressed by an equation of the general form Caled SOE, 6 aw + & oe Ge) then Com(’ to) =H ty’ +2) f ME Sgt ade no G2) The use of the last equation, of course, shortens the work. 868 EXPERIMENTAL ENGINEERING Example. — Suppose that one pound of air is cooled from 2000° F. to 60° F, What is the heat loss? Method 1. Cpm at 2000° = .258; at 60° = .237, from the curves. Heat in air above 32° at 2000° = .258 (2000 — 32) = 507.7 B.t.u. Heat in air above 32° at 60° = .237 (60 — 32) = 6.6B.tu. Heat loss = 501.1 B.t.u. Method 2. Equation for Cpm for air = Com = .237 + .cocorg t, in which t = centigrade degrees. Changing this to the form of equation (21), with #’ = 15.5° C. (60° F.) and t = 1093° C. (2000° F.), we have Com (60 to 2000) = -237 + .00019 (15.5 + 1093) = .258 Heat loss = .258 (2000 — 60) = 500.5 B.t.u. 386. Analysis of Fuel Gases and the Determination of Heating Value. — The chemical analysis of fuel gases is a matter requiring care and experience, and unless both of these requirements can be fulfilled, it will in general be best, if the plant test is made in the field, to collect the gas by some approved method and to send it to some chemical laboratory for analysis. Means for collecting gas are discussed in Chapter XIII, to which the student is referred. Where, in any given plant, the sample of gas should be taken, depends upon the purpose in view. If the test is confined to the engine, the gas should, of course, be collected close to the engine, no attention being paid to the previous history of the gas. In case a producer is under test, it is always well to sample the gas just at the outlet of the producer, and again after leaving the cleaning apparatus on its way to gas holder or to engine. Where a test is made of the plant complete, the two analyses just mentioned are sufficient to cover the requirements. For remarks concerning number of samples, method of averaging the results of the various analyses, etc., see p. 876. The analysis consists in the determination of COz, Os, C:Hy, CO, CHy, and Hz, Nz being found by difference. It may be carried out in two ways: (a) To determine CO:, O., C:H4, and CO by absorption; H2 by catalytic separation by means of palladium; and CH, by combus- tion. GAS ENGINES AND GAS PRODUCERS 869 (6) To determine only CO:, O:, and CH, by absorption, Hy, CO, and CH, by combustion. As far as the work in a chemical laboratory is concerned, there is probably little choice between these two methods, but in field work method (0) offers decided advantages, as the apparatus is simpler and requires less time to operate. A distinction should be made between gases based upon the CO content. Where this is compar- atively low, as in illuminating gas, an absorption method, like (a), gives satisfactory results; but for producer gas or water gas, both high in CO, method (6) would be preferred, especially in the field, on account of the difficulty of absorbing large quantities of CO without thorough agitation of gas and reagent. The reagent used for the absorption of CO; is caustic potash, that for Oy, is either an alkaline solution of pyrogallic acid or phos- phorus. The preparation and handling of these reagents has already been described in Chapter XIII. The reagent used for C,H, is fuming sulphuric acid. The remainder of the constituents, except nitrogen, are combustible. They are transferred to a com- bustion tube or vessel and mixed with a measured quantity of air. The mixture is lighted by means of incandescent platinum. After combustion, the resulting CO, and the free oxygen remaining in the gases are determined by absorption. The reactions occurring in the combustion tube may be written as follows: * 2CO + Oy = 2COn, ie., 2 vols. of CO + 1 vol. O, = 2vols.of CO... . . . (22) CH, + 2 Oz = CO, + 2 HO, ie., 1 vol. CHy + 2 vols.O, = 1 vol. CO, + 2 vols. H2O. . (23) 2 Hp + Oz =e HO, ie.,2vols.H, + 1vol.O, =2vols.H,O. . . . . . (24) With the aid of these expressions we may derive the following equations: * This development of the equations used for the determination of CO, Hz and CH, after combustion was apparently first given by Vignon, Bull. Soc. Chim. 1897, 832. It is contained in Hempel-Dennis’ Gas Analysis. 87 ° , EXPERIMENTAL ENGINEERING Let = =the sum of the contraction volumes appearing in equa- tions (22) to (24). V =the sum of the volumes of CO, CHy, and Hz, and CQ, = the sum of the CO, volumes produced in equations (22) and (23). In equation (22), 3 volumes before combustion contract to 2 vol- umes; hence the contraction amounts to 1 volume, which is 3 of the CO volume concerned in the equation. The contraction vol- ume may therefore be represented by 3 CO. In equation (23), 3 volumes before combustion contract to 1 volume, since the 2 volumes of H,O produced will condense. Hence the contraction volume is equal to 2 volumes, which is twice the volume of CH, concerned in the equation. The contraction volume is therefore represented by 2 CHa. In equation (24), 3 volumes before combustion contract too volume, since the 2 volumes of H,O will condense. Hence the contraction volume is equal to 3 volumes, which is 3 of the volume of H, concerned in the equation. The contraction volume may therefore be represented by $ Hp. Equation (22) shows that the volume of CO, produced is the same as the volume of CO concerned in the equation, while equation (23) shows the same to hold true for the relation between the volumes of CO, and CHy. With this information we now have S=3CO+2CH,+$E,. . . . . (25) COE COG. ow. hw, hy os g Solving these for each one of the combustible gases, we finally derive CO=4CO,+V—-2z, .... . (28) Ea= VS CO ey ad de we 20) CH, =$00,= Par 2 6-6 4 deed) How these equations are practically applied will be shown by a type example. GAS ENGINES AND GAS PRODUCERS 871 There are several types of apparatus, based generally upon the principles of the Orsat, which should be satisfactory for field work. One of the best is probably the Hahn apparatus* described by Dr. C. Hahn in the Zeitschrift des Vereins deutscher Ingenieure for Feb. to, 1906. Another is described in the same journal for April, 1908, and is manufactured by Dr. Siebert & Kuhn, Kassel.t The general appearance of the Heinz apparatus is shown in Fig. 539, while Fig. 540 shows in detail the arrangement of the parts. NE | a ) Fic. 539.— Heinz APPARATUS FOR Gas ANALYSIS. a, b, ¢ and d are the absorption pipettes, e is the measuring burette, and f the combustion pipette. The latest improved forms of absorption pipettes are shown in Figs. 541 and 542, the former of which shows the Hankus, the second the Heinz pipette. Both are designed to promote thorough intermixing of gas and reagent, and * Made by C. Heinz, Aachen. } Another apparatus is described by Paul Fuchs in his “Generator Kraftgas und Dampf-Kessel Betrieb.” It is made by G. A. Schultze, Charlottenburg. 872 EXPERIMENTAL ENGINEERING the rapidity and certainty of action are very much better than in the old type. In the Hankus pipette, gas enters at a and flows out a“, —— offen nonin Fic. 540.— ARRANGEMENT OF Parts oF HEINZ APPARATUS FOR Gas ANALYSIS. Fic. 541.— ABSORPTION PIPETTES — Fic. 542. at 6 into the reagent, through which it rises to the top. It may then be drawn out through the side opening at the top by throwing the cock over into the right position (shown at e in the detail drawing for the Heinz pipette). The action of the Heinz pipette is very GAS ENGINES AND GAS PRODUCERS 873 similar. The gas flows from c to d through the central tube, escapes through a small injector opening and rises in the long spiral. It is removed as in the Hankus pipette. The analysis is carried out as follows: Assuming that the liquids in the absorption and combustion pipettes (mercury or water in the latter) stand at the top of the capillary tube, that the measuring burette and capillary are filled with the displacing liquid (mercury or water), a sample of gas is drawn into the apparatus through the cock 7. After measuring in é, the gas is displaced into a, which contains KOH for the absorption of CO,. After this is complete and the contraction has been meas- ured, displace into 0, which contains fuming sulphuric acid for the absorption of the heavy hydrocarbons (considered as C,H,). From 5 draw the gas back into e, but before determining the contraction, displace over into a again to take out acid fumes. Then draw back into e and measure the total contraction which determines CO, + C,H,. Next displace into c, containing pyro-gallol for the absorp- tion of O,. After absorption in c, the total contraction shown in e measures CO, + C,H, + O;. It is next possible to absorb CO by means of a cuprous chloride solution in the pipette d. But owing to the fact that producer gases contain a good deal of CO (up to 30 per cent in some cases), and that the absorbing power of the solution for CO is very limited, the writer prefers to omit this absorption and to determine CO by combustion, as above stated. To this end, have the pipette d simply filled with water, and at the end of the O, absorption displace all the gas over into d, which may then serve as a storage. Next draw into ¢ a certain quantity of air through #, measure it and force it over into the combustion pipette f. Then draw over from d a certain quantity of gas and measure it. The proportion of air to gas will depend upon the kind of gas; more than enough oxygen to completely burn all of the combustible components (CO, Hz and CH,) must be present. Next pass a cur- rent through the platinum spiral P, by means of the storage battery shown in Fig. 539, so that this wire will be at a bright red heat. Then slowly displace the gas from e into f. The combustion taking place will burn CO to CO;:, H to H,O and CH, to CO, and HO. After combustion transfer the mixture of burned gases first to 874 EXPERIMENTAL ENGINEERING pipette a to absorb the CO; formed by the combustion; measure the contraction in e. Then transfer to pipette c to absorb excess oxygen and again measure the contraction. The analysis is then complete. The apparatus described by Dr. Hahn differs slightly from this in that there is a palladium wire placed in the bend &, Fig. 540, [— z q = 1 EZ rao a : I if | Ground _, -e Joint SCF 1 g SS d Space for pal Spare Parts = 95 = 6 Fic. 543. — SIEBERT-K UHN Fic. 544. ABSORPTION Fic. 545. MEASURING APPARATUS FOR GAS PreetTe, SIEBERT- BURETTE, SIEBERT- ANALYSIS. Kuan Apparatus. Ktan Apparatus. which wire is heated by means of an external flame to a tempera- ture of 400°-soo°C. With the spiral P cold, the mixture of gas and air is forced from e over into f, when combustion of H, alone will take place in &. Afterward spiral P is used to burn CHy, Dr. Hahn using the absorption method for CO. This method then determines H,, CO and CH, separately. The separation of H2 by this method, however, requires considerable care and skill, and GAS ENGINES AND GAS PRODUCERS 875 the writer would, therefore, recommend the straight combustion method for CO, H, and CH, as above outlined. The Siebert-Kiihn apparatus is similar in principle but of differ- ent construction. In Fig. 543, aa are the absorption pipettes, erg, H fl il Fic. 546.— SIEBERT-KUHN APPARATUS READY FoR USE. mounted in a holder that can be revolved on a base, and m is the measuring burette. Fig. 544 shows the construction of the absorp- tion pipettes and indicates the means taken for exposing large surfaces of the reagent. The burette, Fig. 545, consists of the graduated tube e, surrounded by the jacket tube f. The electrodes gg lead the current to the platinum spiral in the top of the burette. When ready for use the apparatus is arranged as in Fig. 546. The burette is connected to each absorption pipette in proper order, the combustion part of the analysis being carried on in the burette itself. Both types of apparatus are put up in compact form in traveling cases. 876 EXPERIMENTAL ENGINEERING The following type example of an analysis of a producer gas is taken from the work by Paul Fuchs, mentioned in footnote, p. 871. Original volume of producer gas........... 94.8 c.c. After absorbing COz............... 02 eee go.2c.c.= 4.6c.c. COz After absorbing O2............ eee eee ee eee 89.9 C.c. = .3c.C. O2 After absorbing CoHy................000- 89.7 C.c. = .2¢.c. CoH, Volume of gas used for combustion........ 34. 2 C.C. re Aitadded .,. owoesaceus ead ho vee stint we ves 36.7 C.c. = gue. Os Volume of air and gas .................45. 70.9 C.c. Volume after combustion... 58.3 c.c.; hence 2 = 70.9— 58.3 = 12.6 c.c. After absorbing COz........ 52.1 .c.; hence CO, = 58.3 — 52.1 =6.2C.c. After absorbing Oz......... 50.9 C.Cc. Volume of Nz added........ 29.0 C.C. Remaining difference. ...... =21.9 c.c.= (Volume left of original 34.2 c.c. of gas used) hence V = 34.2 — 21.9 = 12.3 C.c. Substituting these values of 2, CO2, and V in equations (23) to (25), we obtain: CO =3C0.4+ V —#2, = 2.1 + 12.3 — 8.4 = 6.0C.c. Hz = V = CO,, = 12.3 —6.2 =6.1C.c. CH, =}CO,. -V 472, = 4.1 — 12.3 + 8.4 =.2C.c. The ratio between the original volume of gas taken and.that used for com- bustion is re = 2.77. Therefore in the original volume there were contained 6 c.c. of CH,; 16.9 c.c. of He, and 16.7 c.c. of CO. The 94.8 c.c. of gas originally taken therefore contained COz O2 CoH CHa He co Nz (by difference) 4.0C.c. 3CC. .2CC .6¢.c. 16.9¢.c. 16.7 cc. 55-5 C.C. The percentage composition by volume therefore is C02 O: CH: CH He co Ne 48% 37% 2% 1% ~=— 17.9% ~— 176% 58.5% The heating value of a fuel gas is best determined directly in a calorimeter (see Chapter XIII). Where a continuous calorimeter, like the Junker, is available, and the gas is under some pressure, it is easy to make arrangements by which the determination is made continuous over the entire time of the test by furnishing facilities for accurately weighing large quantities of water. Where no calorimeter is available, the heating value may be computed by GAS ENGINES AND GAS PRODUCERS 877 the method outlined and data given in Article 384, in this chapter. In such a case, in order to avoid a complicated and generally un- satisfactory time-average* computation, it is well to see that gas samples are taken for analysis at stated intervals equally spaced over the test, and to make the time of collecting as long as possible. The straight average of all the results may then be taken. The number of samples taken depends largely upon the constancy of the gas composition, fluctuations requiring more frequent analysis. The ideal method of collecting would, of course, be to arrange an aspirator of the type shown in Fig. 362, p. 515, of sufficient capacity to last for several hours. The sampling may in that way be made practically continuous. 387. Analysis of the Exhaust Gases, and Computation of the Heat Lost in Exhaust. — For methods of collecting exhaust gas samples see Chapter XIII, since the precautions to be observed are the same as for flue gas. Usually the exhaust gases are under some pressure so that no aspirating apparatus is required. As far as the analysis is concerned, what is said in Chapter XIII, with reference to flue gas, applies with equal force to exhaust gases; in fact, if only COQ:, Oz, and CO (Ny by difference) are tested for, the same apparatus may be used. It has, however, been shown by Giildner and others, that in spite of the fact that there is a considerable excess of air in most gas-engine mixtures, incomplete combustion often results. Gtildner cites cases where the heat loss due to com- bustible components in the exhaust gas amounted to as high as 15 * A time average is obtained as follows. Assume that on a 12-hour test, samples were taken at the times stated below: Interval = The analysis of sample A is assumed to cover the period from the start of the test to half the interval between samples A and B. This is 2 hours, from 8 to 10 A.M. Similarly, Test begins 8 aa Sacks beds Sample 4 at 9AM z “Bat rram.pes tS | “ Cat ram. $o--7tS “c ‘ ‘ & Dat: apport? sample B covers the next 1.5 hours, etc. The “ Eat 4gpa.go:?-5 results of each analysis are then multiplied by “Fat 7PM. ie this time interval, and the summation of the Test endsat 8PM. individual products is divided by the total length of the test, in this case, 12 hours. 12 hrs. Since this whole computation is based upon a somewhat unwarranted assumption, its value is doubtful. 878 EXPERIMENTAL ENGINEERING per cent of the total heat supplied in the fuel. It must be evident from this that where it is desired to establish a scientifically correct heat balance for a gas-engine test, the exhaust gases should be completely analyzed, and in the field the Heinz or Siebert ap- paratus may be used for this purpose. It is stated that the heat loss in exhaust may be found in two ways: (a) By measuring the fuel and the air used, and determining the ratio of fuel to air. With a known fuel composition it then becomes easy to compute the weights or volume of the various products of combustion passing into the exhaust pipe. (6) To analyze the exhaust gases and from the results of this analysis to compute the products of combustion by the method outlined in Chapter XIII for flue gas, or by some other method. Method (a) assumes that there is complete combustion of the fuel, and is correct only under that assumption. How far that assumption may be incorrect’ has been shown above. In method (b) the determination of combustible constituents makes it possible to allow for the effect of incomplete combustion, and on the score of accuracy the latter method is therefore to be preferred to the former. Of course method (a), if properly carried out, will give the accurate total weight or volume of the gas passing through the engine under all circumstances, but it may fail to definitely indicate the distribution of this total among the various kinds of gas present, and thereby lead to an erroneous determination of the exhaust loss. To make the computation of the exhaust loss a general case assume that a complete exhaust gas analysis is made and that some combustible components are found. The method of pro- cedure will then be as follows: Example. — Fuel used is producer gas with the following composition by volume: 18.73 per cent H2; 25.07 per cent CO; .31 per cent CH,; .31 per cent C:H,; 48.98 per cent No; 6.57 per cent CO; .03 per cent O. Higher heating value 159 B.t.u. per cubic foot. The exhaust gases showed by volume: 13.9 per cent COz; 5.2 per cent O2; .9 per cent Hz; 1.4 per cent CO; 78.6 per cent Nz. Temperature in exhaust = 752° F. GAS ENGINES AND GAS PRODUCERS 879 The problem consists of the following parts: (a) The computation of the quantity of the products of combustion. (b) Ratio of air to fuel used, and the excess air. (c) The heat loss in exhaust. For the purpose of comparing them with the results of the exact method for computing the quantity of the products of combustion, as found under (a) below, the figures under (d) below show the results when the usual ap- proximate method, that is the one assuming complete combustion, is used. (a) Computation of Quantity of Products of Combustion. Exact Method. The method used is essentially that developed for the flue gases from fur- naces in Chapter XIII, and‘the student is referred to that chapter for the development of the formulas and equations used. The first step is to convert the per cent by volume composition of the fuel gas to the weight per cent basis. The following table shows the computation involved. Composition, Weight per Standard |Weight of the Individual} Composition, Per Cent by Cu. Ft. of the Individ- | Gases in One Standard | Per Cent by Volume. ual Gases. Cu. Ft. Weight. Lbs. Lbs. Fae nicadtaseces 18.73 - 00561 - 00104 1.54 CO seis aces 25.07 .07807 -01957 29.02 CHa y astegienstars : QI -04464 . 00012 17 CsHae seceees + 31 .07809 .00023 435 Noes ae eegenee 48.098 .07831 .03835 56.89 CO ves cerninse ines 6.57 . 12341 .00806 12.00 Oo aed acbegin 03 .0892T . 00002 03 IO00.00 .06739* I00.00 * Summation is weight per standard cubic foot of fuel gas. From the weight analysis, it is now possible to compute the actual weights of carbon and of hydrogen that went through the engine per pound of the fuel gas. If we next assume that all of the carbon contained in the fuel gas must in some form or other reappear in the exhaust gases, we can at once determine the relation existing between the weight of fuel gas used and the weight of exhaust gases formed by aid of the exhaust gas analysis. The only factor that might invalidate this assumption is the carbon deposit in the cylinder. This per pound of gas, however, would be so small as to be negligible. The actual weight of carbon contained in a pound of the fuel gas is: 43X .2902 = .1244 pound (from CO content); }% X .co17 = .0o13 pound (from CH, content); $$ X .0035 = .co30 pound (from C;H, content); and 42 X .12 = .0328 pound (from CO, content); making a total of .1615 pound of carbon (= ¢, see below). f 880 EXPERIMENTAL ENGINEERING Similarly the actual weight of hydrogen is: 0154 pound (from Hz content); #; X .c017 = .ooo4 pound (from CH, content); and zs X .0035 = .o005 pound (from the C2H, content): making a total of .o163 pound of hydrogen. From the equation on p. 535, the relation between the carbon in fuel and that in the flue (exhaust) gas is =n(4or 4 BO). 3.66 2.33 By substituting in this the value of c as above computed, also the percentage of CO, and CO from the flue gas analysis, we will have _ (44% 13.9 , 28 X 1.4 615 = n (42759 + see ); from which 7 = .00088. With this value of 1, and in connection with the exhaust gas analysis, we may next compute the actual weight of the various products of combustion by aid of the equations developed on p. 535. Weight of free O2 = .00088 X 32 X 5.2 = .1465 pound. Weight of COz .00088 X 44 X 13.9 = .5360 pound. Weight of CO .00088 X 28 X 1.4 = .0345 pound. Weight of N2 00088 X 28 X 78.6 = 1.9350 pound. Weight of H, (not burned) = .c0088 X 2X .g = .oo16 pound. ll ll H, actually burned is therefore = .0163 — .oo16 = .o147 pound, and the water vapor (H,O) resulting will be 9 X .o147 = .1312 pound. This determines the weight of all of the products of combustion, with the exception of the water vapor as humidity in the air used, which may be neg- lected.* The sum total is Oz CO2 co Ne He H:0 1465 + .5360 + .0345 + 1.9350 + .0016 + .1312 = 2.78 pounds. (b) Ratio of Air to Fuel Used, and the Excess Air. Since the exhaust gases weigh 2.78 pounds per pound of gas, the air added to each pound of fuel gas to form the mixture must evidently have been 1.78 ds, ANE 2x 78 ‘ pounds. The ratio = is then cn by weight. The gas weighs .0674 pound, (see table above) and air .o807 pound, per standard cubic foot. This would make the mixture under these conditions consist of : = 14.84 cubic feet of gas. 74 * Water brought in as humidity in air amounts to about .oor pound per cubic foot of gas. GAS ENGINES AND GAS PRODUCERS 881 and aE 22.05 cubic feet of air. This makes the ratio of aE by volume .0807 gas = 22:05 _ 1.49, 14.24 I From equation (12a), p. 859, the theoretical volume of air required by this gas per standard cubic foot _ F 18 807 LAS + (2 X.0031) + (3 X.0031) — .0003 Ss = 1.12 cu. ft. 21 49 — 1.12 1.12 This would indicate an air excess equal to = = 33 per cent, by volume. But the result of the computations above has shown that .0345 pound of CO and .oo16 pound of H, remained unburned per pound of fuel gas, and therefore required no oxygen. These weights amount to .o3 cubic foot of CO and .o2 cubic foot of Hz per standard cubic foot of fuel gas. So that only .2207 cubic foot of CO and .1673 cubic foot of H, actually burned. This reduces the theoretical air supply necessary to 1.00 cubic foot per cubic foot of gas, and the real ‘ .. 1.49 — 1.00 excess of air therefore is eee I = 49 per cent, by volume. (c) The Heat Loss in Exhaust. — This is, of course, made up of the heat lost in the combustible components of the gas plus the quantity of sensible heat carried off, measured above some assumed datum temperature, say 32° F. (t) Heat lost in combustible components: In CO = .0345 X 4,380 = 151 B.t.u. In H, = .oo16 X 61,950 = 99 B.t.u. 250 B.t.u. (2) Sensible heat lost. This is in any case (except that of water vapor) equal to the weight of the particular gas multiplied by the temperature range = 752 — 32 = 730°, and by the mean specific heat, Cpm between 32° and 752°, as taken from the curve sheet, Fig. 537. Sensible heat lost in O2 Sensible heat lost in CO: Sensible heat lost in Nz -1465 X 730 X .222 = 24 B.t.u. .5300 X 730 X .227 = 89 Btu 1.9350 X 730 X .251 = 354 B.t.u. ll 467 B.t.u. (3) Heat lost in water vapor (see p. 467) 1312 (1058.7 + .455 t, — te + 32) 11312 (1058.7 + .455 X 752 — 32 +32) = 184 Btu 882 EXPERIMENTAL ENGINEERING Total heat loss per pound of fuel gasis 250+467+184 = gor B.t.u. Higher heating value of gas (computed) per standard CUBIC TOO Ce ies oaccaoaads dts uae sononinere re toate pean ee dae eee 159 B.t.u. Higher heating value of gas (computed) per pound. 2360 B.t.u. Total exhaust gas loss... ....... 0.00. e ee eee eee 38. 2 per cent Loss in combustible gases ............. 0.000002 e ee ro. 6 per cent Tsoss: in; sensible:-heats cn vows ia wares dhaw eri se ey Seuss 27.6 per cent (d@) Approximate Method of Computing Quantity of Products of Combustion. — Where the combustible components of an exhaust gas have not been determined (ie., are assumed not present), a somewhat shorter method, giving a result which will be more or less correct, depending upon the error involved in such assumption, may be used. In that case, the exhaust gas analysis above given would have been, by volume: 13.9 per cent COz; 5.2 per cent Oz, and 80.9 per cent N; (by difference). From equation (15a), p. 859, the total number of cubic feet of N2 that would have resulted from the combustion of one cubic foot of the fuel gas with the theoretical air supply of 1.12 cubic feet per cubic foot of gas, is No = (.79 X 1.12) + .4898 = 1.3746 cu. ft. é A 4898 = 64. t is due t dy ae 856 4.37 per cent is due to air used; Tare 35-03 per Of this total, 28848 1.3746 cent is due to Nz already in fuel gas. The computation for total air really supplied may now be made as follows: Total N, from exhaust gas analysis = 80. 90 Of this amount, N: due to excess air (as measured by free O-) ald = = X 5.2 19. 60 Leaves N; due to fuel gas and to air actually needed 61. 30 Of this remainder, 35.63 per cent is due to Nz content in fuel gas = 21. 85 Leaves N: due to air actually needed 30.45 From this data : N, due to excess air + N¢ in air Excess coefficient = —~2 + Ns in air needed 2 N; in air needed = 19.60 + 30-45 _ 59.05 _ 1.50. 39-45 39-45 This result would show that the volume of air supplied per cubic foot of gas is 1.50 X 1.12 = 1.68 cubic feet, and that the volume ratio is po instead of I = as the exact method shows. The discrepancy is primarily due to the fact GAS ENGINES AND GAS PRODUCERS 883 that the approximate method is compelled to assume that the air actually used in the combustion is that shown to be the theoretical volume necessary, i.e., 1.12 cubic feet. The fact is, however, that on account of incomplete combus- tion, the real volume of air used up is only 1.00 cubic foot per cubic foot of fuel gas. Therefore this is the figure which should have been multiplied by the excess coefficient 1.50 to obtain the total air supply, and we have 1.50 X 1.00 = 1.50 cubic feet, which agrees very closely with the exact result. The computation by the approximate method is here primarily made to indicate what the degree ‘of error involved in some cases may be. Of course not having the complete analysis of the exhaust gases, we are compelled to assume com- plete combustion, i.e., that the theoretical amount of air that was required is 1.12 cubic feet (in this case). The result is that the ratio of = is de- termined too large by LOO 2 ans per cent. I.. 388. Experimental Determination of Ex- haust Loss. — The heat lost in exhaust has also been experimentally determined. Staus* constructed an exhaust gas calo- rimeter of which the details are shown in Fig. 547. The gases find their way from the exhaust pipe a into the muffler C. The latter is enclosed in the calorimeter, which consists essentially of a wooden box A lined with galvanized iron. The lower end of the box is open and rests in the i trough B, in which a water-seal of constant Fic. 547.—Sraus ExHavst height is maintained by means of the Gas CALORIMETER. overflow funnel m. The exhaust gases pass from C into six pipes #, arranged as shown, and escape into the box A through elbows at the lower end. The box being sealed below, the funnel opening also being covered by the hood u, the gases rise in A and finally escape through b. In their ascent they meet fine streams of water produced by the spray nozzles k, the water-supply head being * A. Staus, Zeitschrift des Vereins deutscher Ingenieure, May 3, 1902. 884 EXPERIMENTAL ENGINEERING maintained constant by the constant head apparatus F. Valve e controls the rate of supply. Thermometers at J and K determine the temperature of water entering and leaving; thermometer L, the sensible heat still remaining in the gas above any assumed datum. Two small windows / are furnished to watch the operation of the spray nozzles. Means must, of course, be furnished to accu- rately determine the quantity of water used.* The method of computation is obvious. It should be noted that the results obtained can be accurate only as long as the gases contain no combustible parts. If these are present, the heat of combustion in them will escape through 6 unaccounted for. 389. The Determination of the Quantity of Producer Gas Made per Pound of Fuel. — There are two methods open, one of which may be called mechanical, the other chemical. The mechanical method consists in the use of gas meters, Venturi meters, Pitot tubes, etc. Concerning these instruments the student is referred to Chapter XII, for discussions regarding theory, accu- racy, precautions necessary, etc. It may be said that where the flow of gas from a producer is fairly steady, i.e., in a pressure plant, the means above mentioned will give excellent service if properly used, but in a suction-gas plant, the difficulties encountered on account of the rapid fluctuations of velocity, are in most cases insurmount- able. In pressure-gas plants the gasometer method, which con- sists in determining the rate of fall of the gasometer bell while the gas inlet is closed (purge pipe on producer open) and the engines or other apparatus are drawing on the gasometer, is sometimes used. Unless the demand is fairly constant, these determinations have to be made often in order to obtain an average rate of fall. This coupled with the difficulty of accurately rating the capacity of the gas holder for a given drop, especially in large sizes, operates against the accuracy of this method, although it is often the only one available. The chemical method of determining the volume of gas made is of interest and of general applicability. It depends upon the fact that all of the carbon contained in a fuel used in a gas producer * An exhaust gas calorimeter of similar construction is now on the market, made by Junkers & Co., Dessau. GAS ENGINES AND GAS PRODUCERS 885 must reappear in some form or other in the following four ways: (a) as gaseous carbon in CO and in CO in the producer gas, or in CHu, C2Hg, etc., as distillation products in the gas; (0) as solid carbon in the refuse (ash) from the producer; (c) as gaseous carbon in the hydrocarbon gases (tar) not included in the distillation prod- ucts under (a); and (d) as dust or soot carried mechanically out of the producer by the gases and deposited in the pipes. All of these items are susceptible of determination with a degree of accu- racy sufficient for engineering work. If we let C; represent the weight of total carbon in a pound of the fuel used, as determined by chemical analysis; C, the total weight of carbon that can be accounted for, by computation from chemical analysis, in a standard cubic foot of the producer gas made; C, the weight of carbon which appears in the refuse per pound of fuel fired; C, the weight of carbon that appears in tar per standard cubic foot of producer gas; C, the weight of carbon appearing in soot or dust per standard cubic foot of producer gas; and V the number of standard cubic feet of producer gas made per pound of fuel fired, we must have the relation C,-C,=V(C,+C,+C,), from which ve eae standard cu ft. per Ib. of fuel fired. (31) C; and C, are determined from the chemical analysis of fuel and refuse. See Chap. XIII. C, is computed from the volumetric chemical analysis of the producer gas. The determination of C, and of C, needs further consideration. | Determination of Tar and Soot.— There are several types of apparatus which may be used for the quantitative determination of tar. In some of them the tar is taken out of the gas by means of alcohol, in others some kind of a dry filter (dried asbestos fiber 886 EXPERIMENTAL ENGINEERING or wool) is used. The method given by Tieftrunk* belongs to the first class. The apparatus is shown in Fig. 548. It consists of a cylinder a which is fitted with a tight-fitting cover b held on by clamps kk. The tube cg, through which the gas enters, reaches nearly to the a oe Mm <== Wa ( ped Fic. 548. — TrErTRUNK APPARATUS FOR Tar DETERMINATION. bottom of a. Over the lower end of g there are slipped five or six bell-shaped brass plates /, perforated with holes 1.5 mm. in diam- eter and 5 mm. apart. Cylinder a is filled with alcohol (30 to 35 per cent by volume) to a height sufficient to cover the last plate. The gas, after bubbling up through the alcohol, leaves through d and passes next through a U-tube f filled with cotton. The last cylinder in the series, which the gas enters at e, is filled at o with cellulose, and upon this rests a column mm of bog-iron ore, separated from the cellulose by a filter paper. This cylinder is used to take H,S out of the gas, which is done for the purpose of protecting the delicate gas meter connected to the outlet p. The gas is drawn through the entire apparatus by means of some type of aspirator pump connected beyond the gas meter. In case of producer gas, the use of the H,S absorption apparatus may be dispensed with, and the same may be done for any gas if some device other than a gas meter, as for instance a gasometer, be used to draw and measure the gas. * Winkler, Industriegase, Vol. IT, p. 51; also Hempel-Dennis, Gas Analysis. GAS ENGINES AND GAS PRODUCERS 887 Since the gas sample for this test must be taken close to the pro- ducer, ahead of the scrubber, the gas is apt to be too hot to be taken directly into the apparatus, and for that reason a glass condenser (not shown in Fig. 548, see E in Fig. 549) is interposed between the tube c and the gas-sampling tube in the gas flue. The porcelain sampling tube is open at the end, and is introduced into the gas main through a gas-tight stuffing box. The end of the sampling tube must, of course, face the gas stream. The connection between sampling tube and condenser cannot be made by rubber tubing, on account of the heat, and it is usually necessary to make some kind of a coupling with a stuffing gland at each end. The con- denser is tilted toward the alcohol cylinder, so that the tarry gases condensing in it will flow into the cylinder by gravity as far as possible. The minimum quantity of gas that should be passed through the apparatus is about 20 cubic feet, the suction pump being so regu- lated that not more than 1.5 to 2.0 cubic feet passes per hour. The soot and tar collect in the sampling tube, the condenser, and in the alcohol cylinder. If any of the tar should pass the latter, the cotton in f will be colored brown. At the end of the test, after noting the exact volume of gas that has passed, together with pres- sure and temperature at the meter, the apparatus is taken apart and transported to the chemical laboratory. Here all traces of soot and tar in condenser and sampling tube are carefully washed out with alcohol and added to the contents of the cylinder (the tar is extracted from the cotton by means of carbon disulphide, if that should be necessary). The chemical determination of the amount of carbon carried by the material collected is then made. Since neither the operation of washing, nor extraction, can be done by the engineer in the field, and since the determination of the carbon must be done by a chemist, no further directions will be given, but the student is referred to books on chemistry. The second type of apparatus is simpler, and by means of it, tar, soot, and water vapor may be determined. It is known as Lord’s apparatus, Fig. 549. The following description of its action is teken from Wyer.* * S. S. Wyer, “ Producer Gas and Gas Producers.” 888 EXPERIMENTAL ENGINEERING “ B is the sampling tube made of o.5-inch pipe which is placed in the gas flue; A is an annular jacket surrounding it, and has pipe connections at D and C. Live steam is blown in at D, and out at C, the object of this being to keep the temperature of the iron pipe below the point at which the iron would act on CO:. This will secure a sufficient cooling, and yet will leave the temperature high enough to prevent the condensation of moisture. £ is an ordi- nary condenser through which cold water is circulated. F is a Fic. 549.— Lorp’s APPARATUS FOR TAR AND Soot DETERMINATION. small flask filled with ignited asbestos fiber and containing a ther- mometerG. J and L are tanks filled with water and connected at K. JIisavalve. 4 is a rubber tube, connecting J and F. Q is a thermometer placed in a stopper in a pipe with valve R, the object of this valve being to make it possible to remove the thermometer when gas is in the tank J. WM is a float to which is fastened the curved tube NV, which acts as a siphon and which has a small nozzle O, with a pinchcock P on the rubber connection. The object of the float and tube is to keep a constant head above the nozzle, and thus insure a uniform flow through it. The operation of the tank is as follows: Disconnect the rubber tube H and fill the tanks J and L with water until they overflow at the valve J; fill the siphon N with water and close the stopcock P, attach the rubber tube H to stopcock J, circulate water through the condenser E, and steam through the water jacket A. Then open valve P; the water will be drawn out of tanks L and J, and the gas will be drawn through GAS ENGINES AND GAS PRODUCERS 889 condenser £, flask F, and tube H into the top of the tank J. The water in excess of the saturation of the gas at the temperature of the small flask is condensed, and any tar and soot in the gas retained in the ignited asbestos in the flask. After the test, the flask and its contents are weighed, and the increase over the weight taken before the test gives the quantity of the tar and water condensed from the volume of the gas which has passed through the flask. This volume is determined by measuring the quantity of water which had run out of the aspirating tank J. “The quantity of water remaining in the gas, after passing out of the little flask used as a receiver, is calculated from the temperature of the issuing gas, which was saturated with water vapor. The water in the gas is then the sum of the permanent vapor and that condensed. The water in the flask is determined by drying the contents over sulphuric acid to constant weight and determining the loss. The dry contents are then ignited and the further loss of weight estimated as soot and tar. “Let B = barometric pressure. Tt = temperature of gas in tank. Tb = temperature of gas in flask. Vit = volume of wet gas in tank at temperature T?. Vs = Vt reduced to 32° F. and 14.7 pounds per square inch. Vd = volume of dry gas at 32° F. and 14.7 pounds per square inch. Bt = aqueous tension of water vapor corresponding to T?. Bb = aqueous tension of water vapor corresponding to Td. W = weight of 1 cubic foot of water vapor corresponding to Tb. Wb = weight of water vapor condensed in flask. Wt = weight of permanent water vapor in volume Vs. 2 = percentage by volume of water vapor in flask. = = percentage by volume of water vapor in Vs. Bt Vd = Sie); Vs (: 4 Vs > = total volume of permanent water vapor in Vs. Bb Vs B W =Wt. Wt + Wb = total weight of water carried in volume, Vd, of gas.” 890 EXPERIMENTAL ENGINEERING If in this apparatus a porcelain collecting tube instead of the iron be used, the heater may be dispensed with, in case the test is made on raw (hot) producer gas. Further, for the purpose in view, which is the determination of the weights of carbon in the tar and soot, this procedure must be changed in so far that, after drying the flask to constant weight, the percentage of C in the excess weight remaining must be determined by chemical means. It need hardly be said that, where a good meter (of the type of the Junker calorim- eter) and a suction pump is available, vessels J and L may be dis- pensed with. The following is an example of the chemical method of determin- ing the volume of gas made per pound of fuel. Analysis of coal: H,0, 1.61 per cent; C2, 74.95 per cent; He, 4.41 per cent; S, 1.17 per cent; ash, 14.09 per cent. Analysis of gas: COs, 2.11 per cent, by vol.; C2Hy, .30 per cent; Ox, 2.63 per cent; CO, 25.83 per cent; CH,, 2.10 per cent; He, 8.10 per cent; No, 58.93 per cent. Analysis of ash: ro per cent C,, Percentage of refuse is 15.60. Tar and soot determination: 15.96 cubic feet of gas (at a vacuum of 3 inches of water and a temperature of 80° F.) showed .3909 gram of C in tar and soot. Here Cy = .7495 (see page 885). C, is found as follows (the gases carrying carbon being CO2, CO, CH,, and C:H,) é Cubic Feet Present in x | Weight of Carbon in r Weight of Carbon in Kind of Gas. Standard Cubic Foot Standard Cubic Foot Each Kind of Gas of Producer Gas. of the Kind of Gas. Present. GOR ath 3S aes & Sa ooes -O211 0334 * . 00070 COs. “Saaaeed 2583 0334 . 00868 CHa 34 sageeeoeie’ .0210 0334 . 00070 GCLEugs2 2 gee eee . 0030 . 0668 . 00020 Cg = .01028 * To show the derivation of this, we have: 1 lb. C produces 3.66 lbs. CO2; and under standard con- ditions the weight of COz = .12341 Ib. per cu. ft. Hence the weight of carbon per cu. ft.= es 3.66 X .12341 = .0334 lb. C,, the weight of carbon lost in ash = 10 per cent of .1560 = .or56 pound per pound of fuel. C,+C, = hae ee = .00005 pound per cubic foot of gas. GAS ENGINES AND GAS PRODUCERS 891 Here 453.6 is the number of grams per pound. The volume of gas (15.96 cubic feet) has not been changed to standard conditions in this case, as the correction would not amount to anything, in view of the small weight of carbon. The gas made per pound of coal from the above data and equation (31) will then be Ve Cy—C, — _ _-7495 — .0156 Cy t+Cr+Cs .01028 + .000085 = 71.0 standard cubic feet. 390. The Testing of Gas Producers and of Gas Engines. — A code for testing gas engines was adopted and published by the American Society of Mechanical Engineers as an Appendix to the “Steam Engine Code” in Vol. XXIV (1902) of the Transactions. This was followed in 1905 by a code adopted by the British Insti- tution of Civil Engineers. Finally in 1906 the Verein deutscher Ingenieure adopted a code which was translated by Mr. F. E. Junge and published in Power, Feb., 1907. The latter code also takes up the matter of testing gas producers. While these codes contain a lot of valuable information, it is true, particularly of the American code, that the information given in many cases is not sufficiently detailed to guide a student com- pletely. These matters have therefore been taken up at greater length in the preceding paragraphs in this chapter, and their dis- cussion will be completed in the paragraphs following. Other provisions of the code (those referring to the calibration of instru- ments, determination of brake horse-power, etc.) have already been fully discussed in other parts of this book. It is therefore judged best not to publish any of the gas-engine codes in full, but to set forth the main viewpoints determining the arrangements necessary for a test of a gas producer or a gas engine, and to incorporate into the discussion those parts of the codes that are pertinent and are not covered in any other parts of this book. 391. Directions for Testing a Gas Producer. — The object of the test is, in general, to determine either efficiency, or capacity, or both. Secondary objects may be to find the most suitable fuel for any given type of producer, to determine the best ratio of water to air for any given fuel, to determine the tar and water-vapor content of the gas made, etc. The capacity of a producer is usually stated either as the horse- power it is capable of supplying in gas engines, or as the number 892 EXPERIMENTAL ENGINEERING of pounds of coal that each square foot of producer-grate area will convert into gas per hour (so-called gasification capacity). Since engines differ as to the amount of gas required per horse-power hour, and different fuels show quite different gasification qualities, it must be evident that either method of rating capacity requires definite specifications as to engines or fuels. This is a matter that must be carefully covered in the guarantee. Capacity tests are a simple matter as it is generally only neces- sary to load up a producer either by sufficient engine capacity or by removing the gas made in some other manner and observing whether the plant will stand up to this service for the time specified in the contract. Measurement of engine output, or of fuel con- sumed, is really all that is required. It will be assumed, however, that it is desired to make an efficiency test and to establish, as far as possible, a complete heat balance. For that purpose the following requirements should be met and arrangements must be made to determine the following items. In any given case, modifications and simplifications may be intro- duced to suit the particular object in view. 1. Examine the producer for defects and remedy these if a max- imum efficiency test is to be made. Determine the dimensions of the grate, the contour of the walls, and make sketches of any un- usual constructive details. 2. Duration of Trial.—The viewpoints which control this are very much the same as for a boiler test. On account of the difficulty of properly judging the contents of a producer, a trial should never be less than 8 hours in duration, and preferably not less than 12. It depends, of course, upon the usage in the particular plant if a plant test is desired, as to whether a test can be extended beyond 8 or ro hours or not. 3. Starting and Stopping. — The producer should be thoroughly heated before starting a test, i. e., it must be in operation for a suffi- cient length of time(not less than 24 hours)under normal conditions, and if possible on the same grade of fuel, to allow of the attainment of average normal temperature in brick work, flues, etc. The condition of the fuel bed must, of course, be the same at the end as at the beginning. Note, at the beginning, the position of the ash GAS ENGINES AND GAS PRODUCERS 893 and incandescent zone, the upper level of the fuel bed, and its con- dition with respect to covering of green fuel, etc. During the trial, maintain these conditions as nearly as possible, cleaning out ash, poking fire, etc., the same as in ordinary operation, and at the end have the conditions the same as at the beginning, as nearly as possible. Clean out the ash pit immediately before the beginning and before the end of the trial. Ifit is not possible to remove ashes and clinker during the trial, shut down the producer immediately after the expiration of the time, clean out the refuse, and bring the fuel bed to the initial condition at the start. The fuel so used must be added to that used during the trial. If the plant uses an auxiliary boiler to furnish steam to the pro- ducer, the start and stop of the test with respect to this auxiliary should be managed exactly as laid down in the code for boiler testing. 4. Conducting the Trial. — Arrangements must be made to make the demand for gas uniform, as far as possible. Uniformity of con- ditions should also prevail with respect to steam pressure and air blast (in the case of a pressure plant); quantity of water supplied to the air (in case of a suction plant); thickness of fuel bed and ash column; frequency of firing and amount of fuel fired; poking fire and interval between cleaning fires. Keep as complete a record as possible. Record the time of every observation of weight, temperature, etc., and take note of every event, however unimportant it may seem at the time. 5. Observations and Calculations Required. — (a) Weight of fuel and refuse. The sampling is carried out as outlined under Boiler Tests. In some types of producers the raking out of ash may bring down some unburned fuel. This may either be returned to the producer or its weight may be subtracted from the weight of fuel used. Any unburned fuel, however, that falls through the grate while the producer is operating normally must be counted as refuse. Neither can an allowance be made for any fuel dust that gathers in the pipes and flues during a long-continued test. Any fuel used by an auxiliary boiler for furnishing steam must be added to the fuel used by the producer. 894 EXPERIMENTAL. ENGINEERING Laboratory samples of fuel and refuse must be taken in the usual way. In some cases the ash is wet down during drawing, or it is wet as it leaves a producer of the water-bottom type. In such cases, determine the weight of the wet ash, after allowing the water to drain off, and then immediately take a laboratory sample in order to be able to allow for the water content and thus to obtain weight of normal ash. (b) Weight of water supplied to the producer. In case of a pressure plant, this is found by weighing the feed water to the auxiliary boiler and determining the quality of steam at the pro- ducer. When the steam for blowing purposes is taken from a battery of boilers which are also used for other purposes, nozzle or orifice measurement of the flow in the supply pipe to the pro- ducer may be resorted to. In a suction-gas plant the water supplied the vaporizer must be accounted for. If the vaporizer is fitted with an overflow to main- tain constant level, the water wasted, together with its temper- ature, must be determined. Another way to determine the steam or water supplied to a producer of either type is based upon the consideration that the hydrogen and water vapor in the resulting gas must come from the following sources: moisture in coal, hydrogen gas in coal, humidity in air used, and steam supplied. The supply from all of the sources but the last can be easily found, so that the last may be determined by difference. (c) Weight or volume of air supplied. This measurement is difficult, in some cases impossible, to make directly. The weight of the air that must have been supplied can usually be obtained by computation on the basis of gas or fuel analysis and volume or weight of gas produced. This computation is similar to that made for flue gas. See Chapter XIII. (d) Humidity of air supply. This should be determined in every case. It may be found by the wet and dry bulb thermometer or some other form of hygrometer. See Chapter XXIII. (e) Analysis of fuel and gas, and heating value of gas. A com- plete producer test requires the ultimate analysis of the fuel used. See Chapter XIII. The methods of sampling and analyzing the GAS ENGINES AND GAS PRODUCERS 8905 gas have already been discussed in Art. 386. The gas should be examined for tar and dust. See Art. 389. The heating value of the gas should, if possible, be determined during the test by means of a calorimeter. » ° (f) Volume or weight of gas made. This may in some cases be directly measured, but can in all cases be computed with fair accuracy on the basis of fuel, gas, ash, and tar analysis. See Art. 389. (g) Temperature observations. The following temperatures should be taken: of external air and of air in the producer room, air entering and leaving the economizer or preheater, if one is used; of mixture of air and steam entering the producer; of gas leaving the producer, leaving the economizer, leaving the washing apparatus (or in the gas main); of feed water to auxiliary boiler in a pressure plant; or of water entering vaporizer in a suction plant (and leaving overflow from vaporizer if necessary). All of these temperatures can usually be obtained with the ordi- nary mercury thermometer, except the temperature of the gas leaving the producer, which will require a pyrometer. (h) Pressure observations. These should be as follows: barom- eter in producer room, steam pressure (in pressure plant), pressure in inches of water or mercury of mixture of air and steam enter- ing producer, of gas leaving producer, and of gas in main beyond the washing apparatus. The following form for recording observations and the results of computations based upon them is, with a few minor changes, given by S. S. Wyer in his book on “‘ Producer Gas and Gas Producers.” Data AND RESULTS OF GAS PRODUCER TEST. General Data. = Mest Made By4 vita Hate Sess eel ea inner esd pa hewmen es Ga Gatane- eer Lest. made to determitte.s392 ene peers sand De fees eh oe eee MEd e BESS Chémical analyses made bY: 2), ..00c6 00 ged da eG nena eeeus ee dice gna din’ BY PE: OL PLOMUCELY, 206 guts dans pee Avnet ae NERS eae i ERR : « Producer built bytissnc cco decd toch weed te de vss eieean 2h ides sist toss See . DatenofinstallatiOtis . tse cuca ek aya deer Wee Ran melee eee aenal ed ae eee Kand:0f fel ncoccccpsieagou «gaia d MA Aaah tae do AERA aS eee Form Of grate. oc .ioes ise cine i phe ee hile Seales HQT e wa aw eg re ees Ow An Pw dH 896 Io. II. 12. 13. 14. EXPERIMENTAL ENGINEERING General Data. — Continued. Forma Of @shpities wis oid ca ded shag oes OSs Pee ee ae ded A Ae de we ioe POrtt OF DIO WER sadn cag rains d eed PAAR he Heth ey ariel ee Sah SR BRAS eee State of weather: sick i sad dn na odraw oe had SEES We Se Hw ee A ele TS ies she ews Barometer in producer room... 6... 6... ete TAGS OF CES Cocictad. exteenseene bu ava oun Wile ba laeaie th hed useuuwihioravy ate aud) GY ie tee aetek ee Sa Duration of tests gu ac cae hese. wees BSE RA ee es Se ee een eg es Dimensions of Producer. A complete description and drawings of producer should be given on an annexed sheet. 15. 16. 17. 18. I9. 20. ar. 22. 23. 24. 25. 26. 25% 28. 20. 30. 31. 32. 33- 34- 35. 36. 37: Grate surface............... Width................. Length.......... Diameters»: occas eae eae DEVO A oars racy) wine, Ate ace anced amasee teak Caame nnd Height: of bed ofiashes:cic00:0. eva decdedtecaty adhe ee ee dieses shee Aas Height of top of fire above grate..........0.0... 0... c cece eee eee Ehickniéss: Of ash ZONE. ec.6 s paaee deal ned Mew BAe HR AAS SERV A Meda weddes Position of ait pipesisisi: 24s eyes BP Se eee ob ME Rae Ee Le eee cea nue Position of stéam ilets...2.. c-ce6 ecccedc aged du te eee cea ce ened oe RE SA wD Didmeter of producers... s.4w5i noes tae etek deoewa ts et eeenap seus ou Inclination‘of ‘bosh ‘walls os 422 2cgaq wings deo Merde dedicate deg dda wie oats Average Pressures. Steam pressure near nozzle (Ibs. per sq. in.) ...........0000 000020000. Force of draft in ash pit (in. of water)........0... 0.00 cece eee eee eee. Force of draft in gas flue (in. of water).......00000.0.0.0.0..0000000 00 eee. Steam pressure in auxiliary boiler (Ibs. per sq. in.)..................... Average Temperatures 30. 40. 41. 42. 43- . Percentage of moisture in ashes............0.0.00 0 ccc cece ee cece cece 45. 46. 47. 48. 49. GAS ENGINES AND GAS PRODUCERS 897 ‘Total weightsof dhy asheS.c. cc0ulscaueyacaves dove ounapei nae abe dees Percentage of carbon in dry ashes. Total combustible consumed Percentage of incombustible in dry fuel....................... aoa ytaed Total combustible consumed in auxiliary boiler 50. Total combustible required to generate the steam used in producer, if the producer was used without its own auxiliary boiler. .................. 51. Total amount of combustible used in the production of the gas.......... Proximate Analysis of Fuel. Of Fuel, Of Combustible, Per Cent. Per Cent. 152 3). URER EA TD OM isrpisde-cacash bo Sony Han Oe eo ea eed ees 2G Ophea dk eee sane | oe Babess BO 53. Volatile matter........ ea Weel ee Pais twine alee aretaceons | hes wade he Bol Sas MOIStUTG 2 x cietan scene cesveon ale tomes tg ea nll test evearhe dan ee aes BG NSIS osu gard se veid eegutanst peace wind SY MMS ae Siok dll sasha send aie PS RS BA Toul Ree Ioo per cent 1oo per cent 56. Sulphur, separately determined...................0. 00sec eee eee Ultimate Analysis of Fuel. Of Fuel, Of Combustible, Per Cent. Per Cent. Sr. Carbon (CO). sas can ineaseone e| ou veres yi eel ay caneers Abele oes teas 58: Hydrogen (A)s-ie9: i eses cu sage a vie ties are) aa cessed |e dan aedued se 59. Oxygen (O)....... 2 eee cece feces ete eee ee afer teen reece Go. Nitrogen: (N) ccs sc cae chee eases: pire ve ated ve de ier es|erebear gents 61, Sulphur: (S)s.sreanexe aa venes Moe iawe eae eet pans ceed oh au ed pees G9. NSH ahi seas acceso harvauee ate SANS |e Ba ONE erga nS oad on aah Sie and pe eR tans Ioo per cent roo per cent Moisture in sample of fuel as received. 898 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73- 74- ne 76. 77- 78. 79+ 80. 81. 82. 83. 84. 85. 86. EXPERIMENTAL ENGINEERING Analysis of Ash and Refuse. CarDOW: ce aneidne duu viaged Sea ee STO ee Seas BEA RR eG we egiewr ys we Karthy matters xvas gene xen eds os Sam oMineeadyaity gh ansg eS ag eaty A ee Consumption of Fuel. Total fuel consumed per hour in running producer..................0045 Total combustible consumed per hour in running producer.............. Dry fuel per square foot of grate surface per hour consumed in producer SESE 3 se a sche seni cic dd mae top h ear eg nA atone adn ai teatesadta leh ee rar thie eek Se Calorific Value of Fuel. Calorific value by oxygen calorimeter per pound of dry fuel...... B.t.u. Calorific value by oxygen calorimeter per pound of combustible... .B.t.u. Calorific value by analysis per pound of dry fuel............... B.t.u. Calorific value by analysis per pound of combustible............ B.t.u. Quality of Steam. Percentage of moisture in steam... 0... 2. eee Number of degrees of superheating............0.....00 000 ccc eee Quantity of Steam. Actual weight of steam per hour...... Aik Saw pe Blase eseah a Sal LOG Sasa aie Ratiouwk steam to-air supply... ayo5100% od sea dy weade bade d sw eaeeeey Ge’ Quantity of Air. Absoltitedh timidity cs any2eaekh aloe athe wen Werte ve eee ee fae Piped Actual weight of air per hour. ..... 0.0.00... ccc ec cece eee eee Water. Total weight of water used in vaporizer... ........0. 0.00. c eve eee eeeeee Number of heat units carried out per pound of fuel.................... Grate efficiency of producer.....0 2.00.0... c cece eee eee neue eeueeeens Hot=24s' efi ienGyig. sn osx vev beck es uga Hada oa ehaue (auled Suge eee Cold=paseMCene yy. ccuaed ae uc, ween sorte Geena eae wae diac Mody aatieam Cost of Gasification. Cost of fuel per ton delivered in producer room..................000005 Cost per British thermal unit in gas...................0.. sa gd Sesion Poking. Method of POkim ec i.c 2e5 Sawn oa Wart Aun eons eae ERT ONE RO ee Toe Ae Frequeiicy of poking,» cai. cic aha sv dosacaaiea gaa he ede tohaad bow ede am GAS ENGINES AND GAS PRODUCERS 899 875 Method of GHingiing-sieeatanie Ae tea beak ee besa Doon pence eh Goes 88. Average intervals between firing... ..........0. 0.0.0.0 cece .89. Average amount of fuel charged each time.................000000.000. Gas Analysis, 60. Carbon dioxide (COs). 6 sic cccna cn anceuhivwe une dh cade ebeeecdad bares gt. Carbon monoxide (CO) ..... 0.0.6.0 e cee e ee g2s Oxygen (O) wate va¥erctanesaias ek: Det casa Ot Sana sBanldce WN cat Anton euneeees aloes O33 Hydrogen (A) cadainw ance anes oh aauiee sO ands Seed toe kia eke Ode Marsh gas: (GE) (3540. S34 con Ai pain 2d aa Rae Deano ake ny eau gies os. Olefiant ‘gas: (CpH a) ss2ieasre se Sea ds co Gbad bol s eps aaianbavadiwers on 96. Sulphur dioxide (SOg)... 20... e cece ccc eee. 97. Nitrogen (N) by difference............0 00.0000. 0 0 ccc ccc cece ee ceee 98. Pounds moisture in gas per pound of fuel............0.00..0.00.0.0.... o9. Pounds soot and tar in gas per pound of fuel.............0...000..0.... too. Calorific value of gas from analysis............ 0000.0... cece eee eee tor. Calorific value of gas determined with calorimeter.................... ro2:- Specific heat of asco stack Ge geen eee da aead iden dese i eadbacaeweg aac 163.: Figure of Merit OF ‘BAS. vcew a Teas aes owed ete PEG eae ake es 104. Carbon ratio 5 asa i acetate RUA psa Sia SCTE fe a ros. Volume of gas per pound of fuel... 0... 0000 eevee cece e eee ees In this table the method of obtaining all of the items with the possible exception of the efficiencies (items 80 to 82) and of the figure of merit (item 103) should be clear. These will be considered in the next article in connection with the heat balance. 392. The Heat Balance of a Gas Producer. — There are two methods of establishing a heat balance for a gas producer. In the first, the heat interchanges in the endothermic and exothermic reactions occurring in the process are computed and a balance established between these in connection with the heat supplied in air and steam and that accounted for in sensible heat of the gas. The item necessary to complete the balance is the radiation loss. This method is scientifically very interesting but rather involved.* * See an article by K. Wendt on “Untersuchungen an Gaserzeugern,” in the Zeitschrift des Vereins deutscher Ingenieure, Nov. 28, 1904. Detailed computa- tions are there given. me ee goo EXPERIMENTAL ENGINEERING The second method is much s.:mpler and serves very well for all ordinary purposes. It is based simply upon the principle of (I) accounting for all the heat supplied to a producer, and (II) account- ing for all the heat that reappears in gas, etc. The discrepancy between these two accounts is assumed to be the loss by radiation, conduction, etc. The heat balance is nearly always established on the basis of unit weight of fuel. (1) Heat Supplied to Producer. — This consists of the heat in the coal and of the heat in the air-steam mixture per unit weight of coal. (t) Heat value of unit weight of fuel = Q, B.t.u. (32) (2) Heat in air-steam mixture consists of three parts: (a) heat in air; (b) heat in humidity in air, and (c) heat in steam supplied. All these are computed above some reference temperature /,, which is usually taken at the temperature of the room that obtained during the test. The mixture has a final temperature, ¢,,, as it enters the producer, while the pressure is either slightly below or slightly above barometer pressure, depending upon the type of producer. Under item (c) the weight of steam is determined as outlined on page 894. It may be assumed that this steam is super- heated as it enters the producer. The computations are as follows: (a) Heat in air supplied. =G,Com (tm — t,) = Qe B.t.u., (33) where G, = weight of dry air per unit weight of fuel supplied to producer alone, and Cym = mean specific heat between ft, and tp. (b) Heat in humidity in air = GC ym (im — t,) = O03 B.tau., (34) where G, = weight of water vapor as humidity carried by G, pounds of air, and Cym = mean specific heat of the water vapor, which for all practical purposes may here be assumed = .46. (c) Heat in steam supplied = G, id oe Cas: @., = t,) = (t, af 32)} = Ou B.t.u., (35) GAS ENGINES AND GAS PRODUCERS QOL in which G, = weight of steam supplied per unit weight of fuel, , >» = total heat in steam at the partial pressure due to it in the blast or suction pipe, Cym = mean specific heat between /,, and #,, in which the latter is the saturation temperature at the same pressure for which \ was found. For all practical purposes, the expression G, (1090.7 +455 bn ia t,) ae Q4 B.t.u. (35a) may be substituted for the above expression. See Chap. XIII. (II) The Heat Accounted for.— This appears in the following items: (1) heat value of the clean gas; (2) total heat of the water vapor in the gas as made; (3) heat of combustion of the tar in gas as made; (4) heat of combustion of the soot in gas as made; (5) sensible heat of the gas and its impurities; (6) heat value of the fuel in refuse; (7) sensible heat of the refuse, and (8) heat lost in radia- tion, conduction, etc. (x) Heat value of the clean gas where V = the number of standard cubic feet of gas produced per pound of fuel supplied to producer, and H = the heat value in B.t.u. per standard cubic foot. (2) Total heat of water vapor in gas = Gy id + Com (t, 4 ty) a (t, oo 32)! = Qe B.t.u., (37) in whichG, = weight of water vapor carried by V cubic feet of gas, dX = the total heat in steam at the partial pressure due it as the gas leaves the producer, t, = temperature of gas leaving the producer, Com = mean specific heat between #, and #,, the latter being the saturation temperature for which \ was de- termined. I - Here again, as for (I, c) above, the expression Gy (1090.7 + .455%, — t,) =Q5B.t.u. (37a) may be substituted with sufficient accuracy. 902 EXPERIMENTAL ENGINEERING (3) and (4). Loss in tar and soot. These are usually deter- mined together. The loss is somewhat indeterminate, because the heat value of the tar varies with its composition. It may be ex- pressed by GH, =Q7B.t.u., (38) in which G, = the total weight of tar and soot determined in V cubic feet of gas, and H, = heat value of tar and soot, which may be assumed at about 14,000 B.t.u. per pound. (5) Heat loss in sensible heat in gas and impurities. This loss is computed from the weight of the individual gases (CO, He, COz, No, CHy, C2Hy, etc.) made per pound of fuel supplied the producer, and for each one of these is equal to GC om (ty — t,) = QOgB.t-u., (39) where G, = weight of each gas per pound of fuel supplied to pro- ducer, Cym = mean specific heat between gas temperature ¢, and room temperature f,. Another method is to compute the average Cyn for unit weight of the producer gas, and to substitute this in equation (34), in which caseG, = total weight of gas made per pound of fuel. It should be noted that under this head the sensible heat of the water vapor, if the gas should contain any, is not considered, having been taken care of under (II, 2), equation (37) or (37a). The sensible heat lost in tar and soot is a negligible quantity in most cases. (6) Heat value of the fuel in refuse. This computation is made in exactly the same way as for the similar loss in boilers. See Chap. XVII. On the assumption that the combustible part of the refuse is coke, the loss may be put equal to 14,540(A — B) =Q,B.t.u., (40) the weight of refuse (dry) per pound of coal, and the weight of true ash (as found by calorimeter) per pound of coal. in which A B I ll (7) Sensible heat in refuse. This quantity is difficult to deter- GAS ENGINES AND GAS PRODUCERS 903 mine on account of uncertainty as to the specific heat of the ash and of the temperature of the ash as it leaves the producer. If the ash is allowed to rest in the ash pan for a considerable period, a great deal of the heat originally carried down by it is likely to be returned to the producer by upward currents of air. In any case the loss through this source is small and may be neglected. (8) Heat lost by radiation, conduction, etc., is determined as the difference between the heat supplied and the heat accounted for, and may be expressed by R= ZQi tos — ZOsto9, ‘ (41) 393. Computation of Gas Producer Efficiency. — The commercial efficiency of a producer varies not only with the manner in which the various actions and reactions in the process are carried out, but also with the use to which the gas is to be put. The gas as it leaves the producer carries two very distinct quantities of heat, that bound as chemical energy in the combustible part of the gas, and that designated as sensible heat, due to its temperature above some reference temperature. There are commercial uses, as for instance the heating of steel furnaces, reheating furnaces, etc., in which we should strive to utilize, as fully as possible, both of these quantities of heat. There are others, notably the operation of gas engines, in which we must have a cold gas in order to realize full engine capacity. Incidentally, we get this cold gas because the gas must be thoroughly washed for engine operation. In such a case the sensible heat is evidently almost entirely lost. The part not used in a preheater is carried away by the scrubber water. In the first case the useful effect is the sum of the heat of combustion plus the sensible heat; in the last it is practically only the heat of com- bustion. Evidently, since efficiency is the quotiént of useful effect divided by heat supplied to produce this effect, the efficiency will be different in the two cases. That efficiency which credits the producer with the sensible heat in the gas is known as the hot-gas efficiency, that which does not is called the cold-gas efficiency. Let H; = heat value of one pound of the fuel as fired, H, = total quantity of heat of combustion in the gas made per pound of fuel, and go4 EXPERIMENTAL ENGINEERING H; = the sensible heat above some reference temperature (usually room temperature) in the gas made per pound of fuel as it leaves the producer. Then is Cold-gas efficiency = ah (42) 1 Hot-gas efficiency = at is . (43) 1 Referring to the previous article, Hi, in a suction gas producer, is equal to item (I, 1), equation (32), of the heat balance. HH, is the same as item (II, 1), equation (36), of the heat balance, while H; is the sum of items (II, 2), equations (37) or (37a), and (II, s), equation (39). The computation of the efficiencies from the heat balance sheet is therefore a simple matter. Since, however, the heat balance is established on the basis of the fuel used in the producer only, the above efficiency computa- tions, if based on the heat-balance items referred to, will apply only to a suction-gas plant. In a pressure-gas plant, in which fuel is also used in an auxiliary boiler, the items of the heat balance above enumerated must therefore be modified. In most cases the kind of fuel used for the boiler is the same as that used for the producer and this will be assumed here. Then H; is the same as before, but for the computation of H, and Hs, items (II, 1), (II, 2), and (II, 5) must be modified because, on account of the greater amount of fuel now entering the computation, the yield of gas per unit weight of fuel is less. The new values of H, and H3 can be found by multiplying the items mentioned by the ratio coal used in producer coal used in producer + coal used in boiler The “ figure of merit” is a term invented to compare the per- formances of various producers or of the same producer under different conditions. It is defined as the heat value of the gas produced per unit weight of carbon it contains, and is computed by dividing the heat value per standard cubic foot of the gas by the weight of carbon the standard cubic foot contains. Wyer gives the following computation as an example: GAS ENGINES AND GAS PRODUCERS 905 Heat Value Due to the | Weight of Carbon Rep- Various Combustible | resented by the Various Components, B.t.u. Component Gases, Lbs. Component of Gas, Volume Per Cent. AOD =| heres aeoeon elaine 3 . 00134 25.4 86.86 .00848 I.5 16.05 . 00050 fist BAO |) Fraiadawtaaeaed oaes 580° ee teeene ys ee muwarn|s maken Aan eadamieh e 100.0 I41.31 01032 Hence figure of merit = Fans =13,690 B.t.u. per pound of carbon. 394. The Testing of Gas Engines. — Gas engines, like steam engines, may be tested for a variety of purposes. The ordinary test consists of the determination of I.H.P. and B.H.P., and of fuel consumption. If this is carried out for a series of loads, the test is practically one for efficiency and capacity. These are the usual items covered in contract guarantees. There are, however, a number of other things which may serve as the objects of a test on a gas engine, as for instance, the interrelation between economy and speed, economy and proportion of fuel mixture, capacity and proportion of fuel mixture, economy and capacity with variation in jacket temperatures, speed regulation tests,* and a number of others. The important thing, of course, is to keep the ultimate object clearly in mind and to make the arrangements of the test to meet this object. In the following directions it is assumed that it is desired to make a complete capacity and economy test, from the computed results of which it will be possible to establish a complete heat balance. If in any given practical case the aim of the test is different, changes from the scheme can be easily made and will readily pre- sent themselves. 1. Examine the engine externally and internally, especially with reference to the condition of valve and piston rings, and take note of all the conditions that may bear on the object of the test. Fur- nish drawings or sketches of any essential parts that cannot be clearly described in words alone. * For speed regulation tests, see Chap. XVIII. 906 - EXPERIMENTAL ENGINEERING If the test is to be for maximum efficiency and capacity, all de- fects should be remedied before the tests. In case of a service test, the work is, of course, done with the engine as found, unless the conditions should be clearly abnormal. 2. Determine the principal dimensions of the engine —— cylinder diameter or diameters, length of stroke, etc. This should be done in all cases, whether dimensions are already known or not, and the cylinder should be hot when the measurement is taken. Find the clearance volume. For the method of doing this, see the Steam Engine Test Code. 3. Calibrate all the instruments used — indicators, gauges, water- meters, etc., —if possible, both before and after the test. For methods of doing this, see previous chapters in this book. 4. Starting and Stopping a Test.—In tests to determine the maximum efficiency or economy of an engine always operate the machine for a sufficient length of time, as nearly as possible under test conditions, to make sure that all conditions have become fairly constant. Then start the observations and continue for the time decided upon under (5) below. If the test is to determine the performance under working con- ditions, the test should start when the engine starts, and should continue to the close of the period covering the day’s work. 5. Duration of Tests.—The length of the test depends somewhat upon the object of the test. In the case of economy or efficiency tests on an engine using liquid fuel or a “‘ ready-made ”’ gas, like natural gas or illuminating gas, the time of test, after constant conditions have been reached, can be made comparatively short, and may in fact be stopped after several successive readings, say one-half hour apart, have shown that power developed and fuel con- sumedare fairly constant. Testsonsmall and very high-speed liquid fuel engines, like automobile engines, sometimes last less than one hour for each load, the reading being taken every 5 or ro minutes. Where engines are tested in connection with their gas producers, and the guarantee is based upon the coal consumption, as it usually is, the test should last not less than 12 hours and should preferably continue for more than 24, on account of the difficulty of determining the total fuel consumption. GAS ENGINES AND GAS PRODUCERS 907 In case of service tests (plant tests) the test, of course, continues for the usual period of time covering the hours of work in the particular plant. 6. Apparatus Required, Observations, and Calculations. — Means must be furnished to determine the following items: (a) Indicated horse power. The factors determining this quan- tity are the mean-effective pressure in the cylinder, and the number of revolutions or of explosions. The pressures and rotative speeds encountered in gas-engine work are generally much higher than those found in steam-engine practice. This calls for compact indicators with moving parts as light as possible consistent with stiffness, the use of strong springs, and the substitution of the half-size piston for the normal one. On account of the high temperature of the working medium, ex- ternal spring indicators are of special service, although many of them labor under the disadvantage of having rather heavy moving parts. Engines operating at speeds exceeding 500 R.P.M. (auto engines will run up to 1500 or 2000 R.P.M.) either are not indicated at all, or some form of optical indicator (see Chap. XV) must be employed. The indicator pipe must be as short as possible and without sharp bends. This is for the purpose of preventing the accumulation of an explosive mixture in the piping and to reduce pressure loss as far as possible. The reducing motion may be of any type best adapted to the speed. See Chap. XV. The number of diagrams to be taken varies with the kind of engine and largely also with the kind of service under which the engine is operating. For an engine which governs by regulating the size of the charge, i.e., in which there are no misstrokes, and where the load is fairly constant, a single diagram every 10 or 15 minutes is quite sufficient. If the load varies, the diagrams may either be taken oftener, or a bundle of diagrams may be taken on the same card. Where the load is very fluctuating, a good method is to operate the indicator for 2 minutes and to apply the pencil to the paper at successive intervals of 10 seconds during that period. The average of all the diagrams so obtained is, of course, used for the determination of I.H.P. 908 EXPERIMENTAL ENGINEERING In an engine governing on the hit-and-miss principle, the succes- sive cycles occurring between any two miss periods are usually not at all of the same size. In such a case, therefore, the pencil should be allowed to trace all of the “ hit’ diagrams between two successive miss periods, the average being used for the computation. In a multicylinder or double-acting engine, one indicator must be furnished for each cylinder end. The use of a three-way cock, even where this is possible, is not permissible. The general horse power formula is Tope: 33,000 (44) where, as before, p = mean effective pressure per sq. in. of piston 1 = length of stroke in feet, and @ = area of piston in sq. in. x is the number of impulses (explosions) per minute for each operating-cylinder end, and it should be pointed out that this is not necessarily the number of revolutions per minute in a single-acting 2-cycle machine, or one-half this number in a single- acting 4-cycle engine. It would be equal to these numbers if the engine governs by any of the so-called “ precision’ methods (throttling or regulating fuel supply), but in an engine governed upon the hit-and-miss principle, x is the number of “ hits ” per minute and depends upon the load. For the determination of its value in this case, see (c), p. 909. If the mean effective pressure p is found from the work diagram in a 4-cycle engine (not taking the lower loop area into account), or from the power diagram area in a 2-cycle engine, the I.H.P. com- puted is the gross indicated horse power. In either engine this gross I.H.P. is used in three ways: useful effect (B.H.P.), loss in mechanical friction (friction horse power), and loss in the pump work (fluid friction), the last being represented either by the area of the lower loop in a 4-cycle diagram, or by the pump card in a 2-cycle engine, assuming, of course, that the engine drives its own pumps. The net I.H.P. is equal to the gross I.H.P. less the I.H.P. represented in fluid friction. In a 2-cycle engine, the fluid friction horse power is determined by indicating the pump cylinder GAS ENGINES AND GAS PRODUCERS gog or cylinders. The ordinary 4-cycle-engine diagram does not show in the ordinary case a sufficiently clear lower loop to admit of integration. For accurate work,a weak spring card should be taken in this case. In many cases, in tests on 4-cycle engines, the power loss represented by the lower loop is neglected, although it may amount to 3 or 4 per cent of the gross I.H.P. (b) The horse power output. This is determined for a gas engine the same as for a steam engine, and the student is referred to the Steam Engine Code and to Chap. X. “3 (c) Speed and number of explo- 4 sions. The number of revolutions ; All Ip | may be found by means of any of = fs | ; ml i the speed-recording instruments de- Wee Tm scribed in Chap. VIII. The number elf of explosions per minute either bears -=es— CH) some definite ratio to the R.P.M., in engines that do not govern by hit-and-miss, or the number is irreg- ular in engines that are governed that way, as above pointed out. The 8 number of explosions in such a case usually can be found by attaching a 2 stroke counter to any reciprocating part of the valve gear which fails to move every time the engine makes amisstroke. Another method, and | \\ cue which also gives 2 peter of Fic. 550. — Matuot ExpLosion the force of the explosions, is to use RECORDER. an explosion recorder of the type de- signed by Mathot. This instrument is shown in Fig. 550. The following is the description of its method of operation, given by the inventor in his book on ‘‘ Modern Gas Engines and Gas Producer Plants.” The instrument is somewhat similar in form to the ordinary indicator. Its record, however, is made on a paper tape which is continuously unwound. The cylinder ¢ is provided with a ! I | L gio EXPERIMENTAL ENGINEERING piston, about the stem of which a spring s is coiled. A clock train contained in the chamber 6 unwinds the strip of paper from the roll p and draws it over the drum p”, where the pencil ¢ leaves the mark. The tape is then rewound on the spindle p’. A small stylus or pencil f traces the atmospheric line on the paper as it passes over the drum p”. . In order to obviate the binding of the piston when subjected to the high temperature of the explosions, the cylinder c is provided with a casing e in which water is circu- lated by means of a small rubber tube which fits over the nipple e¢’. This recorder analyzes with absolute precision the work of all engines, whatever may be their speed. It gives a continuous, graphic record from which the number of explosions, together with the initial pressure of each, can be determined, and the order of their succession. Consequently the regularity or irregularity of the variations can be observed and traced to the secondary influences producing them, such as the action of the inlet and outlet valves and the sensitiveness of the governor. It renders it possible to estimate the resistance to suction and the back pressure due to expelling the burnt gases, the chief causes of loss in efficiency in high-speed engines. Furthermore, the influence of compression is markedly shown from the diagram obtained. The recorder is mounted on the engine; its piston is driven back by each of the explosions to a height corresponding with their force; and the stylus or pencil controlled by the lever ¢ records them side by side on the moving strip of paper. The speed with which this strip is unwound conforms with the number of revolu- tions of the engine to be tested, so that the records of the explo- sions are placed side by side clearly and legibly. Their succession indicates not only the number of explosions and of revolutions which occur in a given time, but also their regularity, the number of misfires. The pressure of the explosions is measured by a scale connected with the recorder spring. By employing a very weak spring which flexes at the bottom simply by the effect of the compression in the engine cylinder, it is possible to ascertain the amount of the resistance to suction and to the exhaust. It is simply sufficient to compare the explosion record with the atmos- pheric line, traced by the stylus f. By means of this apparatus, GAS ENGINES AND GAS PRODUCERS gil and of the records which it furnishes, it is possible analytically to regulate the work of an engine, to ascertian the proportion of air, gas, or hydrocarbon which produces the most powerful explosion, to regulate the compression, the speed, the time of ignition, the temperature, and the like. (d) Measurement of the fuel supply. The common means for measuring the fuel supply for gases like illuminating or natural gas is the gas meter. This may also be used for pressure-producer gas. On account of the nature of the demand, which is strongly fluctuating, especially if only one cylinder is in operation, it is always best to install a reservoir of some kind between engine and meter. This may be a gas bag, for a small engine, some form of pressure regulator, or nothing but a tank of sufficient capacity to tone down the pressure fluctuations. Without this precaution the determina- tion of average gas pressure at the meter becomes difficult. Besides the pressure and volume, the temperature of the gas at the meter must also be taken. The volume should be reduced to standard conditions, 14.7 pounds and 32° F., in the report. The most common method of determining the fuel consumption in a suction-gas plant is to measure the coal used in the producer. The measurement of liquid fuels is made most simply by supply- ing the engine from a tank, calibrated and fitted with a gauge glass andscale. Asa general thing, however, it is more accurate to weigh the fuel. In that case the level of the oil in the tank is noted at the beginning of a test, and the fuel necessary to maintain the level at the same point, or to bring it back to the same point, is weighed and poured in. Where the fuel consumption is large, and a small error in weighing causes only a very small percentage error, a method that has been used is to put the fuel tank directly upon scales, and to connect the tank by flexible piping to the supply piping of the engine. Besides the weight of the liquid fuel, temperature and density should also be recorded. In any engine using a fuel supply for the maintenance of an ignition flame, or for any other purpose, the quantity so used must be taken into account and separately determined if possible. (e) Measurement of air supply. This measurement may be gi2 EXPERIMENTAL ENGINEERING made in two ways: by meter on the air-inlet pipe, or by compu- tation from the exhaust-gas analysis in connection with the fuel analysis. Incase a meter is used, the remarks under (d) with refer- ence to pressure fluctuations apply. For the method of computing the air supply, see Art. 387. (f) Measurement of jacket water. This may be determined by the use of water meters or of weighing tanks. The latter method is preferred where it can be applied. The arrangement of tanks, and whether the water should be measured before entering or after leaving the jackets, is largely a question of expediency, and must be decided for every particular case. If an engine uses a separate supply for cylinder jackets, and for piston and rod cooling, each supply must be determined separately. (g) Analysis of fuel and exhaust gases. A complete test should always include the chemical analysis of fuel and exhaust gas. For the methods of analyzing solid fuels and exhaust gases, the student is referred to Chapter XIII. For the analysis of fuel gases, see Art. 386, of this chapter. Methods of sampling, etc., are also discussed in the places referred to. (i) Heating value of the fuel. In the case of solid fuels (gas producer plants), the heating value is determined upon the labora- tory sample taken on the test. The same thing may be done in the case of gas fuels, samples being taken as described in Arts. 275 and 386. Whenever possible, however, a gas calorimeter should also form a part of the test apparatus and the determinations of heating value should be made during the test. The computations of heating value based on the laboratory analysis will then serve as a check upon the calorimeter work. In stating gas-heating values in B.t.u. per cubic foot, the volume should be reduced from the conditions of test to standard conditions, 14.7 pounds pressure and 32°F. (i) Pressure, temperature, and other observations. The pressure observations required are: pressure of gas at meter and barometer pressure. The temperature readings are: outside air, air in engine room, inlet and outlet of jacket water, gas at meter, or fuel oil at reservoir, and temperature of exhaust gas. The latter is best taken by means GAS ENGINES AND GAS PRODUCERS 913 of some reliable pyrometer and as close to the exhaust valve as possible. Other observations should be: density of fuel oil, if an oil engine is tested, and humidity of atmosphere, by wet and dry bulb ther- mometer, or by some other form of hygrometer. 7. Recording the Data, and Preparation of Report. —The time of taking weights and of recording every observation should be care- fully noted in the logs. Note every occurrence on the test. Read- ings 20 or 30 minutes apart are satisfactory when the conditions are uniform. Where they vary, readings at more frequent intervals should be made. It is good practice to carefully make all readings with special care at the end of every hour, so as to divide the test into hour periods for the purpose of checking uniformity of condi- tions as the test proceeds. It is also desirable to plot during the test curves of the fuel consumption per hour against brake horse power (similar to Willan’s Law, see Chap. XVIII). This will at once reveal any abnormal conditions that may become operative after the test is started. The following table, published in the Code established by the American Society of Mechanical Engineers, shows the items that should be computed for a complete report. This is followed by two abridged forms of report, used in Sibley College, one for a gas, the other for an oil engine. These forms give quite sufficient information for the ordinary commercial report and furnish space for the recording of a series of “runs.” Where these have been made at a series of loads, curves of efficiency and fuel consumption should be plotted, and should accompany the report, to graphically represent the results. (See type examples on such curves for steam engines in Chap. XVIII). Data AND REsutts OF TEST OF GAS OR OIL ENGINE. Arranged according to the Complete Form advised by the Engine Test Com- mittee, American Society of Mechanical Engineers. Code of 1902. t. Made by.. ..............000- OLS Hd cuned AV Aan EGER SRT e ES on-enginé located at ec coccaa vag ad nad sete reader se yea see eed epees EO! ELE MINe ls eins once tots AA Aa eek Keg GA ER eS we aT 914 EXPERIMENTAL ENGINEERING 8, Gasor oil US8éd sos oacc as eoee eee ee rade eee he ad 6 eek OY esd eaws op eennd eR (@) Specie gra vityends seeks get waa £06 os he Bwee we Seals deg. F. (6) Buran: POs «as. vise 4 iy cea ole mala meals aca eegeeNS (¢) Flashing points.sos4.0 550. s6ngo4 sees ea sedan deeds 9. Dimensions of engine: 1st Cyl. 2d Cyl. (a) Class of cylinder (working or for compressing CHesChargeyic.. hays ois aera one Peake Maced (6) Vertical or horizontal...................-. (c) Single or double acting.................... (d) Cylinder dimensions...................... Strokes Mayen vee ates ae hee ee ft. Diameter piston rod.................. in, Diameter tail rod................0.... in. (e) Compression space or clearance in per cent of volume displaced by piston per stroke... Headsend acs scans hae emer een cea gtnele e AVETARC acu aa) gente hae se eee ay (f) Surface in square feet (average)............ Barrel of cylinders ..................... Cylinder? heads. ive vues aves Wate s Mae no's Clearance and ports..............0000005 Ends of piston. 6... eee Biscomrod,.'s Ahsan oh, aoa alncea ede stan (g) Jacket surfaces or internal surfaces of cylinder heated by jackets, in square feet......... Barrel of cylinder.................000005 Cylinder heads: ..s.s,cssacve.ceesdes ves Clearance and ports..................... (tS Horse-power constant for one pound M.E.P. and one revolution per minute......... Io. II. 12. 13. I4. I5. 16. 17. 18. 19. 20. 2i. 22. 23. 24. 25, 26. GAS ENGINES AND GAS PRODUCERS gI5 Give description of main features of engine and plant, and illustrate with drawings of same given on an appended sheet. Describe method of governing. State whether the conditions were constant throughout the test. Total Quantities. Duration: Of t6steccis dasa vageie eek aia nae Feoe Pomg dee g hours. GasiOr, O11 COMSUMEM: 3). 52 pissed aula dcelaien Gdn ae aoe AS cu. ft. or lbs. Air supplied in cubic feet... ......... 0.00. c eee eee eee cubic feet. Cooling water supplied to jackets...................00. cu. ft. or lbs. Calorific value of gas or oil by calorimeter test, determined Dyeachve wees Calorimetets:,.ote disse eyed Shee B.t.u. Hourly Quantities. Gas or oil consumed per hour. .................-.00005 cu. ft. or lbs. Cooling water supplied per hour. ...................... pounds. Pressures and Temperatures. Pressure at meter (for gas engine) in inches of water..... inches. Barometric pressure, inches of mercury................. % Temperature of cooling water: GG) Tre tiie, caste Scales cea ttcbiane ants gedcavas tune Siparansee MoM SANS aie deg. F. (b) Outletya oss oceyeawabs ow bag Bhai coke ree ees ee S Temperature of gas at meter (for gas engine). ........ Temperature of atmosphere: (a) Dry-bulb thermometer..................0..0006. es (b) Wet-Bulb thermometer..................0020-055 - (c) Degree of humidity... 0.00.0 cc suaeteeee cess per cent. Temperature of exhaust gases................0.00ee eee deg. F. How determined... .. 0... ee tees Data Relating to Heat Measurement. Heat units consumed per hour (pounds of oil or cubic feet of gas per hour multiplied by the total heat of combustion). gx.qe00n4 shoey de werd ehh eet B.t.u. Heat rejected in cooling water: (a) Total per-houtics oy aeeseiesandy se eees eyeseess (b) In per cent of heat of combustion of the gas or oil CONSUMED... ejogene ote Sea eee Se dewey eee per cent. Sensible heat rejected in exhaust gases above temperature of inlet air: (a) Total pet hours scsi. mad oucsee as oe oe we eee ees B.t.u. (b) In per cent of heat of combustion of the gas or oil CONSUME Ye... coe tebe tas whe aeddne pe Mite per cent. 916 EXPERIMENTAL ENGINEERING 27. Heat lost through incomplete combustion and radiation per hour: (a) ‘Total per hour...0.sveeessy os eerae ae per eee ore (0) In per cent of heat of combustion of the gas or oil con- SUMEd eH Aad eles , and 47.1 D?Lx (53) 4 In case of an engine using a liquid fuel, the computation becomes uncertain because of the fact that the volume of the liquid fuel vapor is a function of cylinder temperature. The volumetric efficiency may be approximately computed directly from a lower loop card. Let Fig. 552 represent the lower Fic. 552. loop on a 4-cycle card. The piston displacement is measured by the distance a. The volume of the mixture in cylinder under atmospheric pressure is measured by the distance 6. Hence volu- metric efficiency is approximately equal to a The computation a is not exact because the temperature factor is left out of account. s CHAPTER XXII. HOT-AIR ENGINES 397. Types of Engines and Methods of Operation. — Hot-air engines belong to the class of external combustion engines, as dis- tinguished from ordinary gas engines, which are true internal com- bustion engines. The difference lies in the fact that in external combustion engines the working medium, which is usually air, receives its stock of heat for conversion into work from an external source. As stated, a part of this stock of heat is converted into work, the rest is discharged by cooling the working fluid by an external source. No actual discharge of working fluid, except for leakage, takes place, the same body of fluid serving for every cycle. In gas engines, on the other hand, a new charge of working fluid is taken in every cycle, and the heat supplied for conversion into work is chemically generated by the process of combustion in the cylinder itself during a certain part of the cycle. The heat remain- ing at the end of each cycle is discharged with the working fluid. There are at present only two types of hot-air engines in the market, the Ericsson and the Rider. These are commonly used as pumping engines. Their capacity is generally small, owing mainly to two causes. In the first place, air used as a working medium requires large cylinder capacities per unit of power as compared with those required by other media, like steam or fuel gas. This is especially true if it should be attempted to use the Carnot cycle. Neither the Ericsson nor the Rider engine operates on this cycle, even in theory, but the disadvantage stated still exists. In the second place, it is not easy actually to construct large engines of this type with a satisfactory furnace in which the heat can be generated and transferred. For the same reason the thermal efficiency of even the small machines is in practice generally low. Nevertheless, they have certain advantages where small power is all that is required, and there is no skilled attendance 925 926 EXPERIMENTAL ENGINEERING available, since, in order to operate them, it is merely necessary to light a coal or gas fire in the furnace. 398. The Ericsson Engine. — Fig. 553 gives a clear idea of the construction of this engine. The cylinder 1 contains two pistons, — — O29 oO : 4" a 10 © 5 ©) ‘ 15 y 16 26 L oO Ie oa | | @ | 18 ‘a, Vi a I 12 ) 17 ¥ 20 oO 5 +4 Nin 19 3 N —__#! ws o_i=e eh 21 | | | 28 98 al TTI L, i Fy fea TT 6 6 | 24 Fic. 553. Ericsson Hot-arr ENGINE. the disk piston 2, called the air or power piston, and the transfer piston 3. The power piston 2 is connected through rod 1 5 to the main beam 8. At one end the main beam operates through rod 16 the single-acting plunger pump 17. This pump lifts the water on the up stroke and forces it through the jacket surrounding the HOT-AIR ENGINES 927 upper part of cylinder 1 and into the discharge main. This jacket constitutes the cooler for the working medium. On the other end the main beam through rod 10 operates the crank 26, to which in turn are connected the rod 11 and the bell crank 12. How this motion is transmitted from the bell crank to the transfer piston 3, by means of side rods, is best shown in the small elevation, Fig. 554. The transfer piston 3, Fig. 553, = is made of light metal and is Ne 4 NS hollow, acting as a non-conductor. we wat The space 4 is the seater, heat i f being in this case furnished by a set, 6, of Bunsen gas burners. The space 5 is called the furnace. The method of operation of this engine is best explained by refer- ence to Fig. 555, which represents curves of the movements of the two pistons for one complete turn of the main crank. The link mo- tion is drawn for position 1, with the main crank vertical. Motion is counter-clockwise. The other crank positions are taken at 2, 3, and 4, as shown. The cor- responding piston positions are located on vertical lines marked with the same numbers. Connecting the 5 points (since position 1 is repeated at the right) so located gives the curve AB for the motion of the power piston and the curve CD for that of the transfer or displacement piston. Curve C’D’, parallel to CD at all points, follows the motion of the lower end of the transfer piston, showing the volumes contained between it and the bottom of the heater, which is indicated by line EF. In following out the pressure and volume changes in the body of working fluid in this engine, it is necessary to remember (a) that only the working piston can change the volume, and (bd) that the temperature is controlled by the action of the transfer piston. The changes can now be outlined as follows: — in Fic. 554.— Ericsson ENGINE. 928 EXPERIMENTAL ENGINEERING 1st Quadrant (1 to 2). Power piston rises, causing expansion. Transfer piston rises, forcing air into heater. Heating effect ap- parently strong enough to overcome pressure drop due to expansion, and net result is fairly constant pressure. Line 1-2 in Fig. 556, ~ [e gen Transfer Piston peel i F Fic. 555.— Diacram OF OPERATION OF ERICSSON ENGINE. Q m which represents an actual indicator diagram from an Ericsson engine. (Full size, scale of spring 10 pounds.) 2d Quadrant (2 to 3). Power piston completes rise, causing expansion. Descent of transfer piston forces air into cooler, lower- 2 At. Line 4 Fic. 556.—Inpicator DIAGRAM FROM ERICSSON ENGINE. ing temperature. The net result is a pressure drop, forming line 2-3 on the card, Fig. 556. 3¢ Quadrant (3 to 4). Power piston starts to descend, causing compression. But at the same time the further descent of the transfer piston, forcing more air into the cooler, intensifies the cool- HOT-AIR ENGINES 929 ing action to such an extent as to practically maintain constant pressure. Line 3-4 on the card. 4th Quadrant (4 to 1). Power piston completes descent, causing compression. Transfer piston rises, forcing air into the heater, raising the temperature. The net result is a rise in pressure, forming line 4-1 on the indicator card. The theoretical cycle upon which the engine operates (two constant pressure lines crossed by two isothermals) and to which Fig. 556 approximates is discussed in Art. 185, p. 348. 399. The Rider Engine.— Fig. 557 shows the construction of this machine. The essentials are: a power piston D and a transfer piston C, rigidly connected by cranks to the shaft JZ. The two cylinders in which these pistons are working are connected across by the passage HH which forms the regenerator. The regenerator chamber is partly filled with some loosely packed material (sheet steel) which serves to abstract a part of the heat from the working fluid as it flows from the heater to the cooler, and restores this heat when the flow reverses. Below the power cylinder B is located a furnace F. In this case the fuel is coal, although of course any source of heat may be employed. The work done in the power cylinder is expended in the transfer cylinder and in the pump which is operated from the transfer piston, as shown. The water pumped is first forced through a jacket £, serving as a cooler for the transfer cylinder. To follow the pressure and volume changes which occur in the working fluid during one complete turn, see Fig. 558. Crank posi- tions 1, 2, 3, and 4 represent those of the power piston. The trans- fer crank has somewhat smaller throw than the power crank and lags behind the latter a few degrees over 90. This gives 1’, 2’, 3’, and 4’ as the corresponding positions of the transfer crank. Al- though in the drawing the transfer piston and cylinder should be located directly behind the power cylinder, it has been drawn to one side for the sake of clearness. Curve AB represents the motion of the lower end of the power piston and line CD the bottom of the power cylinder (heater). Similarly, EF shows the motion of the lower end of the transfer piston and line GH the bottom of the transfer cylinder (cooler). Vertical distances between AB and CD, 930 EXPERIMENTAL ENGINEERING z i i] om sr m a is = \ NW : E qr Ck of S- @ yi Tr (fh U A on WO 8 HELL: Fic. 557.— RWER Hot-arr ENGINE. HOT-AIR ENGINES 931 and between EF and GH, represent at any instant the volumes in the two cylinders. Curve JJ shows the sum of the volumes in the two cylinders. This is not the total volume of the working fluid as the regenerator volume HH, Fig. 557, is not accounted for; but curve IJ will serve to show volume changes, as the ph Power Piston Transfer Piston Pa Pelz] IN NGA Resultant Theoretical Diagram Fic. 558.— DiacRAM OF OPERATION OF RIDER ENGINE. regenerator volume is constant. (The regenerator passage is at no time closed by either piston.) 1st Quadrant (1 to 2). Practically constant volume change. Descent of power piston and rise of transfer piston indicates ab- straction of heat by regenerator and cooling in the transfer cylinder. The net result is a constant volume pressure drop. (See line 1-2 in the theoretical line drawn in Fig. 558.) ad Quadrant (2 to 3). The volume curve JJ shows decided 932 EXPERIMENTAL ENGINEERING compression. The power piston completes its descent, but the transfer piston also starts to fall, so that the temperature changes are less pronounced than in the first quadrant. The net result is a rise in pressure with volume decrease. (Line 2-3 in diagram in Fig. 558.) 3d Quadrant (3 to 4). Practically constant volume change, accompanied by a rise in pressure as the working fluid is trans- ferred across the regenerator into the heater by the further descent of the transfer piston and the ensuing rise of the power piston. (Line 3-4 in the diagram in Fig. 558.) 4th Quadrant (4 to 1). Marked expansion according to curve IJ. This expansion is accompanied by smaller movement of working fluid, on account of simultaneous rise of both pistons. Hence, the heating effect is less strong than in the third quadrant and the net result is expansion with pressure drop. (Line 4-1 in the diagram in Fig 558.) It will appear from this analysis that the theoretical cycle to which the series of changes approximates is one composed of two constant-volume lines crossed by two isothermals. This is the Stirling (regenerator cycle) which is discussed in Art. 185, p. 348. In actual testing practice, two indicator diagrams are taken from this engine. The single indicator used is connected to the regenerater chamber and is connected in turn with two reducing motions, the first of which gives the proper reduction for the power piston, the second for the transfer piston. Fig. 559 shows actual diagrams taken from a Rider engine (full size, scale of spring 10 pounds). The methods by which they are traced can be easily followed by noting the periods of piston movements, that is, out- stroke and instroke, from curves AB and EF, Fig. 558, and com- bining with this the knowledge concerning pressure changes gained from the analysis above. Thus for the curve AB of the power piston, the first and second quadrants represent the ‘‘down” or “‘in” stroke. From the analysis above, the first quadrant is accom- panied by a pressure drop, the second quadrant by a pressure rise. Hence line 1-2-3, Fig. 559, is evidently the one traced during these two periods. The other lines may be identified in a similar manner. The larger area is that for the power piston, the smaller one that HOT-AIR ENGINES 933 for the transfer piston. The lines are traced in opposite direc- tions (see arrows), as can be discovered if the method of tracing the lines above indicated is fully carried out. The larger area shows work developed in the power cylinder; the smaller, work done upon the transfer piston. Hence the difference between the power At. Line 7 Fic. 559.— InpicaTor D1acGRAMS FROM RWER ENGINE. represented by these two cards is the net power developed by the engine and is that available for pumping and for overcoming mechanical friction. 400. The Testing of Hot-air Engines. — A complete test of a hot-air engine should include the following items: (a) The indicated horse power. The indicator can be operated directly from the pump rod in the Ericsson engine without the interposition of any reducing motion. In the Rider engine, motion is taken from the pistons, but on account of the length of stroke some type of reducing motion must be used. The maximum pres- sures are in either case low, a 10-pound spring being satisfactory in most cases. (b) The pump horse power. On account of the small size of the pump cylinders no pump diagrams need be taken, the useful output being computed directly from the water pumped and the head pumped against. The quantity of water may be determined by weighing, although a nozzle may be used to advantage. The head pumped against is of course the sum of suction and discharge heads with proper allowance for velocity heads (see Chapter XVIII, Pp. 774). (c) Measurement of the fuel used. Where gas is used, the best means is of course the gas meter. In case coal is fired, the test should be extended over a considerable period of time. In 934 EXPERIMENTAL ENGINEERING the case of gas, a trial lasting one hour for each set of conditions, after the latter have become constant, is satisfactory; but in the case of solid fuel a duration of test of 6 or 8 hours is none too long, on account of the errors involved in judging the beginning and end conditions of the fuel bed on the grate. (d) Analysis of the fuel with determination of heating value. This is necessary for the computation of efficiency and the estab- lishment of heat balance. (See Chapters XIII and XXI.) (e) Analysis of the waste gases from the furnace, together with a determination of their quantity. Required where it is desired to establish a fully itemized heat balance. (See Chapters XIII and XXI.) (f) Other observations are: Suction head; discharge head; revo- lutions of fly-wheel shaft; range of temperature of jacket (cooler water); pressure in gas mains, if gas is used; temperature of room; barometer reading; dimensions of engine. The usual method of testing is to divide the total head against which the engine can pump into a number of equal parts, 5 or 6, and at each one of the heads to make a trial run, maintaining the head constant and adjusting the fuel supply to maintain the speed. The following blanks show two convenient forms, the first of which is for recording data, the second for recording results. 401. Computations and Report. — These are comparatively sim- ple and need little comment. The mechanical efficiency in the case of the Rider engine is the ratio between the pump horse power and the net indicated horse power. Thermal efficiency may be computed on the basis of indicated work or of pump work. Im the latter case it is the ratio of the heat equivalent of the pump work done in a given time, divided by the total heat above room temperature in the fuel supplied in the same time. On the other basis, the numerator of the ratio is the heat equivalent of the indicated work. The former efficiency, that is, that based on the pump work, is of course the real com- mercial efficiency. For the definition of duty see Art. 363, p. 775. Since in these engines the weight of the working fluid remains HOT-AIR ENGINES 935 constant for the cycle, the temperatures around the cycle may be computed from Pv = RT = 53.2 T, provided the temperature at one point is known. The heat balance should show the following items: B.t.u. Per cent. (1) Total heat supplied in fuel above room temperature.. ....... 100 (2) The heat equivalent of the pump work............. (3) The heat equivalent of the work lost in mechanical fICHION,.7 3.29 4 Kecut eee aw ke eer eae es MEG ee cone (4) The heat carried away by the jacket water.......... (5) The heat lost in waste gases...............00 00 eee (6) The heat lost in radiation, and otherwise unaccounted For the determination of Item (1) see Chapter XIII. Item (5) in the above heat balance is computed exactly like the similar loss in the case of boilers or gas engines. See Chapters XIII and XXI. The report should include a graphical representation of the results by means of the following curves: Abscissas Ordinates. (a) Total head pumped against Capacity in gallons or pounds per hour. (0) as “ Percentage of slip. (c) sf “ Thermal efficiency. (d) = a Duty per 1,000,000 B.t.u. 936 EXPERIMENTAL ENGINEERING "sqT *ssoIy) “sqT ‘aIvy, Second Tank. “sq “ssOIn) Water. First Tank. “sqyy ‘AIR, Joy au, "Inoy sod yoag WIND Fuel. “SuIpvay Jayour-seg ‘UIP Jod SUOTINJOAIY Speed. a oe 8) camel “SULATOT Jacket. “Buliaquq LOG OF TEST. Temperatures. “OOY “u0ystg JoJsuvIL, .Hot-air Pumping Engine. M.E. P. “uoystg BULyIOM "Taye jo soysuy ‘ganssailg sey DAU U NE sok so ek eae se een oane Pressures. Wa ‘pray worjons “sqyT ‘asney amssarg DEPARTMENT OF EXPERIMENTAL ENGINEERING, SIBLEY COLLEGE, CORNELL UNIVERSITY. Test Of ccc cuakes pave k eo Renee EEL HER ESS “UIT, Tec Saucank hs So GAAS REO ERE DS OB aces [ki seve wet alhase ected to Seal he ora all ee ae eae sr sorbed steed eadl pvt ogee fb dha disubamebdes| duh & alla Ale vail) eRe sot ws ans ANEDS: case ltrs aera 4 [seh stots HOT-AIR DEPARTMENT OF EXPERIME ENGINES 937 NTAL ENGINEERING, SIBLEY COLLEGE, CORNELL UNIVERSITY. Hot-air Pumping Engine. Observers AVERAGE DATA AND GENERAL RESULTS. Diameter of Working Piston ‘ ce “ Area Stroke “ at t Diameter of Transfer Piston Area “ “ce Str ‘ok e “cc “ “ee Diameter of Pump Plunger Diameter of Pump Plunger-Rod Stroke of Pump Scale of Indicator Springs Thermal units per cu. ft. of fuel at standard ‘temperature and pressure (32°F. and 14.7 Abs.) = Run No. IL. | III. Iv. Remarks. Suction head, feet Head pumped against, feet Total head, feet Water delivered, lbs. per hr., actual Ft.-lbs. work per hour Revolutions per min. Plunger displacement per hr., Ibs Slip, per cent Indicated H.P., working cylinder ““ “cc “ce transfer ce “ce Developed H.P...............000000 0s Mechanical efficiency Range of temp. of water-jacket Cu. ft. of fuel per hr., standard press. and LEMP ak adhd cea Rend Ge Pee ek sp eee Rees | Dore loaa spears eeeesee wags Heat supplied per hour (=100%).. B.t.u.}....J....{..--feeee[ecee fee eee eee eee ee Thermal equiv. ind. work.......... Betis. cual ceeds | Seestens oy ahaletelye ef Soyenaes i Ke RES Sa areata PEM CENCE ctl Neda alianisalmnnel maja eb tage eaee Heat absorbed by jacket-water..... BCS ees. lediae. |e ayegallemace hs Sebeel Maeauap hive df aero as sf o % JAPON CONC. | ays'l ecu 6 sacha cecal tv aetna ba beeaseese a ethane Radiation and loss................ Bittle cts s inal seu lepee lec thaammrt nied caren Heat supplied per D.H.P. per min...... Thermal efficiency Duty, actual (ft.-lbs. per million B.t.u.).. per centsleg saleses|siealecesbeass CHAPTER XXIII. AIR-COMPRESSING MACHINERY. 402. Types of Air-Compressing Machinery. — Air-compression or air-moving machinery may be divided into the following distinct classes: (a) piston air compressors, (0) rotary or positive blowers, (c) centrifugal or volume blowers or fans, (d) turbine compressors, (e) injector blowers, and (f) hydraulic compressors. The following paragraphs will give the main features of each one of these types. It will be found that, in general, each class is best adapted to some particular class of service. Thus, for high-pressure work the piston compressor is about the only one used; for low-pressure work, generally simply the work of moving large volumes of air, the centrifugal fan is mostly employed. As far as motive power is concerned, any of the mechanisms, with the exception of classes (e) and (f), may be belt-driven or operated by any of the prime movers, as steam engines, steam turbines, electric motors, gas engines, etc. In other chapters of this book will be found full information concerning the methods of determining the power input in case any of the sources of power mentioned are used, so that this chapter will confine itself principally to the investigation of the operation of the compressing element of the machines. 403. Piston Compressors. — The construction of the compressor cylinders is very similar to that of a steam-engine cylinder. The cylinder may be single- or double-acting. Each working end is fitted with inlet (suction) valves and outlet (discharge) valves. There is a great number of different designs of cylinders, valves, and valve gears, and the student is referred to special works on the subject.* The valves may be located in the sides of the cyl- inder, or in the heads; in some cases the suction valves are located in the piston itself. The valves may be slide, piston, or poppet * See A. Von Ihering, Die Geblise; Hiscox, Compressed Air and Its Applications; Peel, Compressed-air Plant. 938 AIR-COMPRESSING MACHINERY 939 valves. In every case the aim in view is to cut down clearance as much as possible, in order to eliminate as far as possible re- expansion of the compressed air caught in the clearance spaces. (See Art. 413.) There are several ways of classifying piston compressors. On the basis of the cooling system employed, we distinguish (a) dry compression, (b) compression with water injection, and (c) “‘ wet” compression. Under (a) no cooling whatever may be employed. This method of operation is sometimes used where the final pressures attained are not high and where the resulting temperatures of compression are an advantage rather than a loss. This is the case in blowing engines for blast-furnace work. In general, however, compression under (a) is done with water cooling in cylinder jackets and in the intercooler, if one is used. The advantage of this method lies in the fact that the compressed air is nearly dry, which is an essential for some uses. The disadvantage is that, on account of the inefficiency of the cooling action, especially in the cylinder jackets, the work of compression is not as efficiently done as in other cases, assuming, of course, that the standard of efficiency is isothermal compression. In the operation under method (6), a certain quantity of water in a fine spray is injected into the air for the purpose of cooling. The result is a more effective cool- ing than is possible under (a), but the mois- ture in the air is seriously increased, and some objection is also made on the score of in- creased wear of the sliding parts of the cyl- inder. In“ wet ” compression, method (c), the working piston does not act upon the air direct, but moves a water column by which the air is compressed. To explain the prin- ciple, in Fig. 560,* F is the working piston, A the suction valve, and G the discharge Fic. 560.—“Wer” Arr valve. As the piston moves to the right, ;OMPRESEOR: the water column follows it, and air is drawn into the cylinder, together with the water seal that covers A, and is maintained by * Von Ihering, Die Geblise, p. 168. 940 EXPERIMENTAL ENGINEERING the arrangement B,C, D. On the back stroke, A closes, the water column compresses the air into the vertical chamber at the end of the cylinder until G opens, after which the piston forces all of the air, together with a small quantity of water, into the dis- charge space. K is the high-pressure pipe, while H is a float arrangement to allow the water pumped over to drain out. The advantages of this system— that is, lower temperature of compressed air, higher volumetric efficiency —are fully balanced by slower speed, greater water and power consumption, etc. The efficiency of cooling has great influence upon the power input for a given amount of compressor work to be done. This fact has led to the subdivision of the total compressor work among several cylinders where the air is to be highly compressed. De- pending upon the number of cylinders used for the work, we then distinguish single-stage, two-stage, or multistage compressors. A common pressure to which air is compressed for a variety of uses is about 125 pounds. In this case, two- or perhaps three-stage com- pression should be employed. The former would be more common, the air being compressed up to about 40 pounds in the first stage and to 125 pounds in the last. Unless the pressures are very high, as in liquid-air work, it is not common to exceed two stages be- cause the gains due to efficient cooling are, beyond the second or third stage, soon overbalanced by mechanical losses. ‘The several cylinders may be arranged one behind the other, in which case we have what is known as a tandem arrangement, or they may be placed side by side with the intercooler between them, in which case we have the duplex arrangement. A two-stage compressor of the former design, steam-driven, is shown in Fig. 561, where D is the steam cylinder, A the low-pressure compression cylinder, B the intercooler, and C the high-pressure compressor cylinder. When the engine end is also compounded, a favorite arrangement is to cross-compound the engine and to place an air cylinder behind each steam cylinder in tandem. This makes a very good design as far as stress conditions in frames and crank shafts are concerned.* * The question of the best arrangement of cylinders in motor-, belt-, or steam- driven air compressors is discussed by E. W. Koester in Zeitschrift des Vereins deutscher Ingenieure, Tan. 23, 1904. AIR-COMPRESSING MACHINERY 941 Discharge Fic. 561.— Two-stace TanpEmM Arr COMPRESSOR, A special form of the piston compressor is the air pump used in condenser work. The conditions of operation are somewhat dif- ferent, in so far as in the ordinary compressor the suction pressure is constant, while the discharge pressure may vary; in the air pump the suction (condenser) pressure varies while the pump delivers 942 EXPERIMENTAL ENGINEERING against a constant pressure,— that of the atmosphere. Otherwise, the conditions of operation are similar. 404. Rotary or Positive Blowers. — These generally consist of two blades, pistons, or displacers, A and B, which revolve in oppo- site directions, as indicated in Fig. 562. They are actuated by gear- ing or other devices outside of the case C. Each displacer on the one side maintains continuous contact with the inner surface of the case and on the other side with the mating displacer. As a con- sequence, a certain volume of air is picked up on the suction side Fic. 562. —RoTARY OR PosITIVE BLOWER. (the volume represented by the space £ in Fig. 562) and transferred to the discharge side F. The pressure that can be maintained at F depends, of course, upon the amount of compressed air used and upon the speed of rotation of the displacers. If the blower delivers into a closed system, the pressure will build up until the leakage back past the contact surfaces of the displacers prevents further increase. Hence a close fit at the contact surfaces is essential for the attainment of highest pressure. The gain thus made, may, however, be counteracted by an increased friction loss, decreasing the total efficiency of operation. These machines are, therefore, not adapted to high-pressure work, and 10 pounds per square inch is about the outside limit. For lower pressures than this, but higher than those that can be efficiently handled by the centrifugal blower, they are quite satisfactory on account of their large volume capacity, in spite of the fact that the volumetric efficiency may not be over 75 per cent and is frequently lower than that. AIR-COMPRESSING MACHINERY 943 405. Centrifugal or Volume Blowers. — Two fundamental types of these blowers are recognized: (a) the disk or propeller fan, in which the air moves through the fan practically parallel to the shaft and perpendicular to the plane of rotation of the wheel; and (b) the machine generally known simply as the blower or fan, in which the air enters the fan wheel at right angles near the center, is deflected through a right angle as it goes through the wheel and leaves the periphery of the wheel at high speed owing to the centrifugal force imparted. Disk fans are constructed either with straight or curved blades, as shown in Fig. 563. The action of these fans is the reverse of Fic. 563.— Types oF DIsK oR PROPELLER Fan. that of a windmill. In the latter, the wind moving with a certain velocity imparts to the wheel a certain rotative speed which is utilized to do certain work. In the disk fan, a certain amount of work is put in at thevshaft, the wheel attains a certain rotative speed, which produces a certain velocity of translation in the air in which it moves. These machines, therefore, produce a pressure difference which must be proportional to the velocity of the moving air. They are, however, not adapted to give large pressure dif- ference, and are consequently mostly used for ventilating purposes, where the pressure or depression produced need not exceed .2 to .5 inches of water. As compared with the ordinary centrifugal blower, their power consumption for a given quantity of air moved under given conditions is less. There are a number of different types of fans or blowers. They may be divided into two classes, —those with and those without 944 EXPERIMENTAL ENGINEERING diffusers. Under each class there are then two subclasses, based upon the blade form, whether straight or curved. A fan is said to be without a diffuser if the fan casing is concentric with the wheel all around, except, of course, at the point of outlet. When, on the other hand, the casing forms a gradually increasing scroll, so that the space between periphery of wheel and of casing gradually increases toward the outlet, the fan is said to have a diffuser. The purpose of this construction is to gradually decrease the velocity of the air leaving the fan wheel itself and to convert some of the velocity head into pressure head. Hence the use of this construc- tion in all pressure blowers. The advantage of the curved blade Fic. 564.— Fan wita Dirruser, Fic. 565.— Fan witHout DirFuser, STRAIGHT BLADES. CurvED BLaDEs. ~ lies mainly in the avoidance of shock as the air enters the wheel. This not only increases the efficiency but makes the operation smoother and less noisy. Figs. 564 to 566 show several exam- ples of the constructions mentioned above. Any fan may serve to create a pressure at the outlet, or to produce a depression (pressure below atmosphere) at the inlet. In the former case it is called a blowing fan or blower, in the latter case an exhaust fan or exhauster. With reference to the pressures or depressions produced, cen- trifugal fans are sometimes classified as low-pressure or volume fans and as high-pressure fans. The distinction is, however, not clearly drawn, since the pressure may, in most cases, be consider- ably changed by changing the speed of rotation. In actual service the pressures or depressions used range about as follows: .5 inches AIR-COMPRESSING MACHINERY 945 or less for the ventilation of schools, theaters, factories, etc.; 3-6 inches for mine fans; 4-8 inches for forge fans; and 8-15 inches for fans used for melting-furnaces, like cupolas, etc. La ypH a Yee “= A oe ae BLN ae 3 fo 1G Py \\) Gg FP} SPS | LA 7 ues Fic. 566.— Fan witHd DIFFUSER, CURVED BLADES. 406. Turbine Compressors.— This type of compressor has been developed in the last few years. The principle of its operation is practically the same as that of the multistage turbine pump (see Chap. XXV). There is, however, this important difference: In the water pump there is no change in the density of the medium, and each wheel causes the same absolute pressure increase in the water. In the case of the turbine compressor, on the other hand, the density of the medium changes from stage to stage, and, as- suming that the temperature does not increase, each wheel only causes the same relative pressure increase. Thus, if each wheel causes a relative pressure increase of 10 per cent, it will take 10 stages to reach an absolute pressure of 2.6 atmospheres, and 10 more stages to reach a final pressure of 7 atmospheres absolute. In practice, on account of temperature increase and other losses, from 25 to 30 wheels or stages are required to attain the latter pressure. Where the final pressures are quite high, the wheels are usually made in groups of different diameters, the largest wheels forming the first three or four stages. The peripheral speed of such wheels may be up to 460 feet per second, while the wheels in the final stages have a rim speed of about 330 feet per second. The rotative speeds for high-pressure work may be from 3000 to 946 EXPERIMENTAL ENGINEERING 4ocor.p.m. For low degrees of compression, all the wheels are made of the same diameter; thus the Rateau turbine blower shown in Fig. 567 consists of four stages and compresses the air to about ro pounds per square inch above the atmosphere when making 1875 r.p.m. A favorite method of driving such a compressor is by direct connection to a steam turbine, as illustrated in Fig, 567. = T OT Fic. 567.—RATEAU TURBINE COMPRESSOR. The turbine blower has an advantage over the piston compressor in so far as it is possible to cool more thoroughly, since there are usually many stages and the temperature increase in each stage is small. On the other hand, the turbine compressor, analogous to the steam turbine, shows greater friction losses than the piston compressor. These may be so great in a compressor not cooled as to cause final temperatures in the compressed air even above those due to adiabatic compression. Further, a comparison of turbine and piston compressors should also take into account the characteristics of the machines used to drive them, which in the former case is usually a steam turbine, in the latter case a recipro- cating engine. As a final result it may be said that, at the present state of the development of the turbine compressor, the piston compressor with good compound engines, running condensing, has slightly the better of the argument on the score of efficiency.* 407. Injector Blowers. — The principle of action of these devices is exactly the same as that of the injector used for boiler feeding. * There is an interesting report upon the relative efficiency of these two com- pressor types in the Zeitschrift d. V. d. I. for Oct. 30, 1909. AIR-COMPRESSING MACHINERY 947 The working medium — steam, compressed air, or water — must be under considerable pressure. This pressure is converted into veloc- ity by passing the medium through a nozzle. The high-velocity jet carries along with it the air immediately surrounding it, and, if the space is confined, will create a vacuum in the latter. If this space is then connected by a suction pipe to some other space, the air will be removed from the latter, and the apparatus acts as an exhauster. If, on the other hand, the space around the nozzle or nozzles is unconfined, but the outlet tube of the device is con- nected to some restricted space, the air pressure in the latter will be increased and the apparatus acts as a blower. Among the advantages possessed by these devices may be named the following: Elimination of prime mover, small cost of repair, small space required for installation, easy regulation of ian ay a c Ra Yj D DSSS YX = Fic. 568.— Injector BLOWER. quantity of air handled, etc. Injector blowers are made in capaci- ties ranging from 0.2 to 600 cu. ft. of air per minute, and, according to Ihering, require a steam pressure of from 75-90 lbs., or a water pressure of from 45-75 lbs., or an air pressure of from 45-60 lbs. per square inch. The construction of an injector blower, used for the produc- tion of forced draft under boilers, is shown in Fig. 568. Fig. 364, p. 516, shows one construction used for exhausters. 408. Hydraulic Compressors.*—The method of operation of these compressors is best illustrated by means of Fig. 569. The installa- tion consists first of a receiving bay or chamber in which is placed the suction head. The latter may be constructed in several ways. * See Peele, ‘“‘ Compressed Air Plant,” Chap. XV, for a discussion of the construc- tion and efficiency of operation of several installations of this type of compressor in this country. 948 EXPERIMENTAL ENGINEERING In this case, it consists of a ring pipe a, to the inner circumference of which are fastened a large number of horizontal tubes c. As the water enters the vertical pipe leading into the shaft, suction is created at the opening of the tubes ¢ and the air will be drawn into a and c through 6. This air becomes mixed with the falling water Suction Head = SON AS SANDS TA a 9 IN AAA NCANTANWAN SOON ONION IOS Fic. 569.— HypravuLic AIR COMPRESSOR. in small bubbles and is compressed in the descent, according to the height of the fall. The separation tank is placed at the bottom of the shaft. In it the direction of the falling water is, by means of baffle plates, changed to the horizontal, and the air separates from the now comparatively quiet mass of water. The latter finds its way out through the open bottom of the separator tank and rises in the shaft to the level of the tail race. The compressed air gathers AIR-COMPRESSING MACHINERY 949 in the upper part of the tank and is taken off as desired by means of the air-pipe. One great advantage of this type of compressor is found in the elimination of the prime mover. The compression pressure at- tained depends directly upon the distance from the disengagement surface in the separator tank to the level of the tail race, and is, therefore, independent of the head of water from the receiving bay. The air is compressed isothermally, since each air bubble is surrounded by the water; and, in spite of the fact that at some parts of the compressing operation the air is probably saturated with moisture, it is found that compressed air delivered by these compressors is comparatively dry, which is probably due to the fact that at the low disengagement temperature the absolute moisture content cannot be high. These installations have proved very efficient, over go per cent having been shown in case of high heads. 409. Physical Characteristics of Air.—It has already been pointed out (Chap. XI, under Laws of Gases) that air may be considered as a permanent gas following the law a constant = R. (1) T In this equation, substitute for standard conditions, P = 144 X 14.7 = 2116.8 lbs. per square foot, T = 460 + 32 = 492°F., and specific volume v = > where .0807 is the weight of a cubic .0807 foot of dry air under standard conditions. Then Pu _ __2116.8 pp _ * T 492 X .0807 R= §3:35- (2) * The value of R changes slowly both with pressure and temperature. Another expression for R is A4-R=Cp— Cv = o(Z =- :) =Cy(y—1). The values of v and C, change with temperature. See Chap. XXI under Specific Heats. The change with pressure is less important, although appreciable at very high pressures. Ihering gives the following figures, computed from an equation given by Antoine in Comptes Rendues, 1890: p=ti1atm. 4oatm. 6oatm. 80atm. Icoatm. 200 atm. R= 53.30 53-30 54.25 55-30 56.40 62.30 These notes refer, of course, only to the case of dry air. 950 EXPERIMENTAL ENGINEERING From this = a fe {t. per lb., (3) and weight per cubic foot of dry air I eB P 6 = - = ——_ = .01874 = lbs. (4) q Soeur T Eq. (4) enables us to compute the weight per cubic foot of dry air for any condition of P and T. Example. — Pressure = 80 lbs. per square inch by gauge, barometer = 28.5 inches Hg, temperature = 120° F. P= (8 + oa) 144 = 13,577 lbs. per square foot; T = 460+ 120 = 580°, 03 Weight per cubic foot = = ee EL -438 Ibs. 53-35 X 580 Under nearly all conditions of practical operation, however, air is not dry but has associated with it a certain amount of moisture (water vapor, humidity). This fact not only changes the weight per cubic foot of the mixture for given P and T conditions from the value computed for dry air, by Eq. (4), but it also affects the relations involved in the compression and expansion of air. For any given values of P and 7,a given space can contain, as a maximum, a certain weight of water vapor. When the maximum weight is present, the vapor is said to be saturated. In actual practice, however, it is found that this 100 per cent degree of saturation is rarely ever attained, but that the weight of water vapor is less than the maximum. The vapor is then said to be only partly saturated (it is, as a matter of fact, superheated), and the degree of saturation is expressed by the ratio of the weight of water vapor actually contained in a given space to the maximum weight that the space can contain under the P and T conditions existing.* * Tt is common usage to say that the air in any given space has a certain capacity for water vapor. Asa matter of fact, the presence of air in any given space has nothing to do with the amount of water vapor the space contains; that is, the weight of moisture in the space is controlled only by the pressure and temperature conditions existing in the space. It is more correct to say, therefore, that the space is either completely or partly saturated. In the first case, it contains as much water vapor as can exist in the saturated state for the existing temperature. In the latter case, the weight of water vapor present is less than this, and it is consequently superheated, since it is at a higher temperature than that of saturation for the pressure existing. AIR-COMPRESSING MACHINERY g5t Humidity may be expressed in two ways, — absolute and relative humidity. Absolute humidity is the weight of water vapor that any given space (one cubic foot usually) actually contains. If the vapor is saturated, the absolute humidity may be found from the Steam Table. Thus in Table 3, I, Appendix, if the temperature of the air is 75° F., the density of the water vapor is seen to be .001346 Ibs. per cubic foot; that is, the absolute humidity for 100 per cent saturation is .co1346. Relative humidity is the ratio between the actual weight of water vapor that a given space contains under given conditions and the maximum weight that the same space may contain under the same conditions. Thus, if the weight actually present at a temperature of 75° is only .co0587 lbs. per cubic foot (absolute humidity = .000587), the relative humidity 2 .000587 = 436 = 43.6 nt. oe 436 = 43.6 per cen 410. Determination of Humidity. — Absolute humidity may be found by drawing a definite volume of air through tubes containing chloride of calcium or sulphuric acid. The increase in weight of the absorbent determines the actual weight of water vapor in the quantity of air used. The method, while accurate, is not of easy application in every-day practice and little used. It is easier to determine relative humidity, for which there are several methods. The general method is based upon the assump- tion that the vapor pressures of water at any one temperature are directly proportional to the absolute weights of water vapor present in a given space. This assumption is very nearly true. If we let w, = the maximum possible weight of water that the space can contain (that is, at roo per cent saturation), at a given temperature, w= the weight actually contained, », = the vapor pressure for Ioo per cent saturation, and p the actual vapor pressure, then cae (5) p and the relative humidity = 100*- per cent. p, may be obtained from steam tables as soon as temperature is known, but # must be found by experiment. One method of doing 952 EXPERIMENTAL ENGINEERING this is to find the dew point by cooling the air down to saturation. A very simple instrument for this purpose is illustrated by Gram- berg,* Fig. 570. A small vessel A, containing ether, has fastened 0 | i ry i Fic. 570.— Dew Point APPARATUS. to it a nickel mirror B. By means of an aspir- ator bulb connected at C, air is drawn through the apparatus, entering at D. The vaporization of the ether causes cooling, which chills the mirror and the air surrounding it. At the instant that the air in contact with the mirror reaches 100 per cent saturation, fog will appear on the mirror, and the temperature ¢ of the ether is noted. For this temperature ¢ the maximum vapor pressure may be obtained from steam tables, which de- termines the factor p in the above equation. Thus, suppose that the dew point is found to . be 55°, with the air temperature at 75°. From the steam table, p, = .4288 Ibs. per square inch, and p (= #, for 55°) = .2170 lbs. per square inch. Fic. 571.—Psycurom- 214 ETER (WET AND Then relative humidity = ao 50 = 50 per Drv Burs THER 8 MOMETER). cent. A second method of determining relative humidity, that by wei and dry bulb thermometer, is radically different. The apparatus is called a psychrometer and is more used than the dew-point ap- paratus. It consists essentially of two thermometers fastened to a frame (see Fig. 571), which represents the swing type used by * Gramberg, Heizung & Liiftung von Gebiuden. AIR-COMPRESSING MACHINERY 953 the U. S. Weather Bureau. ‘the buib of one of the thermometers is surrounded by a piece of thin muslin, which, during the use of the instrument, is kept thoroughly wetted with water. The bulb of the other thermometer is left free. If the water vapor in the air is saturated, the two thermometers will continue to indicate the same temperature, which is that of the surrounding air. But if the relative humidity is less than 100 per cent, vaporization of water takes place from around the wet-bulb. This action is neces- sarily combined with the rendering latent of a certain amount of heat, which causes the wet-bulb temperature to sink. The lower this temperature, the greater the absorption of heat from the surrounding bodies, and at some point there must be established an equilibrium between the heat which the wet bulb is losing and that which it is gaining by conduction. This equilibrium tempera- ture is called the wet-bulb temperature for the conditions existing, and must not be confused with the dew point for the same conditions. From the difference between the dry-bulb temperature ¢ and the wet-bulb temperature ?’, it is possible to compute directly the rela- tive humidity for the conditions existing from the equation / € = py — .000367 B(t — ?’) (: + oe (6) given in the Psychrometric Tables published by the U. S. Depart- ment of Agriculture, 1900. Here e = relative humidity; pv = the saturation pressure at the temperature /’ (taken from a steam table); B = barometer pressure; t = air temperature = temperature of dry bulb; t’ = wet-bulb temperature; p, and B are expressed in inches of mercury. Example. —Let t= 75° F., t/ = 55°, B= 30" Hg. From the Steam Table, Appendix, for 55°, pe’ = .4357; then 23 € = .4357 — .000367 X 30 X 20(1 + i.) = .213 = 21.3 per cent. At a temperature of 75° F., the weight per cubic foot of saturated aqueous vapor is .00134 lbs., hence the absolute humidity under the conditions stated is .00134 X .213 = .00028 lbs. 954 EXPERIMENTAL ENGINEERING In practice, instead of making the above computation, humidity tables are used. There are a number of these, computed by dif- ferent authorities, none of which exactly agree, although the difference is negligible for engineering work. Table 6, in the Ap- pendix, is taken from the above-mentioned Psychrometric Tables of the Department of Agriculture. It is extensive enough for ordi- nary work. The relative humidity percentages even in this table do not exactly agree with results obtained by the formula above. Thus for 75 degrees and a depression of 20 degrees, the table gives 24 per cent, while the formula gives 21.3 per cent. Some of this difference may be due to barometric corrections which were not applied in the computation above. In connection with the formula’ and the table, it should be stated that the results are strictly appli- cable only to readings obtained with the same form of psychrometer, that is, the swing type. To use this instrument, thoroughly wet the muslin around the wet bulb. Then by means of the handle at the top, which can be extended at right angles, whirl the frame with the thermometers rapidly for 15 or 20 seconds. Stop and quickly read the wet bulb. Repeat until at least two consecutive readings agree very nearly. Fig. 572 gives a graphical representation of a humidity table, constructed for 30-inch barometer, by means of which quick deter- minations, intermediate between those of the table in the Appendix, may be made. As an example of its use, if the air temperature = 80° (point A) and the wet-bulb temperature = 60° (point B), the relative humidity will be 29 per cent, while the absolute humidity, the weight of water vapor per cubic foot, is a .00045 pounds 10,000 (point D). On the consideration that this weight represents the maximum, that is, 100 per cent saturation (point C), we may also locate the dew point F, at slightly over 42 degrees. 411. The Theoretical Work of Compressing Air.* — The formule developed in this article apply only to the theoretical work of compressing air and enable the student to compute theoretical horse power necessary. No account is here taken of the effect of clearance, nor is the effect of the heating of the intake air upon the * The text of this article is largely adapted from Ihering, ‘‘ Die Geblise.” Grains per Cu. Ft. 1¢ Dry Bulb Temperatures (Degree F) Fic. 572. 80 % HUMIDITIY D YCHRO CCH ‘ 20% ATR-COMPRESSING MACHINERY 955 volumetric efficiency considered. In other words, it is assumed that there is no clearance and that the volumetric efficiency is Ioo per cent. The changes produced in the results obtained when both of these factors are considered are outlined in Art. 413. It is hardly necessary to add that friction losses in the machine are also neglected. The work of compression consists of three parts: W1, the work of charging the cylinder; W2, the work of raising the pressure of the air from some pressure ~; and volume V; to some pressure pz» and volume V2; and Ws, the work of forcing the compressed air out of the cylinder. W, is done on the side of the piston opposite to that on which W, and W3 are performed in the same cycle, hence the total work of compression W =W.+ W3 — Wi. Let P; = absolute pressure during suction stroke, pounds per square foot. P, = absolute pressure during discharge stroke, pounds per square foot. Vi = volume of one pound of air at pressure P,, end of suction stroke, in cubic feet. V2 = volume of one pound of air at pressure P,, end of com- pression, in cubic feet. T, = absolute temperature at end of suction stroke. T, = absolute temperature at end of compression. ‘SS = stroke of piston, in feet. S, = stroke during which air is discharged, in feet. F = area of piston, in square feet. , r= UE ratio of compression. 2 A. Compression of Dry Air.— (a) Isothermal compression. Work per pound of air. Wi= FPS = PiVi ft.-lbs. (7) W3 = FPS, = P, Vo ft.-lbs. (8) But PV, = P, Vo, hence W, = Ws3. 956 EXPERIMENTAL ENGINEERING From Art. 177, p. 33°, W,= W= P, Vi log. Vs = Py Vi low! (9) V2 P, P, = RT, log. ? = RT, log, r ft.-lbs. (ga) 1 ?) The term “ free air” refers to the volume of air under suction conditions of pressure and temperature. To compute the work W; per cubic foot of free air, divide Eq. (9) by the specific volume of air for P; and 7, that is, by Vi. Then Py P W, = P, log. P. (10) To find the work Wy; done per cubic foot of compressed air, we have Wu = P.Vi log! = PyVe log. 1 1 Since Vz = volume of compressed air, it follows that P Wr = P. : i 2 log Re (11) (6) Adiabatic compression. Work per pound of air. In this case: W, = P, Vi ft.-lbs. (12) yl Ws = PiVa = PAViF = Pav (Z) "tbs. a 1 i From Art. 177, p. 331, the work of compression is oe a1 2.00 -(2)7 | 22] ey" te eu, pe | p—aiee EP The total work, then, is = y-1 ae aw. (2) -]eanlG) ee ie P. = PV a (ey = ile = 7W, ft.-lbs. (15) AIR-COMPRESSING MACHINERY 957 Work W; done per cubic foot of free air, y-1 W, = P,— (2) ne |e (16) St 1 Work W7; done per cubic foot of compressed air at temperature To, 1 Fils Ae al = | . Wi = V, le 1 | ft.-lbs. 1 e p(s) : (2) | ft-lbs. (17) The compressed air may not remain at the temperature 7», but may be cooled back to some temperature J’. The volume will then change from V2 to some value V,’, so that t iw i oe from which JV,’ = Vea (18) Work Wizz per cubic foot of compressed air cooled back to some temperature T,', then, is yol yal ~BYi_2 |(By7 | jae Ge = Ls ea: V," y—IL\Pi “ee V2 y-1I 1 : Ty 1 _p 2 Pi) _ (BY |Tae. p(B B) | gotta. (<9) For the particular case that the compressed air is cooled back to 7), substitute 7,’ = Ty in the second form of Eq. (19) above. The work Wry done per cubic foot of compressed air cooled back to T, will then be found to be y-1 Wry = P; — (2) ies | ft.-lbs. (20) y¥—IL\Pi Comparing this with Eq. (16), it will be seen that Wr _P aes vo or Wiy=W;, P, ft.-lbs. (21) The temperature rise during compression may be found from yal P. Y T, = T1 (2) ? (2 2) 958 EXPERIMENTAL ENGINEERING which is derived from a combination of the equations an = = and P,Vi" = P2V2". The examples at the end of Art. 412 will show that more work is required, for the same amount of free air compressed, when the compression line follows the adiabatic than when it follows the isothermal. This becomes apparent also when we consider the compressor-indicator diagram. In Fig. 573, BC is the isothermal and BC’ the adiabatic compression line. The work of compression is in the first instance represented by the area ABCD, in the second by the area ABC’D. Since in most applications ant D ccc v Fic. 573. of the use of compressed air the latter cools down practically to the temperature at B before use, it follows that the area BCC’ is lost work. The aim in actual practice should, therefore, be to compress as nearly along an isothermal as possible; hence the use of cooling during compression. The exponent m, in the equation pv” = const., is equal to 1.0 for the line BC, and to 1.408 for the line BC’. In any given case the value of » for the actual compression line BC’’ will be between these values. The more perfect the cooling, the nearer will the ideal value m = 1.0 be approached. B. Compression of Moist Air.— The presence of moisture in air modifies the work formula above developed. The differences introduced are, however, so small in the average case that they may be neglected even for high-pressure work. The example at the end of Art. 412 shows this clearly. For the purpose, however, AIR-COMPRESSING MACHINERY 959 of giving the method of computation involved in the case, the following formulas were adapted. Let P = absolute pressure per square foot of any given volume of moist air, P, the absolute partial pressure per square foot due to the dry air contained in the volume, and P.,, the absolute partial pressure due to the water vapor. Then PuP at P. (23) P., must in every case be determined by one of the methods given in Art. 410, after which P, becomes known. The weight of a cubic foot of saturated moist air may now be computed as follows: Let 6 = weight of a cubic foot of dry air, in pounds at a tem- perature T; 6, = weight of a cubic foot of moist air, in pounds at a tem- perature T; and weight of a cubic foot of the water vapor contained in the saturated moist air. This is found from steam tables. From Art. 409, Eq. (4), be Py = 01874 (24) Hence Py 65 = 6+ & = .01874 Tp + 6, = or87q- > + 6 lbs. per cu. ft. (25) If the air is not saturated, but the relative humidity = e, then P—-eP,, T + eb. (26) 6, = .01874 Example. — Absolute pressure P = 14.7 Ibs. per square inch = 2117 lbs. per square foot; ¢ = 100° F., so that T = 460 + 100 = 560°. Find 4, for the fully saturated condition, and for relative humidity = so per cent. For 100° F., 52 = .002851 lbs. per cubic foot, while for saturation P, = 144 X .946 = 136.2 Ibs. per square foot, both figures derived from the steam table. 960 EXPERIMENTAL ENGINEERING For the saturated condition, then, 2117 — 136.2 560 For the relative humidity of 50 per cent, e = .5, 6, = .01874 + .002851 = .0692 Ibs. per cu. ft. 2117 — .5 X 136.2 +.5X .002851 = .o699 lbs. per cu. ft. 560 61 = .01874 The weight of absolutely dry air would have been SETT .0709 lbs. per cu. ft. 6, = .01874 sn The work of compression of moist air is composed of two parts: (a) the work required to compress the dry air contained in a given volume of moist air, and (0) the work required to compress the water vapor contained in this volume. For the work under (a) the formulas above developed for dry air directly apply. Work under (0) may be found as follows: The water vapor before com- pression has the partial pressure P,,, properly computed for the relative humidity existing, and the temperature 7;. At the end of compression its volume is V2, and it must have the temperature T2, the same as the air. With this data we may compute the artial pressure P,,’ at the end of compression from Pp p Pp y-1 Ty _ Pe Ge (27) In this case the value of y = a2 for superheated steam in the range 7, to T» (see the article on specific heat, in Chap. XXI). From Eq. (15), the work of compressing one pound of dry air would be yl es ¥ 7.) Pos, alee’ W,= Pw: 7 (zs | ft.-lbs, (28) in which P,’ is determined by an equation of the form of Eq. (27). For superheated water vapor, the work of compressing one pound will by analogy be y-1 Savi = (e) a= / ft.-lbs. (29) AIR-COMPRESSING MACHINERY 961 If now in one pound of moist air there are G, pounds of dry air and G, pounds of water vapor (so that G; + G, = 1.0), the work of compressing one pound of the moist air will be W = GW, + GW, ft.-lbs. (30) The above method is probably not quite correct on account of heat interchanges between air and water vapor, the values of + being different. A more exact and simpler way is to compute an average value of y for the mixture of air and water vapor, but this does not separate the two amounts of work to bring out their relative importance. The error in the first method is in any case not great, and it may be used for the purpose of obtaining an idea of the relative proportion of the two amounts of work. ar, Gx) Average y = Ciel in which C,’ and C,’ are the specific heats for air, and C,” and C,” those for the superheated water vapor, while m is‘ the weight ratio of water vapor to air in one pound of moist air = a. This ratio 1 may be computed from the equation a Pw _ 53:35 Po 65, Px RB, tose Bg, (32) The theoretical work required for one pound of the moist air between total pressures P; and P, is then computed from Eq. (15), except that for the value of y for dry air the average value of y for the mixture is substituted. 412. Theoretical Compressor Horse Power. — Let the theoretical work required to compress one cubic foot of free air under given condition be in general W foot-pounds. If d = cylinder diameter in feet, J = stroke of piston in feet, 7 = revolutions per minute, and m = number of cylinder ends in operation, the volume capacity of the theoretical compressor will be 2 i = nm cu. ft. per min. 962 EXPERIMENTAL ENGINEERING The theoretical horse power, then, is -7854 @? lnmW 33,000 HP. = (33) The following examples are intended to bring out the differences in the theoretical work required in isothermal compression as compared with adiabatic, and in the compression of dry air as compared with moist. Example. — Cyl. dia. d = 5 feet; stroke ] = 4.5 feet; m = 35 r.p.m.; com- pressor is two-cylinder double-acting, so that m = 4; suction pressure = 14 Ibs. per square inch absolute; discharge pressure = 40 lbs. per square inch absolute. Case I. Isothermal Compression, Dry Air. — Brom dee) UP ee loge! =14X 144 log. = 2130 ft.-lbs. 1 Hp. — 27854 X 5) X 4.5 X 35 X 4 X 2130 _ 33,000 795+ Case II. Adiabatic Compression, Dry Air. — Assume y = 1.408. aa 408, 1.408 From Eq. (16) W = P; (2) 7 = r= sax ran 224 (8) oe ym ELye .408 L\14 = 14 X 144 X 3.45 (2.85 — 1) = 2460 ft.-lbs. HP. = 17854 X 5' X 4.5 X 35 X 4 X 2469 33,000 = 919. Assuming that the initial temperature of the air was 70° (= 530° abs.), the final temperature will be y-1 0.408 P.\ v o\1-408 T,=T,(~2 = 4° Sere 2 1(5)" = s0(E) = re and the temperature rise = 717 — 530 = 187°. Case III. Compression of Moist Air.— Assume temperature = 70° F.; relative humidity e = .5; suction pressure = 14 lbs. per square inch absolute; discharge pressure also as before. From the steam table the partial pressure for the saturated vapor at 70° F. = .3626 lbs. per square inch. For e =.5, the actual partial pressure then is Pw = .§ X .3626 = .1813 lbs. per square inch. From this Py = P — Py = 14 — .1813 = 13.818 lbs. per square inch. Hence m= 621 Pw =, = Pa 13.818 Assume for air, Cp’ = .238, Cy’ = .169; for water vapor, Cp” = .453, Cy” = .345. AIR-COMPRESSING MACHINERY 963 Then -238 + .0082 X .453 _ -2417 -169 + .0082 X .345 = .1718 mean y = = 1.406. With this value of y, the work of compressing one cubic foot of moist air is v1 406 1.406 W=P, ¥ (B)” = | aigeaaes iit (*:) 2 y-1L\Pi .406 |\14 = 14 X 144 X 3.46 (2.85°% — 1) = 2456 ft.-lbs. Hp. = 27854 X 5° X 4-5 X 35 X 4 X 2455 33,000 =o14. 413. Effect of Clearance, Volumetric Efficiency, and Slip. — The fact that there is clearance in the cylinder and that the air caught in this clearance reéxpands, does not in any way affect the work formulas for pounds or for cubic feet of air handled. Its only effect is to reduce the capacity of the compressor. In Fig. 574, let the volume in the cylinder at the end of the suction Vv Vr} p A = A Tine BE 2 ENp 7 ae - es A Vv ; Fic. 574. stroke = V,, the volume after compression = V2, and the clearance volume = V3. At the end of the instroke the clearance volume V3 is filled with air under pressure = P;. On the next outstroke the air expands, following the piston, until at the suction pressure P; the volume V, is reached. Not until this condition is attained can the cylinder draw in a fresh supply of air from the outside. Volumetric efficiency, E,, is defined as the ratio of the volume of free air actually compressed in a given time to the piston dis- 964 EXPERIMENTAL ENGINEERING placement in the same time. If multistage compression is used, piston displacement, of course, refers to the low-pressure cylinder only. Engineers use several methods of computing volumetric efficiency, but there is only one accurate way, and that is to deter- mine it experimentally by actually measuring the air taken in, or discharged, or both, as a check. The free air thus determined divided by the piston displacement is the true volumetric efficiency, Ey: The best approximate computation is the following: Let P, = the pressure of the free air outside of the cylinder (= barometer pressure); P; = pressure in the cylinder at end of suction stroke (less than P, on account of losses through the intake valves); T, = absolute temperature of free air outside of cylinder; T, the absolute temperature at the end of the suction stroke (usually higher than T, on account of heating of the incoming air by the cylinder walls); V, = piston displacement per stroke; V, = useful or effective piston displacement per stroke (see Fig. 574); G,= the weight of free air in the volume V,; and G, = the weight in the volume V,’. Then approximate, or apparent, volumetric efficiency PiVy 6 Pee Exa= G, ~ PV,~ P,V.T, I (34a) RT, Of the factors in this equation, P; may be measured from an indicator diagram, P, is found by barometer, V, is proportional to the distance Vi — V3 (Fig. 574), and V,- to the distance Vi — Vu. T, is easily found, but the value of 7, is uncertain and can only be assumed. On account of this uncertainty, the ratio 7 is 1 sometimes neglected or assumed equal to 1.0, and the equation for apparent volumetric efficiency is, then, PiV, Eva = = PyV, Il (34b) This form of the equation corrects for pressure differences, but neglects temperature effects; it is equivalent to the ratio of the AIR-COMPRESSING MACHINERY 965 JI RI distances WB’ Fig. 574. Finally, in rough computations a further approximation is made, neglecting 21, so that b f= oS, OT (34c) There is, however, no good reason for ever using form III. Form II is largely employed in estimating capacity, but none of these forms should be used in computing air delivered on tests. Even assuming that T) is known, form I is approximate, in that it neglects losses through leakage. On all tests the air taken in or discharged should be actually measured.* Where computations must be based on apparent volumetric efficiencies, the lower part of the diagram should be taken with a weak spring. Slip is defined as the difference between the piston displacement and the actual volume of free air delivered, both based on the same time unit. The percentage of slip is the cubic feet of slip in a given time divided by the piston displacement in the same time. 414. The Efficiency of Compression and the Mechanical Efficiency of the Machine. — The efficiency of compression is the ratio of the theoretical work Wy, required to compress isothermally a given volume of free air under stated conditions from a pressure P, to a pressure P2, to the work W, required to do this in an actual case. The efficiency of compression, therefore, is Wa W, * It is perfectly easy to obtain high apparent volumetric efficiencies, that is, as computed from the cards. With mechanically operated intake valves, for instance, it is possible, by opening the intake at the inner end of the stroke, allowing the air compressed in the clearance spaces to flow into the intake pipe, to obtain a vertical drop from receiver to intake pressure, as far as the indicator diagram is concerned. It must be apparent that this scheme has not in any way improved the true volumetric efficiency of the compressor. Another method, used in an attempt to decrease the effect of clearance, is to equalize the pressure on both sides of the piston near the end of the stroke by having the piston open a by-pass connecting the two ends of the cyl- inder. This method, while it helps the end of the cylinders in which the pressure is being relieved, must decrease the effective charge volume on the other side, and the gain as far as volumetric efficiency is concerned is, therefore, fictitious. i, (35) 966 EXPERIMENTAL ENGINEERING W., may be directly computed from Eq. (9) or (ga), while W, is found from actual indicator diagram. The mechanical efficiency E, of an air compressor is defined as the ratio of the air horse power to the horse-power input used to operate the compressor. If the prime mover is a steam engine, as is most often the case, the power input is the I.H.P. of the steam cylinder or cylinders, if the engine is direct-connected. If any prime mover used to run the compressor is belt-connected, some allowance for the efficiency of transmission must of course be made. This point should be made a matter of specification in every guarantee contract, as the proper allowance to be made for the efficiency of a belt drive is not at all definite, but depends upon circumstances. Ninety-five per cent at full load is a common figure. The air or compressor horse power is computed from indicator diagrams, speed, and engine constants in exactly the same way as for the indicated horse power of a steam engine. It should be noted that the mechanical efficiency of the machine as above computed not only takes into account the friction losses in the machine members, but also the fluid friction losses incident to taking in and discharging the air. If the ideal isothermal compression line is drawn in on the average Fic. 575. compressor diagram of a test, as is done in Fig. 575, some of these losses become apparent and may be estimated.* Thus, in Fig. 5755 * For a detailed mathematical discussion of the estimation of the various losses in an air compressor, the student is referred to v. Ihering, “ Die Gebliise.” AIR-COMPRESSING MACHINERY 967 Shaded area F; = Loss due to heating of air during compression; Shaded area fF, = Loss due to work required to force the air (and in some cases also cooling water) through discharge valves and ports; Shaded area F; = Loss due to resistance encountered by the incoming air in passing intake valves and ports. 415. Multistage Compression. —It has already been pointed out that one of the main reasons why the actual work of compression is greater than the theoretical isothermal work lies in the fact that the air is imperfectly cooled during compression. This is one of BD Fic. 576. the practical difficulties that cannot be overcome by any system of cylinder cooling. To minimize this loss as far as possible, especially for high-pressure work, it is common practice to divide the total work into stages and to cool the air between the stages; thus a two-stage compressor consists of a low-pressure cylinder, in which the air is compressed from atmospheric pressure P; to some pressure P2 (see Fig. 576). It is then transferred to an intermediate receiver, called an “‘ intercooler,” in which it is cooled more or less, depending 963 EXPERIMENTAL ENGINEERING upon the efficiency of the cooler. The ideal case, of course, is to cool the air back to the temperature 71, which it possessed at the beginning. The air from the intercooler next passes into the second or high-pressure cylinder, in which the pressure is raised from the intercooler pressure P, to the discharge pressure P3. Similarly, a three-stage compressor has a low, an intermediate, and a high-pressure cylinder with intercoolers between the cyl- inders. How many stages can be economically employed depends largely upon the pressure to which the air is to be raised. It is a fact that each stage will show a saving in work as far as the compression itself is concerned, but there is a point at which such saving is balanced by increased friction and leakage losses and beyond which it does not pay to increase the number of stages. Two-stage com- pression is commonly employed where the pressure to be attained exceeds 60 to 80 Ibs. per square inch; the use of three stages is not very common. Even in two-stage compression, bad valve design and inefficient intercooling may easily make the two-stage opera- tion less economical than single-stage between the same pressure limits would have been. Confining the discussion to two-stage compression, and con- sidering intercooling to initial temperature 7, the ideal case, the theoretical saving over single-stage adiabatic compression can be easily shown. In Fig. 576, BC is the isothermal and BC’ the adia- batic compression line. In single-stage compression the loss due to the absence of cooling is measured by the area CBC’. If now we compress in a low-pressure cylinder to some intercooler pressure P, along the adiabatic BE, the work done in the low-pressure cylinder will be represented by the area ABEF. The intercooler is assumed to cool at constant pressure P; to the initial temperature T,, locating the point E’. The volume represented by FE’ is then drawn into the high-pressure cylinder and compressed along the adiabatic EC” to the pressure P;, the work done in this cylinder being FE’C’D. The total work done in both cylinders is repre- sented by the area A BEE’C’’D, which is less than the work ABC’D by the area EE’C’C’, which therefore represents the saving under the conditions assumed. ATR-COMPRESSING MACHINERY 969 The work done in the two cylinders should be equal, which means that there is some theoretically best intercooler pressure P: which should be maintained. The student is referred to Peele, ‘“‘ Com- pressed Air Plant,” for the development of ‘mathematical expres- sions for the work done in each cylinder and for the best intercooler pressure. 416. The Construction of the Combined Diagram for a Two- stage Compressor and the Saving due to Cylinder Jackets and Intercooler. — In practice the discussion of the previous article is modified by the following factors: The compression in each cylinder is not adiabatic, but, owing to the use of cylinder cooling, the com- pression line lies between the adiabatic and the isothermal; the action of the intercooler may not be effective enough to cool the air to the initial temperature, or if the cooling is very efficient the temperature may be less than 7) at entrance to the high pressure; owing to losses in passing through valves and intercooler, the dia- grams for the two cylinders may overlap instead of meeting in a line like FE’, Fig. 576. The overlapping area means lost work. Finally, the clearances in the two cylinders, which are usually not s the same percentage of the stroke 0 volumes, has a certain effect 4 upon the relative position of the » cards. To construct the combined dia- gram, select average high- and low-pressure cards from the set obtained on the test, and proceed to combine these in exactly the same way as explained for steam- | ~~~7~-77 777000 Soa engine diagrams in Chap. XVI, Fic. 577. setting off the diagram for each cylinder from the zero volume line a distance proportional to the clearance for that cylinder. Fig. 577 shows the high- and low- pressure cards for a two-stage compressor, for which the following table contains the main data: Atm.Line Seesens---- ee == Zero; Press, 30 10 Atm.Line 97° EXPERIMENTAL ENGINEERING Diameter, H.P. cylinder........... 24.25” Diameter, L.P. cylinder........... 38.5" Sttok@u. 2 gNGiGadegaknecs dae 48” Piston displacement, H.P. cylinder.. 12.83 cu. ft. Piston displacement, L.P. cylinder.. 32.34 cu. ft. Rapin 63 ice apace ee eka ey 72 Clearance, H.P.cylinder........... I per cent. Clearance, L.P. cylinder........... I per cent. Clearance volume, H.P. cylinder... .128 cu. ft. Clearance volume, L.P. cylinder.... 323 cu. ft. Total volume, H.P. cylinder....... 12.958 cu. ft. Total volume, L.P. cylinder........ 32.663 cu. ft. Barometer reading, 28.6” =....... 14.0 Ibs. absolute. Intercooler pressure, 26 Ibs. =..... 40.0 Ibs. absolute. Reservoir pressure, 65 Ibs. =....... 79.0 lbs. absolute. Fig. 578 shows the two diagrams combined. To show the saving effected by the low-pressure jacket, draw from E the isothermal EC and the adiabatic EG. Since, without any cooling whatever, the compression line would have followed EG, the area EGFE will represent the saving due to the low-pressure jacket. Assume that, beginning with F, the air is discharged into the intercooler at constant pressure. The volume discharged is represented by FX. Now, if the reéxpansion lines of the two diagrams crossed the inter- cooler pressure line at the same point, and if there were no intercooling whatever, the suction line of the high-pressure card would bring us back exactly to the point F. But there is usually a difference in the volumes shown by the reéxpansion at intercooler pressure, owing to differences in clearance in the two cylinders, which dif- ference in this case is equivalent to the distance XD. Hence, still assuming that there is no intercooling, the high-pressure suction line will extend only to F’ instead of to F. Adiabatic compression in the high-pressure cylinder would then have given the line F’/. Intercooling, however, has decreased the volume at the end of high-pressure suction to the point K, and adiabatic compression from that point gives the line KL. Hence the saving due to inter- cooler action is measured by the area F’TLK'F’. From K draw also the isothermal KN. The area KLMK included between the adiabatic KL and the actual compression line, KM, measures the saving due to the high-pressure jacket. oie ‘ISH], YOSSTAAWOD-ALy ‘SUAGNIIAD AY AOI WVAOVICE AANIaWOD —‘gLS ‘ory “WJ AD ‘sUINTOA FS “es 0g 82 96 46 os 06 SL 91 1 el ot 8 9 F é 3 qd ‘ 5 ee —— pbLoury may , So P= ~s oe = = ve aouvivald jd’ ~L Po] —P~ aouriva[o * Se. re \ ae ¥, oh - u oa Nd foe “SSaIg 1a]000IaIUT SS SN So << _| WANN | Os AK SN X&yv > NSN 1 ih AIR-COMPRESSING MACHINERY yout "bs sad *sq’T ainssaay aynposqy “BSAIg MOAIISAY 7 972 EXPERIMENTAL ENGINEERING The combined diagram here given is not a good example of practice in two-stage compression. This will become apparent when we compare the actual gains made with the possible gains and actual losses. The possible saving in cooling the cylinders is measured by the area EGCE in the low-pressure, and by area KLNK in the high-pressure cylinder. Both cylinder jackets, therefore, appear to be inefficient. The intercooler, when efficient, should cool the air back to the initial temperature, that is, back to the isothermal EC. Its inefficiency is consequently apparent. The actual friction and valve losses are in this diagram indicated by the area below the atmospheric-pressure line, the area above the reservoir-pressure line, and the overlapping area of the two cards, above and below the intercooler-pressure line. It may be assumed that two of these losses, that at low-pressure suction and high- pressure discharge, are present also to a similar extent in single- stage compression; but the loss, due to the friction in low-pressure discharge valves, intercooler, and high-pressure suction valves, measured by the overlapping area KPX RK, is directly chargeable to the use of the two-stage principle and should be offset against the intercooler saving. In this case, the net result is a positive loss, owing to inefficient intercooling and bad design of intercooler and valves. 417. The Computation of Efficiencies in Multistage Compression. — The true volumetric efficiency E,, and the mechanical efficiency E,, are computed exactly as for the single-stage compressor (see Arts. 413 and 414). The apparent volumetric efficiency E,, is, of course, computed from the low-pressure card. The efficiency of com- ' pression £, is again the ratio of the theoretical (isothermal) work of compression to the actual work. In Fig. 578, the actual work is the equivalent of the sum of the areas of the two cards, that is, EFPXSE and KMTDRK. The theoretical work may either be computed from the equation given in Art. 411, or it may be de- termined from the combined diagram. The area representing the theoretical work for the low-pressure cylinder is ABCXA, the line XA being the isothermal reéxpansion line. To determine the theoretical work for the high-pressure cylinder, set off the distance CB’ equal to the distance DX, and draw the isothermals B/C’ AIR-COMPRESSING MACHINERY 9073 and D’A’. The theoretical work for the high-pressure cylinder is then represented by the area A’B’C’D’A’. The higher the efficiency of cooling, the greater, of course, will be the value of £,. With a very efficient intercooler and low tem- peratures of cooling water, it is even possible to cool to such an extent that the point K will lie to the left of the isothermal EC, in which case the efficiency of compression may approach or exceed roo per cent, provided, of course, that friction losses are reduced to the minimum. 418. Arrangements for Testing Piston Compressors. — The main items to be determined for an efficiency and economy test are: (A) the power input (steam horse power, motor horse power, etc.); (B) the air horse power; and (C) the weight or volume of air handled. A complete test should further record speed, pressure, and tem- perature of surrounding air, inlet and outlet pressures and tem- peratures, and all intermediate pressures and temperatures, if multi-stage compression is used; also the temperatures of all the water entering and leaving all of the jackets. A. The Power Input.— The most common motive power is steam; next electric energy is largely employed. For methods of determining the power delivered to the air cylinders by any of the types of prime movers ordinarily employed, see the particular chapters concerned. When the prime mover is an electric motor, hydraulic motor, or when a belt drive is used, the measurements on this end confine themselves generally to the determination of the horse-power input. In case a steam engine is used, the test may of course be extended to a complete test of engine and boiler plant, for which see Chaps. XVII and XVIII. B. Air Horse Power. — This is the indicated horse power as computed from cards taken from the air cylinders. The computa- tion is exactly the same as for horse power from steam cylinders. The rules to be observed in the attachment and use of indicators on the air cylinders are also the same as for steam (see Chaps. XV and XVI), and no special precautions are necessary. C. Weight or Volume of Air Handled. — This measurement is very important and is the one hardest to make accurately in con- 974 EXPERIMENTAL ENGINEERING nection with an air-compressor test, especially if the plant is large. In that case some of the most reliable means available, that is, gasometer and meter, can no longer be used on account of the cost of the apparatus. In fact, under any circumstances, the measure- ment is not a simple one, and for that reason it is often agreed to compute the quantity of air delivered from the piston displacement and the apparent volumetric efficiency (as computed from the card). It should be distinctly understood that this method is approximate and may lead to considerable errors. If used, Ey, should be computed only from a card taken with a weak spring and stops. For very accurate work, air may be measured both at inlet and outlet of the compressor. The means available at the inlet are: gasometer, meter, anemometer. Of these the former is the most accurate. The anemometer is not recommended, although it pos- sesses the decided advantage of large capacity as compared with the other two. At the outlet, besides the three methods above given for the inlet, any one of the following methods is also avail- able: orifice, Venturi meter, Pitot tube, nozzle, pumping up a tank from a lower to a higher pressure, calorimetric means. The theory underlying any of these methods, together with the accuracy attainable and the limitations to applicability in individual cases, has been discussed at length in Chap. XII. One or two illustrations of actual apparatus used may, however, be of service. Fig. 579 * shows the method employed by Professor Josse in the laboratory at Charlottenburg for small-sized air compressors. The compressor C is in this case driven by belt from a steam engine D. The air is measured both at inlet and outlet. G is a gas meter connected to the inlet; R, being a small receiver to deaden the pressure fluctuations due to suction, and V, a valve to control the suction pressure if desired. Manometers are indicated to observe the pressures both at the meter and in the suction receiver. The high-pressure air is first delivered into a smal] receiver R, and from this is either allowed to escape at O or is pumped into the large measuring tank R;. The valve V» serves to regulate the pressure, * Zeitschrift des Vereins deutscher Ingenieure, Feb. 4, 1905. AIR-COMPRESSING MACHINERY 975 shown by gauge G2, against which the compressor is discharging, and this is kept constant during a trial of air delivery. The capacity of the large tank is about 700 cubic feet. The method of operating this apparatus is practically that outlined in Art. 230, p. 438. iT Fic. 579.— METHOD oF Mzasurinc Arr By PuMPING UP A RESERVOIR. Air is allowed to escape at O, until the pressure at G, and that in the tank, measured at G3, are determined. Observe also the tem- perature at JT. Then, closing O, let the pressure at G; increase to Bs a ca ir ele To open Se ’ Receiver = Fic, s80.— OriricE MerHop or MEasurING AIR AT OUTLET FROM CoMPRESSOR. the desired limit, keeping G, constant. At the end observe G3 and the temperature. The formula for computing weight of air from this data is also given in the article mentioned. Fig. 580* shows an orifice method of measurement used in the * Zeitschrift des Vereins deutscher Ingenieure, Oct. 30, 1909. 976 EXPERIMENTAL ENGINEERING test of a compressor delivering about 140,000 cubic feet of air per hour against a pressure of about 115 Ibs. The compressor delivered first into a receiver having a capacity of 1050 cubic feet. The in- terposition of a receiver is practically a necessity for any method of measurement, to obtain steady flow. ‘The orifice used was bell- mouth, diameter at small end 1.42”, large end 2.32”, length 2.16”, radius of curvature at entrance 80”, constant C = .975. For dis- charge formula see Arts. 220 to 223. The arrangement of apparatus for measuring pressure and temperature are indicated. V is a regulating valve to maintain at the proper level the pressure P; against which the compressor is discharging. Another orifice method, capable of large capacity, is shown in Fig. 581. Here the compressor delivers into the receiver Ri, in Fic. 581.—Oririce MretHop or MrasurING Arr, FOR LARGE CAPACITIES. which the desired pressure is maintained by means of valves Vi and V2,asread atG;. The air discharges into Ry, which is furnished with a number of discharge orifices around the bottom as indicated. The pressure in R, is determined by the open mercury column M, which may also be used to measure the pressure in R; by throwing over the three-way cock H, unless the pressure is too high. Tem- perature is measured at JT. The water seal merely serves the pur- pose of deadening noise. By substituting plugs for the orifices the capacity of the apparatus may be changed at will. The computa- tion of delivery is of course the same as for any orifice measurement. AIR-COMPRESSING MACHINERY 977 f 419. Record of Data and Computations for Air-compressor Test. — The forms on pages 979 and 980 show the necessary data to be observed for a test on a two-stage compressor driven by a compound engine. The method of air measurement is in this case by convergent nozzle. The pressure discharged against by the com-- pressor is kept at the desired point by a valve just ahead of the nozzle. The first form takes care of the data and computations obtained from the steam and air cards. The second records the general readings of speed, pressures, temperatures, etc. The principal data and results to be reported are given in the following table: RESULTS OF AIR-COMPRESSOR TEST. Ty (Date: OF CES Bryece dt ore bs ve ok RAS Oe A ae iss ee reg Bee 2. Duration of test, hours........ 0.0... c cece eee ee eee eee eee 3. Diameter of cylinders, inches: (a) Steam, H.P....... 5 (0) Steam, LBs ceccc ees : (c) Air, H.P....... 3 (@) Ar, LP. . ee on 4. Stroke, inches: (a) Steam cylinders........ ; (0) Air cylinders........ 5. Diameter piston rods, inches......... Av. per cent of clearance in air cylinders, H.P......... eG Pie Revolutions per minute: (a) Prime mover........ ; (0) Air cylinders.............. 6. Average observed readings: (A) Pressure, absolute: (a) Steam...... ; (0) Vacuum, condenser....; (c) Barom- eter..... ; (d) Air suction...... ; (e) Intercooler...... fs (f) Receiver...... ; (g) Pressures at measuring apparatus..... (B) Temperatures, °F.: (a) Steam...... ; (6) Air at intake...... ; (c) Air leaving L.P. CYlies nes ; @) Air leaving intercooler..... ; (e) Air leaving H.P. cyl......: (f) Jacket water, L.P. cyl., entering...... : leaving...... ; (g) Jacket water, H. P. cyl., entering...... ‘ leaving...... ; (hk) Jacket water, intercooler, entering...... leaving...... ; (4) Temperatures at measuring apparatus..... (C) Weights, pounds total: (a) Condensed steam, or feed water to boiler........ ; (b) Steam to steam jackets...... ; (c) Cooling water, L.P. air-cyl. jacket eens ; (d) Cooling water, intercooler jacket......; (e) Cooling water, H.P. air-cyl. jacket........ 978 EXPERIMENTAL ENGINEERING RESULTS OF AIR-COMPRESSOR TEST, — Conlinued. LH:P., H:P.steam: cylinder -5 vce a.ce 3 os 26 oe nwa wegen apa TEH.P), GP stéamt, CYMER a. oe4 agence pa dendtaniacen set Meee BEB Total-LH-P.; steamrend: .4a.4 ca Fy cei wie eo Peele rors geee antes © 16, J¢H-P:, HR, air €ylindets cuccned cum iotcas ene tad e@ eae one A ery 1, EP: Ry air cylinder. aj.2 aod acs aw eck See ee Beet ea ETE ro: Total air T-HeP ss takes seen beak es a bas ee ee eee sma e He 13. Pounds of wet steam per steam I.H.P. per hour .................... TH. Ouahty-Ob Steam, Per CONE jis viGsenis ae gteaaas GP eee aS 15. Pounds of dry steam per steam I.H.P. per hour....................- 16. Pounds of dry steam per air IL.H.P. per hour...................-..- 17. Heat supplied in one pound of steam, B.t.u..............0. 00000000. 18. Heat supplied per hour per steam I.H.P., B.tu...............2.... 19. Heat supplied per hour per air I.H.P., Btu........00.. eee 20. * Actual volume of free air delivered per hour, cu. ft................- 21. Piston displacement of L.P. cylinder, per hour, cu. ft................ 22. Theoretical horse power required to deliver the actual volume of free air compressed to receiver pressure, adiabatic compression.......... 23. Theoretical horse power required to deliver the actual volume of: free air compressed to receiver pressure, isothermal compression........ eq. Slip, cubié feet per hours, cca pshca ea beckineatond #@an gala mn aeda wh was 25. SUP. Der CChty alain desi ee veras tap aaseae SEEM Eee a vee oe See la es 26. Efficiencies: (a) Mechanical efficiency, Em... 05.0.0 c cece eee cece (6) Volumetric efficiency, true or actual, Eyt...........0.......0. (c) Volumetric efficiency, apparent, Eyg..... 00.02... eee (d) Efficiency of compression, Ee...........0. 0.0 c eee eee eee 27. Saving effected by cooling jackets, as compared with adiabatic com- pression and no intercooling; computed from combined diagram: (a) Saving due to L.P. jacket, horse power...................0.. (6) Saving due to H.P. jacket, horse power..................... (c) Saving due to intercooler jacket, horse power................ Se ca! In consideration of the explanations given in previous para- graphs of this chapter, none of the items of the above table need any extended comment. For items 22 and 23, see Arts. 411 and 412. Items 24 and 25 are explained in Art. 413. For the com- putation of the efficiencies, see Arts. 413 and 414. * Free air means air under the conditions of barometer pressure and air tempera- ture existing at the intake to the compressor. The item is computed from the data observed on the measuring apparatus used, and full details of this apparatus and che observations made should be given in the report. It has already been stated that if no actual measurement is made, ‘the quantity may be taken equal to piston displace- ment multiplied by apparent volumetric efficiency. 979 ATR-COMPRESSING MACHINERY Spal alaewicpuleuetanladewsale daee els taccdesansx|eearss| ees cecllyeay es |aeegeal cone esl ede toile ees a nfW RFs PR AGIGSE OR RG Helse oe - S actzcpncted | ec tenn al Hbeigeal-cit | detoeeece lDeteiorneadedl| isle POR eng. os¢ laine Hees awl leama’ oe fnenetial randall beware aaeaense Het /Leimeh me PSH SH eG EES b didita'y wl-oe ane Sleek ears Baw ae eS BASS ese ed ee we al RS SSS BESTS 2 Shee FE ELSE OTe we Se he ee OE Oe ee ee eRe SRS ore ¢ Sei ev chewaas deme e| veeaual les eaclle ee Ga] 4eeess eed daca allh #49 < [aes ole Se ERR w EET eR Sg eine e aarti fo marie | wma z sunglslios Vow acdrs|adacca #) ee eacelle sd grexeleuenwe wl wore wifes pee allege aaa [eet aed| Ge heats quad a [fancies] SS gH 4 wIIS Bees] ga 6 Mik [ies oelateve I UTA “UNA ‘CHI | a W | 8007] vary || THT | LAW | WB0ET) “wry wd | eH [aa |wsueq| “wary |) FHT | aa | WsueT) “wory | sed ON AY | “AY “suIRIgeIq, Japul[AD ly “SUIvISUIG suIsUy WIeI3S UCT ae eae es pro yueige pray “WMad 4a 9OUDADIID UI UNIO A ee ee ard fee Hele ory tte quBIy cette 05) ore yuery ct peagy See teeeguprys tr peayy yueID ees 4 ee peoH “Ja9yT I1QND Ut JuaMaIDIGstg OIL : A yoy ur ayoys joywsuey yoy mayonsjomsaey | yung pep t query proxy ques pew yume pray “p29 2QnD ut juauarvjgsiq uojsig “sayguy aspnby ut spoy uopstg fovasp 99} Ul ayOI}s JO YIBuIT ss ++" g99] Ul ayorys Jo YISUET ee gmerg sts prog ve eeequpag ts peep seesessss Ss sgayput “bs uf wary ++ +++ +sayour “bs uf vary “sayouy ut spoy uojsig fo sjomDig: fe Ul UI por uoysid “wei ‘Ul Ul por uO sId “WRI, seurcbsutlearyo atcbsureary fetter ‘ur “DS ut vary vos + seur *bs uf vary saqoururmerq soqoururmrerqg pe sopput ur merq@ Sayqoul ul “Wed “adnSSOLT NOT “adnSSadgd 4ST “OANSSOLY MOT aanssa4g y81T “SUHANTIAD UY “SUTGNITAD WSIS : “SNOISNA WIG Ras +seegsoad mop Iny'*' 61 ssord y8rq ary’ *ssaid mop wreayg' +--+ + * “ssord ysty ureayg sn “sSurids Jo a[eag SiS Oe ee Re Re ke ae BREE Se RR FAG Aq poypayg tess sess sess sess cs ssssesss ss Ka payersaqur Sprey) final ay ah ings r61 he atc op Sabra She a Belden fe ue Te reumuaisaee Ba oe aqeq pS Be hoa ly Aa ele ae os a acta im) aes, OTe Sn AR Sree eae are. Aba Boa, a Se ees, ebay ease ye peIsat, ix kag A AMO RS Oo OM BRE eae Ver teeter eee ener essen ees sesee ees esese sess ssesKq yim sossarduros any ‘ALISUTAINA TIANUOD ‘ADATION AATAIS 980 MECHANICAL LABORATORY, SIBLEY COLLEGE, CORNELL UNIVERSITY. 0 | a) 2 TOT hasan HDAbE; spaeoee .Coefficient Air Nozzle.......0000.00 00. cece ee ee «Air Compressor ats ecco. .ccacce sa gata enews .Area of Air Nozzle in sq. ft......... ‘ Diam. of Air Nozzle in inches.......... EXPERIMENTAL ENGINEERING | ‘TRIOL | ete fh gS Ss ‘JAE ‘sseid-y3IZ Wor BE DQ <2 *[A % 4 ou, *Jaquin Ny Etc. Aver- age AIR-COMPRESSING MACHINERY 981 420. The Action of the Centrifugal Fan. — A centrifugal fan, of whatever type, takes gas having a pressure of f, pounds absolute, a velocity of v, feet per second, and a temperature of 4,°, and com- presses it to a pressure of pf. pounds absolute, with a velocity of v, feet per second, and a temperature of #°. In practice the degree of compression is generally so small that there is no sensible devel- opment of heat, and consequently the compression may be con- sidered isothermal. The work done by the fan upon the gas is expended in three ways: (a) compressing from the pressure p; to the pressure 2; (b) forcing the weight of air handled against the pres- sure 2; and (c) raising the kinetic energy of the gas by increasing the velocity. The work of compressing the gas is, under ordinary conditions, very small. Thus, if the pressure is raised to 12” water above atmosphere, the percentage of pressure increase, assuming atmos- pheric pressure at 14.7 lbs., is only = .029 = 2.9 per cent. It 14. is therefore usual to neglect this work item, that is, to assume that the density of the gas is not changed. This modification, or assumption, however, makes the condition of operation for the fan the same as for a centrifugal pump, except that air or gas instead of water is the fluid pumped. The centrifugal pump theory is discussed in Chap. XXV, and it is there shown that this can be based upon that for the radial outward-flow reaction turbiné. The fundamental theory of this turbine therefore applies directly to the centrifugal fan. It is shown (Art. 471) that the theoretical lift or head produced by the centrifugal pump may be expressed by 1 m te lita 608 0) sg 6) ? in which uw, = the linear velocity, in feet per second, of the fan blade at the tip (exit); w, = the relative velocity, in feet per second, of the air leaving the fan wheel (= the volume Q of air flowing, in cubic feet per second, divided by the peripheral area of the fan wheel in square feet, around the exit circumference) ; and 982 EXPERIMENTAL ENGINEERING a =the angle made by w (drawn perpendicular to the radius from the center of the wheel) and w, (drawn tangent to the last blade element). See Fig. 611, p. 1054. It is also shown (p. 1075) that the general equation for gross head pumped through by a centrifugal pump (or produced by a centrifugal fan) is Vg? — V," h = hg—(+h,) that Saar ae feet, (37) in which hg = static head above atmosphere measured at some point in the discharge pipe; h, = static head above atmosphere measured at some point in the suction pipe (A, is to be used with the minus sign when the pump lifts water, with “ the plus sign when the water is supplied under some pressure) ; i, = vertical height between the points of measurement in discharge and suction pipe; 2 ed velocity head in the discharge pipe at point where 28 ha is measured; and 2 oS velocity head in the suction pipe at point where 28 h, is measured. It is needless to say that for the fan all these heads are expressed in feet of air or gas. The above equation applies, as it stands, to the case of a fan drawing from a closed space and discharging into another limited space. That is not the usual case. Usually the fan either draws from the air and discharges into a limited space, or it draws from a limited space and discharges into air. In the case of the fan drawing from the atmosphere, both h, and v, may be considered zero. There is, of course, velocity near the inlet of the fan, but where velocity exists, / is no longer zero. AIR-COMPRESSING MACHINERY 983 Away from the fan, however, h, and v, are zero. The gross head then becomes ae : ‘ 4 h= @ thy + = feet. (38) In practice /, is neglected, so that finally 2 h= (i + - feet. (39) . . . 2 Where the fan discharges into air, hg and a may be considered equal to zero, and, neglecting /, the gross head in that case becomes equal to : hd 2 7 feet. (40) ies 421. Work done by a Fan: Air Horse Power. — It has already been stated that work done by a fan consists of (a) the work of compressing the gas from suction pressure to discharge pressure. It has been shown that this is a small quantity and is usually neglected. (b) the work of forcing the gas against the discharge pressure. This work is equivalent to lifting the weight of gas handled through a height corresponding to the difference of static head on the two sides of the fan. (c) the work of increasing the velocity of the gas flow from the velocity on the suction to the velocity on the discharge side. Take the case of a fan drawing from the atmosphere and dis- charging through a main against a resistance. At any section A of the discharge main, Fig. 582, let the static pressure be equal to pq (measured above atmosphere, in inches of water, mercury, ounces per square inch, or other units), and let the velocity be v, feet per second. Also let Q be the volume in cubic feet of gas delivered per second, and 6 be the density of the gas (= weight per cubic foot at the pressure and temperature in the discharge main). Compute the equivalent height of gas column /, in feet corre- sponding to the pressure pf, (see Art. 233). Then, since the weight 984 EXPERIMENTAL ENGINEERING | —— Fic. 582. of gas handled is G = Q6 pounds per second, and since this weight is raised against the pressure p,(= equivalent to the height 4,), the work done under heading (6) above will be W, = Ghq = Osh, ft.-lbs. per'sec. (at) The general formula for kinetic energy is vy? = G V_” — v2 = =e in which 2; is the velocity of the mass M at the beginning, and 2 the velocity at the end. In this case, since the fan is drawing from the atmosphere, 7,=%,= 0, and % =v. Hence the work equivalent to the kinetic energy under heading (c) above is KE=M2— J@M a ahs. kaa) 2 28 —- CM = 0322 tt. W.= Go - Q6 ze ft.-lbs. per sec. (43) The total work done by the fan upon the gas, therefore, is 2 W=W,+ W.=(Q6 (i + =) ft.-Ibs. per sec. (44) The last factor of the right-hand member of this equation is equal to the total or gross head by Eq. (39). The foot-pounds of work done in a given time, therefore, is equivalent to the weight in pounds of gas handled in that time, multiplied by the total head in feet. AIR-COMPRESSING MACHINERY 985 The result would have been the same if other conditions of operation (discharge into atmosphere or drawing from a closed space and discharging against a resistance) had been assumed, and the general work formula is (neglecting /, as is usual) Va" 5 2,” W = 05 (hat ht ee ft.-Ibs. per sec. (45) Returning to the fan of Fig. 582, a simpler way of obtaining the necessary data for the computation of work done would have been to determine at once the total head at A by using an impact tube (Pitot tube without the static opening). The reading of the in- strument is then directly equivalent to the sum of static and dynamic 2 heads (= hat vt). In making this measurement, traverses of the 28 main must be made to obtain the average reading. Another method of determining the total head against which the fan works is to construct a large box or receiver just beyond the outlet of the fan (CD in Fig. 582), so that the velocity vg across this box is negligible. The total head produced by the fan then exists as static head, and this may be found by simply connecting a manometer to the box. It is, however, not particularly easy to get a box large enough and to so baffle it that the air currents in it do not manifest themselves sufficiently to affect the manometer reading, and for that reason the determination of total head by impact is probably just as reliable. Since one horse power is equivalent to 550 foot-pounds of work per second, any of the formulas (41), (43), (44), and (45), divided by 550, will give the corresponding horse power. Eq. (44) for the fan of Fig. 582, and Eq. (45) for the general case, will give the total horse power of work done by the fan. This is called the air horse power. 422. Fan Efficiencies. — (a) Manometric Efficiency is the ratio of the gross head produced by a fan to the theoretical head, or h Eman. aa WT (46) in which H and / are found by means of the equations given in Art. 420, taking care to use for /: the expression applying to the case. 986 EXPERIMENTAL ENGINEERING (b) Mechanical Efficiency, or simply Efficiency of the Fan, is the ratio of the total work done by the fan in moving air or gas divided by the horse power input to the fan (not to the prime mover). This efficiency, therefore, equals Air horse power __ Wh a= Applied horse power AHP X 33,000 : (47) in which W = air or gas handled per minute, and / is the gross head produced in feet. (c) Volumetric Efficiency* is defined as the ratio between the actual volume of air or gas passing the fan in a given time divided by the volume of the fan wheel multiplied by the number of turns the wheel has made in the same time; that is, pd E, = Vn 7 (48) in which Q = volume of air or gas handled, V., = volume of wheel, and nm = revolutions per minute. This ratio seems to assume, as a standard, that the fan should discharge a volume of air every turn equal to the volume of the wheel. Not much weight is attached to this efficiency in fan testing. 423. Arrangements for Testing Fans.— For a capacity and economy test, the determinations must include the following: (A) Power input; (B) power output (air horse power); (C) vol- ume of gas delivered (capacity); (D) readings of velocity and pres- sure at inlet and outlet; (Z) speed of fan; (F) humidity and temperature. (A) Power Input. — Any type of prime mover may be used; those usually employed are steam engines, electric motors, belt drives from main shafting. The first two may be direct- or belt- connected. Where belt-driven, a direct-connected transmission dynamometer should be employed for very accurate work. When direct-connected to a steam engine or motor, the I.H.P. of the engine or the watts input to the motor corrected for the mechanical efficiency of the machine will be the power input to the fan. If the mechanical efficiency of the prime mover is not known, a curve * This term is practically obsolete. “Relative delivery ” is a better term for this ratio and is coming into use. AIR-COMPRESSING MACHINERY 987 between mechanical efficiency and power input to the prime mover (I.H.P. or watts) must first be found by disconnecting the fan and taking off power by means of a Prony brake. In the form below this horse-power input is called applied horse power (A.H.P.). (B) Power Output. — This is the air horse power and is computed as shown in Art. 421. (C) Volume of Gas Delivered. — This is, of course, equal to the product of cross section of tube or main through which the gas is moving by the velocity of passage. For the method of measuring the latter, see next paragraph. Calorimetric methods (see Art. 235) may also be used. (D) Measurement of Velocity and Pressure. — The instruments commonly used for measuring velocity are the anemometer, Pitot tube, and the Venturi meter. Orifice methods are also used. For the theory, characteristics, and method of use of any of these instruments, see Chap. XII. The anemometer determines the velocity directly. To obtain an average reading, divide the inlet and outlet areas into partial areas by the use of string or fine wire. Obtain the average velocity at the center of each partial area. If the latter are equal, the average velocity is the arithmetical mean of all of these readings. The capacity is to be computed from the velocity and cross sections of the outlet. If this volume is smaller than that computed for the inlet, the difference is due to leakage and back flow. The difficulty of calibrating an anemometer with ease and certainty of results makes this instrument less dependable than some of the others. The Pitot tube is commonly used in the discharge main only. To determine average velocity head, it is necessary to make very careful traverses of the main. For the method of doing this, see Chap. XII. The ratio of the center velocity to the average velocity for the entire pipe section is known as the pipe factor, and for extended investigations with the same apparatus it is common to determine the pipe factor by a preliminary investigation and to set the tube once for all at the center of the main. It has been shown that the Venturi meter is a satisfactory in- strument for measuring flow of gas, and it certainly deserves a 988 EXPERIMENTAL ENGINEERING more extended trial for this service than has up to this writing been given it. See Art. 234. Orifices may be placed either across the discharge main some distance back from the outlet, or in the outlet itself. For the con- ditions to be met with reference to pressure difference and the precautions to be observed in order to obtain reliable results, see Chap. XII. Static pressure is commonly measured by a simple manometer, which may be of the multiplying type (see Chap. VI) if the pressure is very small. It is of the greatest importance to see that the inner end of the pressure tube is not affected by velocity (impact), and to that end it is necessary not to have the end of the tube project beyond the inside surface of the wall of the main. It is hardly necessary to say that for the purpose of determining total head (for computing air horse power) the static pressure must be meas- ured at the same cross section of the main as the velocity head. In case the air horse power is determined from the measurement of static pressure in a pressure box (velocity head assumed negli- gible) it is well to measure this pressure at several points in the box, as it is not at all easy to obtain a uniform transformation of velocity into pressure head, especially near the fan. It will be found that careful baffling is required. Total pressure head may be determined at any section of the main by traversing with an impact tube, that is, a Pitot tube with- out the static tube. The manometer reading will then be the sum of the static plus the velocity head (= total head). (E) Fan Speed. — This may be determined by any of the forms of counter mentioned in Chap. VIII, the choice of the type of in- strument depending of course primarily upon the speed. (F) Determination of Humidity. —See Art. 410. The effect of humidity upon the work formulas developed is to change the den- sity 5 in the equations. In most cases this is not of sufficient impor- tance to take into account. 424. Scope of Test and the Report.— A complete fan investiga- tion should include the following: (a) Determination of the pressure produced with the fan outlet closed ; ATR-COMPRESSING MACHINERY 989 (b) A series of runs at constant speed, varying the size of outlet opening by predetermined amounts; (c) Repeat the series under (0) for a series of speeds maintained constant in each case for the same series of outlet openings. The observations required have been discussed in the previous paragraph. The following forms for recording the observations and the results of computations apply directly to the fan-testing set used at Sibley College. This consists of a Sirocco fan driven by belt through a direct-current motor. The fan delivers into a receiver or pressure box in which the velocity is theoretically zero. The total head (all pressure head) is here determined by means of a manometer. In the discharge pipe a Pitot tube is used and finally a Venturi meter is connected beyond the Pitot tube. An anemometer is also used. This determines the flow of air, first, by anemometer at inlet and outlet, second, by static pressure head in the pressure box, third, by Pitot tube, and fourth, by Venturi meter. The purpose of the experiment is not only to test the fan but also to give practice in several methods of measuring the flow of gas. The complete report should show the results graphically as follows: , With the series of ratios “2 (actual outlet opening to full opening) 0 as abscissas, draw curves with the following ordinates: (a) Efficiency of fan, E,,; (6) Air horse power; (c) Volume of free air delivered in cubic feet per minute. This will give one curve sheet for each speed used. The first of the following forms shows the scheme used for re- cording the observations, the second shows the principal items to be computed from the observations. EXPERIMENTAL ENGINEERING 99° PA Ip i ‘asreyp | , A Kc ey °y 7 ayeyy ‘sy |qoeduy | ‘AqID07aA, ‘o19t1S Ty ‘xo ’ st tf t Y XOG 3 I aap * a % “Tn ua A. ainssalg 7M ‘soroduy TSUN eal AHO ase aed “IaquUNnN, ‘10]0JM{ Ul “oy valy [MJ OF YF any “AIDOPA ‘aqny, OU 380] SHB Raly [INO Jo oney ‘JoJWMIOWBUy “sZulpeay JojaMoury “100 0} nduy ‘Wau ‘paeds “Og =) SS TE SE FS 4, & yy ‘bs 9271NO uey jo ealy ma Pe ee sjurysuod r3q1O Se 4. So eee SOs) aoe, Behr] -wouryy surAqdnnpy So Joya UNquoA Ss aqny, woug ft JoJaMIOMIBUY :S]Ue}SUOD UOl}eIqITeD PPR eR ee ew RO ee ee ee em me he qua. rad ‘AyIprunyy ca Rhee he ES “y 6 ‘gmyerodwa a i Hee eee ‘3H soyoul ‘oyoWoleg PA UM Br ee Re RO Sg ae ee ee a ee eo Ce wwe een eee rw eee fre seerss eres: SIQATISaC Seemann t £28 9B Ey ‘Isa], 40 90T ‘NIV JO MOTI JO LNAWAMASVAW GNV ‘NVE HO LSHL AIR-COMPRESSING MACHINERY QgI TEST OF FAN AND MEASUREMENT OF FLOW OF AIR. RESULT SHEET. Tests made by.............. Bt ena see ae ean a adds Pha aes obed, 5) Date sa osasucsan Igor Notation: # = head in inches of water; #’ = head in inches of other fluids; h = h’K, where K is the ratio of density of manometer liquid to that of water; H = kr = #’Kr is equivalent head in feet of air, in which 7 is the number of feet of air column. giving same pressure per sq. inch, as 1 inch of water; F= area in sq. ft.; V = velocity in feet per sec.; Q = volume in cubic feet per sec.; W = weight in pounds per sec. Ty per ob fais iss siccxnia win ance ate sty ole Sele hls olde one For anemometer readings: Manufacturer. «3.2554. sa¢453- 564 504583 tes beens Area of pipe where used, inlet, sq. ft., Fi......... Outside diameter of wheel, ins.................... Area of pipe where used, outlet, sq. ft., Fe........ Width of wheel, ins.............0...0..000 eee eee For Pitot tube readings: Dimensions of blade, axial, ins... Area of pipe where used, sq. ft., F3.............- Dimensions of blade, radial, ins. .|For Venturi tube: Form of blade............... Area upstream section, sq. ft., Fa.............0-. Diameter fan inlet, ins... ......... 000.0 cee eee eee Area throat section, sq. ft., Fs..........-.--0055 Area fan inlet,-sq. ft., Fo... sec e cece ee eee eee Angle of convergence, degrees...............-.04 Diameter fan outlet, ins...........-..-..000ee eee Angle of divergence, degrees................000- Area fan outlet, sq. ft., Fo... ccc. cece eee eee eee Weight of air per cubic foot under actual condi- Diameter discharge pipe, ins. . HONS! 10S 8:6 set ose ease etee Tam ORT Length of discharge pipe, ft................--.0-- Wumber of Run. I 2 3 4 5 6 2 Speedvof- fan; RPE Miva icocms katate wdst Sas Mint See Pat os . Velocity of fan blade tips, ft. per sec................42- . Pressure head in receiver, inches water, /y............. . Height of equivalent air column, ft.,.................. . Velocity head of discharge, Pitot tube, inches water, /;.. Discharge by Pitot tube, cu. ft. per sec., Qj......-..-.. . Velocity head of discharge, Venturi meter, inches water, hs . Discharge by Venturi meter, cu. ft. per sec., Qs......-. . Discharge velocity by anemometer, ft. per sec., Vay.... to. Discharge by anemometer, cu. ft. per sec., Qag....---++ 11. Intake velocity by anemometer, ft. per sec., Va;....-.-- 12. Intake by anemometer, cu. ft. per sec., Qay-..--------- 13. Average discharge, cu. ft. per sec.,Q ...-..--.--+- 00> 14. Equivalent discharge, under standard conditions, cu. ft. Per SCO! saci ews casesnenee adele bus #4 bees 15. Weight discharged, Ibs. per sec., W........... 16. Air horse power, based on average discharge... . ou 17. Applied horse power, A.H.P........0- 0 eee ee eee eens 18, Manometric efficiency... .......0 000 e eee e renee ences 19. Fan efficiency COM ANEO?E Q 20. Ratio discharge to intake, by anemometer, —......... 21. Slip and leakage, by anemometer, per ceNt...........4+ CHAPTER XXIV. MECHANICAL REFRIGERATION. 425. Theory of Mechanical Refrigeration. The statement is often made that the refrigerating machine is a heat engine run backward. As a matter of fact, a refrigerating plant using a liquid refrigerant bears a much closer analogy to the steam boiler. The boiling temperature of a liquid depends upon the pressure upon the liquid. The'temperature of the liquid cannot be raised Fic. 583. beyond this point as long as any liquid remains, except by raising the pressure. Likewise, a reduction of the pressure upon a boiling liquid means a lowering of the boiling point, the difference in the heats of the liquid between the two boiling points serving to vapor- ize a part of the liquid. Suppose that a liquid, with a boiling temperature at atmospheric pressure considerably below average room temperature, be confined in the vessel A, Fig. 583. Suppose next that the liquid is kept at room temperature, so that the vapor pressure exerted by it will be higher than atmospheric. If this liquid is drawn off through pipe P and allowed to expand to atmos- 992 MECHANICAL REFRIGERATION 993 pheric pressure through a suitable valve B, its temperature will drop, owing to partial or complete vaporization, and if allowed to circulate through coil C, the space in which coil C is placed will be cooled. This will supply a further stock of heat for vaporizing the remainder of the liquid. Theoretically, therefore, we need nothing more than a constant supply of a proper liquid (refriger- ant), under a pressure higher than atmospheric, to produce a cooling effect. There are two practical objections to this simple type of plant: first, the refrigerant used may, in the case of ammonia and sulphur dioxide, after vaporization be dangerous to health; and, second, the Cooling Fic. 584.— Diacram oF StmpLE VAPOR COMPRESSION REFRIGERATING MACHINE. process is uneconomical. There are then two things to be done: the vaporized refrigerant must be prevented from escaping, and it must be brought back to its initial condition and returned to the vessel A. One method of doing this is shown in Fig. 584. The vapor is drawn into the compressor E, where its pressure is raised. It is then discharged into the condenser G, in which it is liquefied at constant pressure. From here it is then returned to the receiver A and used over again. es 994 EXPERIMENTAL ENGINEERING In its simplest form, then, a refrigerating system using a vapor may consist of a compressor E, pumping the vapor out of the Jow- pressure side BCD of the installation, a condenser G in which the high-pressure vapor is liquefied, being stored in receiver A. That part of the system including E,G, H, A, P, and B is known as the high-pressure side of the installation. If a gaseous instead of a liquid refrigerant is used, the cycle of operations is similar, but there are two changes. In the first place, the condenser G merely cools the gas but does not condense it to the liquid state. In the second, if the high-pressure gas were simply allowed to expand through an ordinary expansion cock or nozzle B, the cooling effect would be inappreciable, because no work is done. For that reason this part of the system is replaced by an expansion cylinder in which the high-pressure gas expands behind a piston, doing work. This work may, of course, be used to help operate the compressor. 426. Refrigerating Agents.— A good refrigerating medium should have low boiling point at ordinary pressures, large latent heat of vaporization, and small specific volume. The first is de- sirable because it makes operation possible without the use of very high pressures in any part of the system, thus allowing the use of lighter machines, with smaller loss by leakage, etc. The latent heat of vaporization is in a sense a direct measure of the cooling effect; the greater the heat of vaporization, the better the agent. In this respect water is best, but on account of its very high specific volume it is not used. The specific volume of the agent controls the cylinder volume of the compressor per unit of refrigeration, — in other words, controls the size of the machine. The agents that have been used or proposed are: water, air, am- monia (NHs), carbonic acid (CO:), sulphurous acid (SO2), sulphuric ether, ethyl and methyl chloride, Pictet fluid, etc. Of these only air, NH;, COz, and SO. are of any commercial importance. Pictet fluid is a combination of SO, and CO. It is seldom used. The table, p. 995, gives the main characteristics of NH3, CO:, and SOx. Various authorities give figures that are somewhat at variance with the figures of the table, particularly with reference to specific heats. MECHANICAL REFRIGERATION 995 Relative Press. in ¥ a Specific Boiling Vol. of Lbs. per Vol in: Cus Latent Specific Heat of the | Point °F. | Compressor Ft. per Lb. Heat. Heat of the Sq. In. at at o° F Liquid Vapor. at Atmos. | for Equal oF, pon te naa: Cp. Press. Refrigera- tion Effect. NH; .... 30.0 9.00 556.0 I.05* -53 —28.5 23.3 COR aac 310.0 = 204 117.8 54 .217 —140.0 3.2 SO,..... 10.3 7.20 170.6 32 -I55 +15.0 61.7 * Wood, in Vol. X, Trans. A. S. M. E., gives for NH; : t = —40° Cp = 1.001 =+8.1 = 1.086 = +46.58 = 1.056 = +100.0 = 0.976 In comparing these three agents, two sides of the question should be taken into consideration. From the practical standpoint, assuming that the limits of operation are not below —5° F., nor higher than 85°, it will be found (see tables in the Appendix) that the absolute operating pressures are: for NHs, from 27 to 175 lbs.; for CQ2, from 290 to 1000; and for SOs, from g to 65 Ibs. These pressures are ordinary for both NH; and SOs, but high for CQ. The lower pressure for SO; is below the atmosphere and any inleak- age of air may cause serious corrosion of metal by the formation of sulphuric acid. The pressures for CO, are so high as to cause trouble in keeping tight joints, although any leakage does no harm except for the loss of refrigerating agent. The high pressures necessary and the small specific volume make a very compact machine (see the last column in the above table), and this, com- bined with the fact that any leakage causes no discomfort what- ever, makes CO, a favorite agent for use on shipboard. As between NHsg and SO:, the much greater latent heat of vaporization gener- ally decides in favor of NHs, in spite of the lower operating pres- sures for SO,. Ammonia has the practical disadvantage that it corrodes brass, or any other copper alloy, very readily, and only iron can be used in the construction of those parts of the machine with which the agent comes in contact. From the standpoint of thermal efficiency, there are again cer- tain differences between the three agents. If the Carnot cycle is considered the standard of efficiency for the refrigerating proc- 996 Temperature Fahrenheit ~40 4 EXPERIMENTAL ENGINEERING AMMONIA TEMPERATURE-ENTROPY DIAGRAM —2 0 2 A 6 8 1.0 Entropy Fic. 585. 12 14 16 MECHANICAL REFRIGERATION 907 ess, the liquid used would be a matter of indifference, because the efficiency of this cycle depends only upon the temperature limits. The real cycle is, however, different from the Carnot, and there is a certain loss connected with this modification. It can be shown* that the loss is least for NH; and greatest for COs, and this is, of course, another factor operating in favor of NHs. Tables 7, 8, and 9, in the Appendix give the thermal proper- ties for NHs, SO:, and CO; respectively. They are similar to the steam table, and the columns need no further explanation. The NH; table is usually given on the basis of temperature, but has in this case been recomputed to the pressure basis, following steam- table practice. The SO. and CO, tables have been left in the com- mon forms, as these two agents are little used in this country. Fig. 585 gives the entropy diagram for NH3, the meaning of which should be clear from its analogy to the steam entropy diagram, Chap. XI. The only gaseous refrigerant that has been used is air. Its low heat capacity and the fact that there is no change of state during the process require a much larger plant than does a liquid refrig- erant for the same capacity, increasing the cost of operation. This is offset by the fact that air is cheap and has no dangerous or offensive properties. It has been used on shipboard on the latter account. 427. Classification of Refrigerating Machines. — The following scheme shows at a glance the various classes of refrigerating machines now in use. 1. Machines in which the air is used over and over again without coming actually in contact with | substance to be cooled, called the closed-cycle I. Machines using air. machine. 2. Those in which the cold air is circulated through the rooms to be cooled, called the open-cycle machine. i. Machines which use heat directly to produce II. Machines using an agent cold. Absorption machines and vacuum ma- that is alternately con- chines. densed and vaporized. 2. Those which produce cold by the expenditure of mechanical energy. Compression machines. * See Ewing, The Mechanical Production of Cold, p. 66. 998 EXPERIMENTAL ENGINEERING 428. Air Machines. — The principle upon which these machines operate is very simple. In Fig. 586, if air at 60° F. and atmospheric pressure is taken into the compressor A and compressed adiabatically to 60 lbs. per square inch, the temperature will be raised to 320° F. This air is then transferred to the water-cooled condenser C, cooled to 60° F., and is then allowed to do work in the expansion cylin- der B, expanding to atmospheric pressure. In going through this Cooling 60% Water eI | 8B 4 Cold Room Fic. 586.— DIAGRAM oF REFRIGERATING MACHINE USING AIR, CLOSED CYCLE. cycle, the theoretical end temperature should be — 113° F. Prac-. tical losses of course modify this theoretical result. The expan- sion cylinder B is connected to the same shaft as the compressor cylinder A, so that the work of expansion is utilized to help com- press the air. The deficiency produced by friction and leakage losses is made up by some source of power D. Ii the air, after expanding in B, is next circulated through a system of cooling pipes, in which case expansion in B need not be down to atmos- phere, we have Class 1 of air machines,— the closed-cycle machine. The air, after doing its work, forms the suction supply for com- pressor A. In the .open-cycle machine, the cold air is forced directly into the rooms to be cooled and is continuously displaced MECHANICAL REFRIGERATION 999 by a new supply. The latter type of machine is to-day more used than the closed-cycle machine. , Cold-air machines have the advantage of great simplicity, and, neglecting efficiency, are satisfactory for small capacities. For large capacities, the capital cost of the installation makes the operation no longer profitable in competition with other machines. The difficulty of moisture freezing in the expansion cylinder and choking up ports and valves can be overcome by the interposition of a drier between the cooler and the expansion cylinder, so that smooth operation is possible. The efficiency of operation is low as compared with other machines. 429. The Absorption System.— This will be described with ammonia as the refrigerating agent. An absorption plant consists of the following essential parts: the generator, the condenser, the refrigerator, the absorber, the interchanger, exchanger, or econo- mizer, the rectifier, and the analyzer. The interrelation of all these parts is shown in the conventional sketch, Fig. 587. The operation of the plant depends upon the fact that water will absorb NH; gas, the quantity depending upon pressure and temperature conditions. Table 10, Appendix, gives some figures for the ab- sorbing power of water for NHs, from which it will be seen that at any one temperature the absorbing power increases with the pressure, while at any one pressure the absorbing power decreases as the temperature increases. The latter fact is made use of in the absorption machine to obtain NH; vapor under pressure, and the reverse of this action is used to make the vapor combine again with water after it has done its work. To explain the operation from the sketch of Fig. 587, the genera- tor contains a quantity of water holding a large quantity of NH; gas in solution (strong liquor). The temperature of this liquor is raised by admitting steam to the heating coils shown, the conden- sate being removed by trap or other means. The heating starts to drive the NH; gas out of the liquor, but, since the system is a closed one, the vapor pressure above the liquor will also be raised until equilibrium is established, depending upon temperature, pres- sure, and initial strength of liquor. The NH; gas liberated, which carries with it a certain small quantity of water vapor, rises and 1000 EXPERIMENTAL ENGINEERING passes through a vessel called the analyzer. Here it meets with a descending rain of comparatively cool, strong liquor, which is on its way to the generator. Fine subdivision is produced by having the incoming strong liquor run down over a number of perforated Cooling Water Out Wet N Hg Gas i to Rectifier, | | Rectifier se : y a Cooling Water Strong Liquor Cooler Weak Liquor Co! g <4 Heated O ld g = —— ARN : Weak Liquor z = we g Strong NH,Gas & Claes Pump (—— 3 S Liquor: at 8 <> [| i 3S A & Cs T i 3 Steam w s|<— Ul ss) 2 —e 4 a => = ; — > 5 zi —e a Strong Liquor SD 5 Cold o Cond = : "f ‘ondensate P= = <= é LWeak Liquor (- NH Gas > i Trap Na as A yt} = 32 _—_— a so so) 3 Brine o from Pump = 3 Coy ey — 3 Receiver Wate 5 c) | Liquid N Hg Brine Cold i Expansion or Control Valve Fic. 587. — PARTS oF AN AMMONIA ABSORPTION SYSTEM. trays. The result is that the descending liquor takes a certain quantity of heat from the ascending NH; gas. This is desirable, because the liquor must be heated in the generator, and the gas must be cooled before it can be used. Hence the analyzer acts as an economizer. The wet gas rising through the analyzer next passes into a rectifier, which is practically a condenser cooled by water circulation. Here the gas is cooled, not enough to liquefy, but sufficient to condense the water vapor carried by it, which is returned to the analyzer by a drip pipe. The NHs, therefore, leaves the rectifier in a dry state. The gas is next passed into a_water-cooled condenser, where liquefaction is produced by the cooling. The liquid NH; is stored in the receiver and is from here MECHANICAL REFRIGERATION IOOI passed through a control or expansion valve into the cooler. A brine cooler is here indicated. The liquid NH; partially gasifies on passing the valve, the rest of the gasification being finished in the brine cooler. The NH; gas leaving the cooler then passes into the absorber, in which it meets and is mixed with cold, weak liquor, by which it is absorbed. This produces strong liquor, which is forced by the pump through the exchanger into the analyzer, and so into the generator. This closes the cycle. In the generator, weak liquor works toward the bottom on account of its greater specific gravity. It is passed through coils in the exchanger, in which it is cooled by contact with the cold, strong liquor on its way to the analyzer. This again is a desirable heat interchange, because the strong liquor must be heated in the generator and the weak liquor, which is hot coming from the generator, must be cooled before entering the absorber. The ex- changer, like the analyzer, is therefore simply an economizer. The cooling of the weak liquor is generally completed in a separate cooler between the exchanger and absorber. It must have been noticed that all possible precautions have been taken in this system to economize heat. The same may be said with regard to the consumption of cooling water. This does service first in the condenser and then cools in order the absorber, the weak-liquor cooler, and the rectifier. That part of the plant including the generator, the analyzer, the rectifier, the condenser, the receiver, and the piping from one side of the liquor pump to the generator and from the receiver to the control valve, is the high-pressure side of the plant. The low-pressure side includes the brine cooler, from the expansion or control valve, the absorber, and the piping up to the pump. Fig. 588 gives a better idea of the actual relative size and con- struction of the various parts of an absorption plant. In this installation the rectifier is combined with the condenser, being located above it. 430. The Vacuum Process. — This process employs water as the refrigerating agent. It is one type of absorption process. The principle of operation is quite simple. In Fig, 589, let the water to be cooled or frozen be placed in the 1002 EXPERIMENTAL ENGINEERING aw Ammonia Fump in \ slog 04 emg Weak Am nania Liquor. > 3 ens dang wo oujag { iO £ & I oe ll ieee oa nae e 7 PO 2 eanug s]o0D OL a vracwury 2 snospsquy ie eK PINT 2 $ z Sr: 3 oO a ©) AQ 3 = al ee 5 x Z Ft E * a ge] 3 3 53] Se a3 5 eo |]| Se cp ms a -}——— > Ono] Tel aowEy AE sonbyT wranamy ¥p2, A A o} A 4 § iAhA Ai il | Ja <| | wet iayeay gee ae eS iF dazAjuuy To Gauge wTAIg a Strong Ammonis Absorber —a Strong Ammonia Liquor Receiver Cooler Fic. 588. — AmMontA ABSORPTION PLANT. Condenser Generator MECHANICAL REFRIGERATION 1003 vessel B, and let this vessel be connected to a vacuum pump 4, by means of which the pressure above the water is lowered to below the vapor pressure. The water then begins to boil, taking its heat of vaporization from the water itself and lowering the tem- perature. The water vapor fills the space E over the water and the space D in an absorber, which is filled with strong sulphuric acid. Arrangements are made to promote thorough mixing be- tween the vapor and the acid to cause rapid absorption. The pump A handles practically no vapor and serves merely to main- Fic. 589.— PRINCIPLE OF Vacuum PRocEss. tain a high vacuum. The cold water is either circulated through rooms to be cooled, or the operation may be carried on until the water freezes. The ice made is rather “mushy” and must be compressed. The rest of a commercial vacuum plant consists of arrangements for continuous concentration of the acid, which of course is con- stantly diluted in the absorber during the operation of the plant. The efficiency of the vacuum process is probably as high as that of any of the other methods discussed, but in practice it is found that the strongly corrosive action of the acid fumes makes it hard to keep the system tight, which is of course a necessity on account of the high vacuum that must be maintained for best efficiency. 431. The Vapor-compression System. — The principle of opera- tion of this system has already been outlined in Art. 425 and Fig. 584. Except for the difference introduced in operating pressures, 1004 EXPERIMENTAL ENGINEERING temperatures, compressor sizes, etc., pointed out in Art. 426, vapor- compression machines are very similar whether they employ COk, SO:, or NH3. Since the first two agents are not used in this country ‘to any extent, the discussion will be confined to the ammonia machine. A common arrangement of compression plant is shown in Fig. -590.* The compressor used is of the double-acting steam-driven Blow Off Condenser Water Outlet Insulation Suction Return Valve —<——t Expansion Seale ‘oils = Saas Valve Gauge Board Liquid Line Expansion Valve to Expansions Fic. 590. — ARRANGEMENT OF VAPOR CoMPRESSION REFRIGERATING MACHINE. horizontal type. The main discharge line from the compressor, carrying the hot high-pressure gas, is connected to a so-called pressure tank, entering at the side. This gives the gas a rotary motion which serves to remove by centrifugal force any oil coming over from the compressor. Some type of oil separator is a neces- sity to prevent the coating by oil of the condenser coils, which would seriously decrease the efficiency of heat transfer. The gas then passes through the hot-gas line, which makes a loop, and enters a header connected with the bottom coils of the condenser. The purpose of the loop is to prevent liquid NH; from running down into the pressure tank if the compressor should be shut * Reproduced from an article by F. E. Matthews in Power, Sept. 29, 1910. MECHANICAL REFRIGERATION 1005 down. The type of condenser here used is the atmospheric, the hot gas passing from the bottom coils toward the top, while water is trickled down from above over the outside of the coils. As the NH; gas liquefies, it is carried out of the coils by smaller drip pipes connected to a common liquid header. The pipe from this header should rise in a small loop, to keep the header always full of liquid and to prevent gas from entering the liquid line. The liquid line leads down to the liquid tank. If gas should come down this line, it may be led back to the condenser by means of the equalizer line shown. From the liquid tank or receiver the liquid NH; next flows to the expansion valve. This in most cases is nothing but a valve, the opening of which can be readily controlled to any desired size. The pressure on the liquid, in passing this valve, is suddenly reduced from 150-200 lbs. to say 20 lbs. per square inch. This of course causes immediately a partial vaporization, but, since it takes time to supply to each pound of liquid NH; the total latent heat of vaporization required (about 550 B.t.u. in the ordinary case), the vaporization is by no means instantaneously completed, as is often supposed. The vaporization is completed in the expan- sion coils, the heat in this case coming from a room to be cooled. The vapor is returned through a return valve and through the suction line to the compressor, passing on its way a scale trap in- tended to prevent any scale forming in the pipe system from being carried over into the compressor. Between the liquid receiver and the expansion valve there is usually placed a side branch supplied with a valve. This serves as a charging connection, the ammonia drum containing liquid NH; being connected at this point and as much ammonia being allowed to flow into the line as the system requires, as shown by control gauges on the gauge board. There is a small pipe line running from the liquid receiver to the suction side of the compressor (in the figure called “ Expan- sion Line to the Compressor’’). This line is furnished with an expansion valve through which cold gas may be supplied to pre- vent undue heating of compressor on starting or when the return gas is not cold enough for satisfactory operation. The compressor is also often furnished with by-passes and pump-out lines, by means of which the compressor may reverse its operation, taking NH3 1006 EXPERIMENTAL ENGINEERING from the condenser and forcing it into the expansion coils, for the purpose of pumping out parts of the system when repairs become necessary. Commercial plants show numerous modifications in construc- tion, but not in principle, from the features above described. Compressors are built single- or double-acting, horizontal and ver- tical. A favorite combination is a pair of single-acting vertical Fic. 591. — VaPor CoMPRESSION REFRIGERATING MACHINE. compressor cylinders operated by a horizontal Corliss engine con- nected to the same shaft, as in Fig. 591. The tendency to-day is toward single-acting compressors with the suction valve located in the piston and with poppet-lift discharge valves in the head. Some builders construct the head so that it may be bodily lifted by the piston against the resistance of springs (see Fig. 592). In single-acting compressors, the suction end of the cylinder is always MECHANICAL REFRIGERATION 1007 under suction pressure only. The stufliing box, through which the piston rod passes, is therefore called upon to hold tight only against this pressure, and leakage at this point is materially reduced. One of the most important features of compressor-cylinder design is the attainment of the smallest possible clearance, to decrease the amount of gas remaining at the end of the stroke. If this matter is not taken care of, there will be a large amount of re- expansion with consequent loss of compressor capacity (low volumetric efficiency). Condensers may be of three types: the submerged coil, the at- mospheric, and the double or concentric. In the first the or- dinary coil is placed in a tank of water, the water being con- tinuously circulated. | Where water is expensive, the atmos- pheric type or the concentric type is used. The former of these is shown in Fig. 590. In this condenser the use of the counter-current principle, in con- nection with the fact that a considerable part of the finely divided water is evaporated (the Fic. 592. — Cvi1npER or ComPRESsION heat for the latter process com- REFRIGERATING MACHINE, SHOWING ing from the NHs), makes this pa Secs oF, Eeneeane type more efficient than the sub- merged coil type. The most efficient type is probably the double or concentric condenser. In this condenser each pipe element con- sists of an outer and an inner tube. The cooling water is circulated through the inner tube, while the NH; fills the annular space. Thus cooling is done both by water on the inner surface and by air surrounding the outer pipe. The cooling system may be the direct or the indirect or brine system. The former is shown in Fig. s90, the cold gas being circulated ey 1008 EXPERIMENTAL ENGINEERING through pipes in the room to be used. If, however, an ammonia leak would do damage in the cold-storage room, the indirect system is used, in which some other liquid, usually brine on account of its low freezing point, is cooled by the ammonia and circulated for cooling purposes instead of the ammonia. One type of brine cooler is the submerged coil cooler, where the ammonia-expansion coils are immersed in a brine tank, the cold brine being pumped from the bottom, circulated, and returned warm at the top. The concentric pipe cooler is rather more convenient, however, and is very largely used. The brine flows in the inside pipe, while the expanding ammonia is in the outer one. The principle of counter- current flow is used in the concentric pipe to get the maximum possible heat exchange. 432. Ice Making. — There are three systems of ice making in use: the can, the plate, and the cell system. Only the first two, however, are of any importance in this country. In the cansystem, tapered galvanized-iron cans of the size of ice cake desired are filled with water and placed in a brine tank through which pass the pipes circulating the cold brine from the cooler. The tem- perature of the brine in the tank is usually kept at about 14° F. The time required for freezing depends of course upon the size of the cake, a can 8” X 8” X 31” requiring about 20 hours’ immer- sion, forming 50 lbs. of ice, while one 11’ X 22’” X 44” requires about 60 hours, the ice weighing about 400 lbs. After the water is frozen, the cans are hoisted out of the tank, and the ice is loos- ened by steam. The economy of this system depends of course upon conditions of operation and grade of machinery used. With a head pressure of 190 lbs., a suction pressure of 15 lbs., and con- densing water at 70°, Professor Denton estimates that the average- economy figures should be about 6 lbs. of ice per pound of coal used. In the plate system, plates through which the freezing solution circulates are immersed in a tank of water. The water next to the surface of the plate freezes, and the thickness of the ice in- creases with time. After the desired thickness is reached the plate, with the ice attached, is lifted out of the tank, the ice being thawed off by passing hot gas or brine through the plate coils. It is not common to place the plates so close together that the ice MECHANICAL REFRIGERATION 100g formed on the adjacent plates will meet, as the core so formed is usually ice of poor quality. Good practice in the use of the plate system should show an economy of from ro to 12 lbs. of ice per pound of coal. The cell system is a modification of the plate system. The water is placed in cells constructed of hollow walls through which the freezing solution is circulated. This system is not in use in this country. As far as the quality of the water required for ice making is concerned, it is necessary, unless distilled water is used, to agitate the water during freezing to free it from air, if clear ice is desired. In any case, of course the water should be as pure as possible, and hence the extended use of distilled water. The preference shown for clear ice is largely sentimental; for the opaque ice, which results if the water is neither agitated nor distilled, is fully as satisfactory for most ordinary cooling purposes as clear ice, provided the water is pure, and is certainly cheaper to make. 433- Properties of Brine Used for Cooling. — Two kinds of brine are in use, —calcium-chloride and sodium-chloride brine. The addition of either chemical to water lowers the freezing point of the latter. Naturally the brine is made of such strength that its freezing point is somewhat below the lowest temperatures of opera- tion. The brine tables in the Appendix* show that for the same strength of brine, as measured by the per cent by weight of the chemical contained in the water, CaCl, brine shows a much lower freezing point than NaCl brine. It is therefore easier to obtain a low freezing point brine by the use of CaCh. Sodium brine, if very strong, shows a tendency to deposit salt in the coils, which may seriously interfere with operation. It also strongly rusts any iron parts with which it comes in contact, a disadvantage not possessed by calcium brine. The specific heat of calcium brine is higher than that of sodium brine of the same strength, which is another advantage, as less of the brine needs to be circu- lated. Thus, although calcium brine costs somewhat more than sodium brine, the former is generally used and preferred. A 20 per cent solution is commonly employed. * Taken from H. Williams’ ‘‘ Mechanical Refrigeration.” IOIO EXPERIMENTAL ENGINEERING The strength of brine is best expressed on the ordinary specific- gravity scale, using a hydrometer. In practice, an instrument called a salometer or salinometer is often employed for measuring strength. This instrument reads o in clear water and the strength of brine is indicated by a reading in degrees between o and too. It is stated by some authorities that the roo” mark corresponds to the saturated solution, but existing brine tables do not quite agree on this; hence the statement above, — to use specific gravity to avoid errors. 434. Insulation. — With the extended application of cold-storage work, the proper insulation of cooling rooms has become one of the most important questions of refrigeration practice. It must be evident that, once products have been cooled to the tempera- ture desired, it is merely necessary to supply enough refrigeration to make up the heat gain from without to maintain that tempera- ture. The heat gain is less, the greater the efficiency of the insu- lating material. The materials used are hair felt, mineral wool, different varieties of cork products, rock wool, wood shavings, etc., used in combina- tion with wood, cement, masonry, and air spaces. Dead air is a good nonconductor, but a simple air space, unless of exactly the proper width, may have set up in it down-currents on the cold surface and up-currents on the outside warm surface, favoring convection. It is therefore the common practice to break up the air space by filling it with some porous material, to form an in- finite number of small dead-air spaces, effectually preventing the setting up of any air circulation. Too small air spaces, resulting from material too tightly packed, may, however, again favor the conduction of heat across. Insulating material should be mois- ture-proof, if possible, and at least slow-burning. For the method of constructing nonconductive walls, see any good book on Re- frigeration.* If a block of any material is exposed to a certain temperature * Lorenz-Pope-Haven-Dean, Modern Refrigerating Machinery, gives a number of examples. A good discussion is contained also in “ Refrigeration, Cold Storage, and Ice Making,” by Wallis-Taylor. See also Géttsche, Die Kaltemaschinen und ihre Anlagen. MECHANICAL REFRIGERATION IOII on one side and to another lower temperature on the other side, there will be a transfer of heat from the former to the latter. side, which transfer is a function of the temperature difference of the kind of material and of the thickness used. The number of heat units that will be so transferred per degree difference of tempera- ture per hour and for 1 in. in thickness is called the coefficient of the material. It should be noted that this heat loss is also largely a function of the velocity of air on both faces of the material. The constants given in the following table for some of the well- known material holds for still air only. They increase if there are air currents over either face. COEFFICIENT OF HEAT TRANSMISSION. rt Sq. Fr., 1” THickness, 1° F. DIFFERENCE OF Temp., 1 Hour. Material. ee Material. a Air: stilleecs ncaeasaaees vee 30 Corks ey ibee se ese ee 1.0-1.8 ASDEStOS! wiichis Sua tng. e aneaene 25 1.20 Papery.<.4 cisvacns we ad bd? 28 COROT. hosigere.ned au Gdnkieecitins 28 SANG ss cecduedatesces bad 2.1-3.0 GLASS ins cove aa neiesne Honea? 3-5-5.2 Shavings............ +45-.65 Hatt: telt: taccconpaaeengeses a .5§0-2.1 Mineral wool......... .5--7 Wood, average............... I.10 Masonry, brick....... 5.0 Wood ashes... ........-..--4. 45 Masonry, stone...... 3h, ' Kieselgur (infusorial earth). ... .50 Coal ashes.......... ei Coke, pulverized............. 1.20 : There are several methods of testing insulation. One of the most common is to erect a length of steam piping on a slight slant and to furnish to the higher end of the pipe steam under any given pressure and quality. At the lower end a collector for the con- densed steam is arranged. This may be simply constructed of a vertical length of pipe furnished with a gauge glass and fittings at the side. The steam condensing flows into the collector by gravity and is drawn off and weighed from time to time, a nearly constant level being maintained in the collector. Since the con- densate drawn off is under the pressure of the steam, and would consequently largely flash into steam if this pressure is suddenly released, it is necessary to draw off into cold water. The quantity of heat radiated from the pipe in a given.time is then computed IO12 EXPERIMENTAL ENGINEERING from the weight of the condensate in the same time multiplied by the quality of the steam and by the heat of vaporization of the steam for the given pressure. The other important item in this test is the temperature difference. This should strictly be taken as the difference between the temperatures of the inner and the outer wall skin and not of the usually gaseous media adjacent to these walls. In this case the temperature of the steam under the given pressure may be fairly taken as the temperature of the inner wall. To get that of the outer wall would require the use of a resistance thermometer. Instead of this, the common practice is to suspend thermometers at several points in the air close to the pipe but not in contact, and to assume the temperature difference equal to the steam temperature minus the average air temperature so found. The common practice is to first test the pipe bare and then again when covered with the insulation to be tested. In each case the quantity of heat transmitted per square foot of pipe sur- face per degree difference of temperature per hour is computed. If Q, represents this quantity for the bare pipe and Q, the quan- tity for the covered pipe, then the efficiency of the insulation is E= Qs c, Qs Note that Q, is not the coefficient spoken of above, because the definition of this coefficient requires that the insulation be 1 in. thick. It should be stated that it will not do to divide Q, by the thickness of the insulation to obtain the coefficient, for the reason that the efficiency of insulation does not vary directly with the thickness. Referring more specifically to the kind of insulation used to protect cooling compartments, another method of testing would be to determine the electrical energy input to keep a compartment at a certain temperature with a given temperature outside of the compartment. Depending upon circumstances, a number of other methods will suggest themselves. 435. The Ideal Vapor-compression Refrigerating Cycle. — The ideal cycle for a vapor-compression machine is the Carnot. Start- ing with the liquid NHs and leaving the condenser at an absolute MECHANICAL REFRIGERATION 1013 temperature 7}, we locate point A on the liquid line of the entropy diagram, Fig. 593. This liquid next enters the expansion cylinder, vaporization taking place in this cylinder until the lower absolute temperature T> is reached, locating point B. The vaporization is only in part completed, the quality of the mixture after leaving / an Va- porization is continued in the refrigerator (really the heater as the expansion cylinder being represented by the ratio Z * ‘ mw 7, 0 D} ct Cl wee oO > oy e G’ @-----— Fic. 593. — IDEAL VAPOR COMPRESSION REFRIGERATING CYCLE. far as the refrigerating agent is concerned). At the end of the refrigerator action and by the time the compressor is reached, the vapor may be wet saturated, as indicated by any point between B and C, dry saturated at C, or superheated as indicated at C”. What the end condition of the vapor is depends largely upon the amount of refrigerating medium in circulation. At C’ the quality is such that the ensuing adiabatic compression C’D’ (wet compres- sion) to the temperature 7; just renders the vapor saturated. This is indicated by D’. After compression the hot high-pressure vapor is then sent to the condenser, in which it is assumed that IOI4 EXPERIMENTAL ENGINEERING heat is abstracted to the extent that liquefaction is just completed. This process is indicated by line D’A, which completes the cycle. If the refrigerator action is stopped so that the vapor quality is fe even less than Bee the complete ideal cycle, if carried out as BIC before, will be represented by the area ABC’’D’’A: If vapor- ization is continued to dryness at C, the ensuing adiabatic com- pression will superheat the vapor, the process being shown by line CD (dry compression). The superheated vapor is then cooled int the condenser, first at constant pressure along DD’, and then liquefied along D’A. Finally, if the action of the refrigerator is such as to superheat the vapor at the inlet to the compressor, the compression will proceed along a line C’D”, and the complete ideal cycle is the area A BCC” D"D’A.* 436. The Ideal Coefficient of Performance. — It will be noted by inspection that the ideal cycle outlined in the previous article is an ideal heat-engine cycle (Carnot) reversed. In the heat-engine cycle, a certain quantity of heat Q1, represented by the rectangle AG in Fig. 593, is taken in along the line AD’. A certain other quantity of heat Q2, represented by the rectangle BG, is discharged along the line C’B. The external work W done is represented by the rectangle AC’, and we have of course W = Qi — Q. (1) The same reasoning may also be applied to the other cases indi- cated in Fig. 593. In the refrigerating cycle, we remove from the body to be cooled the heat Q2, equivalent to rectangle BG; in the compressor we do a certain amount of work W, equivalent to rectangle AC’, and discharge a certain amount of heat Q,, equivalent to rectangle AG, into the condenser. If we define efficiency as the ratio of the useful effect of an opera- tion to the effort or energy expended to gain this effect, we evi- dently will have for the heat engine : a O-@ N= Efficiency = a = O; T, , (2) * ABCDD'A and ABCC’D"D’A are not Carnot cycles. MECHANICAL REFRIGERATION IOI5 and for the refrigerating machine Efficiency = & = on = an (3) The latter expression is nearly always greater than unity, and can in a certain sense only be looked upon as an “ efficiency.” What the factor really expresses is the number of times the heat W expended in compressor work is regained in cooling effect, and the term ‘‘zdeal coefficient of performance” instead of “efficiency” Qa, Ww The last form of the expression for the ideal coefficient of per- formance in Eq. 3 will serve to point out one or two important facts with reference to efficiency of operation. T> is the tempera- ture of the cooler, while 7,.is that of the condenser. By inspec- tion of the expression we note the following: (1) For any given T>, the lower T, the higher will be the coefficient of performance; (2) for any given 7, the higher T. the higher the coefficient; (3) in general, the nearer to- gether. 7, and 72, the better 480° the performance. The entropy Tiwi’ diagram also shows these facts | very clearly. Thus in Fig. 594, let the condenser temperature be fixed at T,; = 460+ 70 = 530° F. abs., and let the tem- perature of the cold body be in case (a) — 10° (= 450° abs.); case (b), o° (= 460° abs.); and case (c), 20° (= 480° abs.). For the same amount of energy W expended (shaded areas equal), the heat Q2 removed is in case (a) equal to rectangle AB, in case (0) to rectangle A’B, and in case (c) to rectangle AB. The ideal coefficients of performance are 5.6, 6.6, and 9.6 respectively. Or, conversely, for the same quantity Q2 of heat to be removed, it requires a greater expenditure of energy W to do this between — 10° and 7o° than between 20° and 70°, as will be clear from a study of an entropy diagram applying to the two cases. Finally, the ideal coefficient is therefore commonly used for the ratio 530°abs, 1016 EXPERIMENTAL ENGINEERING of performance depends only upon absolute temperature and is therefore independent of the working medium used. 437. The Actual Vapor-compression Refrigerating Cycle.—In an actual refrigerating machine the cycle of operation fails to meet the conditions of complete reversibility, as outlined in Art. 436, and for that reason the actual coefficient of performance is less than in the ideal case. To see the causes for this, it will be in- structive to follow the refrigerating medium around an actual cycle. The study is best made on the basis of entropy diagram, and, since in the majority of cases in actual operation the vapor is superheated at the suction valve to the compressor, this will be the only case considered in detail. Starting with the liquid in the condition defined by the point A on the entropy diagram, Fig. 595, this liquid is next allowed to pass e wt D’ Dp” --—------------9g g NaHS a See ae Fic. 595.— ACTUAL Vapor COMPRESSION REFRIGERATING CYCLE. through the expansion valve, which results in a lowering of pres- sure. We have in this process the first deviation from the ideal cycle, since an expansion valve is substituted for the expansion cylinder. The expansion is largely unresisted, the process is no MECHANICAL REFRIGERATION IO1l7 longer adiabatic, and is irreversible. The reduction of the pressure from that existing at A to that corresponding to the temperature T, results in a partial vaporization of the liquid as it passes the valve. The problem is to locate the point B. If the temperature Tz is measured at a certain distance beyond the expansion valve, so that the kinetic energy changes that accompany the passing of the liquid through the valve have again disappeared, it may be fairly assumed, neglecting radiation, that the process up to this point is one of constant heat. This means that the area AF’”’F’B’A is equal to the area B’BFF’B’, which at once locates the point B, since the first area and the distance B’F’ are known. Mathemati- cally, the problem may also be solved as follows: The total heat content in the vapor at A is assumed the same as the total heat content at B. Hence Lara + J4 = Xgryt Qp. (4) But at A, x =o, therefore, solving for the quality of the mixture at B, Ga — 4 ty = fA iB, (5) 'B ‘ . BB. : ae Xp is the ratio => in the diagram. The rest of the vaporization BC is carried on in the cooler as before, except that there is some loss of effective cooling due to the heat influx in the piping leading to and from the cooler. It is assumed that the vapor is superheated to C’’, as determined by a thermometer in the suction inlet to the compressor. For the fixing of point C” we have the following data: Entropy at point C can be found directly from the NH; vapor table accord- ing to the pressure, or temperature 72. The temperature at C” is found directly by thermometer in the suction pipe just ahead of the compressor; call it T;. The added entropy due to super- heat is then = Cp loge 5, in which Cp is the mean specific heat 2 of the superheated vapor between T; and 73. The uncertainty of the computations lies in the fact that very little is known about the value of Cp. The data available all apparently apply to 1018 EXPERIMENTAL ENGINEERING atmospheric pressure. Landoldt and Bérnstein give the following: Temp. range, deg. Ciaccceseeeves 237900 27-200 Opec canes 5202 - 5350 It is probable that Cp varies for NH3, with temperature and pres- sure, in a similar manner as for steam, but it is also probable that the changes are not as pronounced. At any rate, in the present state of our knowledge, the best that can be done is to assume Cp constant and equal to 0.53. In passing the inlet valve to the compressor there is a certain loss of pressure due to wire drawing. The extent of this can be found by comparing the suction pressures just ahead of the inlet valve with those on the compressor-indicator diagrams. Consid- ering this a constant-heat change, the process can be indicated on the entropy diagram by the line C’C’”. It should be understood that this change is so small ordinarily as to be negligible; it is much exaggerated in Fig. 595. To construct the compression line C’’”’D’” in the entropy dia- gram, it will be necessary to turn to the indicator card from the compressor. The method of computing temperatures along the compression line of the indicator card will be outlined in Art. 440. Assuming that for any given pressure the saturation temperature is T, and the temperature on the compression line is T,, the total entropy of the superheated vapor at the pressure chosen and the temperature 7, will be Prtotal as Psat. at T, a Cp log. 7 (6) By aid of this equation a number of points may be located to determine line C’’’D’”’ in the entropy diagram. At D’”, the vapor is next forced through the discharge valve, the action being accompanied by a pressure drop, which may be represented by the constant-heat change D’’’D’. In the con- denser side of the system, the vapor is next cooled at constant pressure along line D’’D’ to saturation at D’; the latent heat is removed along D’A. If the condenser action continues beyond that, supercooling the liquid, this action may be represented by a line AA’. In that case the action in the expansion valve will “MECHANICAL REFRIGERATION IOIQ first be to retrace line A’A, and the cycle then starts from A, as before. In the analysis above made, the actions along C’C’” and along D'’D" are much exaggerated. The compression line C’”D’” slopes generally to the left, as shown, on account of heat loss to the jacket of the compressor. The amount of the deviation from the adia- batic C”’’D, is of course a function of the effectiveness of cooling. It will in general be found that the points C’” and D” are in a vertical line, or very nearly so, and that the area OD’’"D” is so nearly equal to area OC’’C’” that the entire analysis may be short- ened by simply drawing in the line C’D”. The effect of this simplification upon the area of the entropy diagram is generally negligible. The entropy analysis for the case of vapor wet at the suction valve is very difficult to carry out because of the practical impos- sibility of determining the quality of the vapor at that point. 438. The Actual Coefficient of Performance and the Real Effi- ciency of the Actual Refrigeration Process. — The total refrig- eration effect shown by the entropy diagram, Fig. 595, assuming that an expansion cylinder is used, is equivalent to the area B’'CC"G"F”’. In the real case, this effect is reduced by the fol- lowing items: (a) The loss due to the substitution of an expansion valve for the expansion cylinder. This is measured by the area B’ BFF”. (b) The useless refrigeration in the piping leading from the expansion valve to the cooler. This may be represented by an area BB’’F’’F, In any practical case this can probably not be directly determined, for its effect would simply be to change the quality of the vapor, and we have no direct means of determining the latter. (c) The useless refrigeration in the piping leading from the cooler to the suction valve of the compressor. This may again be represented by an area HC”G’H’, and is susceptible of direct measurement if the vapor leaves the cooler superheated. The net refrigeration shown by the diagram is then represented by the area B’’CHH’F'’B’”. Call this amount Qnet. The work W expehded is in this case equal to the area ABCC” DD’ A, 1020 EXPERIMENTAL ENGINEERING and, by definition, the coefficient of performance as per entropy Qnet, Ww Now the quantity Qnet is not the useful refrigerating effect. It would be if in the cooler all of the heat given to the NH; came from. useful refrigeration. In practically every case, however, there are radiation and conduction of heat serving no useful pur- pose. Let the actual useful refrigeration be represented by Qs, and the heat added through radiation or conduction in the cooler diagram is then = by Oy then Quet = Os + Qs. (7) Q; may be directly determined. In case brine is used, for instance, Qs = Gc, (ty = 7) B.t.u., (8) in which G = weight of brine in circulation per pound of NHs3; _ C, = mean specific heat of brine; t; = temperature of brine entering cooler; t, = temperature of brine leaving cooler. The compressor work W is the same as before, and the actual coefficient of performance is therefore ee The ratio a may be net regarded as the efficiency of the cooler. In practice the actual coefficient of performance is computed from the useful refrigeration effect and the heat equivalent of the compressor work in a given time. If we define the real efficiency of the refrigeration process as the ratio of the actual useful refrigerating effect to that theoretically obtainable for any given work W in the compressor, we will have in this case ea ia Equivalent of - (9) area B’CC"G"F"" In case the vapor is not superheated at any stage of the process, 2 the ideal coefficient of performance is the refrigeration Ee effect will be = —22 W, and the To Real efficiency = — = Os — ty. (10) 2 ti MECHANICAL REFRIGERATION 1021 439. Wet and Dry Compression.—The meaning of these terms has already been outlined in Art. 435. As far as relative efficiency of the two systems of operation is concerned, this has to be consid- ered from a practical as well as theoretical standpoint. In theory, referring to Fig. 593, the work expended in wet compression is area ABC’D’, the useful effect is area BC’'GF. In the dry com- pression system, starting at C, the work done is ABCDD’4A, the useful effect is BCG’F. The work area is increased by C’'CDD’, the useful effect by area C’CG’G. It will at once be seen that, for the two processes to have the same efficiency, it would have been necessary to increase the work area in dry compression only by the area D'C’CR. The extra area DD’R is therefore a measure of the loss in the dry compression system as compared with the wet. Even in theory this loss is, however, so small as to make no practical difference. It increases, of course, with the degree of superheat in the vapor at the suction valve, while for any com- pression starting between C’ and C the loss is less. In practice it is common in even the wet system to choose a point between C and C’ so that the vapor is slightly superheated at the end of compression. Any other condition at this point would seriously cut down the refrigeration effect. As far as the practical merits of the two systems of operation are concerned, there has been much controversy that cannot be entered into here. Ewing comes to the conclusion that, everything considered, there is little difference in the efficiency either on theoretical or on prac- tical grounds. 440. The Compressor Indicator Diagram. Vol- , ‘ Fic. 596. — Compressor InpicaTor DIAGRAM, umetric Efficiency.— REFRIGERATING MACHINE. The general shape of the compressor diagram is shown in Fig. 596. AB is the reéxpan- sion line, if there is vapor left in the clearance spaces at the end of the compressor stroke. From B to C the compressor draws 1022 EXPERIMENTAL ENGINEERING vapor from the suction pipe. The suction pressure p, is less than the cooler pressure Peooier by the amount of wire drawing in the suction valve. Both on account of reéxpansion and the heating of the incoming vapor, the weight of charge per stroke is less than the piston displacement calls for at the pressure and temperature existing just ahead of the suction valve. The ratio of the actual charge weight per stroke to the weight computed on the basis of piston displacement for the pressure and temperature just ahead of the suction valve may be regarded as the true volumetric effi- ciency E,, of the compressor cylinder. The determination of this efficiency requires a knowledge of the amount of vapor circulated. The apparent volumetric efficiency E,, is determined directly from the card, for it is the ratio of the volume V, to the volume V;. In the case of very small machines, F,, may be as low as 0.6 and does not go above 0.8. For medium sized machines it may be from 0.8 to 0.9, and in large machines from 0.9 to 0.98.* The nature of the compression line CD depends upon whether wet or dry compression is used. The pressure p, at D is greater than the pressure in the condenser by the amount required to overcome the valve resistance. There are three assumptions possible as to the state of the vapor at the point C: (a) Vapor wet at C. The compression line may then be as- sumed to follow the adiabatic for wet vapors. It has been shown that this type of adiabatic for NH; can be closely represented theo- retically by the equation pV" = constant. Starting at point C, we can now draw in the theoretical compres- sion line, and get some idea of the heat interchanges going on during compression by comparing this with the actual compres- sion curve. (b) Vapor superheated at C. In this case the theoretical com- tession adiabatic is closely enough represented by the equation pV'*8 = constant. (c) Vapor dry and saturated at C. In this case superheat im- * Déderlein, Priifung & Berechnung ausgefiihrter Ammoniak-Kompression Kalte- maschinen. MECHANICAL REFRIGERATION 1023 mediately takes place theoretically, and the case is then the same as (0). From the amount of NH; in the cylinder per cycle (consisting of the sum of the NH; taken from the suction pipe per stroke plus the vapor, if any, caught in clearance), it is possible to construct a saturation curve by aid of the specific volumes, by the same Wet Compression- Vapor Wet throughout (a) (b) Dry Compression-Vapor dry Dry Compression: Vapor at C-Superheated at D Superheated at C and D (c) Fic. 597.—a@ To d. method as for steam. The location that this curve may have relative to the compression line is indicated in Fig. 597a¢tod. In case the compression line shows wet vapor, the quality of that vapor at any point may be computed as in the case of steam; ‘ Ve that is, in Fig. 597a, quality at x = v. If the vapor is superheated, the assumption that the vapor acts as a gas will have to be used in the present state of our knowl- edge; that is, in Fig. 597d, the absolute temperature of the vapor at point y may be found from the equation ty Va T, Va in which T, is the saturation temperature at the pressure chosen. 1024 EXPERIMENTAL ENGINEERING 441. The Weight of NH; in Circulation. — The amount of NH; in circulation may be determined experimentally or computed approximately. It is not a necessary item for the computation of the amount of refrigeration or the energy expended, is there- fore not required to determine the coefficient of performance, and is in consequence not often determined experimentally. The direct determination of weight is made on the liquid (high- pressure) side of the machine. It has been done by using a piston meter, or other suitable type, and by interposing weighing tanks on scales between the condenser and the receiver. The former method was used by J. E. Denton in a test on a 75-ton machine, the test being reported in Trans. A.S. M. E., Vol. XII, 1891. The meter used was connected to the outlet of the condenser and was a #-inch Worthington piston meter. It is stated that the valves of this meter were specially made of wrought steel, and that a few extra bolts were used in the top and bottom joints. The meter was tested for tightness against 250 lbs. of air pressure under water. It gave no trouble during a month’s use, except that the packing around the dial arbor had to be renewed. When weighing tanks on scales are used, it is customary to use two connected in parallel in order to obtain a continuous reading. Each is fitted with valves on the inlet and outlet, so that each may be cut out of the system at will, and with a gauge glass so that the level of the liquid NH; may be readily determined. The tanks are connected by piping, on the one side to the condenser, on the other to the receiver, of such length that there is sufficient flexi- bility to give a satisfactory reading of difference on the scale. In the testing plant at Sibley College, the tanks are submerged in water to maintain a constant temperature, but this is probably not necessary. In using this weighing system, suppose that inlet valve to tank A and the outlet valve to tank B are closed, while the other valves are open. This means that tank A is discharging into the receiver while tank B is filling from the condenser. When tank B is filled, A will be down; then the connections are changed. The gross and tare weights recorded for each tank of course deter- mine the total weight passing. A single tank may be made to do service, except that a rate of MECHANICAL REFRIGERATION T1025 flow rather than a continuous determination is made. In this case, with the outlet valve closed, the tank is allowed to fill up from the condenser. The inlet valve is then closed just long enough to take the gross weight, the outlet valve opened wide to quickly drain the tank contents into the receiver and to obtain the new tare weight with the outlet valve closed. The inlet valve is then opened and the operation repeated. It is essential, in any direct system of weighing, to see that the amount of liquid present in any location in which liquid may gather is exactly the same in the end as at the beginning of the test. If this condition cannot be reached, proper allowances must be made. Where a volume measurement of liquid NH; is made, the density must of course be known to obtain the weight. This is given by Denton* as follows: Temp. °F. C3 14 23 32 4I 50 59 68 86 Density, Distilled Water =1.00 = 62.43 + .731 .6492 .6429 .6364 .6298 .6230 .616 .6089 .6018 Ibs. per cu. ft. wy Several more or less approximate methods of computation may be used to determine the amount of NH; in circulation. The common way is to start with the apparent volumetric effi- ciency of the compressor (see Art. 440). If this is represented by £,, and the actual piston displacement is V cu. ft. per stroke, the effective displacement per stroke will be #,,V cu. ft. If we let the volume of 1 lb. of the vapor at the end of the suction stroke be v cu. ft. per Ib. and N the number of compressor cycles per hour, the weight of NH; in circulation per hour will evidently be = FeeT ths, (a2) The uncertain factor in the computation is the quality of the vapor at the end of the suction stroke, if wet compression is used, or the temperature at the same point, if dry compression is em- ployed. Both affect the value of v. It is certain that the vapor * Trans. A.S.M.E., Vol. XII, 1891. 1026 EXPERIMENTAL ENGINEERING is drier (or more highly superheated) at the end of the suction stroke than it is ahead of the suction valve, owing to the heating effect of the cylinder walls. Both DeVolson Wood* and J. E. Denton} have made compu- tations on the latter point for superheated vapor. The former, for a case in which the suction pressure was 28.9 lbs., the suction temperature 57.7°, and the outlet temperature 116.1°, assumes a temperature at the end of suction equal to 105°. Zeu- ner’s equation for the specific volume of saturated or superheated NH; vapor is oe 0.667 T ; 4.9 p> Ga) in which T = absolute temperature and p = absolute pressure in pounds per square inch. Using the values T = 460 + 105 = 565° and p = 28.9 lbs., this equation gives v = 12.4 cu. ft. per Jb. Using the values T = 460 + 57.7 = 517.7° and p = 28.9 lbs., the value of v = 11.4 cu. ft. per lb. If the latter value is used, as is often done, the weight of NH; determined is too large by 12.4 — 11.4 = 8.1 per cent. 12.4 oe In the test reported by Denton, in which the NH; was actually metered, the computation on the basis of volumetric efficiency and specific volume at suction pressure and temperature showed a weight of NH; in circulation 21.4 per cent greater than the actual. Evidently there must have been considerable heating of the gas as it entered the cylinder, and Denton computed that the tempera- ture at the end of the suction stroke must have been 80° instead of 14°, as shown just ahead of the suction valve. The suction pressure was in this case 42 lbs. abs. It will be evident from the above that everything depends upon the proper assumption of temperature at the end of the suction stroke. If the vapor at the end of the suction stroke is still wet, the problem is even more difficult. In that case, Déderlein (see reference, p. 1022) makes the assumption that the vapor is just * Trans. A.S.M.E., Vol. XI, 1890, p. 833. { Trans. A.S.M.E., Vol. XII, 1891, p. 372. MECHANICAL REFRIGERATION 1027 dry at the end of compression. Assuming that the process is isentropic, he computes the quality at suction pressure on the card from the relation To Th bor + “oT = op + “Dp (13) in which ¢, and ¢p, are the entropies of the liquid at C’ and D’ respectively, in Fig. 593. %q and xp, are the qualities of the vapor at C’ and D’, and eo rep- resents the entropy of the dry vapor. By assumption, %p, = 1.0, and since the absolute pressures at C’ and D’ are known, the other quantities may be obtained from the NH; table, and xg, may be computed. The volume per pound of the vapor then follows from the relation v=au+o=x(0' —o) — o = approx. xv’, (14) in which « = quality of vapor. “ = increase in volume during vaporization at the pres- sure under consideration. = specific volume of the liquid at the same pressure. v’ = specific volume of the dry and saturated vapor at the same pressure, obtained directly from vapor tables. This value of v is then substituted in Eq. (11). ‘ The computation above outlined requires, for the case of super- heated vapor, an estimate of the temperature at C’’, Fig. 593, while that for the wet vapor determines the quality at C’, on the assump- tion that D’ is on the saturation line. As an alternative method, it is possible to obtain an approximation to the weight of NH; in circulation by aid of the entropy diagram of the real cycle. The area of this diagram represents the work input per pound of NH. If, therefore, we divide the heat equivalent of the actual compressor horse-power per hour (= Comp. H.P. X 2545) by this heat input per pound of NH, the result will be the weight of NHs in circula- tion per hour. This method holds for the vapor under any condi- tion of quality or superheat. 442. Capacity and Rating of Refrigerating Machines. — The amount of heat actually removed from the cold body by a refrig- Q | 1028 EXPERIMENTAL ENGINEERING erating machine (in case brine circulation is used, equal to the weight of brine circulated per unit of time times range of tempera- ture of cooling times specific heat) is known as the cooling or refriger- ating effect. One measure of efficiency or economy would therefore be to state the cooling effect produced per compressor horse-power, or per steam horse-power, or per pound of coal used. The heat of fusion of ice, from ice at 32° to water at 32°, equals 144* B.t.u. Hence to freeze 1 ton of water under these conditions requires 2000 * 144 = 288,000 B.t.u. This quantity is sometimes called the unit of refrigeration. The cooling effect per day of 24 hours divided by the unit of refrigeration gives the so-called ice-melting capacity of the plant. The number of tons of ice-melting capacity is called the tonnage of the installation. Sometimes the ice-making capacity is spoken of. This term has no definite meaning, for in any given plant the quantity of ice that can be made in any given time depends upon the temperature of the water to be frozen and upon the temperature of the ice leaving the cooler. Assume, for instance, that the water has a tempera- ture at 60°, and that the ice is cooled to 20°. Taking the specific heat of ice at 0.5, this would mean heat removed per pound of water frozen = (60 — 32) + 144 + {0.5 X (32 — 20)}= 178 B.t.u. The ice-making capacity is therefore only 144 = 80.6 per cent of the ice-melting capacity. A secondary standard of economy also sometimes given in test reports is the amount of ice made per pound of fuel used. This is not definite for the reasons above mentioned and also because the quality of the coal differs from plant to plant. It cannot, therefore, be used as a general standard of comparison, and applies only to the plant in question. 443. Arrangements for Testing of Vapor-compression Refriger- ating Machines. { — As in the case of a steam plant, there may be a number of objects in view in the testing of a refrigerating plant. The main objects, of course, generally are the determination of * Different authorities give from 142 to 144 B.t.u. for this figure. } For a complete discussion of the testing of an absorption machine, see Trans. A.S.M.E., Vol. X, p. 792. MECHANICAL REFRIGERATION 1029 economy and capacity; but there are a number of secondary tests that may be made, such as for the efficiency of the cooler, the proper operation of the condenser, the action of the valves of the compressor, the efficiency of the compressor itself apart from the rest of the apparatus, etc. It will be assumed in what follows that a complete test for capacity and economy is to be made. Each compressor refrigerating plant consists of several very dis- tinct parts, on each of which certain measurements must be made. These are: the compressor with its motive power, the condenser, and the cooler or refrigerator. Compressor and Prime Mover.— The usual source of motive power for the compressor is a steam engine, commonly of the low- speed type. The arrangements necessary for the determination of the power developed (I.H.P.) are fully taken up in Chap. XVIII, to which the student is referred. The work done by the compressor (Compressor H.P.) is deter- mined directly by means of indicator cards. The indicators must be of special make, that is, of steel, since brass, the metal ordi- narily employed, is attacked by NH;. The indicator connections should be as short as possible, to reduce clearance space, and each indicator should be fitted with a special quick-acting valve. The indicator pistons should fit fairly tight, to prevent the escape of the disagreeable gas, but of course they must not be so tight as to affect the accuracy of the instrument. The driving mechanism used for the indicator depends altogether upon the type of machine, the points made in Chap. XV also governing this case. Other readings besides power determination required on the compressor are: (a) Quantity of jacket water, if a cooling jacket is used. (6) Temperatures of jacket water in and out. (c) Temperatures of NH; vapor just ahead of the suction valve and just beyond discharge valve. (d) Pressure of NH; vapor in the same places in which tempera- tures are measured. (e) Speed of compressor. . (f) Quantity of oil fed to cylinder, if that system of eliminating clearance is used. 1030 EXPERIMENTAL ENGINEERING (g) If possible, quantity of liquid NH; injected, if the wet system is used. The Condenser.—The readings on the condenser are the following: (a) Quantity of condensing water, best obtained by meter. (b) Temperature of condensing water, in and out. (c) Temperature of NH; vapor in and NH; liquid out. Between the cooler and the expansion valve is interposed the means for determining the quantity of NH; in circulation (see Art 441). The Cooler.— Readings required, assuming that brine circulation is used: (a) Quantity of brine in circulation, best obtained by meter. (b) Temperature of brine in and out of cooler. (c) Specific gravity of brine. (d) Temperature of NH; entering or leaving cooler. When a plant is to be tested for capacity and the conditions are such that the heat taken up by the brine in doing its normal work is not sufficient to heat back to the upper temperature, means must be provided to supply the extra heat. This can usually be done by immersing a part of the brine coil in water, which may be heated by steam. No account need be taken of the amount of heat so supplied. The log blanks, pages 1031 and 1032, for recording observed data were constructed primarily for the 15-ton York machine used at Sibley College, but show a general and concise arrangement of the readings necessary. The greatest difficulty to contend with in the making of an accurate test of a refrigerating plant consists in the fact that it is very difficult to be absolutely certain that all parts of the plant, particularly the cooler, contain the same amount of heat, esti- mated above some datum, at the end as at the beginning of the test. To reduce the possible error in this respect, two things are necessary: first, keep all temperatures the same as nearly as pos- sible; and second, prolong the test over a considerable period of time. The latter should never be less than 12 hours, and may preferably be several times that length. MECHANICAL REFRIGERATION = n n n a c. 9 a ch < ® ° ca ° ct a 3 ee 2 B x. @ a a 2 Dp ‘oe oe a a Sie) Ee) Ss eee lel ele ise eB | ele |e |e |g a F = ‘a wa a ‘ g wR A : Ri ; a3 a. ei! a4 oR a Se | ® a a ° 8 gS Io & 8 mares ° ° & 5 Gu By o Bl 3g p> “r9ye 2 8 | 2 AL “eruommy | Bo veAN “RIUOTIUY e 2 &| wyoef 25] wpef ‘aanssolg e ‘onqeieduay, ‘aimyrieduay, Leiiahe l.! kiadrpintee Bik GoaaAe aUENJoA |rrees coer seers egmmrog [octes ceeeseeeeee= -guanto Pa ae ee -amssolg Senn, spake ous srepaysg jocoy [ott ttepany fore ccs pony | praca ap Sbs ates ete siee fat latoie> seesaw ses Bere ee cee nee e ene e eee eee BoIV Japureiq 3 Iq Pariceniy QOGME Rabe eRe TS aqons teteteretsees saan BhiGe abet delay Owexd reyoureIq 9 GREG teen e eon aqons is “@ JepulyAD al Rafe e arene, wal winelio un. aw pysen “ee binee eal BE age “AY n yn & wo 3 pie tele le ye le 5 3 2 g 5 S @ Fy = o B EB a pleleiel [3 a a 5 A : 8 0 > : 3 g 8 s P ‘ainqyersdway, abse hin iges wep & 0 BOO hoo & » Vadis Saeed eee impel. eed ieee H Ray ee See | gece yoyoueiq |..... “+ -ra0rRIq ieee Papeete ayong *repurpsg ‘poy uowstg ‘dung oulg “SuljOV-apsUIg ‘yeoIaA “Iossaidui0d, euouMy “Buljoe-a]qnoq ‘[eyoezw0p ‘oUIsU T1e37S “£9 Wang unig Suypsasrafoy fo yay EXPERIMENTAL ENGINEERING 1032 duay, | ‘ssarg mg] ‘ur |-ang] ‘ur |amQ| ‘uz | yng | ‘ur ‘mo| ‘ar |‘3nQ] ‘ur |-3mQ] ‘uz | yng | ‘uy “Toe < . ‘oul, “8 Jaye, Jaye ai au eer “HN fas “HN yo “oulag, “HN ‘sung “HN Ros jo aumnjo,, Sauce “oUary, eo ‘ou, UIyS1a poe foe 70 WRPM | io Wasa ‘II “ON TOD “TON HD SIM ‘TI “ON TlOD ‘TON [109 ‘samnyeraduiay, “somyeraduay, ‘asuapuog tuomMy on ea Aiea SS Bs. hap ie sea ah Oa IR nd 0G SK HE RRR WSK 3. cieailsunsn Susie: Rete Shiga telah nde pease aes &q jing auryovyy Suypsasiafoy fo 4saZ MECHANICAL REFRIGERATION 1033 The frequency of taking readings depends upon conditions. Where these are fairly constant, half-hour readings are probably quite sufficient. Where this is not the case, the number of read- ings must be increased, but the matter must be left to the judg- ment of the testing engineer. 444. Computation of Results. — The forms on pages 1034 and 1035 contain the items of computation for a complete test. The first of these shows average pressures, temperatures, weights, etc., computed from observed data; the second contains the final results. In view of the explanations contained in previous articles in this chapter, but few of the items on the two forms need any further comment or recapitulation. Item (63). Compressor horse-power is computed from the com- pressor-indicator cards in exactly the same way as I.H.P. for a steam engine. Items (65) to (71). See Art. 440. Item (88). Mechanical efficiency of set = Them 03, Item 60 : Item 81 . ffi ao. Item (89). Actual coefficient of performance Tren 6; See Art. 438. : Item 81 Item (90.) Coefficient of performance of set = peace Item (g1). Theoretical coefficient of performance. See Art. 436. Item (92). Efficiency of refrigeration process = Actual coeffi- cient of performance + Ideal coefficient of performance. See Art. 438. Item (93). Tonnage. See Art. 442. 445. The Heat Balance for the Refrigeration Process. — This balance is established by following the refrigerating agent through the complete cycle, balancing the sum of all the amounts of heat received by the agent against the sum of the amounts of heat given up by it. 1034 Test of Refrigerating Plant built by EXPERIMENTAL ENGINEERING SIBLEY COLLEGE, CORNELL UNIVERSITY. AVERAGE DaTA, OBSERVED OR COMPUTED. rE. HoH I3. I4. I5. 16. 17. 18. 9. 20. ai. 22. 23; 24. 25. 20. 27. 28. 29. 30. AOS DI ON Aw Duration of test, hours......... Dimensions, Volumes, Etc. Diam. steam cyl., in............ Stroke, steam cyl.,in........... Diam. piston rod, steam cyl., in. . Area steam cyl., head, sq. in.... Area steam cyl., crank, sq. in... . Diam. compressor cyl. A, in... .. Diam. compressor cyl. B, in..... Stroke, compressor cyl. A, in.. .. Stroke, compressor cyl. B, in... . Piston displacement, compressor cyl. Ay Cus ites 5c even ia eee oe . Piston displacement, compressor CVs By CU Pticccnscasaemtegs 084 Sone Diam. brine pump, in.......... Stroke, brine pump, in......... No. of cy!s. brine pump........ Piston displacement per cyl., brine pump, cu. ft........... Revolutions per Minute. Steam engine................. Compressor. .................. Brine PUMP: os od. esos be cuns Pressures. Steam pressure, lbs............. Back press. on steam calorimeter, “we Condenser press., ” Hg... ...... Barometer, ’’ Hg.............. Suction press., compressor, lbs.. Discharge press., compressor, lbs. Suction press., brine pump, lbs... Discharge press., brine pump, lbs. Pressure of liquid NH; at weigh- ing system, lbs.............. Temperatures, Deg. Fahr. 31. 41. 42. 43- 44. 45. 46. 47- 48. Condensing water, steam engine, IMC bs 4.6 2 esa gehs. co wkdie ba cates - Condensing water, steam engine, OUT ECs a scdecrcdiun-ntehint Gace seamen . Temp. in steam calorimeter... ... . Suction temp. NH3............. . Discharge temp. NH3........... . Jacket water, compressor, inlet.. . Jacket water, compressor, outlet. . Condensing water, NH; condenser, TNO ico, 5, Seashutie-a.te-a ainancne yeh a 5 Soe Temp. of NHz, inlet to condenser. Temp. of NHs, outlet from con- GENS ER i.'5 g-vin oan RA peeing oe Meas Temp. of brine, inlet to cooler... Temp. of brine, outlet from COOLET Yagi i audue har aa ECS Temp. of NHs, inlet to cooler... Temp. of NH; outlet from cooler. Temp. of NHs, in front of ex- pansion valve............... Temp. of liquid NH; at weigh- ING! SVSECM: Sie a5.4 2 Huo N's Seas Weights of Water and NH3, per Hour. 49. 50. SI. 52. 53+ 54. 55+ 56. 57. 58. 59. Weight of steam............... Weight of NH; in circulation if measured directly............ Weight of jacket water, compr. . Weight of water, NH condenser. Weight of condensing water, steam engine................ Weight of brine in circulation... General Data. Quality of steam.............. Specific heat of brine.......... Specific gravity of brine........ oquate feet of NH; condenser sur- GE Be Nee 2 nate ncirticwnsed nia es abe Test of Refrigerating Plant built by MECHANICAL REFRIGERATION 1035 SIBLEY COLLEGE, CORNELL UNIVERSITY. Fina RESULTS. 60. 61. 62. 74. 75. Steam Engine. TAD ako Gaile ann Aystihe Water rate per I.H.P. hour..... B.t.u. supplied per hour........ Compressor. fc LODGP echiegecinns wean ae ok . B.t.u. hour equivalent of I.H.P. . Apparent volumetric efficiency, . Effective piston displacement, CU Thess stance es Oendem ya eeas Specific volume of NH; at suction pressure and temperature... .. . Weight of NH; per stroke, lbs... . Weight of NHs; per hour, lbs., Compuledin sas ci samaeeed oats . Ratio of weight of NH; computed to actual weight . Range of temp., jacket water... . B.t.u. per hour in jacket water. . Condenser. Weight of water per hour....... Range of temperature, water.... B.t.u. per hour in condensing Watelens yy sce gabe ease 77- 78. 79- 80. 81. 82. 83. 84. 85. 86. 87. 88. 89. go. or. 92. 93- 94. 95- . Tonnage per lb. of steam uscd. . Gallons of condensing water per Total heat removed from each pound of NH3.............. Heat removed from NH; per hr.. Cooler. Weight of brine per hour. ..... Temperature range of brine.... B.t.u. per hour from brine... ... Heat given to each pound of NH3 B.t.u. per hour to NH;........ Efficiency of cooler........... Brine Pump. Work done by pump.......... Power input to pump......... Mechanical efficiency......... General Results. Mechanical efficiency of set... . Actual coefficient of performance Coefficient of performance of set Theoretical coefficient of per- formance .vea sins yas to Efficiency of refrigeration process TOnnag@a. sp aaeeueesaee dass Tonnage per pound of NH3.... Tonnage per steam I.H.P....... ton of refrigeration......... A. Heat Received by Agent per Hour. 1. Heat taken from brine (= 2. Heat due to radiation (= Item 83 — Item 81) in B.t.u. Per cent of Total. Item 81). cooler 3. Heat due to radiation in piping, cooler to compressor............- 4. Heat equivalent of compressor I.H.P. 1036 EXPERIMENTAL ENGINEERING B. Heat Given up by Agent per Hour. 1. Heat removed by compressor jacket Stemi 73) cca teuekie eeu 2. Heat radiated from piping to con- COENSCR ies taoa eae e eas 3- Heat removed in condenser (= Item 77 X lbs. of NH; in circulation Per WOUt yas and eres acnetes 4. Heat radiated from piping, conden- ser to expansion valve....... Be B.t.u. Per cent of Total. a ey CHAPTER XXV. HYDRAULIC MACHINERY.* 446. Classification. — The broadest classification divides all hy- draulic machinery into two classes: hydraulic motors and pumps. Machines belonging to the former class are prime movers and take energy imparted to them by water, converting a part of it into other forms of mechanical energy. Pumps, on the other hand, impart energy to water, being operated by some type of prime mover. Hydraulic motors are again divided into the following classes: (A) Water-bucket engines, in which water is allowed to flow into suspended buckets, which in their descent lift weights and overcome resistances. This type is practically obsolete and will not be considered further. (B) Hydraulic rams and jet pumps, in which the energy of one mass of water is utilized to impart energy to a second mass. These machines may also be looked upon as pumps. (C) Water-pressure engines, using the direct pressure of water against moving machine members. The latter may be either reciprocating or rotary. (D) Water wheels, with horizontal shaft, in which the water may act either by weight or by impulse, or by a combination of both. This class includes both the old-fashioned water wheels and the impulse wheel. (E) Turbines, rotating either about a vertical or a horizontal shaft, in which the water acts by pressure and by impulse. The different classes of pumps correspond broadly to the different classes of water motors, with the mechanical principles of operation reversed. Thus the reciprocating pump corresponds to the water- * For a general study of this wide and very important field, the student is referred toI. P. Church, Hydraulic Motors; Bovey, Hydraulics; Merriman, Treatise on Hydrau- lics; F. C. Lea, Hydraulics. 1037 1038 EXPERIMENTAL ENGINEERING pressure engine; chain-and-bucket pumps to water wheels, in which the water acts principally by weight; centrifugal pumps are closely analogous to turbines. A broad general classification is into (A) Reciprocating pumps and (B) Rotary pumps. The former class includes steam pumps, direct water-pressure pumps, etc. Rotary pumps may again be subdivided into two distinct kinds: (a) centrifugal pumps and (8) rotary pumps in the narrower sense of the word. The working parts of these latter pumps are usually gears or cams meshed together. Pumps are also sometimes classified according to the power driving them. Thus we distinguish steam pumps, motor-driven pumps, power pumps if driven from shafting, etc. Three other types of pumps will have to be mentioned. The first of these is the pulsometer, which uses the direct action of steam to pump water; the second is the Humphrey gas pump, in which the explosive force of a combustible gas mixture is directly used; and the third is the method of pumping by compressed air. Hydraulic Motors. 447. The Hydraulic Ram. — This is a machine which uses the momentum of a stream of water falling through a small height to raise a part of the water to a greater height. Fig. 598 shows a conventional sketch of a simple type of ram. It consists essentially of an air chamber C connected to the discharge pipe eD, a check or delivery valve O, a waste or clack valve Bd, and a sup- Fic. 598.—Hvyprauuic Ram. — ply chamber SS. MN is the supply or drive pipe. The action may be explained as follows: Assume that the waste valve is open and the delivery valve closed. This is always the case when the water is at rest, for gravity alone will open the first valve and close the second. If now the water starts to flow, it will HYDRAULIC MACHINERY 1039 escape past the waste valve, acquiring greater and greater velocity, until the pressure difference between the under and upper sides of the valve becomes sufficiently great to close the valve abruptly against the action of gravity. The sudden closing of the valve arrests the motion of the water and causes a rapid rise of pressure in the supply chamber SS to such an extent as to lift the delivery valve O against the resistance acting on the other side. A portion of the water thus passes into C, compressing the air in it. The recoil of the water in the chamber SS next causes the pressure to fall again, so that the delivery valve closes and the waste valve opens, after which the operation is repeated. While the water in the drive pipe is accumulating velocity for the next operation, the air in C expands, forcing the water up to delivery pipe eD. The flow up eD is fairly constant if a large enough air chamber C is provided. To keep the air chamber properly filled with air, a small snifting valve, not shown in Fig. 598, opening inward below the delivery valve, is provided, through which, when the pressure on the recoil falls below atmospheric, a small quantity of air is drawn in. This air is delivered to the chamber C along with a certain quantity of water oh the next forcing operation. The waste-valve stem is furnished with an adjustment at 5, so that the length of stroke may be changed. The drive pipe should be straight and as free from friction as possible. It must be of a certain minimum length for satisfactory operation; a length not less than five times the supply head is recommended. 448. The Efficiency of the Hydraulic Ram. — In Fig. 599 the ram R receives its supply water from a reservoir A at a head h, above the level of the waste valve, and delivers a part of it into a reservoir B at a height h, above the level of the valve. Let W, = weight of water passing down the supply pipe in a given time, W,, = the weight of water wasted at the waste valve, and W, = weight of water delivered. There are two methods of computing the efficiency of a ram. The first considers that the useful work consists in lifting W, pounds of water a distance ha — h, above the level of the supply. The useful work, therefore, is Wa (ka —,) foot- pounds. It also considers that the total power expended to do 1040 EXPERIMENTAL ENGINEERING that work is that due to the waste water W,, falling through the supply head f,, that is, W#,. From this we have Wa (ha oe h,) o ae (z) The other method states that the total energy expended is W,h,, and that the useful effect is W zg, so that Efficiency = Efficiency = mes ; (2) The first equation for efficiency is known as the Rankine formula and is the one mostly used. The last form is due to d’Aubisson. Fic. 599. — Hyprautic RAM AND CONNECTIONS. 449. Testing of Hydraulic Rams. — A test of an hydraulic ram requires the following observations: (a) supply head, (6) discharge head, (c) waste water, (d) water pumped, (e) length of stroke (or spring setting) of waste valve and strokes per minute of this valve, (f) dimensions of the ram and details as to length and course of supply and discharge pipes. Where the supply and discharge pressures are small, the best instrument with which to measure them is the ordinary manometer. HYDRAULIC MACHINERY IO41 In the ordinary case, however, a gauge must be used for the dis- charge head. Convert the head in pounds to feet, and add the distance from the center of the gauge to the level of the waste valve, if the gauge is located above the ram, as it usually is. Except for very large rams, both waste water and water pumped may generally be directly weighed. The independent variables that may be changed in the operation of a ram are (a) the supply head, (6) the discharge head, and (c) the number of strokes in unit time of the waste valve. The latter variable is adjusted by changing the length of the stroke of the waste valve, or the tension of the waste-valve spring. The following series of tests may be made: (A) With setting of waste valve constant, take a series of supply heads, and for each supply head change the discharge head by a series of steps from a minimum to the maximum. The discharge head is most easily adjusted by putting a throttle valve above the gauge in the discharge pipe. The action of this valve is equivalent to adding or subtracting from the lift, as the case may be. (B) For any setting of the supply and discharge heads, make a series of runs by changing the setting of the waste valve. Each run should last about one-half hour. The form on page 1042 shows the data to be recorded, together with the quantities to be computed. In the report, plot curves for each setting of waste valve be- tween discharge heads hy as ordinates and the following ab- scisse: (a) capacity in gallons per twenty-four hours; (d) effi- ciency (Rankine); (c) waste water per twenty-four hours (gallons). 450. The Jet Pump. — The principle of operation of the jet pump inay be explained from Fig. 600. Water under pressure is supplied through the pipe A, which ends in the nozzle B in the suction chamber C. The suction produced in C raises the water through D from the source of supply £, and the combined streams of high- Fic. 600.— Jet Pump. 1042 EXPERIMENTAL ENGINEERING DEPARTMENT OF EXPERIMENTAL ENGINEERING—SIBLEY COLLEGE. Test oF Hypravric Ram. Made Dyce Sib Siena 8 Oe REARS RNS Poke e DD) ae ee I9I Dimensions: Aap Chamber :.isacaadesdescars VohtintsrocncaaakaWe a sicaaebadkos Socket see Water-valve Diam..........- ACs P ourshisiihei'n ab RR RES IR BREE EE RDRAS LOGE ERASE Supply Pipes os cs ccrenicien (iam? lengths pcascwy [x dagen castink eneenad fe Number of Bends, etc., in Supply Pipe......-.020-20 | eee cece erences Discharge Pipe............in diam; length... .0.0.5 |e cece eee eens Number of Run. I 2 3 4 8 Length stroke, inches.............--...-5- Strokes per minute............------5 200 Supply héadi.e. coavedeaas saniwaies eye ns Supply head, feet of water, corrected, he... .. Discharge pressure...........0-2 + ese eee Discharge head, feet of water, corrected, jiu. . Ratio discharge to supply head...........- Time;end of TWN. i052 cetacean ehee oe Time, beginning of run...............---- Duration of run, minutes................. Water pumped, scale reading, end.......Ibs. scale reading, beginning . lbs. weight, Wa. ......-.... Ibs. Water wasted, weight, Ww............. lbs. Work done per stroke.............. ft.-lbs. Capacity, pounds per minute. ............. Capacity, gallons per 24 hours............. Wa (ha— he) Wels Waha Wake Efficiency, per cent (Rankine), Efficiency, per cent (d’Aubisson) pressure and suction water pass through the combining tube F and the discharge pipe G either to a reservoir or to waste. Such pumps are used for small lifts for many purposes, because they contain no working parts, although their efficiency is quite low, not exceed- ing 20 per cent. A modification of the jet pump is the suction pump so extensively used in the chemical laboratory. Here the operating fluid is water, HYDRAULIC MACHINERY 1043 but the fluid pumped is air. Another modification is the steam injector (see Chap. XX), in which the operating fluid is steam and the fluid pumped is water. 451. Efficiency of the Jet Pump. — Let s be the effective head in feet of the supply water, /, the actual suction lift to the center of the nozzle, and hz the actual discharge lift; also let W = weight of supply water in a given time and W, the weight of the suction water. Then energy available is W (hk — hz) foot-pounds, and useful work is W, (A, + ha) foot-pounds, from which W, (ht, + ha) W (h — ha) 3) 452. Water-pressure Engines.— Appliances of this type (hydrau- lic cylinders, hydraulic jacks and hoists, etc.) are largely used where slow motion is desirable and high water pressure is available. The latter is generally obtained by means of steam pumps pumping into an accumulator. The action of a water-pressure engine, of the type that operates continuously, as distinguished from that which operates inter- mittently, like the hydraulic jack or hoist, is very much the same as that of the steam engine, except, of course, that the fluid is used nonexpansively. The admission of the water to and the exit from the power cylinder may be controlled by slide and piston valves exactly as in the steam engine. An interesting type that has lately found application for small powers is shown in sketch in Fig. 601. Efficiency = Fre —F' Fic. 601. — WATER PRESSURE ENGINE. A is a reciprocating hollow piston in a cylinder B. The piston is divided into two compartments by means of the partition C. The two admission valves rigidly connected on the same stem are shown at D, and the two exhaust valves, fastened in the same way, are shown at E. The stems are of such length that when one valve is against its seat the other valve on the same stem is off its seat. 1044 EXPERIMENTAL ENGINEERING The piston and tail rods are hollow. If water is admitted at F, it flows into the upper compartment of the piston, passes the right- hand inlet valve and reaches the end M of the cylinder, tending to force the piston to the left. At the same time the left-hand exhaust valve is open and allows the water on that side to flow into the lower compartment and so out through the rod at F’. When the piston approaches the end of the stroke, springs SS on the cylinder heads come into contact with the valve stems, are compressed until their resistance overcomes the water pressure holding the valves against the seats, when these valves are thrown over and the back stroke commences. 453. Efficiency of Water-pressure Engines.*—In any water- pressure engine A (Fig. 602), consider the stroke of the piston P Ara from left to right. Let #, be the i i equivalent total static supply head nett 1! in feet above the level MN, as 1 ie a shown by a gauge G. It is as- aa ee rk sumed that the motion is slow Pm —|P = Pm *“—* and uniform against a resistance R. The unit pressure ~,, (pounds per HIG: Go2: square foot) is somewhat less than the pressure due to /, on account of entrance losses. Suppose it is equal to a head hy. The unit pressure p,,”, on the other side is somewhat greater than atmosphere on account of friction losses in the exit. Suppose it is equivalent to a head h,. (It is here assumed that the exit water discharges into the air at the level MN 2 If »,= atmospheric pressure, then Pn= Pa t hy 4, and Pmt = Pat had, where 6 = weight of one cubic foot of water. If the area of the piston is F square feet, we have for steady motion Oa R =F (Pn— Pm') = F6 (hy — ha) lbs. (4) Therefore the work done per stroke, if S is the stroke in feet, will be RS = F8S (hy — ha) ft.-lbs., (5) * See I. P. Church, Hydraulic Motors. HYDRAULIC MACHINERY 1045 and if ~ = number of strokes per minute, the horse power developed under the conditions assumed will be Te = FOS (hy — Ma) 0, (6) 33,000 FSné = weight W, of water used per minute. Since 4A, is the supply head, the available energy is Wh, foot-pounds per minute. The hydraulic efficiency of the engine consequently is i FaSn (hy == ha) = hs =; ha E, = Wh, ap (7) In practice it would be difficult to determine hy and hz on account of pressure fluctuations, but indicator cards may be taken from both ends of the cylinder. If the water horse power thus shown is I.H.P.,, the cylinder efficiency may be stated to be _ LH.P.,, X 33,000 E,= Wh, ? (8) and if the piston speed is v feet per minute (= 2S), so that the actual work done per minute is Rv foot-pounds, the total efficiency will be Rov ~ Welty E, (9) 454. Vertical Water Wheels. — This includes water wheels of the old type and impulse wheels. The former are again divided into overshot wheels, breast wheels, and undershot wheels. 455. The Overshot Water Wheel. — A general view of one of these wheels, explaining the action, is shown in Fig. 603. The water flows from a head race A into buckets around the circumference of the wheel and is discharged near the bottom. The head of water at the top must be such as to give the falling water greater velocity than that of the periphery of the wheel. In practice the velocity of the water is from g to 12 feet per second, that of the wheel from 5 to ro feet per second. This type of wheel is not adapted to run in back water, and the greatest efficiency for any given head will be found when the wheel just clears the water in the tail race. These wheels have been used with falls from 8 to 70 feet, and 1046 EXPERIMENTAL ENGINEERING deliveries of from 3 to 25 cubic feet per second. When at their best they will show efficiencies of from 70 to 85 percent. They are now, ZZ eC *S Division 4 Circle Fic. 603. — OversHot WATER WHEEL. however, practically obsolete. For that reason no derivation of work and efficiency formulas will be given, stating merely the final results.* The water acts on the wheel both by gravity and by impact. The power derived from the former source is much greater than that from the latter. Church gives the following relation: Power due to weight of water = L, = Q5 [hz + Bhs] ft.-Ibs. per sec. (zo) Power due to impact =L,= Oc COS a — 2] 2% ft.-lbs. per sec. (11) Total theoretical power = (L, + L,) ft.-Ibs. per sec. (x2) Total energy supplied = Qh ft.-lbs. per sec. (13) Theoretical efficiency = E = aa (14) For the significance of most of the symbols used, see the detail Figs. 603 and 604. Q = cubic feet of water supplied per second, 6 = weight per cubic foot of water. During the period that the bucket is passing * For details see any of the books mentioned in footnote, p. 1037. HYDRAULIC MACHINERY 1047 through the vertical head is, the average weight of water contained in it is only some fraction 8 of the weight when full. 6 may be=.s, v, is the tangential velocity at the division circle, c,; the absolute velocity of the jet, « the angle included between them. Fic. 604. Fic. 605.— Breast WATER WHEEL. , 456. The Breast Wheel. — Fig. 605 gives a general view of this type of wheel. The water may be supplied by an overfall weir or through a sluice weir having a gate, as in Fig. 605. The apron of the flume ABE should fit the circumference of the buckets closely ’ (2” to 1”) to prevent the loss of water. The buckets may be radial or turned backward to prevent losses on leaving the back water. Breast wheels have been used in falls from 5 to 15 feet with water supplies of from 5 to 80 cubic feet per second. The power of the breast wheel is due to impact and gravity, as in the case of the overshot wheel, and essentially the same formulas apply. The total theoretical power may be expressed by L=(05 poe + she| ft.-lbs. per sec., (15) § in which the symbols are the same as for the previous article. If h again denote the total head from the surface of the water in the head race to that in the tail race, and / is the vertical distance from the surface of head water to the point of impact on the float, hy =h — hy. The value of 8 depends upon how closely the apron fits the wheel; it may be as high as .g when the fit is very close. 1048 EXPERIMENTAL ENGINEERING The theoretical efficiency is, as before, L — rr 16 E Oak (16) The actual efficiency should range from 65 to 75 per cent. 457. The Undershot Wheel. — See Fig. 606 for a general view of an undershot wheel. These wheels take and reject the water at about the same level. The water enters the guide at a certain velocity due to its head to the surface of the head water and leaves Fic. 606. — UNDERSHOT WATER WHEEL. Fic. 607. it with a velocity about that of the tip of the floats. The power developed is almost wholly due to impact. The equations for this wheel are as follows:* Let Q’ = cubic feet of water per second actually suffering impact, Q = total number of cubic feet per second delivered through the gate, # the supply head in feet, and v the velocity of the center of the float (see Fig. 607). Then since impact is the only agency at work, equation (11), p. 1046, applies, and remembering that a = o (since c and v are in the same direction), we know that the total theoretical power is pee = = (¢ — v) v ft.-Ibs. per sec. (17) In this case, c is theoretically equal to V 2 gh. It can be shown that L is a maximum when v = $c, but that even then it equals only half the kinetic energy available in the water originally. There- fore, even if Q’ = Q, the theoretical efficiency L E=— Osh * See Church, Hydraulic Motors. (8) HYDRAULIC MACHINERY 1049 could not exceed 50 per cent. In actual practice, the actual efii- ciency is from 25 to 33 per cent. The Poncelet wheel is a modification of the undershot wheel in which the floats are concave toward the entering water. This increases the power to some extent, so that actual efficiencies of 68 per cent have been reached. 458. The Impulse Wheel or Tangential Water Wheel. — In this class of hydraulic motors one or more jets of water are made to impinge upon buckets fastened to the circumference of a wheel as they are successively brought into position by rotation. This class is very efficient for high heads of supply and small quantities of water. The best-known impulse wheels are the Pelton, the Doble, and the Leffel (Cascade).* In all these wheels the buckets are char- Fic. 608.— RUNNING PARTS OF AN IMPULSE WHEEL. acterized by a dividing ridge or midriff, as shown in Fig. 608,} which shows the running parts of a small Doble wheel. The tip A pro- jecting from the nozzle B is the needle-regulating valve. A small laboratory motor complete (one side of the case glass) is shown in Fig. 609. Since most of the wheels have curved vanes or buckets, this will * There is one other different type of impulse wheel (more strictly a turbine), the Girard, for the theory of which the student is referred to books on Hydraulics. t Both this and the following figure are from the catalogue of the company. 1050 EXPERIMENTAL ENGINEERING Fic. 609. — DoBLE IMPULSE WATER WHEEL. be the only case considered. Fig. 610 shows a cross section of one of these buckets, moving to the right with the velocity v, while the impinging stream has the velocity 1, greater than v. The relative velocity of the particles of water leaving the bucket at A or B, Fic. 610. neglecting hydraulic friction losses, is 2, -2 = VR in a direction of the tangent to the bucket element at A or B. The absolute velocity w of the particle leaving the bucket at A is evidently the resultant of v and vg, in a direction indicated by %. The component of the absolute velocity in the direction of the axis CD is AF, which is equal to v— vpe cosé =v — (% — v) cosé. The change in the absolute velocity of a small mass AM of water in the direction of the axis CD consequently is 2, —[vy—(v1—2) cos 6] or (4% — v) (1 + cos 6). - HYDRAULIC MACHINERY IOSI Now since the velocity in the direction of the axis has been decreased, there must have been a negative acceleration in the time At, in the direction of v,, equal to p = i eas i Since acceleration is also equal to Hares 2, we may then write Mass M _P _ (mv) (1+ cos), ?= aM At ; (9) or the pressure exerted on the bucket by the small mass of water AM striking the bucket in the time At is pam 9 tos), (20) iF The mass AM = = At, in which Q’ is the volume in cubic feet of water striking the bucket in the time Af, and 6 is the density of the water in pounds per square foot. Hence / P =F ans) (1 + cos 6), (21) and the theoretical power developed by this force will be / L=Pv= ge (v, — v) (t + cos 6) 0 ft.-lbs. per sec. (22) g Note that here Q’ is not the amount of water issuing from the nozzle, but only that striking the bucket per second. That is, if F is the cross section of the nozzle, Q’= F (v, — v), while the water issuing from the nozzle would be Q = Fu. But if a series of buckets be employed, as is of course the case in an actual wheel, the pro- portion of Q’ used will increase, and finally we may put Q’= Q. For any given value of v, the value of L is a maximum when $= 0, in which case cos @ = 1.0, and L= a (v, — v) 0 ft.-Ibs. (23) To discover the value of v for which this will be a maximum, put 1052 EXPERIMENTAL ENGINEERING a =o, that is, 7. — 27 = 0, from which v = . The expression v for maximum theoretical power then becomes equal to 2 Ls 200 (x = a) by *" ft.-Ibs. per sec. (24) g 2/2 g 2 459. Efficiency of the Impulse Wheel. — The total energy per second in the water issuing from the nozzle is evidently equal to the weight of water per second multiplied by its fall, = Q6h, in which h is the total head in feet acting on the nozzle; so that the ex- pression for ideal hydraulic efficiency ( = ratio of energy received to total energy available) may be written Pana) (x + cos 6) v Qbh (v, — 2) aa cos 6) 0 Gas) This efficiency is theoretically 100 per cent if @ = oandy = 2 for EE, = then, remembering that 2, = Vv 2 gh v1? 2 V2 Ce eS. ‘gh 2 gh : 20) In practice, of course, this efficiency is never reached, on account of losses due to imperfect guidance, friction, etc., and the fact that § cannot well be made exactly zero. The actual or gross efficiency of the wheel and nozzle in any case is, if W is the foot-pounds of work done by the wheel per second, as determined by Prony brake or other means, Ww = O6n' (27) The actual efficiencies of these wheels range from 70 to go per cent. 460. Turbines. — Church defines a turbine in general as follows: A water motor consisting of a number of short curved pipes set in a ring attached rigidly to a shaft upon which it revolves, and receiving water at all parts of its circumference from the mouths of other and fixed pipes or passageways. E, HYDRAULIC MACHINERY 1053 Broadly, all water turbines are divided into two classes: Impulse Turbines and Reaction Turbines. —In the first class all of the available head is converted into velocity before the water strikes the vanes. The pressure in the water remains constant during the passage through the wheel; air must, therefore, have free access to the passages, and the latter must not be completely full of water. It is, therefore, necessary that this turbine discharge into free air. The power of this turbine is due to the change in kinetic energy in the water. In the reaction turbine, only a part of the head is converted into velocity before the water enters the wheel, and both pressure and velocity act on the vane. The passages must, therefore, be kept full of water. For this reason this turbine is often placed below the level of back water. The power is due to changes in kinetic energy and changes in pressure. Turbines are also classified according to the direction of flow of the water, and we distinguish: (a) Radial outward-flow turbines, in which the water flows generally at right angles to the shaft and is directed away from the shaft. In this case, the guide blades are placed within the wheel and the latter receives the water at the inner circumference. (0) Radial inward-flow turbines, in which the water flows at right angles to the shaft, but the guide vanes are placed around the outer circumference of the wheel, the water flowing toward the shaft. (c) Axial- or parallel-flow turbines, in which the path of a particle of water lies practically on the surface of a cylinder whose axis is that of the shaft; that is, the distance of the particle from the center of the shaft is constant. (d) Mixed-flow turbines, in which the path of a particle of water is changed from radial inward flow at entrance to axial as the particle passes through the wheel. In order to aid in understanding the action of the reaction tur- bines (the principal one to be considered), two fundamental prin- ciples should first be dealt with: the action of a stream upon a rotating vane, and the general case of amount of power developed by a turbine.* * Hoskins’ method of treatment is followed; see Hoskins, Textbook on Hydraulics. 1054 EXPERIMENTAL ENGINEERING 461. Action of a Stream upon a Rotating Vane: General Case. — AB, Fig. 611, is a vane rotating about the center C with a uniform angular velocity w. The vane receives a stream at Band discharges at A. Let the absolute velocity of the entering stream be 1, the Fic. 611. relative velocity (relative to the vane) be w,, and the velocity of B about C be m. At A, let the relative velocity (tangent to the last vane element) be w»,, the velocity about C be m, and the abso- lute velocity (resultant of u2 and w») be 2. The angular momentum of a particle of water of mass AM at B is AM2,R, cos a, in which R; is the radius CB, and aq is the angle between 2, and #. Similarly, the angular momentum of the HYDRAULIC MACHINERY 1055 particle of mass AM at A is AMv,R: cos a, in which R, is the radius CA and az the angle between x and 1. The action of the vane, therefore, causes a change in the angular momentum equal to AM (u,Ri cos a1 — Rez COS ap). (28) If W’ is the weight of water striking the vane per second, the iE mass per second will be a and the change of angular momentum per second is / a (v,R1 COS a1 — Re COS ae). (29) It can be shown that this is also the total moment* of the forces exerted by the water upon the vane. If there is a constant suc- cession of these vanes, the weight W’ becomes equal to the weight W furnished the wheel per second, and hence the Total moment = = (v, Ry COS a1 — U2Re COS a). (30) Now, energy or work is equal to moment times angular velocity. So if we let w = angular velocity, the energy received by the wheel in one second will be _ aE (Ry CoS ay — 02Rz COS a). (31) To simplify this expression for work, put % cos a = S2, and 2, COS a1 = S;. These are the components tangentially to the wheel of the absolute velocities v, and v respectively, and are sometimes called velocities of whirl (see Fig. 611). Also, Raw = m = velocity of rotation of point A about center C, and Riw =m. We may then write energy received per second = mp (es — UpS2) ft.-lbs. (32) * With reference to this, Hoskins makes the following statement: Since the total increment of momentum of a particle per second is equal to the average value of the force acting upon the particle, it follows, by taking moments about any axis, that the total increment of the moment of momentum (= angular momentum) per second is equal to the average value of the moment of the force. 1056 EXPERIMENTAL ENGINEERING 462. The Radial Outward-flow Reaction Turbine. — Fig. 612* shows a vertical cross section and a plan view of a Fourneyron Fic. 612.—Raprat OutTwarp- FLOW REACTION TuRBINE (FoURNEYRON). bay @ enters the penstock P. At the lower end of the pen- stock it enters the guide passages gg, in which its di- rection of motion is changed to the horizontal and with the direction of motion of the wheel W to avoid shock. The wheel passages are in- dicated at g’g’, The ar- rangement for controlling the quantity of water flow- ing, that is, the gate, is not turbine, which is the best-known example of this type. An outline sketch of this turbine is shown in Fig.613. The water from the head ‘i Fic. 613.— Outtine SkEetcH, RADIAL OuT- WARD-FLOW REACTION TURBINE. shown in the sketch. Fig. 612, however, shows one method of doing it (gates at CC). * Church, Hydraulic Motors, p. III. HYDRAULIC MACHINERY 1057 463. Power and Efficiency of the Radial Outward-flow Reaction Turbine. — Let Q be the cubic feet of water delivered to the wheel per second, 6 = density of the water, and h be the total head from the level in the head bay to the level at which the turbine dis- charges (see Fig. 613), assuming that the discharge is into air. Then the weight of water supplied per second is 08 pounds, and the total available energy is Qh foot-pounds per second. According to the previous paragraph, the actual energy received by the wheel from the water is L= = (1S, — M22) ft.-lbs. per sec., (33) so that the actual hydraulic efficiency is W (151 a UaS2) EE — US1_— U2So Qsh Wh gh In this equation, the values of g, h, u:, and “ are known, but $, and sz must be determined. The value of s, depends upon the absolute velocity 7 (see Fig. 611) with which the water leaves the guide passage, which in turn is a function of the quantity Q of water flowing and the total cross section of the streams F,; measured normal to .the direction of 2. s, depends upon %, which is the resultant of w, and uw (see Fig. 611). w, in turn depends upon Q and the total cross section F, of the streams leaving the wheel. F, is measured normal to the direction of w.. Without entering into the derivation of the transformed equation, the final form is E, (34) MAS A we = 66 — C242 Hydraulic Efficiency £, = ceases a Pity CM (35) in which a, and a» are the angles indicated in Fig. 611, » is the absolute velocity of the water entering the wheel, m is the velocity R of the inner end of the vane about the center of the wheel, c = R,’ 1 and ¢’ = fi, All of these quantities may now be determined if 2 Q and the dimensions of the wheel are known, by constructing a diagram like Fig. 611. 1058 EXPERIMENTAL ENGINEERING Equations (34) and (35) give the actual hydraulic efficiency of wheel and setting, because / is the total head from the level in the head bay to that in the tail race. Losses due to friction in penstock, to shock at wheel entrance, to kinetic energy in water leaving, etc., may each be expressed as an equivalent loss of head ’, so that the net head will be k—h’. The efficiency equation may then be modified to express the actual efficiency of any part of the installation. Equation (35) involves only turbine dimensions, wheel velocity and velocity of the water entering the runner. Since from any test % may be found for any value of m, the actual hydraulic efficiency may be readily computed. The actual or gross efficiency is, of course, the useful work done by the turbine, as determined by Prony brake or other means, divided by the available energy. If W, represents the useful work in foot-pounds per second, so determined, the actual (sometimes called gross) efficiency will be Be = Oat (36) Actual efficiencies for the turbines range in practice from 80 to go per cent. In the above development of the equations, the head / was taken to be the distance between the surface level in the head bay to the level at which the turbine discharged in air. Discharge into air is not the usual case. The turbine is either submerged, that is, placed below the level of the water in the tail race, or, if placed above the level, it discharges into a draft or suction tube. In the case of the submerged wheel, the head # which is to be used for computing the available energy supplied to the wheel will be the distance from the surface of the water in the head bay to the level of the water in the back bay or tail race. The use of a draft or suction tube is primarily for the purpose of making the turbine accessible, and it is found that if the tube is properly designed there will be no appreciable loss in efficiency. The end of the tube must be kept submerged and the tube must be air-tight. It need not necessarily be vertical. If /, is the height in feet from the discharge periphery of the wheel to the level of the water in the back bay, and 34 feet is taken as the height of the HYDRAULIC MACHINERY 1059 water barometer, the pressure, in feet, at the top of the draft tube will be 34 — hfeet. The tube cannot be longer than 34 feet to the level of the back bay, or else the pressure at the top becomes nega- tive and the tube will not remain full. In practice, 25 feet cannot usually be exceeded. As far as the effect upon the turbine is con- cerned, the use of the tube does not affect the head h to be used for computing available energy supplied. As before, this is equal to the distance between levels of head and back bays. If the lower end of the draft tube have a gradually enlarging section, it can be shown that there is a saving in energy,* so that turbine efficiencies may be increased 2 or 3 per cent. Such an appliance is known as a diffuser. 464. Radial Inward-flow, Parallel-flow, and Mixed-flow Reac- tion Turbines. — One type of the radial inward-flow turbine is the Francis, another is the Thompson Vortex wheel. The best-known example of the parallel-flow is probably the Jonval, while most American turbines are mixed- (inward and downward) flow turbines. Fig. 6147 shows a Francis turbine. The wheel is supported by a collar bearing above the staging S. The casting C acts as a guide for the cylindrical gate F and also carries the wheel bearing B. The water flows as shown by the arrows, being first directed by the guide passages against the wheel vanes, flows radially through the wheel vanes, and then down and out of the turbine. The work, however, is done while the water is flowing radially. This type of turbine is sometimes called center-vent turbine. It may be sub- merged or discharge above the level of the back bay into a draft tube. The Thompson vortex turbine differs from the foregoing in the method of controlling the quantity of water and in some details of guide- and wheel-blade design.t The principle of the Jonval turbine is illustrated in Fig. 615, and Fig. 616 shows a double vertical turbine of the type discharging into draft tubes.|| In Fig. 615 the water is received by the guide passages * See Church, Hydraulic Motors, p. 127. { Lea, Hydraulics, p. 320. t See Lea, Hydraulics, pp. 323 to 326. || Church, Hydraulic Motors, p. 123. 1060 EXPERIMENTAL ENGINEERING G and discharged against the wheel vanes G’ in a direction ». The absolute path of a particle of water is shown by line AB, this path =) YY Regulating Sluice “sa C—B a ! y ES Yy Fic. 614.— RapIaL INwARD-FLow REACTION TURBINE (FRANCIS). hs eZ, Tks Fic. 615.— PRINCIPLE OF PARALLEL-FLOW REACTION TuRBINE (JONVAL). being at all points practically at a constant distance from the center of the turbine shaft. Figs. 617 and 618* illustrate the Risdon-Alcott cylinder-gate * From the catalogue of the company. HYDRAULIC MACHINERY 1061 Fic. 616,— Parr OF HorizonTAL PARALLEL-FLOW REACTION TURBINES, WITH Drart TuBes (Jonval). Fic. 617.— RUNNER or A MIxED-FLow Fic. 618. — MIxep-rLow REACTION REACTION TURBINE. TurRBINE (RISDON-ALCOTT). mixed-flow turbine. The wheel or runner clearly shows how the flow is changed from radially inward to vertically downward. In Fig. 618, C is the cylindrical gate which is moved up or down by the gearing shown, carrying with it the extension pieces D between 1062 EXPERIMENTAL ENGINEERING the guide blades B. Pieces D form the upper limiting surface to the guide channels at any position of C. Guide blades B are fastened to the ring R. 465. Power and Hydraulic Efficiency of Radial Inward-flow, Parallel-flow, and Mixed-flow Reaction Turbines. —It would be beyond the scope of this book to enter into any exhaustive discus- sion of the theory of these turbines. For this the student must be referred to books on Hydraulics and Hydraulic Motors. The main concern here is to establish theoretical efficiency standards for comparison with actual efficiencies obtained on tests. Velocity diagrams may be drawn for entrance and exit of each wheel, similar to the one outlined in Fig. 611. It will be found, after going through a demonstration like that in Arts. 461 and 463, that the final formulas there developed generally apply also to the case of the other wheels, that is, the equations for power and hydraulic efficiency are practically the same. To point out some of the changes and approximations in the use of the hydraulic effi- ciency formula, note first that ¢ = ® is equal to 1.0 in the axial 1 flow, and is less than 1.0 in the inward- and mixed-flow turbines, because R, is always the radius at the inlet and R; that at the outlet. Second, the formulas were derived on the assumption that R, and R, are constant. In the axial-flow turbine this is not quite true, but a fair approximation is possible. In the mixed-flow tur- bine, however, the outflow radius varies through a wide range and it is not easy to determine a fair value for Ro. 466. The Testing of Water Motors. — The objects of the test usually are the determination of efficiency and capacity at some constant speed of operation. Tests are run with various “gates,” meaning different positions of the gates to control the admission of water, to determine variation of efficiency and power with variation in quantity of water supplied. Tests may also be made with vary- ing heads of supply and at various speeds. ‘There are also a number of special investigations that may be made.* Tests for efficiency and capacity with various gate openings at * See the article by Schuster in the Zeitschrift des Vereins deutscher Ingenieure for methods of determining pressure and velocity conditions in the wheel of a Francis turbine. HYDRAULIC MACHINERY 1063 one speed are often simply tests to determine whether manufac- turers’ guarantees are met. To bring out the full characteristics of a given wheel, however, a series of such tests at different speeds is desirable. The test of any type of water motor calls for the determination of the following items: A. Volume or weight of water used in a given time. B. The head through which the supply acts. C. The power developed. D. Speed of operation and gate opening (the latter of course applies only to turbines). (A) Volume or Weight of Water Supplied. —The methods of deter- mining the water supplied for a large wheel practically narrow down to a weir or current meter measurements in the tail race and to Pitot tube readings, if the conduit is closed. For the necessary precautions to be observed in these measurements and the method of comput- ing the flow, see Chap. XII. See also the apron method of meas- urement in the same chapter. Measurement in head bays, if of regular construction, may be made by means of current meters and Pitot tubes. For small wheels, the water supplied may often be measured at the inlet as well as at the outlet. Small flows may be caught in tanks and actually weighed. Somewhat larger flows may be deter- mined in weir boxes. This is a good method in laboratory inves- tigations. If the water is delivered to the wheel in a closed pipe, water meters, Venturi tubes, and Pitot tubes (see Chap. XII) be- come available. If the water is supplied through a nozzle, as in the Pelton or Doble wheels, the discharge from the nozzle (= water supplied to the wheel) may be found from the discharge coefficient of the nozzle and the pressure on the nozzle. For turbines which are set in a penstock, the leakage of the pen- stock should be determined and allowed for, if the measurement of water supply is made by some means in the head bay. (B) The Supply Head. — This may be determined either directly by measuring the vertical distance between surfaces of water in head and back bay, or indirectly by means of pressure gauges. The first method is used where the heads are not great and where 1064 EXPERIMENTAL ENGINEERING a datum plane of measurement may be easily established. The head so measured should be corrected for loss of head at entrance ° to penstock and loss due to friction in penstock, to give the effective head h on the turbine. These losses are not properly chargeable to the turbine as a machine. In properly designed installations these losses should be small. When the water enters the turbine through a pipe, a pressure gauge may be placed in the pipe near the turbine to register the pressure head. To this pressure head, reduced to feet, must be added the velocity head in the pipe at the point where the static pressure is measured. The sum gives the head on the turbine at that point. To obtain the effective head h, add to this the vertical distance from the center of the gauge to the level of the water in the tail race. That is, if p is the pressure registered by the gauge, v is the velocity in the pipe as computed from quantity flowing and cross section, and h’ is the distance from gauge to tail race, the effective head will be h= (444 + oe + i) is (37) in which 6 = weight of one cubic foot of water. In impulse wheels, like -he Pelton or Doble, the head & is deter- mined by the same equation, except that here h’ is the distance in feet from the center of the gauge to the center of the nozzle. In either case the sum of (7442 + vi might have been found directly by using an impact tube, instead of static pressure tube, to determine the total pressure in the pipe. (C) The Power Developed. — Equations for theoretical power developed have been given in previous articles. In the actual case the power developed is best determined by some form of absorption dynamometer, like the Prony or fluid friction brake (see Chap. X). If the turbine is direct-connected to an electric generator, the out- put of the generator corrected for efficiency may be taken to be the power developed by the wheel. Where neither of these methods can be used, and a sufficiently long length of shaft is available, some type of torsion meter (see Chap. X) may possibly find application. HYDRAULIC MACHINERY 1065 (D) Speed and Gate Opening. — In high-speed wheels, the revolu- tions should be determined by some form of indicating or recording counter. For slow-speed wheels the ordinary counter may be used, although, since the power developed is a direct function of the speed, it is desirable in any case to have recording devices in order to determine the revolutions as accurately as possible. In turbines it is necessary to have the gate-control arrangements calibrated or properly marked so that the ratio of the “ part gate” to “full gate ” can be readily set and determined during the tests. The necessary length of a‘‘ run” in a series of tests depends only upon the length of time required to accurately determine the flow of water after the conditions for the run have been adjusted and have become constant. This length of time of course differs with the arrangements made for measuring the flow. 467. Report and Computations. — The form on page 1066 shows the observations necessary for a test of a water motor, together with the principal computations. It is assumed that a Prony brake is used to determine power developed, and that the flow is measured by a weir in the tail water. Make runs as follows: (A) With constant speed and a given head, vary the load from light loads to overloads, using, say, six different loads to obtain sufficient data for graphical representations. Compute the items called for on the blank. (B) Repeat at the same loads for a number of speeds in a series from the lowest to the highest practicable, keeping the head constant. (C) If it is possible to change the head, vary it by a series of steps and for each step repeat series A and B. The form needs little explanation, the meaning of most of the quantities having been given in previous articles. For the com- putation of “total effective head,” see Art. 466. The actual or gross efficiency is the ratio of D.H.P. (reduced to foot-pounds) to the available energy Wh. The ratio of velocity of periphery of wheel to velocity due to the head /is, in the case of the impulse wheel, computed to show how nearly the wheel meets the requirement that for maximum efficiency the ratio of these speeds is about o.5. 1066 TEST OF WATER MOTOR. -Ig1 Dates. commieis ogaanke kd aeateneson Prindipal: Dimiensionsof Motors i sigs.cechdadus oo dose o CLAS A lamsSpaig ss Ae undeh bag ad euMbnabmeathea meas oe ses meen eh as By pero Moto tees ocr ng ceed By boa Sane Rds ade ceauebdagS 2a Swag SEES & Brake Zero; Wbsiesaageaninccenees MkGhnok tedden BS MSOC his ch boca taceseder aealarteansrsigrdane Details of Brake: Length of Arm, ft..........00 00.0000. cece ee eee eee EXPERIMENTAL ENGINEERING .; Weir Zero (Hook Gauge).................. Details of Weir: Type................... OBSERVERS jeter 3 ja ene ewe eee aula “(924A as[nduay I0;) pray 0} ang AWop2A, 0} PP2eq MA Jo Araydueg Jo AWOOTAA, Jo O1FeY “quad rad ‘Aqua SsOIX) 10 [enpYy “(4M =) “sqi-"3y ‘eynurpy Jad ABOUT IQupleay [eIOL, (dH =) Jemog asioyy padojaaaqg. “sql ‘Peoy eyeIg 79N “Sq ‘2T9S ayeig jo Julpray ‘aMNUIPT Jad suornjoaay *1OJUNOD UOINTOAIy “(M=) puosas Jad spunog “(O =) puosag Jad 3a3.J 91qnD Water Used. “Vy TOA I3A0 Jaze Jo q3daqy “SuIpvay o3nvs-WoosyT “(4 =) “IF ‘IOJOP uO peal aaooagy [210L ‘al ‘bs Jad ‘sq] ‘adig Ajddng uo asnex) “(auIqiny, & 10J) 97eH TINA 07 97eH neg Jo oney HYDRAULIC MACHINERY 1067 In the report compute, for the conditions for which best actual efficiency was found, the theoretical power and the hydraulic efficiency. (See Arts. 458 and 459 for these computations for the impulse wheel and Art. 463 for the equations for the reaction turbine.) Represent the results of the tests graphically by drawing the following curves: For a turbine, for a given head and constant speed, plot as abscisse ratios of “part gate” to “full gate,” and as ordinates (a) horse power developed, (6) actual efficiency, (c) quantity of water per second. For an impulse wheel, for a given head and constant speed, plot as abscisse quantity of water supplied per minute or per second, and as ordinates (a) horse power developed, (6) actual efficiency. If either type of water motor were tested at other speeds, plot these curves for each speed. Include in the report, if possible, drawings to scale to show the setting of the motor, the principal dimensions of motor, penstock or supply pipe, discharge tube, etc., and location and arrangement of testing apparatus. PUMPS. 468. Reciprocating Pumps.— These are usually steam-driven, and in that case their testing is considered under the head of pumping engines in Chap. XVIII, to which the student is referred. Where the prime mover is an electric motor, or the pump is operated by belt, the arrangements for testing the water ends remain the same. The input to the electric motor multiplied by the motor efficiency gives the power delivered to the pump. Where a pump is belt-driven some type of transmission dynamometer if one can be applied, (see Chap. X) is the best means for determining input. 469. Rotary Pumps. — These pumps are often confused with cen- trifugal pumps, but they are distinctly different (see next article), although, of course, the centrifugal pump is a rotary pump in the broad sense. There are a number of rotary pumps on the market, differing mainly in construction of impeller. One type is that exemplified 1068 EXPERIMENTAL ENGINEERING by the rotary blower, Fig. 562, p. 942. The advantage of these pumps seems to be that they possess no valves. On the other hand, it is difficult to keep them tight along the surfaces in sliding or rolling contact, so that the slip is very high against medium or light heads. The efficiency is correspondingly low. The pumps may be operated by any type of prime mover, but are very often belt-driven. Their testing does not differ essentially from that of centrifugal pumps. 470. Centrifugal and Turbine Pumps. — These pumps are closely related to turbines; in fact, the radial outward-flow turbine could be made to pump water, if it were operated in a reverse direc- tion by an external source of power. It will consequently be found that the equations developed for this turbine very nearly apply to the centrifugal pump, but it is perhaps better to develop a separate theory for the pump. 471. The Action of the Centrifugal Pump. — The following ex- planation of the action of a simple centrifugal pump follows mainly that of Hoskins.* No attempt will be made to discuss shapes of guide or impeller vanes, or proper angles of entrance or exit, the intention being merely to show how such a pump succeeds in lifting water. If a simple vertical cylindrical vessel, A (Fig. 619), partly filled with water, is rotated about its vertical axis XY, the water soon takes up the motion of the cylindrical shell, and the two move as one body. It will be noted, however, that the surface of the water takes on a curved form, rising at the circumference and falling at the center. At any one speed of ro- tation the rise and fall will be a definite amount above and below the original level, It can be shown mathematically that the surface 1s a pa- Fic. 619. raboloid of revolution, and that the distances DE and DF are equal. Let the head of water over the bottom at the point E be = 4, then the head at any other point, such as G, will be =h+y. This extra head y is caused by the velocity ¢ with which the particle of water at G revolves around the axis * Hoskins, Textbook on Hydraulics. HYDRAULIC MACHINERY 1069 XY, its position being due to the energy of rotation. The poten- tial energy of the particle G of weight W at a distance y above the low point £ is evidently = Wy, and this must be equal to 2 2 the kinetic energy = a From this y = a , that is, y is the head corresponding to the velocity c of rotation. Next take a closed vessel A of the shape shown in Fig. 620, assume that this vessel is completely filled with water, and that there is in the vessel a paddle wheel B rotating with uniform velocity about Fic. 621. the axis XY. Then the body of water will take up the motion of the wheel, revolving with it (all effects of friction neglected). From the statement of the previous paragraph, there should then be set up pressures in the fluid varying from center to circumference as the square of the speed, and if piezometer columns C and D are inserted as shown, the liquid will rise to the heights indicated, that 2 2 at C being equal to, that at D tor , where c, and ¢ are the 28 velocities indicated. The pressure head at D, therefore, exceeds 1070 EXPERIMENTAL ENGINEERING that at C by e — - feet. This is the fundamental principle upon which the centrifugal pump operates. To make the application of this to the pump a little clearer, consider Fig. 621. Here the wheel B revolves in the case A which is surrounded by an outer case A’. A communicates with A’ through a number of passages OO. Water is furnished from a reservoir R under a head #,. If the wheel B stood still, the water would rise in the pipe ZN to the same height /, above the center of the wheel. But if the wheel is now rotated by external power, the pressure in the outer vessel A’ will rise in the delivery pipe MN to some greater height /p. The strong resemblance of even this crude construction to the actual centrifugal pump is very striking. See Fig. 622,* which shows the construction of a horizontal ‘ centrifugal pump. The wheel B, rotating in the chamber 4, is / formed of an upper and lower i sheet, the space between which is divided into a number of pas- sages by vanes, corresponding to the arms of the paddle wheel. These vanes are not radial, like paddles, but generally of a curved shape, as shown, because that form is more efficient. Neither : do they extend quite to the center, but leave a central opening B’ > 7 for the suction water to enter. The water pumped enters the chamber A’, from which it flows into the discharge pipe MN. The water is raised from the level of the supply by suction through a height h, and is delivered through a height /,, so that the total lift is kh, + hg. A centrifugal pump cannot commence to discharge unless the Tic. 622. — HorizontaL CENTRIFUGAL Pump. * From Lea, Hydraulics, p. 393. HYDRAULIC MACHINERY Io71. wheel, casing, and suction pipe are full of water. For this reason, either a foot valve V must be provided in the suction pipe, or arrangements must be made so that the pump may be primed after it is started up. The modern centrifugal pump is usually run upon a horizontal axis. The various constructions, by different makers, differ mainly with respect to shape of impeller passages, and means employed to convert the high velocities of the water leaving the impeller into useful pressure head, thus raising the efficiency of the pump. The following classification and discussion of characteristics is due to Prof. G. F. Blessing.* I. Impulse Pumps without Volute (Fig. 623). — This is the cheap- est and least efficient form. The impeller is a close fit in the Fic. 623. —Imputse Pump wiTHOUT Fic. 624.— Pump witH VoLUTE, No VOLUTE. WHIRLPOOL CHAMBER. concentric casing, and discharges the water at high velocity into the casing, in which there is no provision made for reducing the high velocity. These pumps are not much better than simple rotary pumps, because the water can be discharged from each passage for only about one-quarter of a turn. They are used mostly against small heads, — 2 to 6 feet, — and show efficiencies ranging from 30 to 45 percent. They are largely used in dredging or irrigating operations, and show good resistance against shock or wear caused by solid material carried by the water. II. Pumps with Volute, but without Whirlpool Chamber (Fig. 624). — The construction differs from the foregoing. mainly in that a spiral discharge pipe, the volute chamber, is added to the casing. The form of the volute is practically that of the spiral of Archimedes, * Sibley Journal, April, 1908. 1072 EXPERIMENTAL ENGINEERING that is, its cross section increases from practically zero up to the full area of discharge in such a manner as to keep the velocity of water in the chamber practically constant while the wheel is discharging all around the circumference. As in class I, no special provision is made in this class to convert the kinetic energy of the water into static pressure. Some transformation does take place, — that of the tangential component of the velocity with which the water leaves the impeller, — but the radial component is lost. The advantage of this type over class I, however, exists in the fact that the impeller is continuously discharging all around the circumference. This type of wheel is used for heads from 5 to so feet, and may show efficiencies up to 60 per cent. III. Pumps with Volute and Whirlpool Chamber (Fig. 625).— The whirlpool chamber is a passage of annular ring form which is interposed between the impeller and the volute chamber. The water discharges into this chamber (which is usually filled with vanes having the same direction as the stream lines) with high (Q) | MM > hs Fic. 625.— Pump with VoLUTE AND Fic. 626.— Pump witH VOLUTE AND WHIRLPOOL CHAMBER. BELL-MouTH DISCHARGE. velocity of whirl, by which is meant the tangential component of the absolute velocity of the water leaving the impeller. The water continues rotation in the whirlpool chamber, changing velocity into pressure head in so doing. The increase in efficiency due to the whirlpool chamber depends upon the construction of the latter. IV. Pumps with Volute and Bell-mouth Discharge (Fig. 626). — These pumps are the same as class II, except that the discharge pipe gradually enlarges, to convert velocity into pressure head. This construction is of importance for pumps of low lifts; for those discharging against high heads it does not add much to the effi- ciency. When the velocity of water in the volute chamber is about HYDRAULIC MACHINERY 1073 15 feet per second (common figure), the gain in head due to the bell- mouth discharge is usually less than 3 feet, which may, of course, be a large percentage for a low lift, but a small percentage for a high head. V. Single-stage Turbine Pump (Fig. 627).— The special feature of turbine pumps is that the impeller discharges into a number of expanding nozzles, which in turn discharge into a concentric case. The ring containing these nozzles is called the diffuser, and the function of the nozzles is to convert kinetic energy into pres- sure head before the water reaches the discharge chamber. Their function is thus the same as that of the whirlpool chamber, but the latter is not suited to great reductions of velocity unless it be made very deep, which would make the pump very bulky. The turbine pump is used as a single-stage pump for heads from 50 to 150 feet and may give efficiencies exceeding 80 per cent. VI. Multistage Turbine Pump (Fig. 628).— The single-stage turbine pump, if used against a high head, requires high velocities Fic. 627. — SINGLE-STAGE TuRBINE Pump. a Fic. 628. — MULTISTAGE TURBINE PUMP. of rotation, which causes excessive skin friction between metal and water. To overcome this, the pump is compounded by mounting several impellers on the same shaft. Each impeller operates in a 1074 EXPERIMENTAL ENGINEERING separate chamber and forms a complete pump in itself, the first delivering the water to the suction of the second, etc. Multi- stage pumps with 8 stages delivering against 2000-foot head have been built. 472. Theoretical Power, Manometric, Hydraulic, and Actual Efficiencies of Centrifugal Pumps. — If the action of a pump im- peller is analyzed in the same way as was done for a turbine runner of the radial-outflow type, which, as stated, is an exactly parallel case, a formula of the same form as equation (32) may be developed for the work done upon the water. This equation is L= ns — MS») ft.-Ibs. per sec. (38) The meaning of u and s may be read from Fig. 611. In the case of the turbine runner, the velocity ™ is higher than m,, and L is positive, meaning that the water does work upon’the runner. In the case of the pump impeller, # is greater than m, hence L is neg- ative, which means that work is done upon the water. To avoid the use of the negative sign, we may write theoretical work done upon the water == = (t#t2S2 — U1S1) ft.-lbs. per sec. (39) The water enters the impeller practically radially, so that s; = 2, COS a; = o (see Fig. 611). We also have sy = us. + wy COs ay. The theoretical work then is = a : Uz (U2 + w» COS az) ft.-lbs. per sec., (40) in which # = tangential velocity at exit from impeller passage; Ww. = velocity of water relative to vane; a = angle between mw and we (see Fig. 611). w, may be computed from the quantity Q of water flowing per second and a: is known from wheel dimensions. If the theoretical work done is divided by the weight W of water flowing, the result will be the theoretical total lift or head. This then is equal to qu (uz + we COS ay) ft. ae HYDRAULIC MACHINERY 1075 The actual gross head through which a pump operates is in prac- tice found as follows: Connect a manometer to the suction pipe of the pump close to the latter, and let the reading of this manometer, when the pump is in proper operation, be equivalent to a static head of h, feet, measured above atmosphere. (The reading will usually be inches of mercury, which must be reduced to the equivalent water column h, in feet.*) Connect a pressure gauge to the discharge main close to the pump, and let the reading of the gauge be equivalent to a discharge head of hg feet, measured above atmosphere. (The reading will usually be in pounds per square inch.) Let the velocity of the water through the suction pipe, at the point where /, is measured, be v, feet per second, and the velocity through the discharge main at the point where /, is measured be vg feet per second. These velocities are computed from the quantity of water flowing and the dimensions of the mains. Let the water barometer (atmospheric pressure) = / feet (about 34 feet). Now, on the basis of Bernouilli’s theorem, write the energy equations for the two points. Neglect friction between the points, for that is directly chargeable to the pump, if the pressure-measuring instruments are connected very close to the pump casing, as is assumed to be the case. If W is the quantity of water flowing per second, and / the gross head in feet produced by the pump, the energy imparted to the water in passing through the pump is evidently = Wh foot-pounds. Express the total pressures acting at the two points of measurement as absolute pressures, and let the vertical distance between the point of manometer connection to the center of the discharge gauge be / feet. Then the energy equation will read Suction Side Discharge Side SS i F Velocity Energy Static Head eo Static Head Head Taput —_—_ es Se ; pe Ww In + (ach) +22} = W(t he tht ie (42) * h, may be intrinsically positive or negative. If the pump is supplied with water under some pressure, then is is intrinsically positive, and in the equation must be written = (+ hs). If, on the other hand, the pump lifts the water, 4s is intrinsically negative, and must be written = (— he). 1076 EXPERIMENTAL ENGINEERING Now, assuming that the pump lifts water, so that #, is intrinsically negative, we have, canceling W, : Ve” Vq? iy l= hy) + = eh yg th to ’ 28 28 from which the gross head through which the pump operates is Di os 2 h= (i +h, +h t+ Be) if, (43) Similarly, if the pump receives water under pressure higher than atmospheric so that #, is intrinsically positive, we have b= (tay thn +) (44) It should be noted here that 4, and / are not simply the actual vertical distances from the point where the gauge is connected to the discharge level, or from the point where the manometer is connected down to the suction level. In each case Az and hk, include besides this the friction loss in the pipe. To find A, and h, simply by measurement of the actual distances assumes negligible friction losses in the piping. The useful head pumped through is equal to 2 I, = (ha! + hy’ + hn) ft, (45) where hj,’ is the actual lift from center of gauge to discharge level and h,’ is the actual suction lift in feet. Manometric or Hydraulic Efficiency of a centrifugal pump is de- fined as the ratio of the actual gross head pumped through divided by the theoretical total head; that is, ha + hy +I ME ite oe © ae Uy (Ua + Wy COS ae) § v, ee Vs? & (he +h, +n +) a — (46) Uz (Uz + We COS ae) The hydraulic efficiency is by some writers computed on another, though equivalent, basis and is defined as the ratio of the total HYDRAULIC MACHINERY 1077 work done by the pump to the power input to the wheel. The latter is not the theoretical input L of equation (40), but the total input to the pump less the power lost in axle friction. Let Ly be the actual power input in foot-pounds per second, and Lz, be the power lost in bearing friction. The input to the wheel is L; = I, — Ly, and, by definition, hydraulic efficiency then is W (ia + hy +n + ——*e) i, = 4s 2 : h ia a (47) The actual efficiency is of course always determined by the ratio of total work done by the pump to the total energy input, so that 0a? “*) o W (i Pa Ey =— => Dh Ly (48) 473. The Testing of Rotary and Centrifugal Pumps. — The test is usually for power input, capacity, and efficiency. The deter- minations and observations required are: (A) Power input; (B) Quantity of water pumped; (C) Total and useful heads pumped against; (D) Power output (foot-pounds per minute or horse power); (EZ) Speed. (A) Power input is determined by any of the means already described if the prime mover is direct-connected (steam engine or turbine, electric motor, etc.). When belt-driven a transmission dynamometer should be used. f (B) The quantity of water pumped may be determined either on the suction or discharge sides by Pitot tubes, by common water meter or Venturi meter on the discharge side, or by nozzles, ori- fices, or weirs, as may be convenient (see Chap. XII for available methods). (C) Manometers and gauge are connected to suction and dis- charge mains and readings taken, as outlined in previous paragraph. The suction and discharge heads may be varied at will, if desired, by placing throttle valves in the suction and discharge mains, the 1078 EXPERIMENTAL ENGINEERING former below the measuring instruments in the suction pipe, the latter beyond the instruments in the discharge pipe. (D) The power output is equal to Wh foot-pounds per second, if W = water pumped per second and h is total head in feet. Horse power is then = Ei 55° (E) Speed should be taken by some recording form of counter. As in the turbine, the length of each test is determined mainly by the time necessary to make sure of the rate of flow of water, after conditions have become constant. The following forms are used at Sibley College in the testing of a small centrifugal pump. The pump is belt-driven by a direct- current motor, and a weir is used to measure the discharge. In view of the explanations given in previous articles of this chapter, none of the items need any further explanation, with the excep- tion, perhaps, of the item “ Duty.” The B.t.u. supplied the pump is in this case obtained by converting the applied horse power or power input to equivalent heat units per hour by multi- plying by 2545. TEST OF CENTRIFUGAL PUMP. Log Sheet. Date of Test........ to . Observers, ............ Gwe e eeSeare ee nen wun sa Details of Weir: Type........ ; Length, ft......... ; Hook-gauge Zero............ Reading Reading of Manom-| of Gauge eter (lbs. per (in. Hg.). | sq. in.). Hook- R.P.M. |R.P.M. gauge of of Volts. | Watts. Reading. Motor. | Pump. " Number. | Time. ft Bib eka os renitataene [eG She Bead eG eerie |S). Beepdoa sere] aaaaateanee eras [iw recta Sil eusines eels aaay avns HYDRAULIC MACHINERY 1079 TEST OF CENTRIFUGAL PUMP. Result Sheet. Type of Pump, sii og seis dstiennks Ga aiale saunas goa aids a weateaane ead ala neg paige ela Details of Impeller: Diameter, inches....... ; Width, inches, .0 24 62.0.5 saa saaxie Diameter of Suction Pipe, inches............; of Discharge Pipe, inches............ Run Number. 2 3 4 5 6 a Av. suction head, by manometer, ft., /is. . Av. discharge head, by gauge, ft., id..... Distance between manometer and gauge, Velocity head in discharge, ft., oe demande Total head, feet, 2.........0ee eee eee Hook-gauge reading. ........eeeee eee Head on weir, feet. ........2eeeee sree Discharge, cu. ft. per sec., Q.....-.-.06+ R.P.M. of motor... 0... eee eee eee eee eee R.P.M. of pump. ....... 00.20 eee eee Velocity of periphery of impeller........ Velocity in discharge main, ft. per sec., vg Velocity in suction main, ft. per sec., vs... Input to motor, H.P. ......---- 2 eee Efficiency of motor, per cent.........-- Input to pump, A.H.P..........-..--- Pounds of water discharge per sec., W... Actual efficiency of pump, per cent, Ea... Hydraulic efficiency, per cent, Ex. ....-.. Manometric efficiency, per cent, Eman... Efficiency of set, motor included, per cent Capacity in gallons per min............ Duty in ft.-Ibs. per 1,000,000 B.t.u. sup- Plied es wcee ca erinetea ees aaa BeEe ests 474. Scope of Tests and Report. — The following series of runs may be made on the pump: (A) With speed and suction head constant, vary the discharge head by controlling the valve in the discharge main. (B) With speed and discharge head constant, vary the suction head. (C) Repeat series (A) and (B) for a series of different speeds. To exhibit the characteristics of the pump, draw the following curves: 1080 EXPERIMENTAL ENGINEERING With capacity in gallons per minute as abscissas, use the follow- ing ordinates: (a) head / in feet; (6) useful horse power; and (c) actual efficiency. If a series of speeds are used, one set of such curves should be drawn for each speed. 475. The Pulsometer. — This is a pump in which the direct pressure of steam upon water is used to drive the water out of a chamber and up a discharge pipe. Figs. 629 and 630* show two sections of a pulsometer. It consists of two chambers, A,As, separated by a parti- tion a. The chambers are connected to a common suction pipe B through suction valves S,and S,. They communicate with a common discharge chamber K by discharge valves D,and D,. Chamber W con- nects with the suction pipe through a side passage and serves as an airchamber. The ball valve E controls the course of the steam, the supply of which is regulated at C. Fics. 629 AND 630.— PULSOMETER. In the position shown, with E closing the left-hand opening, the water is rising in Ai, S; being open, while the pressure of the steam on top of the water in A, forces this out through D; into K and up H. The speed of operation in the two sides is so con- trolled that, as the water is all pushed out of A», the water in A; has risen nearly to the top, pushing any air that may be in A, ahead of itself against the valve E. At the next instant, steam starts to escape through D, and is rapidly condensing or mixing with the water in K. This causes the pressure in A, to fall to such an extent that the overpressure in A, pushes the valve £ over to the right- hand seat. It is understood, of course, that the pressure in A,, * Mechanics of Pumping Machinery, Weisbach & Hermann, p. 287. HYDRAULIC MACHINERY 1081 up to the instant the valve £ shifts, is not up to atmosphere, be- cause it is produced by water flowing into A, under the influence of atmospheric pressure, but the pressure difference between A, and A, is enough to throw £. The steam then does work in A, while A; is filling. The operation is then repeated. The rapidity with which a chamber is emptied depends of course upon the steam pressure. It is essential for steady operation that the filling and emptying operation should take about the same length of time. To regulate this, each chamber is fitted with an air valve L opening inward, so set that at each operation a certain amount of airis takenin. This controls the pressure in the suction chamber and hence the time of filling. The rapidity of emptying is controlled by regulating the valve C. The analysis of the operation of this instrument is very similar to that of the steam injector, except that the steam acts by pressure and not by impact. Let w = weight of steam used per hour; W = weight of water pumped per hour; ha = discharge head in feet; hh, = suction head in feet; h, = distance in feet between centers of suction and discharge gauges; p and x = pressure per square inch and quality of steam in the main; t, = temperature of suction water; & = temperature of discharge water. Neglect changes in velocity heads, as the velocities are low in any case. Then, assuming that the loss of heat by radiation from the pulsometer wall is R heat units per hour, we may write the ti HEH DOD or tog) = Wea +R, (49) in which 7 and q are taken from the steam table for the pressure P, and qj is the heat of the liquid corresponding to the temperature bh. Tt is here assumed that the steam loses no heat in passing the ad- mission valve. If it is possible to make a close approximation to the value of R,.and W is determined, the amount of steam w used may be approximately computed from the equation. For an 1082 EXPERIMENTAL ENGINEERING accurate test, of course, both W and w should be determined for which the injector set-up described in Chap. XX may be used. The heat equivalent of the mechanical work done by the pulsom- eter per hour is US Waco fetta) hs B.t.u. (50) 778 The heat expended in thermal units per hour is H =w(ar+q— qq) B.t.u. (st) Hence the pump efficiency is pau _ WiMu + ha + Iu) + why | (52) H 778 w (ar + q — qa) 476. The Humphrey Internal-combustion Pump.— This pump uses the expansion of a combustible mixture of gases, after explosion, Fic. 631.— Humpurey INTERNAL-COMBUSTION PuMP. for the pumping of water. Fig. 631 shows a conventional sketch of the principal parts of a four-cycle pump.* Its operation is rather complex, but may be explained briefly as follows: C is a conical combustion chamber with inlet and exhaust valves at the top. There is also a scavenging valve, which is not shown. An inter- locking gear is arranged so that either valve 7 or E is locked shut when the other is operating. Suppose that a charge of gas is com- pressed in the upper part of C, the water standing at some level in C, and let the charge be exploded by spark in the ordinary way. * From an article on the Humphrey Internal-combustion Pump, by E. N. Trump, in the American Machinist, Jan. 5, 1911. This article also shows the two-cycle pump, applications of this type of pump to air compression, etc. HYDRAULIC MACHINERY 1083 Valves I and E being shut, the pressure generated starts to depress the water column, forcing it toward the high-level tank B. The pressure falls as the water column attains velocity, so that by the time the gas pressure has reached atmospheric pressure the water column has considerable velocity. Since this motion cannot be suddenly arrested, expansion below the atmosphere in C takes place, which opens both the exhaust valve E and the water-suction valves V. The water coming in mostly follows the column of water moving towards the high-level tank, but the level will also rise in C in the effort to attain the level in the suction tank A. The kinetic energy of the water column is of course finally used up in forcing part of the water into the high-level tank. After this the water starts to surge back, filling the combustion chamber C and shutting the exhaust valve E by impact. This imprisons a quantity of burned gas in the space Ci, which gas, owing to the inertia of the water column, is compressed to a pressure higher than that of the static head due to the suction tank. » Sp. Vol., 0,47 B.t.u. 1098 APPENDIX STEAM TABLES. — Concluded. TABLE II.— PRESSURE TABLE. Internal Sp. Z Latent] Total E A Entropy. Press.| T€™P:| press. | Vol., cen ae Heat | Heat a " Py Press. Ibs. — Atmos.*] cu. ft. ae Liquid of of sees a Ibs. : per lb. : Evap.|Steam.| Eyap.|Steam.|Water or Steam. p t — |vors I/v |hkorg|Lorr| H |Iorp| E |nor@\orr/T\Nord| 6 I50 | 358.5| 10.21 | 3.012] 0.3320 | 330.2] 863.2/1193.4| 780.4]1110.1]0.5142/1.0550|1.5692| 150 152 | 359.5| 10.34 | 2.974] 0.3362 | 331.4] 862.3/1193.6| 779-4|1110.3]0.5155|1.0525|1.5680| 152 154 | 360.5] 10.48 |} 2.938) 0.3404 | 332.4] 861.4|1193.8| 778.5|1110.4/0.5169|1.0501|1.5670] 15 156 | 361.6] 10.61 | 2.9021 0.3446 | 333.5| $60.6|1194.1] 777.6|/1110.6/0.5182|1.0477/1.5659| 15| 158 | 362.6] 10.75 | 2.868] 0.3488 | 334.6| 859.7|1194.3] 776.7|r110.8]o. 5195/1.0454/1.5649| 158 160 | 363.6] 10.89 | 2.834] 0.3520 | 335.6) 858.8|r104.5| 775.8|1110.9]0.5208/1.0431|1.5639| 160 162 | 364.6] 11.02 | 2.801] 0.3570 | 336.7] 858.0/1194.7| 775.0/1111.1|0.5220/1.0400|1.5629| 162 16 365.6] 11.16 | 2.769] 0.3612 | 337.7] 857.2/1104.9| 774.1]/IIII.2/0.5233|2.0387|1.5620| 164 16 366.5| 1r.30 | 2.737] 0.3654 | 338.7] 856.4/1195.1| 773.2|111I.4|0.5245|1.0365|1.5610| 166 168 | 367.5] 11.43 | 2.706] 0.3606 | 339.7] 855.5|1105.3| 772-4/ITII.5|0.5257|1.0343|1.5600| 168 170 | 368.5] 11.57 | 2.675] 0.3738 | 340.7] 854.7/1198.4| 772.5|/11Z1.7/0.5269/1.0321|1.5590|] 170 172 | 369.4] 11.70 | 2.645] 0.3780 | 341.7] 853.9|1195.6| 770.7/1111.8)0.5281|/1.0300/1.5581) 172 17. 370.4| 11.84 | 2.616] 0.3822 | 342.7] 853.1\1195.8| 769.8]1112.0]0.5293|1.0278]1.5571| 17. 17! 371.3| 12.97 | 2.588} 0.3864 | 343.7] 852.3/1196.0] 769.0/1112.1/0.5305|1.0257|1.5562| 17! 178 | 372.2| 12.11 | 2.560) 9.3900 | 344.7| 85r.5/1196.2|] 768.2/1112.3/0.5317|1-0235|1.5552| 178 180 | 373.1] 12.25 | 2.533] 0-3048 | 345.6] 850.8]1196.4] 767.4]1112.4]0.5328]/1.0215 1.5543 180 182 | 374.0] 12.38 | 2.507| 0.3089 | 346.6] 850.0/1196.6] 766.6|r112.6]0.5339|1.0195|1.5534| 182 184 | 374.0] 12.51 | 2.481] 0.4031 | 347.6] 849.2/1196.8] 765.8|1112.7/0.5351|1.0174|1.5525| 18. 186 | 375.8] 12.66 | 2.455] 0.4073 348.5] 848.4]1196.9] 765.0/1112.8]0.5362]1.0154]1.5516| 18 188 | 376.7| 12.79 | 2.430] 0.4115 | 349.4] 847.7|1107.1| 764.2/1113.0]0.5373/Z.0134|/1.5507| 188 190 | 377.6] 12.93 | 2.406} 0.4157 | 350.4] 846.9/1107.3) 763.4/1113.1]0.5384/1.0114|1.5498] I90 192 | 378.5] 13.060 | 2.381] 0.4199 | 351.3] 846.1/1197.4| 762.6]1113.2/0.5395|1.0095|1.5490| 192 194 | 379.3] 13.20 | 2.358] 0.4241 | 352.2| 845.4|1197.6] 761.8/1113.4/0.5405|1.0076]1.5481| 194 196 | 380.2] 13.34 | 2.335] 0.4283 | 353.1] 844.7/11907.8| 761.1/1113.5|0.5416|1.0056|1.5472| 196 198 | 381.0] 13.47 | 2.312] 0.4325 | 354.0] 843.9/1197.9| 760.3/1113.6]0.5426/1.0038|/1.5464| 198 200 | 381.9] 13.61 | 2.290] 0.437 354.9] 843.2/1108.1] 759.5|1113.7/0.5437|1.COT9|L.5456| 200° 205 | 384.0] 13.95 | 2.237] 0.447 357-1] 841.4/1198.5] 757.6/1114.0]0.546310.9073/1.5436| 205° 210 | 386.0] 14.29 | 2.187] 0.457 359.2| 839.6/1108.8] 755.8]/1114. 410. 5488]0.9928|1.5416| 210 215 | 388.0] 14.63 | 2.138] 0.468 361.4] 837.9/1190.2| 754.0]1114.6/0.5513/0.9885|1.5398) 215 220 | 389.9] 14.97 | 2.091] 0.478 363.4] 836.2/1199.6] 752.3,1114.9/0.5538/0.9841|1.5379) 220 225 | 391.9] 15.31 | 2.046] 0.489 365.5] 834.4|1199.9] 750.5/IIIS5.2/0.5562]0.9799|1.5361| 225 230 | 303.8] 15.65 | 2.004] 0.409 367.5] 832.8]1200.2] 748.8/1115.4]0.5586]0.9758|1.5344| 230 235 | 395.6] 15.99 | 1.964] 0.509 369.4] 831.1/1200.6| 747.0/1115.7]0. 5610]/0.9717|1.5327| 235 240 | 397.4] 16.33 | 1.924] 0.520 371.4] 829.5]1200.0] 745.4|/1115.9]0.5633/0.9676|1.5309| 240 245 | 399.3] 16.67 | 1.887] 0.530 373-3| 827.9/1201.2| 743.7]/1116.2]0.5655)0.9638!1.52093| 245 250 | 401.1) 17.0r | 1.850] o.s54r 375.2) 826.3/1201.5] 742.0/1116.4]0.5676)0.g600|1.5276| 250 260 | 404.5] 17.69 | 1.782] 0.56 378.9] 823.1]1202.1] 738.9]/1116.9]0.5719|0.9525/1.5244| 260 270 | 407.9] 18.37 | 1.718] 0.582 382.5] 820.1]/1202.6] 735.8]1117.3]0.5760/0.9454/1.5214| 270 280 | 411.2] 19.05 | 1.658] 0.603 386.0} 817.1]1203.1] 732.7/1117.7|0.5800]0.9385/1.5185] 280 290 | 414.4] 19.73 | 1.602| 0.624 389.4] 814.2]1203.6] 729.7/1118.1|0. 5840]0.9316/1.5156] 290 300 | 417.5} 20.41 | 1.551] 0.645 392.7| 811.3/1204.1] 726.8}1218.5]0.5878]0.9251/1.5120] 300 350 | 431.9] 23.82 | 1.334) 0.750 408.2] 797.8]1206.1] 713.3/1120.2/0.6053/0. 8949/1. 5002} 350 400 | 444.8) 27.22 ) 1.17 | 0.86 422. | 786. |1208. | zor. |1122. |o.621 |o.868 |1.489 | 400 450 | 456.5] 30.62 | 1.04 | 0.06 435. | 774. |1209. | 690. |1123. 0.635 Jo.844 |1.479 | 450 500 | 467.3] 34.02 | 0.93 | 1.08 448. | 762. |x210. } 678. lr124. |0.648 |o.822 |1.470 | 500 * 1 atmo. (standard atmosphere) = 760 mms. of Hg. by def. = 29.921 ins. of Hg. = 14.696 Ibs. per sq. in. T° = t° + 459.6; J = 777.5 ft-lbs. per B.t.u. flog = 0.1852 [log = 1.26764]. 2.89071]; A = 1/J = 1.286 X 103; 144A = _ ice at 215 Ibs., sp. vol., v or o = 0.0185 cu. ft. per Ib.; 1/e” = 54.0 Ibs. per cu. ft.; 144 Apv = 0.83 B ee rater. at 240 lbs., sp. vol., »” or ¢ = 0.0186 cu. ft. per Ib.; 1/v’ = 53.6 Ibs. per cu. ft.; 144 Apo! = APPENDIX 1099 TABLE 4.— HORSE POWER PER POUND MEAN PRESSURE. (Chap. XVI, p. 647.) 5 a : Speed of Piston in Feet per Minute. 29 za a o a 100 240 300 350 400 450 500 550 600 650 750 4 -038 .OQI -1I4 +133 +152 -I71 +19 +209 -228 +247 «285 43 048 -IIS «144 -168 «192 +216 +24 .264 - 288 +312 .360 5 .06 +144 .18 .210 +240 +270 +30 #33: -36 -39 +450 5 .072 +173 -216 252 -288 +324 .36 -396 +432 -468 +540 : -086 +205 «256 -299 +342 | | .385 -428 -471 +513 +555 -641 6} «102 +245 +307 +391 «409 464 +512 +563 O14 -698 .800 7 -116 -279 -348 -408 -466 +524 -583 -641 -699 +756 -874 7y +134 «321 «401 -468 +534 -602 . 669 735 -802 .869 | 1.002 8 -152 -365 -456 -532 -608 685 -761 -837 -Q12 -989 | 1.121 84 .172 “413 -516 -602 -688 “174 -86 -946 | 1.032 | 1.118 | 1.290 9 «192 -462 -577 -674 +770 -866 -963 | I.059 | 1.154 | 1.251 | 1.444 9} +215 .515 -644, 7ST .859 .966 | 1.074 | 1.181 | 1.288 | 1.395 | 1.610 10 -238 -571 714 -833 -952 | 1.071 | 1.190 | 1.309 | 1.428 | 1.547 | 1.785 10} -262 63 «787 -Q19 | 1.050 | 1.18r | 1.313 | 1.444 | 1.575 | 1.706 | 1.969 Ir . 288 -69r -864 | 1.008 | 1.152 | 1.296 | 1.44 1.584 | 1.728 | 1.872 | 2.160 11y +314 +754 -943 | 1.100 | 1.257 | 1.414 | 1.572 | 1.729 | 1.886 | 2.043 | 2.357 12 +342 .820 | 1.025 | 1.195 | 1.366 | 1.540 | 1.708 | 1.880 | 2.050 | 2.222 | 2.564 13 -402 -964 | 1.206 | 1.407 | 1.608 | 1.809 | 2.01 2.211 | 2.412 | 2.613 | 3.015 14 .466 | 1.119 | 1.398 | 1.631 | 1.864 | 2.007 | 2.331 | 2.564 |:2.707 | 3.029 | 3-495 15 -535 | 1-285 | 1.606 | 1.873 | 2.131 | 2.409 | 2.677 | 2.945 | 3.212 | 3-479 | 4.004 16 .609 | 1.461 | 1.827 | 2.131 | 2.436 | 2.741 | 3.045 | 3.349 | 3.654 | 3-958 | 4.567 17 -685 | 1.643 | 2.054 | 2.396 | 2.739 | 3.081 | 3.424 | 3-766 | 4.108 | 4.450 | 5.135 18 .771 | 1.849 | 2.312 | 2.607 | 3.083 | 3.468 | 3.854 | 4.230 | 4.624 | 5.009 | 5.780 19 .859 | 2.061 | 2.577 | 3.006 | 3.436 | 3.865 | 4.205 | 4.724 | 5.154 | 5-583 | 6.442 20 .952 | 2.202 | 2.855 | 3.331 | 3.807 | 4.285 | 4.759 | §-234 | 5.731 | 6.186 | 7.138 21 1.049 | 2.518 | 3.148 | 3.672 | 4.107 | 4.722 | 5.247 | 5-771 | 6.206 | 6.820 | 7.869 22 1.152 | 2.764 | 3.455 | 4.031 | 4.607 | 5.183 | 5.759 | 6-334 | 6.912 | 7.486 | 8.638 23 1.259 | 3.021 | 3.776 | 4.405 | 5.035 | 5.664 | 6.294 | 6.923 | 7.552 | 8.181 | 9.44 24 1.370 | 3.289 | 4.111 | 4.797 | 5-482 | 6.167 | 6.853 | 7.538 | 8.223 | 8.908 j10.279 25 1.487 | 3.560 | 4.461 | 5.105 | 5.948 | 6.692 | 7.436 | 8.179 | 8.923 | 9-566 |11.053 26 1.609 | 3.861 | 4.826 | 5.630 | 6.435 | 7.239 | 8.044 | 8.848 | 9.652 |10.456 |12.065 27 1.733 | 4-159 | 5.1909 | 6.066 | 6.932 | 7.799 | 8.666 | 9.532 |10.300 11.265 |12.998 28 1.865 | 4.477 | 5.596 | 6.529 | 7.462 | 8.305 | 9.328 |10.261 |11.193 [12.125 |13.901 29 2.002 | 4.805 | 6.006 | 7.007 | 8.008 | 9.009 |10.01 |11.O1I /12.012 |13.013 |15.015 30 2.142 | 5.141 | 6.426 | 7.407 | 8.568 | 9.639 [10.71 [11.782 |12.852 |13.923 16.065 31 2.288 | 5.486 | 6.865 | 8.oo1 | 9.144 [10.287 j1r.43 |12.573 |13.716 14.866 |17.145 32 2.436 | 5.846 | 7.308 | 8.526 | 9.744 |10.962 |12.18 13.308 14.616 |15.834 |18.270 33 2.590 | 6.216 | 7.770 | 9.065 |10.360 |11.655 |12.959 |14.245 |15.54 16.835 |19.425 34 2.746 | 6.59 8.238 | 9.611 |10.984 |12.357 |13.73 |15-103, |16.476 17.849 |20.505 35 2.914 | 6.993 | 8.742 |10.199 |11.656 |13.113 |14.57 16.027 |17.484 |18.941 |21.855 36 3.084 | 7.401 | 9.252 |10.794 |12.336 |13.878 |15.42 16.962 |18.504 |20.046 |23.130 37 3.253 | 7-819 | 9.774 11.403 13.032 |14.861 |16.29 |17.919 |19.548 [21.177 |24.435 38 3-436 | 8.246 |10.308 |12.026 |13.744 15.462 |17.18 |18.898 }20.616 [22.334 |25.770 39 3.620 | 8.648 |10.86 |12.670 |14.480 |16.290 {18.10 |19.91 21.62 |23.53 |27-150 40 3.808 | 9.139 |11.424 |13.328 15.232 |17.136 |19.04 |20.944 22.848 |24.752 |28.560 4r 4.002 | 9.604 |12.006 {14.007 |16.008 /18.009 |20.00 |22.011 |24.012 26.013 |30.015 42 4.198 |10.065 |12.594 |14.693 |16.792 {18.901 |20.99 23.089 |25.188 |27.287 |31.485 43 4.40 |t0.56 |13.20 |15.40 |17.60 [19.80 |22.00 |24.20 26.40 |28.60 |33.00 44 4-606 |1r.046 |13.818 |16.121 |18.424 [20.727 |23.03 25.333 27.636 |29.930 |34.545 45 4.818 |11.563 |14.454 |16.863 |19.272 [21.681 |24.009 26.399 |28.908 |31.317 |30.135 46 5.043 |12.086 |15.128 |17.626 |20.144 [22.662 25.18 {27.698 |30.216 |32.754 |37-770 47 5.256 |12.614 |15.768 |18.396 |21.024 [23.652 26.28 |28.908 |31.536 134.164 139.420 48 5.482 |12.846 |16.446 |19.187 |21.928 24.669 |27.41 |30.151 |32.152 |35.633 |4r.115 49 S.714 |t2.913 |17.142 |19.999 |22.856 |25.713 |28.57 31-427 |34.284 37.141 [42.855 5° 5.950 |14.28 |17.850 |20.825 |23.80 [26.775 |29.75 {32-725 |35-70 38.675 |44.625 51 6.180 {14.832 {18.540 |21.665 |24.76 |27.855 |30-95 |34-045 37.08 |40.205 aaes 52 6.432 |15.437 |19.206 |22.512 |25.728 28.944 |32.16 |35.376 [38.592 |41.808 |48.240 53 6.684 |16.041 |20.052 |23.304 |26.736 |30.078 |33-42 360.762 [40.104 143.446 |50.130 54 6.940 |16.656 |20.820 |24.029 |27.760 |31.230 |34.79 38.17 141.64 45-12 ee 55 7.198 |t7.275 |21.504 |25.193 |28.702 |32-301 |35-99 [39-589 |43.188 ]40. 787 53.985 56 7.462 |17.909 |22.386 |26.117 {29.848 |33-579 |37-31 [41-041 44.772 ae 503 55.965 57° 7.732 |18.557 |23.106 |27.062 |30.928 /34.794 [38.66 [42.526 40-302 50.25 57-99 58 8.006 |19.214 |24.018 |28.021 |32.024 |36.027 |40.03 |/44.033 48.03) 52.089 ports 59 8.284 |19.902 |24.852 |28 964 |33.130'|37-278 |41-42 45.562 |48.704 53-84 On.t8 60 8.566 |20.558 |25.608 |29.981 |34.264 |38.547 42.83 147.113 [51.390 |55.679 |64.245 TABLE 5.— RELATIVE HUMIDITY, PER CENT — FAHRENHEIT TEM- PERATURES. (Chap. XXIII, p. 954.) Pressure = 30.0 inches, Air Depression of Wet-bulb Thermometer (¢ — ’). Temp. t -2/.4 |.6 |.8 |r.of|z.2/z.4/1.6)1.8)/2.0]/ 2.2 | 2.4/2.6] 2.8]3.0]13.2| 3.4] 3.6/3.8] 4.0 —40 || 46 —39 || 48 @-f) —38 || sol 2 t —37 || 53] 6 4.214.4]4.614.8]5.0']5.2]5.4]5.6]5.8]6.0 —36 || 56] ro pe mie ee 8 I I —35 || so] 15 ae —34 || 61] 20 TO} 9: 3] 8 33 63] 24 r1|| 12 8 4 ° —32 || 64] 28) r2|| 16] 12 8 4 ° —31 66 32 oO] 13}| 19 Is It 7 4 ° tq} 22 | 18 | 15 | Ir 8 4 ° —30 || 68) 36] 4 15|| 25 | 2x | 18 | rq | xz 7/4] 0 —29 || 70} 41| 9 16]| 28 | 24 | 2x | 18 | 14 |} rr 8 4 I —28 || 72] 45] 15 I7|| 30] 27 | 24 | 21 | 17 14 | Ir 8 5 I —27 || 74] 48] ro] | 18]| 33 | 30 | 27 | 24] 20 |] 17] r¢] rr] BI 5 —26 || 75] st} 24] 0 Ig]} 35 | 32 | 20 | 26 | 23 20.| 17 | t4.] m2 8 ey 58 sak sgl 20|| 37 | 34 | 32 | 29 | 26 23 | 20] 17 | 14 | 12 —24 || 77) 55] 32] Zo =P) = 8 57| 36] 15 t ar 0 | 20) ° eS ea 32 2 fal 0.1}0.2/0.3/0.4] 0.5 —20 || 82] 63) 45] 28] ro] =e ae —T9 || 83) 65} 48) 32] 15 =i ot 2 —18 || 84) 67] sz] 35] roj] 2 —47|| 60 | 17 ou o 69 53 39) 23|| 7 —46|| 63 | 22 omy: fe} 2)| 2 I2 79) 56) 4 7 —45|| 66 | 28 —I5 || 86} 72] 58} 45] 3r]| 17] 4 —44'| 68 | 32 —14 || 87) 74] Or] 48] 34]} 23] 8 —43!| 70 | 36] 3 —13 |] 88] 75] 63] 50] 38|| 25] 13] 0 421) 7h) 40) 9 —12 |! 88] 76] 64) 52] 4z|| 20] 17] 6 ~4T)| 72 | 43 | I4 II || 89) 77| 66} 55] 44/| 32] 21) ro —40)| 73 | 46 | 18 —39]| 74 | 48 | 22 =TO || go} 78) 68) 57] 46)| 36) 25} 4] 4 —38|| 75 | so] 25 | 2 = 9 |} 90} 79] 70} s9} 4o]] 39] 20] 18) 9 —37|| 76 | 53 | 28} 6 — 81] gol 81) 72| 61] sz|| 42] 32] 22] 13] 3 —36]| 77 | 56 | 33 | 10 = o1| 82] 72] 63] 54]| 44] 35) 26) 17] 8 —3sl|| 78 | so | 37 | 25 — 6 |] ot] 82] 73] 64) 56]} 47] 38) 20] 20] 1al| 3 —34|| 80 | 6r | ar | 20] 0 as 5 =, 81 | 63 | 44] 24] § 5 |} ox] 83] 75) 66] 58!) 40] 42) 32] 24] 16|| 7 me — 4 || 92] 84] 76} 68] 6o]| 52] 44] 36) 28) 20]] 12 4 me ne et 46 | 28 | 10 — 3 || 92} 85} 77] 69} 6r/} 54} 46] 30] 31] 23]| 16 8 I —30 3 68 oS 36 a3 = 2 || 92) 85] 78] 7x] 63]] 56| 49] 42/ 34] 27|| 19 | 22] 5 = 2 — 1 |} 93] 86) 79) 72] 65/) 58) sz] 44] 37] 30] 23 | 16 | ro] 3 : © || 93) 87) 80} 73) 67/) Go} 53] 47] 40} 33]| 27 | 20] 14] 7] x + I |} 93] 87] 82] 75] 68]} 62/ 56] 40] 43| 36|] 30 | 24 | 28 | xz = 2 || 94] 88) 82] 76} 7ol] G4] 58) 52) 46] 30] 33 | 27 | 2x | 15 | 9 3 3 || 94} 88) 82) 77] 7x|| 65] 50] 54} 48] 42|| 36 | 30 | 25 | 10 | 13 7 2 4 |] 94] 80] 83) 78) 72]! 66) 62] 55] 50] 44]| 30 | 33 | 28 | 22 | 17 Il 6 ° 5 || 95} 80) 84} 78} 73)| 68) 65) 57) 52] 46|| 4x | 36 | 3x | 25 | 20 || 15 | ro | 4 6 || 95] 90} 84] 79] 74] 60) 64) 50] 54] 4ol| 43 | 38 | 33 | 28] 23 || 8} 23] 8] 3 Z || 95; 90) 85; 80! 751] 7o, 65} Go} 55] sz]! 46 | az | 36 | 31 | 26 || 21 | x7] x2] 7] 2 8 || 95] 90] 86] 81) 76)| 7x) 67] 62] 57] 53l] 48 | 43 | 38 | 34] 20 |] 24] 20] x5 | ar] 6 9 |) 95) 94) 86) 82) 77/} 72] 63] 63) 50) ssl] so | 46 | 4x | 36 | 32 || 27 | 23 | 18] 14] 10 ne 2 91 or 82! 78) 73] 60] 6s] Go) s6l| 52 | 47 | 43 | 39 | 34 || 30 | 26 | 22 | x7 | 33 Fe lf ele & 83] 791] 74) 70] 66] 62] 58|/ 53 | 49 | 45 | 4t | 37 || 33 | 28 | 25 | 20 | 16 os 96 92 = oe 80}! 75] 71] 67| 63] sol] ss | st | 47 | 43 | 30 || 35 | 3z | 27 | 23 | 10 o 26 eel aloes - 76| 73| 60} 65) 6r|| 57 | 53 | 49 | 45 | 4t || 38 | 34 | 30 | 26 | 23 92) 99) 85) 81|! 77] 74] 70) 66] 62/) 50 | 55 | st | 48 | 44 |! 40] 37 | 33 | 20 | 26 re 96} 93] 80] 86] 82 78) 75] 71| 67) 64|| 60] 57 | 53 | 50 | 46 || 42 | 30 | 35 | 32 | 20 r 96) 93] 90] 86] 82 79) 76] 72! 69] 65|| 62 | 58 | ss { 51 | 48 || a5 | ax | 38 | 34] 3r uo 97) 93] 90} 86] 83]| 80] 77| 73] 70] 66|| 63 | 60 | 57 | 53 | so || 47 | 43 | 40 | 37 | 34 : 97) 93] 90] 87) 84); 80} 77) 74) 71| 68]| 65 | 6r | 58 | 55 | 52 || 40 | 45 | 42 | 30 | 36 9 || 97) 94} 90] 87] 84] 8x) 78) 75] 72] 60]; 66 | 63 | 60 | 56 | 53 |] so | 47 | 44 | ar | 38 20 | 97; 94) ot] 88) 85|| 82| 79] 761 73] 70\| 67 | 64 | 6x | 58 | 55 |] 52! 40 | 46 | 43 | 4o TLlOO TABLE 5. — Continued. Depression of Wet-bulb Thermometer (¢ — ?’). I.0 3-5/4.014.5]5.0||5.5/6.0]6.517.017.5 || 8.0] 8.5 | | | | | | | | | | 9-5 10.0 10.5 TIOL TABLE 5. — Continued. Air Depression of Wet-bulb Thermometer (¢ — 2’). t 11.0]11.5!12.0|12.5|13.0)|13.5/14.0/14.5|15.0]15.5||16.0|16.5|17.0/17.5| 18.0|| 18.5) 19.0] 19.5] 20.0) 20.5) 21.0 35 2 36 By 37 Ei 3 38 Io} 6] 2 39 12] 8] 5 21.5| 22.0) 22.5] 23.0] 23.5|| 24.0) 24.5] 25.0] 25.5] 26.0]| 26.5] 27.0| 27.5] 28.0} 28.5 I 62 3 I 63 4 2 ° 64 6 4 2 65 || 7} 5 66 ||} 9} 7 OIA UwWKO COI OR W H I 7z || 15 | 13 | 12 | 10] 9 3 I 72 16 | 15 | 13 | 12 | Io 4 3 I 73 || 17 | 16 | 14] 13 | rz |] 10 | 8 5 4 3 I 74 || 18 | 17: | 13 | I4 ] 13 Ir | Io 7 5 4 3 I 75 |} 20] 18 | 17 | 15 |] 14 12 | It 9 8 7 5 4 3 I 76 || 2x | 19 | 18 | 16 | 1g || 13 | 2] rr 9 8 6 5 4 3 I 77 || 22 | 20} 19 | 17 | 16 |] 14 | 13 | 12 | 10] 9 8 6 5 4 3 78 23 | 21 | 20 | 18 | 17 16 | 14 | 13 | 11 | 10 9 8 6 5 4 79 {| 23 | 22] 2r | 19 | 18 |] 17 | 15 | 14] 13 | IT 10 9 7 6 5 80 24 | 23 | 22 | 20 | I9 18 | 16] 15 | 14 | 12 II # 10 9 7 6 TI02 TABLE 5.— Continued. Air Depression of Wet-bulb Thermometer (¢ — 2’). Temp. = t I 2 3 4 5 6 7 8 9 Io IL 12 13 4 15 80 96} oz] 87} 83} 70 || 75 | 72] 68] 64] 6: || 57] s4] so 47 | 44 82 96 92 88 84 80 76 72 69 65 61 53 55 5r 48 45 84 96] 92] 88] 84] 80 76} 73 | 69| 66| 62 59} 56] 52] ao] 46 86 96 | o2 88) 84] 81 77 73 | 70} 66| 63 60] 57] 53] sol] 47 88 96} o2] 88] 85] 8: || 77] 74] 70] 67] 64 }| 62] 57] 54a] gx] 48 90 96} o2] 89] 85] 81 78 | 74] 71] 68] 65 6r| 58] ss | sz] 40 92 06] 92] 89} 85] 82 78 | 75] 72 | 68] 65 62] 59] 56] 53] 50 94 96} 93 | 80] 85] 82 79! 75| 72| 69} 66 63 | 60] 57] 54] 51 96 96 93 89 86 82 79 76 73 69 66 63 61 58 55 §2 98 96 |} 093 89 | 86] 83 79 | 76] 73 70 | 67 64} 61] 58} 56] 53 100 96} 03] 89] 86] 83 80] 77] 73] 70] 68 65| 62] so} s6|] 54 102 96 93 90} 86 83 80 77 74 71 68 65 62 60 | 57 55 104 97 | 93 | 90} 87] 83 80} 77) 74] 71 | 60 66 | 63] 60} 58] 55 106 97) 93 | 9c | 87] 84 8r| 78] 75 | 72] 70 66] 64] 6r|] 58] 56 108 971 93] 90] 87] 84 81 | 78| 75 | 72] 70 67 | 64| 62] so] 57 IIo 97 | 93] 90] 87] 84 81 | 78| 75] 73 | 70 671 65 | 62] 60] 57 112 97} 94] 90] 87] 84 81 | 79] 76] 73] 70 68 | 65 | 63 | 60] 58 IIg 97 | 94] or | 88] 85 82] 79] 76] 74] 72 68 | 66] 63] 6r] 58 I16 07 | 04] or | 88] 85 || 82] 79] 76] 74] 71 || 69} 66] 64] 61] 50 118 97} o4] ot | 88] 85 || 82} 79] 77} 74] 72 || 60] 67 | 64] 62] So 120 97 oa | or 88 85 82 80 | 77 74 72 69 67 65 | 62 60 122 97/ 94] 9: | 88] 85 83; 80} 77] 75 | 72 70 | 67} 65] 63] 60 124 97 | 94} or] 88] 85 83 | 80} 78] 75] 73 7o| 68 | 65] 63} 61 126 97 94] oF 88 | 86 83 80] 78] 75 73 70 | 68 66 | 64] 61 128 97 94 | 91 89 86 83 81 78 76 73 71 68 66 64 | 62 130 907 94 QOL 89 86 83 81 78 76 73 71 69 67 64 62 132 97 | 94] 92] 80] 86 84 | 8: |} zo] 76} 74 71| 69} 67] 65] 63 134 97 | 94| 92] 89] 86]| 84] 81] 70] 76} 74 |] 72] 69} 67} 65] 63 136 97 | 94] 92] 80) 86 ]| 84) 8: | 7o] 77] 74 || 72] 70] 68] 65] 63 138 97| 94] 92 | 80] 87 84 | 82) vo] 97] 75 72| 70| 68 | 66] 64 140 97} 95 | 92} 89] 87 84} 82) 79] 77] 75 73 | 70] 68 | 66} 64 j Depression of Wet-bulb Thermometer (¢ — #’). 16 17 18 I9 20 ar 23 ; 23 24 25 26 27 28 29 30 80 41 38 35 32 29 26 23 20 18 Is 12 Io 7 5 3 82 42 39 36 33 30 28 25 22 20 17 14 12 10 7 5 84 43 40} 37 | 35 32 29 26 24 2r 19 16 14 12 9 7 86 44 42 39 36 33 31 28 26 23 ar 18 16 14 II 9 88 46 43 40 37. 35 32 30 27 25 22 20 18 15 13 IL 9° 47| 441 42} 39] 36 34] 3m] 29] 26] 24 22} ro] 17] 5] 13 92 48 | 45] 42| 40] 37 || 35] 32] 30] 28] 25 23] 21] 19] 7] 15 94 49 46 43 41 38 36 33 31 29 27 24 22 20 18 16 96 50} 47 |" 44] 42] 39 371 35 | 32| go) 28 20 | 24] 22] 20] 18 08 so | 48] 45] 43] 40 38 | 36] 34] 32] 20 27} 25] 23] 21] 19 100 st|j 49| 46] 44] 42 39 | 37] 35] 33 | 30 28 | 26) 24] 22] ar Io2 52} 40] 47] 45] 42 40] 38] 36] 34] 32 30} 28] 20] 24] 22 104 53 50} 48| 46] 43 4E | 39] 37] 35] 33 3r 29] 27) 25 | 23 106 53} st] 49] 46] 44 42] 40; 38] 36] 34 32 | 30] 28) 26} 24 108 54] 52] 49] 47] 45 43 | 4t | 39] 37] 35 || 33] 31 | 29] 27] 25 110 55 | 52] so] 48} 46 44| 42] 40]; 38] 36 34] 32] 30] 28] 26 112 55] 53] st} 49] 47 || 44] 42] 40} 38] 36 35 | 33 | 32] 29] 27 114 56 | 54] 52] 49] 47 45 | 43 | 41] 39] 37 35 | 34] 32] 30] 28 116 57 | sa] s2] so} 48 46} 44] 42] 40] 38 36] 34] 33] 31] 20 118 57] 55| 53} 5t] 49 || 47] 45] 43 | 4t |] 39 || 37] 35 | 34] 32] 30 120 58} ss | 53] St] 40 47| 45] 43] 42} 40 38] 36] 34} 33] 31 122 58 | 5s6| s4] 52] sol} 48] 46) 44] 42} 40 ]| 39] 37] 35 | 34] 32 124 59] 57] 54] 52] 50 48 | 47 | 45] 43] 41 39} 38) 36] 34] 33 126 59 | 57] 55 | Ss3 | 52 49| 47| 45] 44] 42 4o| 38] 37) 35] 33 128 60] 58} 56} 54] 52 so} 48 | 46] 44] 42 4r| 39] 37] 36] 34 130 60] 58] 56] sa] 52 ]| so} 48] 47] 45] 43 |} 42} ao} 38] 37) 35 132 6r| 58] 56} ss} 53 || st} 40] 47] 45] 44]; 42] 40] 39] 37] 36 134 6r| so} 57] 55 | 53 5st} 49} 48] 46] 44 || 43] 41] 39] 38] 36 136 6 | so | 57) 53 | 84 52] so} 48) 46] 45 43 | ar | 40] 38] 37 138 62| 60] 58] 56] 54 52] So} 49] 47] 45 44) 42] 40] 39) 37 140 62] 60] 58] 56] 54 53] st | 49] 47 | 46 44] 43] 41 | go] 38 I103 I104 APPENDIX TABLE 5. — Concluded. Air Depression of Wet-bulb Thermometer (¢ — ?’). Temp. t 3r | 32 | 33 | 34 | 35 36 | 37 | 38 | 30 | 40 |] 4r | 42 | 43 | 44 | 45 80 ° 82 2 ° 84 5 3 ° 86 7 5 3 I 88 9 7 5 3 Tt 90 Iz 9 71 as 3 = 92 13 Il 9 7 5 3 I 904 14 12 Io 9 7 5 3 I 96 16 14 12 Io 8 7 5 3 2 ° 98 17 I5 14 12 10 8 7 5 3 2 ° 100 19 17 I5 13 12 Io 8 7 5 4 2 I 102 20 18 16 15 13 II 10 8 q 5 4 2 I 104 2m 20 18 16 I4 13 rr Io 8 7 5 4 2 I 106 23 ar 19 17 16 14 13 Il 10 8 7 5 4 3 I 108 24 22 20 19 17 16 14 12 Ir Io 8 7 5 4 3 I10 25 23 ar 20 18 17 15 14 12 II Io 8 7: 6 4 112 26 24 23 2r 19 18 16 I5 14 12 Il 9 8 7 6 Tig 27 25 24 22 20 19 18 16 IS 13 12 Il 9 8 7 116 28 26 25 23 22 20 19 17 16 14 13 12 Ir 9 8 118 29 27 25 24 23 21 20 18 17 16 14 13 12 Ir 9 120 29 28 26 25 23 22 2I 19 18 17 15 14 13 12 10 122 30 29 27 26 24 23 22 20 19 18 16 15 14 13 Ir 124 31 30 28 27 25 24 22 2I 20 18 17 16 Is 14 12 126 32 30 29 27 26 25 23 22 2z I9 18 17 16 Is 13 128 33 31 30 28 27 25 24 23 22 20 19 18 17 16 14 .130 33 32 30 29 28 26 25 24 22 2m 20 19 18 16 15 132 34 33 3r 30 28 27 26 24 23 22 21 20 18 17 16 134 35 33 32 30 29 28 26 25 24 23 2I 20 19 18 17 136 35 34 33 31 30 28 27 26 25 23 22 2I 20 19 18 138 36] 35] 33 | 32] 30 29 | 28 | 27] 25 | 24 23 | 22] 21 | 20] 19 140 37| 35 | 64) 32] 3 30] 29] 27] 26] 25 24.) 23 | ot | 2e| xo Depression of Wet-bulb Thermometer (¢ — ?/’). t 46 | 47 | 48 | 49 | so || st | 52 | 53 | 54 | 5s || S6 | 57 | 58 | 59 | 60 a ey 4 106 ° 108 2 ° IIo 3 2 I I12 4 3 2 I I14 6 5 3 2 I 116 7 6 5 4 2 I ° 118 8 i 6 5 4 3 2 iT 120 9 8 7 6 5 4 3 2 I 122 Io 9 8 7 6 5 4 3 2 I ° 124 Ir 10 9 8 7 6 5 4 3 2 I ° 126 12 Ir 10 9 8 7. 6 5 4 3 2 2 I 128 13 12 IL Io 9 8 7 6 5 4 4 3 2 I ° 130 4 13 I2 Ir Io 9 8 7 6 5 5 4 3 2 I 132 15 14 13 12 Ir Io 9 8 7 6 6 5 4 3 2 134 16 15 14 13 12 Ir Io 9 8 7 6 6 5 4 3 136 17 16 15 14 13 12 Ir Io 9 8 7 6 6 5 4 138 17 16 15 14 14 13 12 Il Io 9 8 7 7 6 5 140 18 17 16 1s 14 13 12 I2 Ir Io 9 8 7 7 6 1105 APPENDIX zbi°Sgor £96" 1g01 £gL-glor 1og'SLor | gib‘zlor ££z ‘6901 Lyo'ggor | 6Sg-zgor | oLg°6Sor | ogb-gSorx gge'fSor | S60 oSor | 106'gbor | Sod Evor | goS-ovor | Go€-L€or | 6orpfor | Lo6-ofor | ol-Lzo1 | o0S$-bzor Oz ‘IZO1 480° 3101 6g vro1 699‘ L101 gsb' goor Svz*Soor 10° ZOOI S1g°966 gOS $66 ogt 266 ogt 696 6£6° $36 411-796 £6616 ggz9L6 Ito £16 £1g°696 £gS +996 zSE° E96 0z1°096 16-986 LoL: €$6 gor -0S6 Lgz'Lv6 SLo'br6 I£gob6 gv9' £6 bch be6 o1z‘'1£6 066°1z26 gol vz6 Svs 126 ooze 916 £60 S16 Sgg "116 S£g° g06 tor S06 1L1°z06 9£6 96g ool $6g zob-z6g £zz 69g £36 °Sgg 6£L°z7gg S6b 64g 6bz ‘91g zoo" fLg £4698 zoS* 998 oSz £98 966688 1bZ-oSg bgp ESQ Szz‘oSg $96°9¢g fol rg obb org SLr-L&g 06: fg obg ofg vee Llzg gbhi'bzg 163 ‘02g gg 41g £6€ bg gel 11g 1gg°Log zzg' tog ZQE* 10g oor -g6L gfe FOL oLS 164 £0€ -gQl b£o Sel £94 1gL 06h glL S1z°Sh georL2 099° g94 ogt “Sod oz1'zgd gSg°gSh bos SS gee zSl ogo 6bL 06L° Sb gis-2r bre 6eL gg6 See 069° z£L orb 62 gz ged beg zzl gs: 614 oLz ‘orl og6'zr 889° 604 POE“ gol g60 "fol 00g * 669 oz ‘969 gez £69 £56 639 999° 989 gle: gq ggo ogg £6L°9l9 gor fL9 o0z ‘olg 006" 999 419° £99 I£E*099 fo" LSq ESL -eSq ogboSg Sg1‘Lto 193° ¢F9 LoS: obo Sgz Leg 096° £f9 £S90f9 fve-Lzg Ifo 'vz9 L1L‘0z9 oob Lig 1g0 big 6SL 019 Sep: Log 601 ‘bog ogZ 00g 6rb 26S S11 76S ogZ “06S Ivy Les oor tgs LSL-ogs Ip LLS £90 PLS f1L°0lS og LoS 110‘ ¥9S 649098 pee LSS Lg6°¢SS gfgoSs Sgz Lbs of6' fhS £18 -ob$ f1z°Les oSg ees 00S ofS obi LzS o6L°€zS zep-ozs olo' L1$ gol €xS gee ors g96° gos 96S £oS zz "00S 693° 96h gis £6r 6S1 ‘06r g6L ‘ogr Sep: fob ggo'ogh 669‘ 9Lt gee ely 0$6 69h oLS- gor coz ‘for gzg OSr ish oSb to’ Sh 339 6bb 108 orb 116°cby Li 6¢h oz ott ocd zh ze 6cr £60: Szp ves zz If 61P Sel Sip S1f-z1V 206 ' gob Sev Sor 90° zor obg g6e bez S6e zg 16¢ IV 9ge 266 -Pge oLS “198 bri'gle pil ple ogz LE zvg Lot oob Foe $36 o9f £9S-°LS¢ LEr-ySe LoL: oS€ ele Lye ££Q°Lve 6g ‘ove 16° 9f€ ggr eee ofo0 off OS gze pS1-eze gol Ore gSz "git 00g zie gee Gof zlg ‘Sot oot zof 226° g6z obb S6z 946° 162 goS ‘ggz 1£0°Sgz oS‘ 1gz £g0°glz oLS blz tlo'1lz 998 ‘Loz 9So°bgz obS -ogz 6£0°LSz 12S eSz - L10'oSz L6vgbz oL6'zbz Lev 6Ez L6g°SEz Ise cz 664° gzz obz Sze gzl-1zz gOoz “giz 619 ‘v1z tvI-11z gS ‘Loz tbo voz fgv coz $16°961 gfe Lor oSZ-6gr O1Z “Ogi 6Sg°zgt g6o°6L1 LeS°SLy Sv6'rLr eS - gor oS ‘vor LEL*IQI bis LS1 ogg Sr 6Lz°oS1 S99‘ gb Slo: fbr 66€ -6Ex gb. Sex £go'ze1 gob gzr LiL ver S1o-1zr oof *L1r 6 8 4 9 s v & z I ° CaTqey suosdwoy yz) (989 ‘d ‘TAX “deyD) “SHNIONA WVALS YO AIAVL NOILVLAMWOSD ULVAYVALVM TVOILAMOAHL — ‘9 ATAVL APPENDIX r106 Loz $661 €L1°z661 | glo: 6g61 €g6°Sg61 | gggzg61 | 16L°6L6r | P6g'9L61 | L6S°SL6r | 66v-0L6r | cob’ Lo6r °9 IOf*vo6r | toz'1961 | cor gS6r | 666°PS6r | g6g 1861 | S6L-gh61 | z6g'SH6x | OgS-zh61 | Sgr 6£61 | oge gf61 6s Slz°¢f6r 691 of6r zgo°' L261 SS6°¢z61 grg oz6r | O€L°L161 | ofg'v161 1zS "1161 113061 oof S061 gs 6gr‘zobr | 410°66gr | tg6'S6gr | 1Sgz6gr | gfL-6ggr | Ezg:oggr | goS-Eggr | C6E-oggr | Léz-Llgr | og1 vlgx 4S Evo rlgr | Sc6-Logt | gog vogt | Lgg°19gt | goS-gSgr | Leh SSgr | gzf-zSgr | Soz'Grgr | Ego'gbgr | og6°zhgr 9$ LEQ 6€gt £xrL°9€QI1 ges feg1 Lgb ofg1 gee Lzgr IIz‘zgr bgo'1zgi LS6°L1g1 6zg‘FIgr ool 11g ss gzg'gogr | OSS:Sogr | tly zogr | g6£°6641 | oz€-g6L1 | zhz-€6L1 | zor-o6L1 | zgoLgl1 | coo'vglr | Oz6-oglr vs stg Lilt | vSL-pldr odg*1LZt | ggS godt | ooS:Sodr | bib zod1 dct OSL gezoSd1 | oS1-€SL1 | ogo’ oSdr1 es 016: obli gig fvlr. | ogi obd1 bog LELI 009 veL1 gos 1eL4 orb gzLr pre Szlr giz‘ 7zLy oz1 6141 zs zzo' gilt zzO-7rdt ZzQOOLI zzL‘gol1 | oz: foL1 giS‘ool1 | vib'L69r | o1f 6x goz ‘1691 O01 *8ggt 18 v66'Pgor | O8g°Ig9I g4Lgtor olg'SLor | o9S-zLg1 | oSb-6g91 gfe -gg91 gzz*fgg1 | P11‘0gg1 | coo LSor of ggg €Sq1 | oLL-oSgr Sg Lvo1 ges ror | och: 1v9r ZOE“ Qlgr zQr°S€or zgo'efgr zv6'gzgr | ozgSzor 6b 369° zzor PLS 6191 oS?’ orgr gze-€19gr | ooz'o1g1 | ¥Lo°Logr gh6° fogr BIg Oogr 069° L6Sr 09S -F6Sr gr off 16ST gOz “gest gor SgSt blo-zgSt 006°gLSt 994° SLS1 ofg9 zLS1 v6r69Sr gSe-goSt ozz €or LY ZO OOST zv6°oSSr zog' eSStr z9gOSSt ozS LbSt gle-prSr | Pez-r1bS1 o60'geSt gr6- vest cog 12S1 gv bSg'gzSt | goS-SzSr OS€-zzSt | o1z-61S1 | ogo'grSr | o16-z1S1 | gSL-60S1 | gog:goS1 | vSh-EoS1 | cof-ooStr Sv obi L6b1 | 066° f6rr b£g-o6F1 glo lgrr | oS bgbr zQf-1gh1 zoz *glbr zvo° Slvr zgg Lb ozL gor ve gSS°Sopr | vOE-zobr | ofz: 6Srz ggogShr | co6-eShr | pel 6hbr | goS-orbr | gOE-Ehbr | Ofc ob | coo LErI ev £l6°Elhr | vogoft1 Slo‘ Lebr brs ber fib izbr | oge: grbr Avr Sir z1O"ZIb1 4Lg° gobi obLSobr cad Log zobr | tor’ 66Er Sz€-g6fr | ber fOr | Cho o6fr | co6'ggtr | LSL° Eger zig‘ogér | Lov LLEr | oz Plex Iv Eli x1l€1 | vzo' goer SLQ° Pol bel lft ELS gSer ozb: SSEr Loz*zSer ZI‘ OFEI £86°SPEx 00g zvet ov frg O€€r | bev ger Sze" Seer vor otfr foo Leer | obg fze1 Llg'ozey z1S"L1er LVC Vier Ogi 111 oe €1o'gokr | bry: Polr Slo" 10€r toS: g6z1 £€e-S6z1 ogi z6z1r 136° 9gzr ZIQ*Sgzr L€g*zgz1 ooh 6Lz1 ge €gz-glzr por lzr Sz6°69z1 bel: ggzz LoS: lgzr | ogl-ogzr 261°LSz1 z10'PSzr Lzg:oSzi obg:' Lezr Le Sbrrer | voc bz Slo: g&z1z gg hfz1 £6g°1€z1_ | ooS gzz1 Lot *Szz1r ZII*ZzzI L16°QIz1 ozL:S1z1 gf gSS*crz1 g6£° Goz1 z€z" gozr ggo*fozr |} 006°6611 z€L-g6rr | voS: e611 6° o61r zzz Lgui oSo' Fgir se gLg*ogii col LLir gzS blr grf-rZr1 | ofr gor 066'ro1r =| O1g'IgII gzg gSir | bry SSir ogz'zSir ve blo: 6b ggg Srrr ool zhvir orS6€11 ozb oftr ger eer 9£6° 6211 zed gz1r gS €z11 oS€-ozo1 ce zSr°d4rr1r | pS6°fr1r =| PSL orr1 zSS:Lor1r | oS€-borr | gbr*1orr zv6° L601 9£L° y601 gzS° 1601 ozf- ggor ze 6 g 4 9 s v € z I ° “ads “papnjauo) — 9 ATAVL APPENDIX II07 TABLE 7.— PROPERTIES OF AMMONIA (NH;). (Chap. XXIV, p. 997.) Abs. Press. Fahr. aN Sp. Vol. Lbs. per; Temp. a : or H br oy %sar Sat. NH. sq. in. 10 |—47.5 |—83.5 | 584.30 | 500.80 |—.1816 | 1.4145 | 1.2329 21.50 1g |—27.5 |—62.95 | 572.25 | 509.50 |—.1355 | 1.3240 | 1.1885 | 17.00 20 |—17.0 |—51.50 | 565.75 | 514.25 |—.1105 | 1.2772 | 1.1667 | 13.50 25 |— 8.5 |—42.50 | 560.50 | 518.00 |—.o0800 | 1.2412 | 1.1512 | 10.35 30 0.0 |—33.75 | 556.00 | 522.25 |—.0706 | 1.2070 | 1.1364] 9.00 35 +6.25 |—27.10 | 551.63 | 524.53 |—.0562 | 1.1830 | 1.1268 7.87 40 I2.0 |—21.00 | 548.00 | 527.00 |—.0433 | 1.1610 | 1.1177 6.92 45 17.2 |—15.65 | 544.90 | 529.25 |—.0322 | 1.1420 | I.1098 | 6.20 50 21.85 |—10.62 | 542.00 | 531.38 |—.0220 | I.1245 | 1.1025 5.60 55 26.35 |— 5.80 | 539-35 | 533-55 |—-O1T7 | I-I075 | T.0g52 | 5.15 60 30.30 |— 1.73 | 536.78 | 535.05 |—.0028 | I.0940 | T.ogt2 | 4.75 65 34.20 |+ 2.40 | 534.30 | 536.70 |+.0060 | 1.0807 | 1.0867 | 4.40 70 38.00 6.40 | 531.88 | 538.28 .0147 | 1.0680 | 1.0827 4.10 75 41.3 9.80 | 529.81 | 539.61 -0215 | I.0565 | 1.0780 | 3.85 80 44.4 13.00 | 527.85 | 540.85 .0278 | 1.0460 | 1.0738 | 3.6 . 8s 47.6 16.18 | 525.83 | 542.01 .0342 | 1.0350 | 1.0692 | 3.4 go 50.6 19.40 | 523.95 | 543-35 .0403 | I.0250 | 1.0653 | 3.22 95 53-4 22.45 | 522.15 | 544.60 .0459 | I.o160 | 1.0619 | 3.04 100 56.1 25.30 | 520.40 | 545.70 -0514 | I.0080 | 1.0594 2.90 105 58.8 28.10 | 518.70 | 546.80 -0570 .9997 | 1.0567 | 2.75 IIo 61.3 30.80 | 517.10 | 547.90 -0619 -9920 | 1.0539 | 2.63 IIS 63.6 33-20 | 515.60 | 548.80 0663 -9842 | I.0505 | 2.50 120 65.9 35.58 | 514.12 | 549.67 .0708 -9766 | 1.0474 | 2.41 125 68.15 | 37.95 | 512.67 | 550-62 10752 .9690 | 1.0442 | 2.32 130 70.45 40.40 | 511.25 | 551.65 .0798 -96030 | 1.0428 2.25 135 72.5 42.55 | 509.90 | 552.45 .0837 .9571 | 1.0408 | 2.15 140 74-5 44.65 | 508.60 | 553.25 | .0875 | -9515 | 1.0390 | 2.07 I45 76.52 40.77 | 507.32 | 554.09 -OQI5 -9457 | 1.0372 2.00 I50 78.52 48.88 | 506.05 | 554.93 -0952 -9402 | 1.0354 1.95 I55 80. 42 50.88 | 504.85 | 555.73 .0988 -9348 | 1.0336 I.90 160 82.15 52.68 | 503.70 | 556.38 .1025 .9292 | 1.0317 1.85 165 83.93 54.55 | 502.50 | 557-05 . 1061 -9234 | 1.0295 1.80 170 85.70 | 56.45 | 501.35 | 557-80 . 1096 .9183 | 1.0279 | 1.75 175 87.05 58.22 | 500.28 | 558.50 . 1130 -9146 | 1.0273 1.70 180 89.12 | 60.05 | 499.15 | 559.20 1163 .9103 | 1.0266 1.65 185 90.85 61.90 | 498.05 |' 559.95 LIQ .9043 | 1.0238 | 1.61 190 92 -35 63.40 | 497.05 | 560.45 .1222 .goog | 1.0231 1.58 195 93.90 | 65.05 | 496.00 | 561.05 .1250 .8962,| 1.0212 1.54 200 95-45 66.75 | 494.97 | 561.72 .1279 .8915 | T.0194 1.50 205 96.18 | 68.30 | 493.95 | 562.25 .1306 .8870 | 1.0176 1-47 210 98.5 69.90 | 492.95 | 562.85 - 1333 .8825 | 1.0158 | 1.43 215 100.05 71.50 | 492.00 | 563.50 . 1360 .8780 | 1.0140 1.30 I108 APPENDIX TABLE 8.— PROPERTIES OF SULPHUR (Chap. XXIV, p. 997.) DIOXIDE (SO:). t ? q r oz oy Sp. Vol. —4o 3.16 23.3 174.1 — .047 305 20.9 — 30 4.5 — 20.0 173.5 — .041 362 16.0 —20 6.1 —16.8 172.5 — .034 358 12.0 —Io 8.0 —13.5 7D 39 — .028 -354 Q.2 ° 10.3 —10.3 170.6 —.021 +350 FD Io 13.3 — 7.0 169.2 — 015 -346 5.0 20 17.0 = B40, 167.3 — .008 341 4.6 30 21.5 — 0.5 165.0 — .0o1 +335 Bay 4o 27.1 2.6 162.0 005 +330 3.0 50 33.5 5.9 158.8 -O12 +324 2.44 60 41.0 Q.2 155.0 .018 -318 2.0 70 50.0 12.5 I51.3 1025 -312 Ty 80 60.0 15.7 147.0 .032 » 305 I.4 go 72.0 19.0 142.3 .038 .298 I.r 100 84.5 22.2 139.5 .045 +290 0.9 TABLE 9. — PROPERTIES OF CARBON DIOXIDE (COQ,). (Chap. XXIV, p. 997.) t ? q r ob; oy Sp. Vol. —30 185 —27.8 130.0 — .060 +240 +490 —20 225 — 23.9 126.5 — .O51 -235 -417 —I0 265 —19.7 122.0 = 042 +230 +350 ° 310 —1I5.2 117.8 — .032 +224 . 294 Io 360 —10.8 II2.0 — .022 218 - 246 20 420 — 5.9 106.5 — .o12 21 - 206 30 490 = O83 100.0 — .OOo1 . 204 ,Ez2 4o 570 + 4.6 93.0 .O1O -197 -145 50 655 10.3 85.9 .O2T .189 .120 60 750 16.8 76.0 .034 . 180 . 100 70 850 24.5 64.0 .048 - 169 .O81 80 965 35.0 46.0 .067 -153 .062 88.5 1070 59.3 0.0 -I12 -112 .035 88.5 is critical temperature for COs, bo fod APPENDIX T10g TABLE 10. —- AMMONIA ABSORPTION IN POUNDS OF AMMONIA ABSORBED PER POUND OF WATER. Pressure Pounds per Square Inch Absolute. Temperature om 15 20 25 30 35 40 Io 1.38 1.76 2.15 2.54 2.92 3-34 20 1.09 1.40 1.70 2.01 2635 2.64 30 -92 1.18 1.43 1.69 1.94 2 2% 40 .80 EiOR 1.23 1.46 1.67 1.91 50 -70 89 1.08 1.38 1.48. 1.68 60 63 -80 .96 1.14 T.3t 2.49 70 56 -71 86 1.02 1.17 1.34 80 50 -64 .78 92 1.06 1.20 go 245 -57 .69 82 95 1.08 100 .40 .51 .62 73 84 -96 IIo 36 - 46 56 .67 .76 .87 120 333: /4I .50 .60 .69 78 130 29 -39 “45 -54 62 .71 140 26 £33 -40 -48 £55 62 150 23 +29 .36 -42 -48 255 160 20 .26 31 38 43 48 170 .18 23 28 33 -38 43 180 16 -19 123 28 33 37 190 13 ey, 20 -24 28 132) 200 3h2 14 17 20 23 26 TABLE 11.— PROPERTIES OF NaCl BRINE. (Chap. XXIV, p. 1009.) Specific Degrees on Freezing Ber a f = Gravity at Salometer at Point. Specific Heat. Salt by Weight. 30° F. 60° F. oF, I I.007 4 +30.5 -992 2 1.015 8 +29.3 984 2.5 1.019 10 + 28.6 -980 3 1.023 12 +27.8 -976 3.5 1.026 14 err 972 4 1.030 16 +26.6 -968 5 1.037 20 +25.2 .960 6 1.045 24 +23.9 -946 7 1.053 28 122.5 , 932 8 1.061 32 +ar.2 919 9 1.068 36 +19.9 905 10 1.076 40 +18.7 892 12 £.091 48 +16.0 874 I5 I.1I5 60 +12.2 855 20 1 155 80 + 6.1 820, 24 1.187 96 SP Es 2 -795 25 1.196 100 + 0.5 . 783 26 I. 204 104 =: Dpt 77D: IIIO APPENDIX TABLE 12. —PROPERTIES OF CaCl BRINE. (Chap. XXIV, p. 1009.) ‘ ‘ Degrees on é : Per cent of the Salt by Weight. Specific Gravity Salometer at Freezing Pont, Specific Heat. at 60° F. 60° F. F. Dp eacwk eeuige ea genienanss 1.007 4 +31.10 -996 Droid accrstsa a paecteie giaeneia eds 1.015 8 +30.38 -988 BZinysigesde g¢¥s CHEE 1.024 12 +29.48 -980 Ae gy kee eee eee Ae eee 1.032 16 +28.58 -972 IG As ed iaed ot alt ata eans 1.041 22 +27.68 -964 Ord cp ito at onand ic tulite Seat aca 1.049 26 +26.60 -960 Wt iiois ih ewe Hak Rank IiReeNCeS 1.058 32 + 25.52 -936 1S Gis rcpt eat renee 1.067 36 +24.26- -925 Usrteagigeuracets a gialan aah spec soae a utebie i 1.169 84 PG -839 20 neues yok ehe ssaueeda 1.179 88 = 1.4 834 QL ecw ee sacha ee ohes ye Atbiees 1.189 92 — 4.9 825 BD hiss seshe tosis Fibs ce nelaidigat 1.199 96 — 8.6 817 DBs Soh 5 Srel qusrese cue td aonb I. 209 Too —11.6 808 BAS oi 5 mecidadurhc tad eenrena 1.219 104 S09 -799 DG 8 Bick Stacie As « Atal. 3 Bement 1.229 108 2118 -790 DOA iets tenncnaetctn ten recat ex choras I.240 I12 27.0 .778 QT vie wht a em Cad te a LS 1.250 116 32.6 .769 DB ssc als niallecgaia a leta a eeu 1.261 120 = 30.2 i757 20 xivenetieeasaxds semen TPF Nissan Nes. aad BOn Bio [rms Readyt inte d BOls sai Hs Stet 4 4 Y Gaanacdnss Te 2Oot | livacesuenn sents SSAA led ceusie a gues Bie ece tie oa a aaa Gis, puke eucuies TE2OM. | Nes nnaiitee sige ’sle clit SAG 225" | Siini wise occas Degrees Fahrenheit APPENDIX 60.5 60 58, ot (56.5 Pounds per Cb. Ft. Curve SHOWING WEIGHT OF WATER IN Pounps PER CuBic Foot FoR TEMPERATURES FROM 20-350° F. IIII I1I2 APPENDIX CRross-SECTION Paper. APPENDIX L113 a = LoGARITHMIC CROSS-SECTION PAPER. INDEX ABRASION test, 135. Absorbing power of reagents in flue gas analysis, 520. Absorption dynamometers, 276. Alden brake, 284. Brakes employing frictionof liquids, 286. Prony brakes of different types, 276-280. Absorption system of refrigeration, 999. Accelerated test for cement, 163. Acid tests for oils, 245. Acoustic current meter, 403. Adiabatic compression of dry air, 956. Adulteration of oils, 243. Air compressing machinery, types of, 938. Air compression, adiabatic, 956. Air compression, combined diagram .for multistage, 969. Air compression, efficiency of, 965. Air compression, efficiency in multistage, 972. Air compression, intercooler, 967. Air compression, isothermal, 955. Air compression, slip, 963. Air compression, temperature rise, 957. Air compression, work of, 954. Air compressor, cooling of, 939. Air compressor, effect of clearance in, 963. Air compressor horse power, 961. Air compressor, hydraulic, 947. Air compressor, mechanical efficiency of, 966. Air compressor, multistage, 967. Air compressors, piston, 938. Dry, 939. Water injection, 939. Wet, 939. : Air compressor, Rateau turbine, 946. Air compressors, rotary or positive, 942. Air compressor tests (see testing of air compressors). Air compressor, turbine, 945. Air, dry, characteristics of, 949. Air, dry, work of compression, 955. Air horse power, 966. Air horse power, centrifugal fan, 983. Air, humidity of, 950. Air lift, 1084. Air machines, for refrigeration, 998. Air, moist, characteristics of, 950. Air, moist, work of compression of, 958. Air, physical characteristics of, 949. Air required for combustion of fuel gases, 858-860. Air thermometer, 199. Air thermometer, corrections for, 199. Air thermometer, directions for use of, 200. Alcohol fuel, 861. Alden brake, 284. American Boiler Manufacturers’ Associa- tion specifications, 143. American Foundrymen’s Association, standard specifications for testing gray cast iron, 149. American Society for Testing Materials, specifications for cement, 163. American Society of Civil Engineers and American Society for Testing Ma- terials, standard method of testing cement, 158. American Waterworks Association, stand- ard specifications for cast-iron water pipe, 151. Ammonia, absorption in water, table, r109. Ammonia compression, wet and dry, 1021. Ammonia compressor, 1004. Ammonia compressor indicator diagram, 1021. Ammonia condensers, 1007. Ammonia, properties of, table, 1107. Ammonia, weight of in circulation, 1024. Amsler polar planimeter, 21. Analysis of coal, Ash, 505. Fixed carbon, 504. Moisture, 502. Volatile matter, 502. Analysis of exhaust gases, 877. Analysis of fuel gases, 868. Analysis of fuels, 500. Anemometer, 439. Anemometer calibration, 440. Anemometers, use of, 441. Angular deformation, definition of, 51. Approximate formula for flow of steam through orifices, 442. Approximate method of determining chemical analysis of coal on basis of proximate analysis, 507. IIIS I1I6 Apron method of determining velocity in channel, 399. Arndt econometer, 528. Ashcroft oil testing machine, 267. Aspirator for flue gas sampling, 514-516. Atomic weight of gases, 855. Atwater bomb calorimeter, 474. Autographic apparatus, combined with extensometer, 107. Autographic diagrams, 14. Autographic tachometers, 23. Barret calorimeter, 550. Barrel calorimeter, directions for use, 552. Barrus continuous calorimeter, 556. Barrus superheating calorimeter, 558. Base metal thermocouples, 213. Bauschinger extensometer, 100. Beam formulas, 60. Beaumé hydrometer, 246. Beaumé hydrometer scale with corre- sponding specific gravities, table of, Iogl. | i Belt dynamometer, 306. Belt testing machine, 318. Belt tests (see testing of belts). Bending test, 135. Blower, centrifugal or volume, 943. Blower, rotary or positive, 942. Blower tests (see testing of centrifugal fans). Bomb calorimeter, 471. Bomb calorimeter, calculations for, 480- 483. Bomb calorimeter, directions for use, 478. Boston micrometer extensometer, 106. Boult’s lubricant testing machine, 268. Bourdon gauge, 181. Boyle’s law, 327. Brakes, Alden, 284. Electric generator absorption dynamom- eter, 291. Electro-magnetic, 290. Employing friction of liquids, 286. Fan, 289. Pump, 288. Prony, 276-280. Self-regulating, 283. Westinghouse, 287. Brauer’s method for measuring continu- ous flow by means of orifices, 367. Brayton cycle, 349. Breaking load, 53. Breast wheel, 1047. Brine used for cooling, properties of, 1009. Brine used for refrigerating purposes, table of properties of, 1109, 1110. Brinell ball test for hardness, 136. INDEX Bristol pyrometer, 214. Bristol recording gauge, 187. Burnham steam meters, 454. Burning point in oils, definition of, 256. Burning point in oils, method of deter- mination of, 256. Busby extensometer, 102. CALCULATING machines, Brunsviga, 49. Fuller rule, 109. Grant, 49. Slide rule, 16. Thatcher rule, 18. Calculation, approximate, rules and for- mule for, 8. Calculations, numerical, accuracy of, 11. Calibration of anemometers, 440. Calibration of current meters, 404. Calibration of gas meters, 437. Calibration of indicator springs, 597-605. Calibration of mercury thermometers, 220. Film or stem correction, 221. Test for boiling point, 220. Test for freezing point, 221. Test for other temperatures, 221. Calibration of Morin dynamometer, 295. Calibration of nozzles, 380. Calibration of orifices, 365. Calibration of Pitot tubes, 409. Calibration of planimeters, 37. Calibration of pressure gauges, 188-101. Calibration of pyrometers, 222. Optical and radiation pyrometers, 224. Resistance thermometers, 223. Thermocouples, 222. Calibration of thermometers and pyrom- eters, 219. Calibration of Venturi meter, 380. Calibration of water meters, 306. Calibration of Webber dynamometer, 3or. Calibration of weirs, 380. Calorific power, 466. Calorimetric methods of engine testing, 799. Calorimetric pyrometers, 206. Calorimetry, fuel, 470. Capacity test of steam engine, 726. Capacity water meters, 389. Carbon dioxide, properties of, table, 1108. Carburetors, 846. Carnot cycle, 347, 351, 352. Carnot efficiency of steam engines, 720. Carpenter coal calorimeter, calculations for, 489. Carpenter fuel calorimeter, 485. Cathetometer, 47. Cement test, accelerated or hot, 163. Cement test, normal, 163. INDEX Cement testing (see testing of cement). Cement testing machines, 96. Center vent turbine, 1059. Centrifugal blowers, 943. Centrifugal fan, action of, 981. Centrifugal pump, 1068. Centrifugal pump, testing of (see testing of centrifugal pumps). Centrifugal pump, theoretical lift or head, 1074, 1075. Centrifugal pump, theoretical power, 1074. Centrifugal pump, theory of action, 1068- 1071. Centrifugal pumps, classification of, 1071- 1074. Change of entropy at constant pressure in gases, 333. Change of entropy at constant volume in Bases, 332. Change of entropy in gases, general case, 333- Charles’s Law, 327. Chemical or ultimate analysis of coal, soz. Chemical steam calorimeter, 575. Chill point, determination of, 252. Chronograph, 232. Cistern manometer, 171. Clearance determined from diagram, 652. Clearance, effect of in air compressors, 963. Clausius cycle, 352, 353- Coefficient of contraction, 361. Coal analysis, sor. Coefficient of discharge for orifices used + for measuring gas, 424-429. Coefficient of discharge for steam in orifice measurements, 449-452. Coefficient of discharge for Venturi meter, Herschel’s experiments, 371. Coefficients of discharge for water through mouthpieces, 364. Coefficient of efflux or discharge, 361. Coefficient of friction, belt transmission, indicator 23. Cosffrient of friction, flow of water in pipes, 414. : Coefficient of friction for oils, measure- ment of, 256. Coefficient of friction in oils, 236. Coefficient of friction in belt drives, 323. Coefficients of friction, table of, 1ogo. Coefficients of heat transmission, table of, Ioil. Coefficient of performance, ideal, ror4. Coefficient of velocity, 361. Coffin planimeter, 31. Coffin planimeter, theory of, 31. Cold gas efficiency of gas producer, 903. Combination gas producer, 853. I1I7 Combined diagram for multicylinder steam engine, construction of, 661-670. Combined diagram for two-stage air com- pressor, 969-972. Combustion, 465. Combustion, air required for, 858. Combustion calculations, 512. Combustion, heat of, 466. Combustion, losses in, 531. Combustion of elementary fuels, 466. Combustion of fuels containing hydrogen, 467. Combustion of hydrogen, 467. Combustion, temperatures attained in, 468. Combustion, weight and volume rela- tions, 465. Composition of fuels, 498. Compressed air, pumping by, 1084. Compression loading, formulas for, 56. Compression micrometers, Olsen, 112. Riehlé, 111. Compression of ammonia, wet and dry, 102i. Compression of dry air, 955. Compression of moist air, 958. Compression refrigeration plant, 1004. Compression test machines (see testing machines). Compression tests, directions for, 125. Compression tests, form of test piece, 125. Compressor horse power, 966. Computations, aids to, 48. Condensing calorimeter, forms of, 550. Constancy of volume in cements, 163. Constant-pressure engines, 841. Constant-volume engines, 841. Continuous jet calorimeter, 552. Continuous speed counter, 228. Contraction in weirs, 373. Cooling effect of refrigeration, 1028. Cooling of air compressors, 939. Cooling systems in refrigeration, 1007. Counting devices, 227. Cradle dynamometers, 314. Critical pressure for steam in orifice measurements, 448. Critical pressure in orifice and nozzle measurements with gases, 421. Crosby gauge testing apparatus, Ig1. Crosby indicator, 586. Cross section paper, logarithmic, 14. Crude oil, 860. Current meters, 402. Current water meters, 387. Curtis turbine, 812. Cycles and their efficiencies, 346. Cycles for steam, 351. Carnot, for saturated steam, 351. II18, Cycles, Carnot, for wet, dry, or super- heated vapor, 352. Clausius, for saturated steam, 352. Clausius, for superheated steam, 353. Rankine, for saturated steam, 354. Rankine, for supetheated steam, 355. Cylinder condensation, 657. Cylinder efficiency of steam engines, 729. Deap weight calibration of indicator Springs, 597. ; Deflection in transverse loading, 58. Deflectometer, 111. Deformation, definition of, 51. DeLaval steam turbine, 810. Denny & Johnson torsion meter, 313. Density of gases, 855. Density of oils, method of determination, 247. | By weighing, 247. With hydrometer, 247. Depth of water over weirs, 372. Determination of average velocity in streams, 404. Determination of radiation rate for bomb calorimeter, 476, 482. Dew point apparatus, 952. Diagram, stress-deformation, 53. Diagram water rate, 653. Diagram water rate, approximate for- mulas for, 656. Diagram water rate for multicylinder engine, 655. Diagrams, autographic, 14. Diaphragm gauge, 182. Diesel cycle, 350. Differential dynamometer, 300. Diffuser, in fan blowers, 943. Dilution coefficient flue gas analysis, 538. Directions for compression testing, 125. Directions for taking indicator diagrams, 636 Directions for tension tests, 118. Directions for torsion testing, 129-131. Directions for transverse testing, 127. Direct shear, 61. Direct shear tests, 132. Disc fan, 943. Displaced diagrams and time diagrams, 676. Doble impulse wheel, 1049. Dosch smoke observer, 542. Double zone producer, 854. Down draft producer, 854. Draft gauges 175. Drifting test, 135. Drop tests, 94, 133. Dry air, characteristics of, 949. Dry gas meters, 434. Ductility, definition of, 52. INDEX DuLong’s formula, 511. Durability of lubricants, 266. Durability testing machines, for oil, 267. Durability tests of oils, directions for, 270. Durand dynamometer, 306. Duty of pumping engine, 775. Dynamometer car, locomotive tests, 795. Dynamometer, traction, 292. Dynamometer, transmission, 293. Belt, 306. Denny & Johnson, 313. Differential or Webber, 300. Durand, 306. Emerson power scale, 304. Fottinger, 314. General types, 293. Kenerson, 310. Lewis, 298. Morin, 293. Pillow block, 297. Steel yard, 296. Torsion, 309, 312. Van Winkle, 305. ECKHARDT steam meter, 457. Economy test of steam engine, 726. Edson recording gauge, 185. Efficiency in multistage air compression, 972. Efficiency standard for locomotives, 787. Efficiency standards for steam engine, 728, Efficiency of actual refrigeration process. IOIQ. Efficiency of air compression, Mechanical, 966. Volumetric, 963, 964. Efficiency of belt transmission, 323. Efficiency of centrifugal fans, Manometric, 985. Mechanical, 986. Volumetric, 986. Efficiency of centrifugal pumps, 1074. Actual, 1077. Hydraulic, 1076. Manometric, 1076. Efficiency of cooler in refrigeration, 1020. Efficiency of gas engine, Cylinder, 921. Mechanical, 923. Thermal, 922. Volumetric, 924. Efficiency of gas producers, 903. Efficiency of hydraulic ram, 1039. Efficiency of impulse wheel, 1052. Actual or gross, 1052. Hydraulic, 1052. Efficiency of injector, 833. Efficiency of injector, as a pump, 834. Heat, 835. INDEX Efficiency of insulation, ror2. Efficiency of jet pump, 1043. Efficiency of pulsometer, 1082. Efficiency of refrigeration process, 1033. Efficiency of steam engine, Carnot, 729. Cylinder, 729. Mechanical, 730. Thermal, 729. Thermodynamic, 729. Efficiency of steam turbines, Cylinder, 821. Potential or Clausius, 821. Thermal, 820. Efficiency of water-pressure engines, 1044. Efficiency of water turbines, 1057, 1062. Efficiency of water wheels, 1046-1048. Efficiency, mechanical, of ammonia plant, 1033. Efficiency, plant, 730. Efficiency tests, 3. Ejector, 832. Elastic curve in transverse loading, 58. Elastic limit, definition of, 52. Elastic limit strength, definition of, 52. Elasticity, modulus of, 52. Electric generator absorption dynamom- eter, 291 Electric meters for measuring gas, 444. Electric pyrometer, compensating device for low resistance type, 215. Electric pyrometer, high resistance type, 212% Electric pyrometer, low resistance type, 213. Electrical measurement of power input and output, 315. Electrical methods of measuring tempera- ture, 209. Electromagnetic brake, 290. Elementary fuels, combustion of, 466. Ellison universal steam calorimeter, 578. Elongation, equivalent in tension tests, 123. Bogen bomb calorimeter, 475. Emerson power scale, 304. Emery material testing machine, 72, 78, 82. Empirical formulas, deduction of, 7. Engineering or proximate analysis of coal, 50. Engines, water pressure, 1043. Entropy diagram for ammonia, 996. Entropy diagram for gas engine, 685. Entropy diagram for steam engine, 670- 675. Entropy of gases, 332. Entropy of vapors, 340. . Equation of state or condition for ideal gas, 327. IIIQ Equivalent elongation in tension tests, 123. Ericsson cycle, 348. Ericsson engine, 926. Errors, accidental, 4. Errors, combination of, 7. Errors, experimental, classification of, 4. Errors in different types of planimeters, 40. Errors in engine indicators, 595. Errors in engine indicators, discussion of effects, 612-620. Errors in flue gas analysis, 530, 531, 538. Errors in weighing, 360. ee in weir measurement, effects of, 380. Errors of single observations, 5. Errors, mean, 5. Errors, neglect of, 10. Errors, probability of, 5. Errors, systematic, 4. Ertel current meter, 402. Evaluation of, indicator diagrams taken with faulty springs, 608-612. Evaporation, factor of, 722-724. _ Excess air, computation for, in gas engine tests, 880. Excess coefficient, flue gas analysis, 538. Exhaust gas analysis, 877. Exhaust, heat loss in, 877-883. Exhaust loss, experimental determina- tion of, 883. Expansion and fusion pyrometers, 205. Expansion, ratio of, 645, 748. Experiments, classification of, 3. Explosion recorder, 909. Extensometer, Bauschinger, roo. Boston, 106. Busby, 102. Combined with autographic apparatus, 107. Henning, 104. Johnson, 103. Kenerson autographic, 110. Marshall, ros. Olsen, 106. Olsen wire, 107. Payne, 102. Strohmeyer, 101. Thurston, 103. Extensometer, forms of, too. Extensometer and aufographic apparatus combined, 107. External latent heat, definition of, 334. Factor of evaporation, 722-724. ‘Factor of safety, definition of, 53. Fairbanks automatic cement tester, 96. Fan, air horse power, 983. Fan blowers, 943-945. TI20 Fan blower, diffuser, 943. Fan brakes, 289. Fan, centrifugal, action of, 981. Fan, disc, 943. Fan, head produced by, actual, 982. Fan, head produced by, theoretical, 981. Fan tests (see testing of centrifugal fans). Fan, work done by, 983. Fatigue test, 137. Favre & Silbermann fuel calorimeter, 483. Fery absorption pyrometer, 216. Fery radiation pyrometer, 217. Figure of merit, gas producer tests, go4. Fineness of cement, 159. Flash point of oil, method of determina- _ tion, 254, 255. With open cup, 254. With closed cup, 255. Float measurement of velocity, 397. Flow of air, formulas for, 432. Flow of steam, Grashof’s formula, 452. Flow of steam in pipes, 463. Flow of steam, Napier’s formula, 453. Flow of steam through orifices, approxi- mate formulas for, 442. Flow of water in pipes, 412. Flow of water over weirs, 372. Flue gas analysis, 512, 517. Flue gas analysis, accuracy of, 530. Flue gas analysis apparatus, automatic types, 527. Flue gas analysis apparatus, forms, 520. Flue gas analysis apparatus, method of operation, 520. Flue gas analysis, Determination of COs, 517. Determination of carbon monoxide, 518. Determination of hydrogen, 519. Determination of moisture, 519. Determination of oxygen, 518. Flue gas analysis, errors in, 530, 531, 538. Flue gas analysis, reagents used, 517, 520. Flue gas analysis, sampling, 513. Flue gas apparatus, Elliott, 522. Hempel, 525. Orsat, 524. Flue loss in boilers, computation of, 531- 538. Flue losses, classification of, 531. Fluid friction in gas engines, definition of, 678. Fluid pressure methods of calibrating indi- cator springs, 602. Forging test, 135. Formulas for beams, 60. Formulas for compression loading for long columns, 56. general INDEX Formulas of compression loading for short columns, 56. Formulas, empirical, deduction of, 7. Formulas for tension loading, 55. Formulas for torsion loading, 61. Formulas for transverse loading, 57. Fourneyron turbine, 1056. Four-cycle gas engines, 843. Fottinger torsion meter, 314. Frahm’s resonance tachometer, 231. Francis turbine, 1059. Free evaporation, 333. Friction brakes, 276-288. Friction, classification of, 237. Friction of motion, 237. Friction of rest, 237. Friction, Angle of repose, 236. Coefficient of friction, 236. Definitions, 236. Normal force, 236. Total pressure, 236. Friction horse power in gas engines, 908. Friction of ball and roller bearings, 271. Friction of cords and belts, 238. Friction of fluids, 241. Friction of pivots and collars, 238. Fuel analysis, 500. Fuel calorimeter, continuous type, 471. Fuel calorimeter, discontinuous type, 471. Fuel calorimetry, 470. Fuel gas, analysis of, 868. Fuel gas analysis, apparatus for, 871-875. Fuel gases, constants for, 858. Air required for combustion, 858. Heating value, 858. Fuels, classification of, 499. Fuels, commercial, 408. Fuels, gas engine, 846 Fuller’s slide rule, 19. Gas analysis, Heinz apparatus, 871. Siebert-Kiihn apparatus, 875. Gas cycles, 347. Brayton, 349. Carnot, 347. Diesel, 350 Ericsson, 348. Otto, 340. Stirling, 348. Gas engine, Constant pressure, 841. Constant volume, 841. Cylinder arrangement, 846. Four-cycle, 843. Two-cycle, 844. Gas ene diagrams, discussion of, 678- 5. INDEX Gas eeeine diagrams, inertia effects in, 4. Gas engine diagram, lower loop, 678, 680. Gas engine diagram, pump, 678. Gas engine diagrams, abnormal features, 680-685. Gas engine, fluid friction loss in, 678. Gas engine, friction horse power, 908. Gas engine fuels, 846. Gas engine, heat balance, 920. Gas engine, indicated horse power, got. Gas engine testing (see testing of gas engines). Gas meters, Dry, 434. Turbine, 436. Wet, 432. Gas meter calibration, 437. Gas meter capacities, 437. Gas producer, Combination plant, 853. Double zone, 854. Down draft, 854. Pressure, 851. Series, 854. Suction, 851. Gas producer efficiency, 903. Gas producer, figure of merit, go4. Gas producer, heat balance, 899-903. Gas producer testing (see testing of gas producers). Gas producer, types of, 850. Gas thermometer, theory of, 196. Gases, Atomic weight, 855. Density, 855. Specific weight, 855. Gases, hydrocarbon, table of contents for, 858. Gases, pressure and volume changes, Adiabatic, 330. Constant pressure, 329. Constant volume, 330. Isentropic, 330. Isothermal, 330. Pv" =constant, 331. Gases, table of constants for, 857. Gases, table of mean specific heats, 469. Gasometer, 430. Gauge calibration, 188. By comparison with mercury column, 189. By comparison with other gauges, 188. By comparison with standard weights, 190. Gauges, corrections for, 192. Gauge syphons, 185. Gauges, pressure, Bourdon, 181. Diaphragm, 182. II21 Gauges (continued), Draft, 175, 181. Recording, 185, 186, 187. Vacuum, 185. Generators used as brakes, 317. Graphical representation of experimental results, 12. Grashof’s formula, flow of steam, 452. Gumming or drying tests for oils, 245. Bailey’s apparatus, 245. Nasmyth’s apparatus, 245. Hammer test, 135. Hammond water weigher, 384. Hand speed counter, 227. Hardening test, 135. Hardness test, 136. Head of water over weirs, 372. Head on weirs, measurement of, 378. Head pumped against, centrifugal pump, 1074, 1075. Head pumped against, steam pump, 774. Heat analysis, 799. Heat analysis applied to multicylinder engines, 806. Heat balance for boiler, 721. Heat balance for gas engine, 920. Heat balance for gas producer, 899-903- Heat balance for hot-air engine, 935. Heat balance for steam engine, 731. Heat chart, 337. Heat diagram for steam, use of, 337. Heat efficiency of injector, 835. Heat lost in exhaust of gas engine, com- putation of, 877-883. Heat of combustion, 466. Heat of the liquid, definition of, 334. Heat transmission, coefficients of, table, IO1l. Heat unit, 325. Heating value, fuel gases, 858. Heating value of fuels, by computation, 510. Heating value of fuels, determination of, 505. Heinz apparatus for gas analysis, 871. Heisler impact testing machine, 94. Hempel fuel calorimeter, 473. Henning extensometer, 104. Hersey rotary meter, 390. Hersey torrent meter, 387. Hess testing machine for friction of ball and roller bearings, 272. Higher and lower heating value of fuels, 407. Hirn’s analysis, 799-806. Hoadley calorimetric pyrometer, 208. Hoadley draft gauge, 181. Hoadley steam calorimeter, 554. Holborn pyrometer, 216. Hook gauge, 378. Hopkinson optical indicator, 640. IT22 Horizontal and vertical shear in trans- verse loading, 59. Horse power, definition of, 276. Hot-air engines, methods of operation, 925. Hot-air engines tests (see testing of hot- air engines). Hot-air engines, types of, 925. Hot gas efficiency of gas producer, 904. Hot-water meters, 394. Humidity, absolute, 951. Humidity chart, 954 Humidity, determination of, 951. Humidity of air, definition of, g5o0. Humidity, relative, 951. Humidity tables, 1100-1104. Humphrey internal combustion pump, 1082. Hydraulic compressor, 947. Hydraulic machinery, classification of, 1037. . Hydraulic ram, 1038. Hydraulic ram, efficiency, 1039. Hydraulic ram tests (see testing of hy- draulic rams). Hydrodynamometer, 400. Hydrometric pendulum, 400. Hyperbola, method of drawing, 648. Icrz machine (see refrigeration). Ice machines, testing of (see testing of vapor compression refrigerating ma- chines). Ice making, 1008. Ice making capacity, 1028. Ice melting capacity, 1028. Impact tests, 132. Impact testing machine, 94. Impulse type of steam turbine, 808. Impulse water turbine, 1043. Impulse water wheel, 1049. Impulse wheel, Doble, 1046. Impulse wheel, theory of action of water on buckets, ro50-1052. Impurities in oils, 243. Indicated horse power, 647. Indicated horse power, formula for, 582. Indicated horse power, gas engines, 907. Indicated horse power, hot-air engines, 033- Indicator diagram (see also steam engine indicator diagram). Indicator diagram, ammonia compressor, 1021. Indicator diagram, directions for taking, 636. Indicator diagram, displaced and time, 676. Indicator diagrams, effects of bad steam connections, leaky valves and pistons, 660. INDEX Indicator diagram, errors due to indica- tors and indicator connections, 658. Indicator diagram, errors due to valve setting, 658. Indicator diagram, evaluation of, 608- 612. Indicator diagram, steam chest and steam pipe, 675. . Indicator diagram for four-cycle engines, 678-680. Indicator diagram for two-cycle engines, 685. Indicator diagrams for gas engines, dis- cussion of, 678-685. Indicator diagrams, various forms, 657. Indicators for ammonia machines, 592. Indicator, optical, 637, 638, 640. Indicator springs, calibration of, 605. Indicator springs, forms of, 597. Indicator springs, scale of, 608. Indicator, steam engine (see steam engine indicator). Inferential water meters, 387. Injectors, Monitor, 832. Penberthy, 830. Schiitte-Koerting, 831. Injector blower, 946. Injector, general theory of, 827. Injector, heat efficiency of, 855. Injector, pump efficiency of, 834. Injector tests, 835. Injector tests, report, 837-840. Injectors, construction and operation, 829. Insulation, toro. Insulation, efficiency of, rorz. Insulation, testing of, to11. Intercooler, in air compression, 967. Internal horse power, steam turbine, 8109. Internal latent heat, definition of, 334. Isentropic or adiabatic curve for steam, 650. Isothermal compression of dry air, 955. JET pump, 1041. Jet pump efficiency, 1043. Johnson extensometer, 103. Jonval turbine, tos. Junker gas calorimeter, 493. KENERSON, Ilo. . Kenerson dynamometer, 310. Kerr turbine, 816. autographic extensometer, Latent heat of vaporization, definition of, 334. Laws of friction, 242. Laws of vapors, 333. INDEX Leakage test for boilers, 712. Leakage test for pumping engines, 783. LeChatelier electric pyrometer, 212. Lewis dynamometer, 208. Liquid fuels, characteristics of, 860. Limits of separating calorimeter, 573. Limits of throttling calorimeter, 564. Liquid pressure pyrometer, 202. Lloyd’s specifications for quality and testing of ship steel, 145. Locomotives, testing of (see standard method of conducting efficiency tests of locomotives). Logarithmic cross section paper, 14. Lord’s apparatus for tar and soot deter- mination, 888. Losses in pipe fittings and valves, flow of water, 413-416. ’ Losses in steam turbines, 822. ie loop diagram for gas engines, 678, 1. Low pressure water meters, 386. Maater bomb calorimeter, 472. Manograph, 638. Manometer, 168. Manometers, Cistern, 171. Differential, 174. Multiplying, 174. U-shaped, 169. Mathot explosion recorder, go9. Manufacturers’ standard specifications for structural cast iron, 141. Manufacturers’ standard specifications for special open hearth plate and rivet steel, 141. Manufacturers’ standard for structural steel, 139. Marking gauges, tension tests, 119. Marshall extensometer, 105. Maximum load, 53. Mean ordinate by polar planimeter, 29. Mean specific heat for gases, 469. Measurement of average velocity in channels and streams, 397. Measurement of compression, in materials, IIl. Measurement of elongation, in materials, specifications 99- Measurement of gas by calorimetry, 443. Measurement of gas by determining average velocity, 439. Measurement of gas by Pitot tube, 441. Measurement of gas by Venturi meter, 442. Measurement of gas by volume displace- ment, 430. : : Measurement of gases, classification of methods, 418, 1123 Measurement of gases by means of orifices, theoretical velocity attained, and weight discharged, 419. Measurement of liquids by means of nozzles, 368. Measurement of liquids, gases, and vapors, 356. Measurement of pressure, 168. Measurement of speed, 227. Measurement of strain, 99. Measurement of torsion and deflection, It. Measurement of vapors, classification of methods, 445. Measurement of vapors by determining average velocity, 453. Measurement of vapors by means ‘of orifices, 446. Measurement of vapors by weighing, 445. Measurement of water by means of ori- fices, 361. Measurement of water by weighing, 357. Mechanical equivalent of heat, 325. Mechanical refrigeration, theory of, 992. Mercury and alcohol thermometers, 202. Mercury columns, 172. Mercury column, corrections for, 173. Mercury thermometers, calibration of, 220. Mercury thermometers, rules for care of, 204. Mesuré & Nouel pyrometric telescope, 217. Metallic pyrometer, 205. Meter prover, 432. Methods of testing materials, 115. Methods of testing cement, 158. Micrometer, 43. Micrometer caliper, 44. ; Micrometer screws, accuracy of, 43. Minor tests for materials, 134. Mixed flow turbine, rosq9. Modulus of elasticity, definition of, 52. Modulus of rigidity, 61. Modulus of resilience, definition of, 52, 61. Modulus of rupture in torsion, 62. Modulus of rupture in transverse loading, 59. Modulus of shear elasticity, 61. Moist air, characteristics of, 950. Moisture in steam, direct determination of, 567. Mollier diagram, 337. Morin’s rotation dynamometer, 293. Morin dynamometer, calibration of, 295. Morse thermo gauge, 216. Mosscrop speed recorder, 230. Motors used as transmission dynamome- ters, 310. ‘ 1124 Multicylinder steam engines, heat analy- sis, 806. Multiplying and differential manometers, 174. Multistage compression of air, 967. Multistage impulse turbine, 812. Multistage reaction turbine, 815. Naprer’s formula, flow of steam, 453. Nash disc meter, 391. Natural cement, 164. Neutral loading in transverse loading, 58. Normal consistency in cement testing, 159. Normal stress, definition of, 51. Normal tests for cement, 163. Nozzle measurements for water, 368. OgsERVATIONS, doubtful, rejection of, 10. Oil testing machines, Ashcroft, 267. Boult, 268. Hess, 272. Olsen, 262. Rankine, 256, 257. Riehlé, 262. Thurston, 258-261. Oil tests (see testing of oils). Oils, Adulteration of, 243. Impurities in, 243. Olsen cement testing machine, 99. Olsen compression micrometer, 112. Olsen-Cornell oil testing machine, 262. Olsen material testing machines, 70, 86, 91, 99. Olsen extensometer, 106. Olsen new wire extensometer, 107. Open type water meters, 386. Optical and radiation pyrometer, 216. Optical indicator, 637. Orifice measurement for vapors, 446. Orifice measurements for water, 361. Orifice methods for measuring gas, pre- cautions necessary in, 429. Orifices, calibration of, 365. Orifices in thin plates, coefficients of dis- charge, for water, 363. Orifices for measuring continuous flow, 306. Orifices, submerged, 361. Otto cycle, 349. Overshot water wheel, 1045. Oxygen, preparation of, for fuel calorim- etry, 473. PaNntToGRAPH reducing motion, 627-630. Parallel flow turbine, 1059. Parr fuel calorimeter, 490. Payne extensometer, 102. INDEX Pendulum reducing motion, 621-627. Pennsylvania Railroad Company’s speci- fications for cast-iron car wheels, Ist. Perfect engine, performance of, 730. Perfect engine, steam consumption for, 731. Performance, coefficients of, in refrigera- tion, 1014, Iorg. Pillow block dynamometer, 297. Piston air compressors, 938. Piston water meters, 393. Pitot tube for closed conduits, 406. Pitot tube for measuring gas, 441. Pitot tube for open channels, 405. Pitot tube, Gregory, 408. Pitot tube, modified form of, 409. Pitot tube, Taylor, 408. Planimeter, Amsler, 21. Coffin, 31. Polar, 21. Roller, 35. Suspended, 31. Willis, 34. Planimeter calibration, 37. Planimeter, theory of instrument, 23. Planimeter, the zero circle, 24. Planimeters, directions for care and use of, 36. Planimeters, errors in different types, 40. Planimeters, special, 42. Plant efficiency, 730. Pneumatic displacement pump, 1086. Polar planimeter, 21. Polar planimeter, forms of, 28. Portland cement, 165. Positive water meters, 393. Power and efficiency of overshot water wheel, 1046. Power and efficiency of radial inward flow, parallel flow, and mixed flow turbines, 1062. Power, definitions of, 275. Power, indicated and dynamometric, 581. Power, measurement of, 276. Power of water turbines, 1057, 1062. Power of water wheels, 1046. Power output of turbines, 8109. Power required by centrifugal pumps 1074. Pressure, absolute, 167. Pressure and volume changes in gases, 329. Pressure and volume changes in vapors, 343. : Pressure, barometer, 167. Pressure below atmosphere, 168. Pressure gas producer, 851. Pressure gauge, 181. INDEX Pressure, gauge or manometer, 167. Pressure, measurement of, 168. Pressure stages in turbines, 812. Pressure units, 167. Primary stresses, definition of, 63. Probability of errors, 5. Producer (see gas producer). Producer gas analysis (see gas analysis). Producer gas, quantity made per pound of fuely 884. Producer gas, theory of manufacture, 847. Prony brake, cooling and lubrication, 283. Prony brake, design of, 280. Prony brakes, 276-280. Propeller fan, 943. Properties of steam, tables of, 1092-1098. Psychrometer, 952. Pulsometer, 1080. Pulsometer, efficiency, 1082. Pump brake, 288. Pumps, centrifugal, 1068. Pump diagram for gas engines, 678. Pump efficiency of injector, 834. Pump horse power, hot-air engines, 933. Pump, Humphrey internal combustion, 1082. Pump, jet, 1041. Pump, pneumatic displacement, 1086 Pump, reciprocating, 1067. Pump, rotary, 1067. Pump, turbine, 1068. Pumping by compressed air, 1084. Pumping engine, testing of (see standard method of conducting duty trials of pumping engines). Punching test, 135. Pyrometers, Bristol, 214. Calorimetric, 206. Electric, 212. Expansion, 205. Fery absorption, 216. Fery radiation, 217. Fusion, 205. Hoadley, 208. Holborn, 216. LeChatelier, 212. Liquid pressure, 202. Mesuré & Nouel, 217. Metallic, 205. Morse, 216. Optical, 216. Radiation, 216. Seger cones, 206. Vapor pressure, 201. Wanner, 216. Wedgewood, 205. QuaLity curves on combined steam en- gine diagram, 666. I125 Quality determinations for steam, im- portance of, 544. Quality of steam, definition of, 543. Quality of steam, methods of determining, 544. RaDIAL inward flow turbine, 1059. Radial outward flow reaction turbine, 1056. Radial outward flow reaction turbine, power and efficiency of, 1057. Radiation loss from steam engines, 805.. Radiation rate, determination of, for fuel calorimeter, 476, 482. Rankine cycle, 354, 355. Rankine’s oil testing machine, dynamic apparatus, 257. :Rankine’s oil testing machine, static apparatus, 256. Ranson chronograph, 234. Rateau turbine, 812. Rateau turbine compressor, 946. Ratio of expansion, 645, 748. Reaction type of steam turbine, 808. Reaction water turbine, 1053. Reagents for flue gas analysis, 517-520. Reciprocating pumps, 1067. Recording gauges, 185. Rectangular weir, theory of, 372. Reducing motion for indicators, 621. Reducing wheels, 630-632. Reduction of area, definition of, 52. Reévaporation, 657. Refrigerating agents, 994. Ammonia, 994. Carbonic acid, 994. Ethyl and methyl chloride, 994. Pictet fluid, 994. Sulphuric ether, 994. Sulphurous acid, 994. Refrigerating effect, 1028. Refrigerating machine, compressor horse power, 1033. Refrigerating machine, simple type, 993. Refrigerating machine, Air, 998. Ammonia absorption, 999. Vacuum process, 1oor. Vapor compression, 1003. Refrigerating machines, classification of, 997- Refrigerating machines, capacity of, 1027. Refrigerating machines, rating of, 1027. Refrigeration cycle, actual for vapor compression machine, 1016. Refrigeration, cooling effect, 1028. Refrigeration, cooling systems, 1007. Refrigeration cycle, ideal, for vapor com- pression machine, 1012. 1126 Refrigeration, mechanical, theory of, 992. : Refrigeration process, actual efficiency of, 101g. Refrigeration, tonnage, 1028. Regulation tests for steam engines, 727. Reservoir method of measuring gases, 437- Resilience, modulus of, 52, 61. Resistance thermometer, 210. Riehlé cement testing machine, 99. Riehlé compression micrometer, 111. Riehlé material testing machines, 70, 84, 99, 99. Riehlé oil testing machine, 262. . Rigidity, modulus of, 61. \Ringelmann’s smoke chart, 541. Risdon-Alcott turbine, 1060. Road tests, locomotive, 786 Rod floats, 398. Roller planimeter, 35. Rotary pumps, 1067. Rotary pumps, testing of, 1077. Rules for conducting boiler trials, Am. Soc. Mech. Eng’rs. Code of 1899, 692-707. Alternate method of starting and stop- ping, 695. Boiler efficiencies, 699. Calibration of apparatus, 693. Character of coal, 692. Duration of test, 694. Examination of boiler, 692. Flue gas analysis, 698. Fuel analysis, 698. Heat balance, 700. Keeping the records, 696. Preparation of boiler and connection, 693. Report, 7o1. Sampling coal, 697. Smoke observations, 699. Standard method of starting and stop- ping, 695. Starting and stopping test, 694. Treatment of ashes and refuse, 697. Uniformity of conditions, 695. Rules for conducting steam engine tests, A.S.M.E. Code of 1902, 732. Calibration of instruments, 734. Coal used, 734. Complete engine and boiler test, 738. Condition of plant, 732. Duration of test, 737. Indicated horse power, 742. Indicated diagrams, 747-753. Measurement of coal, 741. Measurement of feed water, 740. Measurement of heat units used, 739. Object of test, 732. INDEX Rules for conducting steam engine tests, A.S.M.E. Code of 1902 (continued), Quality of steam, 745. Report of tests, 755-773. Standards of economy and efficiency, 753. Standard heat test, 737. ‘ Starting and stopping, 737. Steam used by auxiliaries, 741. Uniformity of conditions, 747. SALINOMETER, IOIO. Sampling of coal for analysis, sor. Sarco carbon dioxide recorder, 529. Saturation curve, ammonia compressor diagram, 1023. Saturation curve for steam, construction of, 650. Saturation curve on combined steam engine diagram, 665. Saving due to cylinder jackets and inter- cooler in multistage compression, 970. Scale. of indicator springs, determination of, 608. Schaeffer & Budenberg recording gauge, 186. Schaeffer & Budenberg tachometers, 229. Scleroscope for testing hardness, 137. Secondary stresses, definition of, 63. Seger cones, 206. Separating calorimeter, formula for, 572. Separating steam calorimeter, 567-572. Separating steam calorimeters, method of use, 574. Series producer, 854. Shear, direct, 61. Shear, elasticity, modulus of, 61. Shear, horizontal and_ vertical, verse loading, 59. Shear tests, 132. Shearing stress, definition of, 51. Shop tests, locomotives, 786. ' Siebert-Kiihn apparatus for gas analysis, 875. Siemen’s water meter, 386. Single-stage impulse turbine, 810. Slide rule, 16. Slide rule, directions for using, 17. Slip in air compression, 963. Slip in pumping engines, 775. Smoke determinations, 540. Soot, determination of in fuel gas, 885. Specific gravity of cement, 158. Specific heat, definition of, 326. Specific heat, instantaneous, definition of, 335. Specific heat of gases, 862-868. Specific heat of gases, table of, 328. Specific heat of oxygen, nitrogen, hydro- gen, etc. (see specific heat of gases). Specific heat of vapors, 335. trans- Specific heat, Specific weight of gases, 855. Specifications, . INDEX ean, definition of, 335. standard, for materials (see under name of society or associa- tion issuing same). Speed indicators, 229. Speed variation within a revolution, 235. Standard coal, locomotive test, 787. Standard method of conducting duty trial of pumping engines, A.S.M.E. Code, 777. Arrangement and use of instruments and other provisions for test, 782. Data and results, 784-786. Directions for obtaining feed-water temperatures, 778. Directions for measurement of feed water, 778. oN Leakage test of pump; ee. Main duty trial, 780. Test of feed-water temperatures, 777. Standard method of conducting efficiency tests of locomotives,-A.S.M.E. Code, 788. Preparations for test, 788. Road test, 795. Shop test, 791. pe accounted for by indicator dia- c gram, 653. Steam calorimeters, classification of, 545. Steam calorimeter, condensing, 548. Steam calorimeter, condensing, water equivalent for, 549. Steam calorimeters, comparative values of, 578. Steam chest and steam pipe diagrams, 675. Steam consumption of perfect engine, 731. Steam, dry saturated, definition of, 543. Steam engine, capacity test, 726. Steam engine, Carnot efficiency, 729. Steam engine, cylinder efficiency, 729. Steam engine, economy test, 726. Steam engine, efficiency standards, 728. Steam engine, heat balance, 731. Steam engine indicator, Bachelder, 588. Crosby, 586. . Crosby continuous with external spring, 591. ° Starr with external spring, 591. Tabor with external spring, 590. Thompson with external spring, 590. Steam engine indicator, apparatus for testing various adjustments, 615-620. Steam engine irtdicator, attachment to cylinder, 620. Steam engine indicator, care of, 636. Steam engine indicator, continuous, 593. Steam engine indicator diagram, form of expansion line, 647. 1127 Steam engine indicator diagram, general discussion of events, 642-645. Admission line, 643. Admission pressure, 644. Atmospheric line, 643. Back pressure line, 644. Boiler pressure line, 643. Clearance line, 643. Compression line, 644. Cut-off pressure, 644. Exhaust line, 644. Expansion line, 644. Initial pressure, 644. Mean back pressure, 644. Mean forward pressure, 644. Point of admission, 643. Point of cut-off, 643. Point of exhaust closure, 644. Point of release, 644. Ratio of expansion, 645. Release pressure, 644. Steam line, 643. Terminal pressure, 644. Vacuum line, 643. Wire drawing, 645. Steam engine indicator diagram, measure- ments from, 645. Steam engine indicator, early forms of, 582. Richards, 583. Watt & McNaught, 582. Steam engine indicator, electric attach- ments, 635. Steam engine indicator, errors in, 594- 597- Steam engine indicator, methods of con- necting up, 632-635. Steam engine indicator, piping for, 620. Steam engine indicator, uses of, 580. Steam engine indicators, small piston, 592. Steam engine indicators, large and small, 593. Steam engine indicators with external springs, 588. Steam engine, radiation loss, 805. Steam engine, regulation tests, 727. Steam engine, testing of (see rules for conducting engine tests). Steam engine testing, calorimetric meth- ods, 799. Steam engine, thermal efficiency, 728. Steam engine, thermodynamic efficiency, 729. Steam meter, Burnham, 454. Eckhardt, 457. Float, 460. Gehre recording, 459. General Electric Co., 455. 1128 Steam meter, Hallwachs’, 458. Orifice, 458. Pitot tube, 455. Sargent, 462. St. John, 461. Steam meters, classification of, 453. Steam, properties of, tables, 1092-1098. Steam sampling for quality determina- tions, 546-548. Steam, superheated, definition of, 544. Steam tables, 1092-1098. Steam tables, use of, 337. Steam turbine, Curtis, 812. DeLaval, 810. Impulse type, 808. Kerr, 816. Multistage impulse, 812. Multistage reaction, 812. Pelton type, 816. Pressure stage, 812. Rateau, 812. Reaction type, 808. Single stage, 810. Sturtevant, 816. Velocity stage, 812. Westinghouse, 815. Steam turbine losses, separation and estimation, 822. Steam turbine, power input, 819. Steam turbine testing (see: testing of steam turbines). Steam turbine tests, correcting results for standard conditions, 824. Steam turbine, types of, 808. Steam, wet saturated, definition of, 543. Steel-yard dynamometer, 296. Stirling cycle, 348. Strain, measurement of, 99. Strength of materials, definitions, 51. Stress, definition of, 51. Stress-deformation diagrams, 53. Stress intensity, definition of, 51. Stress, primary, definition of, 63. Stress, secondary, definition of, 63. Strohmeyer extensometer, rot. Sturtevant turbine, 816. Submerged orifices, 361. Subsurface or submerged floats, 308. Suction gas producer, 851. Sulphur determination in fuels, 500. Sulphur dioxide, properties of, table, I108, Superheating of vapors, 335. Superheating steam calorimeter, 558. Surface floats, 308. Suspended planimeter, 31. Sweet measuring machine, 45. INDEX Tas ie of Beaumé hydrometer scale with corresponding specific gravities, 1091. Tables of coefficient of discharge for sub- merged orifices in thin plates, 363. Table of coefficients of friction, to90. Table of constants for principal gases, 857. Table of constants for principal hydro- carbon gases, 858. Table of formulas for beams, 60. Table of horse power per pound of mean pressure, 109g. Table of mean specific heat for gases, 469. Table of melting points and specific heats of metals, 207. Table of properties of ammonia, 1107. Table of properties of CaCl: brine, 1110. Table of properties of carbon dioxide, 1108. Table of properties of NaCl brine, 1109. Table of properties of sulphur dioxide, 1108. Table of relation between pressure in pounds per square foot, inches of mercury, etc., 366. Table of specific gravity of oils, 247. Table of theoretical water rates for steam engines, 1105. Table showing ammonia absorption in water, 1109. Table showing material tests required, 138. Tachometer, Autographic, 230. Centrifugal, 229. Frahm, 231. Schaefer & Budenberg, 229. Veeder, 230. Tachometers for measurement of water, 402. : Tagliabue cold test apparatus for oils, 253 Tangential stress, definition of, 51. Tangential water wheel, ro4o. Tank meters, 383. Tar, determination of, in fuel gas, 885. Temperature, definition of, 193. Pare sane diagram for gas, Si Temperature-entropy diagram for steam, 341. Temperature rise during adiabatic air compression, 957. Tan Ones obtained in combustion, 468. Tensile strength of cements, 163. Tension loading, formulas for, 55. Tension test machines (see testing ma- chines). Tension tests, character of fracture, 123. Tension tests, directions for, 118. INDEX Tension tests, equivalent elongation, 123. Tension tests, form of test piece, 115. Tension tests, laying off gauges, 1109. Tension tests, report on, 124. Tension tests, wedge adjustments, 120. Test pieces for compression testing, 125. Test pieces for special materials, Cast iron, 117. Chains, 118. Hemp rope, 118. Wire rope, 118. Wood, 117. Test pieces for tension testing, form of, 15. Test pieces for torsion testing, 129. Test pieces for transverse testing, 126. Test specimens for cement testing, 161. Tests and specifications, special, 138. Tests for building stone and brick, 152. Tests of cements and mortars, 156. Tests of paving materials, stones, ballast, natural and artificial, 155. Testing machine accessories, 99. Testing machines, 67. Testing machines, cement, Fairbanks, 96. Olsen, 99. Riehlé, 99. Testing machines, tension, compression and transverse, compound lever machines, 70. Differential lever machines, 69. Direct-acting hydraulic, 71. Emery, 72, 78-82. Fairbanks, 70. Frame of, 75. General types of, 68. Hydraulic press, 67. Kellogg-Johnson, 71. Maillard, 72. Olsen, 70, 86. Power system of, 76. Riehlé, 70, 84. Riehlé hydraulic, 70. Shackles and clamps, 68, 76. Simple lever machines, 69. Thomasset, 69. Thurston, Polmeyer, 67. Weighing system of, 74. Werder, 71. Wickstead, Martins, Buckton, 69. Testing machines, torsion, Olsen power torsion, 91. Riehlé power torsion, 90. Thurston, 86. Testing of belts, Coefficient of friction, 323. Efficiency of transmission, 323. Initial tension, 321. ; Methods and computations, 320. 1129 Testing of boilers (see rules for conducting boiler trials). Testing of boilers, notes on rules, 710- 724. Ash determination, 718. Boiler efficiencies, 719-721. Boiler leakage, 712. Factor of evaporation, 722-724. Graphical log, 715. Heat balance, 721. Testing of cements, Constancy of volume, 163. Fineness, 159. Normal consistency, 159. Specific gravity, 158. Strength, 163. Time of setting, 160. Testing of centrifugal fans, 986. Determination of humidity, 951. Measurement of velocity and pressure, 987. Power input, 986. Power output, 987. Scope of test and report, 988-991. Volume of gas delivered, 987. Testing of centrifugal pumps, 1077. Head pumped against, 1078. Length of run, 1078. Power input, 1077. Power output, 1078. Quantity of water pumped, 1077. Scope of tests and report, 1079. Testing of gas engines, gos. Apparatus required, go7. Calibration of instruments, 906. Determination of principal dimensions, go6. Duration of tests, 906. Examination of engine, gos. Observations and calculations, 907- 913. Report, 913-9109. Starting and stopping, 906. Testing of gas producers, 891. Conducting trial, 893. Data and results, 895-899. Duration of trial, 892. Object of test, 891. Observations and calculations required, 893. Starting and stopping, 892. Testing of hot air engines, 933. Analysis of fuel, 934. Analysis of waste gases, 934. Computations and report, 934. Heat balance, 935. Indicated horse power, 933. Measurement of fuel used, 933. Other observations, 934. Pump horse power, 933. 1130 Testing of hydraulic ram, ro4o. Testing of injectors, 835. Testing of insulation, ror. Testing of locomotives (see standard method of conducting efficiency tests of locomotives). Testing of materials, methods of, 115. Testing of oils, Acid, 245. Adulteration, 243. Burning point, 256. Chill point, 254. Density, 246. Durability, 267. Flash point, 254. Friction, 256. Gumming and drying, 245. Viscosity, 248. Volatility, 256. Testing of piston air compressor, Air horse power, 973. Arrangements for, 973. Computations for test, 977 Power input, 973. Report, 977-980. Weight of volume of air handled, 973- 976. Testing of pumping engines (see standard method of conducting duty trials of pumping engines). Testing of rotary pumps, 1077. Testing of steam boilers (see rules for conducting boiler trials). Testing of steam engines (see rules for conducting steam engine tests). Testing of steam pumps (see standard method of conducting duty trials of pumping engines). Testing of steam turbines, Clausius efficiency, 821. Computations, 819. Cylinder efficiency, 82r. *Electrical horse power, 819. Internal horse power, 819. Potential efficiency, 821. Thermal efficiency, 820. Testing of vapor compression refrigerating machines, 1028. Compressor and prime mover, 1029. Computation of results, 1033. Condenser, 1030. Cooler, 1030. Heat balance, 1033. Report, 1031,1032, 1034, 1035. Testing of water motors, 1062. Length of run, 106s. Power developed, 1064. Report and computations, ro6s5. Speed and gate opening, 1065. Supply head, 1063. INDEX Testing of water motors (continued), Volume or weight of water supplied, 1063. Thalpotasimeter, 201. Thatcher rule, 18. Theoretical head produced by fan, 981. Theoretical velocity of steam from the heat chart, 447. Theoretical velocity of steam in orifices, 440. Thermocouple pyrometers, 212. Thermometers, 193. Thermometer, Air, 199. Alcohol, 202. Electric resistance, 210. Employing liquids, 201. Employing solids, 205. Gas, 196. Mercury, 202. Thermometer calibration, 219. Thermometric materials, 193. Thermometric scales, 195. Thermometric standards, 195. Primary, 196. Secondary, 196. Thomas electric superheating calorim- eter, 566. Throttling calorimeter, 560-563. Throttling calorimeter computations, graphical solution, 563. Throttling calorimeter from pipe fittings, 565. Throttling calorimeter, theory of, 562. Thurston oil testing machine, directions for use, 264, 266. Thurston oil testing machine, theory of, 261. Thurston railroad lubricant tester, 259. Thurston standard oil testing machine, 258. Tieftrunk apparatus for tar determina- tion, 886 Time for emptying tanks, 350. Time of setting for cements, 160. Tonnage in refrigeration, 1028. Torsion dynamometer for solid shafts, Rue Torsion dynamometers, 300. Torsion loading, formulas for, 6r. Torsion meters (see torsion dynamom- eters). Torsion test machines (see testing ma- chines). Torsion tests, directions for, with Thurs- ton autographic machine, 131. Torsion tests, directions, with Riehlé or Olsen machine, 129. Torsion tests, form of test piece, 120. Total heat in vapors, definition of, 334. INDEX Traction dynamometers, 292. . Transmission dynamometers, general types, 293. Transverse loading, elastic curve, 58. Transverse loading, formulas for, 57. Transverse loading, neutral surface in, 58. Transverse tests, directions for, 127. Transverse tests, form of test pieces, 126. Transverse tests, report on, 127. Transverse . test machines (see testing machines). Trapezoidal weir, 377. Triangular weir, 376. Tumlirz equation, 344. Turbine compressors, 945. Turbine gas meter, 436. Turbine pumps, 1068. Turbines, water (see water turbines). Two-cycle gas engines, 844. Uttimate strength, definition of, 52. Undershot wheel, 1048. Unit of electrical power, definition of, 276. Unit of heat, 325. Unit of power, 275. Unit of refrigeration, 1028. Unit of work, 275. Universal or combination steam calorim- eter, 577. Vacuum gauges, 185. Vacuum process of refrigeration, root. Van Winkle power meter, 305. Vapor compression refrigerating cycle, actual, 1016. Vapor compression refrigerating cycle, ideal, ror. Vapor compression system of refrigera- tion, 1003. Vapor cycles, 351. : Vapor, pressure and volume changes in Adiabatic (isentropic), 344. Constant pressure, 343. Constant volume, 344. Vapor pressure pyrometers, 201. Vapor tables, 335- Vaporization, 333. Vaporization, External latent heat, 334. Internal latent heat, 334. Latent heat of, 334. Total heat of, 334. Veeder tachometer, 230. | Velocity of approach in weirs, 374. Velocity of water, measurement in chan- nels and streams, 397- m3. oh Velocity of water, measurement In pipes and conduits, 406. — Velocity changes in turbines, 812. Velocity water meters, 387. 1131 Venturi meter, 369, 392. Venturi meter, theory of, 370. Venturi meter used for measuring gas, 443. Venturi tube, 369. Vernier, the use of, 20. Vernier caliper, 42. Vertical water wheels, 1045. Viscosimeter, Gibbs, 249. Perkins, 250. Stillman, 250. Tagliabue, 249. Viscosimeter, other forms of, 252. Viscosimeter with constant head, 250 Viscosity of oils, 248. Volatility tests for oils, 256. Volume relations in combustion, 465. Volume water meters, 389. WANNER pyrometer, 216. Waste detection meters, 392. Water equivalent for bomb calorimeter, 475, 478 Water equivalent, condensing calorim- eter, - Water meter, calibration of, 396. Water meter capacities, 388-392. Water meters, classification of, 385. Water meters, Current, 387. Gem inferential, 388. Hersey rotary, 390. Hersey torrent, 387. Hot water, 394. Inferential, 387. Nash disc, 391. Open type, 386. Piston, 393. Positive, 393. Siemens, 386. Velocity, 387. Venturi, 392. Volume or capacity, 389. Waste detection, 392. Worthington, 394. Water pressure engines, efficiency, 1044. Water turbine, 1052. Water turbine, Center vent, 1059. Fourneyron, 1056. Francis, 1059. Impulse, 1053. Jonval, 1059. Mixed flow, 1059. Parallel flow, 1059. Radial inward flow, 1059. Radial outward flow, 1056. Reaction, 1053. Risdon-Alcott, 1060, 1132 Water turbines, classification, 1053. Water turbines, efficiency of, 1057, 1062. Water turbines, power of, 1057, 1062. Water turbines, testing of (see testing of water motors). Water turbines, theory of action of stream upon vane, 1054-1055. Water wheel, impulse, 1049. Water wheel, tangential, 1049. Water wheels, Breast, 1047. Overshot, 1045. Undershot, 1048. Vertical, 1045. Webber dynamometer, 300. Wedge scale, 100. Wedgewood pyrometer, 205. Weight of vapor discharged from orifices, 440. Weight relations in combustion, 465. Weir measurements, accuracy of, 379. Weir measurements, flow of water, 372 Weirs, contraction in, 373. Weirs, Rectangular, 372. INDEX Weirs (continued), Trapezoidal, 377. Triangular, 376. Welding test, 134. Westinghouse brake for steam turbine tests, 287. Westinghouse-Parsons turbine, 815. Wet and dry bulb thermometer, 952. Wet and dry gas meters, relative accuracy, 437: Wet gas meters, 432. Wet saturated vapor, definition of, 3. Wilcox water weigher, 383. Willan’s Law, 726. Willan’s line, 726. Willis planimeter, 34. Woltman mill, 403. Work done by centrifugal fan, 983. Work of compressing air, 954. Working loads, definition of, 53. Worthington piston meter, 394. YIELD point, definition of, 53. ZERO circle, planimeter, 24. ene