W 799 . v " " ", . . . " hvor ' '' ' * VI 1 . . . . UM. ht the o n D UNCLASSIFIED ORNL . res 532 2_ 3 ORNAR-ssr 7 / / 7. C PROGRESS REPORT FOR TIIE PITYSICAL PROPERTIES GROUP OF TIE REACTOR DIVISION AT TID: OAK I:G NATIONAL AIOIAOLY* OCT 30 1964 Er J. W. Doko** Reactor Division Oak Ridge National Laboratory Oak Ridge, Tennessee INTRODUCTION Our physical properties laboratory has been concerned over the past ten to fifteen years with the measurement of nearly all of the vari- ous thermophysical properties of liquids (primarily molten metals and salts) and of some solids. Our more recent work with thermal conductivity measurements has been with mixtures of the fluoride salts of Li, Be, 2r, U, and Th for the Molten Salt Reactor Program and with certain classified plastics for the Space Power Program. Our investigations with the molten fluoride salts have been carried out from 500 to 1000C using a variable- gap conductivity apparatus. Our measurements with the plastics have been fram -50 to 100°C using a radial-heat-flow apparatus. These two systems will now be described. VARIABLE-GAP APPARATUS at 1. A Wom The report one motore Codex Gua r d the better m , au bout me ma Went the - LEGAL NOTICE d An absolute, variable-gap apparatus is shown in Figure 1. This is an improved design over the comparative, variable-gap apparatus (using Armco iron heat meter's) which was used for the majority of our measure- ments. Heat from the main heater flows downward across the liquid sample gap into the air-cooled sink. Heat flow in the other directions is mini- mized by the use of guard heater's. The de power to the main heater is determined from voltage and current measurements using a standard resistor and a potentiometer. The temperature drop across the gap, Ato, is meas- ured by two thermocouples within the metal wall on each side of the gap. The sample thickness, sx, is variable and can be measured to within 10.1 mils using a dial indicator'. 'Thermal expansion effects are minimized by zeroing the dial indicator for zero-gap spacing at each temperature level and using a fused quartz rod to connect with the dial indicator. The el is maintained by a large L/D ratio, zone controlled than *Research sponsored by the U. S. Atomic Energy Commission under contract with the Union Carbide Corporation. **Research Engineer in the Reactor Division. 7 " . IX " A . VISI11 7 11 . SEOUL . . G' 1 L. . . IN ' . t VA YUX'. NAWATI AX NA MIPA 12 NR . U AUT . 2 . C . 11 2012 DIAL INOICATON VARIABLE-OAP ADJUSTMENT FUSED QUARTI ROO INSULATION FURNACE A SSSSSSS ..... LIQUID LEVEL ..14 QUAND MEATER . .. . MAIN MEATER- . HO CAL MOD HEATERS .. VARIABLE GAP WA THERMOCOUPLES- . SINK HEATER la. # SINK COOLER ## FIGURE 1.. VARIABLE-CAP TIERMAL CONDUCTIVITY APPARATUS FOR LIQUIDS. . L'urnate, The uppuratus 18 VIKulun liglil, alla l'Ullel will holeste purrily alsoli. The apparuluw lo l'illed with an open! In 1 Tube'd' lll powder or liquid form with a 21-gap wpleing. The system las lloes lieulid above the BIKI ting temperature of the upce ime'll and evacuntoil to l'emove any entrained gus bubbleu. Allor llie liyotem la lorought toll deadliest l'Imperature level, a lulative alibration of the Eurocoupled 1:3 mude', s dloudy flow of heut is then cutublished between the main louter and the dilnik whillenin- tuinine u %11'0-tempe l'uturi: difference between the thieMoupleo situated between the imalna liculel' and the mind and laddal nem halal.). When utoudy wlule lu leughed, tihedal indicator lo menos land thai leimpelutulon und voltague recorded. Melintaining the urune hout 110w and tempx: l'aluru level, tile cumple thickne'un lw In renda Ini utapes, with the expertinentul datu l'ecorded for onch ulep utler wloudy utute huu nell roald. The thicinul conductivity lo determined t'r'on a plot of the total theimuil resistance across the gap, Ato NQ (thio includes the specimen, the intel'fucco, and the wall thickness between the imbeduled thermocouples and the opecimon), 43 a function of the sample thickne01, 10 shown in Figure 2. The thermal conductivity is equal to the reciprocal of the Blope of this curve as the sample thickneno approuh'3 ero. The under- lying assumption of this calculation is that the interfacial l'eslotances (crcuted by deposits, corrosion, ctc.) do not very uignificant].y with i time. By being able to vary the oample thicknic88, several very impor- tant problems are el. lininuted. First, the thermocouples do not need to be placed in the liquid, which may be corrosive. Second, tlie uboolute distance between the thermocouples docs not need to be either large or known. Furthermore, by extrapolating the calculated thermal conductivity value to small specinen thickneuses, such uncertaintleo as radial heat flow, natural convection, and rarllation through the specimen should be greatly reduced. Figure 2 shows a lot of experiental data for which either one or all of these uncertainties were present causing the data to deviate below the ideal curve for large specimen thicknesses; however, both curves approach the sune ol.ope for smaller thi:knechce. The variable-gup method 10 best suited for low conductivity fluids (i <0.) w/cm•°C), where it is not pousible to measure directly the temperature gradient within the fluid, and where there is also a good possibility of relatively large interfacial resistances. The method is also well suited to transparent fluids since the two components of heat transfer, radiation and conduction, can be separated to a large extent. The comparative, variable-gup method has been used by our group with good suc.:C88 with molten salto in the past. A summary of these re- sults (including other thermophysical property results is given in References 1 through 5. We hope that the more advanced design will pro- vide not only more acurate results, but al.so results sufficiently precise THERMAL RESISTANCE 20. IDEAL CURVE .. ACTUAL DATA (INDICATING PREMIMCE OF NATURAL CONVECTION OR RADIATION) 0 0.04 0.36 0.40 0.10 0.15 0.20 0.24 0.20 SAMPLE TICKNESS - AX (om) FIGURE 2. TOTAL TIERMAL RESISTANCE (INCLUDING SPECIMEN, METAL WALLS, AND INTERFACES ACROSS THE GAP OF A VARIABLE- GAP THERMAL CONDUCTIVITY APPARATUS AS A FUNCTION OF GAP THICKNESS. XIR. T _ - * + - . .. - - .* that the degree of radiation transfer through molten salts can be examined. -4 .11. S 7 1 RADIAL AT FLOW APPARATUS center of the The radial heat flow apparatus (shown in Figure 3) was for low conductivity materials (k <0.1 w/cm•°C) over the temperature range from -70 to 200°C. The apparatus consists of the usual stack of specimen diuks (5/8-in. ID X 3-in. OD X 1.0 in. long) with the test specimen er of the stack. Heat flows radially from the central electrode, through the disks, and into the coolant bath. The heat 18 supplied by the resistance flow of ac current (~200 amps ) through a 1/-in.-OD Inconel tube which is free to expand through a Teflon bushing at its lower end. The coolant consists of various baths of dry ice and alcohol, ice and water, and nonvolatile oils. The radial temperature gradient in the specimen is measured by three pair of 20-mil diameter sheath thermocouples arranged along three radial lines. The thermocouples are int one end of the apparatus through 40-mil holes in the guard specimens and 25-mil holes in the test specimen. These thermocouples and a thermocouple within the electrode tube can each be used as probes to check the axial temperature gradient. Considerable care was taken in designing the end pieces of the apparatus to produce a heat balance that would minimize axial heat flow in the specimens. During the initial operation of the apparatus, end heaters were attached to induce an axial temperature gradient in the specimens. These tests showed that the axial gradient needed to be several times greater than ever encountered in the actual experiment to noticeably affect the thermal conductivity measurement. The thermal conductivity is determined from the power to the electrode measured by a precision current transformer and voltmeter and from the temperature gradient measured in the specimens. The primary advantage of this apparatus is that it can be conveniently operated both above and below room temperature. Also, the results in this temperature r'ange should be more precise than existing data which have been either extrapolated from higher temperatures or obtained by an apparatus designed for much higher temperature operation. SUMMARY We currently have two thermal conductivity apparatus under development. One, an absolute variable-gap apparatus, will be used for corrosive, low-conductivity molten salts up to 1000°C. The other, a radial flow apparatus, is being used for low-conductivity, solid plastics over the temperature range from -200 to +200°C. We hope that the results . . . . . N . .. the I, will. ; will. PELECTRODE INSULATOR BATH LEVEL 277973 C VOLTAGE TAPS GUARD SPECIMENS -TEST SPECIMEN - THERMOCOUPLES (L) 7112 FIGURE 3. RADIAL-HEAT-FLOW THERMAL CONDUCTIVITY APPARATUS. cbtained for the molten balts will be completed in time for reporting at next year's conference. As part of our broad overall look at thermophysical properties, we are assembling a properties data book for radioactive isotopes and their container materials for the SNAP Program. A180, we are making a I techniques available for determining thermophysical properties, including thermal conductivity. However, at present, only those techniques which show a clear superiority with regard to the follow- ing classifications will be considered: 1. Accuracy or Precision ?. Temperature Range Temperature: Level Simplicity 5. Size and Shape of Specimen 6. Speed of Operation These experimental techniques will be classified, described, and evaluated. REFERENCES Powers, W. D., S. I. Cohen, and N. D. Greene, "Physical Properties of Molten Reactor Fuels and Coolants," Nuclear Sci. and Engr., 17 (1963), pp 200-211. Powers, W. D., and R. II. Nimmo, "Physical Property Measurements," Molten-Salt Reactor Program Progress Reports (1958 to 1960), USAEC ORNI Reports, Oak Ridge National Laboratory. (3) Cooke, J. W., "Physical Property Measurements," Molten-Sult Reactor Program Progress Reports (1960 to 1962), USAEC ORNL Reports, Oak Ridge National Laboratory. Cooke, J. W., "Thermophysical Properties," Aircraft Nuclear Propulsion Project Progress Reports (1959 to 1962), USAEC ORNL Reports, Oak Ridge National Laboratory. 12 Cooke, J. W., "Thermophysical Properties," Space Power Program Progress Reports (1962 to 1964), USAEC ORNL Reports, Oak Ridge National Lab- oratory. ir . 3 ' ,. ; 2 - . 7 2 DATE FILMED 121/ 11 / 64 . 214 WAT -LEGAL NOTICE – This report was prepared as an account of Governmont sponsored work. Neither the United Statos, nor the Commission, nor any person acting on behall of the Commission: A. Makes any warranty or roprosontation, expressod or implied, with roupect to the accu- racy, completoness, or usofulness of the information contained in this report, or that the uso of any information, apparatus, molhod, or process disclosod in this roport may not infringo privatoly owned rights; or B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of any information, apparatus, mothod, or process disclosed in this report. A3 used in the above, "person acting on behalf of the Commission" includes any on- ployee or contractor of the Commission, or omployeo of such contractor, to the oxtont that such omployos or contractor of the Commission, or employee of such contractor prepares, disseminates, or provides access to, any information pursuant to his omploymont or contract with the Commission, or his employment with such contractor. ile LKV ::::STERSTATUS END VIDEOS TV