:Vj•^■;/^;^:y:■•■:^i;;VV.•^■.■.t;;^/;V;;.^.'•vv■•i mMm>i' i-:WAM -^Mi ■''^' i^An • '\Hx4A MOTNE COLD STOtlMiE liifit AND VENTILiVriNG K'ALKER J a , » V 5 D ''.-;• COLD STORAGE, HEATING AND VENTILATING ON BOARD SHIP BY SYDNEY F. WALKER, R.N. N. I. E. E., M. I. M. E., X. C. S. I. A., M. IXST. M. E. ILLUSTRATED SECOND EDITION NEW YORK D. VAN NOSTRAND COMPANY 25 PARK PLACE 1919 O Engineering library Reprinted from INTERXATIOXAL MARIXE EXGIXEERING Copyright, 1 9 1 1 , BY D. VAX XOSTRAXD COMPANY PRESS OF BRAUNWORTH & CO. BOOK MAWUFACTUHER3 BROOKLYN, N. Y. PREFACE Every problem in engineering requires a special solution when applied to marine work. The limitations of weight and space on board ship, and the absolute necessity for reliability and economy .introduce factors which can be disregarded in many similar problems in connection with machinery in- stalled on shore. Refrigerating machines and heating and ventilating apparatus are no exceptions to this rule, and in this book an attempt has been made to treat the problem of cold storage and heating and ventilating exactly as it presents itself to a naval architect and marine engineer. The reader will find the treatment not merely descriptive, but thoroughly practical from an engineering standpoint. About one-third of that part of the book which deals with cold storage is devoted to a discussion of "faults" which may occur in the apparatus. Directions are given for hunting down various troubles and repairing them, and, what is more important, explicit instructions are given for operating various types of plants, so as to avoid breakdowns. Comparatively little has hitherto been published on the subjects covered by this book. Therefore, exceptional pains have been taken to make the present treatment exhaustive and thoroughly up to date. • • • 4Gc317 CONTENTS Cold Storage ox Board Ship Introduction. The Cold Storage Problem. Methods of Cooling the Cold Chambers. Direct Expansion. Cooling the Chamber by Cooling the Air. Cooling the Air Entering Cold Chambers. Methods of Cooling the Air. Cooling the Air by Compression and Expansion. Leading the Cooled Air into the Cold Chambers. The Doors of Cold Chambers. How the Low Temperature of the Brine or Refrigerant is Produced. The Condenser. Lubrication and Stuffing Boxes of Compressors. Absorp- tion Machines. Circulating Pumps. How Refrigerating Apparatus is Measured. The Power Recjuired for Re- frigerating Apparatus. Cooling Water. Forms of Apparatus for Use on Board Ship. Other Applications of Refrigeration on Board Ship. Cooling ^lagazines and Officers' and Men's Quarters. Faults. Watch the Gages. If the Delivery Pipe Becomes Hot. If the Delivery Pipe Becomes Cold. What Follows from a Hot Compressor. Getting Oil and Foreign Bodies Out of the System. To Test Ammonia for Purity. Faults in Evaporating Coils. Troubles with Compressor Valves. Testing the Gages. Faults in the Brine Circulating System. Preparing the Brine Solution. Faults in Air Cooled Plants. Faults in Cold Chambers. Receiving Meat and Produce. Thawing Out. Handling Meat and Produce when Loading and Discharging. Faults in an Absorption Plant. PAGE I ^ CONTENTS PAGE Heating 124 Special Requirements on Board Ship. Difficulties Peculiar to Ship Work. Methods of Heating Available. The System of Heating by Hot Water. Difficulties in Connection with Heating by Water. The Air Trouble. Arrangement of Hot Water Heating Systems. Forms of Heating Apparatus with Hot Water. Heating by Steam. A Combined Air and Steam Radiator. Special Air Heating Stoves, Heating the Air by Means of Steam, Hot Water, and Electric Radiators. Air Heating Apparatus Pure and Simple. The Thermotank System. Application of the Thermotank to S. S. Lusitania. Heat- ing by Electricity. Glow Lamp Radiators. Non-Lumi- nous Heating Apparatus. Spiral Coil Heaters. Low Temperature Air Heater, Tubular Type. Regulating the Heat Delivered by Electric Heating Apparatus. Quan- tity of Heat Liberated in Electrical Heating Apparatus. V^ENTILATION 220 Ventilation by Heating and Cooling. Ventilation of Lavatories and Cattle Spaces. Fans Used in Ventilating. Size of Fans Required. Power Required by the Fan. Testing the Air Current. Estimating the Heat to be Required. Heat Passing Out through the Ship's Side, Bulkheads, etc. Heating by Electricity of a Large Passenger Vessel. Apparatus Estimated to be Required for Heating the Different Saloons, State Cabins, etc. Cost of Furnishing the Heat Required. ' > ^ J > > > , ^ CQLD STORAGE ON BOARD SHIP. It is not much over thirty years since cold storage was first introduced, and not so long since the first cargo of dead mutton was first shipped, yet an enormous industry has since been built up in the transport of dead meat of all kinds, from countries such as the United States, Australia, New Zealand, and the Argentine, where it can be grown cheaply, to countries such as the British Islands and South Africa, where the conditions are not so favorable, and where consumption is large and increasing. The early cargoes of frozen meat were looked upon with great uneasiness in some quarters, and it is on record that the Duke of Beaufort once wrote to The Times, stating that it was flying in the face of Providence to use "such means to preserve pro- duce which was never intended to be preserved in that way." In addition to this, a large fruit-carrying trade has grown up, increasing in dimensions every year, which enables those who reside in the northern hemisphere to enjoy the fruits that are being grown in the southern, at the time when their own fruits are not obtainable ; the fruits that are transported being almost as luscious to the taste, after a journey of several thousand miles, as when picked on the spot. In fact, some of the fruits sold in London, that have been brought from Australia and Cape Colony, taste better than those grown in England itself. There is another very useful office that cold storage has per- formed for those who go down to the sea in ships — It has ena- bled fresh meat to be carried for the whole of the voyage, quitt 2 COLD STORAGE ON BOARD SHIP. arart from the live animals that can be stored ; while the dead meat, properly preserved, is often better than that of the live animals carried, because it is not subject to sea-sickness and other ailments. Refrigeration also offers a means of dealing with the many problems in connection with the service of men- of-war, such as cooling the magazines, the men's quarters, etc. Apart from the actual ability to freeze meat, and other produce that will stand freezing, and is preserved in that condition, mod- ern cold storage apparatus enables the engineer to maintain any temperature that may be advantageous to the produce, and any degree of dryness, which is itself a most important point. Cold storage preserves by arresting the decay that would otherwise commence soon after the animal is killed, or the fruit is removed from the tree on which it grows. What we know as decay is really an organic chemical and bacterial action, and. as in all actions of the kind, heat plays a very important part in this. The presence of heat, up to a certain temperature, assists both the chemical and bacterial actions, while its absence retards them, hence the ability to preserve produce. But this it not the whole story. Different substances demand different treatment in the matter of temperature for preservation. Glutton, lamb, rabbits, and some other meats or animals may be frozen as hard as you please, and if carefully thawed out when required for use are appar- ently little the worse ; but beef, though it can be frozen, and if carefully thawed is quite eatable, does not command so high a price as if merely "chilled," that is. reduced to a temperature a little above the freezing point of the meat. Juicy fruits also must not be frozen, or they are naturally spoiled, from the fact that, the juices expanding in freezing, the other parts are injured. The fruit loses its vitality, its flavor. Eggs, vegetables and other substances also must nut be frozen, for similar reasons. Again, there is a great deal in the matter of the hygroscopic State of the atmosphere in which the produce is stored. If the THE COLD STORAGE PROBLEM. S air in the cold chambers carries moisture, it is likely to condense upon the produce, and that is bad from the viewpoint of pres- ervation, as it assists any chemical actions that have commenced. There is also the question of the carriage of produce, such as apples and onions, with distinct odors of their own, which will be communicated to other produce if the air of the chambers in which the odorous produce is stored is allowed to penetrate to the chambers containing other produce. But all of this can be arranged, and quite simply, by modern refrigerating apparatus. THE COLD STORAGE PROBLEM. Stated briefly, the cold storage problem on board ship consists in the transportation of the heat present in the produce, and the heat which passes into the chamber in which the produce is stored, to the water of the sea, or to the atmosphere. Every substance, whatever its temperature and whatever its composi- tion, carries a certain number of heat units, depending upon its temperature and its specific heat. A heat unit, or as it is usually written, a British Thermal Unit, which is one of the standards of heat employed in calculations, is the quantity of heat that will raise the temperature of one pound of pure water through one degree Fahrenheit, when at a tem- perature of z^ degrees F. The specific heat of any other sub- stance is the ratio which the heat required to raise the tempera- ture of one pound of the substance one degree F. bears to that required for one pound of water. The specific heat of water is taken as the unit, and, as that of the great majority of sub- stances is less than that of water, their specific heats are usually expressed as fractions. The specific heat of every substance varies with the condition it is in. Ice, for instance, has a specific heat of only 0.4, as against i.o for water. To reduce the temperature of any substance to freezing point, therefore, the number of heat units that have to be removed is found by multiplying the weight of the substance in pounds by 4 COLD STORAGE ON BOARD SHIP. the difference between the temperature at which the produce iS received and that at which it freezes, and then by the specific heat of the substance. In addition to this, nearly all produce that is to be stored in cold chambers consists partly of liquids, and when these are reduced to the solid form, the latent heat of the liquid has to be removed before it will freeze. With ice, for instance, the latent heat of water as a liquid has to be removed; this amounts to 142 units per pound. There is usually a still further quantity of heat to be removed, for it may be necessary to hold the frozen masses a few degrees below freezing point, so that in case the refrigerating apparatus does not work well, or if from other causes the temperature to which the sub- stance is exposed is raised, it will not immediately thaw. Ice that is required for domestic or industrial purposes is reduced to a certain number of degrees below freezing point, in the pro- cess. Nature does exactly the same in the production of natural ice. There is one other point. The freezing point of a liquid con- taining other substances in solution is lower than that of the liquid itself. Thus while the freezing point of water is 32 degrees F., that of milk, and of the blood and other liquids con- tained in the carcasses of animals, and that of the juices of fruits, is lower than that of pure water. Hence with such a substance as mutton, whose specific heat is 0.69 when unfrozen, and 0.38 when frozen, and the latent heat of whose liquids is 88 units, and which is held at from 16 to 25 degrees F., the number of heat units to be extracted will be found by first multiplying the weight of the liquids in the sheep in pounds (about 62 per- cent of the total weight) by 88. adding to this the product of the total weight multiplied by 0.69 and by the difference between the temperature at which the meat will be received and its freez- ing point, and adding to this again the product of the weight multiplied by 0.38. and by the difference between the temperature at which the meat is to be held and its freezing point. THE COLD STORAGE PROBLEM. ^ Meat is always allowed to cool to a certain extent before taking into store. As cold store men and butchers express it, the animal heat is allowed to go off, this giving the refrigerating machinery so much less to do. Where the meat is beef, and is only to be chilled, the number of heat units to be taken out is much less than where it is actually frozen, as there is no latent heat to be taken account of, and the temperature has to be lowered only 100 F. CURVE SHOWING CAPACITY OF AIR PER CUBIC FOOT FOR HOLDING WATERY VAPOR. to about 33 or 35 degrees. In this case the quantity of heat units would be found by multiplying the weight of the meat by 0.69, and by the difference in temperature between 33 or 35 and that at which it was received. This is the first part of the problem. The second part of the problem is that of the cold store itself. COLD STORAGE ON BOARD SHIP. A cold Store is a chamber that is built expressly to prevent heat from passing from outside to the produce inside. It is not possible to construct a chamber that will not allow some heat to pass through the walls, floor and ceiling, and this heat which is constantly leaking through into the chamber has to be removed, just as that of the produce itself is. and transported to the sea or the atmosphere. The quantity of heat that leaks through depends upon the difference of temperature between the inside and outside of the cold chamber, upon the construction of the walls, floor and roof, and' upon the extent of the surfaces exposed to the action of the heat. Certain substances are good thermal insulators, just as certain substances are good electrical insulators, and the thermal insulators are used to prevent the ingress of heat into the cold chambers, in the same way that electrical insu- lators are used to prevent the egress of electricity from the conductors. This fact is very often not understood, and is some- times challenged, because the sizes are so different; but if it be borne in mind that the thickness of the walls of the chamber correspond with the thickness of the insulating envelope of a cable, or even of the insulation of the iron core of the armature of a dynamo machine, though they are much greater, while the air inside the chamber corresponds with the copper or the iron, it will probably be appreciated that heat leaks in through the thermal insulator just as electricity leaks out through the elec- trical insulator. Dry, still air is the best insulator known, and the other sub- stances that are good insulators owe their property very largely to the fact that they contain a large number of very small air cells, across which the heat current has to pass. Air in motion is a bad insulator. If the air which is confined in the walls of the cold chamber is able to move, and to set up convection cur- rents, it will by their aid transfer heat from outside to inside. Moisture also is a bad insulator, and if present will very consid- erably lower the degree of insulation. THE COLD STORAGE PROBLEM. The importance of good insulation can hardly be exaggerated. It is quite possible, if the insulation is sufficiently bad, that the VV H\ FLOORING SAMPLES OF VERTICAL AND HORIZONTAL INSULATION. (Black lines show waterproof insulating paper.) refrigerating machinery may be grinding away uselessly the whole 8 COLD STORAGE ON BOARD SHIP. time, because the heat will be passing into the chamber as fast as it is being taken out. This may be seen from the following example: Peclet. an able French savant, gives the rate of trans- mission of heat through one inch of powdered wood charcoal, one of the substances used in cold storage work, as 0.63 units per square foot per degree F. per hour. Take a chamber cubical in form, 12 feet long on the side, giving a surface exposed to the heat of 864 square feet, and assume a difference of temperature of 50 degrees F. This would give a passage of 27,216 heat units through the walls, roof and floor on Peclet's figures, per hour, and would require approximately a 2-ton machine to handle com- fortably, (The measurement of refrigerating machines, i-ton, 2-tons, etc., will be explained later.) If we have, instead of one inch of the substance, six inches, as is far more common, the rate of transfer of heat through the walls will be approximately one-sixth that with the one-inch, and a machine designed for a half ton should easily deal with it. On the other hand, if the insulation is so reduced that the rate of transmission through it is (say) 100,000 units per hour, in a room of that size, the whole power of a machine designed for six tons would be required. Cold stores for ship work, and for a good many other places, are built up as follows: The space to be occupied by the cold chamber is surrounded by a double wall, which should extend to the decks, both above and below, both walls being formed of wood. Where it can be arranged, and where it is strong enough to stand the strains that are brought against the walls, they are built of matched boarding, securely nailed to uprights, the two sets of uprights being braced together and lined on the insides (the sides facing each other), and covered with waterproof paper. There are several papers made, consisting of tough manilla or other substances, saturated with substances impervious to water and to the rays of the sun, and these are used to line the space in which the insulating material is to be placed. Between the THE COLD STORAGE PROBLEM. Q two walls, it will be understood, there is a space, broken up to a certain extent by the supports of the walls themselves, and into this space the insulating substance is poured and tightly packed. It is of great importance that the substance shall be so stowed that it cannot settle, or move in any way. The division of the space by the supporting timbers assists in this. If the insulation settles, leaving a space at the top, convection air cur- Condenser Evaporator DIAGRAM OF COMPRESSOR CIRCUIT, WITH CONDENSER AND EVAPOR.\TOR. rents are set up, which lower the insulation, and moisture may also get in. The best insulating materials are silicate cotton, cork and finely divided charcoal. Silicate cotton, or slag wool, as it is often called, is a substance made from the slag of iron smelting furnaces. It is very largely composed of silicon, and in its preparation the slag is remelted in a small furnace, to which an air blast is attached which blows the molten slag into fine hair-like threads, or wool, something similar to spun glass. In 10 COLD STORAGE ON BOARD SHIP. this condition it is full of small air cells, and when packed tight, and moisture excluded, it makes the best insulator known. Finely divided wood charcoal is prepared in the process of wood distillation. The wood that is employed very largely, in the United Kingdom, is the waste cuttings from the willow used in the manufacture of cotton reels. It owes its property of insu- lation very largely to the air cells before mentioned. It should be packed tight, and dry. Cork in a finely divided state is an- other good insulating substance. Cork is an external growth on particular kinds of oak, which grow in certain parts of Spain, America, and a few other countries. It contains a number of very fine cells with thin walls, all built up together, very much as a honey comb is built up, but with the walls very much thinner and the spaces much smaller. It is used in a finely divided or broken up state, as the other materials are. and also in the form of cork bricks, which can be worked into any posi- tion required. The bricks have the air cells, just as the small pieces of cork have, the latter having in addition the air spaces between the pieces. Cork bricks have the advantage that they enable a much better mechanical job to be made. With a ship knocking about in a sea w^y, this is a matter of considerable importance, as, if the walls are sprung and air admitted, the insulation may be practically destroyed. There are a number of other substances that are available as insulators. The problem, it will be understood, is very similar to that of insulating steam pipes, the same materials being used for the two purposes, where they can be. In the one case the object is to prevent heat of the steam inside the pipes from leaking out, while in the other the object is to prevent heat from outside from passing inwards. There is one important differ- ence that should be noted, however. With high temperatures, still dry air is the insulator par excellence, especially where it can be applied in small quantities, as in the jackets of heating appa- ratus; but with cold storage apparatus air has not always such THE COLD STORAGE PROBLEM. IX a good name, though it is acknowledged to be the best insulator ; the reason being, the writer believes, that it is sometimes difficult to avoid convection currents. Another insulator is sawdust, which has been used a great deal on shore. It is a good and cheap insulator if applied quite dry and well shaken down. These two points are essential, and they are sometimes difficult to insure in sawdust. Other substances are asbestos and mag- DIACRAAr SIIOWIN-G COOLIN'G WATER CIRCUIT. 2). £.— Condenser and Coils. L. — Refrigerant Inlet, iV.— Refriger ant Outlet. Y. — Water Circulating Pump. nesia fiber, peat, ashes, fossil meal and finely divided mica. Felt, cow hair, infusorial earth, cotton wool, sheep's wool— all are used, to a certain extent, but silicate cotton, charcoal and cork are the principal ones. In constructing the cold chambers on board ship, the outside skin of the insulating wall should be kept away from the ship's side, and from any bulkhead that is in metallic connection with the ship, the engine room, or stoke hold. As far as it is possible. 12 COLD STORAGE OX BOARD SHIP. keep the cold chamber with a layer of air around it, but arrange if possible that this air be perfectly still and perfectly dry. The more nearly this can be attained, the lower will be the cost of running the apparatus. The case is exactly similar to that of electricity and to that of steam, though the direction of motion of energy has to be reversed. If steam or electricity are allowed to leak out, more coal has to be consumed to make up the loss, and the accessories are more heavily worked. If heat is allowed to leak {}ito the cold chambers, more coal has to be consumed in carrying it away, and there is also more work on the accessories. It is a good plan, when the mechanical condi- tions will allow it. to divide the insulating wall into two por- tions; the outer portion being simply an air jacket, and the inner portion carrying the insulating substance. Both should be lined with waterproof paper. In small cold stores, air jackets are often used alone with a waterproof paper. It was stated above that the requirements as to temperature varied very considerably with the kind of produce carried, and it follows, therefore, that the construction of the cold chambers will vary though the main lines will be the same. For the large quantities of frozen sheep for instance, that are carried from New Zealand to the London docks — cargoes of loc.ooo to 120000 carcasses being carried — the bulk of the fore and after holds are converted into huge cold chambers, much as the holds are in petroleum tank steamers, except that there is no attempt at division of the holds for meat carriage. Probably the carriage of frozen mutton, with the few crates of frozen rabbits which are taken to fill up, represent the simplest case of cold storage trans- port. Freezing hard is the order, and as long as this is carried out there is no trouble, and freezing hard is comparative!}' easy. It is only a question of driving. The sheep are frozen near where they are killed; each is enveloped in a loose linen bag, with the owner's mark on it. and they are stowed in rows and tiers in the holds. No harm can come to them, so long as the THE COLD STORAGE PROBLEM. 113 temperature is maintained at a certain low figure, and this is easy to accomplish, provided that everything has been properly carried out in the matter of insulation. It is like the case of the ship which has only to drive as hard as its engines and boilers will allow it, without thinking of the cost. If the insulation is good, and even if it is only moderate, low temperatures mean simply more coal and accessories than higher temperatures. ir rr f] K B c. ,. 1 DIAGRAM SHOWING CIRCUIT OF REFRIGERANT. A. — Compressor. B. C. — Piston and Rod. D. E. — Condenser and Coils. F. G. — Evaporator and Coils. //.^Expansion Valve. K. L. M, N. — Delivery Pipes. # It is when we come to the cases where certain definite tempera- tures have to be maintained that the difficulties of the problem begin to appear. With "chilled" beef, for instance, which must not be frozen, but is held at about 2)2> to 35 degrees F., the outer layers will freeze if a much lower temperature is reached, and the condition of the meat on arrival may be seriously deteriorated. On the other hand, if the temperature is allowed to rise to an 14 COLD STORAGE ON BOARD SHIP. appreciable extent, the processes of decay, which the low tem- perature holds in check, may commence, and it is then very difficult to arrest them, particularly as in some cases the pro- cesses themselves generate heat. Further, if one quarter of beef commences to decay, the others may take it up. When first received, the meat has to be very gradually and carefully "chilled," or the outer layers may be chilled while the inside is still warm ; and the inside meat being protected by the outer layers, the processes of decay may be continued somewhat vigorously. The meat is, therefore, allowed to lose its animal heat, is then very carefully chilled, so that the process goes right in to the bone, and is then maintained at the desired temperature. For this purpose, in one arrangement the cold chamber is divided into bays, or longitudinal divisions, to each of which is assigned its own brine cooling pipe, or two bays may have a stack of pipes fixed vertically between them, the flow in all the pipes being controlled by valves on the outside of the chamber. Thermometers are fixed in the flow and in the return pipes, so that the attendant can learn what is going on in each bay, and can allow the brine to flow in that set of pipes accordingly. In the case of fruit, it is necessary that there shall be a gentle cur- rent of dry air all around each fruit throughout the voyage. Fruit ships are. therefore, fitted something on the lines of frozen mutton carriers, but usually with air cooling only. METHODS OF COOLING THE COLD CHAMBERS. We will now examine the method by which the cold is con- veyed to the chambers. Having made a box. so to speak, into which heat is to a certain extent prevented from entering, how is the low temperature to be produced in the box. and how is the heat that does pass through the walls of the box to be carried away? For shipboard work the following methods are permissi- ble: the use of brine, the direct use of carbonic acid where it is METHODS OF COOLING THE COLD CHAMBERS. IS the refrigerating agent, and the use of cooled air. With brine and with carbonic acid directly employed, pipes are laid in the chamber to be cooled, usually in the form of a grid, sometimes on the side, sometimes overhead, sometimes, as mentioned above, a grid of pipes separates two bays, and sometimes the pipes are formed into a wall. The length and size of the pipes are calcu- lated from the quantity of produce that is to be stored, and the leakage into the chamber that may be expected. With brine v_y DIAGRAM SHOWING BRINE CIRCUIT. F. G*.— Evaporator and Coils. A'.— Refrigerant Outlet. M.— Refrig erant Inlet. O.— Brine Grid in Cold Chamber. P.— Brine Discharge Pipe. Q.— Brine Pump, i?.— Brine Pipe L,eading to Grid, cooling, brine is kept in circulation in the pipes. The brine may consist of salt water— not sea water, but water in which common salt has been dissolved— but it more often consists of a solution of chloride of calcium. It was mentioned above that dissolving a substance in water lowers the freezing point of the solution, and that is the reason why brine is used. One percent of common salt in water reduces the freezing point to 30.5 degrees F., 3 percent brings it to 27.8 l6 COLD STORAGE ON BOARD SHIP. degrees, 5 percent to 25.2 degrees, and so on. One percent of chloride of calcium lowers the freezing point to 31 degrees F., 5 percent to 27.5 degrees, 10 percent to 22 degrees, 15 per- cent to 15 degrees, 20 percent to 5 degrees, and 25 percent to — 8 degrees. Common salt is not used now, except in special cases, for reasons that need not be mentioned to marine engineers. A 20-percent solution of calcium chloride is usually employed, or, if especially low temperatures are required, a 25-percent solution. The use of a liquid that freezes at temperatures below that at which the produce is to be held is necessary. The brine itself is cooled by one of the processes that will be described, and it is caused to circulate continually from the tank in which it is cooled, through the pipes connecting it with (and forming) the grid in the cold chamber, and back to the tank again. In passing through the grid in the cold chamber it absorbs heat from the air in the chamber, which in its turn takes heat from the produce, and so on. Heat flows from bodies at higher temperatures to those at lower temperatures, and as the entering brine is at a lower temperature than the air in the room it is to cool, heat flows to it. The brine in the return pipe is. therefore, at a higher temperature than that in the supply pipe, and as the brine which passes through it, back to the evaporating tank where it is cooled, is at a higher temperature than its surroundings in the evaporating tank, heat again flows from it to the refrigerating agent. As explained in connection with tlie apparatus for "chilled" beef, the attendant knows by the difference between the temperature of the flow and that of the return brine pipes of each particular section of the chamber what work in the matter of cooling is going on, and this applies also to each chamber. It is not a difficult calculation to determine the quantity of brine that must pass through a particular cold chamber in a certain, time, to keep the chamber at the required temperature or to reduce the produce to its keeping temperature — having given the METHODS OF COOLING THE COLD CHAMBERS. I/ number of heat units to be carried away in the same time, ascer- tained in the manner explained above. A 20-percent sohuion of calcium chloride has a specific gravity of 1.18, so that a gallon (Imperial) of the solution weighs 11.8 pounds. The specific heat of the solution is 0.834. therefore each gallon that passes through the pipes carries off 9.84 heat units for each degree F. that its temperature is raised. Brine is usually worked with an increase of temperature of from 6 to 8 degrees DIAGRAM SITOWIXG AIR CIRCUIT. O. — Brine Grid in Cold Chamber. P. — Pipe from Evaporator Tdnk. K.~Pipe to Expansion Tank. 5.— Fan. L'.— Cold Air Duct. F.— Cham- ber to be Cooled. X.X. — Air Ports. Z. — Exhaust Air Duct. F. between the entrance and outgoing ends of the grids, hence if we take an average rise of 4 degrees, since the temperature of the brine will be continually rising as it passes through the pipes, each gallon will carry off 39.36 heat units. The pipe used for brine cooling ranges from i-inch bore to 2 inches. The external diameter of a i-inch pipe is 1.3 inches, while that of a 2-inch pipe is 2.4 inches (about). The mean surface of pipe exposed to the heat will be, in the case of the i-inch, 43.3 square inches per running foot of pipe, and that of the 2-inch pipe 83 square inches per running foot. l8 COLD STORAGE ON BOARD SHIP. If we take Peclet again as a guide, we can calculate approxi- mately the number of heat units that will pass through from the air into the brine in any given time. He gives 230 as the number of heat units per square foot of surface that will pass through one inch thickness of iron, in one hour, with a difference of temperature of one degree F. The thickness of i-inch bore iron pipe is approximately 1/8 inch, and of 2-inch pipe 1/7 inch, hence the rate of passage of heat through the walls of the pipe should be respectively 1,840 and 1,610 units per hour per square foot for every degree of rise in temperature of the brine, or again 928 units per running foot with 2-inch pipe, and 550 with l-inch pipe. In practice the grid is made longer than would be apparently necessary, and more surface is exposed to the action of the heat, in order that the brine may flow at a lower veloc- ity, and also because the results obtained in service do not usually come up to laboratory tests. There is an important point in connection with this. Power, it will have been observed, is required for abstracting the heat and carrying it away. Where brine cooling is employed, power is required to keep the brine in circulation, and this power is in direct proportion to the extent of the wetted surface of the pipe, and to the square of the velocity at which the brine is flowing. Hence it will be seen that it would not be difficult to add appre- ciably to the power required by the plant as a whole by giving the brine a high velocity. Practice as usual has solved the question for itself, by the usual methods, and the following figures may be taken as the latest: A cubical space such as that taken, 12 feet on the side, if well insulated, requires, to be held at 32 degrees F., the temperature for "chilled" beef and some other substances, a length of about 432 feet of i-inch pipe, and about half that length of 2-inch pipe, with roughly proportionate lengths of intermediate sizes. Small rooms require more pipe in propor- tion than large rooms. Thus with rooms under i.ooo cubic feet capacity 400 feet of i-inch pipe and half that length of 2-inch METHODS OF COOLING THE COLD CHAMBERS. 19 pipe is given ; while for cold chambers of over lo.ooo cubic feet ux o < OS o a o u O H tn Sx CO > < o o < o capacity 200 feet of i-inch pipe and half that length of 2-incl: is given, in each case per 1,000 cubic feet. 20 COLD STORA&E ON BOARD SHIP. For lower temperatures, again, longer lengths of oipe are required, and approximately in the following proportions : for a temperature of lo degrees F., double the lengths of pipe are required that are given for 2^ degrees F., and for zero F. tem- perature about three times that given for lo degrees. The velocity of the brine is usually kept at or below 3 feet per second. A high velocity has another serious drawback, unless large pipes are employed — all fluids flowing through pipes create friction, which generates heat, and consequently by raising the tempera- ture of the brine lowers its ability to carry off heat from the room it Is" to cool. Brine coils are made in various lengths, according to the work they are to perform and the sizes of the pipes, from 100 feet with small pipes, for low temperatures, up to 1,000 feet with 2-inch pipes, and higher temperatures. DIRECT EXPANSION. By direct expansion Is meant the direct action of the refrig- erating agent, usually carbonic acid gas, on board ship, except where compressed air is employed in the chamber to be cooled. As will be explained, the refrigerant is caused to assume alter- nately the liquid and the gaseous state. A compressor and other apparatus are employed to reduce it to the liquid state, in which condition it is conveyed to the expansion coils, consisting of pipes very similar to those that have been described for the brine. The anhydrous liquid, on passing into the expansion coils, being suddenly released from the pressure under which it is held, is reformed into gas ; but as a liquid can become a gas only by the addition of the latent heat of the gas. it abstracts this heat from surrounding objects, such as the brine with which the expansion coils are in contact, in the brine tank, or from the air of the charhbcr in which tlic coils are placed, where direct expan- sion is employed. The action, so far as the cooling of the DIRECT EXPANSION. 21 chamber and the produce is concerned, is exactly the same as with brine cooling. •J0I0I13J«A\, „1 •jajuj 8u l^nnQWUQ :T;g There is a difference of temperature between the pipe contain- ing the refrigerant and the air surrounding the pipe, because the 22 COLD STORAGE ON BOARD SHIP. refrigerant has been lowered in temperature, immediately on its entrance into the expansion coils, by the evaporation of a small portion of itself. Heat passes from the air of the chamber to the surface of the pipe, and thence through the pipe to the refrig- erant, this heat enabling more of the liquid to evaporate, abstract- ing more of the heat from the air, and so on. Heat passes from the produce to the air surrounding it. so long as any difference cf temperature exists between them, and hence the produce and the air of the chamber are kept at the temperature required, by the aid of the direct evaporation of the refrigerant, just as by the circulation of the brine. The refrigerant is maintained in continual circulation, just as the brine is; for the compressor, which performs also the duty of a pump, causes it to be con- tinually passing from the condenser to the evaporator coils, thence to the compressor, arid to the condenser again, as will be described. The passage of the refrigerant into the evaporator coils is con- trolled by an expansion valve, which is practically a stop valve of particular construction. By its aid more or less of the liquid refrigerant is allowed to pass into the expansion coils. The length of the latter can be found by calculation and has also been determined by practice, though the calculation is somewhat dif- ferent from that for the length of brine coils. Each pound of each kind of refrigerant absorbs a certain number of heat units, in passing from the liquid to the gaseous condition, the number of units absorbed varying with the temperature and the pressure. Carbonic acid absorbs about no heat units per pound at the usual evaporator pressure, in temperate climates, while at higher pressures a smaller quantity is absorbed, 86 units at 650 pounds pressure, and 66 units at 800 pounds pressure. The temperatures corresponding to these pressures arc 32, 50 and 68 degrees F. At lower temperatures the pressures are lower, 380 pounds at 14 degrees F., and 288 pounds at — 4 degrees F, At .32 degrees F., and the pressure given above, one pound of DIRECT EXPANSION. 23 carlbcmic acid measures 0.167 cubic feet, or a cubic foot weigns < o •J to < w < o o S iz; o H < CU w < i-i to w o OS Ui fa o < o < approximately 6 pounds. It will be understood that volmms ^4 COLD STORAGE OX BOARD SHIP. of gaseous substances tliat are pumped to and fro have to be dealt with, rather than zccights. One cubic foot of carbonic acid will, therefore, absorb about 660 heat units in passing from the liquid to the gaseous condition at 32 degrees F. The gaseous carbonic acid formed from the liquid also carries off a certain quantity of heat, just as the brine does, but it is bad engineering to allow much of this to be done. The specific heat of carbonic acid gas is 0.2167, so that while one cubic foot of the liquid, in expanding to a gas, abstracts 660 heat units, the same quantit}' of the gas, in passing through the remaining pipes of the expan- sion coils, will absorb only 1.3 units, for every degree of difference in temperature between it and the atmosphere of the room. With direct expansion the lengths of the pipes will be much less than with brine. Ammonia and sulphurous acid are employed as refrigerants, but there is the great objection to direct expan- sion with ammonia, that the escape of a small quantity of the gas, in the cold chamber, may seriously affect the produce. Sul- phurous acid does not labor under that objection, for the sub- stance itself is used as a disinfectant, but it has not so far been much employed on board ship. The calculation for the quantity of the other refrigerants, and the size and length of the pipes, is practically the same, using different constants, as with carbonic acid. Ammonia absorbs 555.5 units per pound at o degrees F., while sulphurous acid absorbs 171.2 per pound. It will be under- stood that the gas which is formed is pumped through the grid of pipes, and thence to the compressor, to be reconverted into liquid, so that the friction of the gas in the pipes has to be taken into account, in the same way as the friction of the brine, and it follows the same laws, depending upon the surface of the pipe rubbed over by the gas, and upon the velocity at which the gas travels. A low velocity is of some value here. COOLIxr, THE CHAMBER BY COOLING THE AIR. "^5 BRUNSWICK ONS-TON COMPRESSOR. COOLING THE CHAMBER BY COOLING THE AIR. This is the more frequent method adopted where fruit is car- ried, and it is the method that is coming more and more into vogue on shore, wherever it can be arranged. It enables the engineer to have a greater command over his work. But before describing the arrangements for this, another important matter, the ventilation of cold chambers, a matter leading directly to the 26 COi,D SXUIC^GE OX BOARD SHIP. process uf cooling the air entering the chamber, should be con- sidered. The proper ventilation of cold chambers is a very troublesome problem, and it is tne troubles encountered in con- nection with this which, the writer believes, have led very largely to development in the direction of cooling the air itself. In all cold chambers in which produce is stored a certain quan- tity of carbonic acid gas is formed, and other gases are also given ofif, which are more or less deleterious to the produce, and should therefore be kept at as low a percentage as possible. But the air which is laden with these gases can be got rid of only by allowing other air to enter and take its place, while the cleansing action that is advisable — the action of air in the process of ventilation is very similar to that of water in the ordinary processes of cleansing — demands that the fresh air shall be al- lowed to penetrate to every part of the chamber, and to reach every surface of the produce. But if outside air is admitted, it is usually at a higher temperature than that inside the cham- ber — there are exceptions which will be noted — and the incoming air brings heat with it. This may not be a serious matter, where it is known and provided for. Every time the door of the cham- ber is opened, to put in or take out produce, or for the entrance or exit of the attendant, the same thing happens, to an extent depending upon the construction of the doors and the care of the attendant. In many cases no other provision is made for ventilation, but the best practice provides for its being carried out in a thor- oughly scientific manner, and in such a manner as to assist the convection currents that are of so much use in distributing the cooling influence of the brine or expansion grid. Wherever the grid is placed, it will be understood, the air in its immediate neighborhood will feel the effect first, and this, becoming heavier as it cools, will tend to fall, allowing the lighter air to take its place. In some cases the convection currents so set up are hardly sufficient to distribute the cooling effect of the pipes to the COOLING THE CHAMBER BY COOLING THE AIR. 2^ produce efficiently, and this leads to a larger expenditure of coal and accessories. Where the grid is placed on the side of the chamber, for instance, the convection currents are sometimes very sluggish. The ventilation and the convection currents are assisted by fans, placed in any convenient position, driven by any convenient source of power, usually electric motors. The fans are arranged either to suck the air out of the chamber, an inlet being provided in another part, at a distance from the outlet, or to force the air into the chamber, an outlet being provided at the other end. The outlet should be a little above the floor line, in the great majority of cases, as the car- bonic acid gas is heavier than air, while the inlet should be near the ceiling, at the opposite end. Fans should be arranged to assist the circulation of the air in the chamber, apart from the outside circulation. The actual arrangement will vary with each case, and the engineer in charge will have to be guided by the condition of the cold rooms. In some cases the fan may be kept running con- tinually to assist the convection currents within the chamber, there being no ingress of air to the chamber except at certain fixed times and for certain limited periods, and the entrance of the outside air being controlled by valves, opened from the out- side. In a few cases it is possible to allow a small current of air to pass through the chamber all the time, remembering that it brings heat with it, and that the heat so brought must be ab- stracted, and further that it will be in proportion to the differ- ence in temperature between the air from which the supply is taken and that of the chamber. The incoming air will bring moisture, which again must be abstracted, and this means the further abstraction of heat. The quantity of heat brought in by the incoming air is found by multiplying the quantity of air passing in by the difference in temperature between it and the air of the chamber, and by the specific heat of air. We may take the specific heat of air ;i8 COLD STORA(tE ON BOARD SHIP. as 0.2, it being neither at constant volume, nor at constant pres- sure. The weight of a cubic foot of dry air at 60 degrees is approximately 0.08 pound, so that there are 12.5 cubic feet of air in one pound, and one heat unit will, therefore, raise the temperature of 62.5 cubic feet of air one degree F. Conversely, air which is at a temperature of 60 degrees F., entering a cold chamber in which the temperature is say 10 degrees, will bring 50 heat units with every 62.5 cubic feet, or one heat unit with every 1.25 cubic feet, and wnth a chamber of 10,000 cubic feet capacity it would require the services of a machine capable of producing a ton of refrigeration in twenty-four hours, to deal with this in one hour, or a proportionately larger machine if it had to be dealt with in a shorter time ; and this does not take any account of the moisture brought in. The question whether this extra work shall be taken is one for consideration on the lines of the balance sheet. On one side should be put the dete- rioration of the produce, if any, that will take place if the store i*. not ventilated, and on the other the cost of the additional work mvolved in the removal of the additional heat. Another important point must not be last sight of — the effect of the increased temperature upon the produce — but again this is a matter for careful regulation. The figures required are: how much air comes in. how much heat it brings with it. and how quickly the heat must be removed. This enables the work required to be calculated. COOLING THE AIR ENTERING COLD CHAMBERS. There are really two parts to the problem involved in cooling a chamber by cooling the air whicli enters it. There is the removal of the heat of the air itself, in order to reduce it to the temperature at which the air in the chamber is to be held; and there is the removal of the moisture held in suspension in the air. Both objects are accomplished at one operation, and COOLING THE AIR ENTERING COLD CHAMBERS. 29 both Involve the abstraction of a certain number of heat units. Atmospheric air always holds moisture in suspension, the quan- =s^ -■ ^ kAUJ ■'-->.< J- -fy^^' w - ^ < OS o o < o h-t I-) ft. < o z o 1l\ o < < < < Hi o o tity held depending upon the temperature, and increasing very ra-^^aly as the temperature increases. But the moisture in sus- pension is ni the condition of vapor, and it can assume that 30 COLD STORAGE OX BOARD SHIP. condition only by absorbing a certain quantity of heat, from 900 to 1,000 units for every pound of water vaporized. The method of cooling wine by wrapping a wet towel around the bottle and putting it in the sun is well known ; while the case of a man's wet clothes drying on his back and giving him a cold, will per- haps be more familiar. In both cases the heat necessary for evaporation is taken largely from the object upon which the damp fabrics are placed. In order, therefore, that the vapor held by the air shall be deposited, the latent heat of evaporation must be abstracted from it. The mere fact of cooling a certain quantity of air leads to the air's seeking to get rid of a portion of its moisture, and its deposition will lead to a rise of its temperature, owing to the delivery of heat by the vapor. There is another factor in the problem of the deposit of the watery vapor from the air. The question arises, when will the vapor be deposited, and why? The capacity of air for absorbing the vapor of water varies, as shown in the accompanying curve. But the air is very rarely saturated with vapor, that is, it very rarely carries the full quantity of which it is capable, at any given temperature. In damp climates, in the winter months, it may carry as much as 85 or 90 percent of the quantity it would carry if saturated ; while in dry climates, from 50 to 65 percent only will be carried. Evaporation is constantly going on at all temperatures, from the surface of any liquid exposed to the air, and from any objects, such as dress fabrics, wood. etc.. in which liquids are held. So the air above and resting upon the surface of a liquid carries a certain quantity of vapor. This exerts a certain pres- sure upon the surface of the liquid, apart from that due to the weight of the air itself, while the vapor which is being given off from the surface of the liquid also exerts a certain pressure upon the vapor already in the atmosphere above. The pressure of the vapor coming away from the liquid depends upon the tem- perature of the liquid, while the pressure of the vapor in the air COOLING THE AIR ENTERING COLD CHAMBERS. 3X above depends upon the temperature of the air, and the percent- age of possible vapor carried. If the air and liquid are at the same temperature, and the air is saturated with vapor, no evap- oration can take place, as the pressure of the vapor already in the >m. BROWN-COCHRAN CARBONIC ANHYDRIDE COMPRESSOR. atmosphere, and of that issuing from the liquid, are equal. But where, as is nearly always the case, the air is not saturated, evap- oration will go on until the pressures of the two vapors are equal. The converse of the above is also true. Where there is a difference between the pressure of the vapor in the atmosphere and that of the vapor rising from some body with which it is in 32 COT.D STORAGE ON BOARD SHIK contact, in favor of the atmospheric vapor, the vapor will be deposited from the atmosphere, provided that it can deliver up its heat of vaporization to the surrounding objects. Bearing in mind the fact that the capacity of air for carrying vapor rises rapidly with the temperature, it follows that any lowering of the temperature of the air immediately tends to in- crease the percentage of saturation, and to increase the vapor pressure, and its tendency to deposit. The vapor pressure is obtained by first finding the percentage of saturation of the air, by the wet and dry bulb thermometer ; and then consulting a table that has been compiled from observation. From another table, also compiled from observation, the vapor pressure at sat- uration at different temperatures is obtained, the actual pressure of the vapor in the air, at the temperature to which it is reduced, being determined from these two tables, and the thermometer readings. The vapor pressure of the ice or snow on the brine or expansion grids used in cooling the air, as explained below, is also known, from its temperature — vapor is coming away from even ice and snow, if its vapor pressure exceeds that of the air in contact with it — and it will follow that when the vapor pres- sure of the air, at its reduced temperature, is greater than that of the vapor of the ice or snow, or the cooling brine, moisture will be deposited from the air upon the grid, or in the brine, the density of the brine solution being lowered in consequence. The quantity of water per cubic foot of dry air, when the air is saturated, varies from 0.000079 pound at o degrees F., up to 0.0368 pound at 212 degrees F., and at ordinary barometric pres- sure. With air that is to be cooled from 70 to 15 degrees F., and deprived of its moisture, it is necessary to first abstract the heat carried by the air itself, and then to abstract that carried as latent heat by the vapor. The two operations go on together, but the calculation is made separately. Thus the air has to be cooled 55 degrees, so that each pound of air must be deprived of II units, and each cubic foot of 0.88 unit, or 880 units per METHODS OF COOLING THE AIR. 3^ 1,000 cubic feet. Tf we take the vapor saturation of the air as 72 percent, we find that the air will contain 0.0009 pound per cubic foot,, or 0.9 pound per i.ooo cubic feet, and this will mean, approximately, that 900 heat units have to be abstracted, in order that the vapor may assume the liquid condition and be deposited. If it is formed into ice or snow, as usually happens, when the moisture is deposited on the grid, the latent heat of the liquid must also be abstracted, a further 128 units, or a total of 1,908 units per i.ooo cubic feet of the air to be cooled. The above figures are given to enable marine engineers to see how the calculations are made, and how important is the ques- tion of the vapor in the air. The latter is changing from hour to hour, especially when a ship is changing her latitude somewhat rapidly, and therefore any calculations that are made should be on the basis of the worst conditions to be met. If the air is not properly dried, some vapor will pass into the cold chamber, and will there be deposited upon the cold surfaces of the produce. Hence sufficient refrigerating power should be provided to extract the largest quantity of moisture that will be encountered. METHODS OF COOLING THE AIR. There are three methods employed, though only tw^o of them are applicable to the general run of ship work. The air may be caused to pass over the surface of brine that has been cooled to a low temperature ; it may be caused to pass over the surface of a grid in which either brine or the refrigerant is circulating; or again, may be cooled by compression and expansion. The first method is the most economical, and is largely em- ployed in cold stores on shore. The usual arrangement includes cooling the brine in a tank through wdiich the refrigerant is cir- culating. It is then carried to a point where it can conveniently be interposed in the path of the air. At this point a battery of galvanized corrugated iron plates is fixed, the plates being hung 34 COLD STORAGE ON BOARD SHIP. vertically. The brine is made to trickle down over the plates into a trough below, from which it is pumped back to the evap- orating brine tank. The air, which has done its work in the cold store, or which is brought fresh from the outer atmosphere, is forced between the plates of the battery by a fan. In passing between them it is cooled, and its moisture and other substances that are not wanted are deposited in the brine, the air then passing on to the cold chambers. With this arrangement, the brine is diluted by the water taken from the air, and has to be subjected after a time to a process of partial evaporation; it is boiled in a pan having a steam jacket until its density is restored to the proper figure. In the next plan a grid of pipes, somewhat similar to those that have been described for cooling the cold chambers them- selves, is placed in any convenient position where the air can be forced through it on its way to the chamber. The air with ship work is taken usually from the atmosphere, in the first instance, by means of a shaft leading from the fan chamber to a sufficient height above the upper deck to insure its being free from stoke- hold odors, grease, etc. In many cases, however, the same air is used over and over again, being passed around through the fan and over the grid, after it has passed out of the chamber. The fan chamber leads directly to the cooling grid, and is also connected to the exit ducts of the cold chamber, the engineer being able to arrange the air as he finds best, being guided in that by the condition of the produce. He also has it in his power to work directly from the atmosphere, without cooling the air at all, where the conditions warrant his doing so. the air being simply taken in from the atmosphere and expelled to the atmo- sphere again. The cooling grid is made in sections, each section being connected to a header, where valves are arranged, so that any section can be put into service or cut out at will, and the refrigerant, or the brine, circulates through the grid according to the requirements of the chamber. In hot climates the engineer METHODS OF COOLING THE AIR. 35 may have perhaps all the sections in service, while as the ship passes into colder latitudes he will take off one section after another, and possibly in cold weather depend entirely upon the atmosphere for parts of the day. As mentioned above, the moisture present in the atmosphere has a very important bearing upon the question, whether the air @=^ "V\'aste Water Discharge Liquified G£ DIAGRAM OF WEST EVAPORATIVE CONDENSER. shall be used over and over again, or whether fresh air shall be admitted. When it is used in a closed circuit the quantity of moisture present and the temperature of the air coming from the chamber are known, and therefore the quantity of cooling the latter requires ; but when fresh air is admitted from the outside, the engineer does not know, without testing, what its hygroscopic condition is, and how much cold will be required. 30 COLD STORAGE ON BOARD SHIP. Hence it is simpler to use the same air continuously. The mois- ture that is present in the air condenses on the outside of the pipes of the grid, and is then frozen, the frozen skin acting very much as the trickling brine does with the battery of plates. When the machine is stopped, the mass of ice and snow melts and is collected in a trough provided for it under the grid, and dis- posed of in the usual way. COOLING THE AIR BY COMPRESSION AND EXPANSION. This method was employed a good deal in the early days of cold storage, especially for ship work, and it has a great deal to recommend it, even now, for small work, such as the cold store for ship's provisions in a small ship. For large work it is not so economical, and the quantity of air required is so much larger, as is also the apparatus to deal with it. that it has grad- ually fallen into disuse, except for special cases. On the com- pressed air system, air is taken from the atmosphere in the first instance, drawn into a cylinder which performs the office of pump and compressor, and is there compressed by the action of a piston. In the act of compression heat is generated in the air. Now, it would be fatal to the utility of the air as a cooling agent if any moisture were present. Hence, after passing through the compressor, the hot air is passed through a cooling and drying apparatus, where the heat which has been generated by compres- sion is taken out, and any moisture it carried is deposited. There are several forms of cooling apparatus for air, the prin- ciple being the same as already described for cooling the air going into the cold chamber, but there is no brine grid available. One plan is to pass the air through a cylinder containing a num- ber of small glass balls, like marbles, over which a thin stream of water trickles. The air enters the cylinder at the bottom, and the water trickles down from the top. The air is gradua'.lv cooled as it passes upward.s, and as it cools deposits the moisture COOLING THE AIR BY COMPRESSION AND EXPANSION. 37 it carries, so that it issues at the top of the cylinder partially < < < w H in O tn < < > w (/3 P4 O I— I o :3 o o (14 o < O < cooled, and fairly dry. The principal cooling is performed in 38 COLD STORAGE ON BOARD SHIP. the next operation, in a second cylinder, whose piston rod is connected through its own crank to the same crank shaft as that of the compressor piston. This is called the expansion cyl- inder, and performs the same office as the expansion coils where a refrigerant is employed. The air which has been cooled and dried is allowed to pass into the expansion cylinder behind the piston, which it works, expanding in the process. The. cranks of the two pistons are set at right angles to each other, so that the work which the expanding air performs on the expansion piston assists the compressor piston. In expanding, the air is cooled, and as air or an}' other gas can expand only if it has the space, and can obtain the necessar}- quantity of heat to enable it to do so, it abstracts heat from surrounding bodies and becomes itself lowered in temperature. The compression stroke of the compressor coincides with the expansion stroke of the expansion cylinder, and at the suction stroke of the compressor, the piston, of the expansion cylinder forces the cooled air out to the cold chamber, or wherever it is to go. The cooled air is employed only to dilute the air of the cold chamber, so that the temperature of the latter is carried at what- ever figure may be desired. The calculation for the quantity of air to be cooled, and the temperature at which it shall be forced into the cold chamber, is simple. Each cubic foot of the cold air will absorb a certain number of heat units while its tempera- ture is being raised to that of the air in the cold chamber, the temperature of the latter being lowered in the process; but it must be remembered that as the entering air rises in temperature, it also increases in volume, and the cooling effect of a cubic foot of air, at each succeeding temperature, becomes less and less. In practice the average is taken, through the range of tem- perature. The air after expansion may be at as low a tempera- ture as —85 degrees F. Some makers of compressed air refrig- erating apparatus claim to reduce it to —100 degrees F. Takmg it at —85 degrees F.. and taking the mean between this and LEADING THE COOLED AIR INTO THE COLD CHAMBER. 39 the temperature at which the cold chamber is to be held, say 15 degrees F., or a difference of 50 degrees, every 100 cubic feet will absorb 80 heat units. LEADING THE COOLED AIR INTO THE COLD CHAMBER. There is one method of accomplishing this in all cases — by wooden ducts connecting the cooling chamber with the air cham- ENOCK Ij^-TON INCLOSED TYPE MOTOR-DRIVEN MACHINE. ber. These may be very large, where the air is cooled merely by the aid of a refrigerant — large enough for a man to walk in— and will contain ports opening into the cold chamber, fixed in positions where their opening will direct the current of air on 40 COLD STOIL\GE ON BOARD SHIP. to and over the surface of the produce to be cooled. The manipu- lation of the ports for regulating the air furnishes one reason for making the ducts large. Another and perhaps more important reason is the lessening of friction, and of power expended. Air, like brine and other fluids, rubs on the surface of the pipe or duct through which it is passing, and in rubbing sets up friction in proportion to the total rubbing surface, and to the square of the velocity at which it is traveling. Increasing the size of the ducts adds to the rubbing surface for a given length, but it also decreases the velocity of the air, and the gain by the latter is very much greater than the loss from the increased rubbing surface. Further, where produce is carried it is very important that dust and other objectionable matter shall not pass into the chamber, and this can be assured only by so arranging the ducts that they can be kept clean. The velocity at which the air passes over the surface of the produce has an important bearing upon preservation. Where the temperature does not matter, so long as it is below a certain figure, an air current at a high velocity will make no difference, but where the produce has to be maintained at a certain tempera- ture, it has a great effect. When cooling b}- air, a certain quan- tity of air per hour must be passed through the cold chamber at a certain temperature. If the ducts are small, the air must pass through them at a higher velocity than when they are large, and it will issue into the cold chamber at a comparatively high velocity, with the result that the produce in the immediate neigh- borhood of the inlet ports will be exposed to great — possibly injurious — cooling effects, while that at a distance will receive only a much smaller relative effect. It is the same thing as with the drafts from which we catch cold. A draft is merely a cur- rent of air passing over our bodies or portions of them at a higher velocity than is good for us. Every cubic inch of air that passes over us extracts a certain number of heat units from our bodies, and principally from the part over which it passes. If LEADING THE COOLED AIR INTO THE COLD CHAMBER. 41 these heat units are taken out rapidly the temperature of the body is lowered, particularly at the spot exposed to the draft, and congestion results. Similar results occur with produce. The air ducts for ship work are practically passages surround- ing the cold chambers, somewhat on the lines of the wing pas- sages which used to surround the old wooden ships below the CONDENSER GUAGE AEOULATOR ' eVAPORATOR COIL- CONDENSER COIU CONDENSER CASIf^G- rNSULATED DIVISION BETWEEN_^-gl CONDENSER 4 eVAPORATOR PATENT SAFETY VAkVt N HERE SEPARATOR PATENT HOltOW OIL GLANO 'BRINE CIRCULATINQ PUMP SECTION OF HALL CARBONIC-ACID COMBINED MACHINE. water line, along which a man could walk right around the ship, to stop shot holes, leaks, etc. They should form complete cir- cuits for the passage of the air from the cooling grid and back to it again, with doors arranged to connect them to the cooling chamber and the atmosphere. With compressed air cooling, even where it is on a comparatively large scale, there is not much room for ducts, both because warming of the cooled air would 42 COLD STORAGE ON BOARD SHIP. taKe place largely in the ducts, and because of the friction men- tioned above. The air cooled by compression and expansion is led to the cold chamber by the shortest possible route, the air duct being thoroughly well insulated. The use of the large air ducts described has the disadvantage that they absorb a good deal of room that could otherwise be filled with cargo, but the arrangement is much the best for certain classes of produce, such as fruit. Where the cooled air system is employed with two or more substances, having odors of their own, the ducts leading to the different chambers must not be allowed to connect in any way. The inlets of one must not be near the outlets of the other, and separate cooling apparatus and separate fans must be used, if the air returns from the chambers to the cooling plant. The case may be met by the adoption of what electricians would call the parallel system. One supply of air could be employed, and One cooling plant, and one fan, the air for the different cham- bers being directed into separate ducts and then discharged into the atmosphere from the chambers ; but care must be taken, if this plan is adopted, that the air which passes out of the cham- bers does not get to the shaft from which the inlet air is taken. THE DOORS OF COLD CHAMBERS. The doors of cold chambers are very important. They must be constructed on the same lines as the chambers themselves. When a door is closed it must form part of the wall of the cham- ber into which it fits, in the sense that it excludes the heat, just as much as the chamber wall proper does. In ship work the difficulty is, as with so many other things, to find room for proper doors. The thickness of the doors should be the same as that of the walls; and as far as practicable, they should be built in the same way. of two lots of matched boarding, facing each Other, lined with waterproof paper on their inside faces, and THE DOORS OF COLD CHAMBER. 43 the space filled Avith an insulating material. The door itself also must be made to fit air tight into the doorway. There must be Cold Water Inlet- Turbi ine to Operate Agitator, ]. <\ Warm WsTW Overflow Liquified Gas OuUet yrSiST CONDENSER OF THE SUBMERGED TYPB. no cracks, such as we are accustomed to in the doors of our living rooms, and no spaces between the door and the wall, when 44 COLD STORAGE ON BOARD SHIP. the door is closed. Further, the door must be pressed home firmly when closed, and the fastening be such that it cannot easily work loose, even in a heavy seaw^ay. When the cold chamber is in use the door should be opened as infrequently as possible, and then closed immediately; for every time a door is opened, as already explained, heat is admitted to the chamber, which means more work for the machines. On shore, wherever it can be arranged, double doors are fixed, the outer being closed before the inner is opened, so that only the small lobby full of air from outside is admitted. HOW THE LOW TEMPERATURE OF THE BRINE OR REFRIGERANT IS PRO- DUCED. The operation of one method, that of alternately compressin:^ air and allowing it to expand, has been described. The other method, of which there are two variations, has been partly indi- cated. A refrigerant, ammonia, carbonic acid or sulphurous acid, these solutions lending themselves peculiarly to this work, is caused to assume alternately the liquid state, and the gaseous state. In expanding from a liquid to a gas. it abstracts heat from the brine, the air of the chamber, etc., as has been shown. To accomplish this, and to work economically, a circuit is formed, consisting of the compressor or its equivalent, as will be de- scribed, the condenser, the expansion coils, and the connecting pipes. The compressor is practically a pump. After the refrig- erant has done its work, and become a gas, it is sucked back into the compression cylinder, compressed, and then forced into the condenser, passing thence to the expansion coils and back to the compressor. The latter consists of one or more cylinders in which pistons work, very much on the lines of steam cylinders, but with cer- tain modifications. There are one or more suction valves to each compressor, and one or more delivery \jalves. The cylinders may HOW THE LOW temperature; is produced. 45 be dcher single or double acting. If single acting, gas is taken in on one stroke and compressed on the return stroke, some* (/) OS o (/i ui W cs o o Q < u z o w a o o H o < u o I— I « 2 Z5 o IS < < thing on the lines of the old Cornish single acting engine, but with, the operation reversed. When double acting, gas is taken in at each stroke, and compressed ."t each stroke, the rear of the 46 COLD STORAGE ON BOARD SHIP. piston performing the office of suction, while the front com- presses. The valves are all of one type, shaped like the frustum of a cone, seated in extensions of the cylinder covers and kept on their seats by spiral springs, which allow them to open in- wards or outwards, as the pressure is reduced or increased luf- ficiently to allow the spring to operate in the case of the suction valve, and to overcome the spring in the case of the delivery valve. The piston also is slightly different from the ordinary steam or compressed air piston. ^Marine engineers are well acquainted with the evils of clear- ance in engine cylinders. With compressors used for refriger- ating apparatus the trouble is very much increased, because the small quantity of the gas remaining in the cylinder, in the clear- ance space, is in a highly compressed form, and immediately it is released by the return of the piston, expands, occupying the space left vacant, and introducing a pressure against the ingress of the next lot of gas. thus reducing the quantity taken in on the suction stroke. To obviate this, nearly all compressors are made with the ends of the cylinders dome shaped, and the ends of the pistons hemispherical, or as nearly so as they can be made, so that they run very close up to the cylinder end. One firm in the United Kingdom uses a flat cylinder end. a flat piston, and provides a spring which is compressed as the piston moves up to the cylinder end. the spring taking the thrust, keeping the piston away from the end of the cylinder, and helping to start it back on the return stroke. The De La Vergne Company of New York employs another method. A small quantity of oil is injected into the cylinder, shortly before the end of the stroke, and the oil and gas are ejected together, the refrigerant being freed from the oil by a separator before being used again. The delivery valves open automatically when the pressure inside the cylinder on the com- pression side of the piston is sufficient to overcome the tension of the spiral spring, and close immediately when the pressure HOW THE LOW TEMPERATURE IS PRODUCED. 47 is reduced sufficiently for the spring to overcome it; the aiKtion valve doing the same, in the reverse direction. SUBMERGED CONDENSER. a AMMONIA INLET. C WATER INLET. b. AMMONIA OUTLET. d. WATER OUTLET. Compressors for refrigerating machines are often made com- pound. The compression is completed in two cylinders, there 48 COLD STORAGE ON BOARD SHIP. being sometimes an intercooler between the two. The gas is compressed to a certain pressure in one cylinder, and the conv ■ plete pressure obtained in the second. It is the reverse operation to that of a compound engine. In the act of compression the gas is made to take up a smaller volume, and becomes heated, just as air does in compression. It is necessary to compress the gas in order to enable it to be liquefied with a reasonable quan- tity of cooling water. The molecules of the gas are brought closer together, and are then more ready to take on the liquid form. But in order that the gas may become a liquid, the heat of compression, as well as the latent heat of the gas, must be removed. Further, as it be(.omes heated it tends to expand, and to occupy a greater space than it would otherwise do, and than it will do when the heat is removed. It is for this reason that the intercooler, where compound compression rules, is so valuable. By removing the heat of compression of the first cylinder, the volume entering the second cylinder is smaller for the work that is to be accomplished. Besides, the heat generated would other- wise act upon the cylinder itself, and if allowed to become too great, upon the valves. When the compression cylinder is hot the gas entering at the suction stroke is heated and expands, and the weight that is taken in at each stroke is lessened, so that the efficiency of the apparatus is thereby reduced, for more work has to be done by the compressor for the same refrigerating effect. There are several methods of dealing with this matter. One has already been referred to, that of the De La Vergne Company. The oil which is injected into the cylinder to fill the clearance space also cools the cylinder itself, by absorbing some of the heat. Another method is what is termed the "wet compression." A small quan- tity of liquid refrigerant is allowed to pass into the compressor, with the gas. On its entrance into the cylinder, it expands to the gaseous state, absorbing some of the heat of the cylinder walls, etc. One objection to this is that it is difficult to arrange it THE CONDENSER. 49 properly, and its effective operation must depend upon the attendant. The coohng is effected in the expansion coils by the passage of sufficient liquid refrigerant into them, to absorb the heat that is to be taken away. Any additional quantity of liquid refriger- ant that is allowed to pass through lowers the efficiency of the machine, as it has to be handled without giving back any useful result. On the other hand, cooling the cylinder by the aid of the refrigerant adds to the efficiency. It is again a case of the balance sheet. Another method is the well-known one employed with gas engines, of circulating cooling water in a cylinder jacket. Double acting compressors heat more than single acting, as will be easily understood, and for that reason many engineers prefer single acting apparatus. THE CONDENSER. The condenser for refrigerating apparatus is designed to per- form the same office for the refrigerant that the steam condenser does for the steam — to convert it to the liquid form. Its con- struction is very similar. There are two forms of condenser used in refrigerating work, the submerged, and the open. In both forms the hot gas passes through pipes, over which cooling water runs. In the submerged form, the pipes are usually in coils, in a circular tank, and the cooling water is kept contin- ually in circulation over its surface. It is practically a surface condenser. In the open type, the pipes are usually made in grids, the cooling water being allowed to trickle down over them. The cooling effect is largely due. with the open type, to evapo- ration. In fact they are generally known as evaporative con- densers, and are preferred on shore, wherever they can be em- ployed, on account of their higher efficiency and the smaller quantity of cooling water required. A small portion of the water which trickles down over the pipes is evaporated, carrying off so COLD STORAGE OX BOARD SHIP. with it, approximately, lo.ooo heat units for every gallon evapo- rated, where a gallon of water passing over the pipes in liquid form carries off only from lOO to 200 units. Condensers used for refrigerating apparatus are slightly dif- ferent from those used for steam, mainly because it is so impor- tant that there shall be no leakage of the refrigerant. There are no joints in the pipes inside the submerged condenser. The coil is made in one long length, welded sometimes by electricity, sometimes by special lap welds, but never jointed. If joints are necessary, and where they are necessary, the pipe is brought out of the tank, and the joint made there. Whh open type con- densers the pipes are all fitted into headers at each end. In either case, any kind of water may be used, provided that no crust is allowed to form on the outside of the pipe by the salts contained in the water. Sea water may be used, provided that this point is attended to. If a deposit is formed, a certain resistance is set up between the refrigerant inside and the cooling water outside, apart from and in addition to that of the pipe itself, with the result that the cooling water has not its proper effect, and more has to be used. All refrigerating condensers are worked on the counter cur- rent principle, the cooling water and the hot gas circulating in opposite directions. The water usually passes from below up- wards, while the hot gas enters above and passes downwards. The hottest gas meets the hottest water, and is partially cooled, meeting colder and colder water as it passes downwards, and is itself becoming colder and colder, till at the bottom it meets the fresh and coldest water. The liquid refrigerant which is formed runs out at the bottom to a receiver, where one is used, and usually through an oil separator, to the evaporator coils. Obviously the submerged condenser is the one adapted for ship work, but there are cases where the open condenser would do good work. It must be remembered that a current of air is of great service, especially when the air is warm and dry, as it THE CONDENSER. 51 very materially assists evaporation, and cooling with it. In the Savoy Hotel in London the cooling water for the refrigeration condenser is itself cooled by means of the equivalent of a cooling ^oavHosiQ aaivM 14 < o H <: OS u o l-l ei Hi W ei oi < (A w Q a w ►J < O S «; OS o <: NOIlOnS tiilVM tower, fixed in the shaft which carries off the vitiated air from the chimneys, stoke hold. etc. Galvanized iron wire mats are hung in the shaft, and a fan at the bottom directs the air through $2 COLD STORAGE ON BOARD SHIP. them, while the water to be cooled trickles down over them. Something similar to this might be arranged on board ship for the refrigerating condenser, the coils in which the hot gas passes taking the place of the wire mats, and some of the hot air from the ship, if not too much saturated with m^oisture, being driven over it. As already explained, there are three substances employed as refrigerants, ammonia, carbonic acid and sulphurous acid. All are worked upon the same lines, but the sizes of the apparatus and the pressures at which they are worked vary considerably. In addition there is another process employed with ammonia, known as the absorption process, which, after varying fortunes, appears to be coming to the front again, even for ship work. It is described below. The different agents have different latent heats, and therefore different refrigerating capacities. The capac- ity of any refrigerant depends upon its latent heat, that is, its ability to absorb heat in passing from the liquid to the gaseous state. This quantity is usually stated in British thermal units per pound of the refrigerant, just as that of steam is. Perfectly anhydrous (water free) ammonia has a latent heat of 555-5 units per pound at zero F., the pressure being 30 pounds per square inch. Carbonic acid at the same temperature, but at a pressure of 310 pounds per square inch, has a latent heat of 123.2 units per pound; while sulphurous acid at the same tem- perature has a latent heat of 171. 2 units. The latent heat varies with the temperature and pressure. The refrigerants employed have all their critical temperatures, above which they will not assume the liquid state, no matter to what pressure they are subjected. Apart from that, the temperature of the refrigerant varies with the pressure, just as in the case of steam. But as the temperature and pressure increase the latent heat decreases. Thus, at a temperature of — 40 degrees F., and an absolute pres- sure of 10 pounds per square inch, the latent heat of ammonia is 579 units per pound, while at a pressure of 42 pounds per square THE CONDENSER. 53 inch, and a temperature of 15 degrees F.. its latent heat is only 546 units per pound. Similarly carbonic acid, at a temperature of — 22 degrees F.. and a pressure of 195 pounds per square inch, "automatic" 3-HORSEPOWER machine with EtECTRIC DRiva. has a latent heat of 136 units per pound, while at a pressure of 380 pounds per square inch, and a temperature of 14 degrees F., its •latent heat is only 115 units per pound. 54 COLD STORAGE ON BOARD SHIP. It will be observed that the latent heats are expressed in terms of pounds of the different substances, because all of these figures arising out of heat units are naturally referred to weight, since the heat unit goes by weight. But in refrigerating apparatus it is volumes that are dealt with. A certain volume of the gas which has done its work in the expansion coils is dealt with in the compressor at each stroke. Hence it is more important to know the latent heats of the different refrigerants per cubic foot, and then it will be seen that the apparent advantage of ammonia in the matter of latent heat is not maintained. One pound of ammonia measures 10.33 cubic feet at —4 degrees F., while one pound of carbonic acid, at the same temperature, meas- ures only 0.312 cubic foot, and sulphurous acid 8.06 cubic feet. Hence the latent heat of a cubic foot of ammonia at — 4 degrees is 56 units, while that of a cubic foot of carbonic acid is about 400 units at the same temperature, so that carbonic acid has the advantage. In practice there are other matters to take into consideration, which bring the efficiencies of the three agents to about the same value. Carbonic acid is supposed to be not so efficient in hot climates as ammonia, but very good work is being done with it in India and in ships trading to the tropics. In fact, it is the refrigerant most commonly employed for ship work. Its critical temperature is 88.43 degrees F. It was supposed for some time that it would not work where water of high temperature only was obtainable. This has however been fully disproved. It will be noticed that the pressures at which the different refrigerants are worked vary considerably. The working pres- sures are — for ammonia, in the neighborhood of 40 pounds per square inch in the evaporating coils, and 120 to 170 pounds in the condenser; with carbonic acid. 380 pounds per square inch i^i the evaporator, and 800 to Qoo. sometimes going very much higher, in the condenser; while with sulphurous acid the evap- orator pressures are in the neighborhood of 14 pounds, and the THE CONDENSER. 55 condenser pressures about 45 pounds. It will he seen from the above how the various claims set up by the makers of different apparatus, using the dififerent agents, are obtained. AIR COOLER. O. AIR INLET. d. AMMONIA OUTLET. b. AIR OUTLET. e. BRINE INLET. C. AMMONIA INLET. f. BRINE OUTLET. The high pressure necessary with carbonic acid is easily pro- vided for, by mechanical construction. In the United Kingdom Messrs. J, & E. Hall, of London, who have made a specialty oi 55 COLD STORAGE ON BOARD SHIP. carbonic acid machinery, construct the compressor cylinder out of a solid ingot of special steel. tl:e space for the piston, the valves, etc., being bored out with special tools at one setting. Meanwhile the high pressure and sm:'.ll quantity of refrigerant enables smaller compressors to be employed, a matter of con- aiderable advantage in ship work. The makers of sulphurous acid apparatus claim, on the other hand, that their low pressures enable them to work with weaker apparatus. In practice am- monia and sulphurous acid cylinders are of about the same size. The condenser pressure is really the delivery pressure of the compressor, while the evaporator pressure is the suction or back pressure of the compressor. The evaporator pressure corresponds to the back pressure of a steam engine, but In contradistinction to the steam engine, it is an advantage to have the back pressure comparatively high, because it means that the gas weighs more to the cubic foot, and therefore more is taken in at each suction stroke. The work of cooling is done mainly by the conversion of the liquid Into gas. Some heat Is carried off by the refrigerant, after It has become a gas, but this is a small quantitjs and though the cooling effect of each cubic foot of the refrigerant, when In the gaseous state, is reduced b}- the higher pressure and temperature, there is the gain by the greater density of the gas, as explained. As before, it Is a question of a balance sheet. There Is a critical value beyond which it Is not economical to increase the back pressure, because the loss of cooling is greater than the gain by increased density. LUBRICATION AND STUFFING BOXES OF COMPRESSORS. The lubrication of compressors is an important matter, just as is that of steam cylinders. For carbonic acid machines gly- cerine is employed, and for ammonia machines a special lubri- cant that will not saponify, In combination with the ammonia itself, as nearly all of the ordinary lubricants are said to do. LUBRICATION AND STUFFING BOXES OF COMPRESSORS. 57 With sulphurous acid, the substance itself forms a good lubri- cator when pure, but great care must be taken that water is not allowed to penetrate to the cylinder, as then sulphuric acid may be formed, with attendant troubles. Whatever lubricant is em- ployed other than the refrigerant itself a small quantity will mix with the refrigerant and has to be removed before the latter can be again used. For this reason all ammonia and carbonic acid apparatus is fitted with rectifiers, or oil separators, to remove the oil before the refrigerant passes to the condenser. The separator consists of an iron cylinder having a water jacket, so that its temperature Is maintained lower than that of the compressed gas it has to deal with. In the cylinder are fixed baffles of various forms, which arrest the particles of oil, and allow the purified gas to pass on. It is doubtful if the whole of the oil is removed by any of the separators, but a sufficient quantity is taken out to permit the apparatus to continue to run. The matter of the stuffing boxes is another very important one. There are two kinds of leakage to be guarded against, that of the refrigerant out of the cylinder, which is similar to a leakage of steam from a steam cylinder, with the addition that the loss has to be made up, and that of air and moisture from outside into the cylinder. Every cubic foot of air that enters the cyl- inder dilutes the refrigerant to that extent, thereby lowering the efficiency of the apparatus, since a part of the power will be taken up in compressing air instead of the refrigerant gas. and the air will also occupy some of the useful space in the condenser and the evaporator, and may lead to air troubles. With ammonia, also, the refrigerant has such a strong affinity for water that any leakage of moisture into the cylinder may cause a serious loss of efficiency. For these reasons the stuffing boxes of the piston rods of the compression cylinders are made especially long, and are packed with especial care. Usually the packing is in two sections, a dis- tance piece separating the two, and the packing itself soaked Jn ^8 COLD STORAGE ON BOARD SHIP, oil. In some forms of apparatus there is a small reservoir of oil attached to the stuffing box, and the oil is kept by various devices under the same pressure as the condenser. Messrs. J. & E. Hall have a small auxiliary cylinder, the piston of which is exposed, by means of a small connecting pipe, to the condenser pressure, the piston itself acting upon a body of glycerine held in the other part of the cylinder, while the cylinder communicates by another small passage with the stuffing box. ABSORPTION MACHINES. At the present time ammonia is the only refrigerant that is employed with the absorption process. The absorption apparatus takes the place of the compressor and its immediate accessories only. There is the same circuit, with modifications that will be mentioned, but the modifications are confined to parts of the absorption plant itself. There are the same condenser and evapo- rator, as with the compression system, and the same figures for lengths and sizes of pipes for the condenser and evaporator will rule. Also, brine is used with the absorption system, as with the compression system ; and, finally, though it is called an absorp- tion system and works by the alternate absorption and expulsion of ammonia it is really a compression system, the compression being produced by the continuous delivery of the ammonia from solution. It is also the same anhydrous ammonia that is em- ployed to charge the machine when starting up. The operation of the apparatus depends iipon the ability of water to dissolve ammonia, whether in the gaseous or the liquid condition. This capacity for dissolving or absorbing ammonia varies with the temperature of the water, decreasing as the tem- perature rises and vice versa. Further, it will be remembered that, when a gas is dissolved in a liquid, it assumes the liquid form, giving up its gaseous latent heat to the liquid. In the modern absorption apparatus there are two principal vessels, called the generator and the absorber. The erenerator ABSORPTION MACHINES. 59 contains an aqueous solution of ammonia, which is kept as strong as possible, and to which heat is applied, usually by the aid of steam circulating m pipes. The absorber receives the gas which has done its work in the evaporator. The generator corresponds to the delivery side of the compressor, and the absorber to the 60 COLD STORAGE OX BOARD SHIP. suction side. The heat applied to the generator, by raising the temperature of the water, obliges it to expel some of the am- monia it holds in solution, the gas passing from it to the con- denser, after it has been subject to certain other processes. The continual expulsion of the ammonia gas from the generator raises the pressure behind the gas that is entering the condenser, just as the continuous generation of steam in a boiler raises the pres- sure in the steam chest and the pipes leading from it. Suf- ficient compression is produced for the gas to be liquefied in the condenser, as in the compression system. The liquid in the absorber is maintained at as low a satura- tion and as low a temperature as possible, in order that it may be able to absorb all of the gas that comes over from the evapo- rator. In dissolving, the gas liberates the latent heat it pos- sessed as a gas, raising the temperature of the solution. Now it will be evident that unless some arrangement is made for carry- ing the ammonia over to the generator as it is received, the latter will soon run down. In one form of apparatus that was on the market a short time since, the two vessels, which were in the form of cylinders, were made to perform the offices of generator and absorber alternately, the change being carried out by turn- ing valves arranged for the purpose, after a certain number of hours' work. This arrangement has now been abandoned, and the work goes on continuously, without any change of vessels. The absorber is cooled by water circulating in pipes in the cylinder. Further than this, some of the heat that is not wanted in the absorber is delivered to the generator in an apparatus called the exchanger, which is an accessory to every absorption apparatus. The continual expulsion of the gas by the generator has a secondary effect, in lowering the specific gravity of the liquid. Hence the liquid from which the gas has been driven off tends to fall to the bottom of the cylinder of which the gen. erator is composed. In the absorber the same process is going forward, but in the opposite direction, so pipes are arranged to ABSORPTION MACHINES. 6i carry off the weak liquid from the generator to the absorber, and to carry the stronger liquid from the absorber to the gen- erator. These two liquids pass through the exchanger in sepa- rate pipes, arranged so that the hot liquid from the generator, 62 COLD STORAGE OX BOARD SHIP. which is on its way to the absorber, shall deliver its heat, or as much of it as possible, to the liquid that is on its way from the absorber to the generator. The exchanger, in some forms, in- cludes also some pipes through which cooling water passes, so that the weak liquid may enter the absorber at as low a tempera- ture as possible. But the above does not complete the tale of the apparatus required. Marine engineers are familiar with the fact that when steam is generated, small globules of water pass over with the steam, and give more or less trouble after, if not disposed of. The same thing happens with the ammonia — some water passes over with the gas, in various forms, and must be got rid of, for the reasons already given. For this there are two pieces of appa- ratus, usually also in the form of cylinders, called the analyzer and the rectifier. The analyzer sometimes forms part of the generator. Both pieces of apparatus are designed to precipitate the water, however carried, and to return it to the generator. The analyzer consists of baffles of various forms, over which the gas is made to pass on its way from the generator, and which tend to catch any globules of water held mechanically by the gas, these running back into the water from which the gas was expelled. In some apparatus, the rich liquid coming from the absorber is made to run over different obstacles on its way into the generator, meeting the hot gas that is coming away, another exchange taking place, the liquid taking up the water from the gas, and having its temperature increased. The rectifier usually consists of another cylinder, in which the gas is cooled before passing to the condenser. The temperature of the gaseous mixture is lowered to a point below that at which the water held in suspension can exist as vapor, the water being then con- densed and running back to the generator. In the latest form of apparatus made in the United Kingdom, bv Messrs. Ransomc and Rapier.* the apparatus consists of '32 N'ictoria Street, London, W., England. CIRCULATING PUMPS. 63 several cylinders, mounted horizontally, partly side by side, and partly one above the other, the condenser forming one of them. One lot of cooling water answers for the whole apparatus, pass- ing through the different cylinders in succession. There is a small pump employed to carry the ammonia liquid from the absorber to the generator, and there will be a water pump re- quired, where city water under pressure is not employed. CIRCULATING PUMPS. Two kinds of circulating pumps are required for refrigerating apparatus, apart from the compressor, which is itself a pump — that for the condensing water, and that for the brine, where brine is employed. The sizes of the pumps and their arrangement hardly require any explanation to marine engineers. They will depend upon the quantities of water and brine to be circulated, and the sizes and lengths of the pipes through which they pass. The pumps can be driven by any convenient source of power. With small plants it is usual to mount them on the outside of the tank which forms the condenser, and to drive them from the compressor crank shaft. With larger plant, separate arrange- ments may be made. It must be remembered that the metal of the brine pump becomes very cold and that the moisture in the atmosphere condenses on it and freezes. The work done by the heat delivered to the generator in the absorption apparatus is the equivalent of the work done b\' the engine driving the compressor, and the economy of the system, as opposed to that of compression, turns upon this point — ^the relative economy of using the steam direct, and using it to drive a steam engine which in its turn drives a compressor. The heat delivered to the generator must be sufficient to con- vert the liquid ammonia into gas, as well as to raise the tem- perature of the solution, so that the gas may be expelled. A proportion of this heat is obtained from the heat dehvered by 04 COLD STORAGE ON BOARD SHIP. the gas to the water in the absorber, in the act of solution, and the further this can be carried, the more economical must the process be. HOW REFRIGERATING APPARATUS IS MEASURED. In a previous part of these articles, the terms one-ton machine and six-ton machine have been used. These terms express the manner in which refrigerating apparatus is measured. A one- ton machine is ofie that will produce what is called a ton of refrigeration in twenty-four hours. A ton of refrigeration is the equivalent of the cooling effect that the melting of a ton of ice would produce in the same time. Ice requires, as mentioned, the abstraction of 142 heat units for every pound of water that is frozen, from and at 32 degrees F. In melting, each pound of ice will absorb 142 heat units, and a ton of ice therefore will absorb, on American measurement, 284.000 units, and on British measurement, 318.080 units — America using the simpler short ton of 2.000 pounds, while the United Kingdom uses the old-fashioned 2.240 pounds. The above figures mean, respectively, 11,833 and 13.253 units per hour. It is important to remember this latter fact. It may happen that it is required to extract heat very rapidly. The most rapid rate for a one-ton machine is given by the above figures, the capacity of larger or smaller machines being in direct proportion. It is also important to note that a one-ton machine will not make one ton of ice in twenty-four hours. It is usually reckoned that the quantity of ice which will be made by a machine of any given size is one-half its rating. The reason is, there are losses between the refrigerating plant and the water that is being frozen, added to which work has to be done in abstracting heat from the water in reducing it to freezing point, and from the ice after it is actually frozen. The old rule holds here as everywhere — do not cut your plant too fine ; and another HOW REFRIGERATING APPARATUS IS MEASURED. 65 rule which is equally true — you can afford to work closer to the rated capacity of any plant, the greater care you give it. HASLAM NAVAL REFRIGERATING SET^ MOUNTED IN TANDEM. Practice allows a one-ton machine for a cold chamber ranging 66 COLD STORAGE ON BOARD SHIP. from a capacity of 800 cubic feet up to 3.000 cubic feet, a two-ton machine from 3,000 to 6,000 cubic feet, a four-ton machine from 10,000 to 20.000 cubic feet, and so on. THE POWER REQUIRED FOR REFRIGERATING APPARATUS. The power required varies from 0.3 horsepower per ton of refrigeration, up to 1.7 horsepower. Small plants require more power in proportion than large plants, and more power is re- quired, usually, in hot climates than in temperate. Small plants are allowed from one horsepower up to three horsepower for a one-ton machine, the proportion falling as the size is increased. The power required increases as the condenser pressure increases and that is one reason why more power is required in hot cli- mates. In addition, more power is required because more water has to be circulated, when its initial temperature is higher. COOLING WATER. A point that is of importance here is to note that if sea water is employed its specific heat is lower than that of pure water. It may easily have a specific heat as low as 0.95, which means that a little over 5 percent additional cooling water must be allowed. For cooling water having an initial temperature of 55 degrees F., and having its temperature raised to 80 degrees F.. the following quantities of pure water are required : for the ammonia condenser, 50 gallons an hour per ton of refrigeration, and with carbonic acid about 15 percent more, according to the Linde Company's experiments ; larger quantities are required, as explained, when the initial temperature is higher. Approxi- mately, ten gallons per ton additional will be required for every five degrees increase in initial temperature, unless the final tem- perature can also be increased, and again larger quantities for carbonic acid. fORMS OF APPARATUS FOR USE ON BOARD SHIP. ey WEST CARBONIC ANHYDRIDE COMPRESSOR AND CONDENSER. FORMS OF APPARATUS FOR USE ON BOARD SHIP. The apparatus that is most suitable for ship board use is the one that occupies the smallest space, provided other things are equal. Some forms of apparatus are made very compact, the casting upon which the compressor and engine are built inclos- ing the condenser for the refrigerator, while the condenser for 68 COLD STORAGE ON BOARD SHIP. the Steam engine which drives the compressor is carried over- head. The driving arrangements are also made very compact, the steam engine bed being extended at the back of the cyHnder, and the tail rod of the piston being used as the piston rod of the compressor. A useful form of apparatus that has been fitted into some ships has two steam cylinders, mounted on one bed plate, each driving its own carbonic acid compressor by the tail rod of its piston as explained above, and each having its own steam and its own carbonic acid condenser. OTHER APPLICATIONS OF REFRIGERATION ON BOARD SHIP. One useful application of cold temperature is to keep low the temperature of the carbonic acid that is stored. The refrigerants employed are always carried in strong iron or steel bottles, which are tested to a pressure several times that which they are likely to have to stand ; but it is well to keep the spare bottles cool. With increased temperature the gas endeavors to expand, and if it is not able to do so, the pressure increases inside the bottles. With iron and steel it is a very difficult matter to be sure that there are no flaws, hidden away in the body of the metal, which the increased pressure would find. Also, stoppers sometimes be- come faulty after a time. In any case, it is a very simple matter to provide for keeping the bottles cool. A cupboard is built, large enough to take the spare bottles that are carried. It is insulated in the usual way, and has a small grid of pipes carry- ing the refrigerant or brine, as convenient ; or it may be cooled by exposure to the current of air, or a branch of it, that is cooling the cold chamber. COOLING MAGAZINES AND OFFICERS' AND MEn'S QUARTERS. Trouble appears to have arisen in the British Navy over the matter of cooling the magazines. It was reported some time since COOLING MAGAZINES AND QUARTERS. 69 tn w H O O S! O 2; u < S o iz; H-f < o h-i OS b OS < a > Q s < 70 COLD STORAGE ON BOARD SHIP. that fans were put on to cool the magazines, but they produced trickling water on the walls, and so had to be abandoned. With refrigerating apparatus on board, the problem should be solved Avith ease. The air entering the magazine should be dried before its entrance, by one of the methods described. Probably a small grid and a small fan would do the work very well. But it must be remembered that for successful ventilation the air that is dis- placed must be disposed of. It is of no use trying to force fresh air into the magazine unless the air already in the magazine is carried away. There must be a complete ventilating circuit, just as there must be a complete electrical circuit, or no action can take place; but the atmosphere may form part of some ventilat- ing circuits, just as the ground forms part of some electrical circuits. The same remarks apply to cooling the officers' or men's quar- ters, or to cooling the 'tween decks, when live cattle are carried there. Putting a fan in somewhere and churning up the air will not ventilate. It may create drafts, but it will only move the air, not change it. A current of air brought down from the deck, and directed through the space to be cooled, will cool to the extent that its temperature and the quantity available allow, as explained in connection with the cooling of air for cold cham- bers. But where the atmospheric air is at a high temperature, especially if it is heavily charged with vapor, it has very little cooling effect. The figures given above will show this. If the air is cooled a few degrees, and dried, it will then produce a pleasant, cooling effect on both man and beast, because, with men at any rate, nature's cooling apparatus, the evaporation of perspi- ration from the skin, can come into play. This evaporation can take pl?ce in a dry atmosphere, even if it is not a cool one. FAULTS. 71 FAULTS. The term faults, which is a very good one, is borrowed from the practice of electrical engineers, who refer to a fault in a cable, when the insulation has been damaged, and possibly the current refuses to pass the damaged spot in sufficient quantity to work the apparatus beyond ; or to a fault in the armature of a dynamo, when the insulation has been destroyed, and the armature refuses to furnish its proper pressure, and so on ; and the term is used in the same sense in these articles. Faults are causes of failure, things which happen, and which prevent appa- ratus from working properly. There is nothing in cold storage apparatus that the marine engineer who knows his work will not be able to master, if he puts his mind into it, and if he will remember the differences be- tween the freezing apparatus and the steaming apparatus. There is a great similarity between the two in many respects, and on the other hand, there are some very wide and important differ- ences that must be remembered, if the plant is to be kept going satisfactorily. A cold storage plant is very much in the nature of a steam plant reversed. The cold store itself, or the brine tank, or the air cooling apparatus, or whatever may receive "cold" from the expansion coils, stands ver}- much in the same relation to the whole plant as the boiler does to the steam plant. The refrigerating agent, carbonic acid or ammonia, enters the expansion coils — the ''refrigerator" as it is now more common to call it — as a liquid, and there becomes vapor or gas. The vapor or gas passes from the expansion coils to an apparatus, very similar in every respect to a steam engine, even to the fact that it is often divided into two. the process being compounded, but there is the important difference that instead of the refrig- erant driving the piston, the piston drives it, compressing the gas or vapor, preparatory to its being recondensed into the liquid form. Again the gas or vapor passes from the cylinder of the compressor to the condenser, where very much the same thing ']2 COLD STORAGE OX HOARD SHIP. happens as when steam is condensed to water. The gas passes through pipes, over which cooHng water is driven, the cooHng water extracting the latent heat from the gas, and reducing it again to a hquid. But again there is an important difference. With the cold storage condenser there is no air pump. Air must on no account be allowed to enter the refrigerating system. As will be explained later, its presence seriously lowers the efficiency of the apparatus, and one of the most important things the "freezer" engineer has to look out for, is that air shall not get into the system. The presence of air also reduces the work the plant will do, the ''heat it will hft." Again, one of the earliest things the steam engineer gets knocked into him by practical experience, and one of the things that the experienced engineer looks out for almost before any- thing, is leakage. It may be fairly said that no engineer in charge of a steam plant can run it economically who has not a "nose for a leak." The steam engineer learns to know that leakage of steam means waste. But with refrigerating apparatus, leakage of the refrigerating agent means very much more than it does in the case of a leakage of steam. A leakage of steam can be made up, providing it is not too great, by increased gen- eration of steam from the boiler. It is merely a nuisance, as it tends to increase the leakage path, and to make a mess in its neighborhood, but beyond that it merely means an increased quantity of coal, and possibly water consumed. But with a cold" storage plant, leakage of the refrigerant means, and very quickly, a largely reduced efficiency of the system ; and other troubles. The necessary number of heat units that are to be extracted from the brine, the air, or the room, and from the produce itself, are absorbed by the conversion of a definite quantity of the refrigerant, carbonic acid or ammonia, from the liquid to the gaseous condition, and this is possible only if a certain quan- tity of the liquid is present, and is allowed to pass through the expansion valve in each unit of time, or at each stroke of the FAULTS. compressor. If the system is short of refrigerant, as it will be if a leak is allowed to be set up, the requisite quantity of liquid is not available, and the refrigerant passes through the expan- sion valve, partly as a liquid and partly as a gas. The difference between the cooling properties of the refrigerant, as a gas and as a liquid, is enormous. Every pound of liquid ammonia that is converted into gas absorbs in the neighborhood of 500 heat units in the process, while every pound of carbonic acid absorbs in the neighborhood of 120 heat units, but the pound of ammonia gas or carbonic acid gas passing through the expansion coils in place of the liquid, will absorb less than one-half of one heat unit. Hence the importance of keeping the proper charge of the refrigerant present in the system is at once apparent. In addition to that, as marine engineers are aware, when ammonia or carbonic acid is able to leak out, air is able to pass in when the plant is standing. The quantity of air passing in in any given time may be small, but every engineer knows the enormous effect of the continued passage of a very small quan- tity of some troubling agent, and everyone who has had to do with pumps is aware of the trouble caused by the ingress of air. In the refrigerating system the entrance of air operates in two ways. The space occupied by the air is at the expense of a certain quantity of the refrigerant. In addition, air cannot be liquefied. It becomes heated under compression. It is apt to collect in parts of the system, again in a compressed and heated state, and generally to give trouble. One of the first rules therefore to be observed by the marine engineer who takes charge of a refrigerating apparatus is to keep a very careful eye upon all joints, stuffing boxes, glands, etc. Where the pipes carrying the gas enter the condenser, and where the liquid leaves it, the glands through which they pass must be maintained absolutely gas-tight. And perhaps a more important matter is the question of leakage of the refrigerant in the neighborhood of the piston rod. In the case of the steam 74 COLD STORAGE ON BOARD SHIP. engine a little steam passing np by the side of the piston rod does very little harm. Imt in the case of refrigerating apparatus, the passage of the refrigerating agent along the piston rod, and so to the atmosphere outside, has very serious results indeed, as will be explained later on. One of the difficulties in the way of finding leaks of carbonic acid or am.monia lies in the fact that they do not render them- selves visible, as steam leaks usually do. by condensing. Car- bonic acid gas may be leaking into the atmosphere in the neigh- 1 orhood of the compressor, or at other parts of the apparatus, for a very long time, and nobody will know it, except by its effect upon the working of the cold storage plant. Carbonic acid gas is a poison, in the sense that when it is present in certain definite quantities, animals are unable to breathe, but in the ordinary engine room, where there is a certain amount of ven- tilation, there may be a comparatively large leak of carbonic acid gas, carried off by the ventilating air current, without any dan- ger to anybody, and without any effect, even in extreme cases, beyond a headache. Ammonia gas is more easily detected by its pungent odor, but even ammonia gas may be escaping in small quantities, and be carried off, unnoticed. l)y the ventilating air current, and be creating a considerable shortage in the sys- tem, without anybody suspecting it. For carbonic acid gas the rule is. to cover joints and all places wlicre leakage may take place, with soap and water. If there is a leak, soap bubbles are formed. With ammonia the nose is usually a very good apparatus for testing, Init if a more certain one is required, a piece of sulphur held on the end of a stick and lighted, the burning sulphur being held in the neighborhood of joints where leaks are suspected, will show their presence immediately by creating dense white fumes. WATCH THE GAGES. 75 WATCH THE GAGES. In this matter the marine engineer will recognize the similarity with his work, in connection with steam plants. Just as he watches the steam gage and the water gage on his boiler, so his success in keeping his refrigerating plant in good order depends largely upon his watching the gages upon the different parts of the apparatus. The gages in connection with a refrigerating plant have also a greater importance, even, than in connection witli a steam plant. An intelligent interpretation of the gages will tell a good deal of what is going on in the refrigerating plant, and will enable the proverbial stitch in time to be put in. Steam engineers are familiar with the fact that each steam pressure corresponds to a certain temperature of the steam, and the same thing rules with the carbonic acid and ammonia employed in refrigerating plants. Each pressure corresponds to a certain temperature. It is usual to place gages marked in pressures and the cor- responding temperatures on two eccentric circles on what are termed the high-pressure and low-pressure sides of the plant. It will be remembered that the carbonic acid or ammonia comes into the compressor in the form of a gas, and is compressed and delivered to the condenser at a considerably higher pressure. The condenser is therefore the high-pressure side, and the gage is usually fixed at the entrance to the condenser. The liquid, it will be again remembered, passes through the expansion valve, or regulator, as it is often called, into the expansion coils or refrigerator, and is there reconverted into gas with a corre- sponding fall in pressure from that at the entrance to the con- denser. This side, therefore, is the low-pressure side. The low-pressure side may be taken to be that portion of the apparatus between the regulator and the suction valve of the compressor ; while the high-pressure side is between the delivery valve of the compressor and the condenser side of the regulator. 'J^ COLD STORAGE ON BOARD SHIP. It is usual to place another gage on the suction side of the c^:- pansion coils, marked also in pressures and the temperatures corresponding. It will be noted that the reverse of steam apparatus mentioned above is maintained here, the entrance to the condenser with steam is the low-pressure side, while it is the high-pressure side with refrigerating apparatus. The pipe through which tlie newly created vapor issues in the steam plant is the high-pres- sure, whereas it is the low-pressure in the refrigerating plant. In all refrigerating plants there are certain standard pressures that are maintained under ordinary conditions, at the entrance to the condenser, and at the exit from the expansion coils. The pressure at the exit from the expansion coils is not reduced to nothing, as might be at first supposed. In fact, a little considera- tion will shov<- that, other things being the same, the pressure on the suction side of the compressor is all the better for being higher. With high suction pressure there is less work for the compressor to perform than where the suction pressure is low. and therefore less coal, steam, etc., is consumed in compressing the carbonic acid or ammonia. The ordinary standard pressures are for carbonic acid 65 to 75 atmospheres, or 955 to 1,100 pounds per square inch at the entrance to the condenser, corresponding with 76° to 86° F., and 25 atmospheres, or 367.5 pounds per square inch at the exit from the evaporating coils, corresponding to 10° F. ; with ammonia, from 160 to 180 pounds condenser pressure, and about 15 pounds suction pressure, are the standard. The above pressures and temperatures are for cooling water at 60° initial temperature, or thereabouts, on entering the condenser. Where cooling water of a lower temperature is available, say at 40° or 50° F., the condenser pressure may l)e lower, and. on the other hand, where the only cooling water availal)le is at a higher temperature, the condenser pressure also must be higher. WATCH THE GAGES. 77 It was mentioned above that it is an advantage to keep the suction pressure high, within certain Hmits. It is also an ad- vantage to keep the condenser pressure as low as possible, also, of course, within certain limits. The reason will be immediately apparent. The work done in lifting the heat from the cold chamber and delivering it to the sea is performed partly in the compressor, and partly by the circulating pump : therefore it is obvious that the less work both the compressor and the circulat- ing pump have to do, the less coal must be burned, and the cheaper is the storage produced. With low condensing pressure it is evident that less work has to be done by the compressor piston upon the gas coming over from the evaporator coils, than with the higher pressure. Also, as already exp^.ained, the higher the pressure at which the gas comes over from the evapo- rator, the less work the compressor has to perform in compress- ing it to a certain figure. It will be understood that a certain condenser pressure is necessary in all cases, before the gas can be converted to the liquid state, and the lower the temperature of the gas, that is to say, the low'er the pressure at wdiich the cooling water will handle it, the less work has to be done upon it. Further, the colder the circulating water, the smaller the quantity that has to be passed through the condenser to extract a certain quantity of heat from the hot refrigerating gas, and, therefore, the less work has to be done by the pump. Condensa- tion, it will be remembered, means the extraction of a certain definite quantity of heat from the refrigerant. The rule in connection with the condenser pressure is, the pressure must be that which corresponds to a temperature lo degrees above that of the cooling water at its exit from the con- denser. The rule for the pressure at the suction side of the compressor, the exit from the refrigerator, is, the pressure should be that corresponding to a temperature lo degrees below that of the brine in the brine tank, where the expansion coils are made lo cool brine, and are not made to act directly upon the air of 78 COLD STORAGE OX P.O \RD SHIP. the cold cliamber. When the expansion coils act directly, either upon air that is being circulated through the cold chambers, or upon the air of the cold chambers themselves, the rule is, the pressure at the exit of the expansion coils should be that which is equivalent to a temperature 20 degrees below that of the air the coils are cooling. If the pressures named, with allowance for the variation in the temperature of cooling water, are shown on the condenser and on the evaporator, it is probable that everything is working properly. At any rate, it may be taken almost as an axiom', that when the proper condenser and evaporative pressure are show- ing, the compressor, condenser and evaporator are working satisfactorily, and if there is any fault, it is in the chamber itself, or in the brine circuit. It is for this reason that the writer so strongly urges the rule, "watch the gages." The "freezer" engi- neer will watch his gages, allowing for the increase in the con- denser pressure as he passes into a warmer climate, and again allowing for the decrease of pressure as he passes into a colder climate, and will know at a glance that everything is all right up to a certain point, or the reverse, just as he does by looking at the gages on his steam boiler, etc. There are certain signs which show whether things are work- ing satisfactorily, in addition to the gages. The gas in the com- pressor is heated in the act of compression, and therefore the pipe through which it makes its exit from the compressor to • the condenser is slightly warm with ammonia, and fairly hot with carbonic acid. On tlie other hand, the gas which is return- ing from the expansion coils to the compressor is expanding during the whole of its passage, and is extracting heat from everything in its neighborhood, and it therefore follows that the suction pipe leading to the compressor, and generally the whole of the compressor in the neighborhood of the suction valve, becomes covered with snow. The suction pipe and the suction vulve, being cooled by the expansion of the gas inside them, cool IF THE DELIVERY PIPE BECOMES HOT. 79 the atmosphere in their immediate neighborhood, this resuhing in the deposit of some of the moisture previously carried by the atmosphere, in the form of water, upon the pipe, valve, etc., the moisture being immediately frozen. The compressor itself should be cold. When the delivery pipe from the compressor is in the condition named, respectively, with carbonic acid or ammonia, and the suction pipe is covered with frost, things are usually going all right, so far as the refrigerating plant is con- cerned, apart from the insulation of the chamber. If the delivery pipe from the compressor becomes warmer than it should be, or if it becomes cold, and again if the frost disappears from the suction pipe and the neighborhood of the suction valve, or if the compressor becomes hot, these are signs that something is wrong. IF THE DELIVERY PIPE BECOMES HOT. If the deUvery pipe becomes hot, it is a sign that the liquid refrigerant is not passing through the regulator valve as rapidly as it ought to be, there being an increased pressure in front of tiic gas that is coming from the compressor, and therefore in- creased heat. If at the same time the frost either wholly or partially disappears from the suction valve of the compressor, it is usually a sign that the regulator valve is not open suffi- ciently wide. Sufficient liquid is not passing through the system to do the work required of it, and the remedy is to open the regulator valve a little wide.*-. The regulator valve is a very delicate part of the apparatus, and it will be understood that a very small turn, either to open or close, has a comparatively large effect upon the delivery of liquid to the expansion coils. On the other hand, the effect of either opening or closing the regulator valve, more or less, is not apparent for several minutes. If the delivery pipe remains hot after the regulating valve has been ooened wide, it is a sign that there is not sufficient 80 COLD STORAGE ON BOARD SHIP. refrigerant in the system. The cooling effect on the compreiisor, the suction valve, etc., and later on the delivery valve, is due to the continuous evaporation of the liquid, that is going on right from the regulator valve into the compressor. As will be seen later, it is most important that the compressor shall be maintained cool. If there is not the proper quantity of the refrigerant in the system, as explained above, it not only lowers the efficiency of the system, but it tends to upset the working of the system generally. A little consideration will show this very clearly. The condenser performs two offices. It is a reservoir of the liquid refrigerant, and a condenser of the gas into the liquid state. Its office as a reservoir is often assisted by a receiver, into which the liquid is passed after leaving the condenser; and, where a ship is much in the tropics, it is a wise plan to employ a receiver, and it is also wise to arrange to cool the liquid refrigerant after it leaves the condenser, which may be done by passing the circulating water over the pipe leading from the condenser to the receiver. The receiver and the condenser to- gether, however, hold the refrigerant in three conditions, the liquid, the gaseous, and the transition states, the latter being when it is being formed into the liquid from the gaseous state. The gas, it will be remembered, coming from the compressor, is hot. It passes in at the top of the condenser, where it meets the cooling water which has passed over the whole of the re- mainder of the coils of pipe forming the condenser, and from which it receives its first cooling. The operation of condensing may be taken to consist of two parts- — removing the heat of compression, and removing tlie latent heat of the gas. When the plant is working, at each stroke of the compressor a definite quantity of gas is sucked from the refrigerator coils, this being made up in the coils by a certain quantity of liquid, sufficient to expand into the quantity of gas removed by the compressor. If the compressor is double IF THE DELIVERY PIPE BECOMES HOT. 8l actmg, at each stroke a certain quantity of gas is delivered to the condenser, and it may be taken that, when the apparatus is working normally, during the period of each stroke a certain quantity of gas is liquefied and added to the reservoir of liquid, equal to that which has been abstracted by way of the regulator valve, to make up for that which was taken from the refriger- ator by the suction of the compressor. If the condenser and receiver together are short of liquid, the working of the system is upset, because the liquid is abstracted b}^ the suction of the compressor faster than it is replaced by the action of the condenser. The effect is not apparent imme- diately. In all these matters in connection with refrigerating plants, time is an important factor, but after a certain time the liquid in the condenser ceases to act as a barrier or absorber to the gas coming over from the compressor, and at each suction stroke of the compressor, a portion of the gas passes through the regulator valve, with a certain quantity of liquid. As was explained before, this leads to an immediate fall in the efficiency of the apparatus, and in the work done by the plant in cooling the cold store, or whatever the arrangement may be, because, while the liquid passing into the gaseous condition extracts a definite number of heat units for every pound of liquid evapo- rated, the gas which comes over has practically no refrigerating effect at all, and it lowers the refrigerating effect of the liquid which it accompanies. The fact that the system is short of liquid, and that the gas is coming over with the liquid to the expansion coils, may be known for certain by placing the ear in the neighborhood of the regulator valve. When liquid only passes the regulator valve, it makes a hissing sound, to which the engineer soon becomes accustomed, and which he readily recognizes. When gas conies with the liquid, the hissing sound is accompanied by a rattling which is also unmistakable. When the system is short of refrigerant it will easily be understood that, as a SZ COLD STORAGE ON BOARD SHIP. portion of the space in the evaporating coils is occupied by the gas which comes over from the condenser in place of liquid, so also the cooling effect upon the suction pipe and upon the compressor itself, which depends upon the evaporation of the liquid, is also lessened, with the result that the frost is lost from the suction side of the compressor. In addition the compressor itself often becomes very hot, this leading to other troubles, such as the destruction of the packing, leading again to leakage of the re- frigerant, to the vaporizing of the lubricant, and its being carried over with the gas, as vapor into the condenser, this giving troubles that will be explained later on. The remedy is to add liquid to the system in the same manner as when charging, adding carefully until the signs disappear. When a shortage arises, however, it will alwa3-s be wise to find out the cause. Leakage, as before explained, is one of the pos- sible causes. Another cause is the possibilit\- that oil has got into the system, as explained above ; a third that air has got in ; a fourth that the cooling water is not sufficient, that the con- denser is not doing its work properly; and a fifth, which is easil}' looked out for and provided for when the ship passes into warmer climates, that the hotter cooling water is not doing its Work as well as the colder water of a temperate climate. A little consideration will show when the cooling water from any cause is insufficient. If on passing into the tropics the water available is hotter, while the circulating pumps will not allow of a larger quantity being passed through the condenser in the proper proportion, less liquid refrigerant will be formed during the period of each stroke, and the reservoir of liciuid will be- come less, with the result that after a certain time the results of shortage mentioned above will be apparent. The remedy' is to add liquid refrigerant, as described above. Anything which interferes wilh the process of the condensa- tion of the gas will also interfere with the working v)f the sys- tem, and will produce the same results as a shortage of the II" THE DELIVERY PIPE BECOMES HOT. 83 reirigerant. They will lead, in fact, to a shortage in the system, oecause, just as explained with higher temperature cooling water, and with a limited quantity of cooling water, a smaller quantity of the gas will be converted into liquid in a given time, say within the duration of a stroke of the compressor. Among possible causes of interference with the process of condensation are, — higher temperature of cooling water, as already explained ; shortage of quantity of cooling water ; inefficient working of the cooling water circulating pump ; and an}' deposit which forms on the outside of the condenser pipes. Sea water, and most cooling waters, contain salts in solution, some of which are deposited upon the metal surfaces over which they run, such as the condenser pipes, especially when the pipes are hot, as they must necessarily be in a condenser ; and the deposit is increased whenever the velocity of the cooling water is decreased. The best conditions under all circumstances for taking the heat out of gas or out of steam by the aid of circulating water, in a surface condenser, are, that the water shall pass very rapidh' over the surfaces of the pipes, on the other side of which the gas or steam is passing, and that the thickness of the pipes shall be as small as is consistent with mechanical strength, and with the necessary ability to withstand the strains brought by expansion and contraction, under changes of temperature. A deposit is formed from the cooling water, as marine engineers know to their cost. They have it in another form in boilers in Avhich sea water is employed for raising steam. It has a high thermal resistance, as refrigeration engineers express it. The deposit of salts or scale opposes the passage through itself of the heat, and therefore lessens the quantity of heat taken by the cooling water in a given time from the gas or steam that is to be cooled. The result is that, with a given quantity of cooling water passing, say with a given capacity of circulating pump, a smaller quantity only of liquid refrigerant is produced, and the other signs of shortage in the system are ni 84 COLD STORAGE ON BOARD SHIP. evidence. On the other hand, anything which tends to increase the effective working of the condenser, such as the presence of a lower temperature of cooHng water, instantly tends to lower the condenser pressure, because a larger quantity of liquid refriger- ant is produced, a larger quantity will be passing through the regulator valve, unless it is closed a little more than previously, and there will be signs similar to those where there is too much refrigerant present in the system. It need hardly be mentioned that the lower the pressure in the condenser, the less the work the compressor has to perform, and the less the work the cool- ing water has to perform. Hence, the "freezer" engineer will watch the temperatures of the delivery pipe, the suction pipe, and the compressor itself. If he finds his condenser pressure going up, and especially if it is accompanied, as it usually will be, by increased heat of the de- livery pipe, it may be that the refrigerant is not passing through the regulator to the evaporator as quickly as it should; and, again, this may be caused by a greater demand upon the cooling water in the evaporator coils, owing to other causes in the cold chamber which will be dealt with further on. TOO MUCH REFRIGERANT IN THE SYSTEM. It is not often that this arises, though cases have been reported. There is a certain dctinite quantity of refrigerant that is suitable tor each size of plant, each size of compressor, condenser, and so on. The manufacturers in all cases give full particulars of the quantity that should be placed in the system. All manufac- turers recommend that a slight excess should be carried, rather than the reverse. With carbonic acid it appears not to be easy to carry a dangerous excess, but with ammonia the trouble does arise, though not frequently. In either case, an excess of the refrigerant, up to 25 percent of the quantity stated by tlie mpntifacturer, will do no harm, and will probably help to keep IF THE DELIVERY PIPE BECOMES COLD. 85 the plant running efficiently and continuously over a longer time, in the presence of leaks, than when only the exact quantity has been placed in the system. \\'here, however, a large excess of refrigerant is carried, it means that a large portion of the space available in the con- denser is occupied by liquid, a larger space than is necessary, with the result that the gas that is coming over is confined in a smaller space than is intended. A very excessive charge is shown by considerable fluctuation on the pointers of the gages. With regular working, the pointers of the gages go up at each stroke, and then return. With very excessive charge they fluctuate very irregularly. It may be taken that anything which throttles the delivery of the liquid, carbonic acid or ammonia, in its passage to the expansion coils, will increase the condenser pressure, and will raise the temperature at the delivery pipe. IF THE DELIVERY PIPE BECOMES COLD. If the delivery pipe from the compressor becomes cooler than it should be, it is a sign that the liquid refrigerant is passing through the regulator valve in larger quantities than it should do, and the pressure at the condenser will be lowered, the heat at the deliver}' pipe being lowered with it. The remedy is to slightly close the regulator valve, bearing in mind the remark made above as to closing or opening to a very small extent under these circumstances, and as to the efifect not being apparent for a few minutes. WHAT FOLLOWS FROM A HOT COMPRESSOR. It has been explained that the normal condition of the com- pressor when the apparatus is working properh^ requires the bodv of tlie compre^sor to be cold, the suction valve and pipe, and sometimes parts of the compressor in the neighborhood of 86 COLD STORAGE ON BOARD SHIP. the suction valve, being covered with frost. If the system be- comes short of Hqiiid, and if it is not working properly, that is to say, if a sufficient quantity of the liquid refrigerant does not pass into the evaporator coils, and the evaporation does not continue in a minor degree right down to the suction valve, the frost on the suction pipe is lost, and the compressor itself gradu- ally gets hot. As marine engineers will understand, the natural result of working a piston in a cylinder is the generation of heat, unless means are taken to prevent it. Further, those who have had to do with air compressing machinery know also that the natural result of compressing any gas is the liberation of heat in the gas itself, due to the compression ; the heat so liberated being com- municated to the compressor. With refrigerating apparatus, any heat in the compressor, as will be explained, is fatal to the effective working of the apparatus, and it is for this reason that a sufficient quantity of the liquid refrigerant is always allowed to pass through the evaporator coils to bring a certain cooling effect right back to the compressor itself, and to keep the com- pressor cool. The compressor, though very like a steam cyhnder, and still more like an air compressor C3'linder, differs from both in one very important particular already dealt with, viz., that on no account must the gas be allowed to leak, since leakage leads to shortage, and the consequences of that have been explained. To meet this requirement, the piston rod of the compressor works in a long gland, designed expressly to prevent the egress of even the smallest quantity of the gas. It consists practically of four parts. There are two sets of packing, carefully cut and arranged in the gland, so that the piston rod will work easily in them, and at the same time they will prevent the egress of gas. Be- tween the two sets of packing there is nearly always a lantern arranged to be filled witli a special lu1)ricating oil. the oil itself being maintained in the lantern under pressure. The packing is WHAT FOLLOWS FROM A HOT COMPRESSOR. 87 soaked in the special lubricating oil, and in some forms of apparatus there is an oil chamber outside of the outside packing. It is absolutel}' necessary that the piston rod shall run perfectly freely, but gastight in the gland, and that it shall always be absolutely bright. If from any cause the piston rod becomes hot, the immediate consequence is, the packing becomes damaged, and gas com- mences to escape, this leading to a further damage of the packing, and so on. The same result will follow if the packing is allowed to become deteriorated, if it is not changed periodically when it shows signs of deterioration, and also if it is not screwed up tight in the gland. On the other hand, great care is necessary in fitting the packing into its place, and in screwing the gland up when the packing is in. It will easily be understood by marine engineers that where a very small fraction of an inch out of line will produce sufficient friction to heat the piston rod, and all that follows, great care and some skill are necessary in dealing with this matter. In addition to this, the piston itself is packed with leathers, and there is also a special lubricating oil always employed to lubri- cate the piston. For carbonic acid, glycerine of a certain con- sistency and of a certain purity is recommended by some makers, while others prefer a special oil sold by the Vacuum Oil Com- pany. For ammonia compressors, special oils are again em- ployed, recommended by the different manufacturers. Sulphu- rous acid compressors, which, so far as the writer is aware, have not been employed on board ship, have the great advantage that the liquid itself is a lubricant. Outside of the compressor and connected to the delivery pipe is an oil separator, whose office is similar to that of steam oil separators, but of very much greater importance. Its office is to extract any oil which is carried over with the gas from the compressor. If any oil is carried into the system, as mentioned above, it leads to the same results that have been described in 88 COLD STORAGE ON BOARD SHIP. connection with shortage of the refrigerant. It leads to a short- age, b}-- taking the place of a portion of the refrigerant, ami sometimes by combining with a portion of the refrigerant. If the compressor is allowed to become hot. as was explained above, the lubricating oil may become vaporized, and a small portion will be carried over with the gas into the condenser, it not being trapped by the separator in the way that the ordinary- lubricating oil is. In the ordinary way, when the compressor is working cold, the lubricating oil that is carried over is in a fineh- divided state in small globules, just as water is carried over from the boiler during the generation of steam ; and it is. or should be, got rid of by the oil separator, providing this is properly looked after. With ammonia compressors, also, there is another and more serious danger, when the compressor becomes hot. At a certain temperature ammonia gas is resolved into its constituents. Am- monia gas. it will be remembered, is a compound whose mole- cules are formed of one atom of nitrogen gas, and three atoms of hydrogen gas. At a temperature of 900 degrees F. the ammonia gas becomes nitrogen and hydrogen, and these, being incompressible at the temperatures and pressures ruling in the ammonia compression system, remain as permanent gases in the system, giving rise to the same troubles as does air. They get into pockets in the system, being compressed there; they take up space that should be occupied by the ammonia gas ; and under certain conditions they may lead to explosion. GETTlXr, on. AND rORElOX BODIES OUT OF THE SYSTEM. There is a draw-off cock attached to the oil separator in all cases, and it should be drawn off periodically. The frequency of the drawing off will vary with different conditions, but the engineer can hardly go wrong in drawing it off more or less continuously. If it is not drawn off the receptacle into which it GETTING OIL AND FOREIGN BODIES OUT OF THE SYSTEM. 8q falls becomes filled up, and the natural consequence is an increas- ing quantity of oil carried over into the condenser. If, either from this cause, from the compressor's becoming hot, or from any other cause, oil is found in the system, the first thing to be done is to endeavor to draw it off at the separator by continuous attention. If this fails, it must be drawn out of the system by breaking a joint, first between the condenser and the regulator to drive the oil out of the Cvjndenser coils, and afterwards be- tween the evaporator and the compressor to drive the oil out of the evaporator coils. While the oil is being driven out of the condenser coils, the whole of the charge must be carried over to the evaporator coils, particularly with ammonia, and this is accomplished by opening the regulator valve wide, and closing the suction cock. And when the oil is being driven out of the evaporator coils, the charge must be carried over into the condenser coils, by closing the regulator valve and running the compressor slowly until the gage on the evaporator shows a vacuum. If the condenser or evaporator coils appear to be in a very bad state inside, as shown by very irregular working, it will be nec- essary to blow them both through with steam first, and then with air. When a machine is first put into service, after it has been set up, it should always be subjected to a compressed air test, to see that all is in order, all joints tight, and so on ; and the same rule applies whenever the system is opened for cleaning. It will be understood that the same trouble mentioned in connection with the deposit on the outside of the condenser coils may also arise from deposit on the inside of both condenser and evaporator coils, from the oil that has been carried over. Also, it is a rule that, before the machine is started, either when first put into service, or when taken apart for cleaning, the cylinder, the valves, and all pipes that can be got at, are thoroughly cleaned out, and all grit and foreign substances removed. When the condition of the inside of either condenser or PO COLD STORAGE ON BOARD SHIP. evaporator coils becomes bad, as explained, the system is opened up by breaking the joints of the condenser to the delivery pipe, and to the regulator, and the connection of the evaporator coils to the regulator and to the suction pipe. Steam from any con- venient source is employed in any convenient way, to blow through each of the coils in succession, until all the foreign matter, oil and so on, has been thoroughly blown out. After this has been done, and when the engineer has thoroughly satis- fied himself that no foreign substance remains, the system is connected up again, all joints being made except one at the suc- tion pipe. The compressor is then run slowly, air being drawn into the system, and compressed to 200 pounds per square inch. The broken joint is then remade, and the system is allowed to remain subject to this compressed air pressure for some hours, all joints being carefully examined during the process, and the gages watched. It should be noted here that the gages will slightly fall after the compressor is stopped, owing to the fact that the air has become heated while the compressor is at work, the pressure thereby rising ; while after the compressor is stopped, the whole apparatus radiates heat. The air thence becoming cooler, con- tracts, and the gage pressures fall. All joints, and all points where leakage will be suspected, should be painted with :i lather of soap and water, as explained before, and bubbles looked out for. To drive the air out of the system, when all joints are good, the methods employed with ammonia, and with carbonic acid, arp slightly different. It does not matter if a small quantity of car- bonic acid gas is delivered into the atmosphere of the engine room. The small quantity that will be present does no harm, and it f(jrm5 a ready and certain method of insuring that the air is all got out. With ammonia, however, it is not permissible to allow any of the gas to escape into the atmosphere. Hence the methods are as follows : GETTING OIL AND FOREIGN BODIES OUT OF THE SYSTEM. QI With carbonic acid, the joint between the condenser and the regulator is broken, and the air is pumped out of the system through this joint. The system is then partly charged with car- bonic acid, and a certain quantity of the gas is. blown through the condenser coils into the atmosphere, to waste; the result being that the system is completely freed from air. With ammonia the method adopted is as follows: The main delivery stop cock is closed, and the small cock on the delivery side, the one that is usually connected to the gage, opened, the gage pipe having been disconnected if necessary, and all other valves and cocks opened, except those leading to the atmosphere. The compressor is then run very slowly, and the air is gradually withdrawn from all parts of the system, and forced out through the small stop cock mentioned, the gages recording the fact by the gradually decreasing pressures. The fact that the air is all exhausted is known by the gages indicating a vacuum, and by the gradually decreasing noise which the air issuing from the small stop cock makes. As soon as the air has all been driven out, the small stop cock should be closed, and the system at once charged with ammonia in the manner described in the manufacturers' directions. On no account should a vacuum be maintained after the air has all been expelled from the system. ]\Iany engineers, when they have had trouble v.dth their plants, with oil and foreign bodies, have made the great mistake, after they have blown through with steam and with air, of pumping a vacuum, and allowing the vacuum to re- main for a number of hours. This is wrong, as wrong as it can be. as it almost invariably leads to the entrance of air into the system, and to the troubles attendant thereon. Keep the air pressure on as long as convenient, until you have made all the joints quite good, but as soon as you have got all the air out, get rid of tne vacuum by putting a charge in. Another point that should perhaps be mentioned, when the compressor is run for the compressed air test, is that, if the 92 COLD storage: ON BOARD SHIP. delivery pipe and the compressor itself become hot, the com- pressor should be immediately stopped, the plant allowed to cool down, overhauled, and the whole process gone over again. Charging with ammonia or carbonic acid is a very simple affair. The gas is contained in strong steel bottles with a regu- lating valve, to which a flexible or bent metal tube is applied when the gas is to be taken from it, the other end of the tube being connected to the charging valve on the system, which is situated sometimes close to the regulating valve, and sometimes on the other side of the evaporator coils. Only the purest and most perfectly anhydrous carbonic acid or ammonia must be em- ployed. This is one of the most important points in connection with cold storage work. It docs not pay to employ cheap re- frigerant, if cheapness means impurity. In the working of the system the impurities get separated out. They sometimes appear as permanent gases, sometimes form a deposit on the inside of the condenser or refrigerator pipes, and generally cause trouble. It is always wise to put the flask of refrigerant upon a scale, when charging the system. This enables the engineer to see exactly how much he has passed. When the connection is made between the flask and the system, the cock on the flask may be opened gradually, the regulator valve of the system being closed, and the gas gradually allowed to pass in, this being shown by two things, the weight of the flask gradually decreasmg and hoar frost commencing to form on the outside of the flask. When about a quarter of the refrigerant contained in the flask has been carried over into the system, the process may be assisted by slightly warming the flask, but great care should be exercised in performing this operation, and it should never be done until the bottle is partially emptied. It is wiser, in charging the system, to err on the side of a small charge at first, as it is easy to increase the charge if required. After charging, the compressor is run at full speed with the cooling water running over the condenser for a certain TO TEST AMMONIA FOR PURITY. 93 time, and then the compressor is stopped, and the S3'stem allowed to remain at rest, except that the cooling water continues to pass over the condenser. The object of this is to allow any air re- maining in the system to rise to the top of the condenser. This air, in the case of ammonia machines, is carried off from a purge co'ck place for the purpose at the top of the condenser coils, to which a flexible rubber tube should be attached, the other end of the tube being led into a vessel of water, the end of the tube being under water. When the purge cock is open, the air will come away, and will be seen in bubbles in the water in the vessel, and there will be no smell as long as air is coming. When all the air has been driven out, and ammonia commences to pass, its own particular smell will be noticed, and the purge cock should be immediately closed. TO TEST AMMONIA FOR PURITY. Draw off into a stoppered flask with a bent tube, a small quan- tity of the ammonia to be tested, being careful that none of the snow formed on the tube goes over into the flask. The snow is formed on the tube, in all these cases, by the sudden lowering of the temperature on the outside of the tube, due to the evaporation of the ammonia inside the tube ; the lowering of the temperature of the air in the neighborhood of the tube leading to the deposit of moisture, and its immediate freezing. After drawing off the small quantity of ammonia into the flask, allow it to evaporate. If it is pure, the whole of the substance in the flask will dis- appear. If anything remains in the flask, it consists of impuri- ties, such as water or organic substances. Organic impurities are detected by their smell. FAULTS IN EVAPORATING COIES. Faults in evaporating coils are very similar to those in con- denser pipes. There may be leaks at joints, allowing ths 94 COLD STORAGE ON BOARD SHIP. refrigerant to leak out, with the results explained, and if the evaporator is employed to cool brine, which is used for the cold chambers, and the system is allowed to stand for a certain time during the day, and even in some cases when not, a small quan- tity of the brine will probabl}^ work its way into the evaporator coils, and will give rise to the troubles already described. With ammonia, a leak into the brine tank is made manifest by the smell and a litmus paper test, and should be immediately seen to by pumping the refrigerant out of the evaporator coils, emptying the brine tank, and examining all joints, if necessary, with air pressure, as described. Another source of trouble with the evaporator coils has already been alluded to, the deposit on the outside or the inside of the pipes. \\'here the evaporator coils are carried right into the cold chamber, the}' very frequently become covered with a coating of ice. This should be cleared off periodically. Where the evaporator is emplo3'ed to cool brine in a brine tank, the salts contained in the brine are sometimes deposited on the outside of the pipes, forming a crust, as explained in connection with the condenser coils, which resists the passage of the heat from the brine to the refrigerant, with tlie result that a smaller quantity of work is done, a smaller quantity of heat is lifted at each stroke of the compressor, and ei'her the compressor must run faster, or the temperature of the brine will go up. The same thing will happen if there is a deposit of oil or any other substance on the inside of the evaporator pipes. The fact that the evaporator coils are working badly will be known by two things, the temperature of the room or the brine, or the air it is cooling will rise, and the gage pressure on the end of the coils will also rise, because the gas is not properly expanded down. The remedy is, to examine the evaporator coils on the outside, periodically, and to clean off aiiy deposit that is formed. This applies also to the condenser coils, and the cleaning off should be done by means of a brush which eoes TROUBLES WITH COMPRESSOR VALVES. QS right down into the condenser, or the evaporator tank, and gets at every part of each of the pipes to be cleaned. Where the deposit is on the inside of the evaporator coils, there is only one remedy, disconnection and blowing through with steam and air, as already described, though the matter may be temporarily put right by increasing the speed of the com- pressor, where the compressor will stand it, or by opening the regulator valve widely where there is a margin available. The piston speed of refrigerating compressors- is very low, usually not more than i8o feet per minute, and it is not wise to run them faster, because it is apt to lead to heating of the com- pressor. But on occasion they may be run slightly faster, pro- viding that it is done with care, and where it is a case of necessity. When this is done, however, the compressor should be very carefully watched for any heating, and anything of the kind immediately attended to. It may happen that one or more of the refrigerator coils are not doing their work, and from that cause the quantity of heat taken out is less than it would be, approximately in proportion to the number of dead coils. The evaporator coils that are not doing their work may be known by the absence of the frost on the coils themselves, or where they are immersed in a brine tank, on the short exposed piece of pipe leading to the header. Where this happens, the faulty coils should be temporarily bridged over, disconnected from the service, and examined, care being taken, in the case of ammonia, to remove the ammonia either from the faulty coils themselves, or, if that cannot be done, from the whole of the evaporator coils, before disconnecting. TROUBLES WITH COMPRESSOR VALVES. IMarine engineers hardly need reminding that valves give trouble. The compressor valves, as explained in the descriptive part of these articles, are kept on their seats by powerful springs, 96 COLD STORAGE ON BOARD SHIP, the valve box either being part of the casting forming the end of the compressor cyHnder, or in some cases being screwed on the outside. In all cases there is the usual valve rod moving in and out as the valve opens and closes, and there is the usual trouble that the valve rod may be bent, or that grit may get between the valve and its seat. In either case leakage m.ay re- suit ; leakage of the suction valve meaning the expulsion of a portion of the charge, in place of its being compressed to its proper pressure ; and leaking of the delivery valve meaning a reduction of the pressure at which the gas is delivered to the condenser, since there will be a certain amount of suction, as the piston returns after the compression stroke. There is only one rule applying to this class of fault, — watch the working of the valves, and examine them as often as convenient. Usually their proper action, or the reverse, may be heard. There is a more troublesome fault in connection with valves, where the valve rod is slightly bent, and that is. an intermittent sticking. The suction valve may not properly open on one stroke, while it may open on another, and the delivery valve the same. The result of this is, the action of the compressor is irregular, and this is shown by the throw of the gages. Watching the gages, as advised above, will in a great many cases show trouble in time. The same remarks apply to leakage past the piston. This arises when the piston leathers are partly worn out. and the result is, the gas is not compressed to its proper pressure, the condenser pressure falling and the evaporator pressure rising. Again, when this happens, make an examination of valves and piston at the earliest opportunity, unless meanwhile it has been shown that the fall is due to some other cause. If either valves or piston are suspected of leaking, the fact may be ascertained with a fair amount of certainty by closing the regulator valve, and continuing to run the compressor. As the gas is being gradually drawn over from the low pressure TESTING the; gages. 97 evaporator sicJe to the condenser side, the pressure on the evapo- rator side will gradually- fall, and in a certain number of revolu- tions which the manufacturers will give (in one case it is 200 revolutions), the pressure will come down about 80 percent — in the case of carbonic acid, from 2S atmospheres to 5 atmospheres. If the pressure does not come down, it is evident that the gas is leaking past the piston or the valves, and they should be examined. TESTING THE GAGES. Gages, unfortunateh', sometimes vary, even the best, and when carefully handled, and it may therefore happen that misleading indications will be given. The onl}' way to test the gages at sea, or anywhere away from a physical laboratory to which they can be sent, is by stopping the compressor, opening all the valves, and allowing the system to settle down. The whole of the re- frigerant then assumes one temperature and one pressure, the temperature of the brine tank, and consequently the gages at the condenser and at the refrigerator should indicate exactly the same. If they do not, comparison should be made between them, and the only thing that can be done is to bear in mind that there is this difference, and the "freezer" engineer may be guided in reading the indications of his gages by the fact that they do indi- cate differently. When it is found that the gages do not indicate alike the earli- est opportunity should be taken of either changing gages or having them tested. Gages of all kinds are very difficult indeed to construct accurately. In the United Kingdom, manufacturers keep standard test gages, which are frequently compared with those in service, and periodically sent to them for comparison with the standard instruments there. 08 COLD STORAGE OX BOARD SHIP. FAULTS IX THE BRIXE CIRCULATIXG SYSTEM. Brine circulation is adopted, as explained in the early part of these articles, for two reasons. Where ammonia is the refriger- ant, it is a very serious matter if any of it escapes into the cold chamber, where meat or other produce is stored. With carbonic acid this difficulty almost disappears. It quite disappears if a proper system of ventilation is employed, so that the air in the cold chamber is changed, and the vapors given off by the produce are carried away. In any case it would have to be a somewhat large leak that would cause any serious inconvenience. The other reason for employing brine, and it is particularly applicable to shipboard v/ork, is, that it enables the engineer to carry different holds or different cold chambers, at different temperatures, and all from one set or plant. The case is by no mems infrequent where some of the holds are carrying, say, frozen mutton, while one or more of the others are carrying chilled beef. Frozen mutton may be frozen as hard as you please, and it is only a question of keeping the temperature low. With chilled beef the matter is quite different. A fall of tem- perature beyond a degree or two is just as fatal as a rise of tem- perature. In fact, a rise of several degrees of temperature, pro- viding that the subsequent cooling does not take place too rap- idly, will do far less harm than a fall of temperature. Anythin:^ in the nature of freezing, where chilled beef, fruit, or other sub- stances that must not be frozen are carried, is fatal. V.'ith brine circulation the engineer is completely master of the situation, provided that his plant is properly laid out, an:l lliat it is properly attended to. \\'ith this arrangement, as ex- plained, the brine is cooled by the evaporator coils in one or more tanks, and the cooled brine is pumped to the brine grids in the different holds or cold chambers, where it extracts the heat, returns to the evaporator tank at a higher temperature, delivers up its heat, and commences its round again, and so on. FAULTS IN THi: BRINE CIRCULATING SYSTEM. QQ Brine again is employed because it has a lower freezing tem- perature than water. It is hardly necessar}- to point out that it would be impossible to circulate water at a temperature below freezing point, but the addition of any solid to water, providing the solid is properl}- dissolved, immediately lowers the freezing point. In the case of chloride of calcium, which is the substance nearl}^ always employed, almost any degree of temperature can be carried, providing that the solution carries a sufficient per- centage of the chloride. With i percent of chloride the freezing point of the solution is 31 degrees F. ; with 5 percent it is 27^^ degrees F. ; with 10 percent it is 22 degrees F. ; with 15 percent it is 15 degrees F. ; with 20 percent it is 5 degrees F. ; and with 25 percent it is — 8 degrees F. From 15 to 20 percent is the strength of solution usually carried, where freezing tem- peratures are required, but there is no reason to carry this strength of solution, where the higher temperatures are carried for chilled beef, 29^/^ degrees F., and in the neighborhood. It is a disadvantage to cmplo}- a too dense solution of the chloride for two reasons. In the first place, the greater the quantity of chloride in the solution, the lower is the specific heat. \\'ith I percent of chloride the specific heat of the solution is 0.996, practicalh' the same as water. With 5 percent it has sunk to 0.964; with 10 percent to 0.896; with 15 percent to 0.860; with 20 percent to 0.834; ^iicl with 25 percent to 0.79, approximately. This means that with a 20 percent solution, approximately, the heat carrying power of a given quantity of the solution is 15 percent less than that of water, and this means that a larger quantity of the solution must be circulated to carry off the same quantity of heat from the cold chamber, the air, etc. The other disadvantage is, the greater the density of the solu- tion, the greater the tendency to deposit on the pipes in which the solution is circulating, and on the evaporator pipes, in the evaporator tank. And this leads to one of the possible faults. As in all these cases, there are two possible sources of failure. 100 COLD STORAGE ON BOARD SHIP. leakage and obstruction. If the joints of the brine pipe leak, there is not the same quantity of brine circulating, and therefore there is not the same quantity of heat carried ofif. This trouble is very easily located, and the marine engineer can be trusted to grapple with it without difficulty. But the other possible source of trouble, the obstruction, is very much more serious, very much more difficult to discover, and very much more diffi- cult to put right. The same rule applies in this case that has been given in connection with the compressor, and so on, "watch the gages." In this case the gages are the thermometers. When everything is working properly there will be a certain difference of temperature between the ingoing brine and the outgoing brine, from any given cold chamber. If there is an alteration in these quantities, if the incoming brine is at a higher temperature than it should be to produce the proper extraction of heat, the fault is to be found probably in the evaporator tank. The heat is not being properly extracted from the returning brine, and there- fore it is not setting out at the low temperature it should have. The evaporator coils may not be doing their work properly, as described in the previous notes, or again, there may be- a deposit on the inside of the brine pipes, which is preventing the heat from being extracted from the brine, as mentioned several times above. Another possible cause of trouble with brine circulation arises when the brine is not sufficiently strong to withstand the low temperature of the evaporator tank. It will be understood that this is the other side of the question. As explained, the solution must not be too strong, for the reasons named. It also must not be £0 weak that in passing through any part of the system, say the evaporator coils, even a small portion of it will freeze. When this happens there is a formation of ice upon the outside of the evaporator coils, and tliis ice lias the same effect, to a certain extent, in preventing the passage of heat from the brine to the refrigerant, as the deposit of the salt would. B * FAULTS IX THE BRINi; CIRCULATIXX SYSTEM. lOI The methods adopted where brine circulation is emplo3-ed, with frozen produce, and with chilled produce, are sometimes quite different. It is evident that with frozen produce, all that is nec- essary being to maintain the temperature below a certain figure during the whole twent3'-four hours, if a store of cold is pro- vided in the hold or cold chamber, in the shape of a quantit}' of brine whose temperature is reduced to a certain figure, the plant ma\' be worked for only a certain number of hours a day, the store being maintained at its temperature for the remainder of the time b\' drawing upon the reserve of cold in the brine store. This plan has a great deal to recommend it. and is often employed on shore. It has one obvious advantage, in that it allows of a smaller staff being employed. One "freezer" engineer, and per- haps a greaser, can run the plant for, say, a couple of watches during the day, get the brine to its temperature, and allow it to look after itself, with an occasional look at the thermometers, for the remainder of the twenty-four hours. The only thing necessary, and it involves only a very simple calculation, is that there shall be a sufficient quantity of brine, held at a sufficiently low temperature, to provide the necessar\^ cold for the sixteen or eighteen hours during which the plant Is not working. From the figures given for the specific heat of the brine solution, the above calculation is easily made for a given size of hold or cold chamber, with a given quantity of produce stored in it. With chilled meat, fruit, or produce which must not be frozen, and the temperature of which must not vary more than a very few degrees, it is necessary to run the plant continuously during the whole twenty-four hours ; and further, the rise of tempera- ture in the brine supplying the hold in which the chilled beef or fruit is held should be allowed to be only a very few degrees between the inlet and outlet. Again, the temperatures on the inlet and outlet pipe of each hold and of each portion of each hold, will be a guide to the ''freezer" engineer, as to what is going on inside the hold, or that portion of the hold. If the 102 COLD STORAGE ON BOARD SHIP. temperature on the outlet is higher than proper working shows is best, evidently more heat from some cause is being given off mside, and it would probably be wise to deliver a larger quantity of the brine to that hold or that portion of the hold. On the other hand, if the temperature at the outlet is lower than the normal, it shows that there is very little difference in temperature between the brine and the air in that portion of the hold, and as this may mean that the temperature there is lower, or may become lower than it should be, the quantity of brine passing is lessened. This is done, of course, by means of the circulating pumps, and by the valves on the pipes and headers. It will be wise, in the case of chilled meat and fruit, to check the indications of the thermometers in the brine, by thermome- ters in the stores themselves, and, for this purpose, thermometers arranged to indicate the temperature inside on some apparatus outside are of great service. There are several forms of elec- trical apparatus on the market which will accomplish this. In particular, there is a series of instruments made by the Cam- bridge Scientific Instrument Company, of Cambridge, England, and, the writer believes also, by firms in .America, in which the variation in the resistance of a platinum wire is made to show the temperature tale inside of a cold store, at an indicating or testing board, on the outside in the engineer's room, or in any other convenient position. The rationale of the arrangement is, the electrical resistance of all metals increases with a rise in temperature, and decreases with a fall in temperature, in a certain definite proportion, for each degree of rise or fall. Tf. therefore, an electric circuit is formed, including a small piece of platinum wire, a source of current and an electrical indicating apparatus fit may be a gal- vanometer, calibrated in degrees F. or C, the platinum wires beitig fixed upon the tubes arranged to be placed in the cold store, and the connecting wires being led through insulated tubes in the walls of the store to the indicating apparatus), every rise PREPARING THE BRIXE SOLUTION. IO3 and fall of temperature will be seen at the indicating point, and may also be recorded upon a chart, in a manner similar to barometric and other records. There are other arrangements worked electrically, in which a rise of temperature of a certain number of degrees closes an electric circuit and drops an indicator in the engineer's room ; a fall of temperature of a certain number of degrees closing another circuit, and dropping another indicator, and so on. But the electrical thermometer, giving its own records upon a dial or chart, is. in the writer's opinion, far preferable. It has one disadvantage, especially for seagoing work — it is necessarily delicate ; but it is perfectly possible to protect the platinum wire in such a manner that even the knocking about in a ver}' heav}^ seaway will not easily damage it, and the sure indications the thermometers give are worth a great deal of trouble to obtain, where such important results follow, as in the case of a variation of temperature with chilled meat, fruit, etc. With such a set of thermometers, and a careful attendant con- stantly watching the thermometers on the brine pipes and in the cold stores, it should, in the writer's opinion, be perfectly practi- cable to carry chilled meat, fruit, etc., for long voyages, six weeks or more, providing that the other points that have been men- tioned in connection with the operation of the plant are attended to. PREPARING THE BRINE SOLUTION, Tt is very important indeed that the brine solution should be carefully prepared. It is not sufficient to take a tub of water and throw some calcium chloride into it, and allow it to dissolve. A certain definite quantity of the calcium chloride should be dis- solved, in a certain definite quantity of water, and the purest water, distilled if possible, should be employed. On no account should sea water be employed, either as a solvent for the calcium Qhloride, or to take its place. A brine is made from common 104 COLD STORAGE ON BOARD SHIP. salt which an?'.vcrs all the requirements of a brine solution, if made in the proper strength, according to the temperature to which it has to be subject; but it is not wise to employ a salt brine solution, if calcium chloride can be obtained. The reason is one that will be very familiar to marine engi- neers. Common salt acts chemically upon almost every metal with which it comes in contact, and particularly upon iron, while calcium chloride has practically no action upon iron, as long as it is pure. Where calcium chloride is employed, it is m.uch better to use plain iron pipes than galvanized iron. Calcium chloride acts chemically upon zinc, with a liberation oi hydrogen, and sometimes consequent troubles. If the engineer is obliged to employ any salt for his solution, owing to his being in a port where calcium chloride is unobtain- able, the following are the figures he has to work to : With i per- cent of common salt the freezing point of the solution is 20l4 degrees F. ; with 5 percent it is 25 degrees F. ; with 10 percent it is 18 degrees F. ; with 20 percent it is 6 degrees F. ; and with 25 percent 5 degrees F. It will be seen that the freezing points are a little under those of the solution of calcium chloride. The specific heats are as follows : With i percent, 0.992 ; with 5 per- cent, 0.960 ; with 10 percent, 0.892 ; with 20 percent, 0.829 ; and with 25 percent, 0,783, about. There is very little difference again between the specific heats, though calcium chloride has slightly the advantage. If common salt is employed temporarily, as a brine solution, it should be made only with pure distilled water, or if distilled water is not ol:)tainablc, the purest water that can be had. Fresh water in any case, and the earliest possible return to the use of calcium chloride, should be made, the brine pipes being thoroughly washed out before the calcium chloride is admitted into them. Tn preparing either the calcium chloride or the common salt solution, the best plan is to hold the salt cither in a bucket with perforations, or in a cage, or something similar, weighing TREPARIXG THE BRINE SOLUTION. IO5 the proper quantity of the salt for a definite quantity of solution into the bucket or cage, and then either immersing the whole in a vessel containing the definite quantity of water to make the proper density of solution, or pun- ping the water in over the cage into a vessel arranged to hold it, and allowing the whole to settle, etc. There is another point w^hich ought to be mentioned. Com- mercial calcium chloride too often contains impurities, even as much as 25 percent of common salt, and if a solution is made up from this substance, chemical actions will take place between the calcium chloride and the common salt, leading to a reduction in the efficiency of the system. That is to say, a definite quantity of a given solution, passing through a cold chamber in a given time, the liquid having been cooled to a given temperature, will not absorb the same quantity of heat as the pure solution of calcium chloride or sodium chloride would have done. In addition to this, in working, the sodium chloride, being less soluble than the calcium chloride, is apt to somewhat freely deposit on the inside of the pipes, with the results that have been mentioned. When bu3'ing calcium chloride, therefore, it is wise to test it, and the best test is, by making a small quantity of solution, of a definite density, and taking its freezing point. That is to say, freezing it, as can easily be done where there is a refrigerating plant on the ground, and taking the freezing point with a thermometer. Calcium chloride and sodium chloride are very much alike in appearance, and, in addition, commercial calcium chloride con- tains, on an average, 25 percent of water, and will absorb from half to nearly all its own weight of water when the conditions are favorable. In America the calcium chloride, in its com- mercial form, comes from the makers in a solid cake inclosed in air-tight thin iron drums. Before use, it has to be broken up into lumps, the lumps being put into the cage or bucket, as explained. I06 COI,D STORAGE ON BOARD SHIP. FAULTS IN AIR COOLED PLANTS. The principal points to be looked out for in connection with air cooled plants are the condition of the air ducts, and the temperature in different parts of the hold. Dust and dirt of various kinds sometimes collect in the air ducts, and may be carried into the cold chamber, if not removed. The "freezer" engineer should examine the ducts as frequently as possible, particularly after bad weather, when everything has been strained, and when dust will have been created to a certain extent, when everything is more or less upside down ; and should have all dust, and anything that can be carried into the cold chamber, removed. The question of the distribution of temperature within the chamber is also an exceedingly important one, and the engi- neer should give it considerable attention. The ports in the ducts should be so arranged that air currents can be sent through every part of the chamber, and the fruit or other produce that is air cooled should be so arranged that the aii penetrates to all parts. The engineer should look into this matter also after heavy weather. Bananas, crates of rabbits, fruits of all kinds, that are air cooled, should be arranged with an air space all around them. The}^ should not rest on the floor, for instance, but should be supported on laths, or any- thing that will allow a current of air to pass under them, and they should not be stacked closely together, for the same rea- son. Tf they have been thrown together during heavy weather, they should be replaced as soon as it is possible to do any- thing within the cold chamber. There is great danger, in air cooled chambers, of the currents of air passing across from the port of the inlet duct to the port of tlie outlet (hict, and largely avoiding a portion of the pro- duce. This will be especially the case if there are corners in the hold or cold chamber, in which a portion of the produce is FAULTS IX AIR COOLED PLANTS. 10/ Stored, and to which it is difficult for the air to penetrate. A Very Hberal supply of thermometers will inform the engineer as to the temperature, and for this purpose, though the elec- trical thermometers described in a previous note are much better, and will give him the information he wants without his entering the hold, he can still obtain quite reliable information from a number of cheap thermometers, providing that he knows each individual instrument. Ver}^ few thermometers, as already explained, agree. The methods of constructing thermometers vary considerably, and the ordinary method also varies in toto from what is supposed to be the theory of the subject, the theory unfortunately, as often happens, being wrong. But it is an easy matter to compare indi- vidual thermometers, with one thermometer that is known to be fairly accurate, and even where this is not possible, to obtain a sufficient guidance by the readings of thermometers that are not themselves at all accurate, providing that they always read the same number of degrees, for the same temperature. Thus the *''freezer" engineer will be able to judge when his fruit or other produce is all right, and is keeping so, and he can mark that on a thermometer, and it will not matter whether the thermometer is really registering the correct temperature or not — the figure, whatever it may be, will be his guide to w^ork to. If the engineer finds that the temperature rises or falls unduly, (both are bad, as already explained) in any part of the hold or cold chamber, he must alter the current of air, either by means of the ports in the air ducts, by introducing fans, or by putting up temporary partitions, of board or sail cloth, just as mining men do, to direct air currents into particular working places. In any case he must direct more air into an}- corner, or any part where the temperature unduly rises, and he must divert air from any part where it unduly falls. Another point in connection with air cooled chambers is the direction of the air. This, it will be seen, is a most important I08 COI^D STORAGE ON BOARD SHIP. matter, and it is not always easy to determine the direction of the air. The Httle apparatus called the anemometer, which is the correct apparatus for measuring the velocity of air currents, and therefore of the strength of air currents in different parts of a chamber, is very delicate, and requires a certain amount of skill in handling. Equally as good an apparatus is one of the toys that are made for children, consisting of light vanes made of paper, or an}- light material, held very loosely on a pin at the end of a stick. The apparatus looks like a childish one, but it is very useful for measuring the direction and the strength of air currents. It is an apparatus that any engineer can make up quickly for himself, at practically no cost beyond the time in- volved; and by having several of these fixed in different parts of the hold he may see at a glance, from one of the duct ports, how the air currents are going within the hold, and he can also, by constructing them of slightly varying size and form, obtain some very useful and reliable information. Every engineer knows that in practical work, what is required is, not so much absolute measurement, as relative measurement. We do not trouble our heads about the absolute steam pressure, nor the absolute temperature. What we do trouble about is, whether the pressure or the temperature rises or falls above certain figures that we are working to. Similarly, we do not want to know the accurate velocity of tlie air passing through a cold chamber, but we do want to know the relative velocity pass- ing in different parts of the chamber, and that, these little pieces of apparatus will tell us. The revolving paper vanes should be made something on the lines of the vanes of the Blackman's fan, to be effective. They should hold a certain amount of air in a sort of l)ag formation. Another useful arrangement is a piece of vcr}- light dry riblion held on the end of a stick. It is also a primitive arrangement, but one that is very easily fitted up, and very useful where the little revolving paper vanes are not available. FAUI.TS IN AIR COOLED PLANTS. lOQ It is not necessary to repeat the instructions that have been given with regard to the air cooHng plant itself. On board ship it can take only one form, except in very special cases, viz., a stack or grid of pipes through which the refrigerant passes, and in which it evaporates, the air to be delivered to the cold cham- ber being driven over the surface of the pipes by the aid of a fan. If the temperature in the hold rises unduly, or falls unduly, as a whole, not in any particular part, the air is either being cooled too much or it is being driven at too great a velocity through the cold chamber. The engineer in this case has two methods of regulating. He can either increase or decrease the speed of the fan, increasing or decreasing the velocity of the air current, thereby lowering or raising the temperature of the air in the hold, since every cubic foot of air passing through it at a certain temperature carries off a certain quantity of heat; or he can raise or lower the quantity of the refrigerant passing into the evaporator coils, this being accomplished by opening or closing the regulator valve. There may be the same troubles in connection with an air cooled plant as with brine cooling. The inside of the evaporator coils may receive a deposit of grease or other foreign matter, thus increasing the thermal resistance between the refrigerant and the air, and leading to the temperature of the air not being lowered as much as it should be. And again, certain portions of the evaporator coils may not be doing their work, from causes already mentioned, such as pipes having been clogged, or a leak having occurred. In such a case the temperature of the hold will rise, and it will be necessary, either to increase the quantity of refrigerant passing into the evaporator coils, or to increase the velocity of the air. The fan in this case is usually electrically driven, and there should be an arrangement enabling the speed of the fan to be regulated within certain limits, as much as from one to ten, so that probably increasing or decreasing the 110 COLD STORAGE ON BOARD SHIP. air current will be found a very convenient method of regulating the temperature in an air cooled hold. Where a compressed air plant is employed, the air from the cold chamber being drawn into the compressor, compressed, cooled, expanded and redelivered to the chamber, there are two important points to be attended to. The apparatus, whatever it may be, for cooling and drying the air, directly after it leaves the compressor, should be kept in proper working order. It usually consists of some arrangement in which the air passes up- wards over a number of broken surfaces, such as a number of glass marbles, this being one form used by a London firm, and meeting a current of cold water passing down over the same sur- faces. The arrangement is exactly the same as that employed in cooling towers on shore. The apparatus, in this case, performs the double o-ifice of partially cooling the air which has been heated in the compression cylinder, and of removing the moisture which has been brought over from the cold chamber, the moist- ure being removed by the fact of cooling, and b\' the production of a difference between the vapor tension of the air and that of the cooling water. If the temperature of the cooling water rises, as when the ship passes into the tropics, it is evident that the same quantity of water passing will not effect the same cooling. It is of the very liighest importance that the air should be cooled down as much as possible, before it passes into the expansion chamber, where the principal cooling takes place, and also that the moisture shall all be removed from it. as far as possible, for the reason that if there is any moisture present, it will tend to freeze within the evaporating cylinder, and in the delivery ports from the evapo- rating cylinder, and so on. The engineer, therefore, who is in charge of a compressed air plant, will 1)c wise to ''freeze"' his attention on the air drying apparatus. With compressed air. also, there is the great danger of leakage of heat into the duct leading from the evaporating cylinder to the cold chamber, and into the FAULTS IN COLD CHAMBERS. Ill dncts that distribute the cold air. There is only one method of overcoming this, and that is, by maintaining the insulation intact, and there is only one method of ascertaining whether anything of the kind does take place, and that is, by observing tempera- tures everywhere. FAULTS IN COLD CHAMBERS. Faults in cold chambers, cooled by means of brine or expansion coils, are of very much the same kind as those mentioned in con- nection with air cooled chambers, and the ducts of compressed air. The great source of trouble with cold chambers is the low- ering of the insulation of the chamber itself. It has been ex- plained, in the early part of these articles, that there is no such thing as a perfect insulator for heat. Heat always passes through the most perfect insulating wall that has yet been devised, and at a certain rate ; and the cold storage plant, the compressor, con- denser, evaporator, etc., are designed to remove the heat that passes through the insulating walls, as it passes through, and to deliver it continuously to the cooling water of the condenser. So long as the insulation remains at a certain figure, that is to say, so long as heat passes through the walls, floor and ceiling at a certain definite rate, and so long as the plant itself is working normally, the heat passing into the chamber is continually carried away, a certain number of heat units being carried off at each stroke of the compressor. If, however, the insulation fails, an increased quantity of heat passes into the chamber, and unless the evaporator or the brine coils carry off the increased quan- tity, the temperature will rise. Again, the engineer will be wise to watch his temperatures by any means in his power, by the aid of electrical thermometers if possible, but in any case by the aid of any thermometers that he can obtain. If he finds the temperature of his cold store rising, he should first ascertain whether the plant is working all 112 COLD storage; on board SHIP. right. It may be taken as an axiom that in all work of this kind, where testing for faults is necessary, the engineer should commence at the very beginning. He should commence at the compressor, see if that is in the condition described, see if the condenser and evaporator gages are recording as they ought, see if the delivery pipe is in the condition it should be. If all these things are right, and the temperature goes up, it will probably be accompanied by a fall in the pressure at the evaporator gage, since the system will be endeavoring to do more work. With brine cooling, the engineer has then two methods of dealing with the problem. He can increase the velocity of the brine circula- tion, by increasing the speed of the pump, or opening the valve of a particular brine pipe, or he can increase the quantity of the refrigerant passing into the evaporator coils, where the trouble is common to all. He will be guided by circumstances as to which course he takes. In some cases it may be easier and simpler to slightly increase the speed of the pump. In cases where a pump runs at a constant speed he cannot do this, and he must increase the quantity of the refrigerant. In the case of chilled meat, where it is so important, as ex- plained, to maintain the temperature within a few degrees of a certain figure, neither going up nor down, if the engineer finds his temperature going down, probably his best method of dealing with the question will be decreasing the velocity of the brine circulation in the particular chamber, by closing the valve par- tially. Where there is more than one hold or cold chamber sup- plied with brine coils, the matter is regulated simply by altering the valves on each branch of the system. RECEIVING MEAT AND PRODUCE. Meat that is to be carried frozen is usually frn/cn as soon as it has been killed, nt the station where it has been grown, and is, or should be, carried in refrigerating cars to the ship's side. Wlicrc, RECEIVING MEAT AND PRODUCE. 113 However, this is not done, or where meat is received newly killed, to be placed in cold store, and where it is to be held frozen, or chilled, it should on no account be exposed to a very low temperature for some time after it has been killed. What is known as the animal heat should always be allowed to get out of the meat, by radiation, before any cooling is attempted. The time occupied in getting rid of the animal heat varies consider- ably. Where times presses, and where it is not of such a great importance — say where the meat will not have to be kept for a long time, as when it is intended for the use of the ship's com- pan.v or passengers — the meat should be allowed to hang in the ordinary temperature as long as possible, and then it should be submitted to a gradually lowering temperature, the heat being slowly extracted from it in this way, until finally it is frozen or chilled, as required. Meat received in this way should on no account be allowed to He on the floor, nor to touch the walls or the ceiling. In ships which carry chilled meat, it is usual to suspend carcasses or quarters by hooks arranged for the purpose below the ceiling, and in such a manner that the air has free access to every part of the carcass. \\'herc this cannot be done, where it is necessary to lay the meat on something, battens or gratings, or something similar, should be laid on the floor of the cold chamber, and the meat laid on them, being so arranged that the air has a clear passage under the meat, over it and all around it ; and if it is necessary to lay the meat in tiers, successive tiers of battens should be provided, ful- fllling the same conditions. The same remarks apph' to crates of rabbits and similar produce. Rabbits are packed loosely in small open crates, giving clear passage of air through them, and these should be placed a little off the ground, and if obliged to be stacked one above the other, should be arranged by means of battens with air spaces between them. It is particularly import- ant in the case of chilled meat, that the cooling should be per- formed very gradually indeed. 114 COLD STORAGE ON BOARD SHIP. If the meat on the outer surface is frozen first, or even if its temperature is very much reduced before that of the inner por- tions, it is very hable to lead to what is known as "bone stink." In plain terms, the inner portion of the meat sets up organic chemical action, and rots. When this does not actually occur, a lesser evil may be met — the minute cells and vessels of which the muscular portions, the eating portions of meat, are composed, sometimes burst, and the juices they contain are lost, with the result that the meat so preserved, when it comes to be cooked, is found to have no gravy, and very little flavor, and is consequently sold for a very low price. THAWING OUT. It will usually not be within the province of the "freezer" en- gineer to thaw out meat, except for the use of the ship's com- pan\- or passengers. When he has to perform this work, how- ever, it cannot be too carefully done nor too gradually. The meat to be thawed should be removed from the cold chamber to one only a little higher in temperature, or arrangements should be made to slightly increase the temperature of that portion of the chamber in which the meat to be thawed out is placed. This may be accomplished by the aid of temporary screens of board or dry sail cloth. In any case the temperature should be grad- ually, very gradually raised, the object to be attained being that the higher temperature of, say, a very few degrees, shall pene- trate right into the substance of the meat, before the outer sur- face is subject to a further increase of temperature. If this is done carefully, the meat so thawed, providing it has been care- fully chilled or frozen, \n!l turn cmi well when cooked. If tliis is not done, the flavor of the meat and its quality will be very much deteriorated. In thawing out holds it i- best to circulate hot brine in the brine coils, rather than to use fires, or similar arrangements. The HANDLING MEAT AND PRODUCE. llS brine should be gradually increased in temperature, and should be kept in circulation until the hold is thoroughly dried. The insulation will be all the better for it. HANDLING MEAT AND PRODUCE WHEN LOADING AND DISCHARGING. Do not handle the produce more than can possibly be helped. On no account place the hands on the meat or fruit that is to be stored, if it can possibly be avoided. The enormous quantity of frozen sheep which are brought to England from New Zealand are all inclosed, each sheep in its own linen bag, which avoids the necessity of hands touching the carcasses, though the results of touching a hard frozen substance are not so serious as those of touching a chilled meat surface, or the surface of fruit, etc. The linen bags also form a very convenient arrangement for identifA-ing particular consignments, each bag being marked with the owner's, consignor's, or consignee's name. With chilled beef and with fruit the matter is sometimes a very difficult one Fruit should be handled in crates, so that the hands do not touch the produce at all, either loading or unloading. In the case of bananas, they can be handled, or should be, by the stalks. One great source of trouble in connection with chilled meat is the muggy atmosphere that is so common in the United King- dom, and is also met with in every part of the world where fogs prevail at certain times of the 3-ear. This muggy atmosphere contains moisture held in suspension in the w^ell known manner. It is able to hold a certain quantity of moisture when at a cer- tain temperature. If any portion of the air is cooled, a deposit of a certain portion of the moisture it contained follows, usually on the cold surface, bringing the cooling effect. When chilled meat is removed from the hold to the raihvay trucks, sa}-, or to a cold store, where there is one on the dock side, there is always a great danger If the atmosphere is in that muggy condition mentioned, of the deposit of moisture upon the surface of the Il6 COLD STORAGE OX BOARD SHIP. meat, which is nearly always at a considerably lower temperature than that of the atmosphere, with the result that the meat is seriously deteriorated, and its market value reduced. The prob- lem of how to meet this is an exceedingly difficult one. Probably the best method is, to ascertain by means of a hy- grometer the actual humidity of the atmosphere, to note carefully its temperature, and if possible to raise the temperature of the meat to be discharged to that of the atmosphere, or a little above it. Whether moisture deposits from the atmosphere on the meat will depend upon the temperatures of the two, and upon the vapor tensions of the moisture in the atmosphere, and that issu- ing from the meat. It will be better, if possible, for a little vapor to be given off from the meat, than for moisture to be de- posited upon it. If the meat is carried into cold store almost directly from the ship, or at any rate very shortly after, it will be quite easy to reduce the temperature again, and to do it care- fully, and the meat will be preserved. It is not so easy to arrange this where the meat is to be dis- charged into refrigerating railway cars, and it is absolutely im- possible where the meat is to be discharged into ordinary railway cars or carts. In the latter cases all that can be dOne is to wrap each individual carcass with dry substances that are good thermal insulators, so that the hands of the carriers may not touch them, and that the moisture may not be deposited directly on them. Almost any form of cloth, providing that it is thoroughly dry, will answer, and a very good thing for temporary use, if it can be obtained, failing anything else, is brown paper. It must not be forgotten, of course, that all fabrics and paper are porous, and absorb moisture, and therefore they should be removed immedi- ately their work is done, if they have become wet. The wrap- pings also should be as thick as possible, so as to offer the high- est resistance to the passage of heat from the atmosphere to the meat, and also to absorb as much of the moisture that may be deposited, as possible. FAULTS IN AN ABSORPTION PLANT. .II7 In the railway trucks, even if they are not fitted with cooHng apparatus, providing that they are open, constructed in the same manner as crates are, and providing that they are placed in the cars in such a manner that the air can get all around them, if the trains are hauled away quickly as they are loaded, it is probable that not much harm will take place if the above pre- cautions are taken. FAULTS IN AN ABSORPTION PLANT. A large portion of the instructions given in connection with faults in a compression plant apply also to an absorption plant, because, as explained in the earlier part of the articles, the condenser, evaporator, brine circulation and air circulation are common to both compression and absorption plants, but the absorption plant has faults peculiar to itself. In it the generator with its accessories, the analyser and rectifier, represents the compression side of the compressor, and the absorber represents the suction side. It will be remembered that the ammonia is driven off from the aqueous solution in which it is carried in the generator, by the aid of heat, that it then passes through the analyser and the rectifier to the condenser, where it be- comes liquid, and from the condenser takes the same path as with a compression plant, through the expansion valve and the expansion coils, coming back to the absorber instead of to the compressor. The high-pressure side of the plant therefore will consist of the generator, the analyser, the rectifier, and the con- denser, while the low-pressure side will consist of the expansion coils and the absorber. Pressure gages are fixed at any con- venient spot on the high-pressure side. In the form that is most in use in the United Kingdom, that made by Alessrs. Ransomes & Rapier, the gage is placed on the rectifier, the gage registering low pressure being placed on the absorber. Practically the same rules hold good as with the compression Il8 COLD STORAGE ON BOARD SHIP. plant, viz., ' watch the gages," but in addition to the pressure gages mentioned, there are also, in the absorption plant, two very useful glass liquid gages, one on the generator and one on the absorber, showing the height of the liquid in these vessels. Messrs. Ransomes also fix a liquid gage on the condenser, but there is no reason that a liquid gage should not be fixed upon all condensers. Where there is a receiver between the con- denser and the expansion valve, it is always usual to have a liquid gage, showing the height of the liquid in the receiver. It will be remembered also that the continuous working of the apparatus is maintained by the continual exchange of weak and strong liquid, between the generator and the absorber. Weak liquid, as already explained, has a higher specific gravity than strong liquid, and as the gas is driven off from the solution in the generator, the weak liquid sinks to the bottom. In Messrs. Ransomes' plant the weak liquid is forced by the pressure of the gas in the generator towards the absorber, passing through the apparatus called the exchanger, on its way. In the absorber, on the other hand, the continual passage of the gas from the expansion coils into the liquid present in the absorber vessel, constantly increases the strength of the liquid, from the ammonia point of view, and the strong liquid is carried back to the gen- erator, passing on its way through the exchanger, by the aid of a small pump provided for the purpose. In Messrs. Ransomes' apparatus there is an automatic float valve, consisting of a vessel ellipsoidal in shape, in which there is a port opening to a pipe leading &o the exchanger, and thence to the generator. As the absorber becomes charged with weak liquid from the generator on the one hand, and with ammonia from the expansion coils on the other, the height of the liquid gradually increases, its strength also increasing, and at a certain height it overflows into the vessel containing the automatic valve. In this vessel is a float controlhng the valve and when a certain quantity of the strong liquid has passed into the valve vessel, FAULTS IX AX ABSORPTIOX PLANT. II9 the float rises, opens the valve leading to the exchanger, and allows the pump to deliver the strong liquid to the exchanger and the generator. There is the same difference between the pressures on the high-pressure and low-pressure side of the expansion valve as in the compression system, the pressures ranging as in that system, on the condenser side, from 135 pounds to 200 poimds per square inch, while the pressure on the evaporator and absorber side is usually in the neighborhood of 15 pounds per square inch. Both vary, however, as in the compression system, with the conditions ruling. On the condenser side the pressure increases with the temperature of the circulating water of the condenser. Messrs. Ransomes give a list in their instructions, stating that with cooling water at 50 degrees F. inlet, and 95 de- grees F. outlet, the condenser pressure will be 135 pounds; with water at 60 degrees F. inlet the pressure rises to 150 pounds, and so on up to water at 90 degrees F. inlet, 115 degrees F. outlet, when the condenser pressure is 200 pounds. In addition to this, the pressure of the steam employed in driving the ammonia out of the cylinder in the generator varies with the temperature of the condensing water. In other words, the temperature and the quantity of heat it is necessary to dehver to the ammonia solution in the generator increases as the temper- ature of the condenser cooling water increases. Messrs. Ran- somes give the following figures : With cooling water at 50 de- grees F. inlet, and condenser pressure of 135 pounds per square inch, steam at 40 pounds gage pressure is required, the tempera- ture of the steam being about 287 degrees F. With cooling water at 60 degrees F. inlet, and the condenser pressure at 150 pounds, the steam required is at 45 pounds gage pressure, its temperature being about 292 degrees F. With water at 90 degrees F. inlet, and condenser pressure at 200 pounds per square inch, steam at 60 pounds gage pressure is required, its temperature being about 307 degrees F, J20 COLD STORAGE ON BOARD SHIP. As in the compression system, the condenser pressure is ruled by- the temperature of the condenser coohng water, and the pressure of the steam, or the temperature of the steam employed to drive off the ammonia, depends upon the condenser pressure. As with the compression system, anything which interferes with the cooling of the condenser increases the condenser pressure, and increases the pressure of steam required, while on the other hand, anything, such as cooling water of a lower temper- ature, which enables a lower condenser pressure to be carried, enables also a lower steam pressure to be employed, and prac- tically is more economical. As also in the compression system, the pressure in the absorber depends upon the temperature to which the brine or the air to be cooled is reduced, the same rule applying as with the compression system. As in the com- pression system also, the higher the pressure in the absorber, the less work the steam in the generator has to do. The points to be looked to principally in the absorption system, apart from those mentioned in previous portions of the article, as to the deposit upon condenser and evaporator pipes, etc., are that proper circulation between the absorber and the gen- erator shall be continually carried on. If the ammonia pump does not deliver the proper quantity of strong liquid into the generator from the absorber, the quantity of ammonia present. it is evident, will be less than is required for working at the given steam pressure, and consequently the condenser pressure will fall, and the condensation of the liquid will be interfered with. There is also the same trouble in the absorption system from shortage of ammonia. In the absorption system, there is not only the possibility of ammonia leaking out through defective joints, as in the compression systeju, but there is also the possibility of its leaking into cither of the vessels through which it passes. In any case, whatever the cause of leakage, shortage of ammonia leads to the same results as with the compression system, to inefficiency of the plant as a whole. FAULTS IN AN ABSORPTION PLANT. 121 imperfect condensation may also lead to the passage of ?.m- monia gas, with the ammonia liquid, through the expansion valve, and the same results as explained in connection with the compr-ession system. But with the absorption system, properly gaged, the engineer has always a guide in front of him. When the liquid in the condenser is not above a height which prevents gas from passing into the expansion coils, when the expansion valve is open, then the expansion valve must be kept partially closed. Again, the glass gages on the generator and absorber will show him the condition of the liquids in these vessels. To a certain extent, they show the quantity of liquid in each, which is of great importance, and the gage upon the condenser will show the quantity of liquid ammonia being formed. There is the same trouble also in the absorption system from air getting into the system, and, being practically inoompressible, setting up pressures opposing the actual working pressures. In the absorption system the result of the presence of air in the system, or of any other insoluble gas, such as hydrogen in the case of the decomposition of ammonia, is an increase in the pressure on the absorber gage on the low-pressure side of the system. As in the compression system, therefore, a constant watch upon the gages will give early warning that something is wrong, and further examination will show what it is. If there is air in the system, it is discovered, and expulsion is obtained by the same means as in the compression system. There is a valve specially arranged, on the absorber, for the purpose of getting rid of the air. An India rubber tube is attached to this valve, its other end being immersed in a vessel containing water. When the valve is open, the air is driven out. and may be seen bubbling up through the water; and when all the air that can be got out at the moment has passed, the water will commence to smell strongly of ammonia, and the valve is then closed. It is necessary in some cases to repeat the operation several times before all the air is got rid of, as it lurks in 122 COLD STORAGE OX BOARD SHIP. pockets in the pipes, etc., and only gradually finds its way to the point of exit. It will be noted that the absorption system is free from the troubles mentioned in connection with the compression system, arising from the presence of oil. Except from gross careless- ness, there should be no oil in the system at all. Hence the troubles that were mentioned, of oil being carried over as vapor, and being decomposed into its constituents, and deposited upon the inside of condenser and expansion pipes, are absent. On the other hand, the guide offered by the temperature of the delivery pipe of the compressor is also absent, but the glass gages men- tioned offer a very much better and more certain substitute. COLD CHAMBERS IX COLD STORAGE TRAMP STEAMERS. The arrangement of cold chambers, or cold holds, in the steamer that is constantly taking one class of produce, has already been fully described, but the case of the tramp steamer, making more or less of a specialty of carrying produce in cold atmospheres, presents certain ditticukies. Where the produce carried is always the same ( say always chilled beef, or always bananas), the holds can be fitted either with brine pipes, or with cold air circulation, and there is no difficulty about the matter. But it is the essence of the tramp steamer, that it takes any cargo that oft'ers, and it may happen that on one voyage it has to take chilled beef, and on another voyage fruit, dairy products, or other produce requiring cold air. To meet these requirements, a somewhat novel arrangement has been worked out by a Liverpool engineer. He provides brine circulating pipes overhead, and at the sides of the holds, and it is arranged that each of the pipes can be individually shut off. In addition, tlie pipes on the sides of the holds are provided with wood screens made of matched board, having hinged flaps at the top and the bottom, and also, in certain cases, having COLD CHAMBERS IN TRAMP STEAMERS. 123 alternate boards hinged. He further provides hinged port-holes in the fixed boards of the screen. The use of these arrange- ments is to provide a cold aif circulation, or a complete brine cooled atmosphere, with the same plant, without any appreciable alteration to the holds, and without the necessity of the air cooling arrangement that is commonly employed. When chilled meat is being carried, or frozen meat, the whole of the brine pipes, overhead and at the sides, are put into opera- tion, and the hinged boards and hinged port-holes are all arranged wide open. The cooling effect is produced directly by the brine pipes, assisted slightly by a certain amount of air circulation. When fruit or dairy produce, or anything that re- quires only cold air circulation, is carried, the overhead brine pipes are not put into operation, the side brine pipes alone being operated, and to the extent that may be necessary to produce the required temperature. The air is cooled by driving it through a duct arranged for the purpose, over the side brine pipes, out into the hold, and back by another duct, the air being kept in motion by means of a fan placed at any convenient position be- tween the outgoing and return ducts. It is stated that this arrangement has given great satisfaction, and overcomes th^ d'ffi-'ilties mentioned above. THE HEATING AND VENTILATING OF SHIPS. Both heating and ventilating have only within recent years received serious consideration, either ashore or afloat. On shore heating has been confined, in the United Kingdom, almost universally to open coal fires, and ventilation to open- ing windows and doors. In America and Canada, heating on shore has been more seriously studied for some considerable time, because of the more severe conditions of climate at certain times of the year. With the comparatively mild win- ters of the United Kingdom, a well-warmed room in cold weather has been sufficient for most individuals. In parts of America, and practically the whole of Canada, the severe winters have obliged householders to provide means of heat- ing, not onl\- living rooms, but passages, halls, etc., and this has led gradually to the development of the improved forms of heating and ventilation that are now common on both sides of the Atlantic. The same remarks apply practically to heating and venti- lating on board ship. In the great majority of cases until re- cently, and in a very large number of ships, particularly in small craft, even now, just as in large numbers of private houses on shore in the United Kingdom, heating has been ac- complished either by the familiar stove, standing in the middle of the mess room, with its chimney passing up through the deck above, as shown in Fig. i, a cabin on an Ohio ri\-er tow- boat, or in certain cases through the side of the ship. In the saloons of passenger steamers, and the mess rooms of the THE HEATIXG AND VENTILATIXG OF SHIPS. 125 executive officers in the better class of tramp steamers, the iron stove has been displaced by the fireplace, built into a fire- proof recess, similar to those employed on shore. Ventilation on board ship has been confined to opening ports and hatch- ways when the weather allowed, assisted by an occasional windsail, and by ventilators leading from the different messes, saloons, etc., to the upper deck. ■^^^ '■■ FIG. 1. C.^BIN OF AN OHIO RIVER TOWBOAT, SHOWING THE OLD FORM OF CLOSED HEATING STOVE AND PIPE. The advance of modern science, and particularly the advance of medical science, has shown this method of ventilation, or ab- sence of ventilation, to present very grave dangers to those on board who have to remain below; in emigrant ships, for in- stance, in which large bodies of men, women and children, often of all nationalities, often of not too cleanly habits, often again of not too robust health, have been confined between decks, with very little air from outside penetrating to them 126 THE HEATING AND VENTILATING OF SHIPS. whenever the weather was sufficiently bad to oblige ports to be shut and hatchways to be closed. JModern medical science teaches that in such cases diseases, sometimes unknown to their possessors, are rapidly propa- gated. It is now known that diseases are communicated by minute organisms variously known as bacilli and bacteria, and these breed rapidly under the conditions named. The same kind of thing rules on shore, where large numbers of men and women are confined in small spaces, badly ventilated, as in some of the workrooms, etc., that were common not long since in the east end of London. In addition, it is well known that consumptives are frequently sent to sea with the idea that the sea air will arrest the progress of the disease, and if there be any of these among the passengers confined between decks in bad weather, the results can only be the making of additional consumptive patients. Air is to bacilli, and to the various emanations from unhealthy subjects, what water is to dirt. Water, we know, if properly applied, dissolves dirt and other noxious substances, and if allowed to do so, will carry them away. One reason w^hy Englishmen and Americans are so generally healthy and so usually vigorous is because they are fond of water. Some of the other nations of the conti- nent of Europe, as w^e know, and particularly some of those from whom large portions of the emigrants are drawn, are not so fond of water, and the consequence is they bring to the steerage quarters germs that, if allowed under the conditions named, will breed disease, even where it is not already present or incipient. There are two methods of ventilating that may be applied both to buildings on shore and to ships afloat. One corre- sponds to the weekly thorough cleaning that the good house- wife bestows upon ever}'- room in the house. As we are some- times painfully aware, every object in the room is displaced, and every corner is subject to the vigorous cleaning process, THE HEATING AND VENTILATING OF SHIPS. 127 under which disease germs cannot exist. Similarly to rooms on shore, the 'tween decks, cabins, etc., afloat may be cleansed by throwing them open to a vigorous current of air, when the weather allows, by opening all hatchways, all ports, and moving everything and seeing that the air current penetrates to every corner, just as the housewife's broom does in the cleansing process. The other method, which is more rational, and which modern science has approved, is to direct a current of air from the place where it is to be obtained in its purest form into each living room, as far as possible into each corner of it, and to carry it away in a direction different from that at which it entered, carrying with it the disease germs, the emanations referred to, and the carbonic acid that has been formed by the breathing of the occupants of the quarters, and also in minute particles of dust that may be present. Certain conditions are necessary in connection with the ventilating air current, just described. It must be a very gentle current that cannot be felt, except under special conditions, such as when passing through the tropics. In temperate climates what is known as a draft must be avoided, and that is one reason why the ven- tilation of houses is somewhat difficult. By a draft is under- stood a current of air passing through a room or living place, such as a cabin or mess room, at such a velocity that the heat of the body is carried oflf more rapidly than the circulation of the blood, and the chemical action of the food, etc., supplies it, with the result that persons subjected to the draft catch cold. The rationale of the process is as follows: Air, when passing over any object at a higher temperature than itself, abstracts heat from it, every cubic foot of air passing over (say) a human body abstracting a certain quantity of heat, in proportion to the difference of temperature between the air and the body, and in proportion to the velocity at which the air travels, up to, a certain limit. In addition, as we know, the 128 THE HEATING AND VENTILATING OF SHIPS. human body is constantly perspiring and there is ahvays a minute fihn of moisture present on the skin. The quantity of moisture present, due to this cause, varies with the individual. Some persons perspire very freely, others hardly at all. Again, everyone perspires more when the weather is warm than when it is cold, and again more under exertion than when at rest. In any case, the air current, passing over the body, converts the moisture present on the skin, and which pene- trates through the clothes, etc., into vapor, and in doing so, extracts heat from the body. Water and other liquids, it will be remembered, can assume the form of vapor only by absorb- ing into themselves a certain definite quantity of heat. When the perspiration upon the body is transformed into vapor, nearly the whole of the heat required to enable it to become vapor is taken from the body itself. This is the reason why perspiration is so good in hot climates, and wh}" doctors, and those who are accustomed to the tropics, are so insistent upon the production of perspiration. In the tropics one frequently hears "old stagers" say they feel all right as long as they can perspire. The evaporation of the vapor cools the body, and a gentle current of air, passing over the body, accomplishes this. In temperate climates, however, and in cold climates, where it is required to keep the heat in the body, a draft of air pass- ing over it tends to cool unduly the particular part over which it passes, and to produce the unpleasant feelings we know as catching cold. Consequently, one of the first requirements is that the velocity of the air in temperate climates should be such as not to be felt. In the institutions on shore, for in- stance, which have adopted mechanical systems of ventilation, it is impossible to tell, without making special tests for the purpose, that any air current is passing. SPECIAL REQUIREMENTS ON BOARD SHIP. 129 SPECIAL REQUIREMENTS ON BOARD SHJ^. The requirements of ventilation and heating un board ship are different in a great many cases from those on shore. On shore, even in comitries where there are large variations of temperature, as in the United States, Canada, Russia, etc., dif- ferent temperatures are confined to certain parts of the year. Thus, during certain months of the winter, a very low tem- perature rules, while during certain other months of the sum- mer a high temperature may rule. In such countries as the United Kingdom, the variation of temperature is usually verj gradual indeed. On the other hand, a ship trading (say) be tween Liverpool or New York and the Cape of Good Hope, oi between Liverpool or New York and San Francisco, will ex- perience wide differences of temperature in very short periods of time. Thus, supposing the ship leaves either Liverpool New York or Boston in the depth of winter, for San Fran- cisco, the temperature will at first be very low ; it will grad- ually increase until in the tropics it will be very high. It will again decrease, and in the neighborhood of Cape Horn may be very low again, gradually increasing once more as she makes her "northing," and so on. Further, there is a very important matter that has to be con- sidered in connection with the ventilation of ships which pass through the tropics, and of others which go to other climates, viz., that of the humidity of the atmosphere. Humidity, as we know, varies considerably, and the variation has a very im- portant bearing upon the effect of a current of air upon the human body. It was mentioned above that in the tropics, for instance, if one is perspiring, a gentle current of air has a cooling effect, by evaporating the perspiration, but this is only on condition that the atmosphere itself is not already saturated with moisture, as it is at certain times of the year, and as it may be quite easily between decks at almost any time. The capacity of the atmosphere for moisture varies with its temperature, 130 THE HEATING AND VENTILATING OF SHIPS. according to the curve shown in Fig. 2. It will be noticed that the capacity for moisture goes up very rapidly after a tempera- ture of 40° F. is reached. Thus, at 40° F. its capacity is 3 grains per cubic foot; at 60° F., 6 grains; at 80° F., 11 grains, and at 100° F., 20 grains. Dry air, therefore, at a high tem- perature has a larger capacity for moisture than dry air at a lower temperature. But the ability of the atmosphere to evaporate moisture from any substance, or body of liquid, depends very largely upon its own condition of saturation. Thus, if it is already fully saturated with moisture, no evaporation will take place from the body over which it passes, and, under certain conditions, deposit of moisture may even take place from the atmosphere onto the body. The question whether moisture shall be evap- orated from any body, or be deposited from the atmosphere on the body, depends upon the tension of the vapor issuing from the body, as opposed to the tension of the vapor present in the atmosphere. The tension of the vapor in the atmosphere de- pends upon its degree of saturation, while the tension of the vapor issuing from the body depends upon its temperature. Hence, when the atmosphere is in the condition we know as "muggy," that is to say, when it is saturated wath moisture, as it is in the tropics just before the rainy season, and as it may easily be between decks, and particularly in the stoke hold under certain conditions, even with a ventilating current pass- ing, the cooling effect that should be obtained is not present. On the other hand, with a warm, dry air, used as a ventilating current, and having a large capacity for moisture, as explained above, the evaporation from the body, even with a compara- tively gentle air current, may be so great as to produce a serious cooling effect, though the air itself is comparatively warm. Hence, where a ventilating air current is employed, in temperate or cold climates, it may be necessary to add mois- ture to the air current, in order that the cooling effect, owing SPECIAL REOUIREMEXTS OX BOARD SHIP, 131 to the possible evaporation from the body, ma\- be reduced. It will be understood that while in a hot climate, warm, dried air passing over warm bodies produces a delicious cooling effect, in temperate or cold climates, during the cold season, the same warm, dry air may produce an undue cooling effect, •iU / IS / 1 1 IC / / •4^ §14 / / 2 / f / © C a: 10 C d u ^ S d / > / / / § 6 / /^ / / 4 X ^ [x 2 -^ ^ ^ r^ 10' 20' 30= 40- 50' GO- W Temperature Fahrenheit 80' 90' 100' FIG. 2. CAPACITY OF AIR FOR VAPOR, AT VARIOUS TEMPERATURES. a cooling eff'ect that is undesirable, for the same reason, owing to the evaporation of the perspiration. Hence it is necessary in some cases to add moisture to the air current. It is an axiom among heating and ventilating engineers that a moist air current of comparatively low temperature is "warmer" than a dry air current of a higher temperature. 132 THE HEATING AND VENTILATING OF SHIPS. DIFFICULTIES PECULIAR TO SHIP WORK. One of the difficulties in connection with both heating and ventilating on board ship is the fact that in bad weather the ship "knocks about." There may be said to be two distinct problems before the heating and ventilating engineer in ship board work, viz., that presented by the ordinary ship, which behaves like a cork when there is a sea on, and that presented by the modern ship, which keeps a practically even keel. Modern naval architects who have designed warships, and those who have designed ocean liners, have both striven after the same thing, a steady platform under all conditions, but for totally different reasons. A steady platform is required by the modern warship in order that the guns may be properly fought. In the battle of the Sea of Japan, it is stated that the Russian gunners were very much handicapped by the fact that their ships, being very heavily loaded with coal, and not being designed to keep an even keel, rolled very much in the heavy sea that was on, while the gunners were not practiced in firing with the ship rolling. Even the most practiced gunlayer cannot do so well with a ship rolling as with a ship steady, and hence every effort has been made, and with apparently considerable success, to provide a steady platform. The naval architects who have designed the ocean liners have striven after the same results, and with apparently almost equal success, in order to neutralize the effects oi- mal-de-mer. With the increased ocean traffic, particularly between the United Kingdom and America, the ship which can carry its passengers, even through a gale of wind, with little danger of sea sickness, commands the largest share of the traffic. Evidently, ventilating and heating problems are very much simpler in these ships than in those which knock about, and the more a ship knocks about, the more difficult are the two problems. One hears tales of ocean tramps, generally of the DIFFICULTIES PECULIAR TO SHIP WORK. 133 older type, rolling so badly, if there has been any sea on, that the galley fire could not be lighted, say between Bilbao and Cardiff, and so on. The additional difficulties presented by a rolling ship in the problem of ventilation and heating will be dealt with later on, but meanwhile it will easily be understood by anyone who has sailed in a ship which rolls very much that everything is very much strained. In old wooden ships it was quite common to see the ship's side bend inwards, as that side rolled downwards, the resilience of the timbers assisting to bring her up again. The iron shells of modern ships have not the resilience of the old wooden ships, but they must give to a certain extent, and every roll and every pitch strains every bolt, duct, etc., and produces eddies in water, air, and so on, that are used for heating and ventilating. Another difference that arises between ventilating on shore and ventilating on board ship is the air current created by the passage of the ship through the water. On shore the wind has to be taken into account in designing systems of ventila- tion for buildings, and the wind must also be taken into account in connection with ship ventilation, and in some cases with heating, but the passage of the ship through the water is constant, and by itself it creates a powerful ventilating cur- .rent. For instance, the maximum velocity of air in the ordi- nary ventilating air current on shore is 5 feet per second, and many ventilating engineers prefer even the lower velocity of 3 feet. The tramp steamer, running at from eight to ten knots, produces an air current of from 13 feet to 17 feet per second; at 16 knots,' which is a very common speed at the present day. the velocity of the air will be 27 feet per second; while that of the Liisitania is somewhere in the neighborhood of 40 feet per second. In hot climates, the air current produced by the passage of the ship will be very useful indeed in cooling the air between decks, etc., but in cold climates, and in particular in those 134 THE HEATING AND VENTILATING OF SHIPS. regions in which whahng ships, sealers, etc., have to cruise, the air current is a very serious matter, and must be warmed, as will be explained, and possibly humidified, before being allowed to penetrate between decks. Ventilation of ships has one important advantage over ven- tilation on shore in some cases, notably in some of the large and smoky towns, inasmuch as there is no difficulty whatever in ob- taining absolutely pure air, rich in ozone, the most powerful oxidizing agent available, and there is a complete absence of any necessity for cleansing the air. On shore, in large towns, one of the most important matters in connection with the ventilation of public buildings consists in the purification of the air. Various devices are employed, and in all of them the quantity of dirt, — of black coaly matter such as steamers too often have distributed over their decks when burning bad coal, — that is deposited in the receptacle provided for it, is astonishing. METHODS OF HEATING AVAILABLE. The following methods of heating, which are in use on shore, are all available more or less for use on board ship, some of them, as will be explained, being more easily adapted under all conditions, and some of them again not being suit- able for ships that knock about in a sea way, but being quite practicable for those which keep an even keel : 1. The open fireplace, or closed stove burning coal. 2. Pipes or apparatus in which hot water is circulated. 3. Pipes and apparatus into which steam is delivered. 4. Apparatus in which electric currents are employed. 5. Apparatus in which the air is warmed, humidified, and, if necessary, cooled. The last form of apparatus, it will be noted, combines heat- ing and ventilating, and on shore that is the latest develop- ment. Many of the large new buildings, such as hospitals. METHODS OF HEATING AVAILABLE. 135 government and municipal buildings, stock exchanges, etc., are warmed and cooled, where necessary, entirely by means of the air current, which is taken hold of, cleaned, dried where necessary, warmed where necessary, moistened where neces- sary, and so on. The latest development of heating and ventilating on board ship, on the great ocean liners and in men-of-war, is on these lines. The old fireplace and stove, though it still holds a large place in the warming of rooms on shore, has long been con- demned as inefficient, because the larger portion of the heat xberated by the combustion of the coal passes up the chim- ney. It is not necessary to remind marine engineers that a coal fire will burn only with a draft, and that the products of combustion are carried up the chimney, necessary with all coal fires, and with it the larger portion of the heat liberated. A certain quantity of heat passes out into the room from the glowing fire, by radiation, but it does not heat the air of the room, because the air is almost transparent to heat rays. The rays of the sun pass through our atmosphere without heating it to anything like the extent to which they heat any object against which they impinge, and the same thing holds with heat rays from a fire. Rooms, cabins, saloons, etc., however, in which either open fire places or closed stoves are used, are appreciably heated after the fire has been burning for some time, unless they are subjected to cold air drafts, or unless the walls of the cabin, etc., are also the unprotected sides of the ship, and the heat is thus conducted away; because the heat rays emanating from the glowing fuel and striking upon the furniture of the room, the bulkheads, etc., heat them up, and they in turn heat the air with which they are in contact, con- vection currents being set up in the well-known manner, and the whole room being thoroughly warmed. Where closed stoves are employed, and particularly where a certain length of iron chimney connected with the stove is 136 THE HEATING AND VENTILATING OF SHIPS. within the room to be warmed, the heating effect produced is considerably greater than with an open fireplace, because of the radiation from the stove itself, and from the pipe. A somewhat interesting method of heating a cabin, which the writer remembers to have seen in his \'ounger days, may be worth mentioning. In an old wooden frigate of the British Navy, in ivhich he served, the commander had his cabin heated in cold climates, as when going around Cape Horn, by an 8- inch spherical shot, heated to redness and suspended from the deck above by an iron rod screwed into the plug hole of the shot. The ship was armed partly with old 8-inch smooth bore guns firing spherical shot, and as these always had a plug, it was an easy matter for the armorer to screw into it an iron rod having a hook at the other end. for suspending from over- head. The result was very good. The commander's cabin was a fairly large one, and it was well warmed, but the pro- cess of heating was rather troublesome. The shot had to be heated in the galley fire. For many ships, tramps for instance, sailing ships, and the numerous coasting vessels, barges, and so on, the coal stove with its chimney passing up through the deck will probably long remain the only method of heating, though some of the apparatus to be described later would be found very suitable for tramps, whalers, sealers, etc., and even for the five-masted sailing ships that are still in being. THE SYSTEM OF HEATING BY HOT WATER. This is the favorite system on shore, but so far it has not found much favor on board ship, because of the difficulty mentioned above, introduced by the motion of the ship, strain- ing different parts of the apparatus, and causing currents in the water with increased chances of air lock. Heating by hot water is a very simple matter. In its simplest form there is a boiler specially designed for heating water to a temperature HEATING BY HOT WATER. 137 Splash Plate /?! Balance Tank Supply Tank KJ I t Shade mMMmMMzmMMMmMm. I \ \\ W \ Main Cabin Balance Tank Deck Deck Deck mnmm ■nMk _i> c Aft D Stoke Hold Heater Forward w///////m/MMMMM///m FIG. 3. HOT-WATER HEATING SYSTEM APPLIED TO A YACHT. RADIATORS CONNECTED BETWEEN MAIN RISER AND RETURN J ALSO BETWEEN PIPE FROM BALANCE TANK AND THE RETURN. 138 THE HEATING AXD VENTILATING OF SHIPS. of about i8o degrees F., and a system oi pipes connected to the bciler in such a manner that the water is kept continually circulating from the hotter portion of the boiler through the pipes, and the radiators, as they are called, back to the boiler. An addition, however, is usually made to the system, in the shape of a storage tank. Fig. 3 gives a diagram of the usual arrangement of hot-water heating systems, as applied on shore, and as it has been applied in certain cases on board ship. The diagram shown is taken from a hot-water system fitted on board a steam yacht. The special boiler employed for heating the water may be displaced by steam from the boiler supplying the ship's en- gines, or from a special boiler arranged for the purpose, or the exhaust steam from the auxiliary engines may be used. Both of these plans are adopted on shore, the heat from the steam being delivered to the hot-water service by an appa- ratus which goes by the barbarous name of "calorifier," one form of which is shown in Fig. 4. This will be recognized by marine engineers as a feed-water heater. There is the usual cylinder, which may be fixed vertically or horizontally, with pipes inside in which the water to be heated circulates, steam passing all around them in the remaining space inside the cylinder. Or the reverse arrangement may rule : the steam may pa^^s through pipes inside the cylinder, and the water occupy the space surrounding. The calorifier has been arranged, in certain cases, with au- tomatic steam control. Fig. 4 shows Royle's automatic steam control. A rod of steel is stretched between the top plate of the apparatus and the casting forming the bedplate, and is provided with a pair of nuts, enabling it to be tightened or loosened. A valve controlling the steam, supply is fixed about the middle of the rod, as .shown, the opening of the valve being controlled by a spring on the one hand, and the rod on the other. The expansion and rortraction of the body of the HEATING BY HOT WATER. 139 apparatus, with the heat delivered to it, opens or closes the steam valve, by pushing against the head of the valve, or re- leasing it, thus increasing or decreasing the supply of steam. Another form of control consists of a bent tube, inclosed in FIG. 4. — EOYLE CALORIFIER WITH AUTOMATIC CONTROL. a box, operating the steam valve in very much the same manner. On shore, hot-water heating appliances are often combined with hot-water supply. This arrangement is very common in private houses, and also in hospitals, infirmaries, etc. When *.40 THE HEATING AND VENTILATING OF SHIPS. this arrangement rules in large establishments, it is usual to have a hot-water storage tank, in addition to the calorifier. The arrangement is as follows : Steam from the boiler sup- plies heat to the calorifier, the condensed steam being carried back to the hot well. The water pipes from the calorifier are connected to the storage tank, and the water is kept con- tinually circulating through the storage tank, and through the calorifier. The supply of hot water for the establishment is taken from the storage tank. When very little water is used, the temperature of the water in the storage tank increases, and the controlling apparatus of the calorifier reduces the supply of steam, or completely shuts it off, until water is used again. When water is used, cold water, as will be explained, taking its place and the temperature in the storage tank being re- duced, the temperature of the calorifier is also reduced and the steam is readmitted and so on. High and Low-Pressure Hot-Water Heating. — There are two methods of heating by hot water, known, respectively, as high and low pressure. The main difference between the two is in the temperature to which the water is raised, and the velocity at which it circulates. In the high-pressure hot- water system, small pipes, usually of %-inch bore, carry a small quantity of water at a high temperature and a high ve- locity, while in the low-pressure system larger pipes, from i to 6 inches bore, carry a larger quantity of water at a lower temperature and at a lower velocity. There is a further dif- ference between the two systems also, in that the high-pressure system is hermetically sealed, an air vessel being provided to take up the expansion of the water mentioned below. In the low-pressure system a balance tank is usually provided, as shown in Fig. 3, which performs the double office of taking up the expansion of the water and supplying any waste that may take place. DIFFICULTIES IN HEATING BY WATER. 141 DIFFICULTIES IN CONNECTION WITH HEATING BY WATER. There are two principal difficulties to be encountered in heating by hot water — the expansion of the water itself and the presence of air in the system. Water expands approxi- mately 1/23 of its bulk between its point of greatest density (39 degrees F.) and its boiling point at standard barometric pressures. The following are the actual figures : Temperature of the Water. Relative Volume. 39° F. I. 100° F. 1.0075 200° F. 1.038 212° F. 1043 300° F. . 1.086 400° F. 1. 148 500° F. 1.223 600° F. 1. 310 The expansion of the water must be provided for, and in the high-pressure system this is done by the expansion pipe, mentioned above, fixed at the highest point of the system and connected to it. The arrangement is merely a pipe calculated to accommodate a certain quantity of air, in proportion to the quantity of water in the system, and to the temperature of the water. The proportions recommended by Walter Jones, a past president of the Institution of Heating and Ventilating Engineers of Great Britain, are as follows : With water at a temperature of 212 degrees F., the expan- sion pipe should have an air space equal to 1/20 of the water space in the whole apparatus. At 300 degrees F., the air space should be one-eighth of the water space; at 400 degrees, one- fifth ; at 500 degrees, one-third, and at 600 degrees, one-half. The operation of the expansion pipe is really that of a buffer. As the water expands it is forced upwards, and the air in the expansion pipe is compressed. If the expansion 142 THE HEATIXG AND VEXTILATIXG OF SHIPS- pipe and the whole of the system is sufficiently strong to withstand the pressure, and if the quantity of air in the ex- pansion pipe is sufficient, when the water cools, the air ex- pands, and equilibrium is maintained in the system and it works safely. The great danger of the high-pressure system is the possibility of explosion, owing to the very high pressures that are sometimes present. The expansion pipe, it will be seen, acts very much as a safety valve, in addition to its operation as a buffer. With the low-pressure system there is no danger of ex- plosion, except in case of frost in any part of the system, a matter that will be dealt with below ; because, as seen in Fig. 3, the expansion of the water is fully provided for by the balance tank. The increased volume of the water produced by the increased temperature meiely flows into the balance tank harmlessly, and when the system cools, the balance tank re- supplies the water required to fill the pipes. The balance tank or auxiliary tank is usually connected to the water-supply service, so that any shortage of water in the system caused by leakage or evaporation is made up automatically. The balance tank should be fixed above the highest part of the pipe and radiator system. THE AIR TROUBLE. The air trouble is often a very serious one in both high and low-pressure hot-water systems, and it is the trouble that is likely to arise in connection with hot-water systems on board ship, and that is one reason, the writer believes, why hot-water heating has not been adopted. As marine engineers know, air is always present in water. It is lighter than water, and always finds its way to the highest part of the hot- water system, and if allowed to do so will come away harmlessly. On the other hand, if there are bends, particularly in the forms of inverted U's, dips, etc., in the pipe system, air is sometimes trapped, and THE ARRANGEMENT OF HOT-WATER HEATING SYSTEMS. 143 becoming compressed by the expansion and flow of the water, sometimes operates against the flow to such an extent as to even stop it altogether. Engineers are all familiar with the troubles that arise with air when water is being pumped. In particular, the old trouble of the air lock in the bend of a siphon is well known; air, if allowed to collect in the bend, becoming gradually compressed and interrupting the flow of water. Something similar to this is of somewhat too frequent occurrence with hot-water systems, and it will easily be understood that when a ship is knocking about, and when currents are produced in the water circula- tion, quite independent of its circulation proper, and when possibly air may leak into the system through joints being strained, air locks may occur in certain parts of the system, with the result that the circulation of the water is interrupted, heating at the radiators ceases and dangerous heating may take place at the boiler or calorifier. The air locks are easily guarded against by the provision of air valves, which allow the air to escape under the conditions that have been named. It is usual on shore to place either small air pipes, or air valves, at the top of the system, and also at the tops of all bends, etc., and at each radiator, so that any air that is trapped may come away harmlessly. THE ARRANGEMENT OF HOT-WATER HEATING SYSTEMS. There are, broadly, two methods of arranging hot-water heating systems, both on the high-pressure and low-pressure working. It is necessary, as will easily be understood, for the water that is delivering heat to the rooms to be warmed, in order to make a complete circuit. Setting out from the hottest part of the boiler or calorifier it ascends through what is usually known as the riser or flow pipe, to the highest part of the system, and is connected to the balance tank above that, or to the expansion pipe, as explained. Another pipe rises from 144 THE HEATING AND VENTILATING OF SHIPS. the coolest part of the boiler or calorifier to the same level as the riser, or a little below it. This is the return pipe, and in one method of distribution the heating appliances are connected between these two, very much as electric lamps are connected between the two supply cables, and as shown in Fig. 5. The heated water passes from the boiler through the riser, through the different heating appliances, and returns to the FIG. 5. TWO-PIPE SYSTEM, LOW-PRESSURE HOT WATER. boiler by the return pipe, becomes again heated in the boiler or calorifier, and repeats its journey. Where there are two or three floors or decks to be heated from the same apparatus, the different heating appliances are connected to the riser or flow pipe and to the return pipe of each floor or deck. One heating appliance may be connected between the flow and return, or two or more, according to the difference in temperature be- tween the two, and to the sizes of the heating appliances and the quantity of heat required for them. Where a single THE ARRANGEMENT OF HOT-WATER HEATING SYSTEMS. 145 heating appliance is connected between the flow and return it would correspond with the usual arrangement of incandescent electric lamps connected in parallel. Where two or more heat- ing appliances are connected between the flow and return, in such a manner that the water flows through them consecu- tively, the arrangement would correspond to the parallel series arrangement of incandescent electric lamps. There is a third arrangement, corresponding roughly to the series system adopted in electricity, as with a number of arc FIG. 6. CONNECTIONS OF RADIATOR TO A HOT-WATER SYSTEM WITH TWO-PIPE DISTRIBUTION. lamps employed in street lighting, from a Brush arc machine. In this system the flow pipe is taken to the highest part of the service, say to the highest deck, or a little above, if possible, in the funnel casing, and is there connected to the balance tank or the expansion pipe in the usual way; but the two connec- tions to the heating appliance are. made to two portions of the return main pipe, as shown, the heating appliance being bridged across that portion of the pipe. This corresponds to the method known in electrical work as shunting. 146 THE HEATING AND VENTILATING OF SHIPS. Fig. 7 is a diagram of a number of radiators fed on the one- pipe system, the radiators being bridged across a certain length of pipe, but, as will be noticed, two radiators are fed from one bridge, and in this case the connection to the balance tank is separate. Fig. 6 shows the connections between a single radiator and the two pipes on this system. Fig. 8 is a diagram of a system in which the exhaust from a gas engine is used to heat the water, which is carried to a tank above the fIG. 7. DISTRIBUTION OF LOW-PRESSURE HOT WATER ON THE ONE-PIPE SYSTEM. highest radiator, connection being made from the hot-water tank to the balance tank above; and the distributing pipes commencing from the hot-water tank and returning to the water-jacket of the engine, and thence to the heating appa- ratus, the radiators being bridged singly across short lengths of the pipe. Practically, with this method, the heating ap- pliance is fed by a shunt current from the return supply main of the service. THE ARRANGEMENT OF HOT-WATER HEATING SYSTEMS. 147 It will be understood that what is required for the supply of any heating appliance is a sufficient difference of tempera- ture between the inlet and outlet valves, and a sufficient supply of water to keep up a continual flow through it, and of such a temperature that the requisite quantity of heat will be given off by it. In practical hot-water heating, the difference Exhaust if^ (7=- v_/= = = = Cold Water Cistern Hot Water Tank 7^ Rot Water Draw-off - Overflow - Cold Water Supply 1 Cold Water Feed \' \ FIG. 8. DIAGRAM OF A HOT-WATER SYSTEM DRAWING HEAT FROM THE EXHAUST OF A GAS ENGINE. (BRITISH INSTI- TUTION OF HEATING AND VENTILATING ENGINEERS.) of temperature between the two ends of any radiator is usually not more than lo degrees F., and it is evident that this can be obtained either by having a very small difference of tem- perature between the main flow pipe and the return flow pipe, but with comparatively large pipes, bridging the heating ap- pliance between the two pipes, as explained; or by having a larger difference of temperature between the ends of the flow pipe and return pipe at the source of heat, with smaller pipes, and a smaller quantity of water flowing, but with a larger dif- ference of temperature in any given length of pipe. 148 THE HEATING AND VENTILATING OF SHIPS. To take an instance, supposing that ten radiators are to be supplied from a given source of heat, and that each radiator requires a difference of temperature between its inlet and out- let valves of lo degrees, as explained, and a flow of ten gallons of water through it per hour. Evidently this can be supplied by a system of large pipes, giving lOO gallons per hour, but with a difference of temperature between the main flow and return pipes of only ii or 12 degrees F. at the source, or it can be supplied by pipes carrying only 10 gallons per hour, but with a difference of temperature between the main flow and return pipes, at the source of heat, of no to 120 degrees F. Practical men on shore incline very much to the latter system, because it enables smaller pipes to be employed, and they caution engineers to avoid the former system, because the water tends to become "short circuited"; that is to say, the nearer radiators receive the major portion of the heat. Evi- dently the matter is only one of proper arrangement. It should be perfectly practicable, by a proper system of pipes, to arrange that the difference of temperature between the main flow and return at the top of the system shall be very nearly the same as that between them at the lower por- tions of the system. What is required, of course, is proper proportion in the size of the main and return pipes, and proper proportion in the pipes connecting them to the radiators. If the main flow and return pipes are small, and if again the radiators on the lower decks are connected to them by com- paratively large pipes, they will undoubtedly short circuit the system. FORMS OF HEATING APPARATUS WITH HOT WATER. 149 FORMS OF HEATING APPARATUS WITH HOT WATER. Hot-water apparatus for heating rooms, cabins, alleyways, corridors and so on may consist simply of pipes laid around the rooms, the saloons, etc., and through the corridors ; or, as is more frequently arranged, what are termed "radiators" may be employed. The term radiator is a misnomer. As is explained below, the heat delivered by the heating appliance is only partly by radiation. On the other hand, the plain pipes that were employed in the early days of steam and hot-water heating are quite as much radiators as the forms of apparatus usually so denominated. Any pipe in which hot water or steam is passing gives off heat at a rate directly proportional to the difference of temperature between the water and the air on the outside, and again in direct proportion to the extent of surface exposed, and directly to the conductivity of the sub- stance of which the pipe is composed, and inversely in pro- portion to its thickness. This law in its simple form is, however, applicable only to small differences of temperature and small values of tempera- ture of the surrounding air. The heat is given out in two ways, by radiation and by convection. Heat passes from a heated body in all directions, through the air and whatever substances may surround it, by what is called radiation. Ra- diant heat, as the heat delivered by radiation is termed, has the peculiar property that it passes through air without de- livering much heat to the molecules of the air itself. Heating from fires, stoves, etc., though it is due almost entirely to radiation, arises from the fact that the radiant heat is ab- sorbed by the articles of furniture in the room, by the walls, etc., and is afterwards given out by them, partly by re-radia- tion, partly by convection, and partly by conduction. In addi- tion to the above, any heated body present in air, as in any room, cabin, corridor, saloon, etc., gives rise to convection air currents. The air in the neighborhood of the heated body 150 THE HEATING AND VENTILATING OF SHIPS. becomes warmer than that slightly removed from the body and is pushed upwards by the weight of the colder air, a fresh supply of air taking its place, becoming heated again, and so on, the result being that a continual circulation of air is pro- duced, until the temperature of the room is raised to that of the heated body, or as long as heat is delivered to the body, and is carried off by the surrounding air. Every heated pipe and radiator, therefore, gives off heat both by radiation and by convection, or, as it is sometimes termed, by air contact. Different bodies have different radiating properties. Cast iron, for instance, radiates 0.65 B. T. U. per square foot per hour for each degree F. difference of temperature between itself and the surrounding atmosphere; wrought iron, 0.57 unit; rusted cast or sheet iron, 0.67 unit. The heat distributed Dy convection is independent of the nature of the heated body, but varies with the form of the body. Cast iron, wrought iron, wood, etc., if heated to the same temperature, give rise to the same distribution of heat, but the quantity given off varies with the form. The quantity of heat delivered by any hot- water pipe or radiator depends directly upon the difference of temperature between the body and the air, upon the surface of the heated body exposed to the air, and upon its form. This again, as with radiation, is true only for low figures. When the difference of temperature between the heated body and the surrounding air does not exceed 30 degrees F., and when the temperature of the air surrounding the body does not exceed 60 degrees F., the above laws for radiation and for convec- tion or air contact hold good; but when the difference of tem- perature exceeds the above figure, and when the temperature of the air surrounding the heated body exceeds 60 degrees F., the rate at which heat is delivered to the air increases, and at a very much more rapid rate than the increase of the dif- ference of temperature. The French savants Dulong and Petit experimented upon FORMS OF HEATING APPARATUS WITH HOT WATER. 151 the subject some years ago, and their experimental facts have been confirmed by another French savant, Peclet, whose name will be remembered in connection with the laws of transmis- sion of heat in refrigerating matters, and they have produced some very complicated formulae, which need not be given here, but from the results of which Mr. Thomas Box, whose standard book on ''Heating'' is well known, has worked out a table of what he terms ratios, representing the number by which the result of the simple laws referred to above must be multiplied, to give the correct results. The multiplier or ratio, as Box calls it, ranges from unity up to six. That is to say, the results obtained by applying the simple laws given above, for the quantity of heat delivered by a hot water or steam pipe, with a certain difference of temperature, and the other conditions as mentioned, have to be multiplied by a factor varying from a trifle over one up to six, to obtain the actual results. It will perhaps be sufficient if a few figures are given. For a difference of temperature of io8 degrees, which is ap- proximately that which would rule between the temperature of water in a hot-water radiator at 173 degrees F. and the sur- rounding air under conditions showing a temperature of 65 degrees F., the multiplier is 1.4. For a difference of tempera- ture of 160 degrees F., which is what would probably rule with steam heating, the multiplier is in the neighborhood of 1.6. Approximately, therefore, for the conditions of heating by hot water or steam, the laws given above will show the quantity of heat delivered to the air, when a multiplier of 1.5 is brought into the equation. Taking ordinary working conditions, the formula for the quantity of heat delivered by a hot-water radiator would be as follows : Q =R (T -T.) X 14 + A (T - 70 X 1.4, where Q is the quantity of heat in B. T. U. delivered to the 152 THE HEATING AND VENTILATIKG OF SHIPS. air per hour, for each square foot of surface of the radiator exposed to the air; R is the rate at which heat is delivered by radiation ; A that by convection, and T and T^. are the tem- peratures of the radiator and the surrounding air. It was mentioned above that the form of the heated surface exercises an influence upon the heat dehvered to the air by convection currents, or, as it is termed, by contact. Thus a sphere delivers very much more heat per unit of surface, and with a given difference of temperature, than either a vertical or a horizontal cylinder. The apparatus most employed in heating, by hot water or steam, is either a horizontal cyl- inder in the form of pipes fixed as explained, or vertical pipes in the forms that have been given to radiators. For hori- zontal pipes, the quantity of heat delivered to the air in con- tact with the pipe, for every degree F. difference of tempera- ture, and for every square foot of surface of pipe, for the pipes usually employed, is as follows : With 2-inch pipe, 0.728 unit; 3-inch, 0.626; 4-inch, 0.574; 6-inch, 0.523 unit. These figures are the values of A. For radiators the prob- lem is rather more complicated, in the matter of con- vection. The French savants referred to have threshed the matter out, and have produced some formulae applicable to all cases, as a result of their experiments, and the formulae are appar-- ently pretty correct in practice. They are very complicated, however, and it will be perhaps sufficient if it be mentioned that heat liberated by convection from a sphere is consider- ably more for any given surface, and in a given time, than from a cylinder ; and again the heat liberated from a hori- zontal cylinder, of a given diameter, is usually more than from a vertical cylinder of the same diameter. The rates for horizontal cylinders given above were taken from Mr. Box's book. The rate with vertical pipes does not appear to have been FORMS OF HEATING APPARATUS WITH HOT WATER. lo3 measured, but Professor Carpenter* and others have made some very interesting experiments upon radiators of different forms, heated by steam and hot water. The radiators experi- mented on were of various forms, among them those shown in the drawings; also some consisting merely of iron pipes of different diameters and different lengths, arranged some hori- zontally and some vertically; also pipes and other arrange- ments with ribs cast on them, brass tubes plain and corru- gated, and other forms. The net result of the experiments conducted by Carpenter, and by others whose work he quotes, appears to be a liberation of heat, the combined effect of radi- ation and convection, ranging from 1,25 B. T. U. per square foot of surface per i degree F. difference of temperature be- tween the heated surface and the surrounding air, per hour, up to 2.89 B. T. U. The best resuhs are obtained with pipes or radiators of small sectional area, the highest having been obtained from a plain wrought-iron pipe i inch in diameter, 100 feet long, m a single horizontal line. Increasing the size of the pipes or the radiator equivalent, though increasing the total amount of heat liberated from a given length of radiator or pipe, de- creases the rate per square foot per degree, etc. Fixing ribs upon the outsides of pipes, which has been adopted by some manufacturers, with the idea that the increased surface gives increased liberation of heat, are shown by the experiments quoted by Professor Carpenter to have the opposite effect. Thus, a plain cast-iron pipe without ribs liberated 2.54 B. T. U. per degree per hour, while a similar pipe, ribbed, liberated only 1.72 anits. Cast iron gives better results than wrought iron, on account of its higher radiation, apparently, and brass gives a very low result. As mentioned above, the rule with practical heating and ventilating engineers is to estimate for a libera- tion of 1.6 to 2 units per degree F. per square foot per hour. • Cornell University, Ithaca, N. Y. 154 THE HEATING AND VENTILATING OF SHIPS. In the writer's view, in laying out heating appliances, it will be wise to estimate for the liberation of heat at a rate not exceeding 1.5 B. T. U. per square foot of surface of the ra- diator exposed, per i degree F. difference of temperature, per hour. It will be easily understood that the above are standard figures, and that for any given increase of temperature de- sired, say of the air in a room, all that is necessary is to con- vert the rate of liberation of heat given into increase of temperature of air, and then to divide by the number of degrees by which the air temperature is to be increased. Thus, I B. T. U. will raise by i degree F. the temperature of about 55 cubic feet of air. if in the neighborhood of 60 degrees F. ; or, it will raise the temperature of 11 cubic feet by 5 degrees F., and so on. All that is required to find out what quantity of heating surface is necessary, is to apply the following C (7— 70 formula : S = where S is the radiat- 55 X 1.5 X {T, — T,) ing surface in square feet; C is the cubical contents of the room to be heated, in cubic feet ; T\ is the temperature of the air when heat is applied; T that to which it is to be raised; T2 that of the radiator. In the above it will be understood that the question of venti- lation has not been considered at all. Heating appliances are considered entirely by themselves, and on the supposition that the common practice is followed, of placing the heating ap- paratus in any convenient position in the cabin, saloon, etc.. and irrespective of any mechanically-produced air current; and the heating eft"ect produced by the apparatus is such as would follow on the lines of what would be called natural ventila- tion. The temperature of the room in which the appliance is fixed is raised to a certain figure by the operation of radiation FORMS OF HEATING APPARATUS WITH HOT WATER. 155 and convection currents as explained, but without any control having been exercised over the air. Also, in the above formula the heating up of air only is flG. 9. DOUBLE-TUBE AND SINGLE-TUBE RADIATORS FOR STEAM OR HOT WATER, considered when the room is cold and heat is turned low ; but the formula also applies when the room is at its required tem- perature, and the heating appliance has to make good the heat 356 THE HEATING AND VENTILATING OF SHIPS. lost by conduction through the walls of the room, by air cur- rents, etc., if T is taken as the temperature to which the air in the room would otherwise fall in any given time. This is dealt with farther on, when explaining how the heat lost from the room is made up. Another point that should be mentioned is the efifect of the velocity of the flow of water through the pipes. The velocity of the flow of air over radiators, etc., and its effect, will be dealt with when discussing the heating of air, but it may be mentioned that, as is well known to marine engineers, the rate of delivery of heat from a hot-water pipe increases with the velocity of the water, up to a certain figure. The writer believes that experiments have not yet been made with a view of showing what the critical figure is, but, within the limits of ordinary hot-water heating appliances, every increase of the rate of flow tends to increase the heat delivered. Another point should be mentioned in connection with both FIG. 11. KORTING's radiator FOR STEAM OR HOT WATER. CONSISTING OP PARALLEL HORIZONTAL RIBBED PIPES, CONNECTED TO HEADERS AT EACH END. FORMS OF HEATING. APPARATUS WITH HOT WATER. 157 FIG. 10. — EOYLE RADIATOR ON SIR THOMAS LIPTON's YACHT. ROW's TUBES GIVE FLEXIBILITY AND LARGER HEATING SURFACE. Steam and hot-water heating. The radiator has been de- veloped because of the necessity of arranging a large surface of pipe within a comparatively small compass, and in such a form that it can be fixed in rooms, etc., without inconvenience. Forms of the radiator are shown in Figs. 9, 10 and 11. As will be seen, the radiator is simply a pipe arranged in a par- ticular manner. A favorite form consists of a number of vertical columns, each column consisting of a single pipe, a 158 THE HEATING AND VENTILATING OF SHIPS. loop of pipe, or two, three or four columns ; the whole of the columns being held together and standing on feet, raising them a few inches above the floor. The pipes forming the columns are arranged in more or less ornamental form, and their outside surfaces are given the forms shown, in order to present as large a surface as possible to the air which passes through them and over them. As will be explained when dealing with warming air by means of radiators, special ar- rangements are sometimes made to direct the air over the FIG. 12. RADIATOR FOR HOT WATER OR STEAM. NATIONAL RADIATOR COMPANY. whole of the surface of the radiator before passing into the room. The columns of which the radiators are composed are ar- ranged with channels at top and bottom, which, when the columns are assembled together, form pipes for the steam or water, both communicating with the tubular spaces inside the columns. Also, as will be seen from the drawings, it is ar- rangefi in nearly all forms of radiators that connection can be made to either end of the channels referred to, at top or bottom, so that the hot water or steam can be brought to FORMS OF HEATING APPARATUS WITH HOT WATER. 159 either end of the radiator, and where a return connection is made, that also can be taken from either end. This is the usual form, but it will be understood that any design may be arranged that will provide for the connection between the water or steam supply and the radiator, and for the circula- tion of the steam or water through the individual columns, and for the connection to the return, where there is one. FIG. 13. B.^TTERY OF COLONI.AL R.^DI.\TORS FIXED VERTICALLY. Radiators are arranged to go into all sorts of confined spaces, such as cabins. Figs. 12 and 13 show the Colonial radiator, made by the National Radiator Company, of Chicago and London, which has been fitted on board H. 'SI. S. King Edzvard VII. It is arranged to be fixed on brackets, secured to bulkheads, at any convenient height, as shown. One method of fixing to walls is shown in Fig. 14. Its great feature is, as will be seen, the fact that it will he close to a bulkhead, or to the ship's side. It is made in three sizes, respectively, 29, 23 and 16^ inches long, all 131^ inches high, and 2?^ inches deep. When fixed a little way from the bulkhead, the space occupied is very small, and it can be built into any convenient form, several of any size being connected together by right and left-hand threaded npples, and arranged side by side vertically 160 THE HEATING AND VENTILATING OF SHIPS. or horizontally, as may be convenient. Thus, a numher of them may be arranged mider the seats around the stern of a ship, or in any other situation. A form of radiator that is a great favorite in hospitals is fitted with hinges at one end, the valves passing through the FIG. 14. — SIDE OF SINGLE-LOOP RADIATOR. NATIONAL RADIATOR COMPANY. hinges so that it can be turned back against the v/all or brought forward into the room. It appears to the writer that this form would also be useful for cabins and other confined 5ioaces on board ship. It is shown in Fig. 15. Radiators can be arranged to suit any style of decoration, and practically to fit any si>ace. They may be painted to FORMS OF HEATING APPARATUS WITH HOT WATER. 161 match the decorations of the cabin or saloon, and they are fre- qiientl}^ ornamented in various ways, the castings from which they are formed having an ornamental pattern upon them, the decorative work being afterwards added by artists. In the hot-water radiator it is usual to bring the connection of the supply pipe to the top of the radiator, and that from the re- FIG. 15. SWINGING RADIATOR OF NATIONAL RADIATOR COMPANY. THE VALVES ARE IN THE HINGES. turn pipe to the bottom. An air cock or valve should be fitted on each radiator at the end, away from the supply service and at the top, and it should be seen that it is always in order. For positions where appearance is not of consequence, as in the forecastle, and in emigrants' quarters, the radiator may take the form of a grid of iron pipes. There is another system of hot-water heating that has been 162 THE HEATING AND VENTILATING OF SHIPS. fixed in some yachts, known as the Reck, which is the inven- tion of a Danish engineer of that name. In this system the heating effect of steam directly injected into a body of water is combined with the effect of the same steam passing around a body of water, on the lines of the feed-water heater. There is a boiler for generating steam, fixed at the lowest part of the system (it would be in the stoke hold on board ship), and a little above the boiler is an apparatus termed by the inventor a "reheater," a device similar to a feed-water heater. At the top of the system is the principal heating apparatus for the water. It is termed by the inventor the "circulator." There is the usual expansion tank above the circulator, and imme- diately below the circulator is another apparatus called the condenser. Steam is taken directly from the boiler by a pipe to the reheater, where it passes around the pipes, through which the return water from the circulating system is passing, and another pipe is taken from the top of the reheater to a point above the circulator. This pipe is curved around at the top into an inverted U, and is brought into the top of the cir- culator. From the lower part of the expansion tank a pipe passes to the upper part of the circulator, and" a second pipe is also taken from the lower part of the expansion tank along the upper portion of the upper rooms, or the upper deck, to be warmed, and from this the circulating pipes to the radiatorr. are taken. The expansion tank is fitted with a cover; a second pipe passes from its upper part to the condenser, and another pipe from the condenser to the water space of the boiler. The return pipe of the circulator system, which passes along the lower rooms, or the lower deck, to be heated, is connected to the reheater, a second pipe conveying the heater water to the circulator. The working of the arrangement is as follows : The cir- culator, being full of water which has returned from heating the radiators, is heated by steam delivered directly from the FORMS OF HEATING APPARATUS WITH HOT WATER. 163 boiler through the pipe mentioned. When heated, it over- flows into the expansion tank and thence to the pipe forming the main flow pipe of the hot-water circulating system. Branch pipes connect the main flow pipe with the return pipe at the bottom, and radiators are connected to these branch pipes in a manner which may be compared to the shunt system in electrical work. The radiators are bridged or shunted across a portion of the vertical pipe. The heated water, hav- ing passed down through the vertical pipes and the radiators, returns to the reheater by the return pipe, is there heated by the steam circulating around the pipes through which the water is passed, and thence again commences its outward journey, passing up the pipe to the circulator, where it is further heated by steam, and so on. The condenser is similar to the usual surface condenser, with which marine engineers are familiar. It consists of the ordinary cylinder, with a series of tubes, arranged either in a vertical or horizontal position as may be convenient. This device condenses the steam which is delivered in the circu- lator, but which is not fully employed in heating the water for the circulation system, and which finds its way through the pipe into the expansion tank, and thence rising in bubbles, in the well-known manner, passes out of the top of the expan- sion tank by the pipe leading to the condenser. It is con- densed by the flow of the water coming from the reheater, the condensed water being carried off by a pipe to the water- space in the boiler. It will be noticed that the water receives heat from the steam at three places ; in the circulator itself by direct con- tact, in the reheater and in the condenser. Further, the de- livery of steam from the circulator into the closed expansion tank, by setting up a certain pressure above the water in the expansion tank, causes the water to run freely in the circu- lating system, quite apart from the circulation caused by 164 THE HEATING AND VENTILATING OF SHIPS. difference of temperature, etc. The water-supply service is usually connected to the expansion tank with a ball cock, in the usual way, cold water being added to the system when re- quired and passing directly into it. The advantage claimed for the Reck system is, that heat will be got up very much more quickly by its aid than with the ordinary system of hot-water service that has been ex- plained. On the other hand, it is rather more complicated than the simple hot-water system, but the apparatus of which it is composed should present no difficulty to marine engi- neers. The main source of heat is usually a boiler on shore, and, in places where there is no other steam supply, can, of course, be steam from the ship's boilers, or the exhaust steam from the engines or auxiliaries, or any other convenient source. HEATING BY STEAM. The arrangements for heating by steam are practically the same as those for heating by hot water, with a few modifica- tions, due to the difference between the flow of steam and hot water, and to the necessity for draining the condensed steam out of the heating appliances. The source of heat may be the same as with hot water, but arranged, where it is a boiler, to generate steam at low pressure, instead of merely to heat the water. On board ship, steam from the boilers is usually em- ployed, reduced to the required pressure by one of the well- known forms of reducing valve. On shore, pressures of about 5 pounds per square inch gage are employed, and from that downwards. A very favorite form of heating is by exhaust steam, at below atmospheric pressure. As marine engineers hardly need reminding, the volume of steam and its latent heat per pound increase rapid!}' at pressures below the atmos- phere, and in some forms of steam heating, pressures as low as I pound absolute per square inch, or even less, arc em- ployed. On board ship, pressures of from 15 to 25 pounds are HEATING BY STEAM. ] 65 more frequent, because of the inconvenience of reducing to much lower pressures. Heating by steam also differs from heating by hot water, in the temperature of the heating appliance. Thus, with 15 pounds gage pressure the temperature of steam is about 250" F. ; at 5 pounds gage pressure it is 228" F. ; while, as explained, the usual temperature of the hot water employed in heating appliances is in the neighborhood of 170" F. With exhaust steam below atmospheric pressure, practically the same tem- peratures are obtainable as with hot water, and that is another advantage in its favor, apart from its economy. The tempera- cure of steam at 6 pounds absolute is 170^ F., and the latent heat is 994.7 B. T. U. per pound; while at 15 pounds gage pressure it is only 938 units, and at 25 pounds gage pressure only 926. The higher temperatures of the heating appliances are in favor of the liberation of a larger quantity of heat per square foot of the heating appliances per hour, because of the larger dift'erence of temperature between the surface of the heating app'iance and that of the surrounding air. and again because of the peculiar feature mentioned above of the rapid increase of the rate at which heat is liberated, as the difference of temperature increases. On the other hand, however, there are grave objections to heating by steam, and those objections have led to the adoption of hot water heating appliances on shore to a very much larger extent than steam heating. The objections are that the steam heating appliances are not so easily controlled as the hot water appliances, and also there is the constant danger of the tem- perature of the heating appliance rising to a figure which causes it to produce a smell, referred to by heating engineers usually as that of burnt air. It is probable that this is largely burnt dust. There is also probably some action going on betv/een the highly heated surface of the radiator and the air. that is not present with lower temperatures. Where the tem- 166 THE HEATING AND VENTILATING OF SHIPS. perature of the heating apparatus is maintained at about that of boihng water, at ordinary atmospheric pressures, steam heating apphances have presented no difficulty whatever, but steam pressures are sometimes not easily controlled. Where a number of appliances are w^orked from the same source of heat, and the supply of steam is shut off to any considerable portion of them, unless the supply at the source is also re- duced, marine engineers will hardly need reminding, the pres- -Return Valve ^ FIG. 16. TWO-PIPE SYSTEM, LOW-PRESSURE STEAM. sure of the steam — and therefore its temperature — in the remaining portion will rise, and the results mentioned will be produced. The heating appliances used with steam heating are the same as for hot water heating. In fact, many makers list their radiators as applicable for steam or hot water. Pipes, of fourse, can also be used for steam or hot water, providing the ^izes arc in accordance. One or two points of difference have to be noted between the treatment of the two systems. With hot water distribution systems, the pipes are sloped where they arc out of the vertical, so that the water will drain towards the boiler. With steam the pipes are sloped in the opposite direction, in order that any condensed water that is formed HEATING BY STEAM. 167 may be carried with the steam in the direction in which it is going, and may be driven out by the valve provided for it. Air is lighter than water, and therefore, as was explained, air cocks are to be fitted at the highest points of the service and at the tops of radiators. Air is heavier than steam, and therefore works its way downwards, and air cocks are there- fore fitted at the bottom portion of radiators and in similar positions. r Auto FIG. 17. ONE-PIPE CIRCUIT SYSTEM, LOW-PRESSURE STEAM. There are practically two systems of distribution of steam to the heating appliances, known respectively as the two-pipe and the single-pipe systems. In the two-pipe system the steam is carried to the radiator, and. with the condensed water th"t is formed, is carried away to some receptacle, from which it is pumped to the boiler, hot wells, etc. On the one-pipe system the steam is merely delivered to the radiator, and the con- densed water that is formed is carried off from the radiator with the air that is driven out. Figs. i6 and 17 show the two- pipe and one-pipe systems as usually arranged. It is usual with steam systems to have lines of air pipes connected to the 168 THE HEATING AND VENTILATING OF SHIPS. radiators, delivering the air that may have worked into the system with the steam, and that has to be driven out. This air is forced by the pressure of the steam out of the radiator through the air Hues and discharged at a point where it will be harmless. Where exhaust steam is employed, it is usual to employ also a vacuum pump on the return pipes of the system, to bring the condensed steam and air back from the radiators. KORTINg's LOW-PRESSURE STEAM-HEATING APPARATUS. Messrs. Korting Brothers, of Germany, who have made a close study of heating apparatus generally, have worked out a special system of low-pressure steam heating, which will be described. The steam is generated in a special boiler at a pressure not exceeding il^ pounds per square inch, but pre- sumably ordinary steam can be employed, providing that the reducing valve is arranged to lower the pressure to that figure. The very low pressure of operation is provided to meet the ob- jection mentioned above, to the smell that sometimes arises from steam-heating apparatus, owdng to the burnt dirt and burnt air with apparatus at high temperatures. A diagram of this is shown in Fig. i8. For use with exhaust steam, an apparatus is employed in which che reducing valve is controlled by a lever, operated by a float working against a spring, the position of the float in the vessel being regulated by the pressure of the steam supply. When the pressure of the steam supply rises, the water in the vessel in which the float moves is driven downwards through the pipe at the bottom into another vessel at the side, whose position can be adjusted, the float then falling and partially closing the valve; the reverse operation taking place if the steam pressure falls. Where steam is supplied from the special boiler, the draft of the furnace is controlled by the tempera- ture of the steam; a slight increase of temperature partially closing the furnace damper, and vice versa. It is doubtful A COMBINED AIR AND STEAM RADIATOR. 169 whether, under ordinary conditions of sea-going ships, such apparatus would be desirable, but in sailing ships and in yachts, and in some classes of ships, such as whalers, sealers, etc., where the travel of the ship at times is not great, it might be convenient to have an apparatus of this kind. I //, Low PreS' Y/ lui« Steim, I A COMBINED AIR AND STEAM RADIATOR. Messrs. Korting have also introduced a radiator, in which the steam is cooled by the presence of a certain quantity of air. Steam, it will be remembered, unless it is supplied below at- mospheric pressure, must be at or above 212° F., and this is a somewhat high temperature under certain conditions. The temperature may be lowered by employing the partial vacuum method, but it is also claimed by Messrs. Korting that it is lowered in their special radiators by the addition of air. The radiator is of the usual form, with a steam pipe running along the bottom of the sections, and at each section a steam nozzle enters the pipe. The admission of steam is controlled 170 THE HEATING AND VENTILATING OF SHIPS. by the valve at the entrance to the radiator, in the usual way, and the steam passing out of the nozzle is allowed to draw air in with it, on the well-known injector principle. It is claimed that the steam mixes with the air, the former being cooled thereby, and the outside temperature of the radiator being con- sequently lowered, the air and steam circulating together, and the condensed steam being drawn off in the usual way, HEATING BY ELECTRICITY, All electrical heating apparatus is based upon the fact that, when an electric current passes through a conductor, heat is liberated in direct proportion to the resistance of the con- ductor and to the square of the strength of the current. The formula is H = tRC', where H is the quantity of heat liber- ated in time /, C is the current strength in amperes, and R is the resistance of the conductor in ohms. The formula may also be written, EH H = ECt, or H = , R where E is the difference of pressure in volts at the terminals of the conductor. Connection is made with the thermal system by the fact that H is expressed in watts, the electrical unit of the rate of expenditure of energy, and that 17.58 watts equals one B. T. U. This matter is referred to again further on. Heating takes place in all forms of electrical apparatus, in cables, in the conductors forming part of the coils of dynamos, motors, etc., and also in all forms of electric lamps. But, in the case of cables and conductors forming parts of dynamos and motors, the heat is kept as low as possible, and in the case of lamps, the great object striven for is to obtain as large a conversion as possible of the heat waves into light waves. In heating apparatus the great object to be attained is of course heat, and therefore all electrical heating apparatus is designed HEATING BY ELECTRICITY. 171 with a high resistance, so that as large a quantity of heat shall be liberated as possible, within a given space. Electrical heating apparatus has so far divided itself into two main branches, the luminous and non-luminous. Luminous electrical heating apparatus is merely an extension of the well- known electric incandescent lamp. The current passing through the filament of such a lamp, it will be remembered, first liberates heat ; and if the current is not of a certain definite strength, only heat will be liberated, and the lamp filament re- mains black, but it is still giving out some heat, though the pressure is too low for the lamp in question. When the pres- sure and the temperature are a little higher, the lamp becomes red, a larger amount of heat is given out, and the small quan- tity of light possessed by the red rays. As the pressure and the current are increased, the lamp becomes gradually brighter, finally assuming the well-known yellow tinge, or, if allowed, becoming white hot. In all cases, however, whatever the color of the filament, and whatever the temperature to which it may be raised, the whole of the electrical energy delivered to it eventually becomes heat, and is delivered to the air of the room in which the lamp is fixed. Under ordinary circumstances, the carbon filament incan- descent lamp converts from about 3 to 5 percent of its heat into light, but the light rays are, so far as is know^n at present, reconverted into heat in the room. The action is the same as the action of the sun's rays upon a greenhouse. It is well known that it is the light rays of the sun which cause the heating effect in the greenhouse, very much more largely than the heat rays. Glass is transparent to light rays, and they pass through the glass into the greenhouse, as through the glass of the incandescent electric lamp, and are converted into heat waves on the other side. In the case of the greenhouse, as glass resists the passage of heat rays through it, the con- verted light rays cannot escape so easily as they passed into 172 THE HEATING AND VENTILATING OF SHIPS. the greenhouse, and the temperature is raised. Similarly, the light rays from the incandescent electric lamp become heat rays on passing out into the room, and the remainder of the electrical energy^ delivered to the filament becomes heat within the filament globe, and heats the globe in the well-known manner, the heat being then transmitted to the air of the room in the usual way. Consideration of the two types of heaters, luminous and non-luminous, makes it evident that where coiiiinuoiis service is desired, a heater which depends on the setting up and circu- lation of air currents passing through it gives the best results. If immediate heat is required the luminous radiator is prac- tically instantaneous. It heats the person rather than the air in the room, the latter being warmed only indirectly from the heated surfaces on which the rays from the radiator may fall. For immediate, localized heat, for warming the person, it has no superior, and this fact often permits the use of electric heat where it would otherwise be far too expensive. This distinc- tion should be clearly emphasized if an intelligent application of the two forms is to be made. ELECTRIC HEATING APPLIANCES ON SHIPBOARD. Recognizing the vast possibilities in the application of elec- tricity to heating, many manufacturing electric companies have developed a variety of special devices which have already won such favor that it seems certain they will be as commonly used as the incandescent lamp. A ship's lighting plant, usually of more than ample capacity for its intermittent load, offers at once an available source of supply, which, utilized for cooking in the galley or heating in the staterooms, would provide numerous real and profitable conveniences with small increase in cost. The electric heater is ideal for stateroom use. It is com- pact and neat in appearance, and easily turned on and off, thus ELECTRIC HEATING APPLIANCES ON SHIPBOARD. 173 admitting of regulation of temperature for each individual room. It is connected by simple wiring, which is more flexible than steam piping. The wnres take little space and can be run anywhere, while steam pipes are bulky and apt to leak, and FIG. 19. — GLOW-LAMP RADIATOR AND METER. SAPPLIES, LTD. necessarily heat the spaces through which they pass. It is safe to say that the electric radiator, although deriving its heat in- directly from steam, is no less efficient, when the losses due to leakage and radiation are taken into consideration. 174 THE HEATING AND VENTILATING OF SHIPS. F;G. 20. GLOW-LAMP RADIATORS WITH METERS ATTACHED. GLOW-LAMP RADIATORS. Forms of what are termed glow-lamp radiators are shown in Figs. 19 and 20. They are now well known, and consist of from two to four specially made carl)on filament incandescent lamps, usually 9 inches long, with a single horseshoe filament, approximately double the length of the lamp; the two, three FIG. 21.— BRITISH THOMSON-HOUSTOK EDISON RADIATOR LAMP. GLOW-LAMP RADIATORS. 175 or four lamps being held in some ornamental fitting, usually with a reflector behind them, and arranged to throw the whole of the rays from the lamp out into the room. The apparatus is fitted with switches, arranged to connect one, two, three or four lamps, as required, so that the heat delivered to the room may be regulated within these limits. Fig. 21 shows one of the lamps, by the British Thomson-Houston Company, and FIG. 22. — KixG Edward's quarters on the royal yacht victoria and ALBERT, Fig. 22 shows King Edward's cabin on board the royal yacht, heated by one of Dowsing's luminous radiators. Some makers are also providing electric radiators with glow lamps, of the pattern described, inside of various inclosures, the appearance being very much the same as that of the non- luminous radiators or convectors described further on. In one form, two or four lamps are inclosed inside a cylindrical 176 THE HEATING AND VENTILATING OF SHIPS. copper or brass case, with perforations, the whole apparatus standing a little off the floor. The idea here is that the air passes under the apparatus, up over the lamps, and out through the perforations at the top and the side. This is shown in Fig. 23. Other forms are almost copies of the non-luminous ra- diators. They are rectangular in form and inclose two or four lamps inside a framework, raised slightly from the floor by feet, and the front of the apparatus being closed by slips of ruby glass, the effect is pretty. There are also other forms of this arrangement on something the same lines. The British Prometheus Company has also introduced glow-lamp radiators, in which the lamps are maintained at only red heat. THE EFFECT OF THE LIGHT RAYS. It should perhaps be mentioned, e)i passant, that it is claimed by makers of glow lamp radiators that the light rays issuing from the glow lamps have an important office, and, in the writer's view, this is strictly correct. It will be remembered that white light is made up of the different colors forming the solar spectrum, as we see it in the rainbow, and that the rays forming the different colors have different wave lengths, different periods and different properties. Thus, the red rays have comparatively long waves, about double the length of the violet rays, and their property is principally heating. The violet rays at the opposite end of the spectrum have compara- tively short waves, and the principal property is actinic or chemical. It is the violet rays which are most useful in photography. Between the violet and the red is a long range of rays of different colors, whose properties vary, most of them having been thoroughly worked out. Apparently the yellow rays are those which do most in the direction of furnishing light. Glass and some other substances, the human skin of the white man being one of them, according to some experiments that THE EFFECT OF THE LIGHT RAYS. 177 have been made, are apparently transparent to the yellow and green, and some of the other waves at that end of the spec- trum, the waves after passing through the glass or the skin being transformed into heat waves. This has been mentioned as the cause of the heat produced in greenhouses when the sun is bright. FIG. 23. GLOW-LAMP RADIATOR. Mr. Dowsing's work also in connection with the use of the electric glow lamp, of the type described for heating, in con- nection with therapeutics, has shown that the light waves have a very important effect upon the human body. The elec- tric light bath is now well known, and its effects are produced, it is believed, by the light rays issuing from the lamps, and 178 THE HEATING AND VENTILATING OF SHIPS. not by the heat rays. Another peculiar feature about them is, according to Mr. Dowsing, that the pigment under the skin of the black man is not transparent to the light rays. Thus, one cannot give a black man an electric light bath. It does him no good. This would apparently be the reason why the black man can stand the sun's rays. It is not the heat rays which trouble the white man so much as the light rays, which pass through his skin, there becoming heat ; while they do not pass through the pigment in the black man's skin. It will be seen that this has an important bearing upon the question of the warming of living rooms, whether on shore or afloat. Everyone is familiar with the prejudice, as it is thought to be, in favor of a bright, glowing fire; and it is not the fire of red coals that is liked, but one in which white or yellow flames are dancing around the grate bars. If the above reasoning is correct, this tendency, like so many others, is well founded, and the light rays have an important func- tion in the matter of heating. If so, also, the luminous radiator should have an important office to fulfil in the problem of heating saloons, cabins, etc. In the wTiter's experience, when away at sea, nothing is more pleasant than a bright light in the mess or in one's cabin, and a bright radiator will probably have the same effect. The lamps in question consume one-quarter of a kilowatt per hour. That is to say, with the usual lOO-volt service em- ployed on board ship, each lamp would take 2^ amperes; a radiator of two lamps, suitable for a small cabin, 5 amperes; one of four lamps, suitable for a larger cabin, 10 amperes. The question of the quantity of heat liberated by the radiators will be dealt with further on. NON-LUMINOUS HEATING APPARATUS. In the other forms of electric heating apparatus, which are very numerous, conductors, or, as it would probably be more NON-LUMINOUS HEATING APPARATUS. 179 correct to call many of them, semi-conductors, are arranged in various forms, so that electric currents can be delivered to them, and so that the conductors, or semi-conductors, can deliver their heat to the air surrounding the apparatus. One well-known form of non-luminous radiator, made both in America and the United Kingdom, is known as the Prometheus. It consists of strips of mica, upon which a con- FIG. 24. — PROMETHEUS STATEROOM HEATER, ELEMENTS AND DETAILS. ductor has been deposited in a layer or film. The strips of mica are provided with clips at the ends, in connection with the powdered conductor, and these clips form the connection to the source of current. Fig. 24 shows the heating elements. The mica strips with their clips, which are called heating elements, are built into various forms of apparatus, known as "convectors," some of which are shown in Figs. 25 and 26. 180 THE HEATING AND VENTILATING OF SHIPS. In the usual arrangement there are two metalHc uprights, forming the connection to the supply service, and the heating elements are bridged across between the uprights, the whole being inclosed inside of some ornamental arrangement, which may be cylindrical, rectangular or any other convenient form, and which usually has either perforations in the body and at the top, or the equivalent. The whole apparatus stands a / >, > } I 7 ■>. y^'^jm^ i, «^ mjtt «■* FIG. 25. PROMETHEUS HEATER, WALL TYPE. little off the floor, the air passing under, up over the heating elements, and out into the surrounding atmosphere. Another form, mafic by Messrs. Tsenthal, consists of metallic resistances, inclosed within a substance which is an insulator, and which is also highly refractory. The metallic rrsistancc is arranged to have low corfficicnts, both of expansion and of increase of resistance, so that there may be no change in the NOX-LUMIXOUS HEATING APPARATUS. 181 form of the heating elements when in use. The heating elements are sometimes made with ribs, as shown in Fig. 28, and there built up into circular or rectangular forms, as shown in Figs. 29 to 32. and inclosed in various ornamental devices, the arrangement being the same as that of the Prometheus. Other firms have other substances. Messrs. O. C. Hawkes, Ltd., London,, have a special wire which they claim will stand FIG. 26. PROMETHEUS HEATER, FLOOR TYPE. a temperature of i.ooo'' F. The Simplex Electric Heating Company, Cambridge, ]\Iass., uses conductor embedded in white enamel, which is fused at high temperature, the enamel pro- viding the insulation and also being very refractory. The General Electric Company, Schenectady, uses a high resistance conductor, coiled into various forms, and covered with a highly-resisting quartz enamel. Forms of these heating ele- ments are shown in Fig. ^3, and a stateroom heater in Fig. 34. 182 THE HEATING AXD VENTILATING OF SHIPS, FIG. 27. PROMETHEUS CONVECTOR. Unit with Ribs on one side only Circular Unit with Ribs. Unit with Ribs on each side. FIG. 2S. — ISENTHAI-'S }IE- Unit with Smooth Surface ■\TING ELEMENTS. HEATING APPARATUS WITH LOOSE POWDER. 183 NON-LUMINOUS HEATING APPARATUS WITH LOOSE POWDER. There is another form of electric heating apparatus, which has been developed in Germany, principally, in which a loose powder is employed, the necessary resistance being obtained partly by means of the substance of which the powder is FIG. 29. — CIRCUL.\R ELECTRIC HEATER. FIG. 30. BATTERY FOR SAME. composed and partly by the fact that the substance is in a powder, or in loose grains. A loose powder, or loose contact between any two conductors, across which an electric current has to pass, always offers a considerable resistance over and above that due to its own sectional area, length, etc. This is the cause of the heating of badly designed switches. If the 184 THE HEATING AND VENTILATING OF SHIPS. ■Wlif^PS^^^Si^ FIG. 31. — ISENTHAL FLOOR-HEATING APPARATUS. contact portions of a switch do not make good contact with each other, heat is always hberated at the surfaces, and some- times arcs are formed with the attendant enormous heat. One form of this heating appliance is known as "Kryptol." It is a granular mass of very inoxidizable substances, carbon, FIG 32. — ISENTHAL FLOOR-HEATING APPARATUS. HEATIXG APPARATUS WITH LOOSE POWDER. 185 Cartridge Unit, Quartz Enamel Unit. FIG. 33. GENERAL ELECTRIC HEATING ELEMENTS. graphite, carborundum and silicious matters. These substances are ground together and then pressed into blocks, and after- wards made into grains of a uniform size. The grains for different types of apparatus vary in size from a sand to the size of grains of wheat, with varying amounts of graphite and carborundum, according to the particular applications for which they are required. The substance is claimed to stand temperatures up to 3.000° F. ; and, on the other hand, it is claimed that temperatures as low as 50° F. can be obtained. The powder or grain is filled into cartridges, as shown in FIG. 34. GENERAL ELECTRIC STATEROOM HEATER. 186 THE HEATING AND VENTILATING OF SHIPS. Fig. 36. These cartridges consist of tubes of special glass, in which the resistance material is held, the ends of the tubes being hermetically sealed with metallic capsules, which form the connections to the powder. The cartridges are heated with an electric current before they are finally closed by the cap- sules, in order to eliminate grains of un-uniform size, and also to get rid of the moisture. One of the troubles met with FIG. 35. SALOON ELECTRICALLY HEATED BY HAWKEs' STOVES. in working out this form of apparatus, after the capsules had been fixed, w-as the generation of steam within the cartridge w^hen the current was allowed to pass through, the steam bursting the glass-containing tubes. To meet this difficulty, any moisture that may be present is driven off by the heat of an electric current, the moisture forming steam, and the heat- ing being kept up until this has all disappeared, and the whole mass is thoroughly dry, and until dry air is present between the grains of the substance. The cartridges are built into HEATING APPARATUS WITH LOOSE POWDER. 187 various forms, and are arranged as radiators, or convectors, whichever term may be preferred, some of which are shown in Figs. 2)7 and 38. Kryptol is also used, in certain cases, in what are prac- tically open fireplaces. The grains are loosely heaped in a vessel of fireproof clay, the current being led to the mass by FIG. 36. KRYPTOL CARTRIDGES BUILT INTO FRAME. conductors projecting into them. For other purposes also the Kryptol grains are spread loosely on a plate that it is desired to heat, or in an annular space surrounding an object to be heated, etc. The action of the substance is as follows : When the cur- rent is first switched on, small arcs are sometimes formed between the individual grains, this leading to the very rapid 188 THE HEATING AND VENTILATING OF SHIPS. development of heat. But in the cartridge tubes, providing that they are properly prepared, it is claimed that the forma- tion Of arcs has been practically suppressed. In either case, whether arcs are formed or not, the substance settles down usually to a dull red heat, which may be increased up to the high temperature named, if sufficient current is passed through it for a sufficient time. Where the substance is used loose, practically in air. the formation of the arcs mentioned leads to the burning away of the substance itself by the formation of carbonic oxide and carbonic acid, just as in an ordinary FIG. 37. KRYPTOL C.\BIN HEATERS. FIG. 38. furnace or in an arc lamp. It is stated, however, that the powder can remain, with the current passing through it. for several hours before it need be renewed. Some tests that have been made upon a stove intended for' heating rooms and containing twenty cartridges inside a cover of expanded metal are interesting. They are shown by the curve in Fig. 39. In the figure the ordinates are temperatures in degrees Centigrade, and the abscissae represent time in minutes. The stove was used to heat up a room, whose initial temperature was 10° C. (50° F.), the outside temperature being 2° C (35.6° F.). The current employed was 9 amperes, with HEATING APPARATUS WITH LOOSE POWDER. 189 a pressure of 120 volts— a little over one kilowatt, or Board of Trade unit. In the figure, line I. shows the variation of the temperature of the air between the two upper cartridges, with the cover of 15(j £:is=o. ■^^^5^ g^v* 140 / ^ 130 / / 120 I 1 110 / .§100 ^oo , 1/ / II a / ^^ 80 u / >• ^ ^X- « A6U 1 / V / a © E- 50 1 i 7/ / X 40 / / 30 1 '// f / — VT 20 VII 10 J r -^ =^ 5 IC • 1£ » 2C a. > 30 3S Mini 4C ites 45 5C 1 5S 6C FIG. 39. TEMPERATURE CURVES OF CARTRIDGE STOVE. the Stove removed. The cartridges were in two vertical rows of ten each, and the temperatures given would be between the two upper ones, just inside the top of the stove. It will be seen that the temperature rises in 10 minutes from 10° C. (50° F.) to 60° C. (140° R). In 15 minutes it has risen to 190 THE HEATING AND VENTILATING OF SHIPS. 100° C. (212° F.) ; in 20 minutes to 124° C. (255° F.). After this the rise is more gradual, reaching 150° C. (302° F.) in 35 minutes, and 152° C. (305.6° F.), at which it remains con- stant to the end of the test, which occupied an hour. Curve II. shows the temperature on the center of the cover, which was presumably replaced. It will be noticed what a great difference there is between the temperature of the cover and that of the air inside of the apparatus between the cartridges. The rise of temperature is still very equal, and it reaches 65° C. (149° F.) in 15 minutes, but it reaches 88° C. (190° F.) only in 35 minutes, and does not rise any higher to the end of the test. Curve III. is the temperature of the air of the room 20 millimeters (^^ inch) above the top of the cover. It will be noticed that the temperature follows the same course as that of the cover itself, but is about 4° C, say 7° R, less. Curve IV. is the temperature of the top of the frame carrying the cartridges, which, it will be seen, follows the course of curves II. and III. fairly closely, with a certain difference between them. Curve V. is the temperature of another portion of the cover, not subject to side currents of air. It does not present much interest. Curve VI., which is the most interesting one of the whole, is the temperature of the room one meter (39^ inches) above the cover; and curve VII. is the average tem- perature of the air in the room. It will be seen that the tem- perature of the air, one meter above the cover, and the aver- age temperature of the room, are very nearly alike, that a short distance above the cover being slightly higher than the average temperature, and being about 7° C. (12.6° F.) above it at the end of the test. Both curves, however, rise very gradually. It takes 25 minutes to increase the temperature 10° C. (18° F.) one meter above the stove, and 30 minutes for the average temperature of the room to reach the same figure. The temperature of the air, one meter above the stove, risej very gradually, it will be seen, to about 27° C, while the HEATING APPARATUS WITH LOOSE POWDER. 191 average temperature of the room rises to only about 21° C. (70° R). There is another instructive series of curves given of tests with a Kryptol stove, shown in Fig. 40. There are several 2 4 6 8 10 12 14 16 IS 20 22 24 2 4 6 8 10 12 14 Minutes FIG. 40. HEATING TO BOILING POINT OF ONE LITER OF WATER. curves, those on the left of the figure giving the rise of tem- perature in the time shown, with the Kryptol apparatus, and those on the right the rise of temperature in the time shown, with gas. The gas employed appears not to have been by any 192 THE HEATING AND VENTILATING OF SHIPS. means the most efficient for heating. It was an open gas flame, which is certainly not designed for heating. As will be seen, the electrical apparatus takes lo minutes to reach a tem- perature of 28° C. in the best of the three curves shown, and over 20 minutes to reach 100° C, while gas reaches 30° C. in the worst of the curves shown in 4 minutes, and 100° C. in 14 minutes. The above curves are taken from an article in the German Export Zeitschrift, dealing with the subject. The article also gives some other interesting information, which there is hardly space to reproduce here. Some other curves are given, which show that the current required rises to a maximum, and then falls to a "working"' current. This is the common experience with a great many forms of heating apparatus. If the air of a room is required to be heated up quickly, a considerable amount of heat has to be supplied to the apparatus for a short time, and then it may be reduced, the air then keeping its tem- perature with a smaller expenditure. The Kryptol cartridges described are made in the following sizes: 5^/2, 7%, 10, 12^ and 20 inches long, by 0.6 and 0.8 inch diameter respectively. The 12^-inch cartridge takes 0.3 ampere with a pressure of 100 volts, and the cartridge is stated to receive with that current and pressure an increased temperature of 100 degrees. These figures are for the cart- ridge when exposed. When inclosed, the conductivity of the mixture rises with the temperature, and the cartridge will take 0.4 ampere with no volts. It will be understood, as explained in connection with hot water and steam heating, .hat the above remarks apply to heating, without having any regard to the question of venti- lation. As will be explained, heating and ventilation are ^ now usually considered together, the ventilating air current being employed for heating and cooling purposes. In many cases, however, no attention whatever is paid to ventilation. SPIRAL COIL HEATERS. 193 and this is particularly the case with electrical heating ap- pliances. It will be understood that any heating appliance may be fixed in any room, passage, alleyway, etc., and will give off heat, exactly in the proportion described, but the heat given off may or may not be useful heat. In the case of corridors, one very frequently sees here a heating appliance, which is practically useless, because there is an air current constantly passing over it, and constantly carrying off the heat that is liberated, without doing any useful work. The same remark would apply to a room that is very subject to drafts. The heating appliance would do very little good. On the other hand, if a heating appliance is placed in a room, say in the middle of a saloon, and is not exposed to drafts, it will heat up the air of the saloon, by radiation and convection, in a certain time, varying with the conditions, but the heating will be hardly under the control of the engineer in the same manner as it is when the appliances are so arranged, as will be de- scribed later, as to utilize the warmed air currents. SPIRAL COIL HEATERS. A type of electric heater made by the Consolidated Car Heating Company, Xew York, and fitted for marine use, is on the ^IcElroy spiral coil construction, in which the re- sistance coils are perfectly supported at every point, rendering vibration impossible. The spindle supporting the coil consists of a 5^-inch square wrought iron rod. on which are strung porcelain tubes, so designed and fitted that a helical groove extends from end to end. The iron wire for the resistance coil is wound in a close spiral spring, and insulated copper leading wires are attached to both ends by twisted and soldered joints. This coil is wound between the ridges on the porcelain spindle, under suitable tension, and the leading wires are passed through eccentric bushings' at the ends and firmlv 194 THE HEATING AND VENTILATING OF SHIPS. fastened to the exterior part of the circuit. This construction gives the greatest possible length of wire in the given space, and so disposes every portion of the large surface presented that a large quantity of air comes freely inio contact with it, LOW TEMPERATURE TUBULAR AIR HEATER. 195 and passes out in a stead}- stream at such temperature as may- be designed. Two views of this type of heater are given in Figs. 41 and 41 A. The former is designed for the use of i.ooo watts (i kilowatt) of current, measures 27 inches in length. 15? s in height and 3 9/16 in thickness. The "spread" for bolt holes FIG. 41a. SMALL SPIRAL COIL HEATER FOR STATEROOM. is 7 inches, and the heater, which contains four coils, is finished in black japan. The smaller heater shown has only two coils, and measures 4^^ inches in thickness, with a spread of 6^< inches. The length is is-ys inches, while the oval of the case measures 5^4 by 3;^ inches. The case is of heavy, per- forated sheet steel. LOW TEMPER.XTURE AIR H'EATER, TUBULAR TYPE. The latest in air heater design is the so-called "low tem- perature air heater." The specifications of the United States battleship LouisiriJia called for electric heaters which should have an operating temperature equivalent to that of steam piping. As a result, the General Electric Company's engineers designed the tubular type of air heater shown in the accom- panying illustration, and furnished it to the Louisiana. This particular type of heater consizt: of three or more tubular 196 THE HEATING AND VENTILATING OF SHIPS. FIG, 42. TUBULAR TYPE, LOW-TEMPERATURE AIR HEATER. heating elements, inclosed by the metal "chimney" tubes which are shown. Each tube dissipates 250 watts. The principle of this design is the combination of the large radiating surface with a low watt surface density and the chimney effect of the tube. It is manifest that, while all electric air heaters may be said to give 100 percent efficiency, the practical efficiency, which is judged by the uniform and effective distribution of the heat in the room, can be obtained only by passing a relatively large volume of air over the heating surfaces, and raising it only a few degrees above the temperature of the roorri. The oftener the total volume of air in the room passes over the surface of HC. 43. AIR-HEATER, CARTRIDGE UNIT TYPE. LOW TEMPERATtJRE TUBULAR AIR HEATER. 197 the heating source, and the less temperature difference between- the outlet and inlet, the more efficient is the heating system. Three distinct forms of heating elements are used by the General Electric Company. The cartridge unit consists of a thin tape of special resistance metal, wound edgewise, insulated with a fireproof cement and then inserted in a mica-lined brass tube capped with a cement plug through which the leading-in wires are brought. The quartz enamel unit is made up of a resistance wire wound in a coil of small diameter, which is then coiled into the form of a flat spiral, with mica insulating strips between its convolutions, and held against a layer of FIG. 44. GENER.\L ELECTRIC LUMINOUS RADIATOR. quartz grains imbedded in enamel on the bottom of the heater. Both of the foregoing heating units are practically infusible and indestructible, but can be readily replaced if damaged by accident. Great care has been taken in the design of the heat- ing devices to insure the most efficient application of the heat, and at the same time to give proper radiating surface, so that nearly all the apparatus may be left in circuit indefinitely with- out fear of burn-out. (See Fig. 33.) The third form of heating element is the tubular resistance, which is used in the tubular air heater already described. This resistance, while designed only for comparatively low 198 THE HEATING AND VENTILATING OF SHIPS. temperatures, is one of the cheapest and best forms for air heaters up to a maximum of Goo or 700 degrees F., or with a density of 2 or 2^/2 watts per square inch. It was first de- veloped by the General Electric Company for rheostat work, and particularly the heavy service of the railway rheostat. It consists of a tube of asbestos wound on a mandrel, the tube supporting a single layer of resistance wire closely wound, but with turns not touching. The tube is then impregnated with a FIG. 4G. FIG. 45. • PROMETHEUS REGULATOR DET.\ILS. fire-proof insulating compound, which gives the asbestos con- siderable stiffness and forms a protecting coat over the re- sistance wire. REGULATING THE HEAT DELIVERED BY ELECTRIC HEATING APPARATUS. The favorite method is similar to that described in con- nection with the glow lamp radiator. The heating elements are arranged inside the apparatus, in such a manner that either each element individually, or groups of elements, can be REGULATING ELECTRIC HEAT. 199 switched in and out at will. The usual arrangement is, for heating appliances, the heating elements are connected in parallel between what are practically two bus-bars, connected to the supply service. There is a main switch to disconnect the whole appliance, and there are subsidiary switches to connect and disconnect either individual elements, or groups of elements, from the bus-bars. The British Prometheus Company has another system of regulating for some of their apparatus, which is something on the lines of the regulator of the tramway service. There is a sleeve of approximately square section, as shown in Fig. 45, with conductors on the insides of the four faces, connected to FIG. 47. ISENTHAL METHOD OF REGULATING WITHOUT SWITCHES. the heating elements. The corresponding fitting (Fig. 46) consists of a solid piece of insulating material of square sec- tion, carrying conductors on its faces, the conductors being connected to flexible cords, to which the regulator is attached. It is arranged that the conductors on the male portion, w^hen making connection with certain conductors on the female portion, allow full, three-quarters, one-half or one-quarter of the current strength to pass as may be desired, the arrange- ment being made by connecting the different elements in the heating appliance in different order. Thus, for full heat, all the elements will be connected in parallel. For half heat, two sets will be connected in parallel, afterwards being connected in series in each parallel, and so on, for the other heats. 200 THE HEATING AND VENTILATING OF SHIPS. Other methods of varying the heat include that shown in Fig. 47, which is adopted by Messrs. Isenthal. of London, which is somewhat similar, though different in form, to that of the Prometheus Company. The heating apparatus has three pro- jecting pins as shown, and the connecting pipe from the supply service has three plug holes. When the three plug holes are on the three pins, the full current is passing, and the full heat is liberated. \\'hen the two plug holes on the left engage with the two pins on the right, the medium current is passing, and when the two plug holes on the right engage with two pins on the left, a weak current is passing. The strengths of the currents under this arrangement are as one, two and three. The three-hole plug is wired with twin wire, one of the twins being connected to the center plug hole, and the other to the two outside plug holes. The Prometheus Company, of Xew York, has a somewhat similar arrangement for regulating the heat in certain cases. There are three pins on the heating apparatus, and there are three terminals on porcelain holders, connected to three con- ductors of a flexible cord. The three terminals on the flexible cord are colored, one red and the others black. By different arrangements of the terminals by engaging the red terminal and the black terminals with different pins, different heats are provided. THE QUANTITY OF HEAT LIBERATED IN ELECTRICAL HEATING APPAR.\TUS. Referring to the formula, H is given in watts, when E is given in volts, C in amperes, and R in ohms ; these being, as marine engineers know, the units of electrical power, pressure, current and resistance. The watt is the unit of power or the rate of doing work, and it will be familiar to engineers from the fact that 746 watts equal one horsepower. Work is done at the rate of one watt, when a current of one ampere passes ELECTRICAL HEAT QUANTITIES. 201 with a pressure of one volt, or the equivalent. Thus, in the ordinary i6-candlepower incandescent lamp, working with a pressure of lOO volts, and taking a current of 0.6 ampere, the electrical energy expended in each lamp equals loox 0.6 =1 60 watts. Coming to the heat question, each watt liberates 0.0568 British thermal unit per minute, or 3.41 British thermal units per hour. These figures are derived from the figures already given, showing that the heat unit equals 17.58 watts. It is claimed, by makers of electrical heating apparatus, that the whole of the electrical energy delivered to the apparatus^ whether it be in the form of the lamps that have been de- scribed, or any one of the resistance materials mentioned, is converted into heat ; and therefore, where an electrical heating apparatus is employed to heat a room, the whole of the elec- trical energy is applied in heating the air and objects in the room. The writer mentions the claim, and so far scientists appear to have assumed that the principles upon which it is based are correct. It is assumed by scientists that every form of energy, when transformed from the state in which it is at any moment, be- comes heat sooner or later — that heat is the final form of all energy, and that the heat balance sheet is the final court of appeal upon all matters in which any form of energy is con- cerned. It appears to the writer that it is quite possible that other forms of energy may be liberated, when electricity is converted into something else. The question whether this does take place, or not, has not yet been examined in any way by scientists, and therefore the above statement is given with all due reserve, and the calculations which follow will be understood to be subject to that reservation. If all the elec- tricity delivered to the heating apparatus becomes heat, the calculations are correct. In any case, it appears to the writer that any difference there may be would come within the 202 THE HEATING AXD VENTILATING OF SHIPS. margin which every practical engineer allows himself for pos- sible sources of error. The electric lamps described above, which are employed in luminous radiators, absorb, as mentioned, 250 watts each, and that would mean that 250 X 34 1 = 852,^2 British thermal units are liberated by each lamp per hour. As each British thermal unit raises the temperature of 55 cubic feet of air I degree F., each lamp will raise the temperature of 47.000 cubic feet of air i degree F. in one hour, or, say, approxi- mately, 4,700 cubic feet 10 degrees F. in one hour, two and four lamps raising the temperature of proportional quanti- ties of air to the same degree. Leaving out for the moment the question of air currents and ventilation, which will be dealt with further on, it is a simple calculation to find the number of lamps required to raise the temperature of a room of a given cubical content through a given number of degrees. The temperature to which the air has to be raised varies, of course, with the climate and the seasons, but taking 40 degrees F., the figure worked to in the calculations which follow, as the increase of temperature re- quired, this would be provided for in a room having a cubical content of 1,175 cubic feet, by one of the lamps mentioned, in one hour, on the supposition that all of the electricity is con- verted into heat, and that no heat passes out of the room during the time. The above remarks apply equally to non-luminous radiators, which are made to take various quantities of electricity. Ap- paratus is made absorbing from 500 up to 4,000 watts, when taking their full current, and liberating from 1,700 to 13,600 heat units per hour. They are usually made to regulate the current at one-quarter, one-half and three-quarters of the full heating capacity, the heat units liberated being then from 425 to 3,400 with one-quarter, and the other figures in pro- portion. HEATING BY WARMING THE AIR. 203 HEATING BY WARMING THE AIR ENTERING THE ROOM. The tendency of mcde:-^ i, ^„f:- - — .-^'^-nces, hcth on shore r.nd afloat, is to warm each room hidividually, each cabin, saloon, corridor, etc., by warming the air entering the room, ! VERTICAL •' V / SECTION. Co\°- ^/ FIG. 48. AIR-HE.\TING FIRE GR.\TI or a certain portion of it. As will be explained in dealirg with ventilation, the latest application of the system combines heating and ventilating. The ventilating air current is made use of to warm the room by being itself warmed before it enters the room, and similarly the air may be cooled before entering the room, and so keep the temperature down. 204 THE HEATING AND VENTILATING OF SHIPS. There are several methods of warming the air entering the room in which the appliances that have been described are made use of, with slight modifications that will be explained, and in addition to these the whole of the air is warmed by special apparatus, as described above. One of the methods that have been developed on shore is by causing a certain quan- FIG. 49. FRONT OF AIR-IIF.ATING FIRE GRATE. WARM AIR ISSUES THROUGH REGISTER AT TOP. tity of oil to be heated by the stove, or fire grate, as explained below% and to be delivered into the room at a higher tempera- ture than rules outside. SPECIAL AIR-HE.\TING STOVES. On shore a number of stoves have been developed that are doing very good work in hospitals and other institutions, in which a certain quantity of air is warmed before it enters the room by being passed over a hot surface, specially arranged SPECIAL AIR-HEATING STOVES. 205 for it, in the grate or stove with which the room is heated in the ordinary way. The arrangement of the grate is shown in section in Fig. 48, and a complete stove is shown in Fig. 49. This is the form made by George Wright & Company, Rother- ham. FIG. 50, B.'VCK VIEW OF AIR-HEATING FIRE GRATE. It will be seen that in place of the fireplace extending right to the back of the chimney, there is a space behind that devoted to the burning fuel within the chimney proper, and that the hot gases, smoke, etc., from the burning fuel are taken up through an iron flue inside the chimney proper instead of being delivered straight into it from the fireplace. Air is led between the flue and the chimney space from the outside, usually by a duct leading from the outside air through one of the outside walls in the neighborhood, where a grating is 206 THE HEATING AND VENTILATING OF SHIPS. provided that can be arranged to regulate the quantity of air entering. The cold air from outside passes through the duct over the hot surface of the back of the fireplace and that of the flue above, and is delivered into the room through gratings provided for it at the level of the usual chimney breast in front, and sometimes also at the sides. FIG. 51. W.\RM AIR VENTILATING GRATES (gEO. WRIGHT & CO.) In the large hospital stove shown in Fig. 51 the air is de- livered from the front, sometimes the top, and always the sides, and it is a common thing for hospital wards to be warmed by a stove of this kind at the end farthest from the door, and one or more pairs of similar stoves standing back to back in the middle of the ward, at a certain distance from the door. Stoves of this kind are made for smaller rooms as well as for the large rooms of which hospital w^ards usually consist, and it appears to the writer that they could be very well SPECIAL AIR-HEATIXG STOVES. 207 adapted for heating the saloons, mess rooms, etc.. on board ship, the air to be warmed being taken from above the upper deck by a ventilating arrangement, properly protected in the usual way, and brought down at a little distance from the stove and then run in under the deck to the air space de- scribed. A modification of the air-heating stove, which has been used in a school, but which is somewhat crude, consists of a stove of the usual slow-burning type, standing near the middle of the school room, with a chimney carried vertically to within a few feet of the ceiling, and then carried to the outer wall at an angle a little above the horizontal, the chimney being contin- ued outside the outer wall in the usual way. The nearly horizon- tal portion of the flue has a second cylinder surrounding it, into which air is brought from outside at the point where the flue emerges, and the air is warmed by its passage through the annular space between the flue and the surrounding cylinder, and is delivered to the room above the stove, warmed to a certain temperature. The arrangement of the air-heating stoves mentioned for hospitals is a great favorite with some of the superintendents, because they say that the firegrate gives the ward a certain cheerfulness, and the matter of heating the air is fully provided for by the arrangement described. The radiation from the dancing flames of the ordinary cheerful fire has also an im- portant bearing upon the subject. The j'cllow flames that the Anglo-Saxon so likes to see give out light rays principally; but, according to the latest experiments, the light rays are con- verted into heat rays after passing through the skin and warm the bod}', while the red rays and the dark or invisible heat rays do not pass through the skin, and have therefore no useful effect, unless they are made to impinge upon something that will absorb them, such as the furniture of the room. The hospital superintendents referred to find that the ward fires 208 THE HEATING AND VENTILATING OF SHIPS. have a good effect, and under the above reasoning they are scientifically correct. HEATING THE AIR BY MEANS OF STEAM, HOT WATER AND ELECTRIC RADIATORS. The next method of heating the air is by causing it to pass over the radiators that have been described, on its way into the room. It will be understood that there are two methods of arranging radiators in any room that is to be heated. One is by fixing the radiator somewhere near the middle of the room, and allowing the air of the room to be gradually warmed up by the convection currents that are set up and by the radiation from the stove. This method gives the engineer very little control over the temperature of the room, or of any part of the room, at any moment. If a door, for instance, is left open, and the passage or corridor into which it opens contains cold air, the heating within the room will probably be very poor, even with a considerable number of heating appliances, except in their immediate neighborhood and on the opposite side to *hat from which the draft is coming. The case is very similar to that of the coal fire with an open door or a very drafty door. The other method is to place the radiators, or other heating appliances, in the path of the air that is entering the room and that is to be used more or less directly for ventilation. Where ventilation is effected entirely by windows, by open door, or, as is so frequent, by loosely fitting doors, it is practically im- possible to employ radiators in this way. But where doors are properly fitted, and where a supply of air is taken directly from outside of the room, it can always be warmed by passing it over the surface of a radiator. On shore the usual method is to fix the radiators close to the outer walls of the building; under a window is a favorite position. Holes are made in the wall, fitted with gratings of various forms, arranged so that HEATING THE AIR BY MEANS OF RADIATORS. 209 the quantity of air passing through them can be regulated; and the air entering the room through these gratings is caused to pass over the surface of the radiator on its way, and there- fore attains a certain temperature before it mingles with the air already in the room. In a modification of this arrangement, the radiator is fr. FIG. 52. RADIATOR ON SHORE HEATING AIR DRAWN FROM OUTSIDE. NATIONAL RADIATOR COMPANY. specially fitted, as shown in Fig. 52, with a plate on the inner side of the radiator tubes, which acts as a baffle to the air ; and the air is obliged to pass over the full vertical and horizontal length of the radiator, and issues from it at a certain height above the floor. It is given a certain upward tendency, which causes it to mingle better with the air in the room, and produces 210 THE tiEATING AND VENTILATING OF SHIPS. very good heating effects. The question of the exit of the air in these cases belongs to the matter of ventilation and will be dealt with fully in that section. It may be mentioned here that the vitiated air of the room is usually carried off by the chimney, which still forms a part of the equipment of the modern house that is fitted with radiators, a grate also being provided that can be used in case of emergency. On board ship, the equivalent of this would be similar to the arrangement suggested for the air-heating stoves. Venti- lators bringing air from the topmost deck, or from the outside atmosphere, wherever it can be obtained without danger, would carry it by means of pipes down into the saloons, cabins, cor- ridors, etc., and the air would then be directed over the radia- tors, in the manner described, and thence out into the rooms. The difficulty involved in these arrangements is, of course, that of providing the number of ventilators that would be neces- sary, since each radiator would require its own special venti- lator, to provide its own supply of air, though it might possibly be arranged for one ventilator to supply air to two or three radiators. Unfortunatel}', under present conditions of sea- going ships, it does not seem practicable to employ the same arrangement for the supply of air as is used on shore, viz., for air to come in through the ship's side; though if valves can be arranged that will allow air to come in, and not water, when the ship is in a seaway, that portion of the problem would be solved. As will be explained in dealing with venti- lation, something of the kind has been done and may possibly be extended. The above remarks with regard to heating the air, by pass- ing it over the surfaces of radiators, apply equally to steam and hot water, and to electrically heated radiators, and that, no matter whether the electric heating elements are of the lunu'nous or non-luminous form. In fact, the majority of modern electrical convectors are arranged on those lines. HEATING THE AIR BY MEANS OF RADIATORS. 211 The air of the room is heated by passing through the radiator, enfering it at the bottom, passing upwards over the heating elements, whether they are lamps or resistance substances, and ' ■ '- 1 \ ^ /OoV / \ ■ ■■'•/ /" / //Oo^ 1 ' / 1 ■ ^ ?0(fl / / 1 ^ \ • \ / 'A?' '^^^- I . - / H ill / / v ■^^^^^^^^ ^ 1 ^^^^W>f ii WVinill 1 ■H ^ /*m^M.w >. -• - • 1 - (^ ' r t 1 -rf - , ^1 H^^P^^B^ 'iS" 1 * ' )'> - V ■ mj f ^ H *. -1 FIG. 53. DI.\GR.\M SHOWING ACTION OF STOVE .^S AIR-HEATER. issues from the top of the apparatus at a considerably higher temperature. Fig. 53. taken from the catalogue of Messrs. O. C. Hawkes, Ltd., shows the idea. The air issues from the 212 THE HEATING AND VENTILATING OF SHIPS. top of the radiator at a high temperature and gradually cools as it mingles with the air of the room beyond, ra'sing the temperature of the latter air in the process. It may be mentioned that one of the most successful forms of gas-heated radiators, an American invention, operates on these lines. It stands out in the room in any convenient po- sition, and air enters it from below, the products of combustion and warmed air issuing from below a plate on the top and mingling with the air of the room. AIR-HEATING APPARATUS, PURE AND SIMPLE. The air heating apparatus, pure and simple, really belongs to the domain of ventilation. In it the air for a whole build- ing on shore is taken hold of, is cleaned in the case of towns where the atmosphere is foul, such as London and the manu- facturing towns of the United Kingdom, and is warmed by passing over steam pipes, or cooled by passing over pipes containing either water or a solution of cooled brine, and de- livered into the rooms to be warmed or to be cooled by ducts arranged for tlic purpose. The vitiated air is led away out of the rooms by means of other ducts, and is carried away to the outer atmosphere. On shore, the usual method is to build a shaft on one side of the building, sometimes in the middle of the building, and carried up as high as convenient, and to a point where the air is as pure as it can be obtained. At the bottom of the shaft an entrance is made to the building by means of a large duct leading through a hole in the wall, and in this hole and duct are fixed the cleaning arrangements and a fan. On the other side of the hole, ducts lead to the different portions of the building, these ducts branching off to different sections of • each portion of the building, and becoming smaller and smaller as the cnl)ical space they have to supply becomes less. The hole in the wall is usually occupied by the fan, and the AIR-HEATING APPARATUS. 213 cleaning apparatus is fixed on the outside of the fan, and also heating apparatus for the very cold winter months. A favorite form of cleaning apparatus on shore is a kaiar screen, stretched in front of the entrance to the building, and having a stream of water constantly pouring over it, the screen being further cleaned by periodical flushes from a pipe above it, from which also the other cleaning water proceeds. For shipboard work, particularly the modern ship that is divided up into so many watertight compartments, the prob- lem is complicated by the fact that the deck has to take the place of the side of the building. Any air that is taken for ventilating or heating purposes must come from the deck, and any vitiated air that is expelled must be carried up to the deck. Any heating or ventilating appliance must enable the air to be carried separately into each compartment, and sepa- rately taken out of it, back to the deck. Though in the large, modern liners the deck is fairly large, it is not unlimited, and the provision of so many pieces of apparatus leading to dif- ferent compartments and leading from them is sometimes a trouble, seeing that space has to be found for so many other things, such as boats, skylights, winches, etc. On the other hand, a ship at sea has one very great advan- tage over a building on shore, especially a building standing m the middle of a smoky town. The air at sea is as pure as it is possible to obtain, and therefore, provided that reasonable care is taken to prevent the "stokers" from the chimney find- ing their way into the air inlets, and to keep the air inlets clear of outlets from lavatories, etc., any air inlet arranged on a deck that is open to the atmosphere must provide absolutely pure air, and air fairly well charged with ozone. The passage of the ship through the water also necessarily carries off the vitiated air, leaving it behind, and, providing that care is taken that the vitiated air outlets are not placed, with reference to the air inlets, so that under any conditions of wind the 214 THE HEATING AND VENTILATING OF "SHIPS. vitiated air can find its way into the air inlet, the problem of inlet and outlet, subject to the question of space, is a very simple one. Practically all that is required for warming the air sup- plying any part of the ship, say saloons, staterooms, officers' quarters, etc., are ducts leading from inlet apparatus on deck to the different parts of the ship to be warmed, and with a grid of steam pipes arranged in the path of the air to be warmed (the grid being provided with a regulating valve, so that the pressure and temperature of the steam can be regu- lated at will), and some method of driving the air down below. ]\Iodern practice on board ship has settled down to the use of fans, and they are used sometimes for driving the air down below, sometimes for exhausting the vitiated air from below, and sometimes for both purposes. The following is an account of some work done by the American Blower Compau}-, of Detroit. Mich., on board the ferryboats of the Pennsylvania Railroad Company at Xew York. The air is heated by a bank of steam coils, on the lines of those shown in Fig. 54, which is fixed in the hold below the main deck. Fresh air is brought from above the main deck by means of a shaft, and is drawn over the steam coils by means of a fan on the other side of them, and when warmed is forced through a system of galvanized iron ducts into the passenger cabins, saloons, etc. The air enters the cabins, etc., through openings 3 or 4 inches in diameter, closed by louvre gratings, arranged for controlling the supply of air in the usual way. Owing to the limited space, the ducts were obliged to be somewhat small, and the velocity of the air con- sequently rather high. The heating apparatus was arranged in sections, so thnt the duels leading to the different parts of the ship might be separately controlled. Other firms have arranged apparatus on something the same lines. INLETS AND OUTLETS FOR THE AIR. 216 FIG. 54. AMERICAN BLOWER COMPANY'S AIR-HEATER ON FERRY BOAT. INLETS AND OUTLETS FOR THE AIR. The cowl that was introduced a good many years ago for admitting air to spaces below deck has been superseded by short, vertical pipes, fitted with protecting hoods, the air pass- ing up under the hood and down the vertical pipe, instead of passing into the mouth of the cowl, as was usual in older times. The same arrangement answers equally well for an outlet for the vitiated air. The principal requirements for inlets and outlets are that they shall be very strong; shall be firmly secured to the deck; shall not project above the deck more than is necessary to obtain a proper supply of air; shall not be liable to be easily carried away by a heavy sea, and shall not be in the path of any object that may break loose in a heavy seaway. Cases are on record in which the old form of towl has been a serious danger to a ship. 216 THE HEATIKG AND VENTILATING OF SHIPS. One in particular that was mentioned at a discussion upon ventilation, at the Institution of Xaval Architects, was that of a ship which was fitted with cowls, and which shipped a very heavy sea in a storm, the sea breaking in one of the hatchways on the fore deck, and the ship commencing to settle by the Mosbioom Yalre A ValTeB ^Bjpaas TalTe c W^.i^^^ dI P^^izzA ^^^■>-A^ r IihauBt Steam A' aire witii SUam Trap humidifier VilTe Steam Inlet Valve Humidifier Pipe FIG. 00. TOP-SUCTION DECK-TYPE THERMOT.\NK SUPPLYING AIR. head. The hatchway was covered in a comparatively short time with tarpaulins and the pumps got to work, but it was found that the ship was still settling by the head, and eventu- ally it was discovered that the fore trysail boom had carried away one of the cowls, and in the darkness ( it was at 4 A. M. ) this had not been noticed. The ship had a well-deck, and the THE THERMOTANK SYSTEM. 217 sea had left a large quantity of water upon it, which was finding its way down through the hole left by the cowl. THE THERMOTANK SYSTEM. An apparatus that is now very much in use on board the I'^ading great liners and others is that developed by the Ther- ^2^ Humidifier VaWe" Steam.Inlet Valve.' .Humidifier Pipe - FIG. 56. TOP-SUCTION DECK-TYPE THERMOTANK EXHAUSTING AIR. motank Ventilating Company, of Glasgow, in which the venti- lating and heating or cooling arrangements are united in one, as shown in Figs. 55 to 60. The apparatus is arranged either to force air down below under pressure or to exhaust it, the same apparatus being available for either, as may be required. It consists of a tank or cylinder, in which a certain number of tubes are arranged in a vertical position, the air to be warmed or cooled being drawn through them by means of a 218 THE HEATING AND VENTILATING OF SHIPS. fan attached to and forming part of the plant. For heating purposes, steam is allowed to circulate around the tubes, a supply being brought for the purpose from the nearest steam service. For cooling the air, cold water or cold brine, accord- ing to the lowering of temperature required, is circulated. In addition a steam jet is arranged to provide moisture in very- dry climates. There are three forms of thermotank apparatus, which are Bypass Valve c Exhaust Steam Valve- with Steam Trap Humidifier Valve- Steam Inlet Valve.- Humiditier Pipe FIG. 0(. BOTTOM-SUCTION DECK-TYPE THERMOTANK SUPPLYING AIR. known respectively as "top suction," "bottom suction" and "between decks." The top suction type, which is shown very clearly in Figs. 55 and 56, is taken from one fixed on the boat deck of the Lusifania, and has the cylindrical tank, common' to all of the apparatus, in which the pipes are fixed. It has also the mushroom valve that will be seen above the cylindrical tank, and that is marked in the diagrams, and also a protected cowl connected to the fan chamber for the admission of fresh air. THE THERMOTANK SYSTEM. 219 When the apparatus is used to force air down into the state- rooms, etc., the mushroom valve on top of the tank is closed, and the air passes from the hooded cowl through the fan up at the back of the pipes, down through the pipes, and thence into the ducts leading to the rooms to be warmed. When the apparatus is to be used for exhausting, the mushroom valve on top of the tank is opened, and the valves marked D and C at the base of the tank are closed. The air then, instead of Mushroom Valve A £/_ V Bypass Valve I ^gg^^^^fe^^ £xhau3t Steam Valve with Steam Trap ^Humidifier Valve Steam Inlet ValveT N^^Humidifier Pipe FIG. 58. BOTTOM-SUCTION DECK-TYPE THERMOTANK EXHAUSTING AIR. being drawn from the hooded cowl, is drawn from below, and in place of passing through the tubes passes up by the side of them and through the mushroom valve at the top to the atmosphere. The bottom suction apparatus is shown in Figs. 57 and 58. It is very similar to the top suction apparatus, the difference being the absence of the hooded cowl described above. In the bottom suction apparatus air is taken from below the fan, 220 THE HEATING AND VENTILATING OF SHIPS. as seen in the diagram ; is passed through the fan, and thence through the air tubes and down into the ducts leading to the rooms to be warmed or cooled. When the bottom suction apparatus is to be employed for exhausting, the mushroom valve above the tank is again opened, the valves C and D are again closed, and the valve B, which is shown in the diagram, in the suction duct leading to the fan, is also closed, the air EU —J '^Exhaust steam ValYe .Humidifier Valye gteamjnlet Valve Humidi&er pipe FIG. 59. — 'tween deck type thermotank supplying air. from below then passing up through the fan, thence by the side of the air pipes and out through the mushroom valve at the top. Figs. 59 and 6o show a between-deck apparatus. This is very similar to those described above, the difference being that it is fixed between decks, and takes its air from a duct or flue leading to any convenient supply of fresh air. It is used either for exhausting or forcing air down, just as the others are. THE THERMOTANK SYSTEM. 221 In all forms of the apparatus there is a steam pipe leading to the top of the tank, and an exhaust steam valve and steam trap at the bottom. A perforated steam pipe, surrounding the air tubes, provides the moisture when required. It has the usual valves. For cooliag, water or cooled brine, as ex- plained, take the place of steam. It will be seen, from the description, that the thermotank £zhau6t Steam Yalre with Steam .Trap Qumidifier \ dWe Steam Inlet Talve JSumidifler Pipe FIG. 60. — 'tween deck type thermotank exhausting air. apparatus practically does for the compartments of a ship what the shafts and fans do for a coal mine. The thermotank apparatus appears also to have been more thoroughly worked out than the system of mine ventilation has, up to the present. It will be noticed that, providing that thermotank and ducts, etc., are provided for each compartment, the engineer has complete control of the ventilation, and the heating, warming and cooling of each individual part of the ship. It will be 222 THE HEATING AND VENTILATING OF SHIPS. noticed also that any type of the thermotank apparatus can be used either to force air into the spaces to be warmed, or cooled and ventilated, or can be arranged to exhaust the air from them. This follows the practice adopted in ships which carry cold storage for fruit, in which the temperature is not required to be very low. As has been explained under "Cold Storage on Board Ship," in temperate latitudes the "freezer" engineer works the cold store upon the atmosphere. That is to say, he merely takes the air direct from the atmosphere, passes it through the store and forces it out again. In many latitudes it will evidently be more convenient, and more eco- nomical, to adopt this plan with the ventilating air current for shipboard use. Another point that should be mentioned in connection with the thermotank apparatus, as will be seen from some of the illustrations, is that it is arranged to regulate the speed of the motor, and with it the quantity of air passing into, or being sucked out of, the spaces operated upon. The regulating ap- paratus consists simply of an electrical rheostat, arranged to vary the current in the held coils of the electric motor, and thereby to vary its speed. It will be seen that this gives the engineer a more complete control than is possible with any other method, providing that the steps of the regulator can be arranged sufficiently close together. As mentioned, how- ever, in a previous section, the ventilating air current increases very rapidly with the speed, because the volume of air is in- creased with the speed, and the pressure driving the air is also increased. It is necessary, therefore, that any regulating apparatus should be arranged very finely, so that the changes in the strength of the ventilating air current can be made very small indeed, and the changes in the atmosphere of the rooms under control made very gradually. It is claimed by the Thermotank Company that its system is very much more efficient than any system of steam-pipe THE THERMOTANK SYSTEM. 223 radiation, with exhaust ventilation, and as a proof of this claim are given the curves shown in Fig. 6i, in which the time oc- cupied in heating up the air of two Russian ships, one by steam and the other by thermotank, is given. In the figure, the time in hours is plotted on the base line, as abscissae, and the rise of temperature is measured by the vertical distances above the base line, as ordinates. As will be seen, wnth the thermotank, heating commenced immediately. In a quarter of an hour the temperature had risen about ii degrees F. ; in half an hour it had risen 17 degrees F. ; in one hour 22^ degrees F. ; and it continued to rise up to 32^ degrees F. at the end of four hours. With the k ao 2& 20 15 10 6 supplying f resn •■Vir with 1 ^berm ) Tank. II - -^ ■ ~ Kl ISTRC IMA II ^ ^ i / SPT / Opei > Stea a Pij e Rac iatiot with Exha i8t V :ntila ion 1 . 8. S MOi KVA Lower Deck 7 ■ . — • — ; —21 ^-— — -— _• — 1 ' :^ Main Deck | L ««* iir= =^=f^ ~ 3-1 >i ?i 1 rime in Hours. FIG. 61. — THERMOTANK HEATING COMPARED WITH OPEN STEAM PIPES. Steam-pipe heating, the temperature rises only about i de- gree in a quarter of an hour; 2 degrees in half an hour; 5 degrees in one hour and two-thirds on the lower deck, and a little over two hours on the main deck ; the total rise in five hours being only 9 degrees on the lower deck, and about 8 degrees on the main deck. These results are very striking, but though every credit should be given to the Thermotank Company for the way in which the apparatus has been worked out, the test in ques- tion by no means shows that an equal result might not have been obtained by the aid of steam, or by electricity, if the steam or electrical heating apparatus had been as suitably and carefully arranged as the thermotank apparatus was. 224 THE HEATING AND VENTILATING OF SHIPS. In these tests., the Kostroma was fitted with a thermotank supplying fresh air into a compartment of 14,803 cubic feet in extent. The heating surface was 208 square feet. There were 246 persons in the compartment, the air of which was changed 6.9 times per hour. There were 7 cubic feet of air suppHed per person per minute. FIG. 62. TOP-SUCTION DECK-TYPE THERMOTANK FOR FIRST CLASS ACCOMMODATION ON LUSITANIA. The Moskva had open steam pipe radiation, with exhaust ventilation. On the main deck, the compartment in question had a volume of 20,309 cubic feet, contained 262 persons, and was fitted with 202 square feet of heating surface. The air was changed seven times per hour, thus giving each person 9 cubic feet of fresh air per minute. On the lower deck, a THERMOTAXKS ON THE LUSITANIA, 225 compartment of 20.930 cubic feet was heated by a surface of 191 square feet. There were 284 persons, supphed each with II cubic feet of air per minute, the air being changed eight and three-quarter times per hour. FIG. 63. BOTTOM-SUCTION DECK-TYPE THERMOTANK FOR FIRST CLASS ACCOMMODATION ON LUSITANIA. THE APPLICATION OF THE THERMOTANK TO THE STEAMSHIP LUSITANIA. It will perhaps be interesting to describe the application of the thermotank system to one of the latest of the large ocean liners. The whole of the heating and ventilating of the Lusi- tania and Mauretania is practically carried out by thermotanks. These are arranged, a large number of them on the boat deck, and a small portion between decks. They deliver through ducts leading to all the spaces to be warmed and ventilated, and through louvre valves into each compartment, the valves 226 THE HEATING AND VENTILATING OF SHIPS. being fixed near the ceiling. The warmed air passes in at the higher level, and is carried out by means of other valves near the deck, into the allej'ways, etc., from which it is car- ried off to the atmosphere. In warm weather, when cooling is required, the direction of the air current is reversed by altering the arrangement of the valves in the thermotank ap- paratus, as explained, and the air is exhausted from the dif- ferent compartments through the louvre valves, into the ducts, and thence through the thermotanks to the atmosphere. That portion of the ship allotted to first class passengers has twenty-four thermotanks, principally fixed on the boat deck, around the funnels, and they draw air principally from gratings opening on to the promenade deck shelter, so as to avoid drawing in air that is exhausting from the galleys, etc., on to the boat deck. When the thermotanks are exhausting, the air, of course, passes away, and the question of the odors from galleys, etc., does not arise. It appears to the writer that a certain amount of the injector action that has been men- tioned will take place in the thermotank apparatus, when it is being used to exhaust, though the action will be reduced by the special arrangement of the protecting cowl shown. The space devoted to second class passengers has nine ther- motanks ; the third class, eleven thermotanks ; and the officers and crew, five ; the thermotanks being arranged on the tops of deck houses and where convenient. Those in the fore end of the ship are placed between decks, and fresh air is ob- tained for them from the upper deck abaft the navigating bridge, so that, it is claimed, a supply of fresh air is ob- tained in the worst weather without the exposure of cowl heads, etc., in the forward part of the ship. The thermotanks are stated to be capable of changing the air in the different compartments up to eight times per hour, and of maintaining a temperature of 65 degrees F. in the coldest weather. The system of thermotanks is inter-connected, THERMOTANKS OX THE LUSITANIA. 227 so that in case of the breakdown of any individual apparatus a supply can be obtained from one of the others. The arrangement of inter-connection appears to the writer to be a very good one. though it necessarily somewhat compli- cates the apparatus. The large number of thermotanks that it *-^*^ .ijE-fl^i-i FIG. 6i. BOTTOM-SUCTION DECK-TYPE THERMOTANK FOR SECOND CLASS ACCOMMODATION ON LUSITANIA. is necessar}^ to emplo}- (forty-nine in all) is also a matter for consideration, as it takes up a great deal of space on the boat deck and elsewhere, and it adds to the apparatus to look aft'^r. On the other hand, the engineering stafif of a large liner is thoroughly qualified to look after the apparatus, and, in fact 228 THE HEATING AND VENTILATING OF SHIPS. their labors, with ordinary care, should not be greatly in- creased by the employment of the apparatus. In the Lusitania, in addition to the thermotanks, twelve powerful exhaust fans are connected by trunks to all the galleys, pantries, bathrooms, lavatories, etc., the fans being of sufficient capacity to change the air at least fifteen times an hour. The holds and other compartments, forward and aft, are also mechanically ventilated, so that the provision men- tioned above of the air from the compartments finding its way to the alleyways, etc.. and thence to the atmosphere, is easily arranged, and the whole system of ventilation and of heating and cooling the difTerent compartments of the ship appears to be exceedingly well provided for. One serious objection arises from the fact that it has been necessary frequently to supply both inside and outside state- rooms from the same thermotank. The heat generated in the interior of these ships by the immense boiler plants, and dissi- pated and radiated, to a large degree, by both the main tur- bines and the numerous auxiliary engines, keeps the inside of the ship at a relatively high temperature ; with the result that of two rooms, side by side, one being against the side of the ship and the other inside, there will be, particularly in winter weather, a difference of temperature amounting in some cases to as much as lo degrees F., and occasionally much more. If, now, the same heat be supplied to each, the inner room will become insufferably hot before the outer gets comfortable. In such a case as this some auxiliary method of regulation be- comes well-nigh imperative ; and it is reported that this will be supplied by fitting small electric heaters to the outside rooms, and allowing these to make up any difference necessary be- tween a comfortable temperature in the inside rooms and the corresponding temperature in those next the skin of the ship. Automatic regulation of these h.eaters will be provided, so as to minimize the consumption of current and conduce to the laigest comfort of the passenger. VENTILATION. 229 FIG. G5. — 'tween deck type thermotank for third class accommoda- tion ON lusitania. VENTILATION. In the preceding sections, as explained, the writer has dealt with heating alone, but he has mentioned, from time to lirne, that heating and ventilating are very closely allied, that you cannot warm any room, for instance, or have any source of 230 THE HEATING AND VENTILATING OF SHIPS. heat present in an\' room, without producing air currents, which necessarih- ventilate to a greater or less extent. He now proposes to discuss the question of ventilation by itself, having already shown how the two can be worked together. Ventilation, as explained in the opening article of this series, is to the atmosphere of any room, or any space in which men have to work or live, what water is to dirt. Atmospheric air has the property of carrying off noxious gases, such as the carbonic acid gas that is given off at each breath by the lungs of men and animals, the exhalations that are constantly being given off from the skin of everyone, the microbes, bacilli, and even the dust that is always present. If a continuous current of air is provided, passing through living rooms, etc., the whole of these should be carried harmlessly away. In addition to the above, atmospheric air has the property of absorbing the vapor of water, and can therefore be em- ployed in cooling by evaporating moisture, such as the perspira- tion on our skins, and also can be employed to deliver the necessary moisture to the atmosphere of a room when it has become dry from other causes. As is well known, for com- fort, we require that a certain quantity of moisture shall be present in the air we breathe. If less than that quantity is present we experience a sense of discomfort. Our tongues and the insides of our mouths feel dry. On the other hand, if the air has too much moisture we experience another kind of unpleasant feeling. We cannot keep cool. The perspiration does not evaporate, and therefore does not fultil its natural function. It will be seen, therefore, that the provision of a supply of fresh air constantly passing through living rooms, etc., is necessary for health. On shore the test of pure air is taken to be the presence of a minimum percentage of carbonic acid gas. Sea air, which is taken to be the purest form of air, contains about three volumes of carbonic acid gas in lo.ooo volumes of VENTILATION. 231 air. The limit taken on shore, by educational authorities and others, is from eight to ten volumes of carbonic acid in every 10.000 volumes of air. According to the latest view of scientists, carbonic acid gas has been made more or less of a bogey. From tests that have been made it has been shown that human beings can live, without inconvenience, in an atmosphere containing a very much higher percentage of carbonic acid than that given above. On the other hand, however, it appears to be quite correct in the majority of cases to take the percentage of carbonic acid present in the atmosphere, which can be tested, as a guide for the purity of the atmosphere, with reference to the other matters, organic impurities, etc., that have been mentioned above. But this is not always strictly correct. In the case, for instance, of lavatories, the carbonic acid present may be comparatively small, while the organic matters, as evidenced by the smell, may be comparatively large. The special case of lavatories is dealt with later on. Ventilation is known as natural or mechanical, according to whether it is left to take care of itself or is more or less con- trolled. Mechanical ventilation is also sometimes known as either ''plenum" or ''vacuum." Marine engineers have exactly the same division in the matter of their furnace draft, natural ventilation corresponding roughly to natural draft and me- chanical ventilation to forced or induced draft. Plenum venti- lation, which has already been described when dealing witli methods of heating air, corresponds to forced draft and vacuum ventilation to induced draft. Natural ventilation can perhaps hardly be said to correspond to chimney draft. It cor- responds really to a condition that would be present if there were no chimney. Perhaps the different methods of ventilation, and the princi- ples of ventilation itself, will be best understood by a refer- ence to the case where it is of the greatest importance, viz. : 232 -^HE HEATING AND VEXTILATIXG OF SHIPS. in coal mining. In a number of coal mines, it will be remem- bered, as the coal is removed from its bed, gases are given off. which, if mixed with air in certain proportions, will ex- plode and do great damage if a light is presented to them. The explosive mixture is between 5 and 15 percent of the gas in the atmosphere of the mine. When the gas is present in a greater quantity than 15 percent it will not explode, because it cannot contain sufficient oxygen for combination. On the other hand, when the quantity present is less than 5 percent it will not explode, because it is too much diluted with the nitrogen of the atmosphere. These figures apply also to dangers from the vapor of petroleum in tank ships. In the United Kingdom, therefore, successive acts of Parliament have decreed that a certain volume of air shall be passed through all coal mine workings, the volume being sufficient to very quickly dilute, below the explosion point, any gas which comes away. Probably this illustrates, as well as any- thing, the cleansing action of atmospheric air. The majority of mines in the United Kingdom, and a large number in the United States, lie wholly below ground, and are reached by two vertical shafts, one of which conveys fresh air to the mine and the other carries off the vitiated air from the workings. Frorh the two shafts, which are named re- spectively "down cast" and "up cast,'' two main roads run into the mine, called respectively the "in-take," which extends from the down cast, and which carries the fresh air into the workings, and the "return," which carries the vitiated air from the workings to the up cast. RoadwaN's, or air passages, con- nect the two main roads in such a manner that there is a con- stant current of air passing across all working faces from the in-take to the return. In the early days of coal mining, what would now be termed natural ventilation ruled. The air current was left to take care of itself. Usually the warm, moist, vitiated VENTILATION. 233 atmosphere from the workings found its wa}' to one of the shafts, and being lighter than the column of air in the other shaft a certain difference of air pressure was set up between the two, which caused a certain variable and uncertain circu- lation of air through the workings. It was no uncommon thing in those days for the direction of the ventilating air cur- rent to be reversed. In those days also, occasionally, there was only one shaft. It was sometimes divided by brattice cloth into two. the vitiated air finding its way up one half and the fresh air moving down the other half. In some cases even this division was not provided, and the air in those cases formed a division of its own, the warmed air escaping up one side of the shaft while the cold air passed down the other side. The state of the coal mines in those days illustrates very forcibly what natural ventilation reall}' means. Practically there was very little ventilation at all. Any change in the tem- perature of the atmosphere outside might stop the course of the ventilating current entirely. The first improvement was the provision of a furnace in the neighborhood of the bottom of the up-cast shaft, which, by providing a column of hot air in that shaft, created what mining engineers call a motive column, by means of which the air from the outside atmosphere passed down the down-cast shaft and through the workings to the up-cast. In most modern coal mines the furnace has given way to the fan, which is usually placed at the top of the up-cast pit. It is placed there principally because the up-cast pit was cov- ered in when furnace ventilation ruled, to prevent the ingress of the colder air to the shaft, thereby neutralizing the effect of the furnace, and it was simpler to make use of the existing arrangements and to adopt the fan to them than to make new arrangements. In a few cases, however, the fan is fixed at the top of the down-cast shaft, and forces air into the mine, the vitiated air, as before, finding its way out through the 234 THE HEATING AND VENTILATING OF SHIPS. up-cast shaft. In a few cases, also, the fan at the top ol the pit is assisted by fans at the level of some of the seams that are worked from the pit, and also by fans placed in different positions in the workings, to direct the currents of air over particular portions of the working faces, etc. Marine engineers will recognize a practical counterpart to their own arrangement for supplying their boiler furnaces with air. Furnace ventilation of a mine corresponds to the ordinary chimney draft of a boiler, and fan ventilation cor- responds to forced or induced draft, according to whether a pressure or exhaust fan is employed. The writer would call attention to one very striking feature in connection with mine ventilation, which he thinks will assist marine engineers to follow the work that has been done in the ventilation of buildings, ships, etc. It will be noticed that the shafts, the roads, together with a fan or furnace, form a complete circuit, corresponding exactly to an electric circuit. The shafts and the main roads correspond to the main distributing cables of a two-wire electrical supply service. The branch roads, connecting the working faces with the main roads, correspond to the branch cables or wires connecting lamps or motors to the main supply cables. The furnace, where one is employed, corresponds to a battery, where one is used to supply current, and the fan corresponds to an electric generator. The correspondence is even closer than this. Just as suc- cessive coils of wire, passing through the magnetic field of a dynamo machine, produce successive increments of electrical pressure, so the passage of the successive blades of a fan produce successive increments of air pressure. Further, air encounters resistance in its passage through a mine, just as an electric current encounters resistance in its passage through a conductor, and the resistance in both cases varies directly as the length and inversely as the sectional area. Thus, the VENTILATION. 23o greater the length of the main roads of a mine through which the air current has to pass, the greater is the resistance offered to its passage, and the greater must be the air pressure, measured in water gage, to overcome it. Also, the larger the air passages the less is the resistance offered. The latter statement will appear at frrst sight to be incorrect, inasmuch as the resistance to the passage of air through any roadway, pipe or duct depends directly upon the friction of the air against the sides of the duct, roadway, etc.. and evi- dently the larger surface of the larger road will create more friction than a smaller surface of a smaller road. But there is another factor in the problem in connection with air. The resistance offered to its passage varies as the square of its velocity, and its velocity increases with a given air delivery as the area of the road or duct through which it passes is reduced ; and. therefore, though the increase of the size of the road or duct increases the friction offered by the surface, the total resistance is considerably lessened, because the velocity is also lessened. And all this applies to the ventilation of buildings, of ships, etc. Modern ships in particular correspond in a great many respects to the modern coal mine in the matter of ventilation. The modern ship is divided into compartments by athwartship bulkheads, and in the case of very large ships like the Liisitania by fore-and-aft bulkheads. It thus becomes neces- sary to deal with each compartment, from the topmost deck, downwards, by itself. In the Lusitania two compartments that are abreast sometimes communicate by watertight doors, as in the case of the electrical engine room, and while the doors are open they can be dealt with as one ; but the separate compartments as a rule have to be dealt with separately, and, just as with a coal mine, all the fresh air has to be brought from the surface, in this case the deck, and the vitiated air must be carried off, either on the same deck or at some point 23G THE HEATING AND VENTILATING OF SHIPS. where it will not mingle with the air that is going down below. The ventilation of ships has gone through very much the same course of development as the ventilation of mines. In the early days it was left to take care of itself, open hatches and open ports being trusted to do the work. Later on the equivalent of furnace ventilation was established, ducts being led into the holds, mess rooms, saloons, etc.. the other ends of the ducts being carried to the neighborhood of the funnel, and the circulation of the air being set up by the heated column of air produced by the hot gases in the funnel, fresh air being allowed to enter by cowls and other arrangements pro- vided for them. In the early days of heating and ventilating of ships com- pressed air was used in some cases to provide suction of the air out of the hold and between decks on the well-known in- jector principle, fresh air being allowed to find its way down below by air inlets something on the lines of the cowls that have been mentioned ; but all these systems have given way to the use of the fan, since electricity has been established on board ship and the convenience of the electrically-driven fan has been appreciated. Another point of importance should be noted here. Tt is absolutely necessary that there shall be a complete circuit wherever ventilation is to be carried on. In the case of the coal mine, the circuit is from the atmosphere, say at the entrance to the down-cast shaft, through the down-cast shaft, the in-take airway, the branch roads, the return airway, the up-cast shaft to the atmosphere again. In the case of the air supply of a boiler furnace, it will be remembered, there is the same circuit. From the atmosphere, by various passages to the stoke hole, through the ashpit, the fire bars, the fuel, the fire tubes, the up-take and the funnel to the atmosphere again. Just as with an electric circuit, if the circuit is broken, or if the passage of the current is cut off, the working of the VENTILATION. 237 apparatus the current operates is also stopped; so if the venti- lating circuit is broken at any point, if the passage of the air current is cut off by any obstruction, the working of the venti- lating air current is also stopped. Further, just as with an electric circuit, if a resistance is introduced into the path of the current the strength of the current itself is reduced with any given pressure, so if any obstruction is introduced into the path of the air current, whether for ventilation or for a boiler furnace, the strength of the air current, with any given air pressure, is reduced. It was mentioned above that the resistance offered to the air current depends directly upon the length of the path through which the air has to move, and inversely as the sectional area of the path. In other words, the smaller the duct through which the air supply is carried the greater is the resistance offered to its passage, and this means that the greater is the pressure which has to be employed in delivering the air cur- rent, and the greater the velocity of the air current itself. In this matter the ventilation of ships is at a disadvantage compared with the ventilation of buildings on shore and with that of mines, though the advantage is not often taken full advantage of on shore. For perfect ventilation, and for the avoidance of what is known as a draft, the air should circulate with a very low velocity, from 3 to 5 feet per second, but in order to do this the ducts through which it circulates must be large, and on board ship, even in the very largest liners, it is not possible to allow a sufficient space; as usual, a compromise has to be effected. The ducts have to be made as large as the other requirements of the ship will allow, their length as short as can be conveniently arranged, and the requisite current of air must be made up by increasing the velocitj' as required. A striking instance of what may be done by the provision of large ducts w'ill probably make the matter clear. At the 238 THE HEATING AND VENTILATING OF SHIPS. Birmingham General Hospital, where the plenum system has been carried out very carefully under the direction of an able architect, it is not possible to feel any draft anywhere. The whole of the building is subject to a very gentle air current, and as one passes from corridor to ward, or ward to corridor, one is absolutely unconscious of any change. Those who have visited the usual run of hospitals, where the windows are kept wide open on the stairs, while the wards are kept warm in winter, will have sometimes a painful ex- perience of the great change in the temperature between a ward and the landing outside. Further, at this hospital, the smells that are so often in evidence, such as those of dinner, of medicines, etc., are abso- lutely unknown. Everyone will be familiar with the un- pleasant smell there always is about a restaurant immediately after dinner, and usually also in the neighborhood of the wards of a hospital while dinner is going on and immediately afterwards. One can frequently tell, a little way off, if cab- bage is an article of diet, and so on. At the Birmingham General Hospital there is no sign of anything of the kind. The ventilating air current carries off all odors, just as the ventilating current of a coal mine carries off the explosive gases. And this effect is produced with the expenditure of a very small amount of power — 20 horsepower only— and with an air pressure of only i/20-inch water gage. Marine engi- neers hardly need reminding how very small a pressure this is. At Birmingham the result is produced by very large ducts. In the main duct a dozen men can stand abreast, and there is almost head room for a man to stand on another man's shoulders to reach the ceiling. The br-inch ducts are in pro- portion, and the result is as described. As against this the ventilating air current of the majority of coal mines, though the airways in the best of them are wide and high, is very powerful indeed, and it is a serious source of danger to VEXTILATIOX. 239 working miners coming from the coal face, where, in spite of the air current, the temperature in deep mines is very high indeed, and where their physical exertion causes profuse perspiration, for them to come out into the cold air current of the main roads. As explained above, it is not possible to provide large ducts, even in the largest ships, for ventilating air currents ; but, on the other hand, the lengths of the ducts, even those leading to the lower decks, is not great. As mentioned above, the ventilation of ships has settled down to the motion of the air by fans just as has the ventila- tion of coal mines, and just as the tendency of modern boiler work is to provide either forced or induced draft by the aid of fans. As with coal mines, also, and as with boiler furnaces, the air may be forced into the space to be ventilated by a pressure fan, the vitiated air being allowed to escape by any convenient outlet, or the air may be exhausted from the space to be ventilated by a suction fan, and fresh air drawn into the space through any convenient inlet. The one thing to remember in all cases where efficient ventilation is sought is that there must be an inlet and an outlet, and that the same quantity of air which passes in must pass out. A point that should be noted here is that where the space to be ventilated is also heated, whether the air is heated artificially on its way to the space, or whether it is heated in the space, either artificially or by the presence of men or animals in the space, the volume of air passing out will usually be greater than that passing in, and therefore the outlets should have a larger area than the inlets. The prob- lem in this case is the same as that in connection with both mine ventilation and the supply of air to a furnace. The fan supplying induced draft, it will be remembered, must be larger, in the sense that it will allow a larger volume to pass through it than the fan required for forced draft, because the 240 THE HEATING AND VENTILATING OF SHIP5. volume of the hot gases is larger than the volume of the air that is to be delivered to the fan. In the case of the ventila- tion of saloons, cabins, etc., the difference in volume of the air will usually not be great, but the caution given above should be remembered, in order that those who are responsible for the designing of systems of ventilation for ship-board work should be careful not to make the outlets smaller than the inlets, flaking either an inlet or an outlet small throttles the passage of the air through it, increases the pressure at which the air has to be driven through the space to be venti- lated, and increases the tendency to drafts. For ventilation, therefore, whether of the between decks where cattle are carried, the large living spaces where steerage passengers are carried, or the saloons, staterooms, or officers' cabins, the same principle holds good. Air must be brought from the deck to the space to be ventilated, and the vitiated air must be allowed to find its way back to the deck or to the outside of the ship. In some of the White- Star liners air is brought down from the deck under pressure, is directed through ducts into the staterooms, and is allowed to escape through the ports of the staterooms, saloons, etc.. when the ports are open, and when the ports are not open the air escapes by a duct provided specially for it. opening into the the ship on the inside, and opening into the atmosphere on the outside of the ship, but protected by a valve on the outside, which is open when the sea does not rise to it, but which closes automatically when the ship rolls and dips that end of the duct or if the sea washes up to it. The writer understands that this method is giving way to the system that has been worked out by the Thermotank Company, in which all air is taken from the deck and returned to the deck. In the case of cabins, staterooms, etc., opening to the atmos- phere, such as those on the upper decks, boat decks, etc., where there are any, the system of ventilation can 1'e modified- .Mr VENTILATION AND HEATING AND COOLING. 241 may be taken in or expelled from the side of the cabin, but provision must be made for the exit of the air. In the Lusitaiiia, in some of the cabins on the upper deck, an ad- justable inlet is provided for the air in the side of the cabin, and it is exhausted by a duct leading to the boat deck, a small electrically-driven fan providing motive power for the air when required. In some of the cabins on the boat deck of one of the White Star liners the w^riter noticed another ingenious method of ventilation, based upon the injector principle. A T-shaped pipe was fixed on the side of the cabin, the central portion, the stem of the T, projecting into the cabin, and the top, or cross, of the T being arranged fore and aft outside of the cabin. As the ship goes through the water air rushes through the portion of the pipe outside of the cabin, and draws air through the connecting piece leading to the cabin, causing a current of air to pass out of the cabin, through the after portion of the fore-and-aft piece. This would probably make a very efficient ventilating arrangement, but it must again be remembered that some method of providing the inlet air must be arranged or the ventilation cannot go on. The inlet air may be pro- vided by a protected duct leading to the deck above, or in any other convenient way. VENTILATION AND HEATING AND COOLING. The connection between heating and ventilating has already been explained, and that between cooling and ventilating to a certain extent. It will be understood, from what has been said, that once possession is obtained of a current of air passing continuously through a room, a saloon, mess room, cabin, etc., it can be employed for warming the room, cooling it, providing it with moisture, or reducing the moisture pres- ent by merely placing the heating, cooling, humidifying or drying apparatus in the path of the air current, and by i42 THE HEATING AND VENTILATING OF SHIPS. properly proportioning the heat supplied, the heat extracted, or the moisture supplied or e„xtracted. to the requirements of those occupying the room. Also, it will be understood that, with properly arranged apparatus, it should be possible to vary the heating, cooling or moisture at will in each compart- ment dealt with. VENTILATION OF LAVATORIES AND CATTLE SPACF.^ The ventilation of lavatories and between the decks where cattle are carried presents some difficult problems. So far as the writer is aware the between decks for cattle have not been subject to any special method of ventilation, but lavatories have, and in his opinion the between decks for cattle, and even in some cases the steerage quarters, might with advantage be subject to the apparatus to be described. The difficulty in the matter of ventilation in these cases is the effluvia that is too often present, and that even a powerful ventilating cur- rent sometimes fails to get rid of. The remedy appears to be the addition of ozone-making apparatus to the ordinary ventilating current. Ozone, it will be remembered, is oxidized oxygen. Its chemical symbol is Oz; oxygen in the ordinary way usually combining only as O2. Ozone is the great vivifying agent that is so much sought after by invalids who take sea passages and who go to the seaside. It has a ver\- peculiar and by no means a pleasant odor. It may be smelt, especially in the early morning, on open hill sides, and nn the decks of ships at sea, and again at the seaside, in particular, close down to the water's edge. It is oxygen in a very powerful condition, and its office is to oxidize, that is to say, to burn up the microbes, bacilli, etc., which produce the offensive effluvia and which will cause dis- ease if allowed to remain. Ozone is produced by elec- tricity. It may always be smelt by those who know its characteristic odor after a thunder storm. It is created VENTILATION OF LAVATORIES AND CATTLE SPACES. 243 in fairly considerable quantities by every flash of lightning, and by the silent discharges which take place during thunder storms which do not give rise to lightning. It is created industrially by the aid of high-tension alternating cur- rents, combined with what are called electrical condensers. The electrical condenser is quite different from the steam FIG. 6G. — SIMPLEX OZONE PRODUCER, EXTERNAL VIEW, condenser. Ever\- electric cable is an electrical condenser. Whenever two conductors arc close together, but separated by an insulator, an electrical condenser is formed by them, and if an electric current is delivered to one conductor a charge of electricity is delivered to and absorbed by the insulating substance separating the two conductors. For ozone-making apparatus condensers are formed 244 THE HEATING AND VENTILATING OF SHIPS. sometimes of glass tubes with conductors arranged insioc and. out, and sometimes of glass plates, with sheets of metal foil between. In the Anderson apparatus, which is illustrated in Figs. 66 and 67, the condenser consists of the glass tubes shown, with conductors in the form of coils of wire on the outside and other conductors on the inside. In all electrical condensers one of the conductors is connected to earth, in this case to the body of the ship, and a high-tension alternating current is delivered to the other conductor. The condenser is arranged to be placed in the path of an air current, and the constant charge and discharge of the electrical condenser, produced by the passage of the alternating current, converts ozone into the oxygen of the air passing through it, the ozon- ized air being then delivered wherever it is required. The high-tension current is produced on shore by the alter- nating currents of the ordinary town supply service, raised to vcr}' high tension — several thousand volts — by means of stationary transformers, similar to those that are used for the distribution of high-tension currents. Up to the present, so far as the writer is aware, alternating currents have not been employed on board ship, and therefore some arrangement is necessary for converting the continuous currents to alter- nating. This may be done by means of small motor genera- tors, consisting of two distinct machines, a continuous-current motor taking current from the lighting or power service of the ship, and an alternating-current generator, whose armature is driven by the electric motor. The alternating current can be transformed by a stationary transformer to the high pres- sure necessary. Another method which has been adopted b>' Mr. Anderson in his apparatus, and which it is claimed answers tbe puri)osc, is to employ the continuuus current taken from the lighting or power service of the ship and to subject it to very rajiid interruptidn. ver\- nnich sure that may be FANS USED IN VENTILATING. 249 required can be obtained. It is not necessary to mention to marine engineers that air pressure is measured by inches of water gage, but it may be mentioned that with modern centri- fugal fans pressures as high as lo-inch water gage have been obtained, and greater pressures could be produced if re- quired. On the other hand, for ventilating purposes, the pressure should be kept as low as possible. As mentioned, at FIG. 70.— SIROCCO FAN. the Birmingham General Hospital the pressure at the fan is only i/20-inch water gage, but in the great majority of cases pressures from i inch and upwards are employed. Fig. 68 shows one of the Sturtevant Company's* plate fans, constructed for pressure or exhaust. Another type of the same make is shown in Fig. 69. In Fig. 70 is shown a fan built by the Sirocco Engineering Company, New York. Hyde Park, Mass. 250 THE HEATING AND VENTILATING OF SHIPS. SIZES OF FANS REQUIRED. The size of the fans required for driving air through spaces to be ventilated depends upon two quantities : the vohime of air to be delivered per minute and the velocity or, what amounts to the same thing, the pressure at which it is de- livered. The problem is very similar to that of the chimney for the boiler furnace, and to that of the fans employed for furnishing forced or induced draft. It will be remembered that the sectional area of the chimney must be large enough to accommodate the quantity of hot gases that may have to pass through it when the boilers are doing their hardest work, and it must also be high enough to give the requisite motive column to drive the air and gases through the furnace, flues, etc. Similarly, with forced and induced draft the fans must be large enough to allow of the passage of the air or hot gases through them without throttling, and must be able to produce the necessary pressure to drive them. With ventilating the same thing occurs. The fans employed must be large enough to allow of the passage through them of the largest quantity of air that may be required, and they must be able to furnish the pressure necessary to drive that quantity of air through the ventilating system. With the propeller fan, the size of the fan. that which rules the quantity of air it can pass, is its diameter, and the pressure obtained from it depends upon its speed. The pressure ob- tainable with any propeller fan is very small, and in practice on board ship only very small fans are employed, driven usually by small electric motors, and capable of handling the ventilation of cabins, small mess rooms, or of assisting, or as electrical engineers would say, "boosting," the ordinary ventilating current in saloons, etc. There is a point that may be mentioned in connection with propeller fans, though it will hardly come into the practice of heating and ventilating on THE POWER REQUIRED BY THE FAN. 251 board ship. As explained, the propeller blades carry the air from one side of the fan to the other as they move, just as the propeller of a steamship carries the water from one side of it to the other, but while this is true of the outer portions of the blades of the propeller, there is a return air current at the center of the propeller, which may be seen by testing with a ribbon, or something of that kind. This return current, which is in the nature of an eddy, very much on the lines of the eddies that seamen are familiar with in rivers and on the coast, necessarily lessens the efficiency of the fan, and re- quires more power to be employed in driving it. With centrifugal fans, the size, in the sense of the ability to accommodate volumes of air, the size which corresponds to the sectional area of the chimney, is the width of the fan, the width between the disks which usually inclose the blades. The wider the fan the larger the quantity of air it will accommo- date without thrcttling. It will be understood that the air passages in a fan offer resistance to the passage of the air through them, just as the passages through which steam passes in doing work offer resistance to its passage, and that this resistance makes a charge upon the power that must be delivered to the fan shaft by the electric motor, or whatever is driving it. Thus a small fan may require a larger power than would be necessary to do the same amount of work in moving the air by a larger fan. The pressure delivered by the fan varies with the square of its speed. It is not possible to give any rule for the size of fan required for any given work nor the speed, because there are so many fans upon the market, every one of which differs in the pressure it furnishes per revolution and in the capacity for allowing the passage of air. THE POWER REQUIRED BY THE FAN. As marine engineers know, power is required to move the 252 THE HEATING AND VENTILATING OF SHIPS. air under aii}^ given conditions, and it depends directly upon the quantit}' of air to be moved and on the velocity at which it is moved. Air has weight, and creates friction when moving through pipes, ducts, etc. Both of these features demand the expenditure of energy when the air has to be moved. The matter may be put in another way — the power required de- pends upon the velocity at which the air is moved and the pressure that is required to move it. In the case of a com- plete ventilating circuit, from the entrance of a duct leading to a room to be ventilated, to the exit from the duct leading back to the atmosphere, the power required will be measured by the velocity at which the air is moved, multiplied by the difference of pressure between the inlet of the fan and the exhaust of the system. The pressure would be measured, of course, outside of the fan or other apparatus employed to move the air. It will be noticed that the conditions are exactly the same as in the case of an electric circuit. It will be remembered that the power required in an electric circuit is measured by the current passing in the circuit, multiplied by the pressure required to drive the current through the circuit. In the case of air, the w^hole of the pressure employed in the air circuit must be taken into the calculation for finding the power required. Thus, if the air is moving under a pres- sure of 2-inch water gage, and the duct has an area of 12 square inches, the total pressure will be 24-inch water gage, or a total of 13 ounces; i-inch water gage, it will be remem- bered, being equal to 0.55 ounce on the square inch. When the total pressure and velocity arc known the horsepower in the air is given by the formula P X V H. P. = , 33,000 where /> Is the pressure in pounds per squafer inch and v if) TESTING THE AIR CURRENT. 253 the velocity in feer per minute. This, however, is the horse- power in the air onl\-, and takes no account of the efficiency of the fan or other losses ; and in estimating tlie actual horse- power required, when the quantities given above are known, it will be wise to double the figures obtained from the last formula. It was mentioned above that the pressure created by a centrifugal fan varies as the square of the speed. The power absorbed by the fan varies as the cube of the speed. When the speed of a fan is increased two operations take place : the quantity of air delivered by the fan is increased, and the pressure at which the air is delivered is also increased, and hence the cube ratio for the power. When a fan is running, each blade, as it goes around, delivers a certain quantity of air to the duct, or whatever it may be delivering into, and the greater number of revolutions the fan makes the greater is the quantity of air delivered and in exactly the same pro- portion. The velocity of the air issuing from the fan neces- sarily varies as the square of the speed of the fan in accord- ance with the well-known laws. TESTING THE AIR CURRENT. In any system of ventilation, or of combined heating and ventilating, it is necessary to test the course of the ventilating current and also the velocity. The course of the ventilating current can be traced with comparative ease by the use of light pieces of ribbon held on the end of a stick in the air current. The paper windmills that are made for children to play with are also very useful for the purpose, as, if properly made, they are very sensitive. They must be placed, it will be remembered, with their axes facing the direction of the wind, and they will be found to show the direction and a rough approximation of the force of the wind very readily. To estimate the velocity of the air current an anemometer 254 THE HEATING AXD VEXTILATIXG OF SHIPS. must be employed. It is an instrument which requires a con- siderable amount of ;.kill in handling. It consists of a short brass cylinder, carrying what is virtually a small propeller fan pivoted on an axis in the center of the cylinder, and arranged to count up its revolutions on one of the usual dials. The -apparatus must be placed so that the fan blades receive the air current in the same manner as an air current would be created by a propeller fan. and the test is made by counting the number of revolutions in a given time. MEASURIXG THE AIR PRESSURE, The simplest method of measuring the air pressure is by means of the apparatus with which marine engineers will be familiar — the water gage — consisting of a U-tube, having water in the bend and arranged for the two ends of the tube to be open to the portion of the air current between which the difference of pressure is to be measured. ^leasurements of the pressure between the atmosphere and any portion of a ventilating air current are made by allowing one end of the tube to be open to the atmosphere and connecting the other end to the air current whose pressure is to be measured. Water gages are often arranged with one end of the tube bent at right angles, the tube itself being held upon a flat board, very much in the same way as a thermometer is held, and the bent end of the tube being pushed through a hole in the board. A length of india rubber tube can be employed to connect the ends of the tube with the atmosphere to be measured. For measuring very small dift'erences of pressure the micro- manometer shown in Fig. 71 may be employed. It is claimed that readings to 1/2000 millimeter may be obtained. ESTIMATING THE HEAT TO BE PROVIDED. In the preceding sections the writer has explained how the estiMj^tixg the heat to be provided. 255 heat is delivered from the different appliances to the air of the room, how the air entering a room is heated and how the ventilating current is made use of to heat and cool a room, etc. In a later section he proposes to estimate the probable quantity of heating apparatus and the probable current re- quired to heat a large ocean liner throughout by electricity. FIG. Yl. — THE MICROMANOMETER. Before doing so it will perhaps be as well to consider how the heat that is required has to be estimated. In the earlier articles it was pointed out that the heating apparatus in a great many cases was left to heat up the room, the saloon, etc., as best it could; and in other cases the air was heated as it entered the room, either by appliances in the room or by appliances placed in the path of the air current. But he has not dealt In detail with the quantity of heat that 256 THE HEATING AND VENTILATING OF SHIPS. has to be provided. The conditions, of course, will vary with the different climates a ship may be passing through and with the different times of the year, but the same rules will apply in all cases. It is not sufficient to assume that the air of a room is heated up by the heating appliance and remains heated. This is what used to be assumed in the old days of open fireplaces and natural ventilation. The modern heating and ventilating engineer carefully esti- mates the quantity of heat that passes out of the space to be warmed in exactly the same manner as he estimates the quan- tity of heat that he can deliver to the space through the sur- faces of his heating appliances. Evidently there will be two distinct sources of loss of heat in any room to be warmed — the entrance of cold air from outside and the passage of heat, from the room to be heated, through the walls, floors, ceilings, etc. The first source of loss, the entrance of cold air, is ex- ceedingly difficult to estimate for. It is usual to provide against it, as far as possible, by warming the corridors, alley- ways, vestibules, etc., and in tlw present case it will be left out of the calculation, it being assumed that the air of the alleyways, etc., is warmed to a temperature of lo degrees above that of the outside atmosphere. The heat to be provided then consists of two quantities — that ;equired to raise the temperature of the air and the objects in the room to the desired amount, and that required to replace the heat passing out through the walls, floors, etc. THE HEAT PASSING OUT THROUGH THE SHIP's SIDE^ BULKHEADS, * ETC. It will be understood from what has been said with regard to the passage of heat from a higher temperature to a lower, that the rule given as to the passage of heat from a heating appliance to the surrounding air applies equally to the pas- sage of heat from the air in a stateroom to the water outside THE HEAT PASSING OUT. 257 the ship, or to the air on the other side of the bulkheads, the other sides of the deck, etc. That is to say, the passage of heat through the ship's side, t':e bulkheads, etc., will be in direct proportion to the difference of temperature between the inside of the stateroom and the water or air on the outside of the ship or the bulkhead, in direct proportion to the surface exposed to the action and to the thermal conductivit}' of the substance of which the walls of the stateroom are composed. The heating appliance, whatever it is, must deliver heat to the stateroom at the same rate as it is carried off. Assuming the temperature of the stateroom to be main- tained at 70 degrees F., the temperature to be worked to out- side the walls of the stateroom is evidently the lowest that is likely to be met with during the ship's voyage, and this will vary with the climates into which the ship goes and with the seasons. Whalers and sealers, and ships which go into the very cold regions in the neighborhood of the Arctic circle, will be subject to very low temperatures, while those which are engaged in the bulk of the ocean traffic, crossing the Atlantic and the Pacific in various directions, will not have such wide variations. In the calculations which follow, a minimum temperature of 30 degrees F. is taken for the sea and 40 degrees F. for the air outside of the staterooms, with the proviso that for ships in which lower temperatures are met with, these lower temperatures must be substituted in the calculations. It is also assumed that the air in the alleyways, corridors, and generally between decks, will be warmed to a temperature 10 degrees above that of the outside atmosphere. In houses in Canada and America, that are subject to very low temperatures in winter, it is usual to raise the temperature of the halls, passages, etc., to ver}- nearly that of the living rooms, as serious colds might be taken if this were not done. Also, in the case of instittitions in the United Kingdom, such as hospitals, hotels, technical colleges, etc., that are warmed '258 THE HEATING AND VENTILATING OF SHIPS. and ventilated on the plenum s3-stem, the temperature of the corridors, passages, etc., is practically the same as that of the wards, coffee rooms, class rooms, etc. Take a stateroom having a cubical capacit}^ of i,ioo cubic feet — this figure is taken to simplify calculations — the dimen- sions being 12 feet long (fore and aft) by 11^ feet wide and 8 feet high. The surface exposed to conduction from the air of the room to the water outside will be 96 square feet, and that exposed to the air, either of other staterooms or of corri- dors, etc., will be 8 X 35 ^ 289 square feet. The surfaces of the decks, above and below, will be 2 X 138 = 276 square feet. We may consider that the 96 square feet of the ship's side is subject to a difference of temperature of 40 degrees F. Iron has a conductivity, according to Box, of 233 British thermal units per square foot per hour per i degree F. It will be seen, if the stateroom is not lined with wood on the ship's side, how enormous will be the transference of heat from the air of the room through the ship's side to the water. Under the conditions given above the quantity of heat passing out would be over half a million units per hour, requiring a very large heating apparatus to replace it. Incidentally, this shows the difficulty of warming parts of the ship where the naked side plates, etc., are exposed to the water on one side and the air of the ship on the other in very cold climates, and the ad- vantage of wooden ships, in this respect, in cold climates. A study of cold-storage methods enables the problem to be very effectively dealt with, and the passage of heat from the staterooms, saloons or any part of the ship to be effectively prevented. A lining of wood is in itself effective, because wood has a conductivity, according to Box, in the neighbor- hood of 0.8 unit per hour for a thickness of i inch, and if the wood lining is so arranged as to inclose a small air space between itself and the ship's plates, and more particularly if the air space is divided nj) into small spaces, so that convection HEATING A PASSENGER STEAMER BY ELECTRICITY. '^3^ air currents shall not have much room to circulate, and if the wood lining is thoroughly dry, the leakage of heat from the staterooms or saloons, under these conditions, may easily be reduced to 0.5 unit per hour per degree F. difference of tem- perature for each square foot of surface of the room all over. Taking the dimensions given above, the total surfaces equal 652 square feet, of which 96 square feet will be transmitting 1,920 units per hour, and the remaining 556 square feet 8,340 units per hour, making a total of 10,260 units per hour, which would lower the temperature of a room of the size given 9.3 degrees F. per hour, unless it was replaced from a heating appliance. With electrical apparatus this means that 3,000 watts must be delivered to the heating appliances, and this would require three of the usual four-lamp luminous radiators, one non- luminous radiator of 3,000 watts, two of 1,500 watts each, or any other equivalent. With hot water or steam, taking the rate given above of 1.5 heat units liberated per square foot of heating surface per degree F. difference of temperature, and assuming the hot-water apparatus to have a temperature of 170 degrees, 10,260 heat units would require approximately 70 square feet of heating surface. With steam at 210 degrees the heating surface would be approximate!}' 50 square feet. In the estimate for heating an ocean liner entirely by elec- tricity the calculations have been made on these lines, the surfaces through which heat passes out being estimated, and the quantity of heat calculated from the differences of tem- perature, etc. THE HEATING BY ELECTRICITY OF A LARGE PASSENGER STEAMER. The writer has outlined a scheme for heating a large pas- senger steamer throughout by electrical apparatus, and he has selected for the purpose the North German Lloyd steamer Kaiser IVilhclm der Grossc, which has a displacement of 260 THE HEATING AND VEXTILATIXG OF SHIPS. 20,000 tons, carries a crew of 450, and has accommodation for 1,500 passengers — first, second and third class. Her dimensions are: Length, 625 feet; breadth, (i() feet; depth, 43 feet. It will be understood that a scheme of the kind can be only approximate. As engineers know well, the figures for each case, in engineering practice, have to be worked out by them- selves, and the present writer has not the whole of the neces- sary figures before him to enable him to make an exact esti- mate. The figures will, however, he believes, be sufficiently accurate to show what can be done by electrical heating appa- ratus, and what it is likely to cost. The writer has also taken into account in the heating appliances only the passenger accommodation and its accessories. The Kaiser Wilhehn der Grossc has : A first class dining saloon, measuring no by 65 feet, placed amidships on the main deck ; a second class dining saloon, measuring 50 by 55 feet, aft on the main deck; a children's saloon, measuring 44 by 26 feet, aft on the main deck ; a children's dining saloon, measuring 45 by 30 feet, forward on the main deck ; an auxiliary second class dining saloon, 50 by 15 feet, aft on the upper deck; a first class drawing room, 32 by 30 feet, amidships on the promenade deck; a second class drawing room, 25 by 20 feet, aft on the upper deck; a first class smoke room, 2i2> by 40 feet, forward on the promenade deck; a second class smoke room, 38 by 26 feet, aft on the promenade deck ; a reading room, 30 by 20 feet, forward on the promenade deck. It has also accommodation for third class passengers on the lower deck totaling 200 by 34 feet ; also for stewards for third class passengers on the lower deck totaling 120 b}' 20 feet; acconunodation for third class passengers on the main deck, 42 by 40 feet ; accommodation for attendants on the main deck, 40 by 20 feet. In addition there are some 260 spaces to be heated, comprising HEATING A PASSENGER STEAMER BY ELECTRICITY. 261 Staterooms, hospitals, kitchens, pantries, lavatories, etc., and there are the usual vestibules to the saloon, in which the stairs leading from one deck to the other in the passenger departments are fixed. The height between decks for the promenade, upper and main decks, is 8 feet, and that of the lower deck is 7 feet. There is the usual orlop deck, but it is occupied mainly by boilers, coal bunkers, cargo, baggage, chain lockers, etc. The writer has divided the staterooms and similar spaces into two sizes to simplify the calculations. One lot, of which he makes out that there are approximately 100, measure 10 by 10 feet by 8 feet high. The smaller ones, of which there are about 160, measure 8 by 6 feet by 8 feet high. In calculating the heating apparatus required and the quan- tity of current to furnish the necessary heat, the writer has worked to the same figures as were used in explaining how to calculate the quantity of heat that must be provided by any heating apparatus to make up for the heat lost by passing out through the sides of the ship, the bulkheads of cabins, saloons, etc., and the decks above and below. The problem, it will be seen, is similar to that which the refrigeration engineer has to deal with. In the case of cold storage the problem is to carry off the heat that passes in through the walls, decks, etc., of the cold chamber. In the present case the problem is to deliver heat to the rooms to be warmed, to make up for that which has passed out through the walls, decks, etc. To estimate the quantity of heat that must be delivered by any heating appliance, the quantity of heat passing out of the room to be warmed must be estimated by taking the surfaces through which heat can escape, the quantity of heat escaping per square foot, and the difference of temperature between the inside and the outside. The rate of passage outwards of heat the writer has taken at the figure given in a previous article, 0.5 British thermal unit per hour per square foot per 262 THE HEATING AND VENTILATING OF SHIPS. degree F. difference of temperature between the inside and the outside ; with one exception, that of the skylights of the first class dining saloon and the first class drawing room. The rate at which heat passes through glass is very much higher than that at which it passes through wood, and it has been assumed, in all the calculations, that wood is the substance through which the heat from the saloons, state rooms, etc., has to escape, except in the case of the skylights mentioned. The writer has also taken the figures mentioned in a pre- vious section, viz. : a minimum temperature of 30 degrees F. outside the ship and a temperature to be maintained in the rooms to be warmed of 70 degrees F. In a great deal of the passenger service the minimum temperature mentioned, 30 degrees F., will not be reached. Probably a temperature of 40 degrees F. would be more like the average, but even cross- ing the Atlantic in winter very much lower temperatures are met with. The calculation is intended as a guide onh-, and must be altered to suit the temperatures, and it is a verv simple matter to do so. Thus, the extreme range of tem- perature taken in the writer's calculations is a difference of 40 degrees F. For ships which meet temperatures of jo de- rrees F. an addition of 25 percent to the heat required to be delivered will be necessary, and to the heat- furnishing ap- pliance. To ships meeting temperatures of 10 degrees F. an addition of 50 percent to the writer's figures will be required. For the average minimum of 40 degrees F.. which will prob- ably meet the case of a large number of ships, the writer's figures may be reduced by 25 percent. It should also be noted that the writer has taken 70 degrees F. as his standard of temperature within the rooms to be warmed, this being the temperature to which Americans are accustomed. Furopeans arc accustomed to take standard tem- peratures of 60 degrees, or at most 65 degrees F. For those ships where a standard of 60 degrees F. would be sufficient HEATING A PASSENGER STEAMER BY ELECTRICITY. 263 for living places the writers figures may again be reduced by 25 percent. In drawing his estimate, also, the writer has assumed that the heating appliances would be placed in the best position for distributing the heat to the best advantage. On board ship there is not the same trouble as on shore with chimneys, except in those saloons that are furnished with grates, fires and so on, and therefore there is not the danger of the heat liberated by the heating appliance being carried off up the chimney. Ventilation, of course, must be provided, and, as already indicated, the best method is to place the heating appliance in the path of the ventilating air current, where it enters the room to be warmed. Where there is no special ventilating arrangement the heating appliances should be placed as far as possible in the line of the natural ventilating air current, the air which comes in under doors and by other openings as it enters the room. There are two or three important points that should be noted in connection with the calculations for the size of heat- ing appliance required and the quantity of current. Thus, of the two sizes of staterooms, the larger measuring lo by lo feet by 8 feet, or 800 cubic feet, and the smaller 8 by 6 feet by 8 feet, or 384 cul)ic feet, say 400 cubic feet in round figures ; owing to the much larger surface in the lo-foot rooms above that exposed in the 8-foot rooms, the amount of heat passing out through the walls, etc., and the amount of heat therefore required to be delivered to the air of the rooms to make it up, is enormously larger for the large rooms than for the smaller, as will be explained. In the present case, also, the first class dining room arxa drawing room are exceptionally well placed, as far as. the requirement of heating appliances is concerned, because they lie between two funnels. The funnels, of course, are protected on the outside, so that the passage of heat outwards is a 264 THE HEATING AND VENTILATING OF SHIPS. minimum, but the writer has assumed that a certain quantity of heat docs pass from the funnel casing into the dining and drawing rooms. It is a case of heat passing into these rooms in place of passing out of them, and the quantity of heat that has to be delivered by any heating apparatus to these rooms is lessened by the heat delivered from the funnels. In esti- mating the heat required for the dining saloon the writer has taken the heat passing out through the ship's side, the decks above and below and the skylight, and has subtracted from it the heat he estimates will pass in from the funnel casing. In the case also of the alleyways, as the engine-room funnel and stoke-hold casings will line the alleyways for a large portion of the length of the ship, and as a considerable amount of heat must pass from them into the alleyways, the writer has assumed that the temperature of the air in the alleyways will be raised lo degrees above that of the air outside during cold weather. APPARATUS ESTIMATED TO BE REQUIRED FOR HEATING THE DIF- FERENT SALOONS, STATE CABINS, ETC. The electrical heating appliances, it was explained, are made in various sizes to absorb from 200 watts up to 6,000 watts. These heating appliances, it will be remembered, are divided into two distinct varieties, those in which the long incandes- cent electric lamps are employed and those in which non- luminous resistances are employed. The lamps* are usually arranged lo absorb 250 watts each, though the Prometheus Company, of Great Britain, has recently introduced lamps taking 350 watts, and l)urniiig at a red heat in place of a yellow heat. The 250-watt lamp, however, forms a very convenient standard, particularly as it is made up into appliances carrying 2, 3 and 4 lamps, and in the following estimate the writer gives the figures in watts required and in lamps of 250 watts each : The first class dining saloon requires the expenditure of COST OF FURXISHIXG THE HEAT. 265 4.500 watts, or 18 lamps. The first class drawing room re- quires the expenditure of 1,400 watts, or 6 lamps. The second class dining room requires 3.500 watts, or 14 lamps. The children's dining room requires 3,000 watts, or 12 lamps. The children's saloon requires 2.500 watts, or 10 lamps. The auxiliary second class saloon requires 1,250 watts, or 5 lamps. The first class smoke room requires 2.000 watts, or 8 lamps. The second class smoke room requires 1,500 watts, or 6 lamps. The reading room requires the expenditure of 1,000 watts, or 4 lamps. The third class passengers' quarters, stew- ards, attendants, etc.. require 6,000 watts, or 24 lamps. The large staterooms, the writer makes out, require 2.500 watts, or 10 lamps, and the smaller staterooms 250 watts, or even less, or i lamp. Taking the number of the larger state- rooms at 100, this means i.ooo lamps in addition, and the number of the smaller rooms at 160 means 160 more lamps. In addition to the above there are the vestibules mentioned. The total number of 250-watt lamps given in the above list is 1,267, 2i"d it will therefore be wise to allow for a total, to cover all contingencies, of 1.500 lamps of 250 watts, or for a current of 375 kilowatts. The above figures are for the minimum outside temperature mentioned, 30 degrees F. If a temperature of 20 degrees F. has to be provided for 1.875 lamps, or say a current of 470 kilowatts, would be required. With a temperature of 10 de- grees F.. 2,250 lamps and a current of 565 kilowatts would be required. With a temperature of 30 degrees below zero F., or 100 degrees F. difference between the outside and the rooms to be warmed, 3,750 lamps would be required, and a plant capable of furnishing 940 kilowatts, or about 1,250 horsepower. THE COST OF FURNISHING THE HEAT REQUIRED. So far as the writer has been able to ascertain, no figures have yet been accurately taken out giving the cost of generating 260 THE HF.ATI>.G A>:d ventilating of ships. current on board ship. With electric lighting as an auxiliar> the steam required has gone in with other auxiliaries. Or the other hand, it is often not the rule to condense the steam used by auxiliaries, and the consumption of electric light engines is taken at about 40 pounds of steam per kilowatt- hour. But it must be remembered that the steam is being,* generated under the most economical conditions. The steame" crossing the Atlantic, or at sea for any number of days, undei any possible conditions, providing she is continuously steam- ing, is generating steam under the most favorable conditions known to the engineer. There are practically no stand-by losses, such as send up the fuel cost so much on shore. On shore, it will be remembered, lighting is required only for a certain number of hours during the day, and power evei? is required only for a certain number of hours, and there are portions of the day, both with lighting and with such power services as that for tramways and suburban railways, when the quantity of current is very high indeed for a short time, dropping to something very small between those times. Thi.s means that either boiler furnaces have to be banked or they have to be let out and relighted. In either case it means the consumption of a considerable quantity of fuel not required in steamship work. Further, the oil and petty stores and other things required for electrical generating plant on board ship, are part only of a large whole, and therefore should be ob- tained more economically, providing proper care is used in issuing stores, than where the plant, often a comparatively small one, has to buy everything specially for its own use. The attendance, also, in the case of a shipboard electricity generating plant, should be smaller than for a similar plant on shore. Boiler attendance goes in with that of the main engines. Even a very large electricity generating plant will not make much appreciable difference to the stoke-hold labor of a ship of 20.000 tons and of 27000 horsepower, such as the Kaiser Wilhchn dcr Crosse. Attendance, in fa.'t, is COST OF FURXISHING THE HEAT. 267 resolved into that of the electrician on watch, with possibly an assistant to oil, and the electrician to look after the appa- ratus in use, to make good little breakages, keep switches right, etc. The writer thinks that he will not err on the side of optimism if he takes the cost of electricity at o.5d. (one cent) per kilowatt-hour (Board of Trade unit, as it is called on shore in the United Kingdom). In America there are many electrical generating plants, generating current for railways and other purposes, in which the cost is very much less than the figure taken above, and there are cases even in the United King- dom of electrical generating plants at collieries and in other works where the cost of generation is much less than o.5d. If the above figure is taken, therefore, any estimates founded upon it should be fairly safe The heating appliances detailed for the different saloons, etc., total up to 107 lamps of 250 watts each. These heating appliances will probably be required from 8 A. M. to mid- night, or say 16 hours, and in addition a certain number of the smaller staterooms, and possibly a few of the larger ones, will probably be required during the same hours, and therefore it will probably be approximately correct to assume 240 lamps of 250 watts each as being employed for 16 hours per day. This means 60 kilowatts for 16 hours, or 960 kilowatt- hours per day. The writer estimates that probably 60 lamps of 250 watts will be required for the full 24 hours ; this equals 15 kilowatts for 24 hours, or 360 kilowatt-hours. Of the remainder, the staterooms and other places will be re- quired for probably 4 hours during the da}'. In addition there will be some 1.200 lamps of 250 kilowatts, or the equivalent, which will probably be required for 4 hours out of the 24. This means 300 kilowatts for 4 hours, and equals 1,200 kilowatt-hours. Adding these together, the total is 2,520 kilowatt-hours per day. 268 THE HEATING AND VENTILATING OF SHIPS. This would cost, at o.5d. per kilowatt, £5.5.0 ($25.55) per day, or say iji.io.o ($153.30) for a six-day passage across the Atlantic. If 20 degrees F. is taken as the minimum tempera- ture the total cost will be £39.7.6 ($191.62) for the trip; if 10 degrees F, is the minimum, £47.5.0 ($229.95), and for lower figures in proportion. For ships trading to very cold climates, and where economy is essential, where also the heating 'would be required for months together, the cost would probably be prohibitive in the great majority of ships. With a temperature of — 30 degrees R. or 100 degrees F, difference, the cost of heating would be £13.2.6. ($63.88) per day for a ship of the size of the Kaiser JJ'ilhelui dcr Grosse, and with its crew and passengers. But as ships which go on whaling cruises do not carry passengers nor large crews, electric heating even then might be found economical, on account of its convenience, in some cases. The heating can be carried out at less cost by the steam or hot water appliances that have been named, but as in so many other things the great convenience of the electrical method of distribution and of control more than counterbalances the in- creased cost, which, as will be seen, is but a very trifling sum, as against the whole cost of running a steamship of the size of the Kaiser Wilhchn dcr Crosse across the Atlantic. There are, of course, other points to be considered. Additional plant will be required to furnish the current, and it would probably not be safe to have less than 500 kilowatts for the special heating appliances in the case of the ship considered, and under the conditions named, and larger plant in proportion for the lower temperatures. There is the question of finding room for a 500-kilowatt plant and the larger plant where required, though with turbo- generators this question is reduced to a minimuum. There is also the question of the additional cables. Already the cable problem is a somewhat serious one in connection with lighting. COST OF FURXISHIXG THE HEAT. 269 and the addition to it of the requirements for heating will increase the trouble. There is no reason, however, that the heating current should not be taken off the Hghting service, and, providing the conductors for the Hghting service are properly divided up, as they always are in modern steamships, so that it is hardly possible for all the lights to be out at once, the trouble of the increased size of the conductor will not be so great. When a cable reaches a certain size a comparatively small addition in diameter gives it a considerably increased conducting power. For the lower temperatures the cable question would be more serious. Everything, first cost and running cost, in- creases as lower and lower temperatures have to be provided for; but, again, in the case of the whaler, as the whole plant would be small, the matter need not be very serious. VAN NOSTRAND'S NAVAL BOOKS 950 Pages 4J^ X 7 Postpaid $5.00 C70 Illustrations Flexible Binding FOURTH ENLARGED EDIT I. ON The Naval Constructor A VADE MECUM OF Ship Design for Students, Naval Architects, Shipbuilders and Owners, Marine Superintendents, Engineers, and Draughtsmen By GEORGE SIMPSON Members of the Institution cf Naval Architects, Assoc. Member American Society of Naval Engineers. 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