[Written for ICE AND REFRIGERATION.]

MECHANICAL REFRIGERATION.*

THE VARIETIES OF REFRIGERATING MACHINES-ALL HAVE THE
SAME EFFICIENCY WHEN PERFECT-THE COMPRESSION
AND ABSORPTION MACHINES.

R

EFRIGERATING machinery has a singular variety in outward appearance, mode of action, and in the substances employed as agents, but as the object in each and every one is the same, namely, to remove heat, we are prepared to find that one common principle underlies them all.

An observer cannot fail to notice one characteristic common to all such machinery; and if the apparatus were entirely covered from view, it is certain that he would find high temperature heat, or the means of producing it, going in at one end, and low temperature heat, or substances cooled below the surrounding temperature, coming out at the other. Whatever may be the claims as to the advantage of this or that style, and however mysterious its operation may appear, we could certainly predict that a certain amount of coal would have to be supplied for every ton of ice turned out. Moreover, as we have seen, we can predict further (when we know the temperatures involved) the least possible amount of coal which will be needed, and that without considering the details of the process. This fact is of some consequence, for ingenious men can readily make complex combinations, which it would be very difficult. to analyze or examine in detail, the more so as the physical properties involved may be only very vaguely known. The claim in any such case must be limited to the maximum production possible.

Any refrigerating apparatus may be represented by the simple scheme, Fig. 1, in which is a source (namely, the boiler or generator) from which a quantity of high temperature heat, H, is supplied, and B is a refrigerator from which a certain quantity of low temperature heat, h, is drawn. C encloses a mechanism of some kind, by the operation of which the double flow of heat is caused to take place; or, rather, by reason of which the flow of heat from the refrigerator is brought about as a consequence of the flow of heat from the generator.

The object of all refrigerating processes is to obtain the greatest amount of refrigeration with the least exCopyright by Geo Richmond, M. E. All rights reserved.

h H'

$2.00 PER ANNUM.

penditure of heat; that is, to make the proportion of h to H, or the fraction as great as possible. In the perfect machine, of whatever type, as will be shown hereafter, these two quantities of heat are directly proportional to the temperatures at which they are supplied, and inversely proportional to the ranges through which they are used.

The general character of the various machines constituting the compensating device C must be well known to the reader, and he will find descriptive details of nearly every class in earlier numbers of this journal, and particularly in a series of articles by Mr. A. J. Rossi, running through the first and second volumes. They

A

с

B

FIG. 1.

may be conveniently classified as follows: I. Compression machines. II. Absorption machines. III. Mixed. IV. Vacuum machines. V. Liquefaction machines. Compression machines may be again divided into: (a) Those using permanent gas with open circuit, or closed circuit (i. ., dense air system of L. Allen). (b) Those using liquefiable gas, as ammonia, sulphuric acid, carbonic acid, water. (c) With or without expansion cylinder. Air machines must and it would seem that carbonic acid ought to have expansion cylinders. (d) Those using wet or cold compression, and those running with superheated gas. The former is known as the Linde system, while the latter is in more general use in America.

Absorption machines present an endless variety in details, but the mode of operation in all is very nearly the same, with exceptions that will be noticed in the proper place. One characteristic division is that of intermittent and continuous machines. Another is that of those using liquid absorbents and those using dry absorbents.

Mixed machines are those employing partly compression and partly absorption, such as the machine of Harrison, and, more recently, that of Mr. Thomas Rose.

Under the name "Vacuum," two machines are known, one of which is properly a compression machine using water as an agent instead of ammonia; and the other is of the absorption type, in which water is used instead of ammonia, and sulphuric acid in place of water.

The liquefaction apparatus is that employing the solution of solids more generally known as freezing salts. They are generally intermittent in action, but have been designed to run continuously.

In all these machines it is not difficult to trace the compensation above referred to. It may not be so obvious in the last class, but it must be remembered that in order to get the salt back again into condition for doing more cooling it must be evaporated by high temperature heat. It will be sufficient for our purpose to trace the course of the two quantities of heat in question through an apparatus of the compression type and one of the absorption type.

In the compression machine this is very easy; and in Fig. 2 the essential features comprising the compensator C, are sketched in, and are seen to consist of an engine with its condenser and a compressor with its condenser. The heat I passes into the engine, where a portion of it, IV, is converted into work, and the remainder H—W, passes into the engine condenser (which in the case of a non-condensing engine is the atmosphere). The work is transferred to the compressor

T T

X

which proves the general statement with which we set out, so far as the compression machine is concerned. The work done by high temperature heat is equal to the work done on the low temperature heat, and each may be written down as the product of the two sides of the respective work rectangles, that is:

оф

·(4)

• the

W = If the width represent a weight of water and distance through which it can fall, then the work done would be foot-pounds. Again, if Again, if represent another weight of water and the distance through which it is lifted the work necessarily expended is foot-pounds, and, if we had perfect machinery, these two quantities must be equal to enable us to lift the maximum amount of water for the least amount allowed to flow down.

From these hydraulic analogies, Zeuner has termed the width of the heat area the "heat weight."

When the converter C is an absorption machine it is more difficult to trace the course of the two quantities of heat. Stripped of all details the main features are represented in Fig. 4. There is the same general condition of high temperature heat supplied and of low temperature heat flowing to a higher temperature, but there is no trace of work obtained or work performed,

Yet, while it is not recognizable, we know that the transfer of low temperature heat could not take place without the equivalent transfer of the high temperature heat. Moreover, in practice we find that the quantity of heat discharged into the ammonia condenser is approximately the same as that discharged in the compression machine, and the heat discharged from the absorber approximates to that discharged by the engine condenser.

Following the agent as it travels around, the peculiarity of the absorption machine seems to be that it discharges the heat due from the refrigerator and the heat equivalent of the work necessary for the refrigeration in advance of the actual performance of the refrigeration. Thus, as figured above, if H is the heat leaving the generator h+of this is discharged in the ammonia condenser and H-h-I'goes forward with the ammonia to the refrigerator.

We may conceive that the ammonia carries with it a draft drawn by the generator on the refrigerator for the amount of heath to cover what has already been advanced on its behalf. Accordingly the refrigerator honors the draft by supplying the quantity of heat h, and the ammonia goes forward to the absorber where it

delivers the heat II-II. The final result is the same, all the heat discharged from both the generator and the refrigerator, viz., H+h, being the same as in the general scheme, Fig. 1. This, of course, is merely a mental picture of what we may suppose to take place in order to comply with the necessary conditions, and it may be asked what reason we have for supposing that the same relation obtains between two quantities of heat in the absorption machine as obtains in the case of the compression machine. In other words, is equation 3 necessarily true for the absorption machine?

This is a most important matter, the more so as its denial is implied in some explanations of the absorption. machine by authorities entitled to the highest consideration. Suppose that it is not true, and that we have two machines working with identical temperatures and ranges, but one on the compression plan and the other on the absorption, and that they both receive the same supply of high temperature heat, namely H, but that while the compression machine furnishes h T. U. of refrigeration the absorption machine furnishes a larger amount, say 2h. Let the refrigeration 2h be represented

by a certain quantity of ice, and let us remove it from the absorption machine and place it in the refrigerator of the compression machine (supposed to have lain idle up to the present), which will now have a stock of ice representing a capacity for absorbing heat to the amount of 24. Now let the compression machine be reversed. Let the compressor be changed to an engine, and the engine to a compressor. The ammonia can be boiled in the ammonia condenser, and will pass through the ammonia engine; the refrigerator will be a surface condenser for it until all the ice has melted or the quantity of heat 24 has been supplied. When this happens the ammonia engine will have furnished work to the steam compressor equal to 2, but one of these is sufficient to cause the passage of heat I-II' backward to the boiler, and being itself transformed into heat the boiler will receive in all H units of heat. The position we are now in is this: We have imparted to the boiler a quantity of heat, H, and we have quantity of work I left over. The heat I can be transferred to the absorption machine, where it will again produce 24 of refrigeration, so that as a final result we have the quantity of work I' produced at each operation free of cost without the expenditure of any heat at all. Since we cannot admit this possibility we must believe that the absolute efficiency expressed by equation 3 is the greatest that any refrigerating machinery can have, whatever the nature. of its details may be.

On the other hand, the temperature and ranges being the same, no reason can be assigned why any other type of machine should not have precisely the same efficiency. The compression machine was chosen as the standard. simply because it is easily seen how it can be reversed, for it is evident that reversibility is the true test of our having found the correct statement of the law governing the equivalent transfer of the two quantities of heat, which law must be independent of the mechanism employed.

[Reprint from unidentified EXCHANGE.]

FREEZING MIXTURES.

SUBSTANCES WHICH MAY BE EMPLOYED FOR LOWERING TEMPERATURES SOME FAIRLY EFFECTIVE FREEZING MIXTURES -MANUFACTURE OF ICE BY THEM A FAILURE.

proves considerably more energetic and cheap than any of the others, so far as use of the materials only once is concerned. The second mixture, too, cannot be restored; nor can the last, easily, on account of the crys

THE

HE numerous and varied applications which ice has found in these times have greatly enhanced the importance of that product, and while large portions of it have annually been transported from the colder to the hotter regions of the globe, scientific ingenuity has attacked, energetically and successfully, the problem of producing cold by artificial means for industrial and other purposes. In a recent number of Dingler's Polytechnisches Journal, Professor Meidinger has an instructive paper giving an account of the progress made in recent years in the art of ice manufacture.

There are three ways indicated by physics in which temperature may be lowered, and ice formed, viz., solution of solid substances, evaporation of liquids, and expansion of gases. The following is an abstract of that portion of Professor Meidinger's paper relating to production of cold by solution:

Heat is absorbed in bringing solids to the liquid condition; and the cold thus produced may prove sufficient to convert water into ice.

The best known of the numerous freezing mixtures that have been hitherto described is, of course, one involving ice itself; it consists of three parts of ice and one part of ordinary salt.

Dissolving concurrently, these two substances give a temperature of -21° C. (the freezing point of the solution). The melting of only a part of the mixture is sufficient to produce this temperature throughout the mass; and with constant admission of heat, and stirring, the low temperature is maintained until the whole is dissolved. The freezing apparatus of confectioners is well known: a tin pot containing cream, a wooden or metallic vessel inclosing the pot, and the interval filled with ice and salts, which is frequently stirred, that the ice may not sink to the bottom. In a Paris machine for home use the agitation of the freezing mixture is maintained by rotation of the double cylinder containing it and the cream vessel round an axis at right angles to the cylinder's length. Professor Meidinger has constructed a machine based on the observation that a solution of ordinary salt under o° also fuses ice, and, so long as its concentration is maintained, produces the same low temperature as the mixture of salt and ice. He provides a sieve-like vessel, containing salt, to maintain the concentration as the ice melts. The lowering of temperature is uniform throughout the vessel, and no stirring is required. The machine has come largely into use in perfumery.

On the basis of his own experiments, Professor Meidinger has formed a table showing the respective merits of various freezing mixtures. The table in the next column contains the most serviceable.

Salt mixtures give much greater lowering of temperature than simple salts, as they dissolve in much less water. Thus one part of sal-ammoniac is dissolved in three parts water, and lowers the temperature about 19°; saltpeter dissolves in six parts water, and lowers the temperature about 11°. (Compare the fourth and fifth on the list.) It will be seen that the salt-ice mixture

MIXTURE.

1 ordinary salt, 3 ice

3 cryst. Glauber salt, ? concd. muriatic acid.

2 nitrate of ammonia, 1 sal ammoniac, 3 water...

3 sal ammoniac, 2 saltpeter, 10'

water

3 sal ammoniac, 2 saltpeter, 4 cryst. Glauber salt, 9 water..

1 k.

Mixture.

11.

Mixture.

Salt

k.

Water

k.

Cost in

Marks.

tallized Glauber salt. Both are comparatively cheap, however. The mixture in which, by vaporization of the solution, the salt is easily renewed in its original condition, nitrate of ammonia and sal ammoniac, is so costly at the first that it would not do to use it only once. This was the mixture employed in an apparatus first exhibited by M. Charles at the Paris Exhibition in 1867. The tin vessel containing the substance to be frozen is inclosed in a large wooden vessel containing the freezing mixture, and is furnished with screw wings, which stir the mixture as the vessel is rotated. Another form is that of Toselli's glacière Italienne roulante. The cream or other such substance is enclosed in a conical-shaped vessel suspended in the freezing mixture, and the outer vessel, enveloped in cloth, is rolled to and fro on the table. None of these machines have found very extensive use. Large masses have to be operated with to obtain even small results, and the sum of operations must generally prove too troublesome in a private house.

As to the question of manufacturing ice on a large scale by means of solution of salt, Professor Meidinger comes to the conclusion that by means of 1 kilog. of coal (for restitution of salt used) not more than 2 kilogs. of ice can be prepared; not to speak of the machine force required for transport of the large quantity of liquid. This is very unfavorable; an ammonia machine will give four or five times better results. Much improvement is, in the circumstances, hardly to be looked for. It would be necessary to find a salt that, in dissolving, gave a much greater lowering temperature than the mixtures known, and this cannot be expected, since all the known salts have been examined in reference to this point. The real cause of the small productions of such apparatus lies in the fact that restitution of the salt is effected only by change of aggregation (vaporization), and this involves large expenditure of heat. It may be mentioned that, according to experiments by M. Rudorff on cold produced by solution of twenty different salts, the two which gave the greatest lowering of temperature were sulphureted cyanide of ammonium, and sulphureted cyanide of potassium-105 parts of the former dissolved in 100 parts water produce a lowering of temperature of 31.2°; and 130 parts of the latter in 100 parts of water as much as 34.5°.

-The Hygeia Ice Co., New Haven, Conn., has established

a distilled water and ice agency at West Haven.

-The Marion (Ohio) Ice and Cold Storage Co. are having a lucrative trade in distilled water, and are running one wagon for that trade exclusively.

[Written for ICE AND REFRIGERATION.]

CONSERVATION OF MEATS. PRESERVING FRESH MEATS AS INVESTIGATED ON THE CONTINENT OF EUROPE-PARISIAN BUTCHERS' COLD STORAGE-INSTALLATIONS OF COLD STORAGES, SECOND TYPE.

A

BY AUGUSTE J. Rossi, B. S., C. E.

[Continued from May number, page 370.) NOTHER typical disposition is that of Mr. Velly, one of the principal wholesale butchers of Paris. The circulation of the air is obtained, as in the Schroeder system, without the use of any mechanical device, merely by the difference of specific gravity of the cold and warm air, the refrigerating room being likewise distinct from and immediately above the meat room; but the manner in which the air is cooled is characteristic. It makes of this installation a distinct type, and, for this reason, though of a comparatively secondary importance as to extent, it will serve as a good illustration of another example of continental practice.

As in the cold storages of Geneva and Mulhouse, the freezing of the meats is avoided and the temperature maintained in the rooms is only of 2° to 4° C. (35° to 38° F.) The rooms can store thirteen to sixteen tons, 26,500 to 31,000 pounds of meat; their dimensions being thirty-nine feet long by twenty-one feet wide, by ten feet and six inches high; this gives, for the total capacity, 8,600 cubic feet, passages included. Assuming, agreeing to the rule laid down by the commission in such cases, an amount of four pounds of meat per cubic foot of contents, 8,600 cubic feet multiplied by four pounds would give 34,400 pounds as the capacity in stored meats of the room; actually there are 27,000 to 31,000 pounds stored; and we are within the margin, with ample allowance for the facility of the service.

The walls of the meat room are of stone, twenty inches thick. At a distance of four inches from the stone wall, a brick wall, four inches thick, has been built, and the space between the two walls, filled with cork shavings.

The brick walls, on their inside face in the storage, have been cemented to a height of about six feet all

around, and, in order to admit of a thorough washing, the floors have been asphalted. The number of windows has been reduced to the minimum consistent with the necessities of light for the service; and are made of three glass sashes to avoid, as much as possible, the loss of cold on this score.

The ceilings are made of brick arches and iron I beams, covered, first, with a layer of six inches of cork shavings, then with one of clinkers or cinders, four inches thick; over this is applied a bed of concrete, made with clinkers, four inches thick; and the whole has received a thick coating of asphalt. Ventilator shafts 7 T, opening on the roof, and provided with registers inside to regulate their action, permit the introduction of fresh air or evacuation of the vitiated air, whenever it is considered advisable.

Immediately above the cool room R' is the refrigerating room R. It extends in the whole length of the storage, but covers only a part of it in the width, some ten feet or thereabout. Instead of the troughs and of the spray of brine resorted to at the Mulhouse and Geneva markets to cool the air, a system of coil pipes, very much like the refrigerator or expander of an ice machine, has been used for the purpose. In this coil circulates the brine, made cold in separate tanks in a special part of the building devoted to the machinery by the action of the refrigerating machine.

There are, in fact, two distinct systems of coils (see plan, Fig. 3; section A B, Fig. 2), at a certain distance from but communicating with each other, the circulation of the brine being continuous from one to the other, their total length is about 2,000 feet. This disposition facilitates the repairs in case of need, as well as the cleaning of the surfaces. The circulating brine is cooled to such a temperature as may be found proper to obtain the necessary cooling of the amount of air which comes in contact with the piping. In this case, the temperature of the brine is -10° C. (14° F.).

Particular care has been taken to thoroughly insulate this refrigerating room P. The sides are made of two wooden partitions, built with tongued and grooved pine boards, ten inches apart, the space between them having been filled with cork shavings, or such other appropriate insulating materials; the ceiling has been insulated in the same manner, and, on the upper boarding, under the roof proper, a thick layer of cork shavings has been. spread loose all over. The floor which forms the ceiling of the meat room has been constructed as already described. The circulation of the air is induced by the