Vickipedia

Under the head ICE, some notice is given of machines by which it can be prepared artificially; but as the practical importance of refrigerating apparatus is daily increasing, we propose to give here a fuller sketch of one or two kinds. The ice-making machine of Carre & Co., of Paris, being one of the simplest and best of those which produce cold by the evaporation of some volatile liquid, we shall describe it first. It is shown in figures 1 and 2, and consists of two strong cast-iron cylinders A and B, connected together by a metal tube T, all perfectly gas-tight. The whole apparatus is made strong enough to stand seven or eight atmospheres of internal pressure.

The cylinder A is charged with an aqueous solution of ammoniacal gas. Ammonia is a powerful absorber of heat, and is, moreover, so extremely soluble in water that the latter takes up nearly seven hundred times its volume of the gas. Air is completely expelled from the apparatus by opening a screw valve and heating” the cylinder. It is then ready for use. On applying heat to the: cylinder A (fig. 1), which fits into a small stove for the purpose, the solution of ammonia is volatilized, and carried over and condensed in the cylinder B, which is placed in a vessel containing: cold water. The heat reaches to about 220° F., and while it is being applied, the volatilized ammonia condenses into a liquid under very high pressure, produced by its own atmosphere, in the cold cylinder B. When the heating is gone on long enough — about half-an-hour for a small machine — the hot cylinder. A, is removed from the fire, and placed in a vessel of cold water, as shown in fig. 2. The cooling of this cylinder immediately causes the reabsorption, by the removal of the pressure, of the condensed ammonia from the other cylinder B; and as it passes again from the liquid to the gaseous state, intense cold is produced (see HEAT), and, in consequence, heat abstracted from everything in contact with this portion of the apparatus.

The cold cylinder B is shown in section in fig. 2. It is so constructed that the ammonia is contained in an outer jacket, leaving-a hollow space in the center. When ice is to be made, the latter is filled with salt water or other liquid which does not freeze at 32° F., and into this is placed a loosely fitting metal cylinder D, containing the water to be frozen. In this way, with a small machine for domestic purposes, a few pounds of ice can be made in an hour or two; but large machines, on the same principle, are made which produce 440 Ibs. of ice per hour.

There is a well-known refrigerating machine by Mr. D. Siebe of London, in which ether is used as the volatile fluid, its evaporation being produced not by heat, but by the action of an air-pump; the necessary cold is produced in the surrounding brine as the ether passes into vapor.

M. Pictet of Geneva has invented an ice-machine which works with anhydrous sulphurous acid instead -of ether; but otherwise his process somewhat resembles Siebe’s. It is now at work at an Ice-making Company’s works in King’s Road, Chelsea. Some machines are also in use which produce ice by means of freezing mixtures; but they are of minor importance.

Mr. A. C. Kirk, late of the Bathgate Chemical Works, undertook, a few years ago, a series of experiments with a view to the construction of such an apparatus which would produce cold by the simple expansion and compression of air. He ultimately succeeded in producing an ingenious machine, which he patented on the 25th April 1862, the number of the specification being 1218.

Although it is not strictly true that the mere rarefaction of air produces cold, yet it will simplify the explanation of this machine to assume in the meantime that it does so. Its simplest

form is shown in fig. 3, and consists of a cylinder with a piston to compress air, communicating with another cylinder containing a kind of piston or plunger where the compressed air is cooled and expanded. The machine is driven by a steam-engine, audit may be as well to remark, that the actual relative position of the cylinders is different from that shown in the diagram, which is given rather to show the principle of the apparatus than as an accurate representation of it.

The compressed air is forced by the compressing cylinder A, into the refrigerating cylinder BB, just at the moment when the position of the plunger, PP, is close upon the upper cone D. This air, which fills the space aa, between the plunger PP, and, the lower cone E, is of course heated by the compression; and order to cool it again, cold water is made to calculate in the coil E, by an entrance-pipe F, and an exit-pipe at G. The next movement of the machine draws the piston in the cylinder A to the opposite end, and consequently allows the compressed air to expand again; but at the same moment the plunger, PP, descends close upon the cone E, thus allowing the space between the plunger and the upper cone D. to be at its fullest when the expansion of the enclosed air is at its greatest.

By this arrangement, the patentees secures that the air while being compressed will always be at the lower, or what he calls the hot end, of the refrigerating cylinder B; and while being expanded, it will always be at the upper or cold end. There is a regenerator constructed as in the Caloric Engine (q. v.) of wire-gauze, placed in the middle of the plunger at C. This, while it allows the air to move freely through it, prevents the conveyance of heat or cold from one end of the cylinder to the other. The plunger, PP, is filled internally with sawdust or some non-conducting material.

We may now explain that the low temperature of the air which surrounds the cone D during expansion, is not produced by simple rarefaction. That alone would not produce cold. It is necessary as well to abstract heat from the air by giving it some work to do, and here it unavoidably does work, in assisting to force back the piston of the compressing cylinder, while in the act of expanding. The air loses an equivalent of heat exactly in proportion to the amount of force which it expends in moving, or in assisting to move, the piston. See FORCE.

Before air is admitted into the cylinder, it is necessary to dry it thoroughly, by first passing it through a box containing chloride of calcium, because, if any moisture were present, it would freeze in the regenerator, and stop the action of the machine. In the particular form of the apparatus shown in the figure, the substance to be cooled is placed inside the cone D, which is furnished with a lid L. Here not only water, but even mercury, can be frozen with facility.

Most of the machines of this kind which have as yet been made were required for working on a more extensive scale than the one shown in fig. 3 could easily do. In the larger-sized machines, accordingly, instead of one hollow cone like D (fig. 3), a series of circular V-shaped corrugations are fixed to the top cover of the refrigerating cylinder. These form annular passages, through which a continuous current of some fluid not easily frozen, such as brine, flows. This is of course cooled by the expanded air (in the manner already explained) at the cold end of the cylinder, and can be conveyed away in pipes. The most serious objection to this method was its comparative cost.

The increasing imports of dead meat from America gave a new impulse to the improvement of refrigerating processes. The meat chambers were at first cooled by means of currents of air forced over and between ice-blocks. This method kept the air perpetually moist, and produced somewhat deleterious effects on the meat. The Messrs. Bell of Glasgow secured the assistance of Mr. J. J. Coleman, who perfected a purely mechanical refrigerator known as the Bell-Coleman machine. This apparatus has a good deal in common with Kirk’s. The air is taken from the meat chamber and greatly compressed, being played upon the while by small jets of water, in order to abstract the heat developed during pressure. It next circulates through a series of tubes where it is further cooled, and deposits great part of its moisture. The next stage is the expansion process; and by being constrained during expansion to perform a certain amount of j mechanical work in turning cranks, it further loses heat. It is now found to be a powerful refrigerating agent. Machines on the Bell-Coleman principle have been fitted up in many lines of ocean steamers, and have rendered possible the transmission from America, Australia, and New Zealand, enormous quantities of beef and mutton in perfect condition. It is also used for stationary refrigerators in hot countries. For the Haslam machine it is claimed that the air from it is drier than from that of Mr. Coleman.

The ether-machine of Siddeley & Mackay of Liverpool, which is an improvement en Siebe’s, is now a good deal used for making ice, and for other purposes. In it a steam-engine is employed to work two vacuum-pumps, and to supply motive-power to other parts of the apparatus. The refrigerating vessels contain thin pipes, through-which brine or chloride of calcium flows. Ether surrounds these pipes; and under the reduced pressure produced by vacuum-pumps, with which the refrigerators communicate, a portion of the ether evaporates, producing cold in the act of doing so, as already explained. The ether vapor is then condensed at a slight pressure, cooled by a stream of cold water, and returned to the refrigerator. Reece’s ammonia machine is more recent than Carre’s, and is worked with anhydrous ammonia, instead of an aqueous solution of it. In Reece’s process, less fuel is required to distil the ammonia, less water to condense it, and less power to work the moving parts of the machine.

It is only within the last twenty years that much attention has been given to the construction of machines for the production of artificial cold on the large scale; but they have already received several important applications. In this country, besides being available for the production of ice; the extraction of certain salts from mixed solutions, such as sulphate of soda from common salt —the former separating at a temperature above that which keeps I the latter in solution; the separation of paraffin from mineral foils; and in other chemical operations, as well as for cooling worts in breweries and distilleries, they are now turned to good account in bringing fresh meat from distant countries to our shores. In warm countries, besides other uses, they could be applied to cool large hospitals and public buildings, by sending a current of some cold liquid through pipes, just as we in Great Britain heat building with pipes through which hot water flows.