The purposes to which mechanical refrigera•' Lion is applied are, as already stated. numerous.
It possible to group them, however. under a few general heads, and for the present occasion the following heads are selected: Cold storage. ice-making, marine refrigeration, and manufac turing.
Com} Cold storage ineludes practical ly all applications of refrigeration to the preser vation of foodstuffs. A cold-storage plant coin prises a refrigerating plant of one of the forms previonstv described and a store which is kept cold by the refrigerating plant and in which all the provisions to be preserved are placed. cola stores vary in size from the single-room store used by the hotels. residences. hotelier shops. etc.. to lane buildings containing numerous rooms for the storage of all kinds of provisions.
The size of the refrigerating plant varies, of course, with the size of the store which it has to keep cold. The refrigerating processes most used for cooling stores are the cold-air, the compres Sian, and the absorption processes. When the cold air process is employed the air is as a rule admit ted to the store, and after it has done its duty is conducted hack to the compressor for recompres sion. When compression or absorption systems are used the refrigeration is effected in one of three ways: (1) By cooling a non-congealable brine and then pumping it through a system of pipes in the store; (2) by causing a current of air generated by means of a fan or otherwise to impinge against surfaces reduced to a low tem perature by the expansion of the refrigerating agent itself; (3) by expanding the gas direct through pipes placed in the chambers. The agent employed in the brine circulating system consists of a solution of chloride of sodium (common salt), chloride of calcium, or chloride of mag nesium, or any other suitable solution capable of standing very low temperatures without congeal ing. To extract the heat from the brine the
method most commonly employed consists in pass ing it through a tank fitted with suitable coils of pipes through which the chilled liquefied ether, carbonic acid, ammonia, or other agent expands and forms gas. The cooled brine from this tank is then pumped through a system of circulating pipes in the refrigerating chamber. In the direct expansion system the pipes in which the ether, carbonic acid, or ammonia expands and makes gas are located directly in the refrigerating chamber. In the cold-air blast system, the expansion coils are placed in a separate chamber and the cold air from that chamber is blown by fans into the re frigerating chamber, sometimes being washed by passing through a shower of cold brine and then dried by passing through a mass of calcium chlo ride or other hygroscopic material.
The construction of refrlycrating chambers varies with their purpose and the arrangement of piping adopted, but they are always tightly closed rooms with thick walls carefully insulated to pre vent escape of cold and entrance of beat. Speak ing generally, cold-storage rooms or chambers are maintained at a temperature of about 34° F., chilling rooms at about 30° F., and freezing rooms at anything from 0° F. to 10° F. The proper methods of storing and the temperatures for the cold storage of various articles, as meats, fish, butter, cheese, milk, eggs, fruits, and vegeta bles, are intricate problems, which different au thorities solve in different ways; their full dis cussion can be attempted only in special treatises.