REFRIGERATION IN THE DAIRY 697 



The modern refrigerating machine is constructed on 

 the above lines. It consists of a pump specially designed 

 and constructed to deal with the particular refrigerant used, 

 and two coils or sets of coils of iron pipe, in one of which 

 " cold " is produced by the evaporation of one of the above 

 volatile liquids assisted by the suction of the pump ; in the 

 other, the gas produced by evaporation is again liquefied by 

 combined pressure and cooling by means of water, and the 

 liquid is transferred to the evaporator coil to do further 

 service. Here a very important point has to be noted. If 

 the liquid be allowed to flow back freely to the evaporator 

 coil, very little refrigeration is effected. Its flow must be 

 carefully proportioned, and we therefore introduce a regu- 

 lator valve on the transfer pipe, which must be adjusted with 

 the utmost care so that the flow of liquid shall not exceed the 

 maximum which can be evaporated in the suction coil. 

 Other volatile liquids besides the above, and compressed air, 

 are used as refrigerants, and other systems than that described 

 have been developed for the utilisation of the principle of 

 latent heat, but they are not very extensively employed. 



The application of the theory of refrigeration has been 

 the subject of much study, and some considerable literature 

 has been published concerning it. The most important 

 methods may be summarised as follows : 



1 . Brine circulation by means of pipes or brine drums. The 

 brine circulates over the evaporator coils and immediately 

 falls in temperature, owing to the absorption of its heat by 

 the expanding gas inside the coils. From the evaporator it 

 is pumped through pipes or drums in cold chambers or 

 through the corrugations of capillary conical coolers, and in 

 its passage takes up heat either from the surrounding air of 

 the cold rooms or from the milk or cream passing over the 

 coolers. 



2. Direct expansion of a gas through pipes in a chamber or 

 in chambers. This process is not applicable to the cooling of 

 milk, and can only be successfully used in cold rooms. 

 There is no evaporator used, the air of the chambers forming 

 the surrounding medium from which the heat is extracted. 



3. The air cooler is applied also to cold stores, and is not 

 available for cooling the capillary coolers. It is a system, 

 however, which lends itself to use in cheese factories. The 



