MECHANICAL RBPRIGERATION 139 



in a series of pipes placed in the room to be refrigerated ; 

 and (2) by evaporating the Hquid ammonia in a series of 

 coils laid in a tank of brine and using the cold brine for 

 cooling purposes. The former is known as the direct 

 expansion system, the latter as the indirect expansion or 

 brine system. 



Brine System. Brine should be exclusively used for 

 cooling milk and cream and also largely for cooling the 

 refrigerator. It is desirable, however, to have a few 

 direct expansion coils in the refrigerator which may be 

 used when extra cold is desired. The brine tank is 

 located near the ceiling in the refrigerator where it will 

 serve the same purpose as an overhead ice box. Refrig- 

 erating pipes may also be laid in the milk room for the 

 purpose of controlling its temperature during the warm 

 summer months. 



The brine is kept' circulating by means of a brine pump. 



Strength of Brine. The brine is usually made from 

 common salt (sodium chloride). The stronger the brine 

 the lower the temperature at which it will freeze. Its 

 strength shovild be determined by the lowest temperature 

 to be carried in the brine tank. The table by Siebel on 

 the next, page shows the freezing temperature as well as 

 the specific heat of brine of different strengths. 



The fact that the specific heat grows less as the brine 

 becomes stronger shows it to be wise not to have the 

 solution stronger than necessary, because the less the 

 specific heat the less heat a given amount of brine is able 

 to take up. 



