. Market dairying and milk products. ure of their cream, refrigerator, makeroom, etc. Refrigerating Machines. There are four kinds ofmachines used for refrigerating purposes: (i) vacuummachines in which water is used as the refrigeratingmedium; (2) absorption machines in which a liquid of alow boiling point is used as the refrigerating medium, thevapors being absorbed by water and again separated fromit by distillation 5(3) compression machines which operatepractically the same as the absorption machines exceptthat the vapors in this case are compressed instead ofabsorbed; and (4) mixed absorp
. Market dairying and milk products. ure of their cream, refrigerator, makeroom, etc. Refrigerating Machines. There are four kinds ofmachines used for refrigerating purposes: (i) vacuummachines in which water is used as the refrigeratingmedium; (2) absorption machines in which a liquid of alow boiling point is used as the refrigerating medium, thevapors being absorbed by water and again separated fromit by distillation 5(3) compression machines which operatepractically the same as the absorption machines exceptthat the vapors in this case are compressed instead ofabsorbed; and (4) mixed absorption and compression ma-chines. Most of the machines in use at the present timebelong to the compression type; the following discussionwill therefore confine itself strictly to this class ofmachines. Principle. The principle employed in mechanical re-frigeration is the production of cold by the evaporationof liquids which have a low boiling point, like liquidammonia, liquid carbonic acid, ether, etc. 296 MECHANICAL REFRIGERATION 297. Fig. 56.—Showing circulation of ammonia in mechanical refrigeration. 298 MARKET DAIRYING When a liquid evaporates or changes into the gaseousstate it absorbs a definite amount of heat called heat ofvaporization or latent heat. Thus to change water from212° F. to steam at 212° F. requires a considerableamount of heat which is apparently lost, hence the termlatent (hidden) heat. Ether changes into its gas at a much lower temperaturethan water which is illustrated by its instant evaporationwhen poured upon the hand. The heat of the hand in thiscase is sufficient to cause vaporization and the sensationof cold indicates that a certain amount of heat has beenabstracted from the hand in the process. Manifestly for refrigerating purposes a liquid must beused that can be evaporated at a very low temperature;for the cold in mechanical refrigeration is produced,bythe evaporation of the liquid in iron pipes, the heat forthe purpose being absorbed from the
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectdairyin, bookyear1912
