CHAPTER VI 

 MECHANICAL REFRIGERATION 



GENERAL DISCUSSION 



History of Mechanical Refrigeration. — The mechanical 

 system of refrigeration is of rather recent origin. In 1834, 

 Jacob Perkins of London invented an ice machine using volatile 

 liquid. In this machine ether was vaporized and expanded 

 under reduced pressure maintained by the suction of a pump, 

 the heat required for such vaporization being abstracted from 

 the substance to be cooled. The resulting vapor was com- 

 pressed by the same pump into a vessel cooled by water, where 

 it was liquified. 



This machine contained all four of the essential features 

 present in all modern compression systems; namely, the evapo- 

 rator or expansion coil, the compressor, the condenser, and the 

 regulating valve between the condenser and the evaporator. 

 Yet his system was not generally adopted, and it was not until 

 1 86 1 that an ice machine was successfully used for commercial 

 enterprises. 



Principles Involved. — Mechanical refrigeration is based 

 upon the fact that a liquid, when converted into vapor, ab- 

 sorbs heat from surrounding bodies. Chemicals which at 

 boiling point are considerably below the temperature of the 

 surrounding air, which are reasonably cheap, and which can be 

 handled with the least danger to life and property, are therefore 

 used in the refrigeration process. The chemical complying most 

 fully with such requirements is ammonia, and it is the liquid 

 most frequently used for mechanical refrigeration. Other chem- 

 icals, such as carbonic acid and sulphuric dioxide, are used to a 

 limited extent. 



Ammonia. — ^Ammonia is used in one of two forms, either as 



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