Refrigerating machines are of two types 1) Vapour compression machine (Frigidaire)" and 2) "Vapour absorption machine". 


The liquid which on evaporation produces cooling is called refrigerant. Some examples are Ammonia(NH₃), Sulphur dioxide, Freon.

Properties of Refrigerant:

  1. It should have low boiling point & melting point
  2. It should be vapor at normal temperature and pressure.
  3. It should have high thermal conductivity
  4. "Latent heat of vaporization" of the refrigerant must be large.  
  5.  The specific volume should be small in order to reduce the size of compressors. 

The evaporation of liquid under reduced pressure is a cooling process. The reason is that when a substance changes from liquid to vapor phase, it is associated with absorption of heat. If this heat is not taken from any external source, the necessary heat for phase exchange is taken from itself which therefore cools.

Vapor Compression Machine

Production of temperature by making a liquid evaporate rapidly under reduced pressure and circulating evaporating liquid around enclosure.

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