The evaporator is that part of the system where the useful cooling is accomplished by removing the heat from the area to be cooled. This is done by bringing the temperature of the liquid refrigerant below the temperature of the surrounding medium. The heat passes into the liquid refrigerant and is absorbed as latent heat, changing the state of the refrigerant from a liquid into a vapor. It is then withdrawn by action of the compressor.
There are two general types of evaporators: dry and flooded. In the dry type, the refrigerant enters in the liquid state, and the design provides for complete evaporation with the vapors slightly superheated. In the flooded type, not all of the refrigerant is evaporated, and the liquid/vapor mixture leaving the evaporator flows into a surge drain from which the vapors are drawn into the compressor suction line; the liquid is recirculated through the evaporator.
