Refrigeration is used to ensure proper storage temperature of food products. This is most often accomplished by using the vapor compression cycle. In this technique, refrigerant vapor is compressed by a compressor, condensed into a liquid in a condenser by the rejection of heat, expanded by a restrictive device, and fed into an evaporator where heat is absorbed and returned to the compressor to complete the cycle. (See Figure 1.)
Most commonly, the evaporator cools air, which is then used to cool the product. Due to inefficiencies of the heat transfer process, the temperature of the refrigerant in the evaporator is 5˚ to 16˚F (3 to 9K) colder than the air temperature.