Refrigeration is the cooling of substances below ambient temperatures by extracting heat from them. The medium that absorbs the heat from the substance to be cooled is called the refrigerant.Refrigerants can be classified into two main groups. The first absorb heat by undergoing a change of state (for example from liquid to vapor), the second absorb heat without undergoing a change of state (for example they may absorb heat as a liquid and remain a liquid, albeit a hotter one). If the refrigerant is only used to transport "cold" from one place to another it is called a secondary refrigerant.

The most widespread refrigeration method is the vapor compression cycle, which relies on the evaporation of a liquid. This method is used in industry as well as in domestic refrigerators. The vapor compression cycle relies predominantly on two physical principles to work; the tendancy for liquids to...