Refrigerants are substance used for refrigeration. Food items are preserved by cooling to low temperature. Refrigerants are heat carrying medium which during their cycle in the refrigeration system absorb heat at low temperature and discard the heat so absorbed outside. Refrigerants should possess certain physical, chemical and thermodynamic properties to make it safe and economical for use in refrigeration system. The desired properties of refrigerants are:

(i)Safety: The refrigerants should be safe to use; that is, it should be stable, non-toxic, non-explosive, non-inflammable and chemically inert.

(ii) Low boiling point: The boiling point of refrigerants are less than room temperature Mostly, they exist as gases and held in liquid state by freezing then ruder pressure in refrigerants cylinder.

(iii)Stability: The refrigerants should decompose during the operation.

Commonly used refrigerants are carbon dioxide, ammonia, trichlorofluro methane, dichloro difluro methane, chloro difluro methane, chloropenta fluro ethane.
Carbon dioxide and ammonia are not used as refrigerants at present. Chlorofluro hydrocarbons or freors are mostly used.

The chlorofluro hydrocarbons are color less with ethereal odor. It is stable up to 1000°F. Above 1000°F, decomposition occurs and free chlorine atom converts ozone in to oxygen, thus depleting ozone layer in the structure.

The entire chlorofluro hydrocarbon is good refrigerants and air- conditioners. They are also used in aerosol sprayers.

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