How does refrigerant work?

Refrigerant, also known as coolant, is a medium substance utilized for energy conversion in various heat engines.  These substances typically enhance their power through a reversible phase transition, such as a gas-liquid phase change.  For instance, steam in a steam engine and coolant in a refrigerator.  During the operation of a steam engine, the thermal energy of the steam is released and converted into mechanical energy to generate primary power.  The coolant in the refrigerator facilitates heat transfer from low temperature to high temperature.

Some halogenated hydrocarbons (particularly chlorofluorocarbons) have been commonly used as working fluids in traditional industries and daily life;  however, they are gradually being phased out due to ozone layer depletion.  Other widely employed working fluids include ammonia, sulfur dioxide, and non-halogenated hydrocarbons (such as methane).  Despite numerous refrigerants available on the market today, they all operate based on the same principle.