Refrigerants are working fluids that carry heat from a cold environment to a warm environment while circulating between them. For example, the refrigerant in an air conditioner carries heat from a cool indoor environment to a hotter outdoor environment. Similarly, the refrigerant in a kitchen refrigerator carries heat from the inside the refrigerator out to the surrounding room. A wide range of fluids are used as refrigerants, with the specific choice depending on the temperature range needed and constraints related to the system involved.
Refrigerants are the basis of vapor compression refrigeration systems. The refrigerant is circulated in a loop between the cold and warm environments (see figure). In the low-temperature environment, the refrigerant absorbs heat at low pressure, causing it to evaporate. The gaseous refrigerant then enters a compressor, which raises its pressure and temperature. The pressurized refrigerant circulates through the warm environment, where it releases heat and condenses to liquid form. The high-pressure liquid is then depressurized and returned to the cold environment as a liquid-vapor mixture.
