Vapor-compression refrigerationorvapor-compression refrigeration system(VCRS),in which therefrigerantundergoesphase changes, is one of the manyrefrigeration cyclesand is the most widely used method forair-conditioningof buildings and automobiles. It is also used in domestic and commercial refrigerators, large-scale warehouses for chilled or frozen storage of foods and meats, refrigerated trucks and railroad cars, and a host of other commercial and industrial services.Oil refineries,petrochemicalandchemicalprocessing plants, andnatural gas processingplants are among the many types of industrial plants that often utilize large vapor-compression refrigeration systems.

The vapor-compression uses a circulating liquidrefrigerantas the medium which absorbs and removes heat from the space to be cooled and subsequently rejects that heat elsewhere. Figure 1 depicts a typical, single-stage vapor-compression system. All such systems have four components: acompressor, acondenser, athermal expansion valve(also called athrottlevalve or metering device), and an evaporator. Circulating refrigerant enters the compressor in the thermodynamic state known as asaturated vaporand is compressed to a higher pressure, resulting in a higher temperature as well. The hot, compressed vapor is then in the thermodynamic state known as a superheated vapor and it is at a temperature and pressure at which it can becondensedwith either cooling water or cooling air flowing across the coil or tubes. This is where the circulating refrigerant rejects heat from the system and the rejected heat is carried away by either the water or the air (whichever may be the case)