Vapour compression refrigeration cycle is a process used in refrigeration systems to remove heat from a space and maintain a cool temperature.

• Vapour compression refrigeration cycle is based on the pri...read more

which the refrigerant undergoes phase changes, is one of the many refrigeration cycles and is the most widely used method for air conditioning of 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, petrochemical and chemical processing plants, and natural gas processing plants are among the many types of industrial plants that often utilize large vapor-compression refrigeration systems. Cascade refrigeration systems may also be implemented using two compressors.

A representative pressure–volume diagram for a refrigeration cycle

Refrigeration may be defined as lowering the temperature of an enclosed space by removing heat from that space and transferring it elsewhere. A device that performs this function may also be called an air conditioner, refrigerator, air source heat pump, geothermal heat pump, or chiller (heat pump).

Figure 2: Temperature–Entropy diagram

The thermodynamics of the vapor compression cycle can be analyzed on a temperature versus entropy diagram as depicted in Figure 2. At point 1 in the diagram, the circulating refrigerant enters the compressor as a low-temperature, low-pressure saturated vapor. From point 1 to point 2, the vapor is isentropically compressed (compressed at constant entropy) and exits the compressor as a high-pressure, high-temperature superheated vapor. Superheat is the amount of sensible heat added to the vapor above its saturation point, i.e. its boiling point.

From point 2 to point 3, the vapor travels through part of the condenser which removes the superheat by cooling the vapor. Between point 3 and point 4, the vapor travels through the remainder of the condenser and is condensed into a high-temperature, high-pressure subcooled liquid. Subcool is the amount of sensible heat removed from the liquid below its maximum saturation. The condensation process occurs at essentially constant pressure.