A process in which the temperature of a space or its contents is reduced to below the one of their surroundings. The compression cycle of refrigeration is the most common procedure. In this type of a cycle, a refrigerant vapour is compressed and gains energy corresponding to the work of compression. The hot, compressed vapour is then cooled by water or atmospheric air. This cooling process condenses the hot vapour to a liquid. The high-pressure liquid is expanded to a lower pressure and becomes a cold mixture of liquid and vapour. This refrigerant mixture is fed into an evaporator where it absorbs heat and changes back to vapour, the same state as at the beginning of the compression cycle.
The principal components of the compression refrigeration system include a receiver for storing liquid refrigerant, an expansion valve for controlling the flow of refrigerant, an evaporator where the required useful refrigeration is produced, a compressor that maintains the evaporator suction pressure and increases the refrigerant vapour temperature and pressure, and a condenser that cools and condenses the hot refrigerant vapour to its original liquid state.
- Cargo refrigeration – In reefer ships, the refrigeration systems are used for the preservation of perishables such as fruits, vegetables, flowers, and meat to ensure their transfer to distant markets. The cargo space is usually divided into several compartments. The size of the compartments and the conditions in them (temperature, humidity, etc.) vary according to the cargoes carried and their compatibility with respect to odours, method of packing, susceptibility to damage, etc. The cargo may be frozen, requiring a storage temperature as low as –20 F, or chilled, with a storage temperature as high as 55 F. For flexibility, the storage spaces are usually designed to be convertible from frozen cargo to chilled cargo and vice versa.