Refrigeration (from the Latin frigus, frost) is generally the cooling of a body by the transfer of a portion of its heat away from it. Applications include conservation, especially of food, and lowering the temperature of drinks to one that is more agreeable for consumption. Domestic refrigerators are common in kitchens, with separate sections or separate machines for cooling and freezing.
Cooling of something hot is often done by means of material at ambient temperature, for example the fan cooling of computer equipment.
Where temperatures below that of any available natural cooling agent are required, refrigerators are used to produce the required cooling effect by taking in heat at low temperatures and rejecting it at temperatures somewhat above that of the natural cooling agent, which is generally water or air. The function of a refrigerating machine, therefore, is to take in heat at a low temperature and reject it at a higher one, using external energy to drive the process. A refrigerator is effectively a heat pump, a heat engine running in reverse. It is also possible to use eutectic salts.
Most home and automotive refrigerators qualify as phase change heat pumps. They convert a refrigerant from gas to liquid and back again by compression in a refrigeration cycle. In principle, any endothermic process could be used provided it is balanced by an exothermic in another physical location so that it can operate in a cycle. For example, absorption of gaseous ammonia into water is used in most gas absorption refrigerators , and the Einstein Refrigerator is a version of this which contains no moving parts — the cooling effect in this case coming from the heat absorbed by the ammonia when it evaporates from the water.
Other processes which have been used on a small scale include the Peltier effect for thermoelectric cooling.
History of refrigeration
Development of the first refrigerators
Many countries can claim to be the home of the inventor of the refrigerator, as the technology was developed over a period of time all over the world, using different types of technology and for different purposes. Claimants to the name of inventor include Oliver Evans (USA), Jacob Perkins (USA and England), John Gorrie (USA), Alexander Catlin Twining (USA), James Harrison (Australia) and Carl von Linde (Germany). One of the first uses of "home" refrigeration was at Biltmore Estate in Asheville, North Carolina, USA, installed around 1895 , while in commercial refrigeration the Vestey Brothers opened one of the first refrigerated cold stores in London the same year.
The gas absorption refrigerator, which cools by the use of a source of heat, was invented in Sweden by Baltzar von Platen in 1922.  It was later manufactured by Electrolux and Servel . Today it is used in homes that are not connected to the electrical grid, and in recreational vehicles.
Culture and commerce
Refrigerated trucks (or simply refrigerators) are used to transport perishable goods, such as, for instance, frozen foods, fruit and vegetables, and temperature-sensitive chemicals. Most modern refrigerators keep temperature -40...+20°C and have a maximum payload of around 24000 kg. gross weight (in Europe). Surprisingly, refrigerated trucks are most wanted in winter, when there is a significant demand to transport chemicals under relatively high (+10...+20°C) temperature.
Speculative uses of refrigeration