refrigeration, process for drawing heat from substances to lower their temperature, often for purposes of preservation. Refrigeration in its modern, portable form also depends on insulating materials that are thin yet effective. Wherever fresh or frozen food must be stored, processed, transported, or sold, refrigeration is indispensable; thus appropriate refrigeration machinery has been developed for trains, ships, factories, and cold-storage plants (used not only for foods but also for fur storage).

See also air conditioning heat pump is a reversible device that does mechanical work to extract heat from a cooler place and deliver heat to a warmer place. The heat delivered to the warmer place is, approximately, the sum of the original heat and the work done.
..... Click the link for more information. .

Early Methods of Refrigeration

Before the advent of modern refrigeration, perishable foods were kept in cool cellars or in buckets lowered into wells. A device still used in some areas is a room built with porous walls over which water is made to trickle; as the water evaporates the room is cooled. A spring of cold water often determined the site of an American pioneer's home. A springhouse was built over the flowing water, and the cooling fluid was led through troughs in which crocks of butter and cream were placed. In winter, farmers stored ice in icehouses for use in the summer. Similarly, natural ice from commercial icehouses was used in cities until artificial methods of producing ice were initiated in the middle of the 19th cent.

Mechanical Refrigeration Systems

The first patent for mechanical refrigeration was issued (1834) in Great Britain to the American inventor Jacob Perkins. Mechanical refrigeration systems are based on the principle that absorption of heat by a fluid (refrigerant) as it changes from a liquid to a gas lowers the temperature of the objects around it. In the compression system, which is employed in electric home refrigerators and commercial installations, a compressor, controlled by a thermostat, exerts pressure on a vaporized refrigerant, forcing it to pass through a condenser, where it loses heat and liquefies. It then moves through the coils of the refrigeration compartment. There it vaporizes, drawing heat from whatever is in the compartment. The refrigerant then passes back to the compressor, and the cycle is repeated.

Prior to 1996, the refrigerants used in electric refigerators were chlorofluorocarbons Halons are organic compounds that are similar to CFCs. They contain carbon, fluorine, and bromine and may contain chlorine. Halons have been used primarily as propellants in fire extinguishers.
..... Click the link for more information. (CFCs). However, because of increasing scientific evidence that the CFCs are harmful to the ozone layer ozone layer or ozonosphere, region of the stratosphere containing relatively high concentrations of ozone , located at altitudes of 12–30 mi (19–48 km) above the earth's surface.
..... Click the link for more information. of the stratosphere, they were banned by international treaty, the Montreal Protocol Montreal Protocol, officially the Protocol on Substances That Deplete the Ozone Layer, treaty signed on Sept. 16, 1987, at Montreal by 25 nations; 168 nations are now parties to the accord.
..... Click the link for more information. , after Jan., 1996. Transitional compounds, such as hydrochlorofluorocarbons (HCFCs), which are less harmful to the ozone layer, are to be used in their place until the year 2020. By that time compounds such as the hydrofluorocarbons (HFCs), which are benign to the ozone layer, are expected to have replaced HCFCs.

In the absorption system, widely employed in commercial installations, ammonia is usually used as a refrigerant to cool brine (water containing calcium chloride or sodium chloride) that is then sent through pipes to cool the refrigerated space. The steam-jet system is used where temperatures below 32°F; (0°C;) are not required; water is used as the refrigerant. Airplanes are cooled or heated through an air cycle system. Research and development is being carried out to apply the Peltier effect (see thermoelectricity thermoelectricity, direct conversion of heat into electric energy, or vice versa. The term is generally restricted to the irreversible conversion of electricity into heat described by the English physicist James P.
..... Click the link for more information. ) in various practical refrigeration systems.

Preparation of Frozen Foods

An outgrowth of the preservation of foods by refrigeration was the development of a process for preparing frozen foods. Although a number of experimenters contributed to the discovery of a workable process, the name of American inventor Clarence Birdseye is associated with the early successful introduction of the method; one of his chief contributions was his system of freezing perishable foods (packed in individual containers ready for sale) between refrigerated metal plates.

Bibliography

See G. H. Reed, Refrigeration (3d ed. 1974); C. T. Olivo and R. W. Marsh, Principles of Refrigeration (1979).

refrigeration

Components of a refrigerator. A compressor pressurizes the refrigerant gas, heating it and forcing …

Process of removing heat from an enclosed space or from a substance in order to lower the temperature. In industrialized nations and prosperous regions in the developing world, refrigeration is used chiefly to store foodstuffs at low temperatures, thus inhibiting the destructive action of bacteria, yeasts, and molds. Many perishable products can be frozen, permitting them to be kept for months and even years with little loss in nutrition or flavour or change in appearance. See also air-conditioning; cooling system; heat exchanger.