Removal of heat from an enclosure in order to lower its temperature. It is used for freezing water or food, for food preservation, for air conditioning, and for low-temperature chemical processes and cryogenics studies and applications.
The ancient Egyptians and Indians used the evaporation of water from porous vessels; and the Chinese, Greeks, and Romans used natural ice, a method which became a major industry in the 19th-century US. Modern refrigerators are insulated cabinets containing the cooling elements of a heat pump. The pump may used mechanical compression of refrigerants such as ammonia or Freon, or may accomplish compression by the absorbing the refrigerant in a secondary fluid such as water and pumping the solution through a heat exchanger to a generator where it is heated to drive off the refrigerant at high pressure. Other cycles, similar in principle, using steam or air, are also used.
Related category TECHNOLOGY
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