Phase change heat pump

A phase change heat pump employs a liquid with a low boiling point to transfer heat from cooler space to a warmer space; generally in a refrigeration application. It is the most common heat pump used in domestic refrigerators, and heat pumps are also used in air conditioning systems to transfer heat from the outside of a building to the inside or vice versa depending upon a valve position.

Related Topics:
Phase - Heat pump - Heat - Refrigeration - Domestic refrigerator - Air conditioning

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It employs a liquid, known as a refrigerant which has a low boiling point. The liquid requires energy (called latent heat) to evaporate, and it drains that energy from its surroundings in the form of heat (in the same way that sweating cools the body). When the vapour condenses again, it releases the energy, again in the form of heat.

Related Topics:
Refrigerant - Latent heat

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The pump operates a cycle where the refrigerant repeatedly changes state from liquid to vapor and back to liquid, the process being known as a refrigeration cycle. The refrigerant is condensed to release heat in one part of the cycle and is boiled (or evaporated) to absorb heat in another part of the cycle.

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Since the 1930s the liquid has typically been freon (CFC), but its use has been discontinued because of damage that it does to the ozone layer if released into the atmosphere. The liquid now used is usually R-134a (1,1,1,2-tetrafluoroethane), but other substances such as liquid ammonia, or occasionally the less corrosive but flammable propane or butane can also be used.

Related Topics:
1930 - Freon - CFC - Ozone layer - Atmosphere - R-134a - Ammonia - Propane - Butane

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The most common form of phase change heat pump uses an electric motor to drive a mechanical compressor. The compressor does not create a cooling effect directly. The cooling effect is created when the refrigerant boils and absorbs heat from the cooled space through a heat exchanger. The cycle can be divided into two parts — the liquifaction stage and the evaporation stage:

Related Topics:
Compressor - Heat exchanger

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