Both absorption and compressor refrigerators use a refrigerant with a very low boiling point (less than −18 °C (0 °F)). In both types, when this refrigerant evaporates (boils), it takes some heat away with it, providing the cooling effect. The main difference between the two systems is the way the refrigerant is changed from a gas back into a liquid so that the cycle can repeat. An absorption refrigerator changes the gas back into a liquid using a method that needs only heat, and has no moving parts other than the refrigerant itself.
The absorption cooling cycle can be described in three phases:
In comparison, a compressor refrigerator uses an electrically powered compressor to increase the pressure on the gaseous refrigerant. The resulting hot, high-pressure gas is condensed to a liquid form by cooling in a heat exchanger ("condenser") that is exposed to the external environment (usually air in the room). The condensed refrigerant, now at a temperature near to that of the external environment, then passes through an orifice or a throttle valve into the evaporator section. The orifice or throttle valve creates a pressure drop between the high pressure condenser section and the low pressure evaporator section. The lower pressure in the evaporator section allows the liquid refrigerant to evaporate, which absorbs heat from the refrigerator food compartment. The now-vaporized refrigerant then goes back into the compressor to repeat the cycle.
Another difference between the two types is the refrigerant used. Compressor refrigerators typically use an HCFC or HFC, while absorption refrigerators typically use ammonia or water.
Absorption refrigerators are often used for food storage in recreational vehicles.
Vapor-compression refrigeration is the most widely used method for air-conditioning of buildings and automobiles. It is also used in domestic and commercial refrigerators, large-scale warehouses for chilled or frozen storage of foods and meats, refrigerated trucks and railroad cars, and a host of other commercial and industrial services. Oil refineries, petrochemical and chemicalprocessing plants, and natural gas processing plants are among the many types of industrial plants that often utilize large vapor-compression refrigeration systems.
In compression refrigeration the compression is done mechanically with moving parts; in absorption refrigeration it is done chemically, ideally without moving parts. In both cases the heat of compression must be dissipated to the surrounding atmosphere. A simple example of the latter: A deliquescent substance such as calcium chloride can be used to adsorb water vapor --- to compress water vapor chemically --- and thus to reduce relative humidity enough to allow a "swamp-cooler" air conditioner to work in a humid climate. Of course the adsorbed water must then be driven off, say via solar energy, so that the calcium chloride can be reused.
Comparison between vapor absorption and vapor compression refrigeration systems. Low grade energy sources are more than capable of running a vapor absorption system. ... The refrigerating effect or refrigeration capacity decreases with the lowering evaporator pressure.
https://www.youtube.com/watch?v=PjcdqAkP0UA
https://www.youtube.com/watch?v=O52ms15Ot8Q
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