What is vapour compression refrigeration cycle ? Where is is used ?
The basic components of any refrigeration system working on the vapour compression cycle, are the compressor, condenser, expansion valve, evaporator and the refrigerant fluid which is alternately vaporized and liquefied during the refrigeration cycle. The temperature at which a fluid boils or condenses, is known as the saturation temperature and varies with pressure.
The compressor in a refrigeration system in raising the pressure of the vaporized refrigerant, causes its saturation temperature to rise, so that it is higher than that of the sea water or air, cooling the condenser. The compressor also promotes circulation of the refrigerant by pumping it around the system. In the condenser, the refrigerant is liquefied by being subcooled to below the saturation temperature relating to the compressor delivery pressure, by the circulating sea water (or air for domestic refrigerators).
Fig : Vapour compression cycle
Latent heat, originally from the evaporator, is thus transferred to the cooling medium. The liquid refrigerant, still at the pressure produced by the compressor, passes to the receiver and then to the expansion valve. The expansion valve is the regulator through which the refrigerant flows from the high pressure side of the system to the low pressure side. Its throttling effect dictates the compressor delivery pressure which must be sufficient to give the refrigerant a saturation temperature which is higher than the temperature of the cooling medium.
The pressure drop through the regulator causes the saturation temperature of the refrigerant to fall, so that it will boil at the low temperature of the evaporator. In fact, as the liquid passes through the expansion valve, the pressure drop makes its saturation temperature fall below its actual temperature, Some of the liquid boils off at the expansion valve, taking latent heat from the remainder and causing its temperature to drop.
The expansion valve throttles the liquid refrigerant and maintains the pressure difference between the condenser and evaporator, while supplying refrigerant to the evaporator at the correct rate. It is thermostatically controlled in modern systems. The refrigerant entering the evaporator coil, at a temperature lower than that of the surrounding secondary coolant (air or brine) receives latent heat and evaporates. Later the heat is given up in the condenser, when the refrigerant is again compressed and liquefied.
For a small refrigerator the evaporator cools without forced circulation of a secondary coolant. In larger installations, the evaporator cools air or brine which are circulated as secondary refrigerants
Type of refrigerants - Open Loop, Closed Loop & vapour absorption system
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