Wednesday, January 9, 2008

Refrigeration Cycle :

The compression refrigeration cycle which is described earlier is also used in air-conditioner. The basic components are compressor, condenser, capillary and evaporator in addition to filters, accumulators, motors, fan and controls. High pressure, high temperature refrigerant gas coming out of compressor is condensed in the condenser using outside air as coolant. The liquid refrigerant is further passed through capillary to reduce the pressure and then it is passed through the evaporator. The air from the room is passed over the evaporator where it is cooled to require temperature and then discharged in the room itself. The evaporator refrigerant vapour coming out at lower pressure from the evaporator is compressed in the compressor and cycle is repeated. The arrangement of the refrigeration system using a sealed unit in air-conditioner is shown in figure..

The window-unit compressor is of the hermetic type. This kind of unit has the compressor, its motor, and all moving parts operating within a sealed gas tight housing which is welded and closed.

The condenser coil is a continuous coil of copper tubing to which aluminium fins are bonded to increase the heat transfer surface area. A propeller type condenser fan is located immediately in front of the condenser coil. This fan cools the condenser coil and also exhausts air from the air conditioned space when the exhaust air damper is opened. Moisture condensed on the surface of the evaporator coil during dehumidification of the air, is also exhausted by the condenser fan.

The copper capillary tube is 40 cm long with an inside diameter of 0.75 mm. The dimensions are based upon the desired pressure difference between evaporator and condenser.

The evaporator is located at the front end of the room air-conditioner. It is also made of copper tubing and has aluminium fins bonded at right angles to the tubing to increase the heat transfer area. For one kW unit, the evaporator and condenser coils have a total surface area of 7.5 and 14 m2 respectively. This larger surface area for condenser coil is necessary because, in addition to the heat which entered through the evaporator, heat resulting from the compressor action also enters the refrigerant and this total must be discharged.

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