Vapour compression refrigeration system
The most important of all the refrigeration system is the vapour compression refrigeration system with the view point of commercial and domestic utility. This system is the most practical form of refrigeration.
in this system Freon-12 or freon-22 is used as refrigerant. This refrigerant is capable of readily evaporation and condensation without leaving the plant during the evaporation state it absorbs heat from heated body. This absorbed heat is used as latent heat for converting it from liquid to vapour state. In the condensation or cooling process it rejects the heat to the external body. Thus it produces a cooling effect in the working fluid.
Vapour compression refrigeration system consists of the following parts.
Compressor: The purpose of the compressor is to raise the temperature and pressure of the input refrigerant which has low pressure and low temperature.
Discharge line: A discharge line is used for delivering the high pressure, high temperature vapour from the discharge of the compressor to the condenser.
Condenser: The temperature of the hot refrigerant is reduced using a coolant with the help of condenser.
Receiver tank: Receiver tank is used to provide storage for a condensed liquid so that a constant supply of liquid is available to the evaporator as required.
Liquid line: A liquid line transmits the liquid refrigerant from the receiver tank to the refrigerant flow control.
Expansion valve: The proper amount of refrigerant liquid to the evaporator is controlled by the expansion valve.
Evaporator: An evaporator provides a cooling effect to the refrigerated space. The liquid refrigerant absorbs heat from the refrigerated surface and gets converted into refrigerant vapour.
Suction line: The low pressure vapour from the evaporator is transferred to the suction inlet of the compressor with the help of suction line.
A simple vapour compression system follows the following chain,
Compression – condensation – expansion – vaporization
The vapour at low temperature and low pressure enters the compressor where it is compressed which makes the temperature and pressure to increase considerably. From the compressor the vapour enters the condenser where it is condensed to a very high pressure liquid and it is collected in a receiver tank. From the receiver tank, the refrigerant slowly passes through the expansion valve, where it is throttled down to a lower pressure. Finally it reaches the evaporator where it extracts heat from the surrounding where it is being refrigerated and vaporizes to low pressure vapour. Thus the surrounding is cooled. From the evaporator the low pressure refrigerant vapour enters the compressor. This process is repeated as a cycle.
Advantages of vapour compression refrigeration system
· Running cost of this system is low
· For a fixed capacity of refrigeration, it is compact in size.
· This is employed for a large range of temperatures.
· The size of the evaporator is small.
· This system is available in variety of sizes.
Disadvantages of vapour compression refrigeration system
· Cost of the refrigerant is high.
· Refrigerant leakage is a problem.
· Initial cost is high.
· Energy consumption in the form of electricity is high.