Working principle of refrigeration cycle

Working principle of the refrigeration cycle

Process 1-2:(Constant pressure process)(Evaporation process):

  • In this process, low pressure & low enthalpy liquid refrigerant enters the evaporator.
  • The evaporator is a heat exchanger either fin & tube or shell & tube type.
  • Refrigerant passes through the tube and over the tubes,the room air flows.
  • Refrigerant absorbs heat from the room air and thus cools the room air
  • At the outlet of the evaporator, we have saturated refrigerant vapour.

Process 2-3(Compression process)(Isentropic process):

  • In this process, saturated vapour refrigerant coming from the evaporator is mechanically compressed from p2 to p3.
  • P3 is also known as setpoint is so selected that, the temperature corresponds to this pressure is above ambient temperature.
  • The refrigerant compressor required external work in the term of electrical energy and this cycle is inclining with the 2nd law of thermodynamics.

Process 3-4(Constant pressure process)(Condensation process):

  • High temperature and high-pressure vapour refrigeration coming from the compressor enter into the condenser is also a heat exchanger placed near the ambient air.
  • Heat transfer takes place between the ambient air and the refrigerant vapour.
  • Refrigerant vapour gives away latent heat and gets converted into hot liquid refrigerant at the outlet of the condenser.

Process 4-1(Expansion process)(Isentropic process):

  • In this process, hot liquid refrigerant passes through the expansion device.
  • Expansion device consists of a small aperture/capillary, leading to pressure drop at constant enthalpy.
  • Due to change in pressure from p4 to p1, the refrigerant is again available for reuse to carrying cycle 1-2-3-4-1.

Superheating & Subcooling:

  • Liquids are practically incompressible. Hence pressure of liquid may damage the compressor.
  • In order to avoid the liquid refrigerant from entering into the compressor, superheating is done.
  • Refrigerant is slightly heated before it enters the compressor.
  • Similarly, the presence of gas passing through the expansion device reduced the efficiency of the expansion valve.
  • Hence refrigerant is further slightly cooled before it enters the expansion valve.


We can use the cycle without accessories also, but for safety purpose we can use accessories.
Accessories  are,
Oil separator:
  • It is fitted between the compressor and condenser.
  • It helps to remove oil from refrigerant and it passes only vapour refrigerant to condenser and it sent back liquid refrigerant to the compressor.
        Liquid receiver:
  • It is fitted between condenser and filter.
  • It helps liquid refrigerant to pass forward.
  • It is fitted between the evaporator and compressor.
  • It ensures that the refrigerant leaves the accumulator as a vapour and not a liquid state for the compressor to induce.

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