Refrigeration is a process/system by which the temperature of a space is reduced [heat is removed from a space]

Principle of Refrigeration

When a liquid evaporates it produces a cooling effect by taking the heat from the surrounding


  1. Place a drop of volatile liquid [ether (or) eau-de-cologne]on the hand

It gives a cooling sensation

This is because, the liquid evaporates taking the heat from the skin

  1. Water kept in an earthen/mud pot or pail, gets cooled

This is because, the water that gets leaked through the pores in the body/surface of the pot evaporates taking the heat from the body/surface of the pot/the water inside


  1. Take a cylinder containing liquid CO2

Place a Bottle of Water on the coiled outlet pipe of the cylinder

Open the outlet valve of the cylinder to release the CO2

Water in the Bottle gets cooled

This is because, the liquid CO2 evaporates taking the heat from the  Bottle surface/Water inside

Compression Refrigeration Cycle – Vapour Compression System

Components & Operation

In the previous example – Liquid CO2 in the Cyl will soon become empty

Cooling effect will Stop

To continue the cooling effect the cylinder has to be recharged with CO2

In the actual Vapour Compression System, the Refrigerant vapours are not allowed to escape into atmosphere.

Instead it is compressed in a compressor

Pressurised refrigerant vapours are then cooled in a condenser to form liquid

Liquid  Refrigerant is collected in a receiver

It is then sent back to the evaporator coil through a Throttle Valve (Expansion Valve)

This cycle is continued

In the actual Refer system, instead of cooling  a bottle of water the cargo/provision is cooled, by using a fan to circulate the air around the evaporator coil and the cargo/provision

The liquid refrigerant inside the evaporator coil gets vapourised by taking the heat from the cargo