Vapour compression cycle is a cycle employed for obtaining low temperatures in refrigerators and air conditioners.In other words, the vapour-compression cycle is a process used to extract heat from a box or a room that underlies most refrigeration and air conditioning techniques.
The vapour compression cycle consists of four separate stages: vaporization, compression, condensation, and expansion-
It takes heat to vaporize a liquid. Therefore, when a liquid refrigerant evaporates, it cools the surrounding fluid as it extracts heat. As shown in the diagram below, warm air flowing across an evaporative radiator will cause a refrigerant to undergo a phase change from liquid to a gas, cooling the fluid flowing across the radiator, which in this case is air. This process occurs in the coils located inside a refrigerator or inside the cools side of an air conditioner unit.
After vaporization, the gaseous refrigerant is compressed. The process of compression does work on the refrigerant, thereby increasing its pressure and temperature. By doing work on the refrigerant, the compressor adds energy in the form of heat, which will be released during the upcoming condensation process that converts the refrigerant gas back into a liquid. Compression takes place in the mechanical unit located in the bottom and backside of a refrigerator or on the outside of an air conditioner.
After compression, the superheated vapor is run through a condenser or condensing radiator that converts the refrigerant vapor back into liquid releasing its heat into surrounding fluid. Condensation occurs in the coils on the outside or back of a refrigerator or outside section of an air conditioner.
After the high-pressure refrigerant is condensed, the liquid refrigerant flows through an expansion valve that reduces its pressure and temperature. (When you use a spray can, the nozzle and spray can will get colder due to the expansion of the gas leaving the can.) The expansion process also extracts energy in the form of heat, which causes some of the liquid refrigerant to transition into a gas. The lower pressure and temperature of the refrigerants is necessary for the vaporization process. The expansion valve is located on an air conditioner’s cold side of a refrigerator.