Explain with neat sketch a complete multistage vapour compression system.

Subject : Refrigeration and Air Conditioning

Topic : Vapour Compression Refrigeration System

Difficulty : Medium

  • Applications like cold storages, liquefaction of gases, chemical industries etc. demand very low evaporator temperatures and pressures, reaching even up to -150°C in some cases.
  • Hence difference between condenser and evaporator pressure increases. So when pressure ratio required is more than 8 to 10, a single stage vapour compression cycle is not efficient. Hence multistage VCRS with intercooling is adopted.
  • This reduces the work of compression while keeping refrigerating effect the same. Thus COP of cycle increases, which leads to improved performance of cycle and decreased operational cost.

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  • Process 1-2 represents isentropic compression in L.P. compressor from evaporator pressure to intermediate pressure. The vapour is then passed through intercooler where it is cooled at constant pressure (2-3) and then compressed to condenser pressure (3-4) by the H.P. compressor.
  • The vapour cooling can be achieved by water or flash intercooler depending upon the refrigerant and application.


1) The complexity of compressor body increases

2) Manufacturing and operating costs increase

3) Resistance losses increase in piping, valves and other equipments

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