All About Vapor Compression Cycle

All About Vapour Compression Cycle

Saswata Baksi Refrigeration and Air-Conditioning 2 Comments

Vapour compression cycle generally known as VCC is a refrigeration cycle.

In this cycle, the refrigerant is sealed condition in an airtight mechanism is compressed in a compressor which permits the transfer of heat energy. The refrigerant absorbs heat from one place and releases it to another place. The system repeats over and over again and absorbs heat at low pressure from the refrigerant space.

Main Components of Vapour Compression Cycle

The principle parts which are used in this system are:

  1. Evaporator
  2. Suction line
  3. Compressor
  4. Discharge Line
  5. Condensor
  6. Receiver Tank
  7. Liquid line
  8. Expansion Valve
Main Components of Vapour Compression Cycle
FLOW DIAGRAM OF VAPOUR COMPRESSION CYCLE

Let me discuss these components further on.

Evaporator:

It provides the heat transfer surface through which heat can pass from the refrigerant space into the refrigerant.

Suction line:

It carries the low-pressure vapor refrigerant from the evaporator to the inlet of the compressor.

Compressor:

The function of the compressor is to compressed the vapor refrigerant to temperature and pressure to such a point so that it may be easily condensed.

Discharge Line:

It coveys the high pressure and high-temperature refrigerant from the compressor to the condenser.

Condenser:

It provides heat transfer surface and cools down the refrigerant by water spray or blow of air.

Receiver tank:

It stores the liquid refrigerant coming from the condenser and supplies it to the evaporator as per requirements.

Liquid line:

It carries the liquid refrigerant from the receiver to the expansion valve.

Expansion valve:

It supplies the proper quantity of liquid refrigerant to the evaporator after reducing the pressure.

Working principle of Vapour Compression Cycle

It works as follows:

  • During suction stroke of the compressor, wet vapor refrigerant is drawn from the evaporator and compressed adiabatically to high pressure and high temperature
  • The high-pressure vapour refrigeration is then cooled in the condenser at constant pressure
  • The high-pressure liquid refrigerant is there expanded through a throttle valve or expansion valve and lower its pressure and temperature.
  • The low-temperature vapor refrigerant absorbs heat from the evaporator at constant pressure and cools the space. the vapor refrigerant enters the compressor during suction stroke and the cycle is repeated.

In this cycle, a large amount of work is required to compress the vapor refrigerant for increasing its pressure.

COP of Vapour Refrigerant Cycle

Let,

h1 = Specific enthalpy of refrigerant before compression.

h2 = Specific enthalpy of refrigerant after compression.

h3 = Specific enthalpy of refrigerant after cooling.

h4 = Specific enthalpy of refrigerant after expansion.

Therefore, COP is equal to (Refrigerating effect/Work-done) = (h1-h4)/(h2-h1) = (h1-h3)/(h2-h1) [As h3 = h4]

P-V, T-S, P-H DIAGRAM OF VAPOR COMPRESSION CYCLE
P-V, T-S, P-H DIAGRAM OF VCC

Actual Vapour Compression Cycle

The actual vapour compression cycle differs from the standard cycle due to the following reasons:

  • liquid refrigerant in the condenser is subcooled to ensure 100% liquid entering the expansion valve.
  • The vapor usually leaves the evaporator is superheated to prevent droplet of liquid within the compressor.
  • Isentropic expansion does not occur due to friction and other losses.
  • Pressure drop takes place in the evaporator and condenser due to
  • friction.

Description of Cycle

ACTUAL VAPOR COMPRESSION REFRIGERATION CYCLE
ACTUAL VAPOUR COMPRESSION REFRIGERATION CYCLE
  1. Process a-b-c represent the flow of refrigerant in the evaporator at suction pressure and temperature T2.
  2. Process c-d represents a drop in pressure due to suction valve resistance to the compressor.
  3. Process d-e represent the addition of heat to the refrigerant fro the cylinder wall.
  4. Process e-f represent actual compression of refrigerant in the compressor.
  5. Process f-g represents cooling of refrigerant at compressor exit line as heating d-c.
  6. Process g-h represent pressure drop due to resistance of discharge valve.
  7. Process h-ij-k represents desuperheating of vapor to dry state and removal of latent heat and sub-cooling of refrigerant.
  8. Process k-a represents throttling of sub-cooled refrigerant from condenser pressure to the evaporator pressure.

Comparison of Vapour Compression and Vapour Absorption System

Vapour Compression SystemVapour Abortion System
1. The system has more weak, tear and noise due to moving parts in the compressor.1. The system is quiet in operation due to less number of moving parts.
2. Mechanical energy is supplied.2. Heat energy is supplied.
3. Supply of energy is low. 1/2 to 1/3 of refrigerating effect.3. Supply of energy is high. 1.5 of refrigerating effect.
4. The poor performance of partial loads.4. Performance is not affected by load variations.
5. Charging of refrigerant is simple.5. Charging of refrigerant is difficult.
6. Chances in leakage of refrigerant.6. No leakage of refrigerant due to absence of compressor.

Now for concept clearing, you can watch these videos

VAPOUR COMPRESSION CYCLE 1 BY PROF. RAVI KUMAR, IIT ROOKIE
VAPOUR COMPRESSION CYCLE 2 BY PROF. RAVI KUMAR, IIT ROOKIE
ACTUAL VAPOUR COMPRESSION CYCLE 1 BY PROF. RAVI KUMAR, IIT ROOKIE
ACTUAL VAPOUR COMPRESSION CYCLE 2 BY PROF. RAVI KUMAR, IIT ROOKIE

You can also Check-out Vapor Absorption Cycle and Electrolux Refrigeration System written by me.

Conclusion

Now I love to hear from you, In this guide of VCC, I showed all-important point regarding VCC. And also I shared a couple of videos of Prof. Ravi Kumar. I am pretty sure you have already clear your doubts although If you wanna need some specific question regarding this please comment down below, I would reply to all of your queries.

STILL HAVE QUESTIONS ON YOUR MIND?

ASK-YOUR-DOUBT

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About the Author

Saswata Baksi

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Saswata completed his diploma in Mechanical Engineering from I.C.V.P and now studying B-Tech in School of Mechanical Engineering at KIIT University, one of the best university in India. Apart from that, he loves blogging, Saswata is also the founder of jhargramhub.in and partsofspeech.net

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