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:
- Suction line
- Discharge Line
- Receiver Tank
- Liquid line
- Expansion Valve
Let me discuss these components further on.
It provides the heat transfer surface through which heat can pass from the refrigerant space into the refrigerant.
It carries the low-pressure vapor refrigerant from the evaporator to the inlet of the 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.
It coveys the high pressure and high-temperature refrigerant from the compressor to the condenser.
It provides heat transfer surface and cools down the refrigerant by water spray or blow of air.
It stores the liquid refrigerant coming from the condenser and supplies it to the evaporator as per requirements.
It carries the liquid refrigerant from the receiver to the 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
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]
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
- Pressure drop takes place in the evaporator and condenser due to
Description of Cycle
- Process a-
b-crepresent the flow of refrigerant in the evaporator at suction pressure and temperature T2.
- Process c-d represents a drop in pressure due to suction valve resistance to the compressor.
- Process d-e represent the addition of heat to the refrigerant
frothe cylinder wall.
- Process e-f represent actual compression of refrigerant in the compressor.
- Process f-g represents cooling of
refrigerantat compressor exit line as heating d-c.
- Process g-h represent pressure drop due to resistance of discharge valve.
h-i– j-krepresents desuperheating of vapor to dry state and removal of latent heat and sub-cooling of refrigerant.
- 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 System||Vapour 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 refriger||5. Charging of refrigerant is difficult.|
|6. Chances in leakage of refriger||6. No leakage of refrigerant due to absence of compressor.|
Now for concept
clearing, you can watch these videos
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