# 250+ TOP MCQs on Actual VCR Cycle and Answers

Refrigeration Multiple Choice Questions on “Actual VCR Cycle”.

1. Which of the following is not the difference between theoretical and actual VCR cycle?
a) Pressure drops in the evaporator
b) Pressure drops in the condenser
c) Compression of refrigerant is never polytropic
d) Compression of refrigerant is always isentropic
Clarification: Entropy is the randomness of molecules. Change in entropy cannot be kept constant. As any transfer of energy will provide energy to the particles and increasing the entropy. The entropy of the Universe tends to increase day by day. Hence, the compression process cannot be executed in an isentropic manner. Ideally, it can be assumed, but in the actual cycle, it is impossible to attain such a process.

2. What does process 2-3 represent?

a) Compression
b) Condensation
c) Evaporation with superheating
d) Expansion with subcooling
Clarification: Process 2-3 represents evaporation with superheating. The shift of exit of evaporation from point 2 to point 3 is due to
1) Automatic control of expansion valve
2) Absorbs a larger amount of heat
3) Refrigeration effect and work increases.

3. What does process 3-4 represent?

a) Pressure reduction
b) Compression
c) Condensation
d) Evaporation
Clarification: Due to the frictional resistance offered to the vapor refrigerant entering the compression system pressure drops from point 3 to point 4. Thus, actual suction pressure (PS) lower than the evaporator pressure (PE).

4. What does process 4-5 represent?

a) Temperature rise
b) Temperature fall
c) Compression
d) Expansion
Clarification: After pressure reduction and before compression begins, the temperature of cold refrigerant comes in contact with compression cylinder walls, which are at a higher temperature. Hence, due to heat transfer, the temperature of the refrigerant rises to point 5, which is the heating effect.

5. What does process 5-6 represent?

a) Expansion
b) Compression
c) Condensation
d) Evaporation
Clarification: Actual compression is denoted by process 5-6, which is neither isentropic nor polytropic, due to heat transfer between cylinder walls and vapor refrigerant. The temperature of cylinder walls is between cold suction vapor refrigerant and hot discharge vapor refrigerant. Pressure and temperature are increased in this process.

6. What does process 6-7 represent?

a) Temperature rise
b) Temperature fall
c) Compression
d) Expansion
Clarification: After compression and before Condensation begins, the temperature of hot refrigerant comes in contact with compression cylinder walls which are at a lower temperature. Hence, due to heat transfer, the temperature of the refrigerant falls to point 7, which is a cooling effect.

7. What does process 7-8 represent?

a) Condensation
b) Compression
c) Pressure reduction
d) Evaporation
Clarification: Due to the frictional resistance offered to the vapor refrigerant discharging the compression system pressure drops from point 7 to point 8. Thus, actual discharge pressure (PD) higher than the condenser pressure (PC).

8. What does process 8-9 represent?

a) Compression
b) Condensation
c) De-superheating
d) Expansion with subcooling
Clarification: Before condensing the refrigerant, to reject maximum heat to get stabilized state of refrigerant, the refrigerant must be at saturated state before condensing. Hence, de-superheating is carried out to get the refrigerant at a saturated level and then condensed.

9. What does process 9-10 represent?

a) Compression
b) Condensation
c) Evaporation
d) Expansion
Clarification: Process 9-10 shows the removal of latent heat where the dry saturated refrigerant is converted into a liquid refrigerant. This process is called Condensation.

10. What does process 10-11 represent?

a) Compression
b) Expansion
c) Evaporation with superheating
d) Subcooling
Clarification: The process 10-11 represents sub-cooling of the liquid refrigerant in the condenser before it is expanded. Sub-cooling is carried out as it increases the refrigerating effect per kg of the refrigerant flow. It does reduce the volume of refrigerant partially evaporated from liquid refrigerant while going through the expansion valve. The refrigerating effect can be increased by circulating a large amount of water, which is at a much lower temperature than condensing temperature.

11. What does process 11-1 represent?

a) Expansion
b) Condensation
c) Compression
d) Evaporation
Clarification: Process 11-1 represents expansion. The expansion of sub-cooled liquid refrigerant is carried out by throttling (keeping enthalpy constant) from the condenser pressure to the evaporative pressure.

12. What does process 1-2 represent?

a) Expansion
b) Condensation
c) Compression
d) Evaporation
Clarification: Process 1-2 represents evaporation. In this process, absorption of heat is carried out and converting liquid refrigerant to saturated vapor condition. The evaporation process is known as Refrigeration effect.

13. What is the effect of a decrease in suction pressure on C.O.P.?
a) C.O.P. increases
b) C.O.P. decreases
c) C.O.P. remains the same
d) C.O.P. becomes zero
Clarification: As C.O.P. is the ratio of refrigeration effect to work done. Due to the decrease in the suction pressure, the refrigeration effect is decreases and work required for compression increases for the same amount of refrigerant flow. Hence, resulting in a reduction of the C.O.P. of the system and refrigeration cost also increases.

14. What is the effect of an increase in discharge pressure on C.O.P.?
a) C.O.P. decreases
b) C.O.P. increases
c) C.O.P. remains the same
d) C.O.P. becomes zero