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
Answer: d
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 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
Answer: b
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.
3. 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
Answer: a
Clarification: As C.O.P. is the ratio of refrigeration effect to work done. Due to the increase in the discharge pressure, the refrigeration effect decreases for the same amount of refrigerant flow. Hence, resulting in a small decrease in the C.O.P. of the system.
4. Which of the following factor of the actual VCR affects severely the coefficient of performance?
a) Increase in suction pressure
b) Decrease in discharge pressure
c) Decrease in suction pressure
d) Increase in discharge pressure
Answer: c
Clarification: As C.O.P. is the ratio of refrigeration effect to work done. Due to the increase in the discharge pressure, refrigeration effect decreases, but it is not that severe as is in the case of a decrease in suction pressure. Due to the decrease in the suction pressure, the refrigeration effect severely decreases, and work required for compression increases for the same amount of refrigerant flow. Hence, resulting in a severe decrease in the C.O.P. of the system and refrigeration cost also increases.