Refrigeration MCQs on “Effect of Various Parameters on VCR System – 2”.
1. What is the use of a flash chamber in VCR system?
a) To increase pressure
b) To decrease pressure
c) To separate vapour and liquid refrigerant
d) To evaporate refrigerant partially
Answer: c
Clarification: Flash chamber is used to separate vapour and liquid refrigerant. It is an insulated container and separates both forms by using the centrifugal effect.
2. What is the amount of mass of vapour refrigerant flowing directly from flash chamber to suction of the compressor?
a) m1
b) m2
c) m1 + m2
d) m2 – m1
Answer: d
Clarification: As, m1 = Mass of the liquid refrigerant supplied to the evaporator
m2 = Mass of refrigerant (liquid and vapour) circulating through the condenser
Hence, the amount of mass flowing through the flash chamber to the compressor is given by,
= m2 – m1.
3. What is the ratio of the mass of refrigerant supplied to evaporator and mass of refrigerant circulating through condenser i.e., m1 / m2?
a) h1 – h2 / h1 – h4
b) h1 – h4 / h1 – hf4’
c) h2 – h1 / h4 – h1
d) h1 – hf4’ / h1 – h4
Answer: b
Clarification: As flash chamber is an insulated cylinder. Heat transfer between flash chamber and surroundings is zero. So, by considering thermal equilibrium of flash chamber,
Heat taken by the flash chamber = Heat given out by the flash chamber
m2 h4 = m1 hf4’ + (m2 – m1) h1
m2 (h1 – h4) = m1 (h1 – hf4’)
m1 / m2 = [h1 – h4 / h1 – hf4’].
4. What is the use of accumulator or pre-cooler in VCR system?
a) To supply dry saturated vapour and pure liquid refrigerant to the respective equipment
b) To decrease pressure
c) To increase pressure
d) To condense refrigerant partially
Answer: a
Clarification: Accumulator or pre-cooler does almost the same work as a flash chamber. It receives the discharge of a mixture of liquid and vapour refrigerant from expansion valve and supplies liquid refrigerant only to the evaporator. This discharge again sent to the accumulator, and only dry saturated vapour refrigerant is further sent to the compressor.
5. What is the use of a liquid pump in the VCR system containing accumulator?
a) To maintain the circulation of the refrigerant
b) To provide liquid refrigerant
c) To expand the liquid refrigerant
d) To pre-evaporate the liquid refrigerant
Answer: a
Clarification: Accumulator separates the mixture of refrigerants, and provides dry saturated vapour to the compressor and pure liquid refrigerant to the evaporator. So, to maintain the circulation of the liquid refrigerant in the evaporator, a liquid pump is used.
6. What is the ratio of the mass of refrigerant supplied to evaporator and mass of refrigerant circulating through condenser i.e., m1 / m2?
a) h1 − h2 / h1 − h4
b) h1 − h4 / h1’ − hf4’
c) h2 − h1 / h4 − h1
d) h1’ − hf4’ / h1 − h4
Answer: b
Clarification: As accumulator is an insulated vessel. Heat transfer between flash chamber and surroundings is zero. So, by considering thermal equilibrium of flash chamber,
Heat taken by the accumulator = Heat given out by the accumulator
m2 h4 + m1 h1’ = m2 h1 + m1 hf4’
m1 (h1’ − hf4’) = m2 (h1 − h4)
m1 / m2 = [h1 − h4 / h1’ − hf4’].
7. What is the use of heat exchanger in the following schematic?
a) Compression
b) Expansion
c) Subcooling of liquid by vapour refrigerant
d) Subcooling of vapour by liquid refrigerant