250+ MCQs on Two/Multi Stage Compression with Water Intercooling, Liquid Subcooling and Flash Intercooler

Basic Refrigeration Questions and Answers on “Two/Multi Stage Compression with Water Intercooling, Liquid Subcooling and Flash Intercooler”.

1. Why is multi-stage or compound VCR with water intercooler, liquid sub-cooler, and flash intercooler used?
a) To improve C.O.P.
b) To decrease refrigeration effect
c) To increase work
d) To increase leakage loss

Answer: a
Clarification: By de-superheating or intercooling the refrigerant before the second stage compression but not till the saturated vapor line, can decrease the total work required. By using the liquid sub-cooler, subcooling is done, and an increase in the refrigeration effect is achieved. Use of flash intercooler ensures separation of vapor and liquid form of refrigeration and acts as an intercooler too, which helps to reduce the work. So, the increase in R.E. and decrease in work improves the C.O.P. of the system.

2. What is the purpose of using intercooler?
a) To increase the cost of the compressor
b) To cool the superheated refrigerant
c) To re-heat superheated refrigerant
d) To reduce the volumetric efficiency

Answer: b
Clarification: Intercooler is used to cool the superheated refrigerant by some amount but in this case, not till the saturated vapor line. The superheated refrigerant leaving the first compressor is cooled by suitable method before entering the second compressor. This type of cooling is known as intercooling.

3. What is the purpose of using liquid sub-cooler?
a) To increase the cost of the compressor
b) To reduce the volumetric efficiency
c) To re-heat superheated refrigerant
d) To increase the refrigeration effect

Answer: d
Clarification: Liquid sub-cooler is used to sub-cool the liquid refrigerant coming from the condenser beyond the saturated liquid line. Sub-cooling results in an increase in refrigeration effect and thus increasing the C.O.P.

4. What is the purpose of using a flash intercooler?
a) To increase pressure
b) To decrease pressure
c) To separate vapor and liquid refrigerant and de-superheat
d) To evaporate refrigerant partially

Answer: c
Clarification: Flash intercooler is the combination of flash chamber and intercooler. Flash chamber is used to separate vapor and liquid refrigerant. It is an insulated container and separates both forms by using the centrifugal effect. Intercooler decreases the temperature to the saturated vapor line before entering the second stage of compression.

5. What is the value of Refrigeration effect if m1 = 4 kg/min, and enthalpies for the point 1, 2, 4, 5, 9 are 1350, 1550, 1480, 1620, and 280 kJ/kg. If the refrigeration effect is 4280 kJ/min and work done is 15 kW, then what is the value of C.O.P.?
a) 4.85
b) 5.50
c) 4.75
d) 6.00

Answer: c
Clarification: Given: m1 = 4 kg/min
h1 = 1350 kJ/kg
hf9 = h10 = 280 kJ/kg
h2 = 1550 kJ/kg
h4 = 1480 kJ/kg
h5 = 1620 kJ/kg
As, enthalpies of all points is given but it is a redundant data cause direct values of refrigeration effect and work is given, hence C.O.P. can be found easily.
Refrigeration effect = m1 (h1 – h11)
= 4280 kJ/min
Work = 15 kW = 900 kJ/min
C.O.P. = Refrigeration effect / Work
= 4280 / 900
= 4.75.

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