Refrigeration Questions and Answers – Theoretical VCR with Superheated Vapour before and after Compression

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This set of Advanced Refrigeration Questions and Answers focuses on “Theoretical VCR with Superheated Vapour before and after Compression”.

1. The net effect of superheating is to have ________ COP.
a) higher
b) lower
c) moderate
d) higher or lower depending on the refrigerant used
View Answer

Answer: b
Explanation: Superheating increases the refrigeration effect as well the work done in compressor, as the increase in refrigeration effect is less than the increase in work done for some refrigerants and more in other refrigerants, the net effect of superheating is to increase or decrease the COP.
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2. The COP of vapor compression when vapor is superheated after compression having refrigeration effect (Re) of 360 and work done (W) of 40 is?
a) 8
b) 6.7
c) 7.8
d) 9
View Answer

Answer: d
Explanation: The COP is given by Refrigeration effect by work done,
COP=\(\frac{Re}{W}=\frac{360}{40}\)=9.

3. What is the mass flow rate of the refrigerant when the heat required is 100 MJ/hr, enthalpy at discharge H2 is 434.5 KJ/kg and enthalpy of liquid Hf3 in KJ/kg at point 3 in p-h diagram is 271.97?
a) 10.254 kg/hr
b) 15.56 kg/hr
c) 10.254 kg/min
d) 15.56 kg/min
View Answer

Answer: c
Explanation: mass flow rate = \(\frac{Q}{H_2 – Hf_3}
= \frac{100×1000}{434.5 – 271.97} \)
= 10.254 kg/min.
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4. The cycle in which the evaporation starts at point 4 and continues up to point 1 where it is dry-saturated is called?
refrigeration-questions-answers-theoretical-vcr-superheated-vapour-compression-q4
a) Theoretical VCR with dry vapor compression
b) Theoretical VCR with wet vapor compression
c) Theoretical VCR with super – heated vapor after compression
d) Theoretical VCR with super – heated vapor before compression
View Answer

Answer: d
Explanation: In theoretical VCR with super – heated vapor before compression, the vapor is superheated before entering the compressor up to point 1.

5. What is the COP of performance of the plant when the vapor is superheated 5 degree C before entering the compressor and
H1 – Enthalpy before compression = 180
H2 – Enthalpy after compression = 215
Hf3 – Enthalpy at the end of condensation = 55
H4 – Enthalpy at the end of expansion = 55
refrigeration-questions-answers-theoretical-vcr-superheated-vapour-compression-q4
a) 5.7
b) 4.8
c) 4.7
d) 3.5
View Answer

Answer: d
Explanation: The COP of performance of the plant when the vapor is superheated 5 degree C before entering the compressor = \(\frac{H_1 – Hf_3}{H_2 – H_1}=\frac{180 – 55}{215 – 180}\) = 3.57.
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6. In domestic vapor compression refrigeration, the refrigerant commonly used is?
a) Freon – 12
b) CO2
c) H2O
d) Ammonia
View Answer

Answer: a
Explanation: In domestic vapor compression refrigeration, the refrigerant commonly used is Freon – 12 because of its safe properties, stability, miscibility with oil and suitable to wide range of operating temperatures.

7. Superheating before compression increases the refrigeration effect.
a) True
b) False
View Answer

Answer: a
Explanation: Superheating before compression increases the refrigeration effect and the work done as well, as the superheating increases the enthalpy of the vapor entering the compressor and thus increases the refrigerating effect.
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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn | Youtube | Instagram | Facebook | Twitter