This set of Refrigeration Multiple Choice Questions & Answers (MCQs) focuses on “Theoretical VCR with Dry Saturated Vapour after Compression – 1”.
1. In vapor compression cycle having dry saturated vapor at the end of compression the work done is given by?
H2 – Enthalpy of vapor after compression
H1 – Enthalpy of vapor before compression
a) H2 – H1
b) H2 + H1
c) H2 × H1
d) H2 ÷ H1
View Answer
Explanation: Work is done on the compressor in the compression process (1 – 2), and the external work-done in the remainder process of the cycle is zero. Hence the net work-done equals to the compressor work.
2. In vapor compression cycle having dry saturated vapor at the end of compression the refrigeration effect is given by?
H1 – Enthalpy of vapor before compression
H4 – Enthalpy of vapor before entering evaporator
H2 – Enthalpy of vapor after compression
a) H1 – H4
b) H2 – H4
c) H1 × H4
d) H2 × H4
View Answer
Explanation: Refrigeration effect is the heat absorbed by the vaporizing refrigerant in the evaporator during the process (4 – 1), therefore refrigeration effect = H1 – H4.
3. The COP of vapor compression having vapor as dry saturated after compression having refrigeration effect (Re) of 58.84 and work done (W) of 17.95 is ________
a) 3.278
b) 4.39
c) 4.234
d) 3.865
View Answer
Explanation: The COP is given by Refrigeration effect by work done,
COP=\(\frac{Re}{W}\)
=\(\frac{58.84}{17.95}\)=3.278.
4. Entropy of dry-saturated vapor when Sf is 0.2513 and Sfg is 4.7878, is _______
Sf – Entropy of saturated liquid at pressure p
Sfg – Entropy change during vaporization
a) 6.987
b) 5.987
c) 5.0391
d) 4.776
View Answer
Explanation: Entropy of dry-saturated vapor when Sf is 0.2513 and Sfg is 4.5819, is given by
Sg = Sf + Sfg = 0.2513+4.7878 = 5.0391.
5. One of the assumptions of the vapor compression cycle is that all of the processes are reversible.
a) True
b) False
View Answer
Explanation: Vapor compression cycle with vapor being dry saturated after compression is a theoretical cycle having various assumptions. One of the assumptions is that all the processes are reversible.
6. In which case does the compression process remains in superheated state?
a) Wet state
b) Dry state
c) Semi-dry state
d) Always
View Answer
Explanation: In case of dry state the compression process remains in superheated state i.e. for compression of dry-saturated vapor or superheated vapor.
7. Dry compression is preferred over wet compression.
a) True
b) False
View Answer
Explanation: Dry compression is preferred over wet compression since it gives high volumetric efficiency and mechanical efficiency of the compressor with less chances of damage to it. However, in some cases wet compression is preferred when the compression is done using a screw or rotary compressor.
8. The ratio of COP of vapor compression cycle and COP of Carnot cycle is known as?
a) Relative COP
b) Ideal COP
c) Performance index
d) Theoretical COP
View Answer
Explanation: The ratio of COP of vapor compression cycle and COP of Carnot cycle is known as the Refrigeration efficiency or performance index (P.I). Whereas relative COP is the ratio of Actual COP divided by Ideal COP.
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