Refrigeration Questions and Answers – Coefficient of Performance of Ideal VAR System – 1

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This set of Refrigeration Multiple Choice Questions & Answers (MCQs) focuses on “Coefficient of Performance of Ideal VAR System – 1”.

1. What is the formula for COP of an ideal vapour absorption refrigeration system?
Qg = the heat given to the refrigerant in the generator
Qe= the heat absorbed by the refrigerant in the evaporator
a) $$\frac{Q_e}{Q_g}$$
b) $$\frac{Q_g}{Q_e}$$
c) Qg × Qe
d) Qg – Qe

Explanation: The COP of an ideal vapour absorption refrigeration system is the ratio of the heat given to the refrigerant in the generator and the heat absorbed by the refrigerant in the evaporator.
COP = $$\frac{Q_e}{Q_g}$$.

2. An ideal vapour absorption refrigeration system may be regarded as a combination of _________
a) Carnot engine and Carnot pump
b) Carnot refrigerant and Carnot pump
c) Carnot engine and Carnot refrigerant
d) Carnot engine alone

Explanation: An ideal vapour absorption refrigeration system may be regarded as a combination of Carnot engine and Carnot refrigerant.
COP = $$\frac{Q_e}{Q_g}$$.

3. Find the COP of a vapour absorption refrigeration system using the following data.
Qg = 6600
Qe = 2100
a) 0.45
b) 0.65
c) 0.31
d) 0.35

Explanation: The COP of an ideal vapour absorption refrigeration system is
COP = $$\frac{Q_e}{Q_g}$$
COP = $$\frac{2100}{6600}$$ = 0.31.

4. Find the COP of a vapour absorption refrigeration system using the following data.
Te = 268
Tg = 393.2
Tc = 303
a) 1.53
b) 1.76
c) 1.66
d) 1.98

Explanation: The COP of an ideal vapour absorption refrigeration system is
COP = $$\frac{Q_e}{Q_g}$$
= $$\frac{T_e}{T_c – T_e} × \frac{T_g-T_c}{T_g}$$
= $$(\frac{268}{303-268})*(\frac{393.2-303}{393.2})$$
= 1.76.

5. The expression $$\frac{T_e}{T_c – T_e}$$ in the formula for COP i.e. $$\frac{T_e}{T_c – T_e} × \frac{T_g-T_c}{T_g}$$ refers to __________
Te and Tc are the temperature limits for Carnot refrigerator
Tg and Tc are the temperature limits for Carnot engine
a) COP of Carnot engine
b) COP of Carnot refrigerator
c) COP of Carnot pump
d) COP of Bell-Coleman cycle

Explanation: An ideal vapour absorption refrigeration system may be regarded as a combination of Carnot engine and Carnot refrigerant. Hence the expression $$\frac{T_e}{T_c – T_e}$$ refers to the COP of Carnot refrigerator and the second expression $$\frac{T_g}{T_c – T_g}$$ refers to Carnot engine.

6. In case the heat is discharged at different temperatures in condenser and absorber then the formula for COP would be?
Ta = Temperature at which heat is discharged in the absorber
Te and Tc are the temperature limits for Carnot refrigerator
Tg and Tc are the temperature limits for Carnot engine
a) COP = $$\frac{T_e}{T_c – T_e} × \frac{T_g-T_c}{T_g}$$
b) COP = $$\frac{T_e}{T_c – T_e} × \frac{T_g-T_c}{T_g} × T_a$$
c) COP = $$\frac{T_e}{T_c – T_e} × \frac{T_g-T_c}{T_g} ± T_a$$
d) COP = $$\frac{T_e}{T_c – T_e} × \frac{T_g-T_c}{T_g}$$

Explanation: In case the heat is discharged at different temperatures in condenser and absorber then the formula for COP would be
COP = $$\frac{T_e}{T_c – T_e} × \frac{T_g-T_a}{T_g}$$.

7. Find the COP of an ideal vapour absorption refrigeration system using the following data.
Qg = 1880
Qe = 1045
a) 0.47
b) 0.65
c) 0.69
d) 0.55

Explanation: The COP of an ideal vapour absorption refrigeration system is
COP = $$\frac{Q_e}{Q_g}$$
COP = $$\frac{1045}{1880}$$ = 0.555.

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