1. The coefficient of performance of a vapour compression refrigeration system is quite high as compared to the air refrigeration system.
a) true
b) false
Explanation: VCRS uses a refrigerant having specific properties. The most important properties include heat absorbing and rejecting capacities. Due to the occurrence of phase change of refrigerant in the Vapor compression refrigeration system and high-temperature range applicability, it has higher COP. VCRS used in applications like refrigerators for domestic and industrial applications.
2. In a refrigeration cycle, in which of the following heat absorption takes place?
a) Evaporator
b) Condenser
c) Expansion valve
d) Compressor
Explanation: Evaporator helps to raise the temperature of the refrigerant and convert that liquid form into gaseous form. For that, it absorbs heat energy from the items placed in the system. Utilizing that heat to make the phase change.
3. After which process during the VCR cycle, the highest temperature is achieved?
a) Evaporator
b) Expansion valve
c) Condensation
d) Compression
Explanation: The compression process is used to increase the pressure. So, according to Gay-Lussac’s law,
P ∝ T
As the highest pressure obtained after compression, the temperature obtained is also the highest.
4. The expansion valve in a refrigerator does not control the flow of refrigerant.
a) False
b) true
Explanation: Expansion valve acts as a diffuser, where pressure reduction is carried out using an orifice. By controlling the flow of refrigerant flowing through an orifice, the desired pressure drops obtained
5. In a domestic vapour compression refrigerator, which of the following refrigerants commonly used?
a) CO2
b) NH3
c) Freon
d) Air
Explanation: Freon is a trading name for several gases called refrigerants. Commonly used refrigerants are hydrofluorocarbons and hydrocarbons. Though ammonia and dichlorodifluoromethane have the same boiling point, it is not toxic like ammonia. Hence, it is safe to use Freon than ammonia.
6. 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
Explanation: The COP is given by Refrigeration effect by work done,
COP=\(\frac{Re}{W}\)
=\(\frac{58.84}{17.95}\)=3.278.
7. 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
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
8. One of the assumptions of the vapor compression cycle is that all of the processes are reversible.
a) True
b) False
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.
9. In which case does the compression process remains in superheated state?
a) Wet state
b) Dry state
c) Semi-dry state
d) Always
Explanation: In case of dry state the compression process remains in superheated state i.e. for compression of dry-saturated vapor or superheated vapor.
10. 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
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.