MCQ
61. The temperature of ammonia after compression in a vapour compression system is-
20 to 50°C
70 to 100°C
50 to 70°C
none of these
62. An ordinary passenger aircraft requires a cooling system of capacity-
2 TR
4TR
8TR
10 TR
63. The capacity of a domestic refrigerator is the range of-
0.1 to 0.3 TR
1 to 3 TR
3 to 5 TR
5 to 7 TR
64. The subcooling in a refrigeration cycle-
does not alter COP
dreases COP
increases COP
none of these
65. The function of oil separator in vapour compression refrigerator is to-
lubricate the compressor
Prevent the oil being carried to condenser
reduce the heat transfer effeciency
none of the above
66. The superheating in a refrigeration cycle-
does not alter COP
decreases COP
increases COP
none of these
67. Which of the following refrigerant has the lowest freezing point?
R-11
R-22
R-12
Ammoma
68. A vapour absorption refrigerator uses ........ us a refrigerant.
water
ammonia
freon
aqua-ammonia
69. The COP of a heat pump working on a reversed Carnot cycle is-
T1/T2-T1
T2-T1/T1
T1-T2/T1
T2/T2-T1
70. A refrigerant with the highest critical pressure is-
R-11
R-22
R-12
Ammonia
71. A refrigerating system operating on reversed Brayton refrigeration cycle is used for maintaining 250K. If the temperature at the end of constant pressure cooling is 300K and rise in the temperature of air in the refrigerator is 50K, then the net work of compression will be (assuune air as working substance with Cp=1kJ/kgK-
here ambient air will be at 350 K
Air after cooling effect 300K (air temp ine as i act as refrigerant
Air before cooling effect = 250K
Cooling effect (300-250)=50kJ/kg
Total heat rejected to atm =(350-250) =100kJ/kg
Hence work done by compressor=Total heat rejected-Cooling effect
100-50=50kj/kg
25kJ/kg
50kJ/kg
100kJ/kg
125kJ/kg
72. A condenser of refrigeration system rejects heat at the rate of 120kW while its compressor consunes a power of 30 kW. The coefficient of performance of the system would be-
1/4
3
4
1/3
73. A good refrigerant should have-
high latent heat of vaporisation and low freezing point
high operating pressures and low freezing point
high specific volume and high latent heat of vaporisation
low COP and low freezing point
74. In order to collect liquid refrigerant and to prevent if from going to a----- device known as necumulator is used at the suction of compressor.
compressor
expansion valve
condenser
evaporator
75. The pipe material for the refrigetors sing ammonia as refrigerant should be of--
copper
cast steel or wrought iron
brass
aluminium
76. The COP of refrigerator working on a reversed Carnot cycle is-
T1/T2-T1
T2-T1/T1
T1-T2/T1
T2/T2-T1
77. In vapour compressor is used—
a vapour compressor is used
a liquid pump is used
both a vapour compressor and a liquid pump is used
none of above
78. The COP of the vapour absorption cycle as compared to vapour compression cycle is—
higher
lower
same
none of above.
79. The highest temperature during the cycle in a vapour compression system r occurs after evaporation.
True
False
80. In a domestic vapour compression refrigerator, the refrigerant commonly used is-
CO
Ammonia
R-12
all of these