Refrigeration & Air-Conditioning MCQ Solved Paper for UPSC CDS

1. The ratio of heat extracted in the refrigerator to the work-done on the refrigerant is called
A. Coefficient of performance of refrigeration
B. Coefficient of performance of heat pump
C. Relative coefficient of performance
D. Refrigerating efficiency
Answer : A

2. The optimum effective temperature for human comfort is
A. Higher in winter than in summer
B. Lower in winter than in summer
C. Same in winter and summer
D. Not dependent on season
Answer : B

3. In vapour compression cycle the condition off refrigerant is dry saturated vapour
A. After passing through the condenser
B. Before passing through the condenser
C. After passing through the expansion or throttle valve
D. Before entering the compressor
Answer : D

4. The process of under-cooling is generally brought about by
A. Circulating more quantity of cooling water through the condenser
B. Using water colder than the main circulating water
C. Employing a heat exchanger
D. Any one of the above
Answer : D

5. In a vapour compression cycle, the refrigerant immediately after expansion valve is
A. Liquid
B. Sub-cooled liquid
C. Saturated liquid
D. Wet vapour
Answer : D

6. One tonne of refrigeration (1TR) means that the heat removing capacity is
A. 21 kJ/min
B. 210 kJ/min
C. 420 kJ/min
D. 620 kJ/min
Answer : B

7. In vapour compression cycle, the condition of refrigerant is saturated liquid
A. After passing through the condenser
B. Before passing through the condenser
C. After passing through the expansion throttle valve
D. Before entering the expansion valve
Answer : A

8. The freezing point of R-12 is
A. -86.6°C
B. -95.2°C
C. -107.7°C
D. -135.8°C
Answer : D

9. In a vapour compression system, the condition of refrigerant is dry saturated vapour
A. Before entering the compressor
B. After leaving the compressor
C. Before entering the condenser
D. After leaving the condenser
Answer : A

10. Formation of frost on evaporator in refrigerator
A. Results in loss of heat due to poor heat transfer
B. Increases heat transfer rate
C. Is immaterial
D. Can be avoided by proper design
Answer : A

11. Which of the following statement is correct?
A. The constant enthalpy lines are also constant wet bulb temperature lines.
B. The wet bulb and dry bulb temperature are equal at saturation condition.
C. The wet bulb temperature is a measure of enthalpy of moist air.
D. All of the above
Answer : D

12. The operating temperature of a cold storage is 2°C. The heat leakage from the surrounding is 30 kW for the ambient temperature of 40°C. The actual C.O.P. of refrigeration plant used is one fourth that of ideal plant working between the same temperatures. The power required to drive the plant is
A. 1.86 kW
B. 3.72 kW
C. 7.44 kW
D. 18.6 kW
Answer : D

13. Environmental protection agencies advice against the use of chlorofluorocarbon refrigerants since
A. These react with water vapour and cause acid rain
B. These react with plants and cause greenhouse effect
C. These react with oxygen and cause its depletion
D. These react with ozone layer
Answer : D

14. The dehumidification process, on the psychrometric chart, is shown by
A. Horizontal line
B. Vertical line
C. Inclined line
D. Curved line
Answer : B

15. The index which correlates the combined effects of air temperature, relative humidity and air velocity on the human body, is known as
A. Mean radiant temperature
B. Effective temperature
C. Dew point temperature
D. None of these
Answer : B

16. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process
A. Involves no change in volume
B. Takes place at constant temperature
C. Takes place at constant entropy
D. Takes place at constant pressure
Answer : D

17. The humidity ratio or specific humidity is the mass of water vapour present in
A. 1 m3 of wet air
B. 1 m3 of dry air
C. 1 kg of wet air
D. 1 kg of dry air
Answer : D

18. One ton refrigeration corresponds to
A. 50 kcal/ min
B. 50 kcal/ hr
C. 80 kcal/ min
D. 80 kcal/ hr
Answer : A

19. Mass flow ratio of NH? in comparison to Freon12 for same refrigeration load and same temperature limits is of the order of
A. 1 : 1
B. 1 : 9
C. 9 : 1
D. 1 : 3
Answer : B

20. A good refrigerant should have
A. High latent heat of vaporisation and low freezing point
B. High operating pressures and low freezing point
C. High specific volume and high latent heat of vaporisation
D. Low C.O.P. and low freezing point
Answer : A

21. In a psychrometric chart, specific humidity (moisture content) lines are
A. Vertical and uniformly spaced
B. Horizontal and uniformly spaced
C. Horizontal and non-uniformly spaced
D. Curved lines
Answer : B

22. Vapour compression refrigeration is somewhat like
A. Carnot cycle
B. Rankines cycle
C. Reversed Carnot cycle
D. None of the above
Answer : D

23. The refrigeration effect in a dry evaporator compared to flooded evaporator in a similar plant is
A. Same
B. More
C. Less
D. More or less depending on ambient conditions
Answer : C

24. While designing the refrigeration system of an aircraft, the prime consideration is that the
A. System has high C.O.P.
B. Power per TR is low
C. Mass of refrigerant circulated in the system is low
D. Mass of the refrigeration equipment is low
Answer : D

25. The unit of thermal diffusivity is
A. m/hK
B. m/h
C. m²/h
D. m²/hK
Answer : C

26. The air cooling system mostly used in transport type aircrafts is
A. Simple air cooling system
B. Simple evaporative air cooling system
C. Bootstrap air cooling system
D. All of these
Answer : C

27. The alignment circle is marked on the psychrometric chart at
A. 20°C DBT and 50% RH
B. 26°C DBT and 50% RH
C. 20°C DBT and 60% RH
D. 26°C DBT and 60% RH
Answer : B

28. The bank of tubes at the back of domestic refrigerator is
A. Condenser tubes
B. Evaporator tubes
C. Refrigerant cooling tubes
D. Capillary tubes
Answer : A

29. Allowable pressure on high pressure side or ammonia absorption system is of the order of
A. Atmospheric pressure
B. Slightly above atmospheric pressure
C. 24 bars
D. 56 bars
Answer : D

30. The formation of frost on cooling coils in a refrigerator
A. Increases heat transfer
B. Improves C.O.P. of the system
C. Increases power consumption
D. Reduces power consumption
Answer : C

31. Air refrigeration cycle is used in
A. Domestic refrigerators
B. Commercial refrigerators
C. Air conditioning
D. Gas liquefaction
Answer : D

32. The curved lines on a psychrometric chart indicates
A. Dry bulb temperature
B. Wet bulb temperature
C. Dew point temperature
D. Relative humidity
Answer : D

33. In a saturated air-water vapour mixture, the
A. Dry bulb temperature is higher than wet bulb temperature
B. Dew point temperature is lower than wet bulb temperature
C. Dry bulb, wet bulb and dew point temperature are same
D. Dry bulb temperature is higher than dew point temperature
Answer : C

34. Rick up the incorrect statement
A. Lithium bromide used in vapour absorption cycle is non volatile
B. Lithium bromide plant can't operate below 0°C
C. A separator is used in lithium bromide plant to remove the unwanted water vapour by condensing
D. Concentration of solution coming out of lithium bromide generator is more in comparison to that entering the generator
Answer : C

35. The leakage in a refrigeration system using ammonia is detected by
A. Halide torch
B. Sulphur sticks
C. Soap and water
D. All of these
Answer : B

36. Relative humidity is given by (where pv = Partial pressure of water vapour, pb = Barometric pressure, ps = Pressure of saturated air, pd = Pressure at dry bulb temperature, pw = Saturation pressure corresponding to wet bulb temperature, and ? = Degree of saturation)
A. 0.622 Pv / (Pb - Pv)
B. ?/[1 - (1 - ?) (Ps/Pb)]
C. [Pv (Pb - Pd)]/ [Pd (Pb - Pv)]
D. None of these
Answer : B

37. Freon group of refrigerants are
A. Inflammable
B. Toxic
C. Non-inflammable and toxic
D. Nontoxic and non-inflammable
Answer : D

38. The coefficient of performance of Electrolux refrigerator is the ratio of
A. Heat supplied by the gas burner to the heat absorbed by the evaporator
B. Heat absorbed by the evaporator to the heat supplied by the gas burner
C. Heat supplied by the gas burner minus the heat absorbed by the evaporator to the heat supplied by the gas burner
D. Heat absorbed by the evaporator minus the heat supplied by the gas burner to the heat absorbed by the evaporator
Answer : B

39. Which of the following refrigerant has the lowest freezing point?
A. R-11
B. R-12
C. R-22
D. Ammonia
Answer : C

40. The coefficient of performance (C.O.P.) of a refrigerator working as a heat pump is given by
A. (C.O.P.)_P = (C.O.P.)_R + 2
B. (C.O.P.)_P = (C.O.P.)_R + 1
C. (C.O.P)_P = (C.O.P)_R - 1
D. (C.O.P)_P = (C.O.P)_R
Answer : B

41. The boiling point of ammonia is
A. 100°C
B. 50°C
C. 33.3°C
D. 0°C
Answer : C

42. Most air cooled condensers are designed to operate with a temperature difference of
A. 5°C
B. 8°C
C. 14°C
D. 22°C
Answer : C

43. During dehumidification process, __________ remains constant.
A. Wet bulb temperature
B. Relative humidity
C. Dry bulb temperature
D. Specific humidity
Answer : C

44. In a vapour compression system, the condition of refrigerant before passing through the condenser is
A. Saturated liquid
B. Wet vapour
C. Dry saturated vapour
D. Superheated vapour
Answer : D

45. Which of the following is not a desirable property of a refrigerant?
A. High risibility with oil
B. Low boiling point
C. Good electrical conductor
D. Large latent heat
Answer : C

46. For better C.O.P of refrigerator, the pressure range corresponding to temperature in evaporator and condenser must be
A. Small
B. High
C. Equal
D. Anything
Answer : A

47. The relative humidity lines on a psychrometric chart are
A. Vertical and uniformly spaced
B. Horizontal and uniformly spaced
C. Horizontal and non-uniformly spaced
D. Curved lines
Answer : D

48. In larger industrial and commercial reciprocating compression systems, refrigerant widely used is
A. Ammonia
B. Carbon dioxide
C. Sulphur dioxide
D. R-12
Answer : A

49. The relative coefficient of performance is
A. Actual COP/theoretical COP
B. Theoretical COP/actual COP
C. Actual COP × theoretical COP
D. None of these
Answer : A

50. A refrigerant with the highest critical pressure is
A. R-11
B. R-12
C. R-22
D. Ammonia
Answer : D