RBI Grade B officer - Refrigeration & Air-Conditioning 1000+ MCQ [Solved] PDF Download

1. 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

2. The domestic refrigerator uses following type of compressor
A. Centrifugal
B. Axial
C. Miniature sealed unit
D. Piston type reciprocating
Answer : D

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

4. The wet bulb temperature during sensible heating of air
A. Remains constant
B. Increases
C. Decreases
D. None of these
Answer : B

5. A mixture of dry air and water vapour, when the air has diffused the maximum amount of water vapour into it, is called
A. Dry air
B. Moist air
C. Saturated air
D. Specific humidity
Answer : C

6. In a reversed Brayton cycle, the heat is absorbed by the air during
A. Isentropic compression process
B. Constant pressure cooling process
C. Isentropic expansion process
D. Constant pressure expansion process
Answer : D

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

8. Superheating in a refrigeration cycle
A. Increases C.O.P
B. Decreases C.O.P
C. C.O.P remains unaltered
D. Other factors decide C.O.P
Answer : B

9. The thermostatic expansion valve is also called
A. Constant pressure valve
B. Constant temperature valve
C. Constant superheat valve
D. None of these
Answer : C

10. The ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure, is called
A. Humidity ratio
B. Relative humidity
C. Absolute humidity
D. Degree of saturation
Answer : B

11. In aircraft, air refrigeration Cycle is used because of
A. Low weight per tonne of refrigeration
B. High heat transfer rate
C. Low temperature at high altitudes
D. Higher coefficient of performance
Answer : A

12. 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

13. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about
A. 1
B. 1.25
C. 2.15
D. 5.12
Answer : B

14. 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

15. 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

16. 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

17. Accumulators should have adequate volume to store refrigerant charge at least
A. 10 %
B. 25 %
C. 50 %
D. 75 %
Answer : C

18. 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

19. One of the purposes of sub cooling the liquid refrigerant is to
A. Reduce compressor overheating
B. Reduce compressor discharge temperature
C. Increase cooling effect
D. Ensure that only liquid and not the vapour enters the expansion (throttling) valve
Answer : D

20. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T? = Lowest absolute temperature, and T? = Highest absolute temperature)
A. T? / (T? - T?)
B. (T? - T?)/T?
C. (T? - T?)/T?
D. T?/ (T? - T?)
Answer : A

21. The minimum temperature to which water can be cooled in a cooling tower is
A. Dew point temperature of air
B. Wet bulb temperature of air
C. Dry bulb temperature of air
D. Ambient air temperature
Answer : B

22. During sensible heating of air _________ decreases.
A. Wet bulb temperature
B. Relative humidity
C. Dry bulb temperature
D. Specific humidity
Answer : B

23. Highest pressure encountered in a refrigeration system should be
A. Critical pressure of refrigerant
B. Much below critical pressure
C. Much above critical pressure
D. Near critical pressure
Answer : B

24. The specific humidity during dehumidification process
A. Remains constant
B. Increases
C. Decreases
D. None of these
Answer : C

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

26. Which of the following statement is wrong?
A. The performance of the vapour compression refrigerator varies considerably with both vaporising and condensing temperatures.
B. In vapour compression cycle, the useful part of the heat transfer is at the condenser.
C. In ammonia-hydrogen (Electrolux) refrigerator, no compressor, pump or fan is required.
D. The effect of under-cooling the liquid refrigerant is to decrease the coefficient of performance.
Answer : D

27. During humidification process, __________ increases.
A. Wet bulb temperature
B. Relative humidity
C. Dry bulb temperature
D. Specific humidity
Answer : B

28. When the air is passed through an insulated chamber having sprays of water maintained at a temperature higher than the dew point temperature of entering air but lower than its dry bulb temperature, then the air is said to be
A. Cooled and humidified
B. Cooled and dehumidified
C. Heated and humidified
D. Heated and dehumidified
Answer : A

29. Most of the domestic refrigerators work on the following refrigeration system
A. Vapour compression
B. Vapour absorption
C. Carnot cycle
D. Electrolux refrigerator
Answer : A

30. Most thermostatic expansion valves are set for a superheat of
A. 5°C
B. 10°C
C. 15°C
D. 20°C
Answer : A

31. The boiling point of carbon dioxide is
A. -20.5°C
B. -50°C
C. -63.3°C
D. -78.3°C
Answer : D

32. During humidification process, dry bulb temperature
A. Remains constant
B. Increases
C. Decreases
D. None of these
Answer : A

33. In case of sensible cooling of air, the coil efficiency is given by
A. B.P.F. - 1
B. 1 - B.P.F.
C. 1/ B.P.F.
D. 1 + B.P.F.
Answer : B

34. 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

35. In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = Bypass factor)
A. B.P.F. - 1
B. 1 - B. P.F.
C. 1/ B.P.F.
D. 1 + B.P.F.
Answer : B

36. The sensible heat factor during the heating and humidification process is given by (where h? = Enthalpy of air entering the heating coil, h? = Enthalpy of air leaving the heating coil, and hA = Enthalpy of air at the end of humidification process)
A. (hA - h2)/ (h1 - h2)
B. (h2 - hA)/ (h1 - h2)
C. (h1 - h2)/ (hA - h2)
D. (hA - h1)/ (h2 - h1)
Answer : D

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

38. The refrigerant supplied to a compressor must be
A. Superheated vapour refrigerant
B. Dry saturated liquid refrigerant
C. A mixture of liquid and vapour refrigerant
D. None of these
Answer : A

39. The temperature of ammonia after compression in a vapour compression system is
A. 20 to 50°C
B. 50 to 70°C
C. 70 to 110°C
D. None of these
Answer : C

40. The condensing pressure due to the presence of non-condensable gases, as compared to that actually required for condensing temperatures without non-condensable gases,
A. Will be higher
B. Will be lower
C. Will remain unaffected
D. May be higher or lower depending upon the nature of noncondensable gases
Answer : A

41. The temperature of air recorded by a thermometer, when it is not affected by the moisture present in the air, is called
A. Wet bulb temperature
B. Dry bulb temperature
C. Dew point temperature
D. None of these
Answer : B

42. Chaperon equation is a relation between
A. Temperature, pressure and enthalpy
B. Specific volume and enthalpy
C. Temperature and enthalpy
D. Temperature, pressure, specific volume and enthalpy
Answer : D

43. In a psychrometric process, the sensible heat added is 30 kJ/s and the latent heat added is 20 kJ/s. The sensible heat factor for the process will be
A. 0.3
B. 0.6
C. 0.67
D. 1.5
Answer : B

44. The emissivity of a polished silver body is __________ as compared to black body.
A. Same
B. Low
C. Very low
D. High
Answer : C

45. Highest temperature encountered in refrigeration cycle should be
A. Near critical temperature of refrigerant
B. Above critical temperature
C. At critical Temperature
D. Much below critical temperature
Answer : D

46. 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

47. The lowest thermal diffusivity is of
A. Iron
B. Lead
C. Aluminium
D. Rubber
Answer : D

48. 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

49. The COP of a vapour compression plant in comparison to vapour absorption plant is
A. More
B. Less
C. Same
D. More/less depending on size of plant
Answer : A

50. 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