RRB ALP - Refrigeration & Air-Conditioning 1000+ MCQ [Solved] PDF Download

1. 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

2. The refrigerant widely used in domestic refrigerators is
A. Ammonia
B. Carbon dioxide
C. Sulphur dioxide
D. R-12
Answer : D

3. 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

4. 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

5. Choose the wrong statement
A. Temperature of medium being cooled must be below that of the evaporator
B. Refrigerant leaves the condenser as liquid
C. All solar thermally operated absorption systems are capable only of intermittent operation
D. Frost on evaporator reduces heat transfer
Answer : A

6. An infinite parallel planes with emissivities e? and e?, the interchange factor for radiation from surface 1 to surface 2 is given by
A. (e? + e?)/ e? + e? - e?e?
B. 1/e? + 1/e?
C. e? + e?
D. e?e?
Answer : A

7. 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

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

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

10. The specific humidity during heating and humidification process.
A. Remains constant
B. Increases
C. Decreases
D. None of these
Answer : B

11. The moisture in a refrigerant is removed by
A. Evaporator
B. Safety relief valve
C. Dehumidifier
D. Driers
Answer : D

12. 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

13. In which of the following refrigeration system, waste heat can be effectively used?
A. Vapour compression cycle
B. Vapour absorption cycle
C. Air refrigeration cycle
D. None of these
Answer : B

14. The leaks in a refrigeration system using Freon are detected by
A. Halide torch which on detection produces greenish flame lighting
B. Sulphur sticks which on detection gives white smoke
C. Using reagents
D. Smelling
Answer : A

15. It is desired to condition the outside air from 70% relative humidity and 45° C dry bulb temperature to 50% relative humidity and 25° C dry bulb temperature (room condition). The practical arrangement will be
A. Dehumidification
B. Cooling and humidification
C. Cooling and dehumidification
D. Dehumidification and pure sensible cooling
Answer : C

16. Rating of a domestic refrigerator is of the order of
A. 0.1 ton
B. 5 tons
C. 10 tons
D. 40 tons
Answer : A

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

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

19. 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

20. The evaporator changes the low pressure liquid refrigerant from the expansion valve into
A. High pressure liquid refrigerant
B. Low pressure liquid and vapour refrigerant
C. Low pressure vapour refrigerant
D. None of these
Answer : C

21. Under cooling 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 : A

22. Efficiency of a Carnot engine is given as 80%. If the cycle direction be reversed, what will be the value of COP of reversed Carnot Cycle?
A. 1.25
B. 0.8
C. 0.5
D. 0.25
Answer : D

23. The general rule for rating refrigeration systems (excepting for CO? system) is to approximate following h.p. per ton of refrigeration
A. 0.1 to 0.5 h.p. per ton of refrigeration
B. 0.5 to 0.8 h.p. per ton of refrigeration
C. 1 to 2 h.p. per ton of refrigeration
D. 2 to 5 h.p. per ton of refrigeration
Answer : C

24. The condition of refrigerant as it leaves the compressor in a vapour compression system is
A. Saturated liquid
B. Wet vapour
C. Dry saturated vapour
D. Superheated vapour
Answer : D

25. 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

26. 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

27. The undesirable property of a refrigerant is
A. Non-toxic
B. Non-flammable
C. Non-explosive
D. High boiling point
Answer : D

28. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be
A. 1.33
B. 2.33
C. 3.33
D. 4.33
Answer : B

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

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

31. The C.O.P. of a Carnot refrigerator in winter will be _________ as compared to C.O.P. in summer.
A. Same
B. Lower
C. Higher
D. None of these
Answer : C

32. An evaporator is also known as
A. Freezing coil
B. Cooling coil
C. Chilling coil
D. All of these
Answer : D

33. The vapour pressure of refrigerant should be
A. Lower than atmospheric pressure
B. Higher than atmospheric pressure
C. Equal to atmospheric pressure
D. Could be anything
Answer : B

34. 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

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

36. The bypass factor for a cooling coil
A. Increases with increase in velocity of air passing through it
B. Decreases with increase in velocity of air passing through it
C. Remains unchanged with increase in velocity of air passing through it
D. May increase or decrease with increase in velocity of air passing through it depending upon the condition of air entering
Answer : A

37. The C.O.P of a refrigeration cycle with increase in evaporator temperature, keeping condenser temperature constant, will
A. Increase
B. Decrease
C. Remain unaffected
D. May increase or decrease depending on the type of refrigerant used
Answer : A

38. The bypass factor (B. P. F.) in case of sensible heating of air is (Where td? = Dry bulb temperature of air entering the heating coil, td? = Dry bulb temperature of air leaving the heating coil, and td? = Dry bulb temperature of heating coil)
A. (td? - td?)/(td? - td?)
B. (td? - td?)/(td? - td?)
C. (td? - td?)/(td? - td?)
D. (td? - td?)/(td? - td?)
Answer : B

39. The colour of the flame of halide torch, in case of leakage of Freon refrigerant, will change to
A. Bright green
B. Yellow
C. Red
D. Orange
Answer : A

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

41. 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

42. 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

43. In S.J. unit, one ton of refrigeration is equal to
A. 210 kJ/ min
B. 21 kJ/ min
C. 420 kJ/ min
D. 840 kJ/ min
Answer : A

44. In a vapour absorption refrigeration system, the compressor of the vapour compression system is replaced by
A. Liquid pump
B. Generator
C. Absorber and generator
D. Absorber, generator and liquid pump
Answer : D

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

46. The total pressure exerted by the mixture of air and water vapour is equal to the sum of pressures which each constituent would exert, if it occupied the same space by itself. This statement is called
A. Kinetic theory of gases
B. Newton's law of gases
C. Dalton's law of partial pressures
D. Avogadro's hypothesis
Answer : C

47. 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

48. If a gas is to be liquefied, its temperature must be
A. Increased to a value above its critical temperature
B. Reduced to a value below its critical temperature
C. Equal to critical temperature
D. None of the above
Answer : C

49. 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

50. Ammonia absorption refrigeration cycle requires
A. Very little work input
B. Maximum work input
C. Nearly same work input as for vapour compression cycle
D. Zero work input
Answer : A