Refrigeration & Air-Conditioning 1000+ MCQ with answer for RBI Assistant

1. Nusselt number (N_N) is given by
A. N_N = hl/k
B. N_N = ? c_p/k
C. N_N = ? V l /?
D. N_N = V²/t.c_p
Answer : A

2. For ammonia refrigerating systems, the tubes of a shell and tube condenser are made of
A. Copper
B. Aluminium
C. Steel
D. Brass
Answer : C

3. 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

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

5. The horizontal and non-uniformly spaced lines on a psychrometric chart indicates
A. Dry bulb temperature
B. Wet bulb temperature
C. Dew point temperature
D. Specific humidity
Answer : C

6. The capacity of a domestic refrigerator is in the range of
A. 0.1 to 0.3 TR
B. 1 to 3 TR
C. 3 to 5 TR
D. 5 to 7 TR
Answer : A

7. The bypass factor, in case of sensible cooling of air, is given by (where td? = Dry bulb temperature of air entering the cooling coil, td? = Dry bulb temperature of air leaving the cooling coil, and td? = Dry bulb temperature of the cooling coil)
A. (td? -td?)/( td? -td?)
B. (td? -td?)/( td? -td?)
C. (td? -td?)/( td? -td?)
D. (td? -td?)/( td? -td?)
Answer : B

8. In refrigerator, liquid receiver is required between condenser and flow controlling device, if quantity of refrigerant for system is
A. Less than 2 kg
B. More than or equal to 3.65 kg
C. More than 10 kg
D. There is no such consideration
Answer : B

9. Moisture in Freon refrigeration system causes
A. Ineffective refrigeration
B. High power consumption
C. Freezing automatic regulating valve
D. Corrosion of whole system
Answer : C

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

11. During adiabatic saturation process on unsaturated air __________ remains constant.
A. Relative humidity
B. Dew point temperature
C. Dry bulb temperature
D. Wet bulb temperature
Answer : D

12. 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

13. Air conditioning means
A. Cooling
B. Heating
C. Dehumidifying
D. All of these
Answer : D

14. 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

15. 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

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

17. Wet bulb temperature is the temperature of air recorded by a thermometer, when
A. It is not affected by the moisture present in the air
B. Its bulb is surrounded by a wet cloth exposed to the air
C. The moisture present in it begins to condense
D. None of the above
Answer : B

18. Carbon dioxide is
A. Colourless
B. Odourless
C. Non-flammable
D. All of these
Answer : D

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

20. The C.O.P. of an absorption type refrigerator is given by (where T? = Temperature at which the working substance receives heat, T? = Temperature of cooling water, and T? = Evaporator temperature)
A. [T? (T? - T?)] / [T? (T? - T?)]
B. [T? (T? - T?)]/ [T? (T? - T?)]
C. [T? (T? - T?)] / [T? (T? - T?)]
D. [T? (T? - T?)] / [T? (T? - T?)]
Answer : B

21. The process, generally used in summer air conditioning to cool and dehumidify the air, is called
A. Humidification
B. Dehumidification
C. Heating and humidification
D. Cooling and dehumidification
Answer : D

22. 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

23. 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

24. A refrigerating system operating on reversed Brayton refrigeration cycle is used for maintaining 250 K. If the temperature at the end of constant pressure cooling is 300K and rise in the temperature of air in the refrigerator is 50 K, then the net work of compression will be (assume air as working substance with Cp = 1 kJ/kg)
A. 25 kJ/kg
B. 50 kJ/kg
C. 100 kJ/kg
D. 125 kJ/kg
Answer : B

25. The wet bulb temperature at 100% relative humidity is ________ dry bulb temperature.
A. Same as
B. Lower than
C. Higher than
D. None of these
Answer : A

26. The wet bulb temperature at 100% relative humidity is ________ dew point temperature.
A. Same as
B. Lower than
C. Higher than
D. None of these
Answer : A

27. The coefficient of performance is the ratio of the refrigerant effect to the
A. Heat of compression
B. Work done by compressor
C. Enthalpy increase in compressor
D. All of the above
Answer : D

28. Short horizontal lines on pressure-enthalpy chart show
A. Constant pressure lines
B. Constant temperature lines
C. Constant total heat lines
D. Constant entropy lines
Answer : A

29. The lowest temperature during the cycle in a vapour compression system occurs after
A. Compression
B. Expansion
C. Condensation
D. Evaporation
Answer : D

30. For unsaturated air, the dew point temperature is __________ wet bulb temperature.
A. Equal to
B. Less than
C. More than
D. None of these
Answer : B

31. 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

32. Refrigeration in aeroplanes usually employs the following refrigerant
A. CO2
B. Freon-11
C. Freon-22
D. Air
Answer : D

33. The condition of refrigerant after passing through the condenser in a vapour compression system is
A. Saturated liquid
B. Wet vapour
C. Dry saturated vapour
D. Superheated vapour
Answer : A

34. During sensible cooling,
A. Relative humidity remains constant
B. Wet bulb temperature increases
C. Specific humidity increases
D. Partial pressure of vapour remains constant
Answer : D

35. A valve which maintains a constant degree of superheat at the end of the evaporator coil, is called
A. Automatic expansion valve
B. High side float valve
C. Thermostatic expansion valve
D. Low side float valve
Answer : D

36. The difference between dry bulb temperature and wet bulb temperature, is called
A. Dry bulb depression
B. Wet bulb depression
C. Dew point depression
D. Degree of saturation
Answer : B

37. Reducing suction pressure in refrigeration cycle
A. Lowers evaporation temperature
B. Increases power required per ton of refrigeration
C. Lowers compressor capacity because vapour is lighter
D. All of the above
Answer : D

38. 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

39. 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

40. 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

41. 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

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

43. 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

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

45. Moisture should be removed from refrigerants to avoid
A. Freezing at the expansion valve
B. Restriction to refrigerant flow
C. Corrosion of steel plates
D. All of these
Answer : D

46. The desirable property of a refrigerant is
A. Low boiling point
B. High critical temperature
C. High latent heat of vaporisation
D. All of these
Answer : D

47. 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

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

49. The vertical and uniformly spaced lines on a psychrometric chart indicates
A. Dry bulb temperature
B. Wet bulb temperature
C. Dew point temperature
D. Specific humidity
Answer : A

50. The wet bulb depression indicates _________ humidity of the air.
A. Absolute
B. Relative
C. Specific
D. None of these
Answer : B