1000+ Refrigeration & Air-Conditioning MCQ for RRB Group D [Solved]

1. A vapour absorption refrigerator uses __________ as a refrigerant.
A. Water
B. Ammonia
C. Freon
D. Aqua-ammonia
Answer : D

2. In a pressure enthalpy chart, the space to the left of the saturated liquid line represents
A. Wet vapour region
B. Superheated vapour region
C. Sub-cooled liquid region
D. None of these
Answer : C

3. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is
A. 0.376
B. 0.4
C. 0.6
D. 0.67
Answer : C

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

5. 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

6. 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

7. For proper refrigeration in a cabinet, if the temperature and vapour pressure difference between cabinet and atmosphere is high, then
A. Bigger cabinet should be used
B. Smaller cabinet should be used
C. Perfectly tight vapour seal should be used
D. Refrigerant with lower evaporation temperature should be used
Answer : C

8. During heating and dehumidification process, dry bulb temperature
A. Remains constant
B. Increases
C. Decreases
D. None of these
Answer : B

9. 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

10. 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

11. Critical temperature is the temperature above which
A. A gas will never liquefy
B. A gas will immediately liquefy
C. Water will evaporate
D. Water will never evaporate
Answer : A

12. A heat pump working on a reversed Carnot cycle has a C.O.P. of 5. It works as a refrigerator taking 1 kW of work input. The refrigerating effect will be
A. 1 kW
B. 2 kW
C. 3 kW
D. 4 kW
Answer : D

13. 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

14. The power per tonne of refrigeration is
A. 3.5/C.O.P.
B. C.O.P/3.5
C. 3.5 × C.O.P.
D. None of these
Answer : A

15. 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

16. Pick up the wrong statement. A refrigerant should have
A. Tow specific heat of liquid
B. High boiling point
C. High latent heat of vaporisation
D. Higher critical temperature
Answer : B

17. In a refrigeration system, the expansion device is connected between the
A. Compressor and condenser
B. Condenser and receiver
C. Receiver and evaporator
D. Evaporator and compressor
Answer : C

18. 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

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

20. In chemical dehumidification process,
A. Dew point temperature decreases
B. Wet bulb temperature decreases
C. Dry bulb temperature increases
D. All of these
Answer : D

21. 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

22. 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

23. The operating pressure for refrigerating units using R-12 as a refrigerant is
A. 2 bar
B. 8 bar
C. 15 bar
D. 30 bar
Answer : B

24. The evolution of heat of solution takes place in ammonia absorption plant when
A. Ammonia vapour goes into solution
B. Ammonia vapour is driven out of solution
C. Lithium bromide mixes with ammonia
D. Weak solution mixes with strong solution
Answer : A

25. 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

26. The relative coefficient of performance is equal to
A. (Theoretical C.O.P.)/ (Actual C.O.P.)
B. (Actual C.O.P.) /(Theoretical C.O.P.)
C. (Actual C.O.P.) × (Theoretical C.O.P.)
D. None of these
Answer : B

27. In mechanical refrigeration system, the refrigerant has the maximum temperature
A. In evaporator
B. Before expansion valve
C. Between compressor and condenser
D. Between condenser and evaporator
Answer : C

28. 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

29. 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

30. Condensing temperature in a refrigerator is the temperature
A. Of cooling medium
B. Of freezing zone
C. Of evaporator
D. At which refrigerant gas becomes liquid
Answer : D

31. 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

32. Which of the following refrigerant is highly toxic and flammable?
A. Ammonia
B. Carbon dioxide
C. Sulphur dioxide
D. R-12
Answer : A

33. The value of C.O.P in vapour compression cycle is usually
A. Always less than unity
B. Always more than unity
C. Equal to unity
D. Any one of the above
Answer : B

34. Which of the following refrigerant has the lowest boiling point?
A. Ammonia
B. Carbon dioxide
C. Sulphur dioxide
D. R-12
Answer : B

35. Which of the following statement is wrong?
A. The value of C.O.P. is always greater than one.
B. In a vapour compression system, the condition of refrigerant before entering the compressor is dry saturated vapour.
C. The space between the saturated liquid line and saturated vapour line, in a pressure enthalpy chart, is wet vapour region.
D. None of the above
Answer : D

36. 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

37. The refrigerant for a refrigerator should have
A. High sensible heat
B. High total heat
C. High latent heat
D. Low latent heat
Answer : C

38. In a refrigeration system, heat absorbed in comparison to heat rejected is
A. More
B. Less
C. Same
D. More for small capacity and less for high capacity
Answer : B

39. 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

40. The lower horizontal line of the refrigeration cycle plotted on pressure-enthalpy diagram represents
A. Condensation of the refrigerant vapour
B. Evaporation of the refrigerant liquid
C. Compression of the refrigerant vapour
D. Metering of the refrigerant liquid
Answer : B

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

42. In air-conditioning of aeroplanes, using air as a refrigerant, the cycle used is
A. Reversed Carnot cycle
B. Reversed Joule cycle
C. Reversed Brayton cycle
D. Reversed Otto cycle
Answer : C

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

44. Presence of moisture in a refrigerant affects the working of
A. Compressor
B. Condenser
C. Evaporator
D. Expansion valve
Answer : D

45. 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

46. 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

47. 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

48. The central air conditioning system has ________ overall efficiency as compared to individual systems.
A. Same
B. Lower
C. Higher
D. None of these
Answer : C

49. 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

50. 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