Refrigeration & Air-Conditioning 1000+ MCQ with answer for NMAT

1. 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

2. The COP of a domestic refrigerator
A. Is less than 1
B. Is more than 1
C. Is equal to 1
D. Depends upon the make
Answer : B

3. 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

4. In a spray washing system, if the temperature of water is higher than the dry bulb temperature of entering air, then the air is
A. Heated and dehumidified
B. Heated and humidified
C. Cooled and humidified
D. Cooled and dehumidified
Answer : B

5. In a lithium bromide absorption refrigeration system
A. Lithium bromide is used as a refrigerant and water as an absorbent
B. Water is used as a refrigerant and lithium bromide as an absorbent
C. Ammonia is used as a refrigerant and lithium bromide as an absorbent
D. None of the above
Answer : B

6. The thermostatic expansion valve operates on the changes in the
A. Degree of superheat at exit from the evaporator
B. Temperature of the evaporator
C. Pressure in the evaporator
D. None of the above
Answer : A

7. In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature
A. Which lies between the dry bulb and wet bulb temperatures of the incoming stream
B. Which lies between the wet bulb and dew point temperatures of the incoming stream
C. Which is lower than the dew point temperature of the incoming stream
D. Of adiabatic saturation of incoming stream
Answer : C

8. 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

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. The reduced ambient air cooling system has
A. One cooling turbine and one heat exchanger
B. One cooling turbine and two heat exchangers
C. Two cooling turbines and one heat exchanger
D. Two cooling turbines and two heat exchangers
Answer : C

11. 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

12. 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

13. 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

14. For evaporators and condensers, for the given conditions, the logarithmic mean temperature difference (tm) for parallel flow is ________ that for counter flow.
A. Equal to
B. Less than
C. Greater than
D. None of these
Answer : A

15. 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

16. 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

17. 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

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

19. At lower temperatures and pressures, the latent heat of vaporisation of a refrigerant
A. Decreases
B. Increases
C. Remain same
D. Depends on other factors
Answer : B

20. 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

21. 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

22. 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

23. 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

24. Dry 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 : A

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

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

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

28. In vapour compression cycle, the condition of refrigerant is very wet 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

29. 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

30. In vapour compression cycle the condition of refrigerant is superheated 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 expansion valve
Answer : B

31. 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

32. When the lower temperature of a refrigerating machine is fixed, then the coefficient of performance can be improved by
A. Operating the machine at higher speeds
B. Operating the machine at lower speeds
C. Raising the higher temperature
D. Lowering the higher temperature
Answer : D

33. 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

34. 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

35. In vapour compression cycle, the condition of refrigerant is high pressure saturated liquid
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 expansion valve
Answer : D

36. For air conditioning the operation theatre in a hospital, the percentage of outside air in the air supplied is
A. Zero
B. 20
C. 50
D. 100
Answer : D

37. In Electrolux refrigerator
A. Ammonia is absorbed in hydrogen
B. Ammonia is absorbed in water
C. Ammonia evaporates in hydrogen
D. Hydrogen evaporates in ammonia
Answer : C

38. The coefficient of performance of Heat Pump is always __________ one.
A. Equal to
B. Less than
C. Greater than
D. None of these
Answer : C

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

40. The pressure at the inlet of a refrigerant compressor is called
A. Suction pressure
B. Discharge pressure
C. Critical pressure
D. Back pressure
Answer : A

41. Critical pressure of a liquid is the pressure
A. Above which liquid will remain liquid
B. Above which liquid becomes gas
C. Above which liquid becomes vapour
D. Above which liquid becomes solid
Answer : A

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

43. 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

44. The centrifugal compressors are generally used for refrigerants that require
A. Small displacements and low condensing pressures
B. Large displacements and high condensing pressures
C. Small displacements and high condensing pressures
D. Large displacements and low condensing pressures
Answer : D

45. 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

46. 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

47. The mass of water vapour present in __________ is called absolute humidity.
A. 1 m³ of water
B. 1 m³ of dry air
C. 1 kg of wet air
D. 1 kg of dry air
Answer : B

48. An important characteristic of absorption system of refrigeration is
A. Noisy operation
B. Quiet operation
C. Cooling below 0°C
D. Very little power consumption
Answer : B

49. 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

50. Choose the correct statement
A. A refrigerant should have low latent heat
B. If operating temperature of system is low, then refrigerant with low boiling point should be used
C. Pre-cooling and sub-cooling bf refrigerant are same
D. Superheat and sensible heat of a refrigerant are same
Answer : B