1000+ Refrigeration & Air-Conditioning Multiple Choice Question Answer [Solved]

1. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called
A. Sub-cooling or under-cooling
B. Super-cooling
C. Normal cooling
D. None of these
Answer : A

2. Vapour compression refrigeration is somewhat like
A. Carnot cycle
B. Rankines cycle
C. Reversed Carnot cycle
D. None of the above
Answer : D

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

4. A refrigerant compressor is used to
A. Raise the pressure of the refrigerant
B. Raise the temperature of the refrigerant
C. Circulate the refrigerant through the refrigerating system
D. All of the above
Answer : D

5. 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

6. Domestic refrigerator working on vapour compression cycle uses the following type of expansion device
A. Electrically operated throttling valve
B. Manually operated valve
C. Thermostatic valve
D. Capillary tube
Answer : D

7. 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

8. 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

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

10. In a vapour compression refrigeration system, a throttle valve is used in place of an expander because
A. It considerably reduces mass of the system
B. It improves the C.O.P., as the condenser is small
C. The positive work in isentropic expansion of liquid is very small
D. It leads to significant cost reduction
Answer : C

11. 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

12. 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

13. 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

14. The C.O.P. of a heat pump working on a reversed Carnot cycle is
A. T?/(T? - T?)
B. (T? - T?)/T?
C. (T? - T?)/T?
D. T?/(T? - T?)
Answer : D

15. A standard ice point temperature corresponds to the temperature of
A. Water at 0°C
B. Ice at 4°C
C. Solid and dry ice
D. Mixture of ice and water under equilibrium conditions
Answer : D

16. 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

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

18. 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

19. 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

20. In vapour compression refrigeration system, refrigerant occurs as liquid between
A. Condenser and expansion valve
B. Compressor and evaporator
C. Expansion valve and evaporator
D. Compressor and condenser
Answer : C

21. The coefficient of performance of Electrolux refrigerator is the ratio of A. Heat supplied by the gas burner to the heat absorbed by the evaporator
B. Heat absorbed by the evaporator to the heat supplied by the gas burner
C. Heat supplied by the gas burner minus the heat absorbed by the evaporator to the heat supplied by the gas burner
D. Heat absorbed by the evaporator minus the heat supplied by the gas burner to the heat absorbed by the evaporator
Answer : B

22. The material of pipe lines for a system using Freon as a refrigerant should be
A. Brass
B. Copper
C. Steel
D. Aluminium
Answer : B

23. 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

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

25. 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

26. Which of the following statement is correct for ammonia as a refrigerant?
A. It is toxic to mucous membranes.
B. It requires large displacement per TR compared to fluoro carbons.
C. It reacts with copper and its alloys.
D. All of these
Answer : D

27. 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

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

29. The Freon group of refrigerants are
A. Halocarbon refrigerants
B. Zoetrope refrigerants
C. Inorganic refrigerants
D. Hydrocarbon refrigerants
Answer : A

30. A refrigeration cycle operates between condenser temperature of + 27°C and evaporator temperature of -23°C. The Carnot coefficient of performance of cycle will be
A. 0.2
B. 1.2
C. 5
D. 6
Answer : C

31. 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

32. 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

33. Which of the following statement is correct?
A. In vapour absorption refrigerator, the compression of refrigerant is avoided.
B. Sub-cooling can be achieved by circulating more quantity of cooling water through the condenser.
C. In vapour compression refrigeration, the vapour is drawn in the compressor cylinder during its suction stroke and is compressed adiabatically during the compression stroke.
D. All of the above
Answer : D

34. 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

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

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

37. 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

38. The thermal diffusivity for gases is generally __________ those for liquids.
A. Equal to
B. Less than
C. Greater than
D. None of these
Answer : C

39. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be
A. 0.2
B. 1.2
C. 5
D. 6
Answer : D

40. 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

41. A pressure gauge on the discharge side of a refrigerant compressor reads too high. The reasons will be
A. Lack of cooling water
B. Water temperature being high
C. Dirty condenser surface
D. All of these
Answer : D

42. 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

43. 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

44. 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

45. Where does the lowest temperature occur in a vapour compression cycle?
A. Condenser
B. Evaporator
C. Compressor
D. Expansion valve
Answer : B

46. 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

47. 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

48. Chaperon equation is applicable for registration at
A. Saturation point of vapour
B. Saturation point of liquid
C. Sublimation temperature
D. Triple point
Answer : A

49. The thermostatic expansion valve is used in __________ type of evaporators.
A. Flooded
B. DX coil
C. Dry
D. None of these
Answer : C

50. 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