Refrigeration & Air-Conditioning MCQ Solved Paper for CEED

1. 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

2. The heat rejection factor (HRF) is given by
A. 1 + C.O.P
B. 1 - C.O.P.
C. 1 + (1/C.O.P)
D. 1 - (1/C.O.P)
Answer : C

3. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the
A. Heat dissipated to the surroundings
B. Heat stored in the human body
C. Sum of (A) and (B)
D. Difference of (A) and (B)
Answer : C

4. 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

5. 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

6. During sensible cooling of air ________ decreases.
A. Wet bulb temperature
B. Relative humidity
C. Dry bulb temperature
D. Specific humidity
Answer : C

7. 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

8. 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

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

10. The sub-cooling in a refrigeration cycle
A. Does not alter C.O.P.
B. Increases C.O.P.
C. Decreases C.O.P.
D. None of these
Answer : B

11. 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

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

13. Air refrigeration operates on
A. Carnot cycle
B. Reversed Carnot cycle
C. Rankines cycle
D. Brayton cycle
Answer : D

14. The advantage of dry compression is that
A. It permits higher speeds to be used
B. It permits complete evaporation in the evaporator
C. It results in high volumetric and mechanical efficiency
D. All of the above
Answer : D

15. The superheated vapour region, in a pressure enthalpy chart, is represented by the space
A. To the left of saturated liquid line
B. To the right of saturated liquid line
C. Between the saturated liquid line and saturated vapour line
D. None of the above
Answer : C

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

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

18. The suction pipe diameter of refrigerating unit compressor in comparison to delivery side is
A. Bigger
B. Smaller
C. Equal
D. Smaller/bigger depending on capacity
Answer : A

19. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is
A. Ammonia
B. Carbon dioxide
C. Freon
D. Brine
Answer : B

20. 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

21. A Bell Coleman refrigerator working on dense air system as compared to open air system, for the same range of temperature, results in ________ power per tonne of refrigeration.
A. Same
B. Lower
C. Higher
strong>D. None of these
Answer : B

22. 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

23. The reciprocating refrigerant compressors are very suitable for
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 : C

24. The refrigerant used in small tonnage commercial machines (hermetically sealed units) is
A. Ammonia
B. Carbon dioxide
C. Sulphur dioxide
D. R-12
Answer : C

25. 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

26. 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

27. The ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure, is called
A. Humidity ratio
B. Relative humidity
C. Absolute humidity
D. Degree of saturation
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. 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

30. A vapour absorption refrigeration system
A. Gives noisy operation
B. Gives quiet operation
C. Requires little power consumption
D. Cools below 0°C
Answer : B

31. A thermostatic expansion valve in a refrigeration system
A. Ensures the evaporator completely filled with refrigerant of the load
B. Is suitable only for constant load systems
C. Maintains different temperatures in evaporator in proportion to load
D. None of the above
Answer : A

32. The conditioned air supplied to the room must have the capacity to take up
A. Room sensible heat load only
B. Room latent heat load only
C. Both room sensible heat and latent heat loads
D. None of the above
Answer : C

33. 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

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. 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

36. In order to collect liquid refrigerant and to prevent it from going to a ________, a device known as accumulator is used at the suction of compressor.
A. Compressor
B. Condenser
C. Expansion valve
D. Evaporator
Answer : A

37. 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

38. The humidity ratio or specific humidity is the mass of water vapour present in
A. 1 m3 of wet air
B. 1 m3 of dry air
C. 1 kg of wet air
D. 1 kg of dry air
Answer : D

39. The relative humidity is defined as
A. The mass of water vapour present in 1 m3 of dry air
B. The mass of water vapour present in 1 kg of dry air
C. The ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure.
D. The ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure
Answer : D

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

41. 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

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. During dehumidification process, the relative humidity
A. Remains constant
B. Increases
C. Decreases
D. None of these
Answer : C

44. Which of the following statement is correct?
A. The human body can lose heat even if its temperature is less than the atmospheric temperature.
B. The increase in air movement increases the evaporation from the human body.
C. The warm air increases the rate of radiation of heat from the human body.
D. Both (A) and (B)
Answer : D

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

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

47. 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

48. 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

49. 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

50. 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