Refrigeration & Air-Conditioning Practice Set-5

July 7, 2021

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Page 1 of 5

1. In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = Bypass factor)

1/ B.P.F.

1 - B. P.F.

1 + B.P.F.

B.P.F. - 1

2. In a vapour absorption refrigeration system, the compressor of the vapour compression system is replaced by

Liquid pump

Absorber and generator

Generator

Absorber, generator and liquid pump

3. Degree of saturation or percentage humidity is

The mass of water vapour present in 1 m³ of dry air

The mass of water vapour present in 1 kg of dry air

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

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

4. One ton of refrigeration is equal to the refrigeration effect corresponding to melting of 1000 kg of ice

In 24 hours

In 1 minute

In 12 hours

In 1 hour

5. The specific humidity during cooling and dehumidification

Increases

Decreases

None of these

Remains constant

6. The bypass factor for a cooling coil

Increases with increase in velocity of air passing through it

May increase or decrease with increase in velocity of air passing through it depending upon the condition of air entering

Remains unchanged with increase in velocity of air passing through it

Decreases with increase in velocity of air passing through it

7. The evaporator used in household refrigerators is

None of these

Non-frosting evaporator

Frosting evaporator

Defrosting evaporator

8. Chaperon equation is applicable for registration at

Triple point

Sublimation temperature

Saturation point of liquid

Saturation point of vapour

9. The sensible heat factor during cooling and dehumidification process is given by (where h₁ = Enthalpy of air entering the cooling coil, h₂ = Enthalpy of air leaving the cooling coil, and h_A = Enthalpy of air at the end of dehumidification process)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

10. Air refrigeration cycle is used in

Domestic refrigerators

Commercial refrigerators

Air conditioning

Gas liquefaction

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11. For unsaturated air, the dew point temperature is __________ wet bulb temperature.

Equal to

Less than

None of these

More than

12. In air-conditioning of aeroplanes, using air as a refrigerant, the cycle used is

Reversed Otto cycle

Reversed Joule cycle

Reversed Carnot cycle

Reversed Brayton cycle

13. In aqua ammonia and Lithium bromide water absorption refrigeration systems, the refrigerants are respectively

Ammonia and lithium bromide

Water and lithium bromide

Water and water

Ammonia and water

14. In which of the following refrigeration system, waste heat can be effectively used?

Vapour absorption cycle

Vapour compression cycle

None of these

Air refrigeration cycle

15. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

None of these

Superheated vapour refrigerant

16. The refrigerant for a refrigerator should have

High latent heat

Low latent heat

High total heat

High sensible heat

17. The cooling system used for supersonic aircrafts and rockets is

Reduced ambient air cooling system

Simple air cooling system

Regenerative air cooling system

Bootstrap air cooling system

18. The material of pipe lines for a system using Freon as a refrigerant should be

Aluminium

Copper

Steel

Brass

19. The mass of water vapour present in __________ is called absolute humidity.

1 kg of dry air

1 kg of wet air

1 m3 of dry air

1 m3 of water

20. While designing the refrigeration system of an aircraft, the prime consideration is that the

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

System has high C.O.P.

Power per TR is low

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21. The ratio of heat extracted in the refrigerator to the work-done on the refrigerant is called

Relative coefficient of performance

Refrigerating efficiency

Coefficient of performance of refrigeration

Coefficient of performance of heat pump

22. The temperature of air recorded by a thermometer, when its bulb is surrounded by a wet cloth exposed to the air, is called

Dew point temperature

Dry bulb temperature

None of these

Wet bulb temperature

23. The desirable property of a refrigerant is

High critical temperature

High latent heat of vaporisation

All of these

Low boiling point

24. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

25. The mass of water vapour present in __________ is called absolute humidity.

1 kg of dry air

1 m3 of water

1 kg of wet air

1 m3 of dry air

26. The formation of frost on cooling coils in a refrigerator

Improves C.O.P. of the system

Increases heat transfer

Increases power consumption

Reduces power consumption

27. For ammonia refrigerating systems, the tubes of a shell and tube condenser are made of

Copper

Steel

Aluminium

Brass

28. The power per tonne of refrigeration is

3.5/C.O.P.

C.O.P/3.5

None of these

3.5 × C.O.P.

29. The C.O.P. of an absorption type refrigerator is given by (where T₁ = Temperature at which the working substance receives heat, T₂ = Temperature of cooling water, and T₃ = Evaporator temperature)

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

30. During adiabatic saturation process on unsaturated air __________ remains constant.

Relative humidity

Dry bulb temperature

Dew point temperature

Wet bulb temperature

Page 4 of 5

31. Accumulators should have adequate volume to store refrigerant charge at least

25%

50%

10%

75%

32. In vapour compression cycle the condition off refrigerant is dry saturated vapour

Before entering the compressor

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

33. In a refrigerating machine, heat rejected is _________ heat absorbed.

Equal to

Greater than

Less than

None of these

34. The humidity ratio or specific humidity is the mass of water vapour present in

1 m3 of dry air

1 kg of wet air

1 kg of dry air

1 m3 of wet air

35. Ammonia is

Toxic and non-inflammable

Highly toxic and inflammable

Non-toxic

Non-inflammable

36. In S.J. unit, one ton of refrigeration is equal to

210 kJ/ min

840 kJ/ min

21 kJ/ min

420 kJ/ min

37. The dry bulb temperature lines, on the psychrometric chart are

Vertical and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

38. In vapour compression cycle the condition of refrigerant is superheated vapour

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

Before passing through the condenser

39. Pick up the correct statement about giving up of heat from one medium to other in ammonia absorption system

Weak solution to strong solution

Strong solution to weak solution

Strong solution to ammonia vapour

Ammonia vapours to weak solution

40. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant entropy lines

Constant pressure lines

Constant temperature lines

Page 5 of 5

41. One of the purposes of sub cooling the liquid refrigerant is to

Increase cooling effect

Ensure that only liquid and not the vapour enters the expansion (throttling) valve

Reduce compressor overheating

Reduce compressor discharge temperature

42. Efficiency of a Carnot engine is given as 80%. If the cycle direction be reversed, what will be the value of C.O.P. of reversed Carnot Cycle?

0.8

1.25

0.25

0.5

43. The humidification process, on the psychrometric chart is shown by

Inclined line

Vertical line

Curved line

Horizontal line

44. In larger industrial and commercial reciprocating compression systems, refrigerant widely used is

Ammonia

Sulphur dioxide

R-12

Carbon dioxide

45. Most of the domestic refrigerators work on the following refrigeration system

Vapour compression

Electrolux refrigerator

Vapour absorption

Carnot cycle

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Refrigeration & Air-Conditioning Practice Set-5

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