Refrigeration & Air-Conditioning Practice Set-5

Page 1 of 5

1. 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

None of these

Wet bulb temperature

Dry bulb temperature

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

Coefficient of performance of heat pump

Coefficient of performance of refrigeration

Refrigerating efficiency

Relative coefficient of performance

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

Mass of the refrigeration equipment is low

Power per TR is low

System has high C.O.P.

Mass of refrigerant circulated in the system is low

4. 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

0.5

0.25

5. The specific humidity during cooling and dehumidification

Increases

Remains constant

None of these

Decreases

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

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

Before entering the expansion valve

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

Brass

Steel

Aluminium

Copper

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

Vapour absorption cycle

None of these

Vapour compression cycle

Air refrigeration cycle

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

1 m3 of dry air

1 kg of dry air

1 kg of wet air

1 m3 of water

10. The refrigerant supplied to a compressor must be

None of these

Superheated vapour refrigerant

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

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11. The evaporator used in household refrigerators is

None of these

Non-frosting evaporator

Frosting evaporator

Defrosting evaporator

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

Ammonia vapours to weak solution

Strong solution to weak solution

Weak solution to strong solution

Strong solution to ammonia vapour

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

Increases heat transfer

Increases power consumption

Reduces power consumption

Improves C.O.P. of the system

14. 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.

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

In 1 hour

In 24 hours

In 1 minute

In 12 hours

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

Ammonia and water

Ammonia and lithium bromide

Water and lithium bromide

Water and water

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

Dry bulb temperature

Relative humidity

Wet bulb temperature

Dew point temperature

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

Less than

None of these

Greater than

Equal to

19. The desirable property of a refrigerant is

All of these

Low boiling point

High latent heat of vaporisation

High critical temperature

20. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant pressure lines

Constant temperature lines

Constant entropy lines

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

Copper

Steel

Brass

Aluminium

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

Absorber and generator

Generator

Liquid pump

Absorber, generator and liquid pump

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

R-12

Ammonia

Sulphur dioxide

Carbon dioxide

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

Vapour compression

Vapour absorption

Carnot cycle

Electrolux refrigerator

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

420 kJ/ min

840 kJ/ min

210 kJ/ min

21 kJ/ min

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

Inclined line

Vertical line

Curved line

Horizontal line

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

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

Reduce compressor overheating

Increase cooling effect

Reduce compressor discharge temperature

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

Regenerative air cooling system

Reduced ambient air cooling system

Bootstrap air cooling system

Simple air cooling system

29. Degree of saturation or percentage humidity is

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

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

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

Vertical and uniformly spaced

Curved lines

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

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

None of these

More than

Less than

Equal to

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

Reversed Otto cycle

Reversed Carnot cycle

Reversed Joule cycle

Reversed Brayton cycle

33. Ammonia is

Non-toxic

Non-inflammable

Toxic and non-inflammable

Highly toxic and inflammable

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

1 m3 of water

1 m3 of dry air

1 kg of dry air

1 kg of wet air

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

After passing through the expansion or throttle valve

Before entering the compressor

Before passing through the condenser

After passing through the condenser

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

1 kg of dry air

1 m3 of wet air

1 kg of wet air

1 m3 of dry air

37. Chaperon equation is applicable for registration at

Saturation point of vapour

Sublimation temperature

Saturation point of liquid

Triple point

38. 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)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

39. Air refrigeration cycle is used in

Gas liquefaction

Domestic refrigerators

Commercial refrigerators

Air conditioning

40. The refrigerant for a refrigerator should have

High total heat

High latent heat

Low latent heat

High sensible heat

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41. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Small displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and low condensing pressures

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

1/ B.P.F.

B.P.F. - 1

1 - B. P.F.

1 + B.P.F.

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

75%

50%

10%

25%

44. The bypass factor for a cooling coil

Decreases with increase in velocity of air passing through it

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

45. 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)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

Refrigeration & Air-Conditioning Practice Set-5

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