Refrigeration & Air-Conditioning Practice Set-5

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

Liquid pump

Absorber, generator and liquid pump

Absorber and generator

Generator

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

None of these

Dry bulb temperature

Dew point temperature

Wet bulb temperature

3. The specific humidity during cooling and dehumidification

Increases

Remains constant

None of these

Decreases

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

50%

25%

75%

10%

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

None of these

Vapour absorption cycle

Air refrigeration cycle

Vapour compression cycle

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

Water and lithium bromide

Ammonia and water

Water and water

Ammonia and lithium bromide

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

Power per TR is low

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

System has high C.O.P.

8. The evaporator used in household refrigerators is

None of these

Non-frosting evaporator

Defrosting evaporator

Frosting evaporator

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

In 12 hours

In 24 hours

In 1 minute

In 1 hour

10. 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.

B.P.F. - 1

1/ B.P.F.

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11. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

Superheated vapour refrigerant

None of these

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

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

After passing through the condenser

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

Vertical line

Curved line

Inclined line

Horizontal line

14. The power per tonne of refrigeration is

C.O.P/3.5

3.5/C.O.P.

3.5 × C.O.P.

None of these

15. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant entropy lines

Constant pressure lines

Constant temperature lines

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

Ammonia

Carbon dioxide

Sulphur dioxide

R-12

17. Ammonia is

Non-inflammable

Non-toxic

Highly toxic and inflammable

Toxic and non-inflammable

18. The reciprocating refrigerant compressors are very suitable for

Small displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Large displacements and high condensing pressures

19. 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

0.25

0.5

1.25

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

1 m3 of water

1 kg of wet air

1 m3 of dry air

1 kg of dry air

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

Improves C.O.P. of the system

Reduces power consumption

Increases heat transfer

Increases power consumption

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

Greater than

Less than

Equal to

None of these

23. Chaperon equation is applicable for registration at

Triple point

Saturation point of liquid

Sublimation temperature

Saturation point of vapour

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

Wet bulb temperature

Dew point temperature

Relative humidity

Dry bulb temperature

25. The refrigerant for a refrigerator should have

High total heat

High latent heat

Low latent heat

High sensible heat

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

Less than

None of these

More than

Equal to

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

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

Horizontal and uniformly spaced

Curved lines

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

Steel

Brass

Copper

Aluminium

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

1 kg of wet air

1 m3 of wet air

1 kg of dry air

1 m3 of dry air

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

Refrigerating efficiency

Coefficient of performance of refrigeration

Coefficient of performance of heat pump

Relative coefficient of performance

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31. The desirable property of a refrigerant is

All of these

Low boiling point

High critical temperature

High latent heat of vaporisation

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

1 kg of wet air

1 m3 of dry air

1 kg of dry air

1 m3 of water

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

Steel

Brass

Aluminium

Copper

34. Air refrigeration cycle is used in

Domestic refrigerators

Commercial refrigerators

Gas liquefaction

Air conditioning

35. 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)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

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

Electrolux refrigerator

Vapour absorption

Vapour compression

Carnot cycle

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

Strong solution to weak solution

Ammonia vapours to weak solution

Weak solution to strong solution

Strong solution to ammonia vapour

38. Degree of saturation or percentage humidity is

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

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

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

Simple air cooling system

Regenerative air cooling system

Reduced ambient air cooling system

Bootstrap air cooling system

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

Increase cooling effect

Reduce compressor overheating

Reduce compressor discharge temperature

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

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

After passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

Before passing through the condenser

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

21 kJ/ min

210 kJ/ min

420 kJ/ min

840 kJ/ min

43. The bypass factor for a cooling coil

Decreases with increase in velocity of air passing through it

Remains unchanged 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

Increases with increase in velocity of air passing through it

44. 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)

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

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

Reversed Joule cycle

Reversed Brayton cycle

Reversed Otto cycle

Reversed Carnot cycle

Refrigeration & Air-Conditioning Practice Set-5

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