Refrigeration & Air-Conditioning Practice Set-5

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1. Degree of saturation or percentage humidity is

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

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

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

More than

Equal to

None of these

Less than

3. 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

4. The evaporator used in household refrigerators is

None of these

Frosting evaporator

Defrosting evaporator

Non-frosting evaporator

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

Coefficient of performance of heat pump

Relative coefficient of performance

Refrigerating efficiency

Coefficient of performance of refrigeration

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

1 kg of wet air

1 m3 of water

1 m3 of dry air

1 kg of dry air

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

1 kg of wet air

1 kg of dry air

1 m3 of dry air

1 m3 of water

8. 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

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

1 m3 of wet air

1 kg of wet air

1 m3 of dry air

1 kg of dry air

10. 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 (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

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

Vapour compression cycle

None of these

Vapour absorption cycle

Air refrigeration cycle

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

In 12 hours

In 1 hour

In 1 minute

In 24 hours

13. 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

Power per TR is low

System has high C.O.P.

14. The refrigerant for a refrigerator should have

High total heat

High sensible heat

Low latent heat

High latent heat

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

Vapour absorption

Vapour compression

Carnot cycle

Electrolux refrigerator

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

Equal to

None of these

Greater than

Less than

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

Horizontal line

Curved line

Inclined line

Vertical line

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

Wet bulb temperature

Relative humidity

Dew point temperature

Dry bulb temperature

19. The power per tonne of refrigeration is

3.5 × C.O.P.

None of these

C.O.P/3.5

3.5/C.O.P.

20. 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)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

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21. Chaperon equation is applicable for registration at

Sublimation temperature

Triple point

Saturation point of liquid

Saturation point of vapour

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

Before entering the compressor

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

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

Brass

Steel

Copper

Aluminium

24. 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.

25. Ammonia is

Non-toxic

Toxic and non-inflammable

Non-inflammable

Highly toxic and inflammable

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

Bootstrap air cooling system

Reduced ambient air cooling system

Simple air cooling system

Regenerative air cooling system

27. Air refrigeration cycle is used in

Commercial refrigerators

Air conditioning

Domestic refrigerators

Gas liquefaction

28. 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

29. 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?

1.25

0.8

0.5

0.25

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

25%

75%

10%

50%

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31. 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

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

Generator

Absorber and generator

Liquid pump

Absorber, generator and liquid pump

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

420 kJ/ min

840 kJ/ min

21 kJ/ min

210 kJ/ min

34. The bypass factor for a cooling coil

Increases 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

Decreases with increase in velocity of air passing through it

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

Water and lithium bromide

Water and water

Ammonia and lithium bromide

Ammonia and water

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

Aluminium

Copper

Steel

Brass

37. The desirable property of a refrigerant is

All of these

High critical temperature

Low boiling point

High latent heat of vaporisation

38. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant total heat lines

Constant pressure lines

Constant temperature lines

39. The specific humidity during cooling and dehumidification

None of these

Increases

Remains constant

Decreases

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

Sulphur dioxide

R-12

Carbon dioxide

Ammonia

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

Reversed Brayton cycle

Reversed Joule cycle

Reversed Otto cycle

Reversed Carnot cycle

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

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

Curved lines

43. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

None of these

A mixture of liquid and vapour refrigerant

Superheated vapour refrigerant

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

Before passing through the condenser

After passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

45. 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

Refrigeration & Air-Conditioning Practice Set-5

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