Refrigeration & Air-Conditioning Practice Set-5

Page 1 of 5

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

Less than

More than

Equal to

None of these

2. The refrigerant for a refrigerator should have

High latent heat

High total heat

High sensible heat

Low latent heat

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

Strong solution to weak solution

Strong solution to ammonia vapour

Weak solution to strong solution

Ammonia vapours to weak solution

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

Simple air cooling system

Reduced ambient air cooling system

Regenerative air cooling system

Bootstrap air cooling system

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

Copper

Aluminium

Brass

Steel

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

Vapour absorption

Electrolux refrigerator

Vapour compression

Carnot cycle

7. 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?

0.5

1.25

0.25

0.8

8. 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

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)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

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

1 m3 of dry air

1 m3 of water

1 kg of dry air

1 kg of wet air

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11. The power per tonne of refrigeration is

C.O.P/3.5

3.5/C.O.P.

None of these

3.5 × C.O.P.

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

System has high C.O.P.

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

Power per TR is low

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

Wet bulb temperature

Dry bulb temperature

None of these

Dew point temperature

14. The refrigerant supplied to a compressor must be

None of these

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

15. Ammonia is

Non-inflammable

Highly toxic and inflammable

Non-toxic

Toxic and non-inflammable

16. The desirable property of a refrigerant is

High latent heat of vaporisation

All of these

High critical temperature

Low boiling point

17. The evaporator used in household refrigerators is

Frosting evaporator

None of these

Non-frosting evaporator

Defrosting evaporator

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

Dry bulb temperature

Dew point temperature

Relative humidity

Wet bulb temperature

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

Steel

Brass

Copper

Aluminium

20. 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

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21. 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 condenser

After passing through the expansion or throttle valve

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

75%

10%

50%

25%

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

Horizontal line

Inclined line

Curved line

Vertical line

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

Ammonia and water

Ammonia and lithium bromide

Water and water

Water and lithium bromide

25. 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.

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

210 kJ/ min

840 kJ/ min

21 kJ/ min

420 kJ/ min

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

Increases heat transfer

Increases power consumption

Improves C.O.P. of the system

Reduces power consumption

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

Horizontal and uniformly spaced

Vertical and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

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

1 kg of dry air

1 kg of wet air

1 m3 of water

1 m3 of dry air

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

Reversed Brayton cycle

Reversed Otto cycle

Reversed Joule cycle

Reversed Carnot cycle

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

Less than

Equal to

None of these

Greater than

32. 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 (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

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

Before passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

After passing through the condenser

34. The reciprocating refrigerant compressors are very suitable for

Small displacements and high condensing pressures

Large displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and low condensing pressures

35. Chaperon equation is applicable for registration at

Saturation point of vapour

Saturation point of liquid

Triple point

Sublimation temperature

36. The specific humidity during cooling and dehumidification

Decreases

Increases

None of these

Remains constant

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

None of these

Vapour compression cycle

Air refrigeration cycle

Vapour absorption cycle

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

Carbon dioxide

R-12

Ammonia

Sulphur dioxide

39. 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 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 kg of dry air

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

40. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant temperature lines

Constant entropy lines

Constant pressure lines

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41. 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

42. Air refrigeration cycle is used in

Domestic refrigerators

Commercial refrigerators

Air conditioning

Gas liquefaction

43. The bypass factor for a cooling coil

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

Increases with increase in velocity of air passing through it

Remains unchanged with increase in velocity of air passing through it

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

Increase cooling effect

Reduce compressor discharge temperature

Reduce compressor overheating

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

45. 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

Refrigeration & Air-Conditioning Practice Set-5

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