Refrigeration & Air-Conditioning Practice Set-5

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1. 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

Dew point temperature

Dry bulb temperature

None of these

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

Reduces power consumption

Improves C.O.P. of the system

Increases heat transfer

Increases power consumption

3. The refrigerant for a refrigerator should have

High sensible heat

High total heat

Low latent heat

High latent heat

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

1 kg of dry air

1 m3 of dry air

1 m3 of water

1 kg of wet air

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

Relative humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

6. 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

7. 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.

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

Absorber, generator and liquid pump

Absorber and generator

Generator

Liquid pump

9. The bypass factor for a cooling coil

Increases with increase in velocity of air passing through it

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

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

Inclined line

Curved line

Horizontal line

Vertical line

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

210 kJ/ min

21 kJ/ min

420 kJ/ min

840 kJ/ min

12. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Small displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and high condensing pressures

13. 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

0.5

0.25

1.25

14. 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.

15. Chaperon equation is applicable for registration at

Saturation point of liquid

Sublimation temperature

Saturation point of vapour

Triple point

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

Curved lines

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

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

Brass

Steel

Aluminium

Copper

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

1 kg of wet air

1 m3 of dry air

1 kg of dry air

1 m3 of wet air

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

Reversed Otto cycle

Reversed Brayton cycle

Reversed Carnot cycle

Reversed Joule cycle

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

Ammonia and lithium bromide

Water and lithium bromide

Ammonia and water

Water and water

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21. Air refrigeration cycle is used in

Air conditioning

Domestic refrigerators

Commercial refrigerators

Gas liquefaction

22. The evaporator used in household refrigerators is

Defrosting evaporator

Frosting evaporator

None of these

Non-frosting evaporator

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

Strong solution to ammonia vapour

Ammonia vapours to weak solution

Strong solution to weak solution

Weak solution to strong solution

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

Relative coefficient of performance

Coefficient of performance of heat pump

Refrigerating efficiency

Coefficient of performance of refrigeration

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

10%

75%

50%

25%

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

Sulphur dioxide

R-12

Ammonia

Carbon dioxide

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

Vapour absorption cycle

Vapour compression cycle

Air refrigeration cycle

None of these

28. 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.

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

After passing through the expansion or throttle valve

Before entering the compressor

After passing through the condenser

Before passing through the condenser

30. The specific humidity during cooling and dehumidification

Increases

Decreases

None of these

Remains constant

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31. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

None of these

32. Ammonia is

Toxic and non-inflammable

Non-toxic

Highly toxic and inflammable

Non-inflammable

33. 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

34. 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)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

35. 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

Reduce compressor discharge temperature

Increase cooling effect

36. The desirable property of a refrigerant is

Low boiling point

All of these

High latent heat of vaporisation

High critical temperature

37. 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)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

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

Less than

Equal to

More than

None of these

39. 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 24 hours

In 1 minute

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

Electrolux refrigerator

Vapour compression

Carnot cycle

Vapour absorption

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

After passing through the condenser

Before entering the expansion valve

Before passing through the condenser

After passing through the expansion or throttle valve

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

Copper

Brass

Aluminium

Steel

43. 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

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

Equal to

None of these

Greater than

Less than

45. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant entropy lines

Constant temperature lines

Constant pressure lines

Refrigeration & Air-Conditioning Practice Set-5

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