Refrigeration & Air-Conditioning Practice Set-5

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1. The refrigerant for a refrigerator should have

High total heat

High sensible heat

Low latent heat

High latent heat

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

1 kg of dry air

1 kg of wet air

1 m3 of dry air

1 m3 of water

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

None of these

Less than

More than

Equal to

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

Before entering the expansion valve

After passing through the condenser

Before passing through the condenser

After passing through the expansion or throttle valve

5. 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.

6. 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

7. 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.

8. 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

9. 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

10. 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

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

Increases power consumption

Reduces power consumption

Increases heat transfer

Improves C.O.P. of the system

12. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant pressure lines

Constant total heat lines

Constant temperature lines

13. Air refrigeration cycle is used in

Air conditioning

Gas liquefaction

Domestic refrigerators

Commercial refrigerators

14. Degree of saturation or percentage humidity is

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

The mass of water vapour present in 1 m³ 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 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

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

Horizontal and non-uniformly spaced

Curved lines

Vertical and uniformly spaced

Horizontal and uniformly spaced

16. 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 (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

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

210 kJ/ min

21 kJ/ min

840 kJ/ min

420 kJ/ min

18. 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

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

1 kg of wet air

1 kg of dry air

1 m3 of dry air

1 m3 of wet air

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

Reversed Joule cycle

Reversed Otto cycle

Reversed Brayton cycle

Reversed Carnot cycle

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

Dry bulb temperature

None of these

Dew point temperature

Wet bulb temperature

22. The desirable property of a refrigerant is

High critical temperature

All of these

Low boiling point

High latent heat of vaporisation

23. The evaporator used in household refrigerators is

Non-frosting evaporator

Frosting evaporator

None of these

Defrosting evaporator

24. 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.

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

Ammonia

Sulphur dioxide

Carbon dioxide

R-12

26. 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

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

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the compressor

After passing through the condenser

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

Carnot cycle

Vapour absorption

Electrolux refrigerator

Vapour compression

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

Vapour absorption cycle

Air refrigeration cycle

None of these

Vapour compression cycle

30. 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)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

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

Water and lithium bromide

Ammonia and lithium bromide

Water and water

Ammonia and water

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

75%

50%

10%

25%

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

Horizontal line

Inclined line

Curved line

Vertical line

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

In 24 hours

In 12 hours

In 1 hour

In 1 minute

35. 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

36. 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

37. 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

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

Relative humidity

Wet bulb temperature

Dry bulb temperature

Dew point temperature

39. The specific humidity during cooling and dehumidification

None of these

Remains constant

Decreases

Increases

40. Ammonia is

Highly toxic and inflammable

Toxic and non-inflammable

Non-toxic

Non-inflammable

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41. Chaperon equation is applicable for registration at

Saturation point of vapour

Saturation point of liquid

Sublimation temperature

Triple point

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

Brass

Copper

Aluminium

Steel

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

Aluminium

Steel

Brass

Copper

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

Strong solution to weak solution

Weak solution to strong solution

Ammonia vapours to weak solution

Strong solution to ammonia vapour

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

Equal to

Greater than

None of these

Less than

Refrigeration & Air-Conditioning Practice Set-5

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