Refrigeration & Air-Conditioning Practice Set-5

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1. The specific humidity during cooling and dehumidification

Decreases

None of these

Increases

Remains constant

2. The refrigerant for a refrigerator should have

High total heat

High sensible heat

High latent heat

Low latent heat

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

Vapour compression

Electrolux refrigerator

Carnot cycle

Vapour absorption

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

75%

25%

10%

50%

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

Strong solution to ammonia vapour

Weak solution to strong solution

Strong solution to weak solution

Ammonia vapours to weak solution

6. 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

7. The evaporator used in household refrigerators is

Defrosting evaporator

Frosting evaporator

None of these

Non-frosting evaporator

8. 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

After passing through the condenser

Before entering the compressor

9. 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 refrigeration

Coefficient of performance of heat pump

Refrigerating efficiency

10. In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = Bypass factor)

B.P.F. - 1

1 - B. P.F.

1 + B.P.F.

1/ B.P.F.

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11. The bypass factor for a cooling coil

Remains unchanged with increase in velocity of air passing through it

Decreases 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

12. 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)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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

Horizontal line

Inclined line

Vertical line

Curved line

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

210 kJ/ min

840 kJ/ min

21 kJ/ min

420 kJ/ min

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

Water and water

Ammonia and water

Ammonia and lithium bromide

Water and lithium bromide

16. The desirable property of a refrigerant is

High latent heat of vaporisation

Low boiling point

High critical temperature

All of these

17. The power per tonne of refrigeration is

3.5/C.O.P.

C.O.P/3.5

3.5 × C.O.P.

None of these

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

Generator

Absorber, generator and liquid pump

Liquid pump

Absorber and generator

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

Aluminium

Copper

Brass

Steel

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

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

1 m3 of water

1 kg of dry air

1 kg of wet air

1 m3 of dry air

22. 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

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

1 m3 of dry air

1 kg of wet air

1 m3 of wet air

1 kg of dry air

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

Equal to

Less than

None of these

Greater than

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

Power per TR is low

System has high C.O.P.

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

26. 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 condenser

After passing through the expansion or throttle valve

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

Steel

Copper

Aluminium

Brass

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

Improves C.O.P. of the system

Increases heat transfer

Increases power consumption

Reduces power consumption

29. Air refrigeration cycle is used in

Air conditioning

Domestic refrigerators

Commercial refrigerators

Gas liquefaction

30. 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)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

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31. Ammonia is

Non-toxic

Highly toxic and inflammable

Toxic and non-inflammable

Non-inflammable

32. Chaperon equation is applicable for registration at

Saturation point of vapour

Triple point

Saturation point of liquid

Sublimation temperature

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

Reduced ambient air cooling system

Regenerative air cooling system

Simple air cooling system

Bootstrap air cooling system

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

In 1 minute

In 12 hours

In 1 hour

In 24 hours

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

Reversed Joule cycle

Reversed Brayton cycle

Reversed Carnot cycle

Reversed Otto cycle

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

Equal to

None of these

More than

Less than

37. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant temperature lines

Constant total heat lines

Constant entropy lines

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

Air refrigeration cycle

None of these

Vapour compression cycle

Vapour absorption cycle

39. 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

0.25

0.8

1.25

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

Dry bulb temperature

Relative humidity

Wet bulb temperature

Dew point temperature

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41. 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

42. 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

Wet bulb temperature

Dry bulb temperature

Dew point temperature

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

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

Curved lines

Horizontal and uniformly spaced

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

1 kg of dry air

1 m3 of water

1 m3 of dry air

1 kg of wet air

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

Reduce compressor overheating

Reduce compressor discharge temperature

Increase cooling effect

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

Refrigeration & Air-Conditioning Practice Set-5

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