Refrigeration & Air-Conditioning Practice Set-5

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

25%

75%

50%

10%

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

1 m3 of wet air

1 m3 of dry air

1 kg of dry air

1 kg of wet air

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

Bootstrap air cooling system

Regenerative air cooling system

Reduced ambient air cooling system

Simple air cooling system

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

Carnot cycle

Vapour compression

Electrolux refrigerator

Vapour absorption

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

1 - B. P.F.

B.P.F. - 1

1/ B.P.F.

1 + B.P.F.

6. Degree of saturation or percentage humidity is

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

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

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

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

Steel

Brass

Copper

Aluminium

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

Liquid pump

Absorber, generator and liquid pump

Generator

Absorber and generator

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

Inclined line

Curved line

Horizontal line

Vertical line

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

Copper

Aluminium

Steel

Brass

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11. 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

12. Air refrigeration cycle is used in

Air conditioning

Domestic refrigerators

Commercial refrigerators

Gas liquefaction

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

More than

None of these

Equal to

Less than

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

1 m3 of dry air

1 m3 of water

1 kg of wet air

1 kg of dry air

15. 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

16. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

None of these

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

17. 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

0.25

0.5

1.25

18. 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

19. Ammonia is

Non-toxic

Toxic and non-inflammable

Non-inflammable

Highly toxic and inflammable

20. 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)]

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

Vertical and uniformly spaced

Curved lines

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

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

840 kJ/ min

420 kJ/ min

210 kJ/ min

21 kJ/ min

23. The bypass factor for a cooling coil

Remains unchanged with increase in velocity of air passing through it

Increases 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

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

After passing through the condenser

Before passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

25. 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

Ammonia vapours to weak solution

Weak solution to strong solution

26. The specific humidity during cooling and dehumidification

Decreases

Increases

Remains constant

None of these

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

Coefficient of performance of refrigeration

Relative coefficient of performance

Refrigerating efficiency

Coefficient of performance of heat pump

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

Increases heat transfer

Reduces power consumption

Increases power consumption

Improves C.O.P. of the system

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

Dew point temperature

Wet bulb temperature

Dry bulb temperature

Relative humidity

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

Equal to

Less than

None of these

Greater than

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31. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant total heat lines

Constant temperature lines

Constant pressure lines

32. 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 - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

33. The desirable property of a refrigerant is

High latent heat of vaporisation

Low boiling point

High critical temperature

All of these

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

System has high C.O.P.

Power per TR is low

Mass of the refrigeration equipment is low

Mass of refrigerant circulated in the system is low

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

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

After passing through the condenser

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

Reduce compressor discharge temperature

Increase cooling effect

Reduce compressor overheating

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

37. Chaperon equation is applicable for registration at

Triple point

Sublimation temperature

Saturation point of vapour

Saturation point of liquid

38. 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.

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

Vapour compression cycle

Air refrigeration cycle

Vapour absorption cycle

None of these

40. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Small displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and low condensing pressures

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41. The refrigerant for a refrigerator should have

High latent heat

High total heat

High sensible heat

Low latent heat

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

Reversed Brayton cycle

Reversed Carnot cycle

Reversed Otto cycle

Reversed Joule cycle

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

Sulphur dioxide

R-12

Ammonia

Carbon dioxide

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

Water and lithium bromide

Ammonia and lithium bromide

Ammonia and water

Water and water

45. The evaporator used in household refrigerators is

None of these

Defrosting evaporator

Frosting evaporator

Non-frosting evaporator

Refrigeration & Air-Conditioning Practice Set-5

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