Refrigeration & Air-Conditioning Practice Set-5

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

1 m3 of water

1 kg of dry air

1 m3 of dry air

1 kg of wet air

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

Coefficient of performance of refrigeration

Refrigerating efficiency

Relative coefficient of performance

Coefficient of performance of heat pump

3. 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)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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

1 kg of dry air

1 m3 of dry air

1 kg of wet air

1 m3 of wet air

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

6. Degree of saturation or percentage humidity is

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

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

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

Vertical line

Curved line

Horizontal line

Inclined line

8. Ammonia is

Non-inflammable

Toxic and non-inflammable

Highly toxic and inflammable

Non-toxic

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

In 24 hours

In 1 minute

In 1 hour

In 12 hours

10. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant pressure lines

Constant temperature lines

Constant entropy lines

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

Increases power consumption

Reduces power consumption

Improves C.O.P. of the system

Increases heat transfer

12. 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

13. 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

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

Water and water

Ammonia and water

Water and lithium bromide

Ammonia and lithium bromide

15. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

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

Before passing through the condenser

After passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

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

Reversed Joule cycle

Reversed Carnot cycle

Reversed Otto cycle

Reversed Brayton cycle

18. 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?

1.25

0.25

0.5

0.8

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

Liquid pump

Absorber and generator

Absorber, generator and liquid pump

Generator

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

Aluminium

Copper

Steel

Brass

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

Before passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

After passing through the condenser

22. The desirable property of a refrigerant is

High latent heat of vaporisation

Low boiling point

High critical temperature

All of these

23. The evaporator used in household refrigerators is

Non-frosting evaporator

Frosting evaporator

Defrosting evaporator

None of these

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

Dry bulb temperature

Wet bulb temperature

Relative humidity

Dew point temperature

25. 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

26. The refrigerant for a refrigerator should have

High latent heat

High sensible heat

Low latent heat

High total heat

27. Chaperon equation is applicable for registration at

Sublimation temperature

Saturation point of vapour

Saturation point of liquid

Triple point

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

Vapour compression cycle

None of these

Air refrigeration cycle

Vapour absorption cycle

29. The power per tonne of refrigeration is

C.O.P/3.5

None of these

3.5 × C.O.P.

3.5/C.O.P.

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

Vapour compression

Electrolux refrigerator

Carnot cycle

Vapour absorption

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

Brass

Aluminium

Copper

Steel

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

Ammonia vapours to weak solution

Weak solution to strong solution

Strong solution to ammonia vapour

Strong solution to weak solution

33. The specific humidity during cooling and dehumidification

Remains constant

Decreases

Increases

None of these

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

Greater than

Less than

Equal to

None of these

35. 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

36. Air refrigeration cycle is used in

Gas liquefaction

Air conditioning

Commercial refrigerators

Domestic refrigerators

37. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

Dry saturated liquid refrigerant

None of these

A mixture of liquid and vapour refrigerant

38. 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.

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

50%

75%

25%

10%

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

21 kJ/ min

420 kJ/ min

840 kJ/ min

210 kJ/ min

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41. 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

Increase cooling effect

Reduce compressor overheating

Reduce compressor discharge temperature

42. 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

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

More than

None of these

Equal to

Less than

44. 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

45. 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 (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

Refrigeration & Air-Conditioning Practice Set-5

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