Refrigeration & Air-Conditioning Practice Set-5

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

1 kg of wet air

1 kg of dry air

1 m3 of water

1 m3 of dry air

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

In 1 hour

In 12 hours

In 1 minute

In 24 hours

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

Steel

Aluminium

Copper

Brass

4. Ammonia is

Non-toxic

Highly toxic and inflammable

Toxic and non-inflammable

Non-inflammable

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

210 kJ/ min

420 kJ/ min

840 kJ/ min

21 kJ/ min

6. The desirable property of a refrigerant is

High latent heat of vaporisation

Low boiling point

High critical temperature

All of these

7. 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 (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

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

Equal to

None of these

More than

Less than

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

Coefficient of performance of refrigeration

Refrigerating efficiency

Coefficient of performance of heat pump

Relative coefficient of performance

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

Less than

None of these

Equal to

Greater than

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

10%

50%

25%

75%

12. 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

13. The refrigerant for a refrigerator should have

High total heat

High sensible heat

High latent heat

Low latent heat

14. Air refrigeration cycle is used in

Domestic refrigerators

Gas liquefaction

Air conditioning

Commercial refrigerators

15. 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.

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

1 m3 of dry air

1 kg of wet air

1 m3 of water

1 kg of dry air

17. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

Superheated vapour refrigerant

None of these

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?

0.8

1.25

0.25

0.5

19. The evaporator used in household refrigerators is

Non-frosting evaporator

None of these

Frosting evaporator

Defrosting evaporator

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

Improves C.O.P. of the system

Increases heat transfer

Reduces power consumption

Increases power consumption

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

Mass of the refrigeration equipment is low

System has high C.O.P.

Power per TR is low

Mass of refrigerant circulated in the system is low

22. The power per tonne of refrigeration is

None of these

C.O.P/3.5

3.5/C.O.P.

3.5 × C.O.P.

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

Absorber and generator

Generator

Absorber, generator and liquid pump

Liquid pump

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

Vertical line

Curved line

Horizontal line

Inclined line

25. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant total heat lines

Constant temperature lines

Constant pressure lines

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

Reduced ambient air cooling system

Bootstrap air cooling system

Regenerative air cooling system

Simple air cooling system

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

Brass

Aluminium

Copper

Steel

28. 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 weak solution

Strong solution to ammonia vapour

29. Degree of saturation or percentage humidity is

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

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

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 - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

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

Wet bulb temperature

Dew point temperature

Relative humidity

Dry bulb temperature

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

Reduce compressor overheating

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

Reduce compressor discharge temperature

Increase cooling effect

33. Chaperon equation is applicable for registration at

Triple point

Saturation point of vapour

Saturation point of liquid

Sublimation temperature

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

After passing through the expansion or throttle valve

Before entering the compressor

Before passing through the condenser

After passing through the condenser

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

After passing through the expansion or throttle valve

Before entering the expansion valve

Before passing through the condenser

After passing through the condenser

36. The specific humidity during cooling and dehumidification

None of these

Increases

Decreases

Remains constant

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

Air refrigeration cycle

Vapour absorption cycle

Vapour compression cycle

None of these

38. 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

Dew point temperature

Wet bulb temperature

Dry bulb temperature

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

Electrolux refrigerator

Vapour compression

Vapour absorption

Carnot cycle

40. 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

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

Horizontal and uniformly spaced

Curved lines

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

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

Reversed Carnot cycle

Reversed Otto cycle

Reversed Joule cycle

Reversed Brayton cycle

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

Sulphur dioxide

R-12

Carbon dioxide

Ammonia

44. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

Large displacements and low condensing pressures

45. The bypass factor for a cooling coil

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

Decreases with increase in velocity of air passing through it

Remains unchanged with increase in velocity of air passing through it

Refrigeration & Air-Conditioning Practice Set-5

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