Refrigeration & Air-Conditioning Practice Set-5

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

Mass of the refrigeration equipment is low

Mass of refrigerant circulated in the system is low

System has high C.O.P.

Power per TR is low

2. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant total heat lines

Constant pressure lines

Constant temperature lines

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 - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

4. Ammonia is

Non-toxic

Toxic and non-inflammable

Non-inflammable

Highly toxic and inflammable

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

Vertical line

Curved line

Inclined line

Horizontal line

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

Carnot cycle

Vapour compression

Vapour absorption

Electrolux refrigerator

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

Aluminium

Brass

Steel

Copper

8. The specific humidity during cooling and dehumidification

None of these

Remains constant

Increases

Decreases

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

1 kg of dry air

1 m3 of wet air

1 m3 of dry air

1 kg of wet air

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

21 kJ/ min

210 kJ/ min

840 kJ/ min

420 kJ/ min

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

None of these

Greater than

Equal to

Less than

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

Strong solution to weak solution

Ammonia vapours to weak solution

Strong solution to ammonia vapour

Weak solution to strong solution

13. Air refrigeration cycle is used in

Gas liquefaction

Air conditioning

Domestic refrigerators

Commercial refrigerators

14. 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.

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

Vapour compression cycle

Vapour absorption cycle

None of these

Air refrigeration cycle

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

None of these

Equal to

More than

Less than

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

Regenerative air cooling system

Bootstrap air cooling system

Reduced ambient air cooling system

Simple air cooling system

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

Reversed Carnot cycle

Reversed Joule cycle

Reversed Brayton cycle

Reversed Otto cycle

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

After passing through the condenser

Before entering the expansion valve

Before passing through the condenser

After passing through the expansion or throttle valve

20. 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.

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21. 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

22. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

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

In 1 hour

In 24 hours

In 12 hours

In 1 minute

24. 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)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

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

Dew point temperature

Dry bulb temperature

Wet bulb temperature

Relative humidity

26. 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

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

R-12

Ammonia

Sulphur dioxide

Carbon dioxide

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

Reduce compressor discharge temperature

Reduce compressor overheating

Increase cooling effect

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

29. The evaporator used in household refrigerators is

Defrosting evaporator

Non-frosting evaporator

None of these

Frosting evaporator

30. 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

1.25

0.5

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31. The desirable property of a refrigerant is

High latent heat of vaporisation

Low boiling point

All of these

High critical temperature

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

Refrigerating efficiency

Relative coefficient of performance

Coefficient of performance of heat pump

Coefficient of performance of refrigeration

33. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

None of these

34. The refrigerant for a refrigerator should have

High sensible heat

High latent heat

High total heat

Low latent heat

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

Reduces power consumption

Increases power consumption

Improves C.O.P. of the system

Increases heat transfer

36. 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

37. Degree of saturation or percentage humidity is

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

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

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

75%

25%

50%

10%

39. The bypass factor for a cooling coil

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

Remains unchanged with increase in velocity of air passing through it

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

Generator

Absorber, generator and liquid pump

Absorber and generator

Liquid pump

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41. 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

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

1 m3 of water

1 kg of wet air

1 m3 of dry air

1 kg of dry air

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

Brass

Steel

Copper

Aluminium

44. Chaperon equation is applicable for registration at

Saturation point of vapour

Triple point

Sublimation temperature

Saturation point of liquid

45. 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

Wet bulb temperature

Dew point temperature

Refrigeration & Air-Conditioning Practice Set-5

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