Refrigeration & Air-Conditioning Practice Set-5

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

Regenerative air cooling system

Simple air cooling system

Reduced ambient air cooling system

Bootstrap air cooling system

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

Reduces power consumption

Increases heat transfer

Improves C.O.P. of the system

Increases power consumption

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

25%

50%

75%

10%

4. The bypass factor for a cooling coil

Increases with increase in velocity of air passing through it

Remains unchanged 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

5. The temperature of air recorded by a thermometer, when its bulb is surrounded by a wet cloth exposed to the air, is called

Dew point temperature

Wet bulb temperature

Dry bulb temperature

None of these

6. 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

7. Air refrigeration cycle is used in

Commercial refrigerators

Air conditioning

Gas liquefaction

Domestic refrigerators

8. The refrigerant for a refrigerator should have

High latent heat

Low latent heat

High sensible heat

High total heat

9. 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

Before entering the compressor

After passing through the condenser

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

Less than

More than

None of these

Equal to

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

Steel

Aluminium

Brass

Copper

12. 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)]

13. 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

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

Power per TR is low

Mass of refrigerant circulated in the system is low

System has high C.O.P.

Mass of the refrigeration equipment is low

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

Vapour absorption

Vapour compression

Carnot cycle

Electrolux refrigerator

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

Steel

Brass

Copper

Aluminium

17. Chaperon equation is applicable for registration at

Sublimation temperature

Saturation point of liquid

Saturation point of vapour

Triple point

18. The evaporator used in household refrigerators is

Non-frosting evaporator

Frosting evaporator

None of these

Defrosting evaporator

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

1 kg of dry air

1 m3 of dry air

1 kg of wet air

1 m3 of water

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

Weak solution to strong solution

Ammonia vapours to weak solution

Strong solution to ammonia vapour

Strong solution to weak solution

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

Curved line

Vertical line

Inclined line

Horizontal line

22. The power per tonne of refrigeration is

None of these

3.5 × C.O.P.

C.O.P/3.5

3.5/C.O.P.

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

Increase cooling effect

Reduce compressor discharge temperature

Reduce compressor overheating

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

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

21 kJ/ min

420 kJ/ min

840 kJ/ min

210 kJ/ min

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

Absorber and generator

Absorber, generator and liquid pump

Liquid pump

Generator

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

1 kg of wet air

1 m3 of dry air

1 m3 of water

1 kg of dry air

27. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant pressure lines

Constant temperature lines

Constant entropy lines

28. Ammonia is

Non-inflammable

Toxic and non-inflammable

Highly toxic and inflammable

Non-toxic

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

Dew point temperature

Dry bulb temperature

Relative humidity

Wet bulb temperature

30. 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 24 hours

In 1 hour

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31. 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.

32. 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

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

Before entering the expansion valve

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

34. 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

Refrigerating efficiency

Coefficient of performance of heat pump

35. 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

36. 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)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

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

Reversed Brayton cycle

Reversed Joule cycle

Reversed Carnot cycle

Reversed Otto cycle

38. The specific humidity during cooling and dehumidification

Increases

None of these

Remains constant

Decreases

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

Ammonia

Carbon dioxide

Sulphur dioxide

R-12

40. 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

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41. 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

42. The refrigerant supplied to a compressor must be

None of these

Superheated vapour refrigerant

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

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

Water and water

Water and lithium bromide

Ammonia and lithium bromide

Ammonia and water

44. The desirable property of a refrigerant is

All of these

Low boiling point

High critical temperature

High latent heat of vaporisation

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

Less than

Equal to

Greater than

None of these

Refrigeration & Air-Conditioning Practice Set-5

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