Refrigeration & Air-Conditioning Practice Set-5

July 7, 2021

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

Simple air cooling system

Regenerative 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 power consumption

Improves C.O.P. of the system

Increases heat transfer

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

Dry bulb temperature

Wet bulb temperature

None of these

Dew point temperature

4. Degree of saturation or percentage humidity is

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

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

Curved lines

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

Vertical and uniformly spaced

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

Dew point temperature

Relative humidity

Dry bulb temperature

Wet bulb temperature

7. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant total heat lines

Constant entropy lines

Constant pressure lines

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

75%

50%

10%

25%

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

Steel

Copper

Brass

Aluminium

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

Steel

Copper

Aluminium

Brass

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11. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

Superheated vapour refrigerant

None of these

A mixture of liquid and vapour refrigerant

12. The desirable property of a refrigerant is

All of these

High latent heat of vaporisation

Low boiling point

High critical temperature

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

Inclined line

Horizontal line

Curved line

Vertical line

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

21 kJ/ min

420 kJ/ min

210 kJ/ min

840 kJ/ min

15. Air refrigeration cycle is used in

Commercial refrigerators

Gas liquefaction

Air conditioning

Domestic refrigerators

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

Reversed Otto cycle

Reversed Brayton cycle

Reversed Joule cycle

Reversed Carnot cycle

17. 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.

1 + B.P.F.

B.P.F. - 1

18. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

19. 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)

20. Ammonia is

Toxic and non-inflammable

Non-inflammable

Non-toxic

Highly toxic and inflammable

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

Vapour compression cycle

Vapour absorption cycle

Air refrigeration cycle

None of these

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

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

Before entering the expansion valve

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

Equal to

None of these

More than

Less than

24. Chaperon equation is applicable for registration at

Triple point

Saturation point of liquid

Saturation point of vapour

Sublimation temperature

25. The refrigerant for a refrigerator should have

High total heat

High latent heat

Low latent heat

High sensible heat

26. 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

27. 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?

0.5

0.8

0.25

1.25

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

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the compressor

29. 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 (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

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

1 m3 of wet air

1 kg of dry air

1 kg of wet air

1 m3 of dry air

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

R-12

Ammonia

Sulphur dioxide

Carbon dioxide

32. The evaporator used in household refrigerators is

Defrosting evaporator

Frosting evaporator

None of these

Non-frosting evaporator

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

1 kg of wet air

1 kg of dry air

1 m3 of dry air

1 m3 of water

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

Ammonia and water

Water and lithium bromide

Ammonia and lithium bromide

Water and water

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

Reduce compressor overheating

Reduce compressor discharge temperature

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

Increase cooling effect

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

Less than

Equal to

Greater than

None of these

37. 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

Coefficient of performance of heat pump

Refrigerating efficiency

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

Vapour compression

Vapour absorption

Electrolux refrigerator

Carnot cycle

39. The power per tonne of refrigeration is

None of these

3.5 × C.O.P.

3.5/C.O.P.

C.O.P/3.5

40. The specific humidity during cooling and dehumidification

Increases

Decreases

None of these

Remains constant

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

Mass of refrigerant circulated in the system is low

System has high C.O.P.

Power per TR is low

Mass of the refrigeration equipment is low

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

Liquid pump

Generator

Absorber, generator and liquid pump

Absorber and generator

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

In 1 minute

In 24 hours

In 1 hour

In 12 hours

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

Strong solution to ammonia vapour

Weak solution to strong solution

Strong solution to weak solution

Ammonia vapours to weak solution

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

Decreases with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

Remains unchanged with increase in velocity of air passing through it

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Refrigeration & Air-Conditioning Practice Set-5

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