Refrigeration & Air-Conditioning Practice Set-5

July 7, 2021

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

Regenerative air cooling system

Bootstrap air cooling system

Simple air cooling system

Reduced ambient air cooling system

2. 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

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

50%

10%

75%

25%

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

Curved lines

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

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

Carbon dioxide

Ammonia

Sulphur dioxide

R-12

6. The evaporator used in household refrigerators is

None of these

Defrosting evaporator

Frosting evaporator

Non-frosting evaporator

7. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant total heat lines

Constant pressure lines

Constant temperature lines

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

Liquid pump

Absorber and generator

Generator

Absorber, generator and liquid pump

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

Aluminium

Brass

Copper

Steel

10. 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

0.5

0.25

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

Coefficient of performance of heat pump

Relative coefficient of performance

Coefficient of performance of refrigeration

Refrigerating efficiency

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

420 kJ/ min

21 kJ/ min

840 kJ/ min

210 kJ/ min

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

More than

Less than

Equal to

None of these

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

None of these

Air refrigeration cycle

Vapour compression cycle

Vapour absorption cycle

15. The refrigerant for a refrigerator should have

High sensible heat

High latent heat

Low latent heat

High total heat

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

Inclined line

Horizontal line

Curved line

Vertical line

17. 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

Dry bulb temperature

Wet bulb temperature

18. Air refrigeration cycle is used in

Commercial refrigerators

Air conditioning

Gas liquefaction

Domestic refrigerators

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

Reversed Otto cycle

Reversed Carnot cycle

Reversed Joule cycle

Reversed Brayton cycle

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

Greater than

Equal to

None of these

Less than

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21. 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

Remains unchanged with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

22. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

None of these

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

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

1 m3 of water

1 kg of wet air

1 kg of dry air

1 m3 of dry air

24. 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)

25. 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

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

1 kg of dry air

1 kg of wet air

1 m3 of water

1 m3 of dry air

27. In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = Bypass factor)

B.P.F. - 1

1 - B. P.F.

1 + B.P.F.

1/ B.P.F.

28. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

Small displacements and low condensing pressures

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

Brass

Copper

Aluminium

Steel

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

Reduces power consumption

Improves C.O.P. of the system

Increases power consumption

Increases heat transfer

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31. The desirable property of a refrigerant is

High critical temperature

All of these

Low boiling point

High latent heat of vaporisation

32. The power per tonne of refrigeration is

3.5/C.O.P.

None of these

C.O.P/3.5

3.5 × C.O.P.

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

Increase cooling effect

Reduce compressor overheating

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

Reduce compressor discharge temperature

34. The specific humidity during cooling and dehumidification

None of these

Decreases

Increases

Remains constant

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

After passing through the condenser

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

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

Strong solution to weak solution

Weak solution to strong solution

Ammonia vapours to weak solution

Strong solution to ammonia vapour

37. Degree of saturation or percentage humidity is

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 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 mass of water vapour present in 1 kg of dry air

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

Dry bulb temperature

Relative humidity

Dew point temperature

Wet bulb temperature

39. 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

Power per TR is low

System has high C.O.P.

40. 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)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

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41. Ammonia is

Highly toxic and inflammable

Toxic and non-inflammable

Non-toxic

Non-inflammable

42. Chaperon equation is applicable for registration at

Triple point

Saturation point of vapour

Saturation point of liquid

Sublimation temperature

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

In 1 hour

In 1 minute

In 24 hours

In 12 hours

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

Before passing through the condenser

After passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

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

Electrolux refrigerator

Vapour compression

Carnot cycle

Vapour absorption

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Refrigeration & Air-Conditioning Practice Set-5

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