Refrigeration & Air-Conditioning Practice Set-5

July 7, 2021

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

Carnot cycle

Vapour absorption

Electrolux refrigerator

Vapour compression

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

Generator

Absorber, generator and liquid pump

Liquid pump

Absorber and generator

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

Dew point temperature

Wet bulb temperature

Relative humidity

Dry bulb temperature

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

Vertical and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

5. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

None of these

Superheated vapour refrigerant

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

Less than

Equal to

Greater than

None of these

7. 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

Dry bulb temperature

None of these

Wet bulb temperature

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

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the expansion valve

After passing through the condenser

9. 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 m3 of dry air

1 kg of wet air

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

Improves C.O.P. of the system

Increases power consumption

Reduces power consumption

Increases heat transfer

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

Power per TR is low

System has high C.O.P.

Mass of the refrigeration equipment is low

Mass of refrigerant circulated in the system is low

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

Vapour absorption cycle

None of these

Vapour compression cycle

Air refrigeration cycle

13. 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

14. 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

0.5

1.25

0.25

15. The power per tonne of refrigeration is

3.5/C.O.P.

3.5 × C.O.P.

None of these

C.O.P/3.5

16. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant pressure lines

Constant total heat lines

Constant temperature lines

17. 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

Remains unchanged with increase in velocity of air passing through it

Decreases with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

18. 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

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

Copper

Aluminium

Steel

Brass

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

Carbon dioxide

Sulphur dioxide

Ammonia

R-12

22. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

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

More than

None of these

Less than

Equal to

24. Air refrigeration cycle is used in

Domestic refrigerators

Commercial refrigerators

Gas liquefaction

Air conditioning

25. 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)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

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

1 m3 of dry air

1 m3 of water

1 kg of wet air

1 kg of dry air

27. Ammonia is

Highly toxic and inflammable

Non-inflammable

Non-toxic

Toxic and non-inflammable

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

75%

10%

50%

25%

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

210 kJ/ min

420 kJ/ min

21 kJ/ min

840 kJ/ min

30. The evaporator used in household refrigerators is

None of these

Frosting evaporator

Non-frosting evaporator

Defrosting evaporator

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31. The refrigerant for a refrigerator should have

High sensible heat

High total heat

High latent heat

Low latent heat

32. The desirable property of a refrigerant is

High latent heat of vaporisation

All of these

High critical temperature

Low boiling point

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

Before entering the compressor

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

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

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

Reduce compressor overheating

Increase cooling effect

Reduce compressor discharge temperature

35. Chaperon equation is applicable for registration at

Saturation point of liquid

Triple point

Sublimation temperature

Saturation point of vapour

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

Ammonia vapours to weak solution

Strong solution to weak solution

Strong solution to ammonia vapour

Weak solution to strong solution

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

Simple air cooling system

Bootstrap air cooling system

Reduced ambient air cooling system

Regenerative air cooling system

38. 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

39. 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)]

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

Reversed Joule cycle

Reversed Otto cycle

Reversed Brayton cycle

Reversed Carnot cycle

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41. The specific humidity during cooling and dehumidification

None of these

Remains constant

Increases

Decreases

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

Curved line

Inclined line

Vertical line

Horizontal line

43. Degree of saturation or percentage humidity is

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

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

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

In 24 hours

In 1 hour

In 12 hours

In 1 minute

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

Aluminium

Copper

Brass

Steel

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Refrigeration & Air-Conditioning Practice Set-5

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