Refrigeration & Air-Conditioning Practice Set-5

July 7, 2021

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1. 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

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

Reduce compressor overheating

Increase cooling effect

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

Reduce compressor discharge temperature

3. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

None of these

Superheated vapour refrigerant

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

Refrigerating efficiency

Coefficient of performance of refrigeration

Relative coefficient of performance

Coefficient of performance of heat pump

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

Dry bulb temperature

Relative humidity

Dew point temperature

Wet bulb temperature

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

Wet bulb temperature

Dew point temperature

Dry bulb temperature

None of these

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

Vertical line

Horizontal line

Inclined line

Curved line

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

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

After passing through the condenser

9. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant temperature lines

Constant entropy lines

Constant total heat lines

10. The specific humidity during cooling and dehumidification

None of these

Remains constant

Decreases

Increases

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

Curved lines

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

Horizontal and uniformly spaced

12. 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.

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

Steel

Brass

Aluminium

Copper

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

420 kJ/ min

21 kJ/ min

840 kJ/ min

210 kJ/ min

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

After passing through the expansion or throttle valve

Before entering the expansion valve

After passing through the condenser

Before passing through the condenser

16. The evaporator used in household refrigerators is

Frosting evaporator

Non-frosting evaporator

Defrosting evaporator

None of these

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

75%

50%

25%

10%

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

1 kg of dry air

1 kg of wet air

1 m3 of dry air

1 m3 of water

19. Chaperon equation is applicable for registration at

Triple point

Saturation point of vapour

Sublimation temperature

Saturation point of liquid

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

Improves C.O.P. of the system

Reduces power consumption

Increases power consumption

Increases heat transfer

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21. The refrigerant for a refrigerator should have

Low latent heat

High total heat

High latent heat

High sensible heat

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

Reversed Brayton cycle

Reversed Otto cycle

Reversed Joule cycle

Reversed Carnot cycle

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

1 kg of wet air

1 kg of dry air

1 m3 of wet air

1 m3 of dry air

24. Air refrigeration cycle is used in

Gas liquefaction

Air conditioning

Domestic refrigerators

Commercial refrigerators

25. Degree of saturation or percentage humidity is

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

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

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

Power per TR is low

Mass of the refrigeration equipment is low

System has high C.O.P.

Mass of refrigerant circulated in the system is low

27. 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

28. 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)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

29. The desirable property of a refrigerant is

High latent heat of vaporisation

All of these

High critical temperature

Low boiling point

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

None of these

Greater than

Less than

Equal to

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

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

More than

None of these

Less than

Equal to

33. 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 (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

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

Absorber and generator

Generator

Liquid pump

Absorber, generator and liquid pump

35. 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

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

Air refrigeration cycle

Vapour compression cycle

Vapour absorption cycle

None of these

37. 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

38. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

Large displacements and low condensing pressures

39. 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?

1.25

0.25

0.8

0.5

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

Carnot cycle

Vapour absorption

Vapour compression

Electrolux refrigerator

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41. Ammonia is

Highly toxic and inflammable

Non-inflammable

Toxic and non-inflammable

Non-toxic

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

Brass

Copper

Aluminium

Steel

43. 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.

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

Ammonia and water

Water and water

Water and lithium bromide

Ammonia and lithium bromide

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

In 12 hours

In 24 hours

In 1 hour

In 1 minute

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Refrigeration & Air-Conditioning Practice Set-5

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