Refrigeration & Air-Conditioning Practice Set-5

July 7, 2021

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

Dew point temperature

Wet bulb temperature

Relative humidity

Dry bulb temperature

2. 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)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

3. The desirable property of a refrigerant is

Low boiling point

High critical temperature

All of these

High latent heat of vaporisation

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

840 kJ/ min

21 kJ/ min

210 kJ/ min

420 kJ/ min

5. Degree of saturation or percentage humidity is

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

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

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

None of these

Air refrigeration cycle

Vapour absorption cycle

Vapour compression cycle

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

1 m3 of dry air

1 kg of wet air

1 kg of dry air

1 m3 of water

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

Carnot cycle

Vapour absorption

Vapour compression

Electrolux refrigerator

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

Copper

Aluminium

Brass

Steel

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

Before entering the compressor

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

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11. 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

1.25

0.25

12. The specific humidity during cooling and dehumidification

None of these

Increases

Remains constant

Decreases

13. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

Dry saturated liquid refrigerant

None of these

A mixture of liquid and vapour refrigerant

14. 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

Increases with increase in velocity of air passing through it

Decreases with increase in velocity of air passing through it

Remains unchanged with increase in velocity of air passing through it

15. 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

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

In 12 hours

In 1 minute

In 24 hours

In 1 hour

17. 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

18. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant temperature lines

Constant total heat lines

Constant entropy lines

19. 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

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

Water and water

Water and lithium bromide

Ammonia and water

Ammonia and lithium bromide

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

Inclined line

Curved line

Horizontal line

Vertical line

22. 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

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

R-12

Carbon dioxide

Sulphur dioxide

Ammonia

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

Bootstrap air cooling system

Regenerative air cooling system

Reduced ambient air cooling system

Simple air cooling system

25. The refrigerant for a refrigerator should have

Low latent heat

High total heat

High sensible heat

High latent heat

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

1 kg of wet air

1 m3 of wet air

1 m3 of dry air

1 kg of dry air

27. Ammonia is

Toxic and non-inflammable

Highly toxic and inflammable

Non-inflammable

Non-toxic

28. 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

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

Absorber, generator and liquid pump

Absorber and generator

Liquid pump

Generator

30. Air refrigeration cycle is used in

Air conditioning

Domestic refrigerators

Gas liquefaction

Commercial refrigerators

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31. 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)

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

32. The reciprocating refrigerant compressors are very suitable for

Small displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Large displacements and high condensing pressures

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

Aluminium

Steel

Brass

Copper

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

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the expansion valve

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

Reversed Otto cycle

Reversed Brayton cycle

Reversed Carnot cycle

Reversed Joule cycle

36. 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 discharge temperature

Increase cooling effect

Reduce compressor overheating

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

Less than

Greater than

Equal to

None of these

38. Chaperon equation is applicable for registration at

Saturation point of liquid

Triple point

Saturation point of vapour

Sublimation temperature

39. The evaporator used in household refrigerators is

Frosting evaporator

Non-frosting evaporator

None of these

Defrosting evaporator

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

More than

Less than

None of these

Equal to

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41. 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

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

75%

25%

10%

50%

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

Coefficient of performance of heat pump

Coefficient of performance of refrigeration

Refrigerating efficiency

Relative coefficient of performance

44. The power per tonne of refrigeration is

None of these

C.O.P/3.5

3.5/C.O.P.

3.5 × C.O.P.

45. 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

None of these

Dry bulb temperature

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Refrigeration & Air-Conditioning Practice Set-5

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