Refrigeration & Air-Conditioning Practice Set-5

July 7, 2021

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1. 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 - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

2. Air refrigeration cycle is used in

Gas liquefaction

Commercial refrigerators

Domestic refrigerators

Air conditioning

3. The bypass factor for a cooling coil

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

May increase or decrease with increase in velocity of air passing through it depending upon the condition of air entering

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

Ammonia and water

Water and lithium bromide

Water and water

Ammonia and lithium bromide

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

Equal to

None of these

More than

Less than

6. The reciprocating refrigerant compressors are very suitable for

Small displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and high condensing pressures

Large displacements and low condensing pressures

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

25%

75%

10%

50%

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

9. 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

10. 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 (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

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

Vapour compression

Carnot cycle

Electrolux refrigerator

Vapour absorption

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

None of these

Equal to

Less than

Greater than

13. 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

14. The specific humidity during cooling and dehumidification

Increases

None of these

Remains constant

Decreases

15. 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

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

1 m3 of dry air

1 kg of wet air

1 m3 of water

1 kg of dry air

17. 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

0.25

0.5

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

Wet bulb temperature

Dry bulb temperature

Relative humidity

Dew point temperature

19. 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

20. 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

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

1 kg of wet air

1 m3 of dry air

1 kg of dry air

1 m3 of wet air

22. 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 minute

In 1 hour

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

System has high C.O.P.

Mass of refrigerant circulated in the system is low

Power per TR is low

Mass of the refrigeration equipment is low

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

After passing through the expansion or throttle valve

Before entering the compressor

After passing through the condenser

Before passing through the condenser

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

Liquid pump

Absorber, generator and liquid pump

Absorber and generator

Generator

26. Chaperon equation is applicable for registration at

Saturation point of vapour

Sublimation temperature

Saturation point of liquid

Triple point

27. Ammonia is

Highly toxic and inflammable

Toxic and non-inflammable

Non-inflammable

Non-toxic

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

Horizontal and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

29. 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 mass of water vapour present in 1 kg 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

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

420 kJ/ min

210 kJ/ min

840 kJ/ min

21 kJ/ min

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

Copper

Brass

Aluminium

Steel

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

Curved line

Vertical line

Horizontal line

Inclined line

33. The refrigerant for a refrigerator should have

Low latent heat

High latent heat

High sensible heat

High total heat

34. 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

35. 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

36. The desirable property of a refrigerant is

All of these

High latent heat of vaporisation

High critical temperature

Low boiling point

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. The evaporator used in household refrigerators is

Frosting evaporator

None of these

Defrosting evaporator

Non-frosting evaporator

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

Steel

Brass

Copper

Aluminium

40. 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

Dry bulb temperature

Dew point temperature

Wet bulb temperature

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

Increase cooling effect

Reduce compressor discharge temperature

Reduce compressor overheating

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

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

Ammonia vapours to weak solution

Weak solution to strong solution

Strong solution to ammonia vapour

Strong solution to weak solution

43. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant entropy lines

Constant temperature lines

Constant total heat lines

44. 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

45. The power per tonne of refrigeration is

None of these

3.5/C.O.P.

C.O.P/3.5

3.5 × C.O.P.

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Refrigeration & Air-Conditioning Practice Set-5

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