Refrigeration & Air-Conditioning Practice Set-5

July 7, 2021

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1. 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

Increase cooling effect

Reduce compressor discharge temperature

Reduce compressor overheating

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

840 kJ/ min

420 kJ/ min

21 kJ/ min

210 kJ/ min

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

Brass

Steel

Aluminium

Copper

4. 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

5. 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.

B.P.F. - 1

1 - B. P.F.

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

Carnot cycle

Electrolux refrigerator

Vapour absorption

Vapour compression

7. 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 weak solution

Strong solution to ammonia vapour

8. 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)

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

Carbon dioxide

Sulphur dioxide

Ammonia

R-12

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

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

Before entering the compressor

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

Before passing through the condenser

After passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

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

More than

None of these

Equal to

Less than

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

Coefficient of performance of heat pump

Refrigerating efficiency

Relative coefficient of performance

Coefficient of performance of refrigeration

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

Water and water

Ammonia and water

Water and lithium bromide

Ammonia and lithium bromide

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

Generator

Absorber and generator

Liquid pump

Absorber, generator and liquid pump

16. The specific humidity during cooling and dehumidification

None of these

Decreases

Remains constant

Increases

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

Curved line

Horizontal line

Inclined line

Vertical line

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

Mass of the refrigeration equipment is low

Power per TR is low

Mass of refrigerant circulated in the system is low

System has high C.O.P.

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

1 kg of dry air

1 m3 of water

1 kg of wet air

1 m3 of dry air

20. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant entropy lines

Constant pressure lines

Constant temperature lines

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

Regenerative air cooling system

Simple air cooling system

Bootstrap air cooling system

Reduced ambient air cooling system

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

None of these

Equal to

Less than

Greater than

23. 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

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

Vapour compression cycle

None of these

Air refrigeration cycle

Vapour absorption cycle

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

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

Curved lines

26. 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

None of these

Wet bulb temperature

Dry bulb temperature

27. 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

0.5

0.25

0.8

28. 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.

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

50%

10%

75%

25%

30. Air refrigeration cycle is used in

Gas liquefaction

Commercial refrigerators

Domestic refrigerators

Air conditioning

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31. The refrigerant for a refrigerator should have

Low latent heat

High sensible heat

High latent heat

High total heat

32. The evaporator used in household refrigerators is

Non-frosting evaporator

Frosting evaporator

Defrosting evaporator

None of these

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

1 kg of dry air

1 m3 of dry air

1 m3 of wet air

1 kg of wet air

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

Copper

Aluminium

Steel

Brass

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

1 m3 of dry air

1 m3 of water

1 kg of dry air

1 kg of wet air

36. The desirable property of a refrigerant is

High critical temperature

All of these

High latent heat of vaporisation

Low boiling point

37. Ammonia is

Toxic and non-inflammable

Highly toxic and inflammable

Non-inflammable

Non-toxic

38. 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

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)

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

40. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and low condensing pressures

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

Wet bulb temperature

Dry bulb temperature

Relative humidity

Dew point temperature

42. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

Superheated vapour refrigerant

None of these

A mixture of liquid and vapour refrigerant

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

In 1 minute

In 24 hours

In 12 hours

In 1 hour

44. Chaperon equation is applicable for registration at

Sublimation temperature

Triple point

Saturation point of vapour

Saturation point of liquid

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

Improves C.O.P. of the system

Reduces power consumption

Increases heat transfer

Increases power consumption

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Refrigeration & Air-Conditioning Practice Set-5

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