Refrigeration & Air-Conditioning Practice Set-5

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1. 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

0.25

0.5

1.25

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

System has high C.O.P.

Power per TR is low

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

3. In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = Bypass factor)

B.P.F. - 1

1 - B. P.F.

1/ B.P.F.

1 + B.P.F.

4. The specific humidity during cooling and dehumidification

Increases

Decreases

Remains constant

None of these

5. Chaperon equation is applicable for registration at

Sublimation temperature

Saturation point of liquid

Saturation point of vapour

Triple point

6. The refrigerant for a refrigerator should have

High total heat

High latent heat

Low latent heat

High sensible heat

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

1 m3 of dry air

1 kg of dry air

1 kg of wet air

1 m3 of water

8. The evaporator used in household refrigerators is

Defrosting evaporator

Frosting evaporator

Non-frosting evaporator

None of these

9. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

Superheated vapour refrigerant

Dry saturated liquid refrigerant

None of these

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)

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

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

Horizontal line

Curved line

Inclined line

Vertical line

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

Reversed Brayton cycle

Reversed Otto cycle

Reversed Carnot cycle

Reversed Joule cycle

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

Brass

Aluminium

Copper

Steel

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

Absorber, generator and liquid pump

Liquid pump

Generator

Absorber and generator

15. The power per tonne of refrigeration is

C.O.P/3.5

3.5 × C.O.P.

3.5/C.O.P.

None of these

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

Bootstrap air cooling system

Regenerative air cooling system

Simple air cooling system

Reduced ambient air cooling system

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

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

18. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

Small displacements and low condensing pressures

19. 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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

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

Coefficient of performance of heat pump

Relative coefficient of performance

Coefficient of performance of refrigeration

Refrigerating efficiency

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

Increases power consumption

Reduces power consumption

Increases heat transfer

Improves C.O.P. of the system

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

In 1 minute

In 1 hour

In 12 hours

In 24 hours

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

Vapour compression cycle

Vapour absorption cycle

Air refrigeration cycle

None of these

24. Air refrigeration cycle is used in

Gas liquefaction

Domestic refrigerators

Air conditioning

Commercial refrigerators

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

Brass

Copper

Steel

Aluminium

26. 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

27. Ammonia is

Non-inflammable

Toxic and non-inflammable

Non-toxic

Highly toxic and inflammable

28. The desirable property of a refrigerant is

All of these

Low boiling point

High latent heat of vaporisation

High critical temperature

29. 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

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

21 kJ/ min

210 kJ/ min

840 kJ/ min

420 kJ/ min

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

Vertical and uniformly spaced

Horizontal and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

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

Equal to

More than

Less than

None of these

33. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant entropy lines

Constant temperature lines

Constant pressure lines

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

Water and water

Water and lithium bromide

Ammonia and lithium bromide

Ammonia and water

35. 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 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

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

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

Relative humidity

Dew point temperature

Wet bulb temperature

Dry bulb temperature

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

Greater than

Equal to

None of these

Less than

38. 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

None of these

Dew point temperature

Dry bulb temperature

39. 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

40. 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

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

1 kg of dry air

1 m3 of dry air

1 kg of wet air

1 m3 of water

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

Before entering the expansion valve

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

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

75%

25%

50%

10%

44. 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

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

Vapour compression

Carnot cycle

Vapour absorption

Electrolux refrigerator

Refrigeration & Air-Conditioning Practice Set-5

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