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?

0.25

1.25

0.5

0.8

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

Before entering the expansion valve

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

3. 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

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

In 24 hours

In 1 minute

In 1 hour

In 12 hours

5. The desirable property of a refrigerant is

High critical temperature

High latent heat of vaporisation

All of these

Low boiling point

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

1 kg of dry air

1 m3 of water

1 m3 of dry air

1 kg of wet air

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

Mass of refrigerant circulated in the system is low

System has high C.O.P.

Power per TR is low

Mass of the refrigeration equipment is low

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 - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

9. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant temperature lines

Constant pressure lines

Constant total heat lines

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

None of these

Less than

More than

Equal to

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11. 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

Ammonia vapours to weak solution

Strong solution to weak solution

12. 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

13. 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

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

Aluminium

Brass

Steel

Copper

15. 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

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

Vapour absorption

Vapour compression

Electrolux refrigerator

Carnot cycle

17. 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

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

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

Curved lines

Horizontal and uniformly spaced

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.

B.P.F. - 1

1 + B.P.F.

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

420 kJ/ min

840 kJ/ min

210 kJ/ min

21 kJ/ min

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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. The refrigerant for a refrigerator should have

High total heat

High sensible heat

Low latent heat

High latent heat

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

Greater than

Equal to

Less than

None of these

24. The evaporator used in household refrigerators is

Frosting evaporator

Defrosting evaporator

Non-frosting evaporator

None of these

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

Wet bulb temperature

Relative humidity

Dew point temperature

Dry bulb temperature

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

50%

75%

25%

10%

27. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

None of these

Superheated vapour refrigerant

28. The specific humidity during cooling and dehumidification

Remains constant

Increases

None of these

Decreases

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

1 m3 of water

1 kg of dry air

1 kg of wet air

1 m3 of dry air

30. 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

Dew point temperature

Wet bulb temperature

Dry bulb temperature

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

Horizontal line

Inclined line

Curved line

Vertical line

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

R-12

Carbon dioxide

Sulphur dioxide

Ammonia

33. Ammonia is

Non-toxic

Non-inflammable

Toxic and non-inflammable

Highly toxic and inflammable

34. The bypass factor for a cooling coil

Decreases 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

Remains unchanged with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

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

Reduce compressor overheating

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

Increase cooling effect

Reduce compressor discharge temperature

36. Air refrigeration cycle is used in

Domestic refrigerators

Air conditioning

Gas liquefaction

Commercial refrigerators

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

Absorber, generator and liquid pump

Generator

Liquid pump

Absorber and generator

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

Brass

Copper

Steel

Aluminium

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

Vapour absorption cycle

Air refrigeration cycle

None of these

Vapour compression cycle

40. 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

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

After passing through the condenser

Before entering the compressor

Before passing through the condenser

After passing through the expansion or throttle valve

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

1 m3 of dry air

1 kg of dry air

1 m3 of wet air

1 kg of wet air

43. Chaperon equation is applicable for registration at

Sublimation temperature

Triple point

Saturation point of vapour

Saturation point of liquid

44. 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 m³ of dry air

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

45. 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)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

Refrigeration & Air-Conditioning Practice Set-5

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