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

10%

75%

50%

25%

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

Less than

None of these

Greater than

Equal to

4. 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 (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

5. The evaporator used in household refrigerators is

Defrosting evaporator

Frosting evaporator

Non-frosting evaporator

None of these

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

Vapour absorption

Electrolux refrigerator

Carnot cycle

Vapour compression

7. 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

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

Brass

Copper

Aluminium

Steel

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

In 24 hours

In 1 hour

In 12 hours

In 1 minute

10. 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 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

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

1 kg of wet air

1 kg of dry air

1 m3 of water

1 m3 of dry air

12. 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

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

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

System has high C.O.P.

Power per TR is low

14. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

None of these

15. 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

Before entering the compressor

After passing through the condenser

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

Relative coefficient of performance

Coefficient of performance of refrigeration

Refrigerating efficiency

Coefficient of performance of heat pump

17. The desirable property of a refrigerant is

Low boiling point

High latent heat of vaporisation

High critical temperature

All of these

18. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

Small displacements and low condensing pressures

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

Reduces power consumption

Increases heat transfer

Increases power consumption

Improves C.O.P. of the system

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

1 kg of dry air

1 m3 of dry air

1 m3 of water

1 kg of wet air

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

Absorber and generator

Liquid pump

Absorber, generator and liquid pump

Generator

22. 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

23. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant total heat lines

Constant entropy lines

Constant temperature lines

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

Strong solution to weak solution

Strong solution to ammonia vapour

Weak solution to strong solution

Ammonia vapours to weak solution

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

Horizontal and non-uniformly spaced

Curved lines

Vertical and uniformly spaced

Horizontal and uniformly spaced

26. Ammonia is

Highly toxic and inflammable

Non-toxic

Non-inflammable

Toxic and non-inflammable

27. The specific humidity during cooling and dehumidification

None of these

Remains constant

Increases

Decreases

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

More than

None of these

Less than

Equal to

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

Copper

Aluminium

Steel

Brass

30. The refrigerant for a refrigerator should have

High sensible heat

High latent heat

High total heat

Low latent heat

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

Sulphur dioxide

R-12

Ammonia

Carbon dioxide

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

Vapour compression cycle

Vapour absorption cycle

None of these

Air refrigeration cycle

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

Reversed Otto cycle

Reversed Joule cycle

Reversed Brayton cycle

Reversed Carnot cycle

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

Water and lithium bromide

Ammonia and lithium bromide

Ammonia and water

Water and water

35. Chaperon equation is applicable for registration at

Triple point

Saturation point of vapour

Saturation point of liquid

Sublimation temperature

36. 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

Remains unchanged with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

Decreases with increase in velocity of air passing through it

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

1 kg of dry air

1 kg of wet air

1 m3 of wet air

1 m3 of dry air

38. 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

39. 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

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

Horizontal line

Inclined line

Curved line

Vertical line

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41. Air refrigeration cycle is used in

Air conditioning

Commercial refrigerators

Gas liquefaction

Domestic refrigerators

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

Increase cooling effect

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

Reduce compressor discharge temperature

Reduce compressor overheating

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

21 kJ/ min

210 kJ/ min

420 kJ/ min

840 kJ/ min

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

Relative humidity

Dry bulb temperature

Dew point temperature

Wet bulb temperature

45. 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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

Refrigeration & Air-Conditioning Practice Set-5

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