Refrigeration & Air-Conditioning Practice Set-5

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1. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

None of these

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

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

Vapour compression

Carnot cycle

Electrolux refrigerator

Vapour absorption

3. 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

4. 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)

5. 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

0.8

1.25

0.5

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

10%

50%

75%

25%

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

Increases power consumption

Improves C.O.P. of the system

Increases heat transfer

Reduces power consumption

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

1 + B.P.F.

B.P.F. - 1

1 - B. P.F.

1/ B.P.F.

9. The desirable property of a refrigerant is

High latent heat of vaporisation

All of these

High critical temperature

Low boiling point

10. Ammonia is

Non-toxic

Toxic and non-inflammable

Highly toxic and inflammable

Non-inflammable

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

Liquid pump

Absorber and generator

Absorber, generator and liquid pump

Generator

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

Refrigerating efficiency

Coefficient of performance of heat pump

Coefficient of performance of refrigeration

Relative coefficient of performance

13. Chaperon equation is applicable for registration at

Triple point

Saturation point of liquid

Saturation point of vapour

Sublimation temperature

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

None of these

Air refrigeration cycle

Vapour compression cycle

Vapour absorption cycle

15. The bypass factor for a cooling coil

Remains unchanged with increase in velocity of air passing through it

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

Increases with increase in velocity of air passing through it

16. The specific humidity during cooling and dehumidification

Increases

None of these

Decreases

Remains constant

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

Weak solution to strong solution

Ammonia vapours to weak solution

Strong solution to weak solution

Strong solution to ammonia vapour

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

After passing through the expansion or throttle valve

Before entering the compressor

Before passing through the condenser

After passing through the condenser

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

1 m3 of dry air

1 kg of wet air

1 kg of dry air

1 m3 of water

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

In 1 minute

In 12 hours

In 24 hours

In 1 hour

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

Power per TR is low

Mass of refrigerant circulated in the system is low

System has high C.O.P.

Mass of the refrigeration equipment is low

22. Degree of saturation or percentage humidity is

The mass of water vapour present in 1 m³ 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 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

23. 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

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

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

Before passing through the condenser

25. The evaporator used in household refrigerators is

Non-frosting evaporator

Frosting evaporator

Defrosting evaporator

None of these

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

Dry bulb temperature

Relative humidity

Wet bulb temperature

Dew point temperature

27. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

28. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant temperature lines

Constant entropy lines

Constant pressure lines

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

Aluminium

Brass

Copper

Steel

30. 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)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

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

Inclined line

Horizontal line

Vertical line

Curved line

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

1 m3 of dry air

1 kg of wet air

1 kg of dry air

1 m3 of wet air

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

Brass

Copper

Steel

Aluminium

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

Less than

Equal to

None of these

Greater than

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

Reduce compressor overheating

Increase cooling effect

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

Reduce compressor discharge temperature

36. 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

37. The refrigerant for a refrigerator should have

Low latent heat

High sensible heat

High total heat

High latent heat

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

420 kJ/ min

210 kJ/ min

21 kJ/ min

840 kJ/ min

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

Water and water

Ammonia and water

Ammonia and lithium bromide

Water and lithium bromide

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

Less than

None of these

More than

Equal to

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

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

Curved lines

Vertical and uniformly spaced

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

1 kg of wet air

1 m3 of water

1 kg of dry air

1 m3 of dry air

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

Ammonia

R-12

Carbon dioxide

Sulphur dioxide

44. Air refrigeration cycle is used in

Domestic refrigerators

Air conditioning

Gas liquefaction

Commercial refrigerators

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

Reversed Joule cycle

Reversed Otto cycle

Reversed Brayton cycle

Reversed Carnot cycle

Refrigeration & Air-Conditioning Practice Set-5

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