Refrigeration & Air-Conditioning Practice Set-5

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

Before passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

After passing through the condenser

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

Inclined line

Curved line

Horizontal line

Vertical line

3. 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

4. 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

5. 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)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

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

Regenerative air cooling system

Reduced ambient air cooling system

Simple air cooling system

Bootstrap air cooling system

7. The desirable property of a refrigerant is

High critical temperature

All of these

Low boiling point

High latent heat of vaporisation

8. 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

9. Ammonia is

Highly toxic and inflammable

Non-toxic

Toxic and non-inflammable

Non-inflammable

10. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

Large displacements and low condensing pressures

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11. 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)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

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

Ammonia and water

Water and water

Water and lithium bromide

Ammonia and lithium bromide

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

Dry bulb temperature

Dew point temperature

Wet bulb temperature

Relative humidity

14. 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

Wet bulb temperature

Dry bulb temperature

None of these

15. Chaperon equation is applicable for registration at

Saturation point of liquid

Saturation point of vapour

Sublimation temperature

Triple point

16. 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.

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

None of these

More than

Equal to

Less than

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

Before entering the compressor

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

19. The refrigerant supplied to a compressor must be

None of these

Superheated vapour refrigerant

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

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

1 kg of wet air

1 m3 of dry air

1 m3 of water

1 kg of dry air

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

Strong solution to ammonia vapour

Ammonia vapours to weak solution

Strong solution to weak solution

Weak solution to strong solution

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

Air refrigeration cycle

None of these

Vapour absorption cycle

Vapour compression cycle

23. Air refrigeration cycle is used in

Commercial refrigerators

Air conditioning

Domestic refrigerators

Gas liquefaction

24. 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 dry air

1 m3 of wet air

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

210 kJ/ min

420 kJ/ min

21 kJ/ min

840 kJ/ min

26. 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

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

Curved lines

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

28. The power per tonne of refrigeration is

3.5 × C.O.P.

None of these

C.O.P/3.5

3.5/C.O.P.

29. 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

30. The specific humidity during cooling and dehumidification

Remains constant

None of these

Increases

Decreases

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31. 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 overheating

Reduce compressor discharge temperature

Increase cooling effect

32. The evaporator used in household refrigerators is

Frosting evaporator

Defrosting evaporator

None of these

Non-frosting evaporator

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

Mass of the refrigeration equipment is low

System has high C.O.P.

Power per TR is low

Mass of refrigerant circulated in the system is low

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

Improves C.O.P. of the system

Increases power consumption

Reduces power consumption

Increases heat transfer

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

Copper

Steel

Brass

Aluminium

36. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant pressure lines

Constant entropy lines

Constant total heat lines

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. The refrigerant for a refrigerator should have

High latent heat

High sensible heat

High total heat

Low latent heat

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

75%

10%

25%

50%

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

Sulphur dioxide

Carbon dioxide

Ammonia

R-12

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

Carnot cycle

Vapour absorption

Electrolux refrigerator

Vapour compression

42. 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

Increases with increase in velocity of air passing through it

Remains unchanged with increase in velocity of air passing through it

Decreases with increase in velocity of air passing through it

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

Reversed Carnot cycle

Reversed Brayton cycle

Reversed Joule cycle

Reversed Otto cycle

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

Greater than

None of these

Less than

Equal to

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

Copper

Steel

Aluminium

Brass

Refrigeration & Air-Conditioning Practice Set-5

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