Refrigeration & Air-Conditioning Practice Set-5

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1. Chaperon equation is applicable for registration at

Saturation point of vapour

Saturation point of liquid

Sublimation temperature

Triple point

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

Reversed Brayton cycle

Reversed Joule cycle

Reversed Otto cycle

Reversed Carnot cycle

3. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant entropy lines

Constant total heat lines

Constant temperature lines

4. 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

5. Ammonia is

Non-toxic

Highly toxic and inflammable

Toxic and non-inflammable

Non-inflammable

6. The power per tonne of refrigeration is

3.5 × C.O.P.

C.O.P/3.5

None of these

3.5/C.O.P.

7. 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

Dry bulb temperature

Dew point temperature

None of these

8. The refrigerant supplied to a compressor must be

None of these

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

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

Increases power consumption

Increases heat transfer

Reduces power consumption

Improves C.O.P. of the system

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

840 kJ/ min

210 kJ/ min

21 kJ/ min

420 kJ/ min

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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 off refrigerant is dry saturated vapour

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the compressor

Before passing through the condenser

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

Vapour compression cycle

Air refrigeration cycle

None of these

Vapour absorption cycle

14. The desirable property of a refrigerant is

High latent heat of vaporisation

All of these

High critical temperature

Low boiling point

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

Less than

None of these

Equal to

Greater than

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

17. 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

Decreases with increase in velocity of air passing through it

Remains unchanged with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

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

In 1 hour

In 24 hours

In 12 hours

In 1 minute

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

Bootstrap air cooling system

Simple air cooling system

Regenerative air cooling system

Reduced ambient air cooling system

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

Steel

Aluminium

Brass

Copper

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

Absorber, generator and liquid pump

Absorber and generator

Liquid pump

Generator

22. 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)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

23. 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 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

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

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

1 kg of wet air

1 kg of dry air

1 m3 of dry air

1 m3 of water

25. 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

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

50%

75%

10%

25%

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

Electrolux refrigerator

Vapour absorption

Carnot cycle

Vapour compression

28. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

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

Curved lines

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

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

Mass of the refrigeration equipment is low

Power per TR is low

Mass of refrigerant circulated in the system is low

System has high C.O.P.

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31. 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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

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

Relative humidity

Wet bulb temperature

Dew point temperature

Dry bulb temperature

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

Ammonia and lithium bromide

Water and water

Ammonia and water

Water and lithium bromide

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

Copper

Brass

Steel

Aluminium

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

Weak solution to strong solution

Strong solution to ammonia vapour

Strong solution to weak solution

Ammonia vapours to weak solution

36. The refrigerant for a refrigerator should have

Low latent heat

High total heat

High sensible heat

High latent heat

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

Curved line

Vertical line

Horizontal line

Inclined line

38. Air refrigeration cycle is used in

Gas liquefaction

Commercial refrigerators

Domestic refrigerators

Air conditioning

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

1 kg of dry air

1 m3 of dry air

1 m3 of wet air

1 kg of wet air

40. The evaporator used in household refrigerators is

Defrosting evaporator

Non-frosting evaporator

None of these

Frosting evaporator

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

After passing through the expansion or throttle valve

Before entering the expansion valve

After passing through the condenser

Before passing through the condenser

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

Less than

None of these

More than

Equal to

43. 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

44. The specific humidity during cooling and dehumidification

None of these

Remains constant

Decreases

Increases

45. 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.

Refrigeration & Air-Conditioning Practice Set-5

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