Refrigeration & Air-Conditioning Practice Set-5

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1. Chaperon equation is applicable for registration at

Saturation point of liquid

Triple point

Saturation point of vapour

Sublimation temperature

2. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant temperature lines

Constant pressure lines

Constant entropy lines

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

Ammonia and lithium bromide

Ammonia and water

Water and lithium bromide

Water and water

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

Vapour absorption

Carnot cycle

Vapour compression

Electrolux refrigerator

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

10%

25%

75%

50%

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

Reversed Otto cycle

Reversed Joule cycle

Reversed Carnot cycle

Reversed Brayton cycle

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

Less than

Greater than

Equal to

None of these

8. Air refrigeration cycle is used in

Gas liquefaction

Commercial refrigerators

Domestic refrigerators

Air conditioning

9. 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

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

420 kJ/ min

21 kJ/ min

840 kJ/ min

210 kJ/ min

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11. The refrigerant for a refrigerator should have

High latent heat

High sensible heat

High total heat

Low latent heat

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

Dew point temperature

Wet bulb temperature

Dry bulb temperature

Relative humidity

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

1 m3 of dry air

1 kg of dry air

1 kg of wet air

1 m3 of water

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

Less than

More than

Equal to

None of these

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

Simple air cooling system

Reduced ambient air cooling system

Regenerative air cooling system

Bootstrap air cooling system

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

Vertical line

Curved line

Horizontal line

Inclined line

17. The bypass factor for a cooling coil

Remains unchanged 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

Decreases with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

18. The evaporator used in household refrigerators is

None of these

Frosting evaporator

Non-frosting evaporator

Defrosting evaporator

19. 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

20. 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 12 hours

In 1 hour

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21. The desirable property of a refrigerant is

Low boiling point

All of these

High latent heat of vaporisation

High critical temperature

22. 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

Ammonia vapours to weak solution

Weak solution to strong solution

23. The specific humidity during cooling and dehumidification

Increases

None of these

Remains constant

Decreases

24. 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 condenser

After passing through the expansion or throttle valve

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

Horizontal and uniformly spaced

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

Curved lines

26. 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)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

27. The power per tonne of refrigeration is

C.O.P/3.5

3.5 × C.O.P.

None of these

3.5/C.O.P.

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

Increase cooling effect

Reduce compressor overheating

Reduce compressor discharge temperature

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

29. 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 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 kg of dry air

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

System has high C.O.P.

Mass of refrigerant circulated in the system is low

Power per TR is low

Mass of the refrigeration equipment is low

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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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

32. 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?

0.8

1.25

0.5

0.25

33. The temperature of air recorded by a thermometer, when its bulb is surrounded by a wet cloth exposed to the air, is called

Dry bulb temperature

Dew point temperature

None of these

Wet bulb temperature

34. 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

35. 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

36. 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

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

Coefficient of performance of refrigeration

Coefficient of performance of heat pump

Relative coefficient of performance

Refrigerating efficiency

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

Copper

Aluminium

Brass

Steel

39. Ammonia is

Non-inflammable

Toxic and non-inflammable

Non-toxic

Highly toxic and inflammable

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

Sulphur dioxide

Ammonia

Carbon dioxide

R-12

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

Brass

Steel

Aluminium

Copper

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

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the expansion valve

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

1 m3 of dry air

1 m3 of water

1 kg of dry air

1 kg of wet air

44. 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

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

Increases heat transfer

Improves C.O.P. of the system

Increases power consumption

Reduces power consumption

Refrigeration & Air-Conditioning Practice Set-5

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