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

Triple point

Sublimation temperature

2. 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

3. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and low condensing pressures

Large displacements and high condensing pressures

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

Increase cooling effect

Reduce compressor discharge temperature

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

Reduce compressor overheating

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

10%

75%

50%

25%

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

Ammonia and lithium bromide

Ammonia and water

Water and water

Water and lithium bromide

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

None of these

Dew point temperature

8. The refrigerant for a refrigerator should have

High sensible heat

High total heat

Low latent heat

High latent heat

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

Electrolux refrigerator

Carnot cycle

Vapour compression

Vapour absorption

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

Increases heat transfer

Reduces power consumption

Increases power consumption

Improves C.O.P. of the system

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11. 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

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

Vapour absorption cycle

None of these

Air refrigeration cycle

Vapour compression cycle

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

Copper

Aluminium

Steel

Brass

14. Ammonia is

Non-inflammable

Toxic and non-inflammable

Non-toxic

Highly toxic and inflammable

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

1 kg of wet air

1 kg of dry air

1 m3 of dry air

1 m3 of wet air

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

420 kJ/ min

840 kJ/ min

210 kJ/ min

21 kJ/ min

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

Reduced ambient air cooling system

Bootstrap air cooling system

Regenerative air cooling system

Simple air cooling system

18. The evaporator used in household refrigerators is

Frosting evaporator

Defrosting evaporator

None of these

Non-frosting evaporator

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

Relative humidity

Wet bulb temperature

Dew point temperature

Dry bulb temperature

20. 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 (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

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

Generator

Absorber, generator and liquid pump

Absorber and generator

Liquid pump

22. 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

Mass of the refrigeration equipment is low

Power per TR is low

23. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

Superheated vapour refrigerant

Dry saturated liquid refrigerant

None of these

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

Reversed Otto cycle

Reversed Brayton cycle

Reversed Joule cycle

Reversed Carnot cycle

25. 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 weak solution

Strong solution to ammonia vapour

Ammonia vapours to weak solution

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

Vertical line

Horizontal line

Inclined line

Curved line

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

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the compressor

28. 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 passing through the condenser

Before entering the expansion valve

29. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant temperature lines

Constant entropy lines

Constant pressure lines

30. 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?

0.5

1.25

0.25

0.8

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

Curved lines

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

Vertical and uniformly spaced

32. The desirable property of a refrigerant is

High critical temperature

All of these

High latent heat of vaporisation

Low boiling point

33. Air refrigeration cycle is used in

Domestic refrigerators

Commercial refrigerators

Air conditioning

Gas liquefaction

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

Steel

Aluminium

Copper

Brass

35. 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

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

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

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

None of these

Equal to

Less than

More than

38. The bypass factor for a cooling coil

Decreases with increase in velocity of air passing through it

Increases 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

Remains unchanged with increase in velocity of air passing through it

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

1 kg of dry air

1 kg of wet air

1 m3 of dry air

1 m3 of water

40. 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

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41. The specific humidity during cooling and dehumidification

None of these

Decreases

Remains constant

Increases

42. 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.

43. 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.

44. 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 - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

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

None of these

Equal to

Greater than

Less than

Refrigeration & Air-Conditioning Practice Set-5

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