Refrigeration & Air-Conditioning Practice Set-5

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

Vapour absorption

Vapour compression

Carnot cycle

Electrolux refrigerator

2. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

Superheated vapour refrigerant

None of these

A mixture of liquid and vapour refrigerant

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

After passing through the expansion or throttle valve

Before entering the expansion valve

Before passing through the condenser

After passing through the condenser

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

Ammonia and lithium bromide

Water and water

Water and lithium bromide

Ammonia and water

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

Horizontal and non-uniformly spaced

Curved lines

Vertical and uniformly spaced

Horizontal and uniformly spaced

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

Mass of the refrigeration equipment is low

Mass of refrigerant circulated in the system is low

System has high C.O.P.

Power per TR is low

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

Dry bulb temperature

Relative humidity

Dew point temperature

Wet bulb temperature

8. 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 heat pump

Coefficient of performance of refrigeration

Refrigerating efficiency

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

Simple air cooling system

Bootstrap air cooling system

Reduced ambient air cooling system

Regenerative air cooling system

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

1 m3 of wet air

1 m3 of dry air

1 kg of dry air

1 kg of wet air

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

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

Before entering the compressor

12. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Small displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and high condensing pressures

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

Inclined line

Horizontal line

Curved line

Vertical line

14. The evaporator used in household refrigerators is

Frosting evaporator

Non-frosting evaporator

Defrosting evaporator

None of these

15. The refrigerant for a refrigerator should have

Low latent heat

High sensible heat

High total heat

High latent heat

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

Brass

Aluminium

Copper

Steel

17. 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

18. 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

Dry bulb temperature

Wet bulb temperature

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

10%

75%

25%

50%

20. The desirable property of a refrigerant is

Low boiling point

High latent heat of vaporisation

High critical temperature

All of these

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21. 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

0.25

0.8

0.5

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

Reduces power consumption

Improves C.O.P. of the system

Increases heat transfer

Increases power consumption

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

1 m3 of water

1 kg of dry air

1 kg of wet air

1 m3 of dry air

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

Aluminium

Copper

Brass

Steel

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

More than

Less than

None of these

Equal to

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

210 kJ/ min

21 kJ/ min

840 kJ/ min

420 kJ/ min

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

In 12 hours

In 1 hour

In 24 hours

In 1 minute

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. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant pressure lines

Constant temperature lines

Constant entropy lines

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

None of these

Equal to

Less than

Greater than

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31. Ammonia is

Toxic and non-inflammable

Highly toxic and inflammable

Non-toxic

Non-inflammable

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

Ammonia vapours to weak solution

Strong solution to ammonia vapour

Weak solution to strong solution

Strong solution to weak solution

33. 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

Remains unchanged with increase in velocity of air passing through it

Decreases with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

34. 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)

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

35. 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.

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

R-12

Carbon dioxide

Ammonia

Sulphur dioxide

37. 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)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

38. Air refrigeration cycle is used in

Commercial refrigerators

Domestic refrigerators

Gas liquefaction

Air conditioning

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

1 kg of dry air

1 m3 of dry air

1 kg of wet air

1 m3 of water

40. 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

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41. Chaperon equation is applicable for registration at

Saturation point of vapour

Sublimation temperature

Saturation point of liquid

Triple point

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

Reversed Brayton cycle

Reversed Joule cycle

Reversed Carnot cycle

Reversed Otto cycle

43. 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

44. The specific humidity during cooling and dehumidification

Remains constant

Decreases

Increases

None of these

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

Vapour absorption cycle

None of these

Vapour compression cycle

Air refrigeration cycle

Refrigeration & Air-Conditioning Practice Set-5

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