Refrigeration & Air-Conditioning Practice Set-5

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1. 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

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

Reduce compressor overheating

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

Increase cooling effect

Reduce compressor discharge temperature

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

Absorber, generator and liquid pump

Generator

Absorber and generator

Liquid pump

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

Reversed Joule cycle

Reversed Carnot cycle

Reversed Brayton cycle

Reversed Otto cycle

5. 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

6. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant pressure lines

Constant total heat lines

Constant entropy lines

7. The evaporator used in household refrigerators is

Frosting evaporator

Defrosting evaporator

None of these

Non-frosting evaporator

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

Aluminium

Copper

Steel

Brass

9. 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

Decreases with increase in velocity of air passing through it

Remains unchanged with increase in velocity of air passing through it

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

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the expansion valve

After passing through the condenser

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11. Air refrigeration cycle is used in

Domestic refrigerators

Air conditioning

Gas liquefaction

Commercial refrigerators

12. 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

Coefficient of performance of heat pump

Refrigerating efficiency

13. 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)

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

Equal to

Less than

More than

None of these

15. 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

0.8

0.5

16. 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

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

Power per TR is low

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

System has high C.O.P.

18. Ammonia is

Non-inflammable

Highly toxic and inflammable

Non-toxic

Toxic and non-inflammable

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

None of these

Less than

Equal to

Greater than

20. Chaperon equation is applicable for registration at

Saturation point of vapour

Sublimation temperature

Triple point

Saturation point of liquid

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

Horizontal and uniformly spaced

Vertical and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

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

Curved line

Horizontal line

Vertical line

Inclined line

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

Vapour absorption

Electrolux refrigerator

Vapour compression

Carnot cycle

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 expansion or throttle valve

After passing through the condenser

25. The refrigerant for a refrigerator should have

High sensible heat

Low latent heat

High total heat

High latent heat

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

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

27. 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

Wet bulb temperature

None of these

28. 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

29. 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

30. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

None of these

Superheated vapour refrigerant

Dry saturated liquid refrigerant

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

1 m3 of dry air

1 kg of wet air

1 kg of dry air

1 m3 of water

32. The desirable property of a refrigerant is

All of these

High critical temperature

High latent heat of vaporisation

Low boiling point

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

840 kJ/ min

210 kJ/ min

21 kJ/ min

420 kJ/ min

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

Water and water

Water and lithium bromide

Ammonia and water

Ammonia and lithium bromide

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

In 1 hour

In 12 hours

In 1 minute

In 24 hours

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

Copper

Brass

Steel

Aluminium

37. 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.

38. The specific humidity during cooling and dehumidification

None of these

Increases

Decreases

Remains constant

39. In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = Bypass factor)

B.P.F. - 1

1/ B.P.F.

1 + B.P.F.

1 - B. P.F.

40. Degree of saturation or percentage humidity is

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

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

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

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

50%

75%

25%

10%

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

Dew point temperature

Relative humidity

Dry bulb temperature

Wet bulb temperature

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

1 m3 of dry air

1 kg of wet air

1 m3 of water

1 kg of dry air

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

Vapour absorption cycle

Vapour compression cycle

None of these

Air refrigeration cycle

45. 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 (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

Refrigeration & Air-Conditioning Practice Set-5

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