Refrigeration & Air-Conditioning Practice Set-5

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1. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Small displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and low condensing pressures

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

Reversed Carnot cycle

Reversed Joule cycle

Reversed Otto cycle

Reversed Brayton cycle

3. The evaporator used in household refrigerators is

None of these

Non-frosting evaporator

Frosting evaporator

Defrosting evaporator

4. The refrigerant for a refrigerator should have

High sensible heat

High latent heat

Low latent heat

High total heat

5. 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

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

Vertical line

Curved line

Horizontal line

Inclined line

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

Simple air cooling system

Regenerative air cooling system

Reduced ambient air cooling system

Bootstrap air cooling system

8. 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

Ammonia vapours to weak solution

Strong solution to weak solution

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

Less than

More than

Equal to

None of these

10. The desirable property of a refrigerant is

High latent heat of vaporisation

High critical temperature

All of these

Low boiling point

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

Mass of the refrigeration equipment is low

System has high C.O.P.

Mass of refrigerant circulated in the system is low

Power per TR is low

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

1 kg of dry air

1 m3 of wet air

1 kg of wet air

1 m3 of dry air

13. 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)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

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

In 1 minute

In 1 hour

In 24 hours

In 12 hours

15. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant entropy lines

Constant temperature lines

Constant total heat lines

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

Brass

Aluminium

Copper

Steel

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

After passing through the expansion or throttle valve

Before entering the compressor

After passing through the condenser

Before passing through the condenser

18. Chaperon equation is applicable for registration at

Sublimation temperature

Saturation point of vapour

Triple point

Saturation point of liquid

19. Air refrigeration cycle is used in

Commercial refrigerators

Domestic refrigerators

Gas liquefaction

Air conditioning

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

Vapour compression cycle

None of these

Air refrigeration cycle

Vapour absorption cycle

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

Increases power consumption

Improves C.O.P. of the system

Reduces power consumption

Increases heat transfer

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

Wet bulb temperature

Relative humidity

Dry bulb temperature

Dew point temperature

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

Absorber and generator

Generator

Liquid pump

Absorber, generator and liquid pump

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

Less than

Greater than

Equal to

None of these

25. Ammonia is

Toxic and non-inflammable

Non-inflammable

Non-toxic

Highly toxic and inflammable

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

Vertical and uniformly spaced

Curved lines

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

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

Carbon dioxide

Sulphur dioxide

Ammonia

R-12

28. 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.

29. 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)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

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

Dew point temperature

None of these

Wet bulb temperature

Dry bulb temperature

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

Ammonia and water

Water and water

Ammonia and lithium bromide

Water and lithium bromide

32. 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

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

10%

50%

25%

75%

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

210 kJ/ min

840 kJ/ min

420 kJ/ min

21 kJ/ min

35. 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

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

36. The specific humidity during cooling and dehumidification

Decreases

Increases

Remains constant

None of these

37. 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.

38. 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

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

Carnot cycle

Vapour absorption

Electrolux refrigerator

Vapour compression

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

Brass

Steel

Copper

Aluminium

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

1 kg of dry air

1 m3 of water

1 m3 of dry air

1 kg of wet air

42. 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 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

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

43. 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

44. 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

0.5

0.8

1.25

45. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

Superheated vapour refrigerant

None of these

Dry saturated liquid refrigerant

Refrigeration & Air-Conditioning Practice Set-5

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