Refrigeration & Air-Conditioning Practice Set-5

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1. 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

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

None of these

Vapour compression cycle

Air refrigeration cycle

Vapour absorption cycle

3. 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)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

4. 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

Strong solution to weak solution

Ammonia vapours to weak solution

5. Ammonia is

Non-toxic

Toxic and non-inflammable

Non-inflammable

Highly toxic and inflammable

6. The refrigerant for a refrigerator should have

High latent heat

High total heat

Low latent heat

High sensible heat

7. The power per tonne of refrigeration is

3.5 × C.O.P.

C.O.P/3.5

None of these

3.5/C.O.P.

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

Ammonia and water

Ammonia and lithium bromide

Water and water

Water and lithium bromide

9. 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.

10. Air refrigeration cycle is used in

Commercial refrigerators

Domestic refrigerators

Air conditioning

Gas liquefaction

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11. 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)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

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

Before entering the expansion valve

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

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

25%

50%

75%

10%

14. The evaporator used in household refrigerators is

None of these

Frosting evaporator

Non-frosting evaporator

Defrosting evaporator

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

1 kg of wet air

1 m3 of dry air

1 m3 of water

1 kg of dry air

16. The desirable property of a refrigerant is

Low boiling point

All of these

High critical temperature

High latent heat of vaporisation

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

Copper

Steel

Aluminium

Brass

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

1 kg of dry air

1 kg of wet air

1 m3 of water

1 m3 of dry air

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

Increase cooling effect

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

Reduce compressor overheating

Reduce compressor discharge temperature

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

840 kJ/ min

21 kJ/ min

420 kJ/ min

210 kJ/ min

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21. 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

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

Inclined line

Vertical line

Horizontal line

Curved line

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

None of these

Equal to

More than

Less than

24. 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

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

Brass

Steel

Copper

Aluminium

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

Dry bulb temperature

Wet bulb temperature

Relative humidity

Dew point temperature

27. 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 24 hours

In 1 minute

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

Before entering the compressor

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

29. The specific humidity during cooling and dehumidification

Increases

Remains constant

None of these

Decreases

30. 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

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31. 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

0.8

0.25

0.5

32. Degree of saturation or percentage humidity is

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

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

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

1 kg of wet air

1 m3 of wet air

1 kg of dry air

1 m3 of dry air

34. 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

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

Ammonia

Sulphur dioxide

Carbon dioxide

R-12

36. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant temperature lines

Constant total heat lines

Constant pressure lines

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

Vapour absorption

Electrolux refrigerator

Vapour compression

Carnot cycle

38. 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

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

Regenerative air cooling system

Reduced ambient air cooling system

Bootstrap air cooling system

Simple air cooling system

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

Curved lines

Horizontal and uniformly spaced

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

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41. Chaperon equation is applicable for registration at

Saturation point of liquid

Triple point

Sublimation temperature

Saturation point of vapour

42. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

43. 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

44. The bypass factor for a cooling coil

Decreases 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

Increases with increase in velocity of air passing through it

Remains unchanged with increase in velocity of air passing through it

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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