Refrigeration & Air-Conditioning Practice Set-5

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1. Air refrigeration cycle is used in

Domestic refrigerators

Gas liquefaction

Air conditioning

Commercial refrigerators

2. 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)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

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

Power per TR is low

System has high C.O.P.

Mass of the refrigeration equipment is low

Mass of refrigerant circulated in the system is low

4. Ammonia is

Non-toxic

Toxic and non-inflammable

Non-inflammable

Highly toxic and inflammable

5. 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 entering the expansion valve

Before passing through the condenser

6. 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

7. Degree of saturation or percentage humidity is

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

The mass of water vapour present in 1 kg 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

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

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

Relative humidity

Dry bulb temperature

Dew point temperature

Wet bulb temperature

9. The desirable property of a refrigerant is

Low boiling point

High critical temperature

All of these

High latent heat of vaporisation

10. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant entropy lines

Constant pressure lines

Constant temperature lines

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11. Chaperon equation is applicable for registration at

Saturation point of vapour

Triple point

Sublimation temperature

Saturation point of liquid

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

Strong solution to weak solution

Ammonia vapours to weak solution

Weak solution to strong solution

Strong solution to ammonia vapour

13. The refrigerant for a refrigerator should have

Low latent heat

High latent heat

High sensible heat

High total heat

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

Equal to

Less than

None of these

Greater than

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

R-12

Ammonia

Sulphur dioxide

Carbon dioxide

16. 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

17. 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.

1/ B.P.F.

B.P.F. - 1

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

Increases power consumption

Increases heat transfer

Reduces power consumption

Improves C.O.P. of the system

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

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

Reduce compressor overheating

Increase cooling effect

Reduce compressor discharge temperature

20. The refrigerant supplied to a compressor must be

None of these

Dry saturated liquid refrigerant

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

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21. 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

Dry bulb temperature

Dew point temperature

Wet bulb temperature

22. The evaporator used in household refrigerators is

None of these

Frosting evaporator

Defrosting evaporator

Non-frosting evaporator

23. The specific humidity during cooling and dehumidification

Increases

Decreases

Remains constant

None of these

24. 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

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

Ammonia and lithium bromide

Water and water

Ammonia and water

Water and lithium bromide

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

Brass

Copper

Aluminium

Steel

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

Less than

More than

None of these

Equal to

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

1 kg of wet air

1 m3 of water

1 m3 of dry air

1 kg of dry air

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

Vapour absorption

Vapour compression

Electrolux refrigerator

Carnot cycle

30. The ratio of heat extracted in the refrigerator to the work-done on the refrigerant is called

Refrigerating efficiency

Relative coefficient of performance

Coefficient of performance of heat pump

Coefficient of performance of refrigeration

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

Aluminium

Brass

Steel

Copper

32. The power per tonne of refrigeration is

3.5 × C.O.P.

3.5/C.O.P.

C.O.P/3.5

None of these

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

Horizontal line

Inclined line

Vertical line

Curved line

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

75%

50%

10%

25%

35. 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

36. The bypass factor for a cooling coil

Decreases with increase in velocity of air passing through it

Remains unchanged 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

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

21 kJ/ min

210 kJ/ min

420 kJ/ min

840 kJ/ min

38. 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)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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

After passing through the condenser

Before passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

40. 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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41. 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?

0.8

0.5

1.25

0.25

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

Regenerative air cooling system

Bootstrap air cooling system

Simple air cooling system

Reduced ambient air cooling system

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

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

Vertical and uniformly spaced

Curved lines

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

1 m3 of water

1 kg of wet air

1 kg of dry air

1 m3 of dry air

45. 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

Refrigeration & Air-Conditioning Practice Set-5

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