Refrigeration & Air-Conditioning Practice Set-5

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1. The evaporator used in household refrigerators is

Non-frosting evaporator

Defrosting evaporator

Frosting evaporator

None of these

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

Aluminium

Brass

Steel

Copper

3. Chaperon equation is applicable for registration at

Triple point

Saturation point of vapour

Saturation point of liquid

Sublimation temperature

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

Refrigerating efficiency

Coefficient of performance of heat pump

Coefficient of performance of refrigeration

Relative coefficient of performance

5. 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.

6. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant entropy lines

Constant pressure lines

Constant total heat lines

7. 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)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

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

Aluminium

Steel

Copper

Brass

9. 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 m³ of dry air

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

10. 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)

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

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11. The desirable property of a refrigerant is

High critical temperature

All of these

Low boiling point

High latent heat of vaporisation

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

Sulphur dioxide

R-12

Carbon dioxide

Ammonia

13. 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

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

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?

0.5

0.25

0.8

1.25

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

In 1 hour

In 1 minute

In 24 hours

In 12 hours

17. The specific humidity during cooling and dehumidification

Decreases

Increases

Remains constant

None of these

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

None of these

More than

Equal to

Less than

19. 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

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

1 kg of dry air

1 kg of wet air

1 m3 of dry air

1 m3 of wet air

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

Water and lithium bromide

Water and water

Ammonia and lithium bromide

Ammonia and water

22. 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

Dew point temperature

Dry bulb temperature

None of these

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

Absorber, generator and liquid pump

Liquid pump

Generator

Absorber and generator

24. 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 discharge temperature

Reduce compressor overheating

Increase cooling effect

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

75%

10%

25%

50%

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

Increases heat transfer

Improves C.O.P. of the system

Reduces power consumption

Increases power consumption

27. The refrigerant for a refrigerator should have

High total heat

High sensible heat

Low latent heat

High latent heat

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

Reversed Brayton cycle

Reversed Joule cycle

Reversed Otto cycle

Reversed Carnot cycle

29. Ammonia is

Non-inflammable

Non-toxic

Toxic and non-inflammable

Highly toxic and inflammable

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

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

System has high C.O.P.

Power per TR is low

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

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

Horizontal and uniformly spaced

Curved lines

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

840 kJ/ min

21 kJ/ min

420 kJ/ min

210 kJ/ min

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

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

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

Wet bulb temperature

Relative humidity

Dew point temperature

Dry bulb temperature

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

Horizontal line

Vertical line

Inclined line

Curved line

36. 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

37. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Small displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and low condensing pressures

38. Air refrigeration cycle is used in

Air conditioning

Gas liquefaction

Domestic refrigerators

Commercial refrigerators

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

Vapour compression

Vapour absorption

Electrolux refrigerator

Carnot cycle

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

1 m3 of dry air

1 m3 of water

1 kg of dry air

1 kg of wet air

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41. 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

42. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

None of these

Superheated vapour refrigerant

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

Greater than

Less than

Equal to

None of these

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

Before passing through the condenser

After passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

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

1 + B.P.F.

B.P.F. - 1

1 - B. P.F.

1/ B.P.F.

Refrigeration & Air-Conditioning Practice Set-5

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