Refrigeration & Air-Conditioning Practice Set-5

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1. 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

2. Ammonia is

Non-inflammable

Non-toxic

Toxic and non-inflammable

Highly toxic and inflammable

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

Aluminium

Copper

Steel

Brass

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

Inclined line

Curved line

Vertical line

Horizontal line

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

Equal to

Less than

None of these

Greater than

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

420 kJ/ min

21 kJ/ min

210 kJ/ min

840 kJ/ min

7. 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

Wet bulb temperature

Dew point temperature

8. 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 (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

9. The desirable property of a refrigerant is

High critical temperature

All of these

High latent heat of vaporisation

Low boiling point

10. Air refrigeration cycle is used in

Domestic refrigerators

Air conditioning

Commercial refrigerators

Gas liquefaction

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11. 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

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

Refrigerating efficiency

Coefficient of performance of heat pump

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

Wet bulb temperature

Relative humidity

Dry bulb temperature

Dew point temperature

14. 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

15. 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

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

Vapour absorption

Electrolux refrigerator

Vapour compression

Carnot cycle

17. The power per tonne of refrigeration is

None of these

C.O.P/3.5

3.5 × C.O.P.

3.5/C.O.P.

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

1 m3 of dry air

1 kg of dry air

1 m3 of wet air

1 kg of wet air

19. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

None of these

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

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

Vertical and uniformly spaced

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

Curved lines

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21. 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

22. 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

Weak solution to strong solution

Strong solution to weak solution

23. The refrigerant for a refrigerator should have

High sensible heat

High latent heat

High total heat

Low latent heat

24. 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

0.25

0.5

1.25

25. 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

26. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

27. 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.

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

Generator

Absorber, generator and liquid pump

Liquid pump

Absorber and generator

29. 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

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

None of these

More than

Equal to

Less than

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

Reduced ambient air cooling system

Regenerative air cooling system

Bootstrap air cooling system

Simple air cooling system

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

Ammonia

R-12

Sulphur dioxide

Carbon dioxide

33. 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)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

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

Vapour compression cycle

Air refrigeration cycle

None of these

Vapour absorption cycle

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

Before passing through the condenser

Before entering the expansion valve

After passing through the condenser

After passing through the expansion or throttle valve

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

Reversed Brayton cycle

Reversed Carnot cycle

Reversed Joule cycle

Reversed Otto cycle

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

Ammonia and lithium bromide

Ammonia and water

Water and lithium bromide

Water and water

38. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant temperature lines

Constant pressure lines

Constant entropy lines

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

Aluminium

Copper

Steel

Brass

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

Before entering the compressor

After passing through the condenser

Before passing through the condenser

After passing through the expansion or throttle valve

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41. The specific humidity during cooling and dehumidification

Remains constant

None of these

Increases

Decreases

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

25%

10%

50%

75%

43. Chaperon equation is applicable for registration at

Triple point

Saturation point of vapour

Sublimation temperature

Saturation point of liquid

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

Mass of refrigerant circulated in the system is low

Power per TR is low

Mass of the refrigeration equipment is low

System has high C.O.P.

45. The evaporator used in household refrigerators is

Frosting evaporator

Defrosting evaporator

Non-frosting evaporator

None of these

Refrigeration & Air-Conditioning Practice Set-5

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