Refrigeration & Air-Conditioning Practice Set-5

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1. 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

2. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

None of these

3. The evaporator used in household refrigerators is

Frosting evaporator

Defrosting evaporator

None of these

Non-frosting evaporator

4. 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

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

1 kg of wet air

1 m3 of dry air

1 kg of dry air

1 m3 of water

6. The specific humidity during cooling and dehumidification

Remains constant

None of these

Increases

Decreases

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

Vertical line

Curved line

Horizontal line

Inclined line

8. The power per tonne of refrigeration is

C.O.P/3.5

None of these

3.5/C.O.P.

3.5 × C.O.P.

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

None of these

More than

Equal to

Less than

10. 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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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11. The desirable property of a refrigerant is

High critical temperature

High latent heat of vaporisation

Low boiling point

All of these

12. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant temperature lines

Constant pressure lines

Constant entropy lines

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

Copper

Steel

Brass

Aluminium

14. 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)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

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

Increases power consumption

Increases heat transfer

Improves C.O.P. of the system

Reduces power consumption

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

Liquid pump

Absorber and generator

Absorber, generator and liquid pump

Generator

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

Wet bulb temperature

Relative humidity

Dry bulb temperature

Dew point temperature

18. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

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

After passing through the condenser

Before entering the compressor

Before passing through the condenser

After passing through the expansion or throttle valve

20. Ammonia is

Non-toxic

Non-inflammable

Highly toxic and inflammable

Toxic and non-inflammable

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21. 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

Increase cooling effect

Reduce compressor overheating

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

After passing through the condenser

Before entering the expansion valve

Before passing through the condenser

After passing through the expansion or throttle valve

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

Dry bulb temperature

None of these

Dew point temperature

Wet bulb temperature

24. 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

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

1 kg of wet air

1 m3 of dry air

1 kg of dry air

1 m3 of water

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

420 kJ/ min

21 kJ/ min

210 kJ/ min

840 kJ/ min

27. Degree of saturation or percentage humidity is

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

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 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

28. Chaperon equation is applicable for registration at

Saturation point of vapour

Triple point

Saturation point of liquid

Sublimation temperature

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

Sulphur dioxide

Carbon dioxide

Ammonia

R-12

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

None of these

Vapour absorption cycle

Vapour compression cycle

Air refrigeration cycle

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31. Air refrigeration cycle is used in

Air conditioning

Commercial refrigerators

Domestic refrigerators

Gas liquefaction

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

Ammonia vapours to weak solution

Weak solution to strong solution

Strong solution to ammonia vapour

Strong solution to weak solution

33. 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

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

Relative coefficient of performance

Refrigerating efficiency

Coefficient of performance of heat pump

Coefficient of performance of refrigeration

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

Power per TR is low

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

System has high C.O.P.

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

Reversed Brayton cycle

Reversed Otto cycle

Reversed Joule cycle

Reversed Carnot cycle

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

Vapour compression

Electrolux refrigerator

Vapour absorption

Carnot cycle

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

Equal to

None of these

Less than

Greater than

39. 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

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

Water and lithium bromide

Ammonia and water

Ammonia and lithium bromide

Water and water

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

Brass

Steel

Copper

Aluminium

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

75%

10%

25%

50%

43. 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

1.25

0.5

0.25

44. The refrigerant for a refrigerator should have

High total heat

High latent heat

High sensible heat

Low latent heat

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

1 m3 of wet air

1 kg of wet air

1 kg of dry air

1 m3 of dry air

Refrigeration & Air-Conditioning Practice Set-5

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