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.

B.P.F. - 1

1/ B.P.F.

1 - B. P.F.

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

Reduces power consumption

Increases power consumption

Increases heat transfer

Improves C.O.P. of the system

3. Degree of saturation or percentage humidity is

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

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

4. 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

Dew point temperature

None of these

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

Greater than

Equal to

Less than

None of these

6. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant pressure lines

Constant total heat lines

Constant temperature lines

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

Coefficient of performance of heat pump

Coefficient of performance of refrigeration

Relative coefficient of performance

Refrigerating efficiency

8. Ammonia is

Toxic and non-inflammable

Non-toxic

Non-inflammable

Highly toxic and inflammable

9. The bypass factor for a cooling coil

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

Decreases with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

10. 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?

0.25

1.25

0.8

0.5

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11. 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

12. Air refrigeration cycle is used in

Commercial refrigerators

Air conditioning

Gas liquefaction

Domestic refrigerators

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

Before entering the compressor

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

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

Regenerative air cooling system

Simple air cooling system

Reduced ambient air cooling system

Bootstrap air cooling system

15. 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

16. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

None of these

Superheated vapour refrigerant

17. 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

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

Ammonia and lithium bromide

Ammonia and water

Water and water

Water and lithium bromide

19. The refrigerant for a refrigerator should have

Low latent heat

High latent heat

High sensible heat

High total heat

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

More than

None of these

Less than

Equal to

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21. The desirable property of a refrigerant is

High latent heat of vaporisation

High critical temperature

All of these

Low boiling point

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

1 m3 of dry air

1 m3 of water

1 kg of wet air

1 kg of dry air

23. 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 kg of wet air

1 m3 of wet air

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

Vapour compression

Carnot cycle

Electrolux refrigerator

Vapour absorption

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

Liquid pump

Generator

Absorber, generator and liquid pump

Absorber and generator

26. 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 weak solution

Strong solution to ammonia vapour

Ammonia vapours to weak solution

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

Copper

Aluminium

Brass

Steel

28. The evaporator used in household refrigerators is

Defrosting evaporator

None of these

Non-frosting evaporator

Frosting evaporator

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

Air refrigeration cycle

None of these

Vapour absorption cycle

Vapour compression cycle

30. The reciprocating refrigerant compressors are very suitable for

Small displacements and high condensing pressures

Large displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and low condensing pressures

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

System has high C.O.P.

Power per TR is low

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

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

Ammonia

R-12

Sulphur dioxide

Carbon dioxide

33. 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)]

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

50%

75%

25%

10%

35. 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 12 hours

In 24 hours

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

Reduce compressor overheating

Increase cooling effect

Reduce compressor discharge temperature

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

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

Horizontal line

Curved line

Vertical line

Inclined line

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

Steel

Aluminium

Brass

Copper

39. The specific humidity during cooling and dehumidification

Decreases

Increases

None of these

Remains constant

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

Relative humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

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41. Chaperon equation is applicable for registration at

Saturation point of liquid

Saturation point of vapour

Triple point

Sublimation temperature

42. 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)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

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

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

Before entering the expansion valve

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

420 kJ/ min

210 kJ/ min

21 kJ/ min

840 kJ/ min

45. 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

Refrigeration & Air-Conditioning Practice Set-5

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