Refrigeration & Air-Conditioning Practice Set-5

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

1 kg of wet air

1 kg of dry air

1 m3 of dry air

1 m3 of water

2. Ammonia is

Non-inflammable

Highly toxic and inflammable

Toxic and non-inflammable

Non-toxic

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

Curved lines

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

4. 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 refrigeration

Coefficient of performance of heat pump

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

Brass

Aluminium

Steel

Copper

6. The desirable property of a refrigerant is

Low boiling point

High critical temperature

High latent heat of vaporisation

All of these

7. 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

8. 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.

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

After passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

Before passing through the condenser

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

Ammonia and water

Water and lithium bromide

Water and water

Ammonia and lithium bromide

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11. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

None of these

A mixture of liquid and vapour refrigerant

Superheated vapour refrigerant

12. 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

13. The refrigerant for a refrigerator should have

High sensible heat

High total heat

Low latent heat

High latent heat

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

50%

75%

10%

25%

15. 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

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

Inclined line

Horizontal line

Curved line

Vertical line

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

Vapour compression

Carnot cycle

Electrolux refrigerator

Vapour absorption

18. 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

19. 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

20. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and low condensing pressures

Large displacements and high condensing pressures

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

Carbon dioxide

R-12

Ammonia

Sulphur dioxide

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

Generator

Absorber, generator and liquid pump

Absorber and generator

Liquid pump

23. Air refrigeration cycle is used in

Domestic refrigerators

Gas liquefaction

Air conditioning

Commercial refrigerators

24. 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 weak solution

Strong solution to ammonia vapour

25. The power per tonne of refrigeration is

None of these

3.5/C.O.P.

3.5 × C.O.P.

C.O.P/3.5

26. 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)]

27. The specific humidity during cooling and dehumidification

Remains constant

None of these

Increases

Decreases

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

420 kJ/ min

210 kJ/ min

840 kJ/ min

21 kJ/ min

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

Relative humidity

Dry bulb temperature

Dew point temperature

Wet bulb temperature

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

Reversed Carnot cycle

Reversed Brayton cycle

Reversed Joule cycle

Reversed Otto cycle

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31. 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

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

Equal to

Greater than

None of these

Less than

33. Chaperon equation is applicable for registration at

Triple point

Saturation point of vapour

Sublimation temperature

Saturation point of liquid

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

Dew point temperature

None of these

Wet bulb temperature

Dry bulb temperature

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

Vapour absorption cycle

Vapour compression cycle

None of these

Air refrigeration cycle

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

In 12 hours

In 1 minute

In 1 hour

In 24 hours

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

Before passing through the condenser

After passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

38. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant pressure lines

Constant temperature lines

Constant total heat lines

39. 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.

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

More than

None of these

Less than

Equal to

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41. 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 - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

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

Copper

Aluminium

Brass

Steel

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?

0.25

0.8

0.5

1.25

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. The evaporator used in household refrigerators is

Non-frosting evaporator

None of these

Frosting evaporator

Defrosting evaporator

Refrigeration & Air-Conditioning Practice Set-5

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