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 dry air

1 m3 of water

1 kg of wet air

1 m3 of dry air

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

Dry bulb temperature

Relative humidity

Dew point temperature

Wet bulb temperature

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

840 kJ/ min

210 kJ/ min

420 kJ/ min

21 kJ/ min

4. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant pressure lines

Constant total heat lines

Constant entropy lines

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

After passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

Before passing through the condenser

6. 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

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

Equal to

Less than

Greater than

None of these

8. 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)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

9. The power per tonne of refrigeration is

3.5 × C.O.P.

C.O.P/3.5

3.5/C.O.P.

None of these

10. Ammonia is

Non-toxic

Highly toxic and inflammable

Toxic and non-inflammable

Non-inflammable

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

Carnot cycle

Vapour absorption

Electrolux refrigerator

Vapour compression

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

Coefficient of performance of heat pump

Refrigerating efficiency

Coefficient of performance of refrigeration

Relative coefficient of performance

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

Aluminium

Copper

Steel

Brass

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

Mass of refrigerant circulated in the system is low

System has high C.O.P.

Power per TR is low

Mass of the refrigeration equipment is low

15. 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

16. 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

Wet bulb temperature

Dry bulb temperature

None of these

17. 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

18. 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

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

Curved lines

Vertical and uniformly spaced

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

20. 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

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

Vertical line

Curved line

Inclined line

Horizontal line

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

None of these

Less than

Equal to

More than

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

Absorber and generator

Absorber, generator and liquid pump

Generator

Liquid pump

24. The desirable property of a refrigerant is

All of these

High critical temperature

Low boiling point

High latent heat of vaporisation

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

1 m3 of dry air

1 kg of wet air

1 m3 of water

1 kg of dry air

26. The evaporator used in household refrigerators is

None of these

Frosting evaporator

Defrosting evaporator

Non-frosting evaporator

27. Air refrigeration cycle is used in

Gas liquefaction

Commercial refrigerators

Air conditioning

Domestic refrigerators

28. 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

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

1 kg of dry air

1 m3 of dry air

1 kg of wet air

1 m3 of wet air

30. Degree of saturation or percentage humidity is

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 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 mass of water vapour present in 1 m³ of dry air

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31. 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

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

Water and water

Water and lithium bromide

Ammonia and water

Ammonia and lithium bromide

33. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

34. 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

0.5

1.25

0.8

35. The bypass factor for a cooling coil

Increases with increase in velocity of air passing through it

Decreases 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

Remains unchanged with increase in velocity of air passing through it

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

Carbon dioxide

Ammonia

Sulphur dioxide

R-12

37. Chaperon equation is applicable for registration at

Triple point

Saturation point of vapour

Sublimation temperature

Saturation point of liquid

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

Increases heat transfer

Increases power consumption

Reduces power consumption

Improves C.O.P. of the system

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

Copper

Aluminium

Steel

Brass

40. The refrigerant for a refrigerator should have

High total heat

High sensible heat

High latent heat

Low latent heat

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41. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

Superheated vapour refrigerant

None of these

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

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the compressor

After passing through the condenser

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

25%

75%

10%

50%

44. 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 (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

45. The specific humidity during cooling and dehumidification

Increases

None of these

Remains constant

Decreases

Refrigeration & Air-Conditioning Practice Set-5

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