Refrigeration & Air-Conditioning Practice Set-5

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

50%

10%

75%

25%

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

Brass

Copper

Aluminium

Steel

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

Absorber and generator

Generator

Absorber, generator and liquid pump

Liquid pump

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

210 kJ/ min

840 kJ/ min

420 kJ/ min

21 kJ/ min

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

Carnot cycle

Vapour absorption

Electrolux refrigerator

Vapour compression

6. Air refrigeration cycle is used in

Gas liquefaction

Commercial refrigerators

Domestic refrigerators

Air conditioning

7. The power per tonne of refrigeration is

C.O.P/3.5

3.5 × C.O.P.

3.5/C.O.P.

None of these

8. 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

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

Dry bulb temperature

Dew point temperature

Wet bulb temperature

Relative humidity

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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

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11. Chaperon equation is applicable for registration at

Saturation point of liquid

Saturation point of vapour

Sublimation temperature

Triple point

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

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the compressor

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

Curved lines

Horizontal and uniformly spaced

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

14. Ammonia is

Non-toxic

Highly toxic and inflammable

Toxic and non-inflammable

Non-inflammable

15. The bypass factor for a cooling coil

Increases with increase in velocity of air passing through it

Remains unchanged 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

16. The evaporator used in household refrigerators is

Non-frosting evaporator

None of these

Defrosting evaporator

Frosting evaporator

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

Ammonia and water

Water and water

Ammonia and lithium bromide

Water and lithium bromide

18. 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

19. 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

System has high C.O.P.

Mass of the refrigeration equipment is low

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

1 kg of wet air

1 kg of dry air

1 m3 of water

1 m3 of dry air

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

1 kg of wet air

1 m3 of dry air

1 m3 of wet air

1 kg of dry air

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

Weak solution to strong solution

Ammonia vapours to weak solution

Strong solution to weak solution

Strong solution to ammonia vapour

23. 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 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

24. The refrigerant for a refrigerator should have

High total heat

High sensible heat

High latent heat

Low latent heat

25. 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

Relative coefficient of performance

Coefficient of performance of refrigeration

26. 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

27. 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

28. 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?

1.25

0.25

0.5

0.8

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

None of these

Equal to

Greater than

Less than

30. 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

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

R-12

Ammonia

Sulphur dioxide

Carbon dioxide

32. The desirable property of a refrigerant is

Low boiling point

All of these

High critical temperature

High latent heat of vaporisation

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

Reversed Carnot cycle

Reversed Brayton cycle

Reversed Otto cycle

Reversed Joule cycle

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

Improves C.O.P. of the system

Increases power consumption

Increases heat transfer

Reduces power consumption

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

Steel

Aluminium

Brass

Copper

36. 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

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

None of these

Vapour compression cycle

Vapour absorption cycle

Air refrigeration cycle

38. 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

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

Curved line

Horizontal line

Vertical line

Inclined line

40. 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

Wet bulb temperature

Dew point temperature

Dry bulb temperature

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

Less than

None of these

Equal to

More than

42. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant temperature lines

Constant entropy lines

Constant pressure lines

43. 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.

44. The specific humidity during cooling and dehumidification

Decreases

None of these

Remains constant

Increases

45. 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)]

Refrigeration & Air-Conditioning Practice Set-5

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