Refrigeration & Air-Conditioning Practice Set-5

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1. Chaperon equation is applicable for registration at

Sublimation temperature

Triple point

Saturation point of liquid

Saturation point of vapour

2. 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)

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

Steel

Copper

Aluminium

Brass

4. 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)]

5. The desirable property of a refrigerant is

All of these

High latent heat of vaporisation

Low boiling point

High critical temperature

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

210 kJ/ min

420 kJ/ min

840 kJ/ min

21 kJ/ min

7. Air refrigeration cycle is used in

Gas liquefaction

Domestic refrigerators

Air conditioning

Commercial refrigerators

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

Vertical and uniformly spaced

Horizontal and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

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

Reversed Carnot cycle

Reversed Otto cycle

Reversed Joule cycle

Reversed Brayton cycle

10. The specific humidity during cooling and dehumidification

Increases

None of these

Remains constant

Decreases

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11. 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 overheating

Reduce compressor discharge temperature

Increase cooling effect

12. Ammonia is

Non-inflammable

Non-toxic

Highly toxic and inflammable

Toxic and non-inflammable

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

1 m3 of dry air

1 kg of dry air

1 kg of wet air

1 m3 of water

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

Dew point temperature

Relative humidity

Wet bulb temperature

Dry bulb temperature

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

1 kg of dry air

1 m3 of wet air

1 kg of wet air

1 m3 of dry air

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

Absorber, generator and liquid pump

Generator

Liquid pump

Absorber and generator

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

Improves C.O.P. of the system

Increases heat transfer

Increases power consumption

Reduces power consumption

18. 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

Dew point temperature

Wet bulb temperature

None of these

19. 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.

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

Carnot cycle

Vapour compression

Vapour absorption

Electrolux refrigerator

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

Copper

Steel

Aluminium

Brass

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

Inclined line

Horizontal line

Curved line

Vertical line

23. Degree of saturation or percentage humidity is

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

The mass of water vapour present in 1 m³ of dry air

24. The bypass factor for a cooling coil

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

Remains unchanged with increase in velocity of air passing through it

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

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

Ammonia and lithium bromide

Water and lithium bromide

Ammonia and water

Water and water

27. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant temperature lines

Constant pressure lines

Constant entropy lines

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

Strong solution to ammonia vapour

Weak solution to strong solution

Ammonia vapours to weak solution

Strong solution to weak solution

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

Coefficient of performance of heat pump

Relative coefficient of performance

Coefficient of performance of refrigeration

Refrigerating efficiency

30. 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

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

Before entering the compressor

After passing through the condenser

Before passing through the condenser

After passing through the expansion or throttle valve

32. 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

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

1 m3 of water

1 m3 of dry air

1 kg of wet air

1 kg of dry air

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

Regenerative air cooling system

Simple air cooling system

Bootstrap air cooling system

Reduced ambient air cooling system

35. The refrigerant supplied to a compressor must be

None of these

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

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

In 24 hours

In 12 hours

In 1 hour

In 1 minute

37. 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.

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

None of these

More than

Less than

Equal to

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

Mass of the refrigeration equipment is low

Power per TR is low

System has high C.O.P.

Mass of refrigerant circulated in the system is low

40. The evaporator used in household refrigerators is

Non-frosting evaporator

Defrosting evaporator

None of these

Frosting evaporator

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

Greater than

Less than

Equal to

None of these

42. 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

0.5

0.25

0.8

43. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

Small displacements and low condensing pressures

44. The refrigerant for a refrigerator should have

High total heat

High latent heat

Low latent heat

High sensible heat

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

10%

50%

25%

75%

Refrigeration & Air-Conditioning Practice Set-5

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