Refrigeration & Air-Conditioning Practice Set-5

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

Aluminium

Brass

Copper

Steel

2. The power per tonne of refrigeration is

3.5 × C.O.P.

C.O.P/3.5

None of these

3.5/C.O.P.

3. Chaperon equation is applicable for registration at

Sublimation temperature

Saturation point of vapour

Saturation point of liquid

Triple point

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

840 kJ/ min

21 kJ/ min

210 kJ/ min

420 kJ/ min

5. 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

Refrigerating efficiency

Coefficient of performance of refrigeration

6. 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)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

7. The specific humidity during cooling and dehumidification

Remains constant

Increases

None of these

Decreases

8. 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.

B.P.F. - 1

1 + B.P.F.

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

Greater than

None of these

Equal to

Less than

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

Reduces power consumption

Improves C.O.P. of the system

Increases power consumption

Increases heat transfer

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11. The reciprocating refrigerant compressors are very suitable for

Small displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Large displacements and high condensing pressures

12. 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

0.8

0.5

0.25

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

Copper

Brass

Aluminium

Steel

14. 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

Dew point temperature

Dry bulb temperature

None of these

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

Equal to

Less than

None of these

More than

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

Water and lithium bromide

Ammonia and water

Ammonia and lithium bromide

Water and water

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

Dry bulb temperature

Relative humidity

Dew point temperature

Wet bulb temperature

18. 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

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

1 m3 of dry air

1 kg of wet air

1 m3 of wet air

1 kg of dry air

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

Ammonia vapours to weak solution

Strong solution to weak solution

Strong solution to ammonia vapour

Weak solution to strong solution

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21. 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

22. 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

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

Carnot cycle

Electrolux refrigerator

Vapour absorption

Vapour compression

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

Reduce compressor overheating

Reduce compressor discharge temperature

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

Increase cooling effect

25. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant temperature lines

Constant pressure lines

Constant total heat lines

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

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

Curved line

Vertical line

Horizontal line

Inclined line

28. The bypass factor for a cooling coil

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

Increases with increase in velocity of air passing through it

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

75%

50%

25%

10%

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

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 expansion or throttle valve

After passing through the condenser

Before passing through the condenser

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

Liquid pump

Generator

Absorber and generator

Absorber, generator and liquid pump

33. Air refrigeration cycle is used in

Gas liquefaction

Air conditioning

Commercial refrigerators

Domestic refrigerators

34. 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 (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

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

1 m3 of water

1 kg of wet air

1 m3 of dry air

1 kg of dry air

36. The evaporator used in household refrigerators is

Defrosting evaporator

Non-frosting evaporator

Frosting evaporator

None of these

37. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

None of these

Superheated vapour refrigerant

Dry saturated liquid refrigerant

38. The desirable property of a refrigerant is

Low boiling point

High critical temperature

High latent heat of vaporisation

All of these

39. 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 12 hours

In 24 hours

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

Vapour absorption cycle

Air refrigeration cycle

None of these

Vapour compression cycle

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

1 m3 of water

1 kg of dry air

1 kg of wet air

1 m3 of dry air

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

Bootstrap air cooling system

Regenerative air cooling system

Simple air cooling system

Reduced ambient air cooling system

43. 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

44. Ammonia is

Toxic and non-inflammable

Non-toxic

Highly toxic and inflammable

Non-inflammable

45. The refrigerant for a refrigerator should have

High total heat

Low latent heat

High sensible heat

High latent heat

Refrigeration & Air-Conditioning Practice Set-5

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