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

Brass

Aluminium

Steel

Copper

2. The refrigerant for a refrigerator should have

High total heat

High sensible heat

High latent heat

Low latent heat

3. 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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

4. The bypass factor for a cooling coil

Remains unchanged with increase in velocity of air passing through it

Increases 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

5. 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

None of these

Wet bulb temperature

Dew point temperature

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

Horizontal and non-uniformly spaced

Curved lines

Horizontal and uniformly spaced

Vertical and uniformly spaced

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

R-12

Carbon dioxide

Sulphur dioxide

Ammonia

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

Brass

Steel

Copper

Aluminium

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

Dew point temperature

Dry bulb temperature

Wet bulb temperature

Relative humidity

10. 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 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

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11. 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)]

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

840 kJ/ min

210 kJ/ min

420 kJ/ min

21 kJ/ min

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

1 kg of dry air

1 m3 of dry air

1 kg of wet air

1 m3 of water

14. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

Superheated vapour refrigerant

None of these

Dry saturated liquid refrigerant

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

1 m3 of dry air

1 kg of dry air

1 m3 of water

1 kg of wet air

16. The specific humidity during cooling and dehumidification

None of these

Decreases

Increases

Remains constant

17. The power per tonne of refrigeration is

3.5 × C.O.P.

None of these

C.O.P/3.5

3.5/C.O.P.

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

Less than

Greater than

None of these

Equal to

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

Reversed Otto cycle

Reversed Carnot cycle

Reversed Brayton cycle

Reversed Joule cycle

20. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

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

System has high C.O.P.

Mass of the refrigeration equipment is low

Mass of refrigerant circulated in the system is low

Power per TR is low

22. Air refrigeration cycle is used in

Domestic refrigerators

Gas liquefaction

Air conditioning

Commercial refrigerators

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

50%

75%

25%

10%

24. Ammonia is

Non-toxic

Non-inflammable

Highly toxic and inflammable

Toxic and non-inflammable

25. 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 kg of dry air

1 m3 of wet air

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

Increases power consumption

Increases heat transfer

Improves C.O.P. of the system

Reduces power consumption

27. 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

28. The desirable property of a refrigerant is

High critical temperature

Low boiling point

High latent heat of vaporisation

All of these

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

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

After passing through the condenser

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

Regenerative air cooling system

Simple air cooling system

Reduced ambient air cooling system

Bootstrap air cooling system

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31. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant total heat lines

Constant pressure lines

Constant entropy lines

32. 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

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

Horizontal line

Curved line

Inclined line

Vertical line

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

Strong solution to weak solution

Weak solution to strong solution

Strong solution to ammonia vapour

Ammonia vapours to weak solution

35. 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

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

Equal to

More than

None of these

Less than

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

Electrolux refrigerator

Vapour compression

Carnot cycle

Vapour absorption

38. The evaporator used in household refrigerators is

None of these

Frosting evaporator

Non-frosting evaporator

Defrosting evaporator

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

Before entering the expansion valve

After passing through the condenser

Before passing through the condenser

After passing through the expansion or throttle valve

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

Vapour compression cycle

Air refrigeration cycle

Vapour absorption cycle

None of these

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41. 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?

0.8

0.5

1.25

0.25

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

Ammonia and lithium bromide

Ammonia and water

Water and lithium bromide

Water and water

43. 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.

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

Refrigerating efficiency

Coefficient of performance of refrigeration

Coefficient of performance of heat pump

Relative coefficient of performance

45. Chaperon equation is applicable for registration at

Saturation point of vapour

Saturation point of liquid

Triple point

Sublimation temperature

Refrigeration & Air-Conditioning Practice Set-5

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