Refrigeration & Air-Conditioning Practice Set-5

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

Steel

Brass

Aluminium

Copper

2. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant total heat lines

Constant temperature lines

Constant entropy lines

3. 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

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

In 24 hours

In 1 hour

In 12 hours

In 1 minute

5. 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

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

Absorber and generator

Absorber, generator and liquid pump

Liquid pump

Generator

7. 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.

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

Greater than

Less than

None of these

Equal to

9. 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

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

Vapour compression cycle

Vapour absorption cycle

None of these

Air refrigeration cycle

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11. 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

0.25

1.25

12. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

Superheated vapour refrigerant

None of these

13. Chaperon equation is applicable for registration at

Sublimation temperature

Saturation point of liquid

Triple point

Saturation point of vapour

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

Strong solution to weak solution

Ammonia vapours to weak solution

Weak solution to strong solution

Strong solution to ammonia vapour

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

R-12

Ammonia

Sulphur dioxide

Carbon dioxide

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

Aluminium

Copper

Brass

Steel

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

1 m3 of water

1 m3 of dry air

1 kg of dry air

1 kg of wet air

18. Degree of saturation or percentage humidity is

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

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

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

Water and water

Ammonia and lithium bromide

Ammonia and water

Water and lithium bromide

20. The specific humidity during cooling and dehumidification

Remains constant

Decreases

Increases

None of these

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21. 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 - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

22. 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

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

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

Curved lines

Horizontal and uniformly spaced

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

10%

50%

25%

75%

25. 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

None of these

Dry bulb temperature

Wet bulb temperature

26. 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

27. The desirable property of a refrigerant is

All of these

High latent heat of vaporisation

Low boiling point

High critical temperature

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

Carnot cycle

Vapour absorption

Electrolux refrigerator

Vapour compression

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

After passing through the condenser

Before entering the expansion valve

Before passing through the condenser

After passing through the expansion or throttle valve

30. Air refrigeration cycle is used in

Air conditioning

Gas liquefaction

Commercial refrigerators

Domestic refrigerators

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

21 kJ/ min

840 kJ/ min

210 kJ/ min

420 kJ/ min

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

Increase cooling effect

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

Reduce compressor overheating

Reduce compressor discharge temperature

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

Reversed Joule cycle

Reversed Carnot cycle

Reversed Brayton cycle

Reversed Otto cycle

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

Dew point temperature

Wet bulb temperature

Relative humidity

Dry bulb temperature

35. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

36. The evaporator used in household refrigerators is

Frosting evaporator

Defrosting evaporator

None of these

Non-frosting evaporator

37. 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

38. The power per tonne of refrigeration is

None of these

3.5 × C.O.P.

C.O.P/3.5

3.5/C.O.P.

39. 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

40. Ammonia is

Highly toxic and inflammable

Non-inflammable

Non-toxic

Toxic and non-inflammable

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41. 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

42. The refrigerant for a refrigerator should have

Low latent heat

High latent heat

High sensible heat

High total heat

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

More than

Less than

Equal to

None of these

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

Horizontal line

Curved line

Inclined line

Vertical line

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)

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

Refrigeration & Air-Conditioning Practice Set-5

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