Refrigeration & Air-Conditioning Practice Set-5

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

Reduce compressor overheating

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

Reduce compressor discharge temperature

Increase cooling effect

2. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant temperature lines

Constant total heat lines

Constant entropy lines

3. 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

4. Chaperon equation is applicable for registration at

Triple point

Sublimation temperature

Saturation point of liquid

Saturation point of vapour

5. Air refrigeration cycle is used in

Gas liquefaction

Air conditioning

Domestic refrigerators

Commercial refrigerators

6. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

Large displacements and low condensing pressures

7. 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.

1 + B.P.F.

B.P.F. - 1

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

1 kg of dry air

1 m3 of dry air

1 kg of wet air

1 m3 of wet air

9. 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 - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

10. The power per tonne of refrigeration is

C.O.P/3.5

3.5/C.O.P.

None of these

3.5 × C.O.P.

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11. 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

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

Power per TR is low

System has high C.O.P.

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

13. 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?

0.25

0.8

1.25

0.5

14. 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

Dew point temperature

Dry bulb temperature

Wet bulb temperature

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

Copper

Brass

Aluminium

Steel

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

210 kJ/ min

21 kJ/ min

420 kJ/ min

840 kJ/ min

17. 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

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

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

Vapour absorption cycle

None of these

Air refrigeration cycle

Vapour compression cycle

19. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

Dry saturated liquid refrigerant

None of these

A mixture of liquid and vapour refrigerant

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

Simple air cooling system

Bootstrap air cooling system

Reduced ambient air cooling system

Regenerative air cooling system

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

Absorber and generator

Generator

Liquid pump

Absorber, generator and liquid pump

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

Reversed Otto cycle

Reversed Carnot cycle

Reversed Joule cycle

Reversed Brayton cycle

23. The desirable property of a refrigerant is

High latent heat of vaporisation

Low boiling point

All of these

High critical temperature

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

Equal to

Less than

None of these

More than

25. 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

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

In 12 hours

In 1 hour

In 1 minute

In 24 hours

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

Curved line

Horizontal line

Vertical line

Inclined line

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

Ammonia vapours to weak solution

Weak solution to strong solution

Strong solution to weak solution

29. The refrigerant for a refrigerator should have

Low latent heat

High sensible heat

High latent heat

High total heat

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

Brass

Aluminium

Steel

Copper

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

Relative coefficient of performance

Coefficient of performance of refrigeration

Coefficient of performance of heat pump

Refrigerating efficiency

32. The specific humidity during cooling and dehumidification

Increases

Remains constant

Decreases

None of these

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

After passing through the condenser

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

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

Improves C.O.P. of the system

Reduces power consumption

Increases power consumption

Increases heat transfer

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

Wet bulb temperature

Relative humidity

Dry bulb temperature

Dew point temperature

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

Before passing through the condenser

After passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

37. The evaporator used in household refrigerators is

Defrosting evaporator

Frosting evaporator

Non-frosting evaporator

None of these

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

Equal to

Greater than

Less than

None of these

39. 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 (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

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41. Ammonia is

Toxic and non-inflammable

Non-inflammable

Highly toxic and inflammable

Non-toxic

42. 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

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

50%

75%

25%

10%

44. 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 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 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

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

Vapour compression

Electrolux refrigerator

Carnot cycle

Vapour absorption

Refrigeration & Air-Conditioning Practice Set-5

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