Refrigeration & Air-Conditioning Practice Set-5

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1. 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

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

Vapour compression cycle

Air refrigeration cycle

None of these

Vapour absorption cycle

3. 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

4. Chaperon equation is applicable for registration at

Triple point

Saturation point of liquid

Saturation point of vapour

Sublimation temperature

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

420 kJ/ min

21 kJ/ min

210 kJ/ min

840 kJ/ min

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

Brass

Aluminium

Steel

Copper

7. 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

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

Before entering the expansion valve

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

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

Electrolux refrigerator

Vapour compression

Vapour absorption

Carnot cycle

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

System has high C.O.P.

Power per TR is low

Mass of the refrigeration equipment is low

Mass of refrigerant circulated in the system is low

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11. 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)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

12. The bypass factor for a cooling coil

Increases with increase in velocity of air passing through it

Decreases with increase in velocity of air passing through it

Remains unchanged 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

13. 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 (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

14. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant entropy lines

Constant pressure lines

Constant total heat lines

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

More than

None of these

Less than

Equal to

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

Water and lithium bromide

Water and water

Ammonia and lithium bromide

Ammonia and water

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

Equal to

Greater than

Less than

None of these

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

Copper

Aluminium

Steel

Brass

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

Generator

Absorber and generator

Absorber, generator and liquid pump

Liquid pump

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

In 1 hour

In 24 hours

In 1 minute

In 12 hours

22. The power per tonne of refrigeration is

None of these

3.5/C.O.P.

3.5 × C.O.P.

C.O.P/3.5

23. The refrigerant supplied to a compressor must be

None of these

Dry saturated liquid refrigerant

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

24. The refrigerant for a refrigerator should have

High sensible heat

High latent heat

Low latent heat

High total heat

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

Reversed Brayton cycle

Reversed Carnot cycle

Reversed Joule cycle

Reversed Otto cycle

26. 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

27. 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

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

Increase cooling effect

Reduce compressor discharge temperature

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

Reduce compressor overheating

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

1 m3 of dry air

1 kg of wet air

1 m3 of water

1 kg of dry air

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

Curved line

Inclined line

Vertical line

Horizontal line

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31. 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

32. Air refrigeration cycle is used in

Gas liquefaction

Domestic refrigerators

Commercial refrigerators

Air conditioning

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

75%

25%

10%

50%

34. The desirable property of a refrigerant is

High critical temperature

Low boiling point

All of these

High latent heat of vaporisation

35. 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

Refrigerating efficiency

Coefficient of performance of heat pump

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

Horizontal and uniformly spaced

Curved lines

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

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

Weak solution to strong solution

Ammonia vapours to weak solution

Strong solution to weak solution

Strong solution to ammonia vapour

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

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

39. Ammonia is

Highly toxic and inflammable

Non-toxic

Toxic and non-inflammable

Non-inflammable

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

Regenerative air cooling system

Bootstrap air cooling system

Reduced ambient air cooling system

Simple air cooling system

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

Relative humidity

Wet bulb temperature

Dew point temperature

Dry bulb temperature

42. 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

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

Increases power consumption

Reduces power consumption

Increases heat transfer

Improves C.O.P. of the system

44. The evaporator used in household refrigerators is

None of these

Frosting evaporator

Non-frosting evaporator

Defrosting evaporator

45. The specific humidity during cooling and dehumidification

Decreases

Increases

None of these

Remains constant

Refrigeration & Air-Conditioning Practice Set-5

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