Refrigeration & Air-Conditioning Practice Set-5

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

210 kJ/ min

420 kJ/ min

21 kJ/ min

840 kJ/ min

2. 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 kg of dry air

The mass of water vapour present in 1 m³ of dry air

3. 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

Wet bulb temperature

None of these

Dew point temperature

4. Chaperon equation is applicable for registration at

Saturation point of vapour

Triple point

Saturation point of liquid

Sublimation temperature

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

1 kg of wet air

1 m3 of dry air

1 kg of dry air

1 m3 of water

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

None of these

Equal to

More than

Less than

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

Power per TR is low

Mass of refrigerant circulated in the system is low

System has high C.O.P.

Mass of the refrigeration equipment is low

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

Dry bulb temperature

Wet bulb temperature

Dew point temperature

Relative humidity

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

Greater than

None of these

Equal to

Less than

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

Weak solution to strong solution

Strong solution to weak solution

Strong solution to ammonia vapour

Ammonia vapours to weak solution

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

Refrigerating efficiency

Relative coefficient of performance

Coefficient of performance of heat pump

Coefficient of performance of refrigeration

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

Air refrigeration cycle

None of these

Vapour absorption cycle

Vapour compression cycle

13. Air refrigeration cycle is used in

Air conditioning

Domestic refrigerators

Gas liquefaction

Commercial refrigerators

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

Brass

Steel

Aluminium

Copper

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

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

Curved lines

16. 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 (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

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

Generator

Liquid pump

Absorber and generator

Absorber, generator and liquid pump

18. The specific humidity during cooling and dehumidification

None of these

Decreases

Increases

Remains constant

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

Steel

Brass

Aluminium

Copper

20. The evaporator used in household refrigerators is

Defrosting evaporator

Non-frosting evaporator

None of these

Frosting evaporator

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

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

Before passing through the condenser

22. 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)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

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

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

Before entering the compressor

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

Reduces power consumption

Increases heat transfer

Increases power consumption

Improves C.O.P. of the system

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

Electrolux refrigerator

Vapour absorption

Carnot cycle

Vapour compression

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

Ammonia and lithium bromide

Water and water

Water and lithium bromide

Ammonia and water

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

1 kg of dry air

1 kg of wet air

1 m3 of water

1 m3 of dry air

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

Sulphur dioxide

R-12

Ammonia

Carbon dioxide

29. The reciprocating refrigerant compressors are very suitable for

Small displacements and high condensing pressures

Large displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and low condensing pressures

30. The refrigerant supplied to a compressor must be

None of these

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

Superheated vapour refrigerant

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31. 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

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

25%

50%

75%

10%

33. The refrigerant for a refrigerator should have

High total heat

High sensible heat

Low latent heat

High latent heat

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

1 kg of dry air

1 kg of wet air

1 m3 of dry air

1 m3 of wet air

35. The desirable property of a refrigerant is

Low boiling point

High critical temperature

High latent heat of vaporisation

All of these

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

Horizontal line

Inclined line

Vertical line

Curved line

37. 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

38. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant temperature lines

Constant total heat lines

Constant pressure lines

39. 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

0.25

0.5

40. 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

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41. 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.

42. Ammonia is

Non-inflammable

Highly toxic and inflammable

Toxic and non-inflammable

Non-toxic

43. 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.

44. 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

Decreases with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

Remains unchanged with increase in velocity of air passing through it

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

Simple air cooling system

Regenerative air cooling system

Bootstrap air cooling system

Reduced ambient air cooling system

Refrigeration & Air-Conditioning Practice Set-5

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