Refrigeration & Air-Conditioning Practice Set-5

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

Wet bulb temperature

Dry bulb temperature

Relative humidity

Dew point temperature

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

210 kJ/ min

420 kJ/ min

21 kJ/ min

840 kJ/ min

3. The desirable property of a refrigerant is

Low boiling point

High critical temperature

High latent heat of vaporisation

All of these

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

Aluminium

Brass

Steel

Copper

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

Reversed Carnot cycle

Reversed Otto cycle

Reversed Joule cycle

Reversed Brayton cycle

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

Greater than

Less than

None of these

Equal to

7. 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

Increases with increase in velocity of air passing through it

Remains unchanged with increase in velocity of air passing through it

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

Inclined line

Curved line

Vertical line

Horizontal line

9. 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

Wet bulb temperature

Dry bulb temperature

None of these

10. 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

Increase cooling effect

Reduce compressor discharge temperature

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

Steel

Brass

Copper

Aluminium

12. The power per tonne of refrigeration is

3.5 × C.O.P.

C.O.P/3.5

3.5/C.O.P.

None of these

13. The evaporator used in household refrigerators is

Non-frosting evaporator

None of these

Frosting evaporator

Defrosting evaporator

14. Air refrigeration cycle is used in

Gas liquefaction

Air conditioning

Commercial refrigerators

Domestic refrigerators

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

Refrigerating efficiency

Coefficient of performance of heat pump

Coefficient of performance of refrigeration

Relative coefficient of performance

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

Before passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

After passing through the condenser

17. Degree of saturation or percentage humidity is

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

The mass of water vapour present in 1 m³ 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

18. The specific humidity during cooling and dehumidification

None of these

Increases

Remains constant

Decreases

19. 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

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

Vapour compression cycle

None of these

Vapour absorption cycle

Air refrigeration cycle

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

Sulphur dioxide

Carbon dioxide

Ammonia

R-12

22. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

23. Ammonia is

Non-inflammable

Highly toxic and inflammable

Non-toxic

Toxic and non-inflammable

24. 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)

25. 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 24 hours

In 12 hours

26. The refrigerant for a refrigerator should have

High total heat

High sensible heat

High latent heat

Low latent heat

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

Ammonia and lithium bromide

Ammonia and water

Water and water

Water and lithium bromide

28. The refrigerant supplied to a compressor must be

None of these

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

Superheated vapour refrigerant

29. Chaperon equation is applicable for registration at

Triple point

Saturation point of vapour

Saturation point of liquid

Sublimation temperature

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

More than

Less than

None of these

Equal to

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31. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant total heat lines

Constant entropy lines

Constant pressure lines

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

Simple air cooling system

Reduced ambient air cooling system

Bootstrap air cooling system

Regenerative air cooling system

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

Vapour absorption

Vapour compression

Carnot cycle

Electrolux refrigerator

34. 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

0.5

1.25

0.8

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

Absorber, generator and liquid pump

Liquid pump

Absorber and generator

Generator

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

Curved lines

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

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

Improves C.O.P. of the system

Increases power consumption

Increases heat transfer

Reduces power consumption

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

Before entering the compressor

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

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

Ammonia vapours to weak solution

Weak solution to strong solution

Strong solution to weak solution

Strong solution to ammonia vapour

40. 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)

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

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

1 kg of wet air

1 m3 of water

1 kg of dry air

1 m3 of dry air

42. 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

43. In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = Bypass factor)

B.P.F. - 1

1 + B.P.F.

1/ B.P.F.

1 - B. P.F.

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

Mass of refrigerant circulated in the system is low

System has high C.O.P.

Power per TR is low

Mass of the refrigeration equipment is low

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

50%

75%

10%

25%

Refrigeration & Air-Conditioning Practice Set-5

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