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

Aluminium

Steel

Brass

Copper

2. Air refrigeration cycle is used in

Commercial refrigerators

Domestic refrigerators

Gas liquefaction

Air conditioning

3. Degree of saturation or percentage humidity is

The mass of water vapour present in 1 m³ 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 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

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

Equal to

None of these

Greater than

Less than

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

Absorber, generator and liquid pump

Generator

Absorber and generator

Liquid pump

6. Chaperon equation is applicable for registration at

Saturation point of liquid

Saturation point of vapour

Triple point

Sublimation temperature

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

Brass

Aluminium

Copper

Steel

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

Horizontal and non-uniformly spaced

Curved lines

Vertical and uniformly spaced

Horizontal and uniformly spaced

9. The refrigerant for a refrigerator should have

Low latent heat

High total heat

High latent heat

High sensible heat

10. 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

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11. 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

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

210 kJ/ min

840 kJ/ min

420 kJ/ min

21 kJ/ min

13. 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

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

Water and lithium bromide

Ammonia and water

Water and water

Ammonia and lithium bromide

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

Carbon dioxide

R-12

Sulphur dioxide

Ammonia

16. The evaporator used in household refrigerators is

Non-frosting evaporator

None of these

Defrosting evaporator

Frosting evaporator

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

Increase cooling effect

Reduce compressor overheating

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

Reduce compressor discharge temperature

18. 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

19. Ammonia is

Toxic and non-inflammable

Highly toxic and inflammable

Non-toxic

Non-inflammable

20. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and low condensing pressures

Large displacements and high condensing pressures

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21. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant total heat lines

Constant entropy lines

Constant temperature lines

22. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

Superheated vapour refrigerant

None of these

23. 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

None of these

Wet bulb temperature

Dew point temperature

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

In 1 minute

In 12 hours

In 24 hours

In 1 hour

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

Inclined line

Curved line

Vertical line

Horizontal line

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

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

Before entering the expansion valve

27. The power per tonne of refrigeration is

3.5/C.O.P.

3.5 × C.O.P.

None of these

C.O.P/3.5

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

1 m3 of wet air

1 kg of wet air

1 m3 of dry air

1 kg of dry air

29. 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

Strong solution to weak solution

Weak solution to strong solution

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

1 m3 of water

1 m3 of dry air

1 kg of wet air

1 kg of dry air

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31. 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

32. 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

33. The bypass factor for a cooling coil

Increases 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

Decreases with increase in velocity of air passing through it

34. The desirable property of a refrigerant is

Low boiling point

High critical temperature

High latent heat of vaporisation

All of these

35. The specific humidity during cooling and dehumidification

Decreases

None of these

Increases

Remains constant

36. 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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

37. 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

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

75%

10%

25%

50%

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

Vapour absorption

Carnot cycle

Vapour compression

Electrolux refrigerator

40. 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?

0.5

1.25

0.8

0.25

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

Equal to

More than

None of these

Less than

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

Dew point temperature

Wet bulb temperature

Dry bulb temperature

Relative humidity

43. 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 (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

44. 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

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

1 m3 of dry air

1 kg of wet air

1 kg of dry air

1 m3 of water

Refrigeration & Air-Conditioning Practice Set-5

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