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

Steel

Aluminium

Brass

Copper

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

Steel

Brass

Aluminium

Copper

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

Bootstrap air cooling system

Reduced ambient air cooling system

Regenerative air cooling system

Simple air cooling system

4. The desirable property of a refrigerant is

High latent heat of vaporisation

High critical temperature

Low boiling point

All of these

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

840 kJ/ min

210 kJ/ min

420 kJ/ min

21 kJ/ min

6. 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)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

7. 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

8. 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

Decreases with increase in velocity of air passing through it

Remains unchanged with increase in velocity of air passing through it

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)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

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

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

Curved lines

Horizontal and uniformly spaced

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11. 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

12. 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

1.25

0.5

0.8

13. 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

14. 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

15. 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

16. 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

17. Air refrigeration cycle is used in

Air conditioning

Commercial refrigerators

Gas liquefaction

Domestic refrigerators

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

Equal to

None of these

Greater than

Less than

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

More than

Equal to

Less than

None of these

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

1 kg of dry air

1 m3 of dry air

1 m3 of water

1 kg of wet air

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21. Ammonia is

Non-toxic

Highly toxic and inflammable

Non-inflammable

Toxic and non-inflammable

22. 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

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

Vapour absorption cycle

Vapour compression cycle

None of these

Air refrigeration cycle

24. 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

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

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

After passing through the condenser

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

Generator

Absorber and generator

Liquid pump

Absorber, generator and liquid pump

27. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

None of these

Superheated vapour refrigerant

Dry saturated liquid refrigerant

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

Vapour absorption

Carnot cycle

Electrolux refrigerator

Vapour compression

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

Coefficient of performance of refrigeration

Refrigerating efficiency

Relative coefficient of performance

Coefficient of performance of heat pump

30. 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

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

1 m3 of wet air

1 m3 of dry air

1 kg of wet air

1 kg of dry air

32. The refrigerant for a refrigerator should have

Low latent heat

High total heat

High latent heat

High sensible heat

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

Ammonia

Sulphur dioxide

Carbon dioxide

R-12

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

Reversed Otto cycle

Reversed Carnot cycle

Reversed Brayton cycle

Reversed Joule cycle

35. 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 m³ of dry air

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

36. The evaporator used in household refrigerators is

Defrosting evaporator

None of these

Non-frosting evaporator

Frosting evaporator

37. The specific humidity during cooling and dehumidification

None of these

Decreases

Remains constant

Increases

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

Curved line

Vertical line

Inclined line

Horizontal line

39. The reciprocating refrigerant compressors are very suitable for

Small displacements and high condensing pressures

Large displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and low condensing pressures

40. Chaperon equation is applicable for registration at

Sublimation temperature

Triple point

Saturation point of vapour

Saturation point of liquid

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

Ammonia vapours to weak solution

Strong solution to weak solution

Weak solution to strong solution

Strong solution to ammonia vapour

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. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant entropy lines

Constant temperature lines

Constant total heat lines

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

Dry bulb temperature

Dew point temperature

Relative humidity

Wet bulb temperature

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

75%

25%

50%

10%

Refrigeration & Air-Conditioning Practice Set-5

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