Refrigeration & Air-Conditioning Practice Set-5

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

None of these

Vapour absorption cycle

Vapour compression cycle

Air refrigeration cycle

2. 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.

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

Reduces power consumption

Increases power consumption

Increases heat transfer

Improves C.O.P. of the system

4. The temperature of air recorded by a thermometer, when its bulb is surrounded by a wet cloth exposed to the air, is called

Wet bulb temperature

Dry bulb temperature

None of these

Dew point temperature

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

Steel

Copper

Brass

Aluminium

6. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

None of these

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

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

1 kg of wet air

1 m3 of dry air

1 kg of dry air

1 m3 of wet air

8. 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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

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

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the compressor

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

Carnot cycle

Vapour absorption

Vapour compression

Electrolux refrigerator

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11. The evaporator used in household refrigerators is

Frosting evaporator

None of these

Defrosting evaporator

Non-frosting evaporator

12. 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

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)

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

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

Ammonia and lithium bromide

Water and lithium bromide

Ammonia and water

Water and water

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

In 24 hours

In 1 hour

In 1 minute

In 12 hours

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

Brass

Aluminium

Copper

Steel

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

420 kJ/ min

21 kJ/ min

210 kJ/ min

840 kJ/ min

18. Air refrigeration cycle is used in

Air conditioning

Domestic refrigerators

Gas liquefaction

Commercial refrigerators

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

Bootstrap air cooling system

Reduced ambient air cooling system

Simple air cooling system

Regenerative air cooling system

20. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

Small displacements and low condensing pressures

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21. The refrigerant for a refrigerator should have

High latent heat

High total heat

Low latent heat

High sensible heat

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

Greater than

None of these

Equal to

Less than

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

50%

75%

25%

10%

24. 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

1.25

0.25

0.5

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

More than

None of these

Less than

Equal to

26. Chaperon equation is applicable for registration at

Triple point

Saturation point of liquid

Saturation point of vapour

Sublimation temperature

27. 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

28. The power per tonne of refrigeration is

C.O.P/3.5

3.5/C.O.P.

None of these

3.5 × C.O.P.

29. The specific humidity during cooling and dehumidification

Remains constant

Decreases

Increases

None of these

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

Curved line

Horizontal line

Inclined line

Vertical line

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31. 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 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

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

Curved lines

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

33. The desirable property of a refrigerant is

High critical temperature

High latent heat of vaporisation

All of these

Low boiling point

34. Ammonia is

Highly toxic and inflammable

Non-toxic

Toxic and non-inflammable

Non-inflammable

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

Wet bulb temperature

Dry bulb temperature

Dew point temperature

Relative humidity

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

Mass of the refrigeration equipment is low

Power per TR is low

System has high C.O.P.

Mass of refrigerant circulated in the system is low

37. 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

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

R-12

Sulphur dioxide

Ammonia

Carbon dioxide

39. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant entropy lines

Constant pressure lines

Constant temperature lines

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

Liquid pump

Absorber, generator and liquid pump

Absorber and generator

Generator

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

1 kg of dry air

1 kg of wet air

1 m3 of dry air

1 m3 of water

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

Before entering the expansion valve

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

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

Relative coefficient of performance

Refrigerating efficiency

Coefficient of performance of refrigeration

Coefficient of performance of heat pump

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

Reversed Joule cycle

Reversed Otto cycle

Reversed Carnot cycle

Reversed Brayton cycle

45. The bypass factor for a cooling coil

Remains unchanged with increase in velocity of air passing through it

Decreases with increase in velocity of air passing through it

Increases 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

Refrigeration & Air-Conditioning Practice Set-5

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