Refrigeration & Air-Conditioning Practice Set-5

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

Vapour absorption cycle

Air refrigeration cycle

None of these

Vapour compression cycle

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

Increases heat transfer

Increases power consumption

Improves C.O.P. of the system

Reduces power consumption

3. The desirable property of a refrigerant is

All of these

High critical temperature

Low boiling point

High latent heat of vaporisation

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

After passing through the expansion or throttle valve

Before entering the expansion valve

After passing through the condenser

Before passing through the condenser

5. 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

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

Sulphur dioxide

Ammonia

Carbon dioxide

R-12

7. 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

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

Equal to

None of these

More than

Less than

9. Air refrigeration cycle is used in

Commercial refrigerators

Domestic refrigerators

Air conditioning

Gas liquefaction

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

840 kJ/ min

420 kJ/ min

21 kJ/ min

210 kJ/ min

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

1 kg of wet air

1 m3 of water

1 m3 of dry air

1 kg of dry air

12. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

None of these

13. The refrigerant for a refrigerator should have

High latent heat

Low latent heat

High sensible heat

High total heat

14. The evaporator used in household refrigerators is

None of these

Frosting evaporator

Defrosting evaporator

Non-frosting evaporator

15. Chaperon equation is applicable for registration at

Sublimation temperature

Saturation point of vapour

Saturation point of liquid

Triple point

16. 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

17. 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 kg of dry air

1 m3 of dry air

18. 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

19. 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

20. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant pressure lines

Constant temperature lines

Constant entropy lines

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

Ammonia and water

Ammonia and lithium bromide

Water and water

Water and lithium bromide

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

Increase cooling effect

Reduce compressor overheating

Reduce compressor discharge temperature

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

23. 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

Dew point temperature

None of these

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

Steel

Copper

Brass

Aluminium

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

Inclined line

Vertical line

Horizontal line

Curved line

26. 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

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

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

System has high C.O.P.

Power per TR is low

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

Reversed Joule cycle

Reversed Brayton cycle

Reversed Carnot cycle

Reversed Otto cycle

29. The power per tonne of refrigeration is

3.5/C.O.P.

3.5 × C.O.P.

C.O.P/3.5

None of these

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

Copper

Steel

Brass

Aluminium

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

Electrolux refrigerator

Carnot cycle

Vapour compression

Vapour absorption

32. 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 - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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

Dry bulb temperature

Dew point temperature

Wet bulb temperature

Relative humidity

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?

0.5

0.8

0.25

1.25

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

Strong solution to ammonia vapour

Strong solution to weak solution

Weak solution to strong solution

Ammonia vapours to weak solution

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

In 24 hours

In 1 minute

In 12 hours

In 1 hour

37. 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)]

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

75%

50%

25%

10%

39. The specific humidity during cooling and dehumidification

Remains constant

Decreases

Increases

None of these

40. 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

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

1 m3 of dry air

1 m3 of water

1 kg of dry air

1 kg of wet air

42. Ammonia is

Non-inflammable

Highly toxic and inflammable

Non-toxic

Toxic and non-inflammable

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

After passing through the condenser

Before entering the compressor

Before passing through the condenser

After passing through the expansion or throttle valve

44. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and low condensing pressures

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

Equal to

Greater than

None of these

Less than

Refrigeration & Air-Conditioning Practice Set-5

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