Refrigeration & Air-Conditioning Practice Set-5

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

Vapour compression

Vapour absorption

Carnot cycle

Electrolux refrigerator

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

210 kJ/ min

21 kJ/ min

840 kJ/ min

420 kJ/ min

3. 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)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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

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

Reduce compressor discharge temperature

Increase cooling effect

Reduce compressor overheating

5. The evaporator used in household refrigerators is

Frosting evaporator

Defrosting evaporator

Non-frosting evaporator

None of these

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

Aluminium

Brass

Copper

Steel

7. 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

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

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the compressor

9. The desirable property of a refrigerant is

High critical temperature

Low boiling point

All of these

High latent heat of vaporisation

10. The specific humidity during cooling and dehumidification

Remains constant

Increases

Decreases

None of these

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

Vapour compression cycle

Air refrigeration cycle

Vapour absorption cycle

None of these

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

Ammonia and water

Water and lithium bromide

Water and water

Ammonia and lithium bromide

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

10%

25%

75%

50%

14. The reciprocating refrigerant compressors are very suitable for

Small displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Large displacements and high condensing pressures

15. The bypass factor for a cooling coil

Remains unchanged 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

Decreases with increase in velocity of air passing through it

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

Curved line

Vertical line

Horizontal line

Inclined line

17. Chaperon equation is applicable for registration at

Saturation point of liquid

Triple point

Saturation point of vapour

Sublimation temperature

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

R-12

Sulphur dioxide

Ammonia

Carbon dioxide

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

Improves C.O.P. of the system

Increases heat transfer

Increases power consumption

Reduces power consumption

20. 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

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21. 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

Dew point temperature

Wet bulb temperature

None of these

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

1 m3 of dry air

1 kg of dry air

1 m3 of wet air

1 kg of wet air

23. 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

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

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

Curved lines

25. 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)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

26. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

None of these

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

Reduced ambient air cooling system

Bootstrap air cooling system

Simple air cooling system

Regenerative air cooling system

28. 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.

29. 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

0.25

1.25

0.5

30. Air refrigeration cycle is used in

Commercial refrigerators

Air conditioning

Domestic refrigerators

Gas liquefaction

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

Brass

Aluminium

Steel

Copper

32. The power per tonne of refrigeration is

C.O.P/3.5

None of these

3.5 × C.O.P.

3.5/C.O.P.

33. The refrigerant for a refrigerator should have

High sensible heat

High latent heat

Low latent heat

High total heat

34. Degree of saturation or percentage humidity is

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

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

35. Ammonia is

Non-toxic

Non-inflammable

Toxic and non-inflammable

Highly toxic and inflammable

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

None of these

Equal to

Greater than

Less than

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

1 m3 of dry air

1 kg of dry air

1 kg of wet air

1 m3 of water

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

Dry bulb temperature

Dew point temperature

Wet bulb temperature

Relative humidity

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

Absorber and generator

Generator

Absorber, generator and liquid pump

Liquid pump

40. 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

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

Refrigerating efficiency

Relative coefficient of performance

Coefficient of performance of refrigeration

Coefficient of performance of heat pump

42. 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

43. 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

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

Less than

None of these

Equal to

More than

45. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant temperature lines

Constant total heat lines

Constant entropy lines

Refrigeration & Air-Conditioning Practice Set-5

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