Refrigeration & Air-Conditioning Practice Set-5

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

Reduce compressor overheating

Increase cooling effect

Reduce compressor discharge temperature

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

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

Aluminium

Brass

Copper

Steel

3. The desirable property of a refrigerant is

Low boiling point

High critical temperature

High latent heat of vaporisation

All of these

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

Vapour compression

Electrolux refrigerator

Carnot cycle

Vapour absorption

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

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the expansion valve

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

Mass of the refrigeration equipment is low

System has high C.O.P.

Power per TR is low

Mass of refrigerant circulated in the system is low

7. 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

8. In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = Bypass factor)

B.P.F. - 1

1 + B.P.F.

1 - B. P.F.

1/ B.P.F.

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

Vertical line

Horizontal line

Inclined line

Curved line

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

840 kJ/ min

21 kJ/ min

420 kJ/ min

210 kJ/ min

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11. 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

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

Strong solution to weak solution

Ammonia vapours to weak solution

Weak solution to strong solution

Strong solution to ammonia vapour

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

Relative humidity

Wet bulb temperature

Dew point temperature

Dry bulb temperature

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

Refrigerating efficiency

Coefficient of performance of heat pump

Relative coefficient of performance

Coefficient of performance of refrigeration

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

Water and lithium bromide

Ammonia and lithium bromide

Ammonia and water

Water and water

16. Air refrigeration cycle is used in

Air conditioning

Domestic refrigerators

Gas liquefaction

Commercial refrigerators

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

1 kg of dry air

1 m3 of dry air

1 kg of wet air

1 m3 of water

18. 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

19. 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

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

None of these

Wet bulb temperature

Dry bulb temperature

Dew point temperature

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21. 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

22. The evaporator used in household refrigerators is

Defrosting evaporator

Non-frosting evaporator

None of these

Frosting evaporator

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

1 kg of dry air

1 m3 of wet air

1 m3 of dry air

1 kg of wet air

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

None of these

Less than

More than

Equal to

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

None of these

Vapour compression cycle

Vapour absorption cycle

Air refrigeration cycle

26. 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 - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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

Increases heat transfer

Improves C.O.P. of the system

Increases power consumption

Reduces power consumption

28. 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

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

30. The refrigerant for a refrigerator should have

High sensible heat

Low latent heat

High total heat

High latent heat

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31. 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

32. 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

33. Chaperon equation is applicable for registration at

Saturation point of liquid

Saturation point of vapour

Sublimation temperature

Triple point

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

Equal to

None of these

Greater than

Less than

35. 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?

1.25

0.8

0.5

0.25

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

75%

10%

25%

50%

37. Ammonia is

Non-inflammable

Highly toxic and inflammable

Non-toxic

Toxic and non-inflammable

38. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

Superheated vapour refrigerant

None of these

Dry saturated liquid refrigerant

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

1 m3 of dry air

1 m3 of water

1 kg of wet air

1 kg of dry air

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

In 1 minute

In 24 hours

In 12 hours

In 1 hour

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41. 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 (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

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

Aluminium

Brass

Steel

Copper

43. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant temperature lines

Constant total heat lines

Constant entropy lines

44. The specific humidity during cooling and dehumidification

None of these

Remains constant

Decreases

Increases

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

Simple air cooling system

Bootstrap air cooling system

Reduced ambient air cooling system

Regenerative air cooling system

Refrigeration & Air-Conditioning Practice Set-5

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