Refrigeration & Air-Conditioning Practice Set-5

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1. The desirable property of a refrigerant is

High critical temperature

High latent heat of vaporisation

Low boiling point

All of these

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

Reduces power consumption

Increases power consumption

Improves C.O.P. of the system

Increases heat transfer

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

Equal to

Less than

More than

None of these

4. The specific humidity during cooling and dehumidification

None of these

Remains constant

Increases

Decreases

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

Curved lines

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

Horizontal and uniformly spaced

6. 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

7. 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 ammonia vapour

Weak solution to strong solution

Strong solution to weak solution

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

Air refrigeration cycle

Vapour absorption cycle

Vapour compression cycle

None of these

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

Regenerative air cooling system

Simple air cooling system

Bootstrap air cooling system

Reduced ambient air cooling system

10. Ammonia is

Toxic and non-inflammable

Non-toxic

Non-inflammable

Highly toxic and inflammable

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11. 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)

(h2 - hA)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

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

21 kJ/ min

840 kJ/ min

210 kJ/ min

420 kJ/ min

13. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant temperature lines

Constant entropy lines

Constant pressure lines

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

Greater than

Less than

Equal to

None of these

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

Steel

Aluminium

Brass

Copper

16. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

Superheated vapour refrigerant

Dry saturated liquid refrigerant

None of these

17. 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

18. 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

0.25

0.8

1.25

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

After passing through the condenser

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the compressor

20. The evaporator used in household refrigerators is

Non-frosting evaporator

Defrosting evaporator

Frosting evaporator

None of these

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21. 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

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

Water and water

Ammonia and lithium bromide

Ammonia and water

Water and lithium bromide

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

Electrolux refrigerator

Vapour absorption

Vapour compression

Carnot cycle

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

Dew point temperature

Wet bulb temperature

Dry bulb temperature

None of these

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

Increase cooling effect

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

Reduce compressor discharge temperature

Reduce compressor overheating

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

Relative humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

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

Generator

Liquid pump

Absorber and generator

Absorber, generator and liquid pump

28. 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 (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

29. 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

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

Reversed Carnot cycle

Reversed Otto cycle

Reversed Joule cycle

Reversed Brayton cycle

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

25%

75%

50%

10%

32. 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.

33. Air refrigeration cycle is used in

Air conditioning

Gas liquefaction

Domestic refrigerators

Commercial refrigerators

34. 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

35. Chaperon equation is applicable for registration at

Triple point

Saturation point of vapour

Sublimation temperature

Saturation point of liquid

36. 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 heat pump

Refrigerating efficiency

Coefficient of performance of refrigeration

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

Steel

Brass

Aluminium

Copper

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

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

39. The power per tonne of refrigeration is

C.O.P/3.5

3.5/C.O.P.

3.5 × C.O.P.

None of these

40. The bypass factor for a cooling coil

Decreases with increase in velocity of air passing through it

Remains unchanged 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

Increases with increase in velocity of air passing through it

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41. 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

42. The refrigerant for a refrigerator should have

High total heat

High sensible heat

High latent heat

Low latent heat

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

Vertical line

Inclined line

Horizontal line

Curved line

44. 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

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

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

Before entering the expansion valve

Refrigeration & Air-Conditioning Practice Set-5

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