Refrigeration & Air-Conditioning Practice Set-5

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

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

Horizontal and uniformly spaced

Curved lines

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

1 m3 of water

1 kg of dry air

1 m3 of dry air

1 kg of wet air

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

Water and water

Water and lithium bromide

Ammonia and lithium bromide

Ammonia and water

4. The power per tonne of refrigeration is

3.5/C.O.P.

3.5 × C.O.P.

None of these

C.O.P/3.5

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

Air refrigeration cycle

None of these

Vapour absorption cycle

Vapour compression cycle

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

Reduce compressor overheating

Reduce compressor discharge temperature

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

Increase cooling effect

7. The refrigerant for a refrigerator should have

High total heat

Low latent heat

High sensible heat

High latent heat

8. The specific humidity during cooling and dehumidification

Decreases

Remains constant

Increases

None of these

9. Chaperon equation is applicable for registration at

Triple point

Sublimation temperature

Saturation point of liquid

Saturation point of vapour

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

Equal to

None of these

Less than

Greater than

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11. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

12. Degree of saturation or percentage humidity is

The mass of water vapour present in 1 kg 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 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 mass of water vapour present in 1 m³ of dry air

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

Ammonia

Carbon dioxide

Sulphur dioxide

R-12

14. 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)]

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

75%

50%

10%

25%

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

1 kg of wet air

1 kg of dry air

1 m3 of dry air

1 m3 of wet air

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

Vertical line

Horizontal line

Inclined line

Curved line

18. The evaporator used in household refrigerators is

Defrosting evaporator

None of these

Non-frosting evaporator

Frosting evaporator

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

420 kJ/ min

21 kJ/ min

840 kJ/ min

210 kJ/ min

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

Steel

Brass

Aluminium

Copper

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

Aluminium

Brass

Copper

Steel

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

Increases power consumption

Reduces power consumption

Improves C.O.P. of the system

Increases heat transfer

23. Ammonia is

Highly toxic and inflammable

Non-toxic

Toxic and non-inflammable

Non-inflammable

24. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

None of these

25. The desirable property of a refrigerant is

Low boiling point

All of these

High latent heat of vaporisation

High critical temperature

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

Generator

Absorber, generator and liquid pump

Liquid pump

Absorber and generator

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

Before passing through the condenser

Before entering the compressor

After passing through the condenser

After passing through the expansion or throttle valve

28. 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

29. 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

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

Equal to

None of these

More than

Less than

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31. 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

Coefficient of performance of refrigeration

Relative coefficient of performance

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

Relative humidity

Dew point temperature

Wet bulb temperature

Dry bulb temperature

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

1 + B.P.F.

B.P.F. - 1

1/ B.P.F.

1 - B. P.F.

34. 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

35. Air refrigeration cycle is used in

Gas liquefaction

Domestic refrigerators

Air conditioning

Commercial refrigerators

36. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant temperature lines

Constant total heat lines

Constant pressure lines

37. 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

38. The bypass factor for a cooling coil

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

May increase or decrease with increase in velocity of air passing through it depending upon the condition of air entering

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

Strong solution to ammonia vapour

Weak solution to strong solution

Strong solution to weak solution

Ammonia vapours to weak solution

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

1 kg of wet air

1 m3 of water

1 kg of dry air

1 m3 of dry air

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41. 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)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

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

Reversed Carnot cycle

Reversed Brayton cycle

Reversed Joule cycle

Reversed Otto cycle

43. 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?

0.25

0.8

0.5

1.25

44. 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

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

Vapour compression

Electrolux refrigerator

Vapour absorption

Carnot cycle

Refrigeration & Air-Conditioning Practice Set-5

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