Refrigeration & Air-Conditioning Practice Set-5

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

Before entering the compressor

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

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

In 24 hours

In 1 hour

In 12 hours

In 1 minute

3. Chaperon equation is applicable for registration at

Saturation point of liquid

Sublimation temperature

Triple point

Saturation point of vapour

4. 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)

5. 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

6. The specific humidity during cooling and dehumidification

Increases

None of these

Remains constant

Decreases

7. 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.

8. 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

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

10%

50%

25%

75%

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

Carbon dioxide

Sulphur dioxide

Ammonia

R-12

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11. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant pressure lines

Constant entropy lines

Constant total heat lines

12. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

13. 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)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

14. 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

15. The refrigerant for a refrigerator should have

Low latent heat

High total heat

High latent heat

High sensible heat

16. 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

Dry bulb temperature

None of these

Wet bulb temperature

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

Reduced ambient air cooling system

Regenerative air cooling system

Simple air cooling system

Bootstrap air cooling system

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

Steel

Copper

Brass

Aluminium

19. 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

1.25

0.8

0.5

20. 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

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

Reversed Joule cycle

Reversed Brayton cycle

Reversed Otto cycle

Reversed Carnot cycle

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

1 m3 of wet air

1 kg of dry air

1 m3 of dry air

1 kg of wet air

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

Water and water

Ammonia and water

Water and lithium bromide

Ammonia and lithium bromide

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

Liquid pump

Absorber and generator

Generator

Absorber, generator and liquid pump

25. 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

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

21 kJ/ min

210 kJ/ min

840 kJ/ min

420 kJ/ min

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

Relative humidity

Wet bulb temperature

Dry bulb temperature

Dew point temperature

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

Vapour compression cycle

Vapour absorption cycle

None of these

Air refrigeration cycle

29. 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

Strong solution to weak solution

Weak solution to strong solution

30. 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.

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31. The desirable property of a refrigerant is

High latent heat of vaporisation

All of these

High critical temperature

Low boiling point

32. Air refrigeration cycle is used in

Air conditioning

Domestic refrigerators

Gas liquefaction

Commercial refrigerators

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

Carnot cycle

Electrolux refrigerator

Vapour absorption

Vapour compression

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

Inclined line

Vertical line

Horizontal line

Curved line

35. 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

Remains unchanged with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

36. Ammonia is

Toxic and non-inflammable

Non-inflammable

Highly toxic and inflammable

Non-toxic

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

Less than

More than

None of these

Equal to

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

System has high C.O.P.

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

Power per TR is low

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

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

Improves C.O.P. of the system

Increases heat transfer

Reduces power consumption

Increases power consumption

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

Steel

Aluminium

Copper

Brass

42. 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

43. The evaporator used in household refrigerators is

Non-frosting evaporator

Defrosting evaporator

Frosting evaporator

None of these

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

Less than

None of these

Equal to

Greater than

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

Coefficient of performance of heat pump

Relative coefficient of performance

Coefficient of performance of refrigeration

Refrigerating efficiency

Refrigeration & Air-Conditioning Practice Set-5

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