Refrigeration & Air-Conditioning Practice Set-5

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

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the compressor

After passing through the condenser

2. 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)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

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

In 1 hour

In 24 hours

In 1 minute

In 12 hours

4. The evaporator used in household refrigerators is

Frosting evaporator

None of these

Non-frosting evaporator

Defrosting evaporator

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

Absorber, generator and liquid pump

Absorber and generator

Generator

Liquid pump

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

Copper

Aluminium

Steel

Brass

7. The refrigerant for a refrigerator should have

High total heat

High sensible heat

High latent heat

Low latent heat

8. Chaperon equation is applicable for registration at

Saturation point of vapour

Sublimation temperature

Saturation point of liquid

Triple point

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

1 kg of wet air

1 kg of dry air

1 m3 of dry air

1 m3 of water

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

None of these

Less than

Equal to

More than

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11. Air refrigeration cycle is used in

Commercial refrigerators

Gas liquefaction

Air conditioning

Domestic refrigerators

12. 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 (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

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

Wet bulb temperature

Dew point temperature

Dry bulb temperature

Relative humidity

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

210 kJ/ min

21 kJ/ min

840 kJ/ min

420 kJ/ min

15. 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

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

Vapour absorption

Carnot cycle

Vapour compression

Electrolux refrigerator

17. The desirable property of a refrigerant is

High latent heat of vaporisation

High critical temperature

Low boiling point

All of these

18. Ammonia is

Non-inflammable

Non-toxic

Toxic and non-inflammable

Highly toxic and inflammable

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

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

1 kg of dry air

1 kg of wet air

1 m3 of dry air

1 m3 of wet air

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21. 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 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

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

Equal to

Less than

None of these

Greater than

23. 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

0.8

0.25

1.25

24. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant total heat lines

Constant entropy lines

Constant temperature lines

25. 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

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

Reduce compressor overheating

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

Reduce compressor discharge temperature

Increase cooling effect

27. The power per tonne of refrigeration is

None of these

3.5 × C.O.P.

3.5/C.O.P.

C.O.P/3.5

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

Reversed Brayton cycle

Reversed Carnot cycle

Reversed Otto cycle

Reversed Joule cycle

29. 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.

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

Bootstrap air cooling system

Regenerative air cooling system

Simple air cooling system

Reduced ambient air cooling system

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

Aluminium

Steel

Copper

Brass

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

Before passing through the condenser

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the expansion valve

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

Relative coefficient of performance

Refrigerating efficiency

Coefficient of performance of refrigeration

Coefficient of performance of heat pump

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

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

Curved lines

Vertical and uniformly spaced

35. The specific humidity during cooling and dehumidification

Increases

Remains constant

None of these

Decreases

36. The reciprocating refrigerant compressors are very suitable for

Large displacements and high condensing pressures

Small displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and low condensing pressures

37. 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

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

Horizontal line

Vertical line

Inclined line

Curved line

39. 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

40. 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

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

25%

50%

10%

75%

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

Water and lithium bromide

Ammonia and lithium bromide

Water and water

Ammonia and water

43. 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

44. The refrigerant supplied to a compressor must be

None of these

Superheated vapour refrigerant

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

45. The bypass factor for a cooling coil

Decreases 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

Remains unchanged with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

Refrigeration & Air-Conditioning Practice Set-5

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