Refrigeration & Air-Conditioning Practice Set-5

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

Reduces power consumption

Increases power consumption

Increases heat transfer

Improves C.O.P. of the system

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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

3. 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

1.25

0.8

0.25

4. The refrigerant for a refrigerator should have

Low latent heat

High latent heat

High sensible heat

High total heat

5. 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.

6. Air refrigeration cycle is used in

Air conditioning

Gas liquefaction

Domestic refrigerators

Commercial refrigerators

7. 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)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

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

Before entering the compressor

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

9. The evaporator used in household refrigerators is

None of these

Frosting evaporator

Defrosting evaporator

Non-frosting evaporator

10. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant temperature lines

Constant entropy lines

Constant pressure lines

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11. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

None of these

Superheated vapour refrigerant

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

Ammonia and lithium bromide

Water and lithium bromide

Water and water

Ammonia and water

13. The desirable property of a refrigerant is

High latent heat of vaporisation

High critical temperature

Low boiling point

All of these

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

Vapour absorption cycle

Vapour compression cycle

Air refrigeration cycle

None of these

15. 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

16. The specific humidity during cooling and dehumidification

Remains constant

None of these

Increases

Decreases

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

1 m3 of dry air

1 kg of wet air

1 kg of dry air

1 m3 of wet air

18. The reciprocating refrigerant compressors are very suitable for

Small displacements and high condensing pressures

Large displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and low condensing pressures

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

Relative humidity

Dry bulb temperature

Wet bulb temperature

Dew point temperature

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

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the expansion valve

Before passing through the condenser

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

Inclined line

Vertical line

Horizontal line

Curved line

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

Reversed Otto cycle

Reversed Brayton cycle

Reversed Carnot cycle

Reversed Joule cycle

23. 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

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

Coefficient of performance of refrigeration

Coefficient of performance of heat pump

Relative coefficient of performance

Refrigerating efficiency

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

Equal to

Less than

None of these

More than

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

1 m3 of dry air

1 kg of wet air

1 m3 of water

1 kg of dry air

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

Brass

Copper

Steel

Aluminium

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

25%

50%

75%

10%

29. 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

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

Absorber, generator and liquid pump

Generator

Liquid pump

Absorber and generator

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

32. 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

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

Vertical and uniformly spaced

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

Curved lines

34. The power per tonne of refrigeration is

None of these

3.5 × C.O.P.

C.O.P/3.5

3.5/C.O.P.

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

Less than

None of these

Greater than

Equal to

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

System has high C.O.P.

Mass of the refrigeration equipment is low

Mass of refrigerant circulated in the system is low

Power per TR is low

37. Ammonia is

Highly toxic and inflammable

Toxic and non-inflammable

Non-toxic

Non-inflammable

38. The bypass factor for a cooling coil

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

Decreases with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

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

420 kJ/ min

210 kJ/ min

840 kJ/ min

21 kJ/ min

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

Brass

Copper

Steel

Aluminium

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41. 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

Dry bulb temperature

Wet bulb temperature

Dew point temperature

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

Carnot cycle

Electrolux refrigerator

Vapour absorption

Vapour compression

43. Degree of saturation or percentage humidity is

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

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

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

Simple air cooling system

Reduced ambient air cooling system

Regenerative air cooling system

Bootstrap air cooling system

45. Chaperon equation is applicable for registration at

Saturation point of vapour

Saturation point of liquid

Sublimation temperature

Triple point

Refrigeration & Air-Conditioning Practice Set-5

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