Refrigeration & Air-Conditioning Practice Set-5

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1. 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

2. The evaporator used in household refrigerators is

Defrosting evaporator

Frosting evaporator

None of these

Non-frosting evaporator

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

0.25

1.25

0.8

4. 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

5. 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

Increase cooling effect

Reduce compressor discharge temperature

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

Curved lines

Vertical and uniformly spaced

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

7. Chaperon equation is applicable for registration at

Saturation point of liquid

Sublimation temperature

Triple point

Saturation point of vapour

8. 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)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

9. 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

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

Water and lithium bromide

Water and water

Ammonia and water

Ammonia and lithium bromide

12. 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

Dew point temperature

None of these

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

None of these

Less than

Greater than

Equal to

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

Mass of the refrigeration equipment is low

Mass of refrigerant circulated in the system is low

System has high C.O.P.

Power per TR is low

15. 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

16. 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

17. 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

18. 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

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

21 kJ/ min

420 kJ/ min

210 kJ/ min

840 kJ/ min

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

Copper

Brass

Steel

Aluminium

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

Dry bulb temperature

Wet bulb temperature

Relative humidity

Dew point temperature

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

None of these

Less than

Equal to

More than

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

1 m3 of dry air

1 m3 of wet air

1 kg of dry air

1 kg of wet air

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

Vertical line

Curved line

Horizontal line

Inclined line

25. The desirable property of a refrigerant is

High critical temperature

High latent heat of vaporisation

Low boiling point

All of these

26. Air refrigeration cycle is used in

Commercial refrigerators

Domestic refrigerators

Air conditioning

Gas liquefaction

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

Vapour compression

Carnot cycle

Electrolux refrigerator

Vapour absorption

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

Increases heat transfer

Improves C.O.P. of the system

Reduces power consumption

Increases power consumption

29. 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)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

30. 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.

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

Ammonia

R-12

Sulphur dioxide

Carbon dioxide

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

Absorber and generator

Generator

Absorber, generator and liquid pump

Liquid pump

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

25%

75%

10%

50%

34. The specific humidity during cooling and dehumidification

None of these

Remains constant

Decreases

Increases

35. Ammonia is

Non-toxic

Non-inflammable

Highly toxic and inflammable

Toxic and non-inflammable

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

Before entering the compressor

After passing through the condenser

Before passing through the condenser

After passing through the expansion or throttle valve

37. The refrigerant for a refrigerator should have

Low latent heat

High sensible heat

High total heat

High latent heat

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

Bootstrap air cooling system

Reduced ambient air cooling system

Regenerative air cooling system

Simple air cooling system

39. 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

Remains unchanged with increase in velocity of air passing through it

Decreases with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

40. 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 12 hours

In 1 minute

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41. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant entropy lines

Constant total heat lines

Constant pressure lines

42. 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

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

Vapour absorption cycle

None of these

Air refrigeration cycle

Vapour compression cycle

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

Copper

Steel

Brass

Aluminium

45. 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

Refrigeration & Air-Conditioning Practice Set-5

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