Refrigeration & Air-Conditioning Practice Set-5

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1. Ammonia is

Highly toxic and inflammable

Toxic and non-inflammable

Non-inflammable

Non-toxic

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

Horizontal and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

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

1 m3 of water

1 kg of dry air

1 kg of wet air

1 m3 of dry air

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

75%

50%

25%

10%

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

Absorber and generator

Generator

Liquid pump

Absorber, generator and liquid pump

6. 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

Dew point temperature

Wet bulb temperature

Dry bulb temperature

7. Degree of saturation or percentage humidity is

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 kg of dry air

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

8. 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?

0.8

0.25

1.25

0.5

9. 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

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

Reversed Joule cycle

Reversed Otto cycle

Reversed Brayton cycle

Reversed Carnot cycle

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

Wet bulb temperature

Dry bulb temperature

Dew point temperature

Relative humidity

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

Refrigerating efficiency

Relative coefficient of performance

Coefficient of performance of refrigeration

Coefficient of performance of heat pump

13. The refrigerant for a refrigerator should have

Low latent heat

High sensible heat

High total heat

High latent heat

14. 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)

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

Brass

Steel

Aluminium

Copper

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

Greater than

Less than

None of these

Equal to

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

Reduce compressor overheating

Increase cooling effect

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

Reduce compressor discharge temperature

18. The desirable property of a refrigerant is

High latent heat of vaporisation

High critical temperature

All of these

Low boiling point

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

R-12

Carbon dioxide

Sulphur dioxide

Ammonia

20. 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 wet air

1 kg of dry air

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21. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

22. 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.

1 - B. P.F.

B.P.F. - 1

23. 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

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

Water and water

Ammonia and lithium bromide

Water and lithium bromide

Ammonia and water

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

Strong solution to weak solution

Weak solution to strong solution

Ammonia vapours to weak solution

Strong solution to ammonia vapour

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

1 m3 of water

1 kg of wet air

1 kg of dry air

1 m3 of dry air

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

Horizontal line

Inclined line

Vertical line

Curved line

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

In 24 hours

In 1 minute

In 1 hour

In 12 hours

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

None of these

Less than

Equal to

More than

30. 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)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

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

840 kJ/ min

210 kJ/ min

21 kJ/ min

420 kJ/ min

32. The evaporator used in household refrigerators is

Non-frosting evaporator

None of these

Frosting evaporator

Defrosting evaporator

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

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

Before passing through the condenser

34. 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

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

Electrolux refrigerator

Vapour compression

Vapour absorption

Carnot cycle

36. Air refrigeration cycle is used in

Air conditioning

Gas liquefaction

Domestic refrigerators

Commercial refrigerators

37. Chaperon equation is applicable for registration at

Saturation point of vapour

Triple point

Saturation point of liquid

Sublimation temperature

38. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

None of these

Dry saturated liquid refrigerant

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

None of these

Vapour compression cycle

Air refrigeration cycle

Vapour absorption cycle

40. Short horizontal lines on pressure-enthalpy chart show

Constant pressure lines

Constant total heat lines

Constant entropy lines

Constant temperature lines

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

Steel

Copper

Brass

Aluminium

42. The specific humidity during cooling and dehumidification

None of these

Remains constant

Increases

Decreases

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

Simple air cooling system

Reduced ambient air cooling system

Bootstrap air cooling system

Regenerative air cooling system

44. 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

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

Reduces power consumption

Increases heat transfer

Improves C.O.P. of the system

Increases power consumption

Refrigeration & Air-Conditioning Practice Set-5

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