Refrigeration & Air-Conditioning Practice Set-5

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1. Ammonia is

Non-toxic

Non-inflammable

Toxic and non-inflammable

Highly toxic and inflammable

2. Degree of saturation or percentage humidity is

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 kg of dry air

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

3. 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 (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

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

Reduce compressor discharge temperature

Increase cooling effect

Reduce compressor overheating

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

5. 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

Dew point temperature

Dry bulb temperature

None of these

6. 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

Increases with increase in velocity of air passing through it

Remains unchanged with increase in velocity of air passing through it

Decreases with increase in velocity of air passing through it

7. Air refrigeration cycle is used in

Gas liquefaction

Commercial refrigerators

Air conditioning

Domestic refrigerators

8. 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

Power per TR is low

Mass of refrigerant circulated in the system is low

9. The refrigerant for a refrigerator should have

High sensible heat

High total heat

Low latent heat

High latent heat

10. 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

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11. 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?

1.25

0.25

0.8

0.5

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

10%

25%

50%

75%

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

Carbon dioxide

R-12

Sulphur dioxide

Ammonia

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

In 24 hours

In 12 hours

In 1 minute

In 1 hour

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

Less than

Equal to

More than

None of these

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

None of these

Less than

Greater than

Equal to

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

Simple air cooling system

Bootstrap air cooling system

Reduced ambient air cooling system

Regenerative air cooling system

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

210 kJ/ min

420 kJ/ min

21 kJ/ min

840 kJ/ min

19. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

None of these

Dry saturated liquid refrigerant

A mixture of liquid and vapour refrigerant

20. Chaperon equation is applicable for registration at

Saturation point of liquid

Saturation point of vapour

Sublimation temperature

Triple point

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21. 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

22. The specific humidity during cooling and dehumidification

Decreases

Remains constant

Increases

None of these

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

Reduces power consumption

Increases power consumption

Improves C.O.P. of the system

Increases heat transfer

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

Relative coefficient of performance

Coefficient of performance of refrigeration

Coefficient of performance of heat pump

Refrigerating efficiency

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

Electrolux refrigerator

Vapour compression

Vapour absorption

Carnot cycle

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

1 kg of wet air

1 kg of dry air

1 m3 of water

1 m3 of dry air

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

1 m3 of water

1 m3 of dry air

1 kg of dry air

1 kg of wet air

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

Wet bulb temperature

Dew point temperature

Dry bulb temperature

Relative humidity

29. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

Large displacements and low condensing pressures

30. 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

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

Copper

Aluminium

Steel

Brass

32. In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = Bypass factor)

B.P.F. - 1

1 - B. P.F.

1 + B.P.F.

1/ B.P.F.

33. The evaporator used in household refrigerators is

Defrosting evaporator

None of these

Frosting evaporator

Non-frosting evaporator

34. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant temperature lines

Constant total heat lines

Constant pressure lines

35. 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

Ammonia vapours to weak solution

Strong solution to weak solution

36. 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)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

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

Ammonia and water

Water and lithium bromide

Ammonia and lithium bromide

Water and water

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

Reversed Joule cycle

Reversed Brayton cycle

Reversed Carnot cycle

Reversed Otto cycle

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

Steel

Aluminium

Brass

Copper

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

After passing through the condenser

Before passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

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

Horizontal and uniformly spaced

Curved lines

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

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

Inclined line

Horizontal line

Vertical line

Curved line

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

Before passing through the condenser

After passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

44. The desirable property of a refrigerant is

All of these

High critical temperature

Low boiling point

High latent heat of vaporisation

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

1 m3 of dry air

1 kg of dry air

1 m3 of wet air

1 kg of wet air

Refrigeration & Air-Conditioning Practice Set-5

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