Refrigeration & Air-Conditioning Practice Set-5

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1. The desirable property of a refrigerant is

Low boiling point

All of these

High latent heat of vaporisation

High critical temperature

2. 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

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

4. The specific humidity during cooling and dehumidification

Increases

None of these

Remains constant

Decreases

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

Brass

Steel

Copper

Aluminium

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

Increases heat transfer

Increases power consumption

Reduces power consumption

Improves C.O.P. of the system

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

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the expansion valve

After passing through the condenser

8. The refrigerant for a refrigerator should have

High sensible heat

High total heat

High latent heat

Low latent heat

9. 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

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

Less than

Greater than

Equal to

None of these

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

1 m3 of dry air

1 kg of dry air

1 kg of wet air

1 m3 of water

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

Absorber, generator and liquid pump

Liquid pump

Generator

Absorber and generator

13. 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

14. Ammonia is

Toxic and non-inflammable

Non-inflammable

Highly toxic and inflammable

Non-toxic

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

420 kJ/ min

840 kJ/ min

210 kJ/ min

21 kJ/ min

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

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

System has high C.O.P.

Power per TR is low

17. The refrigerant supplied to a compressor must be

None of these

Dry saturated liquid refrigerant

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

18. 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

Strong solution to weak solution

Weak solution to strong solution

19. 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

20. 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 m³ of dry air

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

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21. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and low condensing pressures

Large displacements and high condensing pressures

22. 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

Increases with increase in velocity of air passing through it

Decreases with increase in velocity of air passing through it

23. Chaperon equation is applicable for registration at

Sublimation temperature

Saturation point of liquid

Saturation point of vapour

Triple point

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

Reduce compressor discharge temperature

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

Reduce compressor overheating

Increase cooling effect

25. 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

26. 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)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

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

Inclined line

Curved line

Horizontal line

Vertical line

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

Curved lines

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

Horizontal and uniformly spaced

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

Equal to

Less than

More than

None of these

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

Brass

Copper

Steel

Aluminium

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

Electrolux refrigerator

Carnot cycle

Vapour absorption

Vapour compression

32. 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

33. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant entropy lines

Constant pressure lines

Constant total heat lines

34. 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 (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

35. 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 expansion or throttle valve

After passing through the condenser

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

Water and lithium bromide

Ammonia and water

Ammonia and lithium bromide

Water and water

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

1 kg of dry air

1 m3 of water

1 m3 of dry air

1 kg of wet air

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

Reversed Joule cycle

Reversed Otto cycle

Reversed Carnot cycle

Reversed Brayton cycle

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

1 kg of wet air

1 m3 of wet air

1 kg of dry air

1 m3 of dry air

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

10%

75%

25%

50%

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41. The evaporator used in household refrigerators is

Non-frosting evaporator

Frosting evaporator

Defrosting evaporator

None of these

42. 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

Wet bulb temperature

Dry bulb temperature

Dew point temperature

43. 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

0.5

1.25

44. Air refrigeration cycle is used in

Gas liquefaction

Domestic refrigerators

Air conditioning

Commercial refrigerators

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

Relative humidity

Dry bulb temperature

Wet bulb temperature

Dew point temperature

Refrigeration & Air-Conditioning Practice Set-5

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