Refrigeration & Air-Conditioning Practice Set-5

July 7, 2021

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

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

Electrolux refrigerator

Carnot cycle

Vapour compression

Vapour absorption

3. The power per tonne of refrigeration is

None of these

C.O.P/3.5

3.5/C.O.P.

3.5 × C.O.P.

4. The refrigerant supplied to a compressor must be

Dry saturated liquid refrigerant

None of these

A mixture of liquid and vapour refrigerant

Superheated vapour refrigerant

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

None of these

Air refrigeration cycle

Vapour absorption cycle

Vapour compression cycle

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

Water and water

Water and lithium bromide

Ammonia and water

Ammonia and lithium bromide

7. 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

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 - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

9. The desirable property of a refrigerant is

High critical temperature

High latent heat of vaporisation

Low boiling point

All of these

10. 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

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

Horizontal and non-uniformly spaced

Curved lines

Horizontal and uniformly spaced

Vertical and uniformly spaced

12. The specific humidity during cooling and dehumidification

Decreases

Remains constant

None of these

Increases

13. 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

0.5

0.25

0.8

14. Ammonia is

Highly toxic and inflammable

Toxic and non-inflammable

Non-inflammable

Non-toxic

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

None of these

Greater than

Equal to

Less than

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

1 kg of dry air

1 m3 of dry air

1 m3 of wet air

1 kg of wet air

17. 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

18. 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 (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

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

After passing through the expansion or throttle valve

Before entering the expansion valve

Before passing through the condenser

After passing through the condenser

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

Generator

Liquid pump

Absorber, generator and liquid pump

Absorber and generator

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

50%

75%

10%

25%

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

Horizontal line

Vertical line

Curved line

Inclined line

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

1 m3 of dry air

1 kg of dry air

1 m3 of water

1 kg of wet air

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

Reversed Otto cycle

Reversed Carnot cycle

Reversed Brayton cycle

Reversed Joule cycle

25. Chaperon equation is applicable for registration at

Sublimation temperature

Saturation point of liquid

Triple point

Saturation point of vapour

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

Before entering the compressor

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

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

Dry bulb temperature

Relative humidity

Dew point temperature

Wet bulb temperature

28. The temperature of air recorded by a thermometer, when its bulb is surrounded by a wet cloth exposed to the air, is called

Dew point temperature

Dry bulb temperature

Wet bulb temperature

None of these

29. Short horizontal lines on pressure-enthalpy chart show

Constant total heat lines

Constant temperature lines

Constant pressure lines

Constant entropy lines

30. 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

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

Increase cooling effect

Reduce compressor discharge temperature

Reduce compressor overheating

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

32. The refrigerant for a refrigerator should have

High sensible heat

High latent heat

High total heat

Low latent heat

33. The evaporator used in household refrigerators is

Non-frosting evaporator

None of these

Frosting evaporator

Defrosting evaporator

34. 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

Decreases with increase in velocity of air passing through it

Remains unchanged with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

35. 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

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

Aluminium

Brass

Steel

Copper

37. Air refrigeration cycle is used in

Gas liquefaction

Domestic refrigerators

Air conditioning

Commercial refrigerators

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

None of these

Equal to

Less than

More than

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

840 kJ/ min

210 kJ/ min

420 kJ/ min

21 kJ/ min

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

Copper

Brass

Steel

Aluminium

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41. 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.

42. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

43. 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

Refrigerating efficiency

Relative coefficient of performance

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

Power per TR is low

System has high C.O.P.

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

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

Improves C.O.P. of the system

Increases power consumption

Reduces power consumption

Increases heat transfer

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Refrigeration & Air-Conditioning Practice Set-5

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