Refrigeration & Air-Conditioning Practice Set-5

July 7, 2021

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

Before entering the expansion valve

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

2. 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

3. Chaperon equation is applicable for registration at

Triple point

Saturation point of liquid

Sublimation temperature

Saturation point of vapour

4. 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

5. 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

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

In 1 minute

In 1 hour

In 12 hours

In 24 hours

7. 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

0.8

1.25

0.25

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

Steel

Copper

Aluminium

Brass

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

420 kJ/ min

21 kJ/ min

210 kJ/ min

840 kJ/ min

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

Steel

Aluminium

Brass

Copper

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

Weak solution to strong solution

Strong solution to weak solution

Strong solution to ammonia vapour

Ammonia vapours to weak solution

12. 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

Decreases with increase in velocity of air passing through it

Remains unchanged with increase in velocity of air passing through it

13. 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

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

None of these

Greater than

Less than

Equal to

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

Vapour compression cycle

Air refrigeration cycle

Vapour absorption cycle

None of these

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

Liquid pump

Absorber, generator and liquid pump

Absorber and generator

Generator

17. Ammonia is

Non-inflammable

Highly toxic and inflammable

Non-toxic

Toxic and non-inflammable

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

More than

Less than

Equal to

None of these

19. Air refrigeration cycle is used in

Domestic refrigerators

Air conditioning

Commercial refrigerators

Gas liquefaction

20. 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

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21. The specific humidity during cooling and dehumidification

Increases

Decreases

None of these

Remains constant

22. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant entropy lines

Constant total heat lines

Constant pressure lines

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

Vapour absorption

Carnot cycle

Electrolux refrigerator

Vapour compression

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

1 m3 of water

1 kg of dry air

1 m3 of dry air

1 kg of wet air

25. 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

Increase cooling effect

Reduce compressor overheating

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

System has high C.O.P.

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

Power per TR is low

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

25%

10%

50%

75%

28. 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

29. The refrigerant for a refrigerator should have

Low latent heat

High total heat

High latent heat

High sensible heat

30. 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

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

Reduced ambient air cooling system

Regenerative air cooling system

Bootstrap air cooling system

Simple air cooling system

32. The desirable property of a refrigerant is

High latent heat of vaporisation

High critical temperature

All of these

Low boiling point

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

Relative humidity

Dry bulb temperature

Wet bulb temperature

Dew point temperature

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

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

Curved lines

Vertical and uniformly spaced

35. The refrigerant supplied to a compressor must be

None of these

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

36. 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

37. Degree of saturation or percentage humidity is

The mass of water vapour present in 1 m³ 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 kg 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

38. 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 heat pump

Coefficient of performance of refrigeration

39. 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)

(h2 - hA)/ (h1 - h2)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

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

1 kg of dry air

1 kg of wet air

1 m3 of dry air

1 m3 of wet air

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

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

Before entering the compressor

42. 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 (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

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

Ammonia

R-12

Sulphur dioxide

Carbon dioxide

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

Inclined line

Horizontal line

Curved line

Vertical line

45. The evaporator used in household refrigerators is

Frosting evaporator

None of these

Defrosting evaporator

Non-frosting evaporator

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Refrigeration & Air-Conditioning Practice Set-5

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