Refrigeration & Air-Conditioning Practice Set-5

July 7, 2021

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1. 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

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

25%

50%

10%

75%

3. Ammonia is

Non-inflammable

Non-toxic

Highly toxic and inflammable

Toxic and non-inflammable

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

Before entering the expansion valve

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

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

Reduce compressor overheating

Increase cooling effect

Reduce compressor discharge temperature

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

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

Increases power consumption

Reduces power consumption

Increases heat transfer

Improves C.O.P. of the system

7. The reciprocating refrigerant compressors are very suitable for

Small displacements and high condensing pressures

Large displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and low condensing pressures

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

1 + B.P.F.

B.P.F. - 1

1/ B.P.F.

1 - B. P.F.

9. 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

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

Horizontal and uniformly spaced

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

Curved lines

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

Relative humidity

Dry bulb temperature

Dew point temperature

Wet bulb temperature

12. The specific humidity during cooling and dehumidification

Decreases

None of these

Remains constant

Increases

13. 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 - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h1 - h2)/ (hA - h2)

14. 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 12 hours

In 1 hour

15. 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

16. Chaperon equation is applicable for registration at

Saturation point of vapour

Sublimation temperature

Saturation point of liquid

Triple point

17. 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

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 (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

19. The bypass factor for a cooling coil

Increases 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

Remains unchanged with increase in velocity of air passing through it

Decreases with increase in velocity of air passing through it

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

Simple air cooling system

Bootstrap air cooling system

Regenerative air cooling system

Reduced ambient air cooling system

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

After passing through the condenser

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the compressor

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

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

23. 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

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

Inclined line

Vertical line

Curved line

Horizontal line

25. Degree of saturation or percentage humidity is

The mass of water vapour present in 1 m³ 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

The mass of water vapour present in 1 kg 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

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

Less than

None of these

Equal to

Greater than

27. The power per tonne of refrigeration is

3.5/C.O.P.

None of these

3.5 × C.O.P.

C.O.P/3.5

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. 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

30. 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

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31. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant total heat lines

Constant pressure lines

Constant entropy lines

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

Aluminium

Steel

Brass

Copper

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

1 kg of wet air

1 m3 of water

1 m3 of dry air

1 kg of dry air

34. The evaporator used in household refrigerators is

Defrosting evaporator

Non-frosting evaporator

None of these

Frosting evaporator

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

Brass

Steel

Copper

Aluminium

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

Reversed Joule cycle

Reversed Carnot cycle

Reversed Otto cycle

Reversed Brayton cycle

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

840 kJ/ min

420 kJ/ min

210 kJ/ min

21 kJ/ min

38. 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

39. Air refrigeration cycle is used in

Gas liquefaction

Air conditioning

Commercial refrigerators

Domestic refrigerators

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

Vapour compression

Electrolux refrigerator

Vapour absorption

Carnot cycle

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41. The refrigerant for a refrigerator should have

Low latent heat

High sensible heat

High latent heat

High total heat

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

None of these

Equal to

More than

Less than

43. 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 heat pump

Coefficient of performance of refrigeration

Refrigerating efficiency

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

Vapour absorption cycle

None of these

Vapour compression cycle

Air refrigeration cycle

45. The desirable property of a refrigerant is

High latent heat of vaporisation

Low boiling point

High critical temperature

All of these

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