Refrigeration & Air-Conditioning Practice Set-5

July 7, 2021

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1. Ammonia is

Toxic and non-inflammable

Non-inflammable

Highly toxic and inflammable

Non-toxic

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

Strong solution to ammonia vapour

Ammonia vapours to weak solution

Strong solution to weak solution

Weak solution to strong solution

3. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant entropy lines

Constant total heat lines

Constant pressure lines

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

Coefficient of performance of refrigeration

Relative coefficient of performance

Refrigerating efficiency

Coefficient of performance of heat pump

5. The desirable property of a refrigerant is

Low boiling point

High critical temperature

High latent heat of vaporisation

All of these

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

More than

Less than

Equal to

None of these

7. The evaporator used in household refrigerators is

Frosting evaporator

None of these

Defrosting evaporator

Non-frosting evaporator

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

Increase cooling effect

Reduce compressor overheating

Reduce compressor discharge temperature

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

9. 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 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

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

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

Dew point temperature

Dry bulb temperature

Wet bulb temperature

Relative humidity

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11. 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

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

Greater than

Less than

Equal to

None of these

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

1 m3 of dry air

1 m3 of wet air

1 kg of wet air

1 kg of dry air

14. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Large displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

15. 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

None of these

Dew point temperature

Dry bulb temperature

16. 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

17. Chaperon equation is applicable for registration at

Sublimation temperature

Saturation point of vapour

Triple point

Saturation point of liquid

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

210 kJ/ min

420 kJ/ min

840 kJ/ min

21 kJ/ min

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

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

Curved lines

Horizontal and uniformly spaced

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

Steel

Aluminium

Copper

Brass

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

Steel

Aluminium

Brass

Copper

22. 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)]

23. 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

Decreases with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

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

Inclined line

Horizontal line

Curved line

Vertical line

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

Ammonia and water

Ammonia and lithium bromide

Water and water

Water and lithium bromide

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

Carbon dioxide

Ammonia

Sulphur dioxide

R-12

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

10%

25%

50%

75%

28. The refrigerant supplied to a compressor must be

None of these

A mixture of liquid and vapour refrigerant

Superheated vapour refrigerant

Dry saturated liquid refrigerant

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?

0.8

1.25

0.5

0.25

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

Carnot cycle

Vapour absorption

Electrolux refrigerator

Vapour compression

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

Mass of the refrigeration equipment is low

Mass of refrigerant circulated in the system is low

Power per TR is low

System has high C.O.P.

32. 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)

(h1 - h2)/ (hA - h2)

(hA - h1)/ (h2 - h1)

(hA - h2)/ (h1 - h2)

(h2 - hA)/ (h1 - h2)

33. Air refrigeration cycle is used in

Gas liquefaction

Domestic refrigerators

Air conditioning

Commercial refrigerators

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

Reversed Brayton cycle

Reversed Otto cycle

Reversed Joule cycle

Reversed Carnot cycle

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

Reduces power consumption

Improves C.O.P. of the system

Increases heat transfer

Increases power consumption

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

Generator

Absorber, generator and liquid pump

Liquid pump

Absorber and generator

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

In 1 hour

In 1 minute

In 24 hours

In 12 hours

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

Regenerative air cooling system

Reduced ambient air cooling system

Bootstrap air cooling system

Simple air cooling system

39. 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

40. The specific humidity during cooling and dehumidification

Remains constant

Decreases

Increases

None of these

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

After passing through the expansion or throttle valve

After passing through the condenser

Before entering the expansion valve

Before passing through the condenser

42. 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

43. The refrigerant for a refrigerator should have

Low latent heat

High latent heat

High total heat

High sensible heat

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

After passing through the condenser

Before passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

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

Air refrigeration cycle

Vapour compression cycle

None of these

Vapour absorption cycle

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Refrigeration & Air-Conditioning Practice Set-5

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