Refrigeration & Air-Conditioning Practice Set-5

July 7, 2021

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1. Ammonia is

Non-toxic

Highly toxic and inflammable

Non-inflammable

Toxic and non-inflammable

2. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

A mixture of liquid and vapour refrigerant

None of these

Dry saturated liquid refrigerant

3. 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 - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h2 - hA)/ (h1 - h2)

4. 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

Remains unchanged with increase in velocity of air passing through it

Increases with increase in velocity of air passing through it

Decreases with increase in velocity of air passing through it

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

Bootstrap air cooling system

Simple air cooling system

Reduced ambient air cooling system

Regenerative air cooling system

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

Vapour absorption

Carnot cycle

Electrolux refrigerator

Vapour compression

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

Mass of the refrigeration equipment is low

Power per TR is low

Mass of refrigerant circulated in the system is low

System has high C.O.P.

8. 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

0.5

0.25

1.25

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

Curved line

Horizontal line

Vertical line

Inclined line

10. The evaporator used in household refrigerators is

Non-frosting evaporator

None of these

Defrosting evaporator

Frosting evaporator

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

21 kJ/ min

840 kJ/ min

420 kJ/ min

210 kJ/ min

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

1 kg of wet air

1 kg of dry air

1 m3 of dry air

1 m3 of water

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

Aluminium

Brass

Steel

Copper

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

1 m3 of dry air

1 kg of wet air

1 kg of dry air

1 m3 of water

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

Vertical and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

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

Less than

None of these

Equal to

More than

17. 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

18. 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

19. The refrigerant for a refrigerator should have

Low latent heat

High latent heat

High total heat

High sensible heat

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

1 kg of wet air

1 m3 of dry air

1 kg of dry air

1 m3 of wet air

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

Equal to

Greater than

None of these

Less than

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

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

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

Absorber, generator and liquid pump

Generator

Absorber and generator

Liquid pump

24. 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 ammonia vapour

Strong solution to weak solution

Ammonia vapours to weak solution

25. The specific humidity during cooling and dehumidification

Decreases

None of these

Increases

Remains constant

26. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant pressure lines

Constant temperature lines

Constant total heat lines

27. 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

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

Reduce compressor overheating

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

Reduce compressor discharge temperature

Increase cooling effect

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

Ammonia and lithium bromide

Water and lithium bromide

Ammonia and water

Water and water

30. Chaperon equation is applicable for registration at

Triple point

Saturation point of liquid

Sublimation temperature

Saturation point of vapour

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

Wet bulb temperature

Dew point temperature

Relative humidity

Dry bulb temperature

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

Aluminium

Steel

Copper

Brass

33. Air refrigeration cycle is used in

Commercial refrigerators

Domestic refrigerators

Air conditioning

Gas liquefaction

34. The reciprocating refrigerant compressors are very suitable for

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

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

None of these

Vapour compression cycle

Vapour absorption cycle

Air refrigeration cycle

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

Improves C.O.P. of the system

Reduces power consumption

Increases power consumption

Increases heat transfer

37. 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

38. 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

39. The desirable property of a refrigerant is

High critical temperature

All of these

High latent heat of vaporisation

Low boiling point

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

25%

50%

10%

75%

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

Before entering the expansion valve

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

42. 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 condenser

After passing through the expansion or throttle valve

43. 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)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

44. The power per tonne of refrigeration is

3.5/C.O.P.

3.5 × C.O.P.

None of these

C.O.P/3.5

45. Degree of saturation or percentage humidity is

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

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

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

Refrigeration & Air-Conditioning Practice Set-5

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