Refrigeration & Air-Conditioning Practice Set-5

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1. The evaporator used in household refrigerators is

None of these

Defrosting evaporator

Frosting evaporator

Non-frosting evaporator

2. Ammonia is

Non-toxic

Non-inflammable

Toxic and non-inflammable

Highly toxic and inflammable

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

Absorber and generator

Absorber, generator and liquid pump

Generator

Liquid pump

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

Wet bulb temperature

Dry bulb temperature

Relative humidity

Dew point temperature

5. Chaperon equation is applicable for registration at

Triple point

Saturation point of vapour

Sublimation temperature

Saturation point of liquid

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

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

Before entering the compressor

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

1 kg of dry air

1 kg of wet air

1 m3 of dry air

1 m3 of water

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

Mass of refrigerant circulated in the system is low

Mass of the refrigeration equipment is low

Power per TR is low

System has high C.O.P.

9. The desirable property of a refrigerant is

All of these

High latent heat of vaporisation

High critical temperature

Low boiling point

10. 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

Dew point temperature

Dry bulb temperature

None of these

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

Simple air cooling system

Bootstrap air cooling system

Reduced ambient air cooling system

Regenerative air cooling system

12. 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)

(h1 - h2)/ (hA - h2)

(hA - h2)/ (h1 - h2)

13. The refrigerant supplied to a compressor must be

Superheated vapour refrigerant

None of these

A mixture of liquid and vapour refrigerant

Dry saturated liquid refrigerant

14. 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.

B.P.F. - 1

1/ B.P.F.

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

1 m3 of wet air

1 kg of dry air

1 kg of wet air

1 m3 of dry air

17. 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

0.8

0.25

18. The power per tonne of refrigeration is

3.5/C.O.P.

C.O.P/3.5

None of these

3.5 × C.O.P.

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

Copper

Brass

Aluminium

Steel

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

Weak solution to strong solution

Ammonia vapours to weak solution

Strong solution to ammonia vapour

Strong solution to weak solution

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

Vapour compression

Carnot cycle

Electrolux refrigerator

Vapour absorption

22. The refrigerant for a refrigerator should have

Low latent heat

High sensible heat

High total heat

High latent heat

23. 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

24. The specific humidity during cooling and dehumidification

Increases

Decreases

None of these

Remains constant

25. 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

26. Short horizontal lines on pressure-enthalpy chart show

Constant entropy lines

Constant temperature lines

Constant total heat lines

Constant pressure lines

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

Reduce compressor discharge temperature

Increase cooling effect

Reduce compressor overheating

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

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

Greater than

None of these

Less than

Equal to

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

Horizontal line

Curved line

Vertical line

Inclined line

30. 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 m³ of dry air

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

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31. The reciprocating refrigerant compressors are very suitable for

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

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

Reduces power consumption

Increases heat transfer

Increases power consumption

Improves C.O.P. of the system

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

Steel

Aluminium

Copper

Brass

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

50%

75%

25%

10%

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

420 kJ/ min

21 kJ/ min

840 kJ/ min

210 kJ/ min

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

R-12

Sulphur dioxide

Ammonia

Carbon dioxide

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

In 1 minute

In 12 hours

In 24 hours

In 1 hour

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

Coefficient of performance of refrigeration

Refrigerating efficiency

Coefficient of performance of heat pump

Relative coefficient of performance

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

Water and water

Ammonia and lithium bromide

Ammonia and water

Water and lithium bromide

40. 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)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₁ (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

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41. Air refrigeration cycle is used in

Gas liquefaction

Air conditioning

Domestic refrigerators

Commercial refrigerators

42. 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

43. 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

44. The bypass factor for a cooling coil

Remains unchanged with increase in velocity of air passing through it

Decreases with increase in velocity of air passing through it

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

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

Equal to

More than

None of these

Less than

Refrigeration & Air-Conditioning Practice Set-5

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