Refrigeration & Air-Conditioning Practice Set-5

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

Water and lithium bromide

Ammonia and water

Water and water

Ammonia and lithium bromide

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

Reduce compressor discharge temperature

Reduce compressor overheating

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

Increase cooling effect

3. The refrigerant supplied to a compressor must be

A mixture of liquid and vapour refrigerant

None of these

Superheated vapour refrigerant

Dry saturated liquid refrigerant

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

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

Before entering the expansion valve

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

Brass

Steel

Aluminium

Copper

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

Dew point temperature

Relative humidity

Wet bulb temperature

Dry bulb temperature

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

None of these

Vapour absorption cycle

Vapour compression cycle

Air refrigeration cycle

8. 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.

9. The desirable property of a refrigerant is

All of these

Low boiling point

High critical temperature

High latent heat of vaporisation

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

Increases heat transfer

Increases power consumption

Improves C.O.P. of the system

Reduces power consumption

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11. 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

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

Equal to

None of these

Greater than

Less than

13. 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 24 hours

In 12 hours

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

1 kg of dry air

1 m3 of dry air

1 m3 of water

1 kg of wet air

15. 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 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

16. Ammonia is

Non-toxic

Toxic and non-inflammable

Highly toxic and inflammable

Non-inflammable

17. The bypass factor for a cooling coil

Increases with increase in velocity of air passing through it

Decreases 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

18. Chaperon equation is applicable for registration at

Sublimation temperature

Triple point

Saturation point of liquid

Saturation point of vapour

19. 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 - h2)/ (h1 - h2)

(hA - h1)/ (h2 - h1)

(h1 - h2)/ (hA - h2)

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

Regenerative air cooling system

Reduced ambient air cooling system

Simple air cooling system

Bootstrap air cooling system

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21. 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

None of these

Wet bulb temperature

22. The specific humidity during cooling and dehumidification

Remains constant

Decreases

None of these

Increases

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

Curved lines

Horizontal and uniformly spaced

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

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

Less than

Equal to

More than

None of these

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

Inclined line

Vertical line

Horizontal line

Curved line

26. The refrigerant for a refrigerator should have

Low latent heat

High sensible heat

High latent heat

High total heat

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

25%

10%

75%

50%

28. 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

29. Air refrigeration cycle is used in

Air conditioning

Gas liquefaction

Commercial refrigerators

Domestic refrigerators

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

Ammonia vapours to weak solution

Strong solution to weak solution

Strong solution to ammonia vapour

Weak solution to strong solution

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31. 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 (T₂ - T₃)] / [T₃ (T₁ - T₂)]

[T₁ (T₁ - T₂)] / [T₃ (T₂ - T₃)]

[T₃ (T₁ - T₂)]/ [T₁ (T₂ - T₃)]

[T₃ (T₂ - T₃)] / [T₁ (T₁ - T₂)]

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

1 m3 of wet air

1 m3 of dry air

1 kg of wet air

1 kg of dry air

33. The power per tonne of refrigeration is

C.O.P/3.5

3.5 × C.O.P.

None of these

3.5/C.O.P.

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

Coefficient of performance of heat pump

Refrigerating efficiency

Relative coefficient of performance

Coefficient of performance of refrigeration

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

Brass

Steel

Aluminium

Copper

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

420 kJ/ min

21 kJ/ min

210 kJ/ min

840 kJ/ min

37. 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

38. The evaporator used in household refrigerators is

Non-frosting evaporator

Defrosting evaporator

None of these

Frosting evaporator

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

After passing through the condenser

Before entering the compressor

After passing through the expansion or throttle valve

Before passing through the condenser

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

1 m3 of water

1 m3 of dry air

1 kg of dry air

1 kg of wet air

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41. Short horizontal lines on pressure-enthalpy chart show

Constant temperature lines

Constant total heat lines

Constant pressure lines

Constant entropy lines

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

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

Reversed Joule cycle

Reversed Otto cycle

Reversed Carnot cycle

Reversed Brayton cycle

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

Vapour absorption

Vapour compression

Electrolux refrigerator

Carnot cycle

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

Absorber and generator

Generator

Absorber, generator and liquid pump

Liquid pump

Refrigeration & Air-Conditioning Practice Set-5

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