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Power Engineering- 4th Class > Chapter 70- Cooling Towers > Flashcards

Chapter 70- Cooling Towers Flashcards

1
Q

The average amount of water volume which evaporates

A

5%

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2
Q

The purpose of a cooling tower

A

To reduce the temperature of the cooling tower

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3
Q

The four ways of heat transfer

A
  • velocity of air and water
  • area of water surface in contact with air
  • length of contact time
  • difference between the inlet water temp and the inlet air wet bulb temp
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4
Q

Transfer heating air passing through the tower

A

Sensible heat

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5
Q

Removed of ________ by evaporation of the water

A

Latent heat

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6
Q

Circulation of atmosphere air is accomplished by

A

Fans, convection currents, natural wind currents, induction effects

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7
Q

When is cooling tower the most common type of heat exchanger

A

When water is scarce expensive and temp within 4-6 degrees

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8
Q

Chimney is also referred to as

A

Hyperbolic tower

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9
Q

How do you Ensure effective operation

A

Regular inspection and maintenance

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10
Q

Advantages of Venturi towers (4)

A
  • quiet
  • no moving parts
  • no electrical connections
  • reduced maintenance
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11
Q

Inhibit growth leads to

A

Legionnaires disease…. Very deadly

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12
Q

Give cause and solution on airborne particles

A

Cause: dust and debris
Solution: strainers and filters are clean and maintain

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13
Q

Cause and solution if scaling

A

Cause: hardness forming salts in the cooling water consisting of ca and mg
Solution: add sulphuric acid…increase ph and temp

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14
Q

Ph in a cooling tower should be

A

6-7.5

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15
Q

Cause and solution of corrosion

A 
Cause: ph levels below 8.5 and dissolved oxygen
Solution: * corrosion resistant metals
* protective coatings
*sacrificial metals 
*protective films
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16
Q

Cause and solutions of biological fouling

A

Cause: algae fungi and bacterial growth
Solution: mechanical and chemical

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17
Q

Cause and solution of wood deterioration

A 
Cause:  due to attack be choline and alkaline solution and biological attack of wood cellulose
Solution: *choosing natural wood
*treatment by wood preservatives 
*limited nails screws or iron hard wear
*water treatment
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18
Q

The rate of heat transfer in a cooler tower system depends on how many factors?

A

4

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19
Q

Which of the following are factors that determine the heat transfer rate of any cooling tower system

A

The difference between wet bulb air

The surface area of the water in contact with the air

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20
Q

What are two classes of cooling towers?

A

Natural air circulation

Mechanical air circulation

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21
Q

What determines how much makeup water is required to maintain the level in a cooling tower water basin

A

The blowdown rate

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22
Q

Natural draft cooling towers operate most efficiently in large open spaces and

A

Where wind is relatively constant

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23
Q

Excessive wind velocity in a natural draft cooling tower may cause

A

High water drift or losses

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24
Q

Atmospheric towers and chimney towers are the two subclasses of what type of cooling tower

A

Natural draft cooling towers

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25
Q

What are atmospheric cooling towers dependant on?

A

Atmospheric conditions

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26
Q

What causes airflow in a hyperbolic cooling tower?

A

Convection currents

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27
Q

Compared to a cross flow tower, a counter flow tower

A

Requires less floor space

28
Q

Water contained in the airstream at the discharge of a cooling tower is removed

A

With drift eliminators

29
Q

How many subclasses of mechanical draft are there?

A

2

30
Q

What are the two classifications of mechanical draft cooling towers?

A

Forced draft

Induced draft

31
Q

A cross flow mechanical draft cooling tower

A

Has a low pressure drop

32
Q

What is used to remove water from the air which exits a cooling tower

A

Drift eliminators

33
Q

In a Venturi type cooling tower, how is airflow created

A

By spray nozzles

34
Q

A car radiator works on the principle of

A

A dry cooling tower

35
Q

The by-pass valve, which prevents water flow over the fill of a tower during cold weather should not be closed until the temperature in the water basin reaches

A

+ 27 Celsius

36
Q

To prevent cooling tower basin water from freezing during cold weather many units are equipped with

A

Electric basin heaters

37
Q

In cold climates, ice formation in a cooling tower may be dealt with by

A

Slowing the fans down

Reversing the fans

38
Q

Scaling is not as severe in towers compared to boilers because

A

Temperatures are not as high

39
Q

What is the purpose of a bleed off line in a cooling tower?

A

To control the amount of scale forming salts

40
Q

Water treatment is necessary in cooling towers because of

A

Scaling
Biological fouling
Corrosion
Wood deterioration

41
Q

To control scaling in a cooling tower, which should be done first?

A

Use the bleed off line

42
Q

What purpose do both water softener and the addition of sulphuric acid to cooling water serve

A

They treat scaling

43
Q

What is steel corrosion in cooling towers mainly due to

A

Dissolved oxygen

44
Q

Corrosion rates in a cooling tower increase as water temperature increases up to this point

A

70 degrees celcius

45
Q

For water temperatures up to 70 degrees Celsius corrosion rates in cooling towers

A

Double

46
Q

In cooling towers, protective films and sacrificial metals are two methods of protecting against what?

A

Corrosion

47
Q

Which chemicals are environmentally friendly alternatives for providing corrosion prevention in cooling towers?

A

Zinc
Polysilicates
Molybdates

48
Q

What could happen if the initial treatment of film forming chemicals in a cooling tower is to weak?

A

Severe corrosion in unprotected areas is possible

49
Q

What makes cooling towers such a good environment for biological growth?

A

An oxygen rich atmosphere

Warm water

50
Q

What are trash bars and chemical methods used to protect a cooling tower against

A

Biological fouling

51
Q

Chemical methods used to prevent biological fouling in cooling towers include

A

Oxidizing chemicals
Non- oxidizing chemicals
Heavy metals

52
Q

The use of oxidizing chemicals is one of the methods used to protect against biological fouling in cooling towers. An example of an oxidizing chemical is

A

Chlorine

53
Q

How are microbiological organisms most efficiently killed in a cooling tower water system.

A

By temporarily raising the concentration of the chemicals to a high level

54
Q

Delignification in a cooling towers wood is a result of

A

Chemicals such as chlorine

55
Q

What gives wood it’s strength

A

Cellulose

56
Q

Microorganisms require carbon to develop. Where would they get this carbon from a cooling tower?

A

The wood

57
Q

Excessive water drift in a cooling tower could be the result of drift eliminator a being out of place or.

A

The water flow rate is to high

58
Q

Reasons for a noisy motor in a cooling tower include

A

Bad bearings
An unbalanced rotor
The motor is running single phase
Electrical unbalance

59
Q

More water droplets =

A

Greater surface area

60
Q

Atmosphere spray towers

A

Have the cheapest and simplest design

61
Q

Packed atmospheric towers have

A

Baffles to create turbulence

62
Q

Maintenance required in cooling towers may include

A

Cleaning louvers, piping and nozzles or debris, scale or algae
Cleaning water basin to check for leaks
Cleaning suction screen
Checking level control operates correctly

63
Q

Advantages of a forced draft fan include

A

Minimal vibration

Fans handle dry air reducing erosion and condensation issues

64
Q

Advantages of an induced draft fan include

A

Increased heat transfer
No recirculating warm air

  • note: these may develop vibration issues and require more maintenance
65
Q

Dry cooling towers

A

Have fluid move through finned tubes

Ex: the radiator in a car works on the same idea

66
Q

A cooling tower that needs no fan or fill is

A

Venturi

67
Q

You are replacing the cooling tower fan motor bearing because

A

The rotor was rubbing the stator

Power Engineering- 4th Class (27 decks)

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