Chapter 70- Cooling Towers

Question 1

The average amount of water volume which evaporates

Answer 1

5%

Question 2

The purpose of a cooling tower

Answer 2

To reduce the temperature of the cooling tower

Question 3

The four ways of heat transfer

Answer 3

• 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

Question 4

Transfer heating air passing through the tower

Answer 4

Sensible heat

Question 5

Removed of ________ by evaporation of the water

Answer 5

Latent heat

Question 6

Circulation of atmosphere air is accomplished by

Answer 6

Fans, convection currents, natural wind currents, induction effects

Question 7

When is cooling tower the most common type of heat exchanger

Answer 7

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

Question 8

Chimney is also referred to as

Answer 8

Hyperbolic tower

Question 9

How do you Ensure effective operation

Answer 9

Regular inspection and maintenance

Question 10

Advantages of Venturi towers (4)

Answer 10

• quiet
• no moving parts
• no electrical connections
• reduced maintenance

Question 11

Inhibit growth leads to

Answer 11

Legionnaires disease…. Very deadly

Question 12

Give cause and solution on airborne particles

Answer 12

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

Question 13

Cause and solution if scaling

Answer 13

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

Question 14

Ph in a cooling tower should be

Answer 14

6-7.5

Question 15

Cause and solution of corrosion

Answer 15

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

Question 16

Cause and solutions of biological fouling

Answer 16

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

Question 17

Cause and solution of wood deterioration

Answer 17

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

Question 18

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

Answer 18

4

Question 19

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

Answer 19

The difference between wet bulb air

The surface area of the water in contact with the air

Question 20

What are two classes of cooling towers?

Answer 20

Natural air circulation

Mechanical air circulation

Question 21

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

Answer 21

The blowdown rate

Question 22

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

Answer 22

Where wind is relatively constant

Question 23

Excessive wind velocity in a natural draft cooling tower may cause

Answer 23

High water drift or losses

Question 24

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

Answer 24

Natural draft cooling towers

Question 25

What are atmospheric cooling towers dependant on?

Answer 25

Atmospheric conditions

Question 26

What causes airflow in a hyperbolic cooling tower?

Answer 26

Convection currents

Question 27

Compared to a cross flow tower, a counter flow tower

Answer 27

Requires less floor space

Question 28

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

Answer 28

With drift eliminators

Question 29

How many subclasses of mechanical draft are there?

Answer 29

2

Question 30

What are the two classifications of mechanical draft cooling towers?

Answer 30

Forced draft | Induced draft

Question 31

A cross flow mechanical draft cooling tower

Answer 31

Has a low pressure drop

Question 32

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

Answer 32

Drift eliminators

Question 33

In a Venturi type cooling tower, how is airflow created

Answer 33

By spray nozzles

Question 34

A car radiator works on the principle of

Answer 34

A dry cooling tower

Question 35

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

Answer 35

+ 27 Celsius

Question 36

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

Answer 36

Electric basin heaters

Question 37

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

Answer 37

Slowing the fans down | Reversing the fans

Question 38

Scaling is not as severe in towers compared to boilers because

Answer 38

Temperatures are not as high

Question 39

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

Answer 39

To control the amount of scale forming salts

Question 40

Water treatment is necessary in cooling towers because of

Answer 40

Scaling Biological fouling Corrosion Wood deterioration

Question 41

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

Answer 41

Use the bleed off line

Question 42

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

Answer 42

They treat scaling

Question 43

What is steel corrosion in cooling towers mainly due to

Answer 43

Dissolved oxygen

Question 44

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

Answer 44

70 degrees celcius

Question 45

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

Answer 45

Double

Question 46

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

Answer 46

Corrosion

Question 47

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

Answer 47

Zinc Polysilicates Molybdates

Question 48

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

Answer 48

Severe corrosion in unprotected areas is possible

Question 49

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

Answer 49

An oxygen rich atmosphere | Warm water

Question 50

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

Answer 50

Biological fouling

Question 51

Chemical methods used to prevent biological fouling in cooling towers include

Answer 51

Oxidizing chemicals Non- oxidizing chemicals Heavy metals

Question 52

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

Answer 52

Chlorine

Question 53

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

Answer 53

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

Question 54

Delignification in a cooling towers wood is a result of

Answer 54

Chemicals such as chlorine

Question 55

What gives wood it's strength

Answer 55

Cellulose

Question 56

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

Answer 56

The wood

Question 57

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

Answer 57

The water flow rate is to high

Question 58

Reasons for a noisy motor in a cooling tower include

Answer 58

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

Question 59

More water droplets =

Answer 59

Greater surface area

Question 60

Atmosphere spray towers

Answer 60

Have the cheapest and simplest design

Question 61

Packed atmospheric towers have

Answer 61

Baffles to create turbulence

Question 62

Maintenance required in cooling towers may include

Answer 62

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

Question 63

Advantages of a forced draft fan include

Answer 63

Minimal vibration | Fans handle dry air reducing erosion and condensation issues

Question 64

Advantages of an induced draft fan include

Answer 64

Increased heat transfer No recirculating warm air * note: these may develop vibration issues and require more maintenance

Question 65

Dry cooling towers

Answer 65

Have fluid move through finned tubes Ex: the radiator in a car works on the same idea

Question 66

A cooling tower that needs no fan or fill is

Answer 66

Venturi

Question 67

You are replacing the cooling tower fan motor bearing because

Answer 67

The rotor was rubbing the stator