Book 2 Chapter 21: Cooling Towers

Question 1

Which of the following is/are the determining factor(s) affecting heat transfer in a cooling tower?
A) Relative velocity of both air and water during contact
B) Area of water surface in contact with the air
C) Length of contact time between the air and water
D) All of the above

Answer 1

D) All of the above

Question 2

Atmospheric towers are used in areas that have __________________.
A) Relative constant winds and large open spaces
B) Economical supply of electricity
C) No need for a large cooling water supply and return temperature differential
D) An economical supply of cooling water

Answer 2

A) Relative constant winds and large open spaces

Question 3

What are the advantages of the Venturi style of cooling tower?

Answer 3

Quietness of operation due to absence of any moving parts and their associate noise and vibration problems
Elimination of the need for electrical connections and starters
Elimination of fill and the reduced maintenance requirements

Question 4

What basin temperature is required prior to allowing full water flow over the tower fill?
A) 10ºC (50ºF)
B) 15ºC (59ºF)
C) 27ºC (81ºF)
D) 20ºC (68ºF)

Answer 4

C) 27ºC (81ºF)

Question 5

What are the cause and remedy of a cooling tower motor turning in the wrong direction?
Cause:
Remedy:

Answer 5

Cause: Wrong sequence of phases
Remedy: Change any 2 of the 3 motor leads

Question 6

Two types of cooling towers are:
A) Mechanical and natural draft
B) Dry and wet
C) Flooded and vapour
D) Concrete and steel base
E) Chandler and MacDonnell

Answer 6

A) Mechanical and natural draft

Question 7

What is the difference between a refrigeration system evaporative condenser and a cooling tower?
A) Water is cooled by the cooling tower, refrigerant by the evaporative condenser
B) Water leaving the evaporative condenser is cooler
C) The evaporative condenser uses drift eliminators
D) Refrigerant is cooled by the cooling tower, water by the evaporative condenser
E) Water is recirculated through the cooling tower

Answer 7

A) Water is cooled by the cooling tower, refrigerant by the evaporative condenser

Question 8

Natural draft cooling towers operate most effectively in large open spaces and:
A) Where the relative humidity is high
B) Where a large body of water is nearby
C) Require a windbreak
D) Must not be in direct sunlight
E) Where the wind is relatively constant

Answer 8

E) Where the wind is relatively constant

Question 9

Compared to a crossflow tower, a counterflow tower:
A) Has a lower pressure drop
B) Is not as tall
C) Requires less floor space
D) Requires less fan power
E) Has much less capacity

Answer 9

E) Has much less capacity

Question 10

A cooling tower which requires neither fan nor fill is the:
A) Natural draft unit
B) Venturi unit
C) Cross flow unit
D) Forced draft unit
E) Counter flow induced unit

Answer 10

B) Venturi unit

Question 11

High discharge water temperature from the cooling tower could be caused by:
A) Fine water spray in the tower
B) Low dry bulb air temperature
C) Low wet bulb air temperature
D) High wet bulb air temperature
E) Low concentration of solids in the water

Answer 11

D) High wet bulb air temperature

Question 12

Heat is removed from the water in a cooling tower by:
A) Fans
B) A refrigerant
C) Evaporation
D) Pumps
E) Bernoulli’s principle

Answer 12

C) Evaporation

Question 13

The rate of heat transfer in any cooling tower system depends on the:
1. Relative velocity of both air and water during contact
2. Volume of water in contact with the air
3. Length of contact time between the air and water
4. Difference between the inlet water temperature and the inlet air wet bulb temperature

A) 1,2,4
B) 1,2,3,4
C) 2,3,4
D) 1,2,3
E) 1,3,4

Answer 13

E) 1,3,4

Question 14

The average amount of water volume which evaporates from a cooling tower is:
A) 10%
B) 15%
C) 5%
D) 3.5%
E) 2%

Answer 14

C) 5%

Question 15

The correct choice to manage algae or microbiological problems in cooling towers:
A) Consult a water treatment specialist
B) Drain the cooling tower and refill with fresh clean water
C) Decrease the circulation rate through the cooling tower
D) Acid clean the cooling tower
E) Increase the temperature to kill off the biological contaminants

Answer 15

A) Consult a water treatment specialist

Question 16

The actual transfer of heat in a cooling tower is accomplished by a sensible heat transfer (heating the air passing through the tower), and by the removal of latent heat as a result of the evaporation of about _______ of the water.
A) 5%
B) 2%
C) 8%
D) 10%
E) 15%

Answer 16

A) 5%

Question 17

The advantages of the Venturi induced draft cooling towers include all of the following except:
A) The absence of any moving parts
B) The elimination of fill
C) The elimination of the need for electrical connections
D) Its quiet fan operation
E) Its quietness of operation

Answer 17

D) Its quiet fan operation

Question 18

Cooling towers are unquestionably the most common type of heat exchanger used when cooling water is scarce, expensive, and a temperature within _______ of the ambient wet bulb temperature is required.
A) 20ºC to 22ºC (68ºF to 72ºF)
B) 4ºC to 6ºC (39ºF to 43ºF)
C) 15ºC to 17ºC (59ºF to 63ºF)
D) 27ºC to 29ºC (81ºF to 85ºF)
E) 10ºC to 12ºC (50ºF to 54ºF)

Answer 18

B) 4ºC to 6ºC (39ºF to 43ºF)

Question 19

The sides of atmospheric natural draft towers area _______ and airflows across the tower by natural currents.
A) Sealed
B) Louvered
C) Lowered
D) Solid
E) Slanted

Answer 19

B) Louvered

Question 20

A monthly inspection of a natural draft cooling tower should indicate all of the following except:
A) Checking that the float control valve is operating properly
B) Checking the atmospheric wet bulb temperature
C) Cleaning the suction screen
D) Cleaning the louvres, piping, and nozzles
E) Cleaning the water basin and checking for leaks

Answer 20

B) Checking the atmospheric wet bulb temperature

Question 21

One of the advantages of the crossflow mechanical draft tower over the counterflow tower is the:
A) Low temperature drop in relation to its capacity
B) Low pressure drop in relation to its capacity
C) High pressure drop in relation to its capacity
D) High pressure drop in relation to its volume
E) Low pressure drop in relation to its volume

Answer 21

B) Low pressure drop in relation to its capacity

Question 22

The rate of heat transfer in any cooling tower system depends on all the following except the:
A) Area of water surface in contact with the air
B) Atmospheric pressure
C) Difference between the inlet water temperature and the inlet air wet bulb temperature
D) Relative velocity of both air and water during contact
E) Length of contact time between the air and water

Answer 22

B) Atmospheric pressure

Question 23

Atmospheric natural draft towers are used in areas that have ___________.
A) Relative constant winds and large open spaces
B) An economical supply of cooling water
C) Economical supply of electricity
D) No need for a large cooling water supply and return temperature differential
E) Low winds and little water

Answer 23

A) Relative constant winds and large open spaces

Question 24

The counterflow mechanical draft tower occupies less floor space than a crossflow tower but is _________ for a given capacity.
A) Taller
B) Shorter
C) Smaller
D) Faster
E) Larger

Answer 24

A) Taller

Question 25

One of the advantages of the crossflow mechanical draft tower over the counterflow tower is the __________ leading to lower energy costs.
A) Lower fan power requirement
B) No fan requirement
C) Higher temperature requirement
D) Higher fan power requirement
E) Lower temperature requirement

Answer 25

A) Lower fan power requirement