cooling tower

1. Thermal Power Plant Engineering
COOLING TOWERS
1
1
Dr. S. VIJAYA BHASKAR
Professor in Mechanical Engineering
Sreenidhi Institute of Science &
Technology, Hyderabad

2. COOLING TOWERS
2
 In power plants the hot water from
condenser is cooled in cooling tower,
so that the water can be reused in
condenser for condensation of steam.
 In a cooling tower, water is made to
trickle down drop by drop so that it
comes in contact with the air moving
in the opposite direction.
 So that some water is evaporated and
is taken away with air.
 In evaporation the heat required for
the evaporation is taken away from
the bulk of water which is thus cooled.

3. 3

4. COOLING TOWERS contd.
4
 Factors affecting cooling of water in a cooling
tower are:
 Temperature of air
 Humidity of air
 Temperature of hot air
 Size and height of tower
 Velocity of air entering the air
 Accessibility of air to all parts of tower
 Arrangement of plates in tower
 Cooling towers are classified as
 Natural draught cooling towers
 Mechanical draught cooling towers
 i) forced draught cooling towers
 ii) induced draught cooling towers

5. Natural Draught Cooling Towers
5
 In this type of tower the hot water
from the condenser is pumped to
the troughs and nozzles situated
near the bottom.
 Troughs spray the water falls in
the form of droplets into a pond
situated at the bottom of the
tower.
 The air enters the cooling tower
from air openings provided near
the base, rises upwards and takes
up the heat of falling water.
 Example: Hyperbolic Cooling
Tower

6. Hyperbolic Cooling Towers
6
 The Advantages of the Hyperbolic Cooling Towers over
mechanical towers are:
 Low operating and maintenance cost
 It gives more or less trouble free operation
 Less ground area required
 Cooling tower structures are self supported and
withstands high speed of winds
 The enlarged top of the tower allows water to fall
out of suspension.

7. Hyperbolic Cooling Towers
7
 The Drawbacks of Hyperbolic Cooling Towers are:
 High initial cost
 Performance varies with DBT (dry bulb temp) and RH
(relative humidity) of the air
 While initial cost may be higher, the saving in fan power,
longer life and less maintenance always favour for this
hyperbolic cooling tower.

8. Mechanical Draught Cooling Towers
8
 In these towers the draught of air for cooling the tower is
produced mechanically by means of propeller fans.
 These are built in cells or units, the capacity depending on
the number of cells used.
 Advantages
 These towers require a small land area and built in all
locations
 The fans give a good control over the air flow and water
temperature.
 Less costly to install than natural draught towers

9. Mechanical Draught Cooling Towers
9
Disadvantages
 Fan power requirements and maintenance costs make
them more expensive to operate
 Local fogging and icing may occur in winter season

10. Forced Draught Cooling Towers
10
 This is similar to natural draft tower
as far as construction is concerned
but the sides of the tower are closed
and form an air and water tight
structure, except for fan openings at
the base for the inlet of fresh air and
the outlet at the top for the exit of air
and vapours.
 There are hoods at the base
projecting from the main portion of
tower where the fans are placed for
forcing the air into tower.

11. Forced Draught Cooling Towers contd.
11
 Advantages
 More efficient than induced draught
 No problem of fan blade erosion because it handles dry
air only
 More safe
 The vibration and noise are minimum
 Disadvantages
 The fan size is limited to 4 metres
 Power requirement is high
 In cold weather, ice is formed on equipments and the
frost in the fan outlet can break the fan blades

12. Induced Draught Cooling Towers
12
 In these towers fans are placed at the
top of the tower and they draw the air
in through louvers extending all round
the tower at its base.
 Advantages:
 Lower the first cost
 Less space requirement
 Capable of cooling wide range
 Coldest water comes in contact with
driest air and warmest with humid
air
 Recirculation is seldom a problem
 Disadvantages:
 air velocities are unevenly distributed
 Static pressure loss is higher because
base tends to choke at high velocity
pressures
END..