Cooling towers working classifications based on heat transfer method,flow generation and flow pattern losses in cooling and performance parameters

1. COOLING TOWERS

2. • A cooling tower is a heat rejection device that rejects waste heat to the
atmosphere through the cooling of a water stream to a lower
temperature.
• Applications include
a. HVAC systems
b. Thermal power plants
c. Oil refineries
d. Chemical plants
e. Electric power generation
INTRODUCTION

3. CLASSIFICATIONS
• Based on Heat Transfer method
• Base on Air flow generation
• Based on Air to Water flow

4. HEAT TRANSFER METHOD
Based on heat transfer mechanism cooling
towers are classified as
Dry cooling towers:
• Uses convection to transfer heat .
• Heat is transferred through a surface that
separates the water from ambient air.
• Used when cooling water is less

5. • Wet cooling tower: Uses evaporation to transfer heat.
Water can be cooled to a temperature lower than the
ambient air “dry-bulb” temperature. Most commonly
used type.

6. AIR FLOW GENERATION
NATURAL DRAFT
• Natural draft utilizes buoyancy via a tall chimney.
• Warm air inside the tower becomes less dense
compared to air outside
• This induces buoyancy forces.
• Due to this the denser air outside replaces the
less denser air inside.
• Natural draft towers are typically about 120 m
high, depending on the differential pressure
between the cold outside air and the hot humid
air on the inside of the tower as the driving force.

8. Mechanical draft tower:
Uses power driven fans to draw air through the
tower.
They are of 2 types
1. Induced Draft : A mechanical draft tower with a
fan at the discharge (at the top) which pulls air
up through the tower.
2. Forced Draft : A mechanical draft tower with a
blower type fan at the intake. The fan forces air
into the tower

9. GIF

10. Induced draft
•A fan mounted on the top of the cooling
towers sucks the air in by creating a
negative pressure gradient
•Smaller compared to natural draught
towers
•Both counter and cross flow
configurations are used.

11. Forced draft
•Uses a blower fan to force
air into the tower
•Requires lesser power
compared to induced , bcoz
cool air is being pumped

12. Air to Water Flow
•Cross flow is a design in which the
air flow is directed perpendicular
to the water flow.
•Air flow enters one or more
vertical faces of the cooling tower
to meet the fill material. Water
flows (perpendicular to the air)
through the fill by gravity.
•Low pumping head
•Water with high residue content

13. • In a counter flow design the
air flow is directly opposite
of the water flow.
• Air flow first enters an open
area beneath the fill media
and is then drawn up
vertically. The water is
sprayed through pressurized
nozzles and flows downward
through the fill, opposite to
the air flow.

14. Performance parameters
• Approach : Difference between the exit
temperature and WBT of water. This
represents a loss in cooling effect. Usual
range is 6 – 8 oC
• Range : Difference between Inlet and exit
temperatures of water. Usual range is 6 –
10 oC.
• Cooling efficiency : Ratio of actual
cooling to the maximum possible cooling
possible.

15. Water Losses
• Evaporation : water that evaporates and leaves along with air. Usually
around 1 -1.5% of water.
• Drift : Fine water droplets entrained and carried away by air. Drift
eliminators are installed to eliminate that.
• Blow down : To maintain a certain solid concentration, some amount
of water is removed from cold water basin. Around 1- 1.5 % of the
amount.
• Makeup water is supplied to makeup for these losses.

16. Parts of Cooling tower
• Frame : Most towers have structural
frames that support the exterior
enclosures (casings), motors, fans, and
other components.
• Fill : Most towers employ fills (made of
plastic or wood) to facilitate heat
transfer by maximizing water and air
contact.
• Drift eliminators: They capture water
droplets entrapped in the air stream
by causing an abrupt change in flow
direction of outlet air.
• Cold water basin: collect cooled water