cooling towers description

1. SUBMITTED BY:
Ajay Ekka
(0812me131013)
Arjun Parmar
(0812me131030)
SUBMITTED TO:
Manish Thakur Sir.
DATE OF SUBMISSION:
1TH MAY2015

2. Introduction
History
Classification
1. Natural draft
2. Mechanical draft
 Counter-flow
 Cross-flow
Terminology

3. SOME TIMES,TWO OR MORE GEARS ARE MADE TO
MESH WITH EACH OTHER TO TRANSMIT POWER
FROM ONE SHAFT TO ANOTHER .SUCH A
COMBINATION IS CALLED “GEAR TRAIN”OR “TRAIN
OF TOOTH WHEELS.THE NATURE OF THE TRAIN
USED UPON THE VELOCITY RATIO REQUIRED AND
THE RELATIVE POSITION OF THE AXES OF SHAFT .A
GEAR TRAIN MAY CONSIST OF SPUR,BEVEL OR
SPIRAL GEARS.

4. • Cooling towers originated out of the development in the 19th century of
condensers for use with the steam engine. Condensers use relatively cool
water, via various means, to condense the steam coming out of the pistons or
turbines.
• By the turn of the 20th century, In areas with available land, the systems took
the form of cooling ponds; in areas with limited land, such as in cities, it took
the form of cooling towers.
• These early towers were positioned either on the rooftops of buildings or as
free-standing structures, supplied with air by fans or relying on natural
airflow.
• A hyperboloid cooling tower was patented by the Dutch engineers Frederik van
Iterson and Gerard Kuypers in 1918. The first hyperboloid cooling towers were
built in 1918 near Heerlen. The first ones in the United Kingdom were built in
1924 at Lister Drive power station in Liverpool, England to cool water used at a
coal-fired electrical power station.

5. A 1902 engraving of
"Barnard's fanless self-
cooling tower", an early large
evaporative cooling tower
that relied on natural draft
and open sides rather than a
fan; water to be cooled was
sprayed from the top onto the
radial pattern of vertical wire-
mesh mats.

6. COOLING TOWERS
NATURAL
DRAFT
(hyperbolic)
MECHANICAL
DRAFT
CROSS FLOW COUNTER FLOW

7. 1.NATURAL DRAFT COOLING TOWER
• A natural draft cooling tower is tall and hyperbolic in construction. It looks and works
like a large chimney.
• As air comes in contact of heated falling water, air is heated, becomes lighter and rises
up in the tower. The cold and heavier air outside fills the vacant space creating an air
flow.
• They do not require external power to induce air flow but their construction cost is
much higher. They are constructed from RCC and have base diameter ranging 75 to
100m and height between 100 to 150m.
• In CROSS-FLOW arrangement, water is sprayed downward near the base of the tower
on a fill material. Air is induced radially inward and flows in across the water.
• In COUNTER-FLOW arrangement, air enters through a peripheral section at the bottom
of the tower and flows upward through descending water spray made from a suitable
height.
• These towers are suitable in desert regions where moisture content in air is very low.
Also, cooling rate is very slow. These are used for water flow rates above 45000 cubic
meters per hour.

9. • These are induced-draft cooling towers. These are compact in size and low height.
• The air movement through the tower is created by induced fans, located at the top
the tower.
• In induced draft counter flow cooling tower, the warm water coming from the
condenser is pumped to the top of the tower and is sprayed into air stream. The
falling water passes through a series of baffles, thus the water breaks into fine
droplets to promote evaporation. The atmospheric air drawn in by an induced fan
flowing upward, counter to the direction of falling droplets. As the two stream
interacts, a small fraction of water evaporates into moist air and cools the
remaining falling water. The cooled water is collected at the bottom of the tower
and pumped back to the condenser. The moist air is discharged from top of the
tower.
• Since some of the warm water is evaporated into the air stream, an equivalent
amount of make-up water is added to the cycle.
• These have lower construction cost.
• These enable control on heat transfer process, which is favourable for varying load
on power plant and changing ambient conditions.

11. In a counter-flow design, the air flow is directly opposite to 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 near the top of the tower, and then flows
downward through the fill, opposite to the air flow.
Advantages of the counter-flow design:
• Spray water distribution makes the tower more freeze-resistant.
• Breakup of water in spray makes heat transfer more efficient.
Disadvantages of the counter-flow design:
• Typically higher initial and long-term cost, primarily due to pump requirements.
• Difficult to use variable water flow, as spray characteristics may be negatively
affected.
• Typically noisier, due to the greater water fall height from the bottom of the fill into
the cold water basin.

13. 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 through the fill by gravity. The air continues through the fill and thus past the water
flow into an open plenum volume. Lastly, a fan forces the air out into the atmosphere.
A distribution or hot water basin consisting of a deep pan with holes or nozzles in its bottom
is located near the top of a cross-flow tower. Gravity distributes the water through the
nozzles uniformly across the fill material.
Advantages of the cross-flow design:
• Gravity water distribution allows smaller pumps and maintenance while in use.
• Non-pressurized spray simplifies variable flow.
• Typically lower initial and long-term cost, mostly due to pump requirements.
Disadvantages of the cross-flow design:
• More prone to freezing than counter-flow designs.
• Variable flow is useless in some conditions.
• More prone to dirt build-up in the fill than counter-flow designs, especially in dusty or
sandy areas.

15. TERMINOLOGY:
• Drift — Water droplets that are carried out of the cooling tower with the exhaust air. Drift droplets have the
same concentration of impurities as the water entering the tower. The drift rate is typically reduced by
employing baffle-like devices, called drift eliminators, through which the air must travel after leaving the fill and
spray zones of the tower. Drift can also be reduced by using warmer entering cooling tower temperatures.
• Blow-out — Water droplets blown out of the cooling tower by wind, generally at the air inlet openings. Water
may also be lost, in the absence of wind, through splashing or misting. Devices such as wind screens,
louvers, splash deflectors and water diverters are used to limit these losses.
• Plume — The stream of saturated exhaust air leaving the cooling tower. The plume is visible when water
vapour it contains condenses in contact with cooler ambient air, like the saturated air in one's breath fogs on a
cold day.
• Draw-off or Blow-down — The portion of the circulating water flow that is removed in order to maintain the
amount of Total Dissolved Solids (TDS) and other impurities at an acceptably low level. Higher TDS
concentration in solution may result from greater cooling tower efficiency. However the higher the TDS
concentration, the greater the risk of scale, biological growth and corrosion.
• Make-up — The water that must be added to the circulating water system in order to compensate
for water losses such as evaporation, drift loss, blow-out, blow-down, etc.

16. • Range — The range is the temperature difference between the warm water inlet and cooled water
exit.
• Fill — Inside the tower, fills are added to increase contact surface as well as contact time between
air and water, to provide better heat transfer. The efficiency of the tower depends on the selection
and amount of fill. There are two types of fills that may be used:
1. Film type fill (causes water to spread into a thin film)
2. Splash type fill (breaks up falling stream of water and interrupts its vertical progress)
• Treated timber — A structural material for cooling towers which was largely abandoned about 10
years ago.[when?] It is still used occasionally due to its low initial costs, in spite of its short life
expectancy. The life of treated timber varies a lot, depending on the operating conditions of the
tower, such as frequency of shutdowns, treatment of the circulating water, etc. Under proper
working conditions, the estimated life of treated timber structural members is about 10 years.
• Leaching — The loss of wood preservative chemicals by the washing action of the water flowing
through a wood structure cooling tower.
• Pultruded FRP — A common structural material for smaller cooling towers, fibre-reinforced plastic
(FRP) is known for its high corrosion-resistance capabilities. Pultuded FRP is produced using
pultrusion technology, and has become the most common structural material for small cooling
towers. It offers lower costs and requires less maintenance compared to reinforced concrete,
which is still in use for large structures.

17. THANK YOU 