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Cooling Tower Design Consideration

Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers make use of evaporation whereby some of the water is evaporated into a moving air stream and subsequently discharged into the atmosphere. 

As a result, the remainder of the water is cooled down significantly.

There are several important factors that govern the operation of cooling tower:

- The dry-bulb and wet-bulb temperatures of the air

- The temperature of warm water

- The efficiency of contact between air and water in terms of the volumetric mass transfer coefficient and the contact time between the air and the water

- The uniformity of distribution of the phases within the tower

- The air pressure drop

- The desired temperature of the cooled water

Cooling Tower Design Consideration

Once a tower characteristic has been established between the plant engineer and the manufacturer, the manufacturer must design a tower that matches the value. The required tower size will be a function of:

1. Cooling range

2. Approach to wet bulb temperature

3. Mass flow rate of water

4. Wet bulb temperature

5. Air velocity through tower or individual tower cell

6. Tower height

Other design characteristics to consider are fan horsepower, pump horsepower, make-up water source, fogging abatement, and drift eliminator.

Operation Considerations

1. Water make-up

Water losses include evaporation, drift (water entrained in discharge vapor), and blowdown (water released to discard solids). Drift losses are estimated to be between 0.1 and 0.2% of water supply.

2. Cold weather operation

Even during cold weather months, the plant engineer should maintain the design water flow rate and heat load in each cell of the cooling tower. 

If less water is needed due to temperature changes (i.e. the water is colder), one or more cells should be turned off to maintain the design flow in the other cells.

The water in the base of the tower should be maintained between 60 and 70oF by adjusting air volume if necessary. 

Usual practice is to run the fans at half speed or turn them off during colder months to maintain this temperature range.

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Thanks for reading - Cooling Tower Design Consideration
Naitik Patel
Industrial Guide

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