Evaporative cooling is a natural process that provides cooling evaporating water into air.
A good example of this is the sudden sensation of getting cold when we step out of a hot shower, or misting fans used to help keep football players cool on the sidelines.
While we are in the shower, our skin is wet and not readily exposed to air, but when we step out into the air, the water on our skin begins to evaporate and pulls heat out of our bodies and we feel the cooling effect.
Cooling towers use this same principle of evaporative cooling to cool a continuous flow of water.
Cooling towers are essentially large boxes designed to maximize evaporation of water.
To do this, they contain material, typically PVC plastic sheets, that create large surface areas for water evaporation to occur.
This material is what fills the inside of the cooling tower and is called "Cooling Tower Fill".
Large cooling towers, like those at nuclear power plants, rely on a natural draft or flow of air through the cooling tower; however, this is only effective on certain very large cooling towers.
Most cooling towers use an electrical fan motor to create an air draft or airflow through the cooling tower.
This type of cooling tower is called an "Induced or Force Draft" cooling tower.