Cooling towers are structures for cooling water or other working medium to near-ambient temperature.

Didcot Power Station
natural draft wet cooling towers

With respect to the heat transfer mechanism employed the main types are:

• wet cooling towers operate on the priciple of evaporation, (see Swamp cooler)
• dry cooling towers operate by heat transmission through a surface that divides the working fluid from ambient air.

In a wet cooling tower the warm water can be cooled to a temperature lower than ambient, if the ambient air is relatively dry. (see: Dew point).

With respect to drawing air through the tower there are three types of cooling towers:

• natural draft , which utilizes a tall chimney,
• fan assisted natural draft, and
• mechanical draft which uses power driven fan motors to force or draw air through the tower.

If ambient conditions are right plumes (fog) can be seen rising out of a wet cooling tower (see image).