A water cooling tower is a structure which is designed to dispose of waste heat. Heat is pulled away from the process which generates it and routed into the cooling tower so that it can be vented away.
Water cooling towers are used in a number of different industries, and many people are familiar with them, even if they are not quite sure what they are for, because they have become visually associated with nuclear power plants. The distinctive towers seen on the grounds of such facilities are, in fact, cooling towers, not the plant itself.
Some cooling towers work with evaporative processes. In this case, warm water is routed through the cooling tower, and part of the water evaporates, allowing the heat to dissipate and causing cool water to settle back into a holding tank.
Other cooling towers use a nonevaporative process in which heat transfer occurs between hot fluids and cool atmospheric air, but evaporation is absent. The choice of dry or wet process depends on the setting and the preferences of the designer.
A natural draft cooling tower relies on natural temperature differences to create a steady flow of air to promote cooling. Others use fans and other mechanical devices for a draft, especially if they are smaller, because height is needed for effective natural draft. One advantage to natural draft cooling is that it will continue to function without electricity and with minimal maintenance, because the draft is entirely automatic.