Cooling towers, as their name suggests, are huge tower-like structures that are used to cool industrial fluids or water using the principle of evaporation; through the use of fans or other natural drafts. The most well known or recognizable types of cooling towers are probably the rounded hourglass cooling towers that are used by nuclear power plants. These are among the largest types of cooling towers that are used. Cooling towers have a wide array of use in the industrial sector and are expensive industrial equipment. A cooling tower is designed mainly as either a: cross flow, counter flow, closed loop or open loop system.
The hourglass shape of some towers is very efficient as these types of towers do not use fans to move air across heated water or other liquid. In this system, the warm water or liquid transfers its heat to the air at the bottom of the cooling tower. The warm air then rises and draws more cool air into the bottom of the tower to replace it. When the cool outside air rushes over the warm water at the bottom of the tower, it also starts to rise and the cycle is continuously repeated.
Smaller cooling towers generally use powered fans to push the air across warm water or liquid. This method is known as an open circuit cooling tower. The water or liquid transfers its heat energy to the air much like a sweating person's skin gets cooler when the wind blows on it. Closed circuit cooling towers, on the other hand, work by conducting the heat exchange internally and don’t use any outside air. In this type of cooling tower, coolants such as propylene glycol are circulated through a network of tubes that are immersed in warm water, drawing off the water's heat. The coolants then transfer the heat to the open air by the use of a radiator which may use a fan. This method is similar to the heat exchange system in an automobile.
Because only pure water evaporates a lot of impurities and/or dissolved minerals are left behind. Over time, the surfaces the warm water is applied to often become covered with salts and scaling will form. Scaling will hamper the effectiveness of the tower and the surface will have to be treated with scale removers to restore full efficiency to the unit. Cooling towers may also lead to the growth of bacterial organisms and algae and should be regularly maintained as the algae may plug up water nozzles.