A cooling tower is a heat rejection device that transfers waste heat to the atmosphere through the cooling of a fluid stream to a lower temperature. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or, in the case of dry cooling towers, rely solely on air to cool the working fluid to near the dry-bulb air temperature using coils.

Cooling towers are used in a variety of applications, including:

• Power plants
• HVAC systems
• Industrial processes
• Food processing
• Chemical plants
• Oil and gas refineries

Cooling towers work by circulating water through a series of wetted surfaces. The water absorbs heat from the surrounding air, and some of the water evaporates. The evaporation of water requires energy, which is taken from the water, thus cooling it down. The cooled water is then circulated back to the heat source.

The amount of heat that can be rejected by a cooling tower depends on the size of the tower, the airflow, and the wetted surface area