How does an evaporative cooling system work?

All evaporative cooling systems use the evaporation of a small amount of water to lower the temperature of the larger mass of water. There are three main types of evaporative cooling systems: open circuit cooling towers, closed circuit cooling towers, and evaporative condensers. In open-circuit towers, the water to be cooled comes into direct contact with the ambient air, evaporating in small amounts and giving off heat. In closed-circuit towers, the water to be cooled does not come into direct contact with the air: it flows in a closed circuit inside a heat exchanger, where it gives up heat to a second circuit of water that partially evaporates. The operating principle of the evaporative condenser is the same as that of a closed-loop cooling tower. As the only structural difference, the process fluid to be cooled is a gas (often ammonia) instead of water.