When it comes to wet cooling towers, the evaporative process may seem rather simple (since evaporation is something that most people learn in grade school science classes); but because industrial cooling towers have been developed so much in order to increase efficiency while decreasing environmental impacts, and because these towers have been designed to accommodate the needs of many different industrial processes, wet cooling towers can get a little complicated.

Here’s a simple breakdown of wet cooling towers, which tend to be the most common types of cooling towers due to their efficiency (compared to dry cooling towers):

Direct/ Open Circuit Cooling Towers:

• In order to absorb the waste heat produced by the system, the water in a direct wet cooling tower is run through a sort of maze, where the heat transfers from the machinery and into the water.
• As the “direct” part of the name infers, these cooling towers involve direct contact between the water (after it absorbs excess heat from the system) and the cool air blowing through the tower.
• When the warm water and cool air come into direct contact, evaporation occurs and the hottest water droplets turn into vapor, escaping into the atmosphere.
• Once the water has cooled down, it can be run through the system again to collect more heat — although there are a few other processes involved before this happens, including the replacement of evaporate water and the dilution of minerals that didn’t evaporate.

Indirect/ Closed Circuit Cooling Towers:

• Unlike direct open circuit towers, there’s no direct contact between the water and air with a closed circuit system.
• Instead, there are two passages next to each other in the cooling tower — one for the cool air, and one for the warm water. The cool air passes upward (or sometimes horizontally) through the tower in one tube as the warm water passes downward in another tube.
• Excess heat can still be transferred in this system, although it often takes longer for the heat to be transferred.
• The main benefit of closed circuit wet cooling towers, therefore, isn’t so much about getting the heat out of the system as quickly as possible; instead, these towers tend to be a bit more friendly to the environment and have a smaller risk or water/air contamination.