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How do cooling towers work?

Processes that generate power or refigeration also generate heat, and this heat must be removed from equipment or facilities and safely and cleanly discharged into the atmosphere. From small electronics to internal combustion engines to computer server rooms to large manufacturing plants, heat must be removed to keep operations running. Water is a proven cooling medium, effective and efficient in removing heat from many applications. Since the first cooling towers were installed in the early 1900s, water from rivers, streams or lakes was used to cool large facilities. The water would pass though the facilty‘s heat exchanger, used to cool the system and then passed back to is source. Although a simple and effective process, this system meant that the returning water was often significantly warmer that when it left its source, causing damage to the environment and life within the water system.

Today, most facilities implement a closed-cycle cooling system. Evaporative  - or wet-cooling  - systems, such as heat exchangers, are one such solution. A heat exchanger does exactly what its name says: it exchanges heat from one source to another - usually from a fluid to a fluid or a fluid to a gas. Cooling towers are one type of heat exchanger that allows air and heated water to come into contact with each other, lowering the temperature of the water. During the cooling tower working process, small volumes of water evaporate, lowering the temperature of the water that’s being circulated throughout the cooling tower. Heated water from the process enters the cooling tower hot, and cooled water goes back into the process. The warmed air is then expelled out of the tower and into the atmosphere.

Inside the cooling tower, heated water is pumped through pipes to a high point in the structure. Nozzles spray the water onto the “fill.” This series of splash bars breaks the water in small droplets and create a waterfall effect, increasing the surface area of the droplets, the distance the water has to travel and the time the water is exposed to the air – all resulting in more efficient cooling. Gravity does the job of pulling the water to the bottom of the tower, while an updraft axial fan, internally mounted near the structure’s ceiling opening - and powered by a special cooling tower motor - pulls air up, over the water droplets and to the sky. When the air and water meet, a small volume of water evaporates, which creates the action of cooling. The cooled water gets pumped back to the process, and the cycle repeats. This type of cooling tower is known as an induced draft tower, because of the use of a fan to move the air, and due to the constant presence of exposed water, the inside of this type of cooling tower is an extremely hot and damp environment. This type of system is also known as a counter-flow tower since the movement of the air is opposite to that of the water. Each cooling tower houses a reservoir at its base. This basin not only catches the falling water but also replenishes the supply as needed to keep the entire cooling system operating optimally.

Cooling towers can be found in power and chemical processing plants, steel mills and many manufacturing facilities requiring process cooling, as well as large commercial buildings such as airports, hospitals, universities, hotels and schools. They can be made of steel, concrete, fiber-reinforced plastic (FRP) and even wood.

As mentioned, a cooling tower is only one type of heat exchanger. To lean more about other types of heat exchangers, the benefits and challenges of each and which motors are right for which heat exchanger application, read my recent Currents blog post.


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