How do cooling towers work?

Evaporative cooling, which has been used in industry for more than a century, is the foundation of cooling towers and other water-cooling equipment. Utilizing water as a coolant, evaporative cooling is a natural process that is used to dissipate extra heat from various thermal processes and machinery into the environment. The process of adiabatic cooling should not be confused with this.

A ventilation system (natural or forced) to encourage and, if necessary, force the passage of ambient air through the heat and mass exchange filling, as well as several auxiliary components like a water collecting basin, recirculation pump, droplet separators, and control instruments, are all included in evaporative cooling equipment such as cooling towers.

How do cooling towers function?

A cooling tower works according to evaporative cooling principles:

By spraying hot water in the form of a rain of droplets that land on a lattice or exchanger filler (a group of thin PVC sheets arranged in a specific way), cooling towers cool hot water. The already cooled water then falls into a tank that collects it and, if necessary, will be distributed by a circuit.

From bottom to top, the tower is filled with air as it enters via the lower holes above the water tank. Depending on the kind of tower, this air intake may be driven by carefully placed fans or generated spontaneously in natural draft towers.

In the tower fill, where heat exchange between the two fluids happens, heat transfer occurs between water (at a higher temperature) and air (at a lower temperature). By increasing the surface area and the duration of air-water interaction, this filler aims to improve cooling effectiveness. The water cools as it evaporates by absorbing the heat from the surrounding, moving water.

For every 7°C of cooling in this process, around 1% of the total water flow evaporates. The so-called "droplet separator" filters the evaporated water as it exits the tower. This prevents the chance of contaminated water from leaking into the outside air, making it one of the most crucial components for the safety of a cooling tower. According to the UNE 100030/2017 standard, this material effectively decreases the outflow of water into the atmosphere with losses of less than 0.002%. Droplet separators must be updated every ten years to meet this standard and for safety.

The remaining chilled water is put in a reservoir and then sent to a circuit, where it will be used for various things like air conditioning, air purification systems, industrial activities, etc.