7th December 2021
How to Improve Filtration Effectiveness in Cooling Towers
Even the most effective filters will only partially stop debris from fouling your cooling tower or air coolers.
In cooling towers filtration is used to primarily reduce the quantity of nutrients that are entrained in the inlet air. This is then removed from the air by the water in the cooling tower, finally settling out in the cold water basins, distribution pipework, process equipment or even lodged in the fill pack. The more nutrients that are introduced into the cooling water circuit, the more chemicals will be dosed and the more frequent internal cleaning will be required.
Interestingly, airborne debris drawn into cooling towers has little or no effect on the effectiveness of the cooling tower until they have built up sufficiently to reduce airflow, or block distribution systems. Because heat rejection is a function of the air coming into contact with the water, lightly fouled fill packs are still very effective.
In air coolers however, lightly fouled coils can have a significant effect on performance. Heat transfer occurs through the coil materials to the external air, so any barrier between the air and the coil materials, even a very thin coating can heavily affect heat transfer.
Additionally due to the small fin spacing, even light fouling will reduce the open area between the fins, leading to airflow reduction.
Adiabatic coolers can exacerbate this fouling by increasing the amount of time the coil gets wet, meaning the build-up of impurities on the coil surface can be higher as a result of wetting the inlet air. A wetted coil creates a surface for impurities to adhere to and also the evaporation of this water can lead to deposits on the fins. Although typically adiabatic dry systems try to avoid directly wetting the coil for this very reason.
So while filtration won’t catch everything, everything it does catch will help to reduce costs associated with fouling in your cooling systems and loss of performance, and cleaning filters is a far easier process than cleaning coils or fill packs. Just a couple of reasons to consider coil and cooling tower filtration solutions as part of your cooling system maintenance regime.
Graphical representation of light fouling on coil surfaces, showing how quickly the open area can be reduced, and the thermal blanket forming.