March 2020

Gary Dicker, director at DHD cooling, explains why the evaporative cooling tower is still a great choice. T here is a lot of bad press surrounding evaporative cooling towers, but they are still one of the best long-term solutions for industrial and commercial cooling challenges and here’s why. In order to reach certain cooling temperatures dry cooling alone is not the answer, in these cases there are a few bolt-on options that you can put on a dry cooler that will reduce cold water temperatures, but these come with their own distinct disadvantages. The downside of dry and hybrid coolers Air coolers typically rely on passing large volumes of ambient air over a finned coil; ambient air temperatures in the UK can soar to nearly 40oC at times, and in some incoming air to reduce the temperature, in order to aid cooling. Many of these methods can still result in the coil surface becoming wet for longer periods, which can help to adhere impurities in the air to the coil fins. Wetting the coil itself will result in evaporation occurring on the coil surface, evaporation of water, only removes pure water leaving any impurities either in the water or in the air on the coil surface. Impurities can then start to build up over the coil fins resulting in a sort of thermal blanket forming creating a barrier between the air and the coil. This barrier will attract more impurities, further building this layer, not only affecting the heat exchange between the air and coil surface, but also restricting the airflow – a double whammy Process, Controls & Plant Focus on: Process Heating & Cooling circumstances the air local to an air cooler can be influenced by other plant, or even the equipment itself resulting in even higher inlet air temperatures. To achieve colder water temperatures there are various methods of wetting the finned coils, or increasing the moisture content of the air which will bring the air temperature down, which will reduce the inlet air temperature improving performance, but here’s the rub. Finned coils are often quite delicate, which makes them very hard to clean, couple this with the need for air to come in direct contact with the base material of the coil in order for the heat exchange to occur and you can start to see the problem. There are various methods of humidifying the Cooling towers reconsidered 28 | Plant & Works Engineering www.pwemag.co.uk March 2020