A key element in open circuit cooling towers is the thermal fill pack (also called the "fill pack").
The greater the surface area of the water that comes into contact with the airflow through the pack, the greater theefficiency in terms of heat transfer. Not only that, but the contact time also plays an important role in ensuring the high efficiency of the cooling tower.
There are basically two types of fill packs: film and splash.
Both have the same function: positioned in the cooling tower below the nozzles, they ensure effective water distribution and the required performance.
What makes the difference between the two fill packs is the passage section. The film pack guarantees better performance thanks to the larger surface area but at the expense of the intimate passage of the water, which must comply with specific requirements, especially as regards the percentage of suspended solids. In addition, the water is not redistributed in the descent: it is therefore of fundamental importance that in the upper part the water - sprayed by the nozzles - uniformly covers the entire horizontal surface of the fill pack.
In applications where the water to be cooled has critical characteristics (concerning to the pollutants contained in it), the splash pack becomes the optimal solution as it guarantees less risk of clogging, while ensuring the required performance. The splash pack, in fact, progressively splits the water droplets into several smaller particles in their descent, thanks to their collision with the structure of the pack to optimize the direct air/water exchange surface to obtain cooling.
The standard material used for the fill packs is PVC, which is suitable for water temperatures up to 55°C. In special cases where the inlet water temperature is higher than 55°C, polypropylene packs are used. Regarding the maintenance of the fill pack, we recommend reading the dedicated article: "Cooling tower maintenance: what to do? "
To date, Decsa offers two types of film pack (wave 12 and wave 19) and two types of splash pack (3D and splash).
The 12-wave pack - Decsapack - is the best performing pack as it provides the largest contact surface area. With this kind of pack, you can get smaller equipment with the same thermal output.
In the case of suspended solids higher than 100 mg/L, wave pack 19 is used instead. With a greater distance between the sheets than wave pack 12, it guarantees a lower risk of clogging, which would otherwise lead to a considerable reduction in performance. Even in the case of a high-temperature difference between water inlet and outlet (generally > 20°C), wave pack 19 is preferred, regardless of the suspended solids content. In this case, there is marked evaporation in the upper part that could lead to the formation of deposits and scaling, which is less problematic with the use of a pack with a larger passage section.
In case one has to cool aparticularly dirty water (suspended solids > 200 mg/L) then the choice inevitably falls on splash-type packs (and the most suitable cooling tower in this case is the SQA series); hence the 3D pack, with a lattice structure, or splash pack proper, which has a drop-break structure that makes it the most suitable and used for this type of application.
Choosing the best fill pack for your cooling tower is ultimately dictated by the quality of the water (suspended solids content above all, but bacteria and oil content are also evaluated in the selection) and the difference between inlet and outlet temperatures.
Decsa, thanks to its decades of experience in evaporative cooling, is always able to offer the best solution concerning the process to be treated: contact us for more information.
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