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Surfaces are ubiquitous , and play a critical role in the operation of heat exchangers . Since , the efficiency of heat transfer is determined by the surface area between fluids , fouling poses a major challenge , as deposited materials on surfaces will decrease efficiency . In this article , we will discuss how surfaces influence fouling rates and explore innovative surface-based mitigation approaches . Further , we will review why predicting fouling remains a challenge .
How surfaces affect fouling build-up The morphology of a surface influences the rate of fouling . The presence of surface features , whether intentionally designed patterns or unintentional roughness , can give rise to unforeseen effects on fluid transport and reaction rates . Research indicates that surface roughness plays a significant role in determining the amount of deposition on a surface and the bonding strength of the foulant . For instance , it has been demonstrated that removing fouling from a rough surface requires a force approximately 30 times greater than that needed for a smooth surface [ 1 ] . The increased deposition on rough surfaces can be attributed to a higher number of sites for fouling formation , more ' hooking ' sites , and improved advection resulting from interactions between the surface and the fluid . In a recent study , we discovered that patterned surfaces have the potential to enhance overall deposition while concurrently increasing the frequency of detachment events . Local protrusions within a flow field can result in deposits that exhibit weak attachment to the surface , making them susceptible to easy detachment in the presence of fluid forces ( see Figure 1 ) [ 2 ] .
The complexity of fouling Fouling is a complex process involving multiple mechanisms , including crystallization , particle sedimentation , and biofilm formation . The adhesive properties of these foulants can vary widely , from being tightly bound to the surface to being more elastic . This diversity in adhesion strength is crucial in determining
Research Series
Predicting fouling : Surface effects
In our previous article , published in Heat Exchanger World ’ s July issue , we discussed recent advancements in modeling and prediction of fouling .
In this article , we will emphasize the significance of surfaces in fouling processes and delve into the shortcomings of existing prediction models .
About the authors
Benaiah U . Anabaraonye is a research scientist and Program Manager at the Danish Offshore Technology Centre . He has a PhD in Chemical Engineering from Imperial College London .
Isaac Appelquist Løge completed a Ph . D . on crystallisation fouling , using novel methods to visualise fouling formation . He is currently researching what makes fouling detach and what makes it stick .
Isaac Appelquist Løge and Benaiah U . Anabaraonye will be publishing regular articles as part of a Research Series across multiple issues of Heat Exchanger World . All articles will be available in our online archive : https :// heat-exchanger-world . com / category / technical-articles /.
By Isaac Appelquist Løge and Benaiah U . Anabaraonye
Smooth surface how well the foulant layer withstands external forces . Unfortunately , current fouling models often overlook the intricate interplay of these multiple fouling modes . This oversight can lead to inaccuracies in predicting fouling rates and assessing the effectiveness of mitigation strategies . In a recent study , we demonstrated how predictions of fouling rates are affected by crystal resilience . We investigated the impact of deposition order on the overall deposition rate in a system containing BaSO 4 and CaCO 3
[ 3 ]
. We found that when BaSO 4 was deposited first , it led to a twofold increase in the deposition rate of CaCO 3
. Conversely , when CaCO 3 was deposited first , the subsequent introduction of BaSO 4 actually displaced
CaCO 3
, resulting in an overall reduction in deposition ( see Figure 2 ). This observation is attributed to the relatively lower resilience of CaCO 3 to detachment forces compared to BaSO 4
, highlighting that when the softer salt acted as a substrate , it facilitated detachment . Particulate fouling , characterized by the sedimentation of solid particles , exhibits weaker adherence to surfaces compared to crystallization fouling . Foreign solid particles can act as nucleation seeds by accelerating the rate of crystallization fouling . Consequently , fouling could be mitigated by filtering out these particles from the solution . However , the influence of particles on fouling is also dependent on their size , shape , and composition . In certain cases , particles can even exacerbate the erosion of already deposited fouling layer . Biological fouling introduces an additional layer of complexity . Biofilms consist of colonies of microorganisms embedded in a polymeric matrix . They can amplify crystal formation , resulting in more build-up , and can even influence the properties of these crystals . Furthermore , biofilms can facilitate the adhesion of crystal nuclei to surfaces . When crystallization fouling grows beyond the biofilm layer , the crystals can protect the flexible biofilm , and a synergy is created between biological and crystallization fouling .
Surface modifications can be used to mitigate fouling Surface engineering is a valuable strategy in the fight against fouling . This proactive approach involves designing surfaces to reduce attachment while concurrently enhancing detachment rates , offering promising solutions .
Patterned surface
Figure 1 . Fouling on smooth and patterned surfaces . The X-Ray CT images show BaSO 4 ( orange-yellow ) deposition on steel surfaces ( grey-blue ). More information can be found in reference 2 . www . heat-exchanger-world . com Heat Exchanger World September 2023
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