Unraveling Effects of Dean Vortices on Membrane Fouling in A Sinusoidally Curved Channel

Particulate fouling is detrimental to membrane-based processes for water/wastewater treatment, water reclamation, desalination, and other applications. Although it has been recognized that curved channels can induce Dean vortices (i.e., the secondary flows arising from the centrifugal instability), the effects of the Dean vortices on the deposition of foulant particles remain unclear. 3D optical coherence tomography (OCT) imaging was employed by this study to quantitatively analyze the cake formation in a sinusoidally curved channel by evaluating the surface coverage and the average of the local cake thicknesses as a function of time. The characterization results for the curved channel were compared with those obtained in a straight channel to reveal the interplay between the cake formation and the Dean vortices. The effects of operating conditions were also studied by varying the crossflow rate of the feed solution. In particular, the evolution of cake morphology was analyzed by identifying the relatively active areas of cake growth and removal at various times. All the characterization results suggest that the Dean vortices induced by the sinusoidally curved channel could favor the reduction of the areas covered by the deposits, though this advantage might be partially offset owing to the formation of an extremely uneven cake layer. This work provides in-depth insights into the fouling behavior in a sinusoidally curved channel, which is of great value in optimizing the design of novel spacers for membrane-fouling control.