Characterization of feed channel spacer performance using geometries obtained by X-ray computed tomography
AuthorsHaaksman, Viktor A.
Vrouwenvelder, Johannes S.
KAUST DepartmentBiological and Environmental Sciences and Engineering (BESE) Division
Water Desalination and Reuse Research Center (WDRC)
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AbstractSpiral-wound membrane modules used in water treatment for water reuse and desalination make use of spacer meshes for keeping the membrane leaves apart and for enhancing the mass transfer. Computational fluid dynamics (CFD) has gained importance in the design of new spacers with optimized hydrodynamic characteristics, but this requires a precise description of the spacer geometry. This study developed a method to obtain accurate three-dimensional (3-D) geometry representations for any given spacer design from X-ray computed tomography (CT) scans. The method revealed that the filaments of industrial spacers have a highly variable cross-section size and shape, which impact the flow characteristics in the feed channel. The pressure drop and friction factors were calculated from numerical simulations on five commercially available feed spacers used in practice. Model solutions compared well to experimental data measured using a flow cell for average velocities up to 0.2 m/s, as used in industrial reverse osmosis and nanofiltration membrane operations. A newly-proposed spacer geometry with alternating strand thickness was tested, which was found to yield a lower pressure drop while being highly efficient in converting the pumping power into membrane shear. Numerical model solutions using CFD with geometries from CT scans were closer to measurements than those obtained using the traditional circular cross-section strand simplification, indicating that CT scans are very well suitable to approximate real feed spacer geometries. By providing detailed insight on the spacer filament shape, CT scans allow better quantification of local distribution of velocity and shear, possibly leading to more accurate estimations of fouling and concentration polarization. © 2016 Elsevier B.V.
CitationHaaksman VA, Siddiqui A, Schellenberg C, Kidwell J, Vrouwenvelder JS, et al. (2017) Characterization of feed channel spacer performance using geometries obtained by X-ray computed tomography. Journal of Membrane Science 522: 124–139. Available: http://dx.doi.org/10.1016/j.memsci.2016.09.005.
SponsorsThe spacer CT scans were performed by Wim Verwaal and Joost van Meel at the Faculty of Civil Engineering and Geosciences from Delft University of Technology. We thank Thomas Lippert from Technical University of Munich, Germany, for fruitful discussions on the CFD meshing strategies. We also acknowledge Victor Koppejan from the Delft University of Technology for insightful ideas on measures to compare hydrodynamic efficiency. This research was supported by funding from King Abdullah University of Science and Technology (KAUST) and Delft University of Technology.
JournalJournal of Membrane Science