Characterization of feed channel spacer performance using geometries obtained by X-ray computed tomography Viktor A. Haaksman a , Amber Siddiqui b , Carsten Schellenberg c , James Kidwell d , Johannes S. Vrouwenvelder a,b,e , Cristian Picioreanu a,n a Department of Biotechnology, Faculty of Applied Sciences, Delft University of Technology, Van der Maasweg 9, 2629 HZ Delft, The Netherlands b King Abdullah University of Science and Technology (KAUST), Water Desalination and Reuse Center (WDRC), Division of Biological and Environmental Science and Engineering (BESE), Thuwal 23955-6900, Saudi Arabia c LANXESS AG, Kennedyplatz 1, 50569 Cologne, Germany d Conwed Plastics, 2810 Weeks Ave SE, Minneapolis 55414, USA e Wetsus, European Centre of Excellence for Sustainable Water Technology, Oostergoweg 9, 8911 MA Leeuwarden, The Netherlands article info Article history: Received 20 April 2016 Received in revised form 24 July 2016 Accepted 3 September 2016 Available online 5 September 2016 Keywords: CT scan Three-dimensional model Hydrodynamics CFD Spiral-wound membrane module abstract Spiral-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. Computa- tional fluid dynamics (CFD) has gained importance in the design of new spacers with optimized hy- drodynamic 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 char- acteristics 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 al- ternating 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 esti- mations of fouling and concentration polarization. & 2016 Elsevier B.V. All rights reserved. 1. Introduction Membrane operations are used increasingly for the removal of various contaminants from water. For instance, microfiltration (MF) and ultrafiltration (UF) separate particulate material, while nanofiltration (NF) and reverse osmosis (RO) retain charged so- lutes. Industrially, the removal of these contaminants in order to produce potable water is performed using spiral-wound mem- brane modules. Optimisation of the performance of spiral-wound modules has been focussed mainly on the development of mem- branes [1] and the design of feed channel spacers [2]. Research into feed spacer design concentrates mainly on the effect of the spacer geometry on the hydrodynamics in the spacer- filled channel. Hydrodynamics, in turn, influences all other per- formance indicators. The spacer geometry determines the power input required to overcome the hydraulic resistance imposed on the flow, which is dominated by form drag of the spacer filaments and losses due to the change in direction of flow [3]. The dis- sipation of momentum and the resulting flow pattern are linked to the distribution of shear stress on the spacer filaments and membranes. Disruption of the hydrodynamic boundary layer by means of liquid recirculation regions influences the transport of solutes from and of particulate material towards the membranes Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/memsci Journal of Membrane Science http://dx.doi.org/10.1016/j.memsci.2016.09.005 0376-7388/& 2016 Elsevier B.V. All rights reserved. n Corresponding author. E-mail addresses: V.A.Haaksman@tudelft.nl (V.A. Haaksman), Amber.Siddiqui@kaust.edu.sa (A. Siddiqui), Carsten.Schellenberg@lanxess.com (C. Schellenberg), James.Kidwell@conwedplastics.com (J. Kidwell), J.S.Vrouwenvelder@tudelft.nl, Johannes.Vrouwenvelder@kaust.edu.sa, Hans.Vrouwenvelder@wetsus.nl (J.S. Vrouwenvelder), C.Picioreanu@tudelft.nl (C. Picioreanu). Journal of Membrane Science 522 (2017) 124–139