Membrane desalination is a pressure driven process which is being employed on a large scale in areas which do not have an easy access to fresh water resources. The large energy consumption of this process has encouraged researchers to explore the different spacer designs for maximizing permeate per unit of energy consumed. Computational fluid fynamics (CFD) was used to simulate the mass transfer enhancement in a reverse-osmosis desalination unit employing spiral wound membranes lined with zigzag spacer filaments of alternating diameters. Finite Volume based open source software OpenFoam was used to resolve the flow properties in a two-dimensional model by varying the Reynolds number until the onset of instability. Diamters of alternate strands were varied between ratios of 1, 1.5 and 2. The research provides guidelines based on comprehensive data set of velocity contours, pressure distribution, wall shear stresses and steady state vortex systems for using alternating strand design in zigzag configuration for maximum mass transfer and least pressure drop taking into account the concentration polarization.

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