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International audienceThe zigzag configuration of spacers appears to have more advantages compared to the so-called submerged configuration for improving the performance of the reverse osmosis process; however, spacers attached to membrane walls may promote fouling. A two-dimensional numerical model coupling fluid dynamics and mass transfer was developed to study the impact of new design spacers, such as ellipse and oval shapes to control concentration polarization and reduce pressure drop. To improve spacer performance, spacers considered here are “tilted” and their performance is compared with the reference spacers (circular). It is shown that elliptical and oval spacers lead to significant reduction of the pressure drop when compared to circular spacers. Based on numerical prediction, mass transfer is enhanced, pressure drop minimized, and the probability of fouling is decreased if oval spacers are tilted at 20° compared to the widely used conventional spacers

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The present work relates to a numerical investigation of double diffusive mixed convection around a horizontal annulus with a finned inner cylinder. The solutal and thermal buoyancy forces are sustained by maintaining the inner and outer cylinders at uniform temperatures and concentrations. Buoyancy effects are also considered, with the Boussinesq approximation. The forced convection effect is induced by the outer cylinder rotating with an angular velocity (ω) in an anticlockwise direction. The studies are made for various combinations of dimensionless numbers; buoyancy ratio number (N), Lewis number (Le), Richardson number (Ri) and Grashof number (Gr). The isotherms, isoconcentrations and streamlines as well as both average and local Nusselt and Sherwood numbers were studied. A finite volume scheme is adopted to solve the transport equations for continuity, momentum, energy and mass transfer. The results indicate that the use of fins on the inner cylinder with outer cylinder rotation, significantly improves the heat and mass transfer in the annulus.

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