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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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Numerical analysis was investigated for steady two-dimensional double diffusive mixed convection boundary layer flow over a semi-infinite vertical plate embedded non-Darcy porous medium filled with nanofluid, in presence of thermal dispersion and under convective boundary conditions. The Buongiorno nanofluid model is used, while the porous medium is described by the Darcy-Forchheimer extension. The governing partial differential equations are transformed into four coupled nonlinear ordinary differential equations using an appropriate similarity transformations and the resulting system of equations is then solved numerically by the finite-difference method. Numerical results are presented to illustrate how the physical parameters affect the flow field, temperature, concentration and solid volume fraction profiles. In addition, the variation of heat, mass and nanoparticle transfer rates at the plate are exhibited graphically for different values of pertinent parameters.

The main objective of this article is to study the effect of 2D coupled mode free convection with surface radiation on the fluid flow behavior in an air filled partitioned and shallow cavity subjected to isothermal or insulated boundary conditions. The dimensionless governing equations under Boussinesq approximation are coupled with a radiative model through the boundaries conditions and solved by the finite volume method. The numerical results are discussed in terms of streamlines, isotherms, convective and radiative Nusselt numbers along the cover plate for various aspect ratios (a, b and c), emissivities and Rayleigh number. These results highlighted the condition of the enclosure performance and revealed among other that isothermal boundaries induce better convective heat exchange compared to adiabatic cases. Also, it is noticed that varying aspect ratio (a) causes strong influence on both Nusselt numbers compared to the aspect ratios (b) and (c). The increase of ( o) raises Nuconv and decreases Nu rad slightly. Whereas, an increase of ( C ) leads to minor changes in Nu rad when (b) or (c) vary, this effect becomes appreciable with increasing (a).

Numerical study has been performed to investigate the combined effects of lid movement and buoyancy on flow and heat transfer characteristics for the mixed convective flow inside a lid-driven arc-shape cavity. The work is motivated by its immense importance due to its wide range of applications. The numerical simulations, therefore, are performed for three different shape concave enclosures (rectangular, circular and triangular) in laminar flow regime and for different Reynolds numbers (10 ≤ Re ≤ 1000) and Grashof numbers (10 4 ≤ Gr ≤ 10 7 ) effects on the flow and heat transfer. Numerical results are presented in terms of streamlines, isotherms, velocity profiles and average Nusselt number along the bottom wall. The comparisons showed that the increase of Reynolds and Grashof numbers enhance the heat transfer for all forms of alveolus. Further, triangular alveolus highlights a higher heat transfer rate for higher Re numbers.