Unstable density driven transport across membranes: Transport across thin porous surfaces, driven by unstable density difference across the surface, occurs in membrane separations, tissue transport, mantle convection, carbon sequestration etc. When a heavier layer of fluid is separated from a lighter layer of fluid below it by a horizontal microporous membrane, various regimes of transport occurs, based on the dominance of advection or diffusion. We discover a new regime of transport where advection balances diffusion, and remains so for about a decade of the dimensionless driving parameter, the Rayleigh number. The figure shows the top view of the pattern formed just above the membrane by the lighter fluid when it mixes with the heavier fluid in this new regime; the yellow lines are the lighter fluid and the green regions the heavier fluid. We propose a phenomenological explanation for the observed linear dependence of the dimensionless flux on the Rayleigh number in this regime.

Submitted by: Dr. A.P. Baburaj

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