Effect of Dispersion on Solutal Convection in Porous Media

Abstract

AbstractSolutal convection in porous media is thought to be controlled by the molecular Rayleigh number, Ram, the ratio of the buoyant driving force over diffusive dissipation. The mass flux should increase linearly with Ram and the finger spacing should decrease as . Instead, our experiments find that flux levels off at large Ram and finger spacing increases with Ram. Here we show that the convective pattern is controlled by a dispersive Rayleigh number, Rad, balancing buoyancy and dispersion. Increasing the bead size of the porous medium increases Ram but decreases Rad and hence coarsens the pattern. While the flux is predominantly controlled by Ram, the anisotropy of mechanical dispersion leads to an asymmetry in the pattern that limits the flux at large bead sizes.