(410a) Dispersion in Combined Pressure-Driven/Electro-Osmotic Flows in Double-Porosity Systems

The aim of this study is to develop an analytical expression for dispersion during transport of a neutral non-reacting chemical species within a coupled double-porosity system comprised of a conduit and a porous medium under the combined effects of pressure-driven and electro-osmotic flows with a sufficiently low wall or zeta potential. To achieve this, a two-dimensional coupled system is introduced, in which the interaction between the conduit and the porous medium is handled by imposing the continuity of concentration and mass flux at the interface between the two media. Then the Reynolds decomposition technique is applied to derive an equivalent one-dimensional equation for advective-dispersive transport with equivalent transport coefficients, including the dispersion and advection coefficients. The coupled dispersion coefficient depends on the Debye-Huckel parameter, Poiseuille contribution fraction, and Peclet number. The developed model also provides a dispersion coefficient for a conduit with impervious walls (a non-coupled system). The ratio of the coupled (porous wall) and non-coupled (impervious) dispersion coefficients reveals that it is essential to include the transport of chemical species from the conduit to the porous medium in several important physical situations. The current work offers a more representative dispersion coefficient for the coupled double-porosity systems, which can have implications for a design of porous microfluidic systems. The presented model can also find applications in fluid flow through shale and clay rocks, separation of emulsions in microchannel-membrane systems, and electrically assisted transdermal drug delivery.