Shear Dispersion in Combined Pressure-Driven and Electro-Osmotic Flows in a Capillary Tube with a Porous Wall

摘要

An analytical expression is derived for the shear dispersion during transport of a neutral nonreacting solute within a coupled system comprised of a capillary tube and a porous medium under the combined effects of pressure-driven and electro-osmotic flows. We use the Reynolds decomposition technique to obtain a dispersion coefficient by considering a sufficiently low wall or zeta potential that accounts for the combined flows. The coupled dispersion coefficient depends on the Debye-Huckel parameter, Poiseuille contribution fraction, and Peclet number. The developed model also provides a shear dispersion coefficient for an impervious capillary tube (noncoupled system). The ratio of the coupled (porous wall) and noncoupled (impervious) dispersion coefficients reveals that it is essential to include the transport of chemical species from the tube to the porous medium in several important physical situations. These findings have implications for design of chemical species transport in porous microfluidic networks and separation of emulsions in microchannel-membrane systems. (c) 2015 American Institute of Chemical Engineers.