Electrokinetic Effects on Solute Mixing Near a Conducting Obstacle Within a Microchannel

Abstract

A numerical study is made on the electroosmotic flow (EOF) near a polarizable obstacle mounted on one of the nonconducting walls of a microchannel. The external electric field induces a Debye layer of nonuniform $\zeta$-potential along the obstacle, which results in a nonlinear electroosmostic flow. The combined effect of surface roughness and nonuniform electric double layer on the polarizable obstacle creates a vortical flow. The form of this vertical flow and its dependence on the bulk ionic concentration is analyzed. Our numerical model is based on the Navier–Stokes equations for fluid flow, Nernst–Planck equations for ionic concentration, and Poison equation for induced electric potential. We have computed the governing nonlinear coupled set of equations by the control volume method over a staggered grid system. Our results show that the form of the vortical flow, which develops in the vicinity of the obstacle, depends on the thickness of the Debye layer along the homogeneous part of the channel. The occurrence of electrical neutrality of fluid outside the Debye layer and recirculating vortex near the obstacle suggests that the fluid flow is influenced by the induced electric field and vice-versa. The vertical flow, which leads to enhanced mixing of solute in the microchannel.