Assessment and Prediction of EOF Mixing in Binary Electrolytes

A two dimensional simulation is made to analyse the mixing enhancement due to surface roughness and geometric modulation in a sufficiently long rectangular nano-channel filled with electrolyte solutions of different concentrations. Geometric modulation is made by mounting non-conducting rectangular blocks on the bottom wall of the channel. An overpotential patch is placed on the upper wall of each block to create surface heterogeneity. Based on a finite volume staggered grid approach, the flow characteristics and mixing efficiency are discussed by a complete numerical solution of coupled nonlinear set of PDEs involving Nernst-Planck equation for ion distribution, Navier-Stokes equation for velocity components and Maxwells equation for potential distribution. A linear pressure drop is observed above the overpotential region which creates a recirculating zone. Mixing efficiency is improved with increasing vortex strength which is enhanced by decreasing EDL (electric double layer) thickness and increasing overpotential patch strength.