Session DC - Micro-Fluid Dynamics II: Flow in Microchannels.
MIXED session, Sunday afternoon, November 21
Grand III, Westin Seattle
Electrokinetic instabilities (EKI) present a major challenge to optimizing sample stacking devices, as well as an opportunity to achieve rapid on-chip mixing. These instabilities are due to electric body forces resulting from the coupling of electric fields and conductivity gradients. In this work a generalized electrokinetic model suitable for the study of microchannel flows with conductivity gradients and shallow channel depths was developed. An asymptotic analysis was performed with channel depth-to-width (z-to-y) aspect ratio as a smallness parameter, and the three dimensional flow equations were reduced to a set of depth-averaged equations governing the in-plane (x, y) flow dynamics. The momentum equation uses a Darcy-Brinkman-Forchheimer type formulation, and the convective-diffusive transport of the conductivity field in the depth (z) direction manifests itself as a dispersion effect on the in-plane motion. The validity of the depth-averaged model was assessed by comparing the numerical results with full three dimensional, direct numerical simulations, and experimental data. The depth-averaged equations provide a convenient quasi-two-dimensional model applicable to a wide class of microfluidic devices.