Curvature-induced secondary microflow motion in steady electro-osmotic transport with hydrodynamic slippage effect

Abstract

In order to exactly understand the curvature-induced secondary flow motion, the steady electro-osmotic flow (EOF) is investigated by applying the full Poisson-Boltzmann/Navier-Stokes equations in a whole domain of the rectangular microchannel. The momentum equation is solved with the continuity equation as the pressure-velocity coupling achieves convergence by employing the advanced algorithm, and generalized Navier's slip boundary conditions are applied at the hydrophobic curved surface. Two kinds of channels widely used for lab-on-chips are explored with the glass channel and the heterogeneous channel consisting of glass and hydrophobic polydimethylsiloxane, spanning thin to thick electric double layer (EDL) problem. According to a sufficiently low Dean number, an inward skewness in the streamwise velocity profile is observed at the turn. With increasing EDL thickness, the electrokinetic effect gets higher contribution in the velocity profile. Simulation results regarding the variations of streamwise velocity depending on the electrokinetic parameters and hydrodynamic fluid slippage are qualitatively consistent with the predictions documented in the literature. Secondary flows arise due to a mismatch of streamline velocity between fluid in the channel center and near-wall regions. Strengthened secondary flow results from increasing the EDL thickness and the contribution of fluid inertia (i.e., electric field and channel curvature), providing a scaling relation with the same slope. Comparing with and between the cases enables us to identify the optimum selection in applications of curved channel for enhanced EOF and stronger secondary motion relevant to the mixing effect. (C) 2011 American Institute of Physics. [doi:10.1063/1.3650911]