Secondary microflows in electro-osmotic transport with hydrodynamic slippage effect

Secondary microflows in electro-osmotic transport with hydrodynamic slippage effect
microflow; electroosmosis; hydrodynamic slip; electric double layer; Dean vortex; velocimetry
Issue Date
10th ELKIN 2012
VOL 10, 49-49
The curved channel is frequently encountered in the lab-on-chips system because it provides a convenient way for increasing the channel length per unit chip area. The behavior of electro-osmotic flow with curvature-induced secondary motion was explored based on a model with full Poisson-Boltzmann/Navier-Stokes and the advanced numerical framework. The pressure-velocity coupling achieves convergence, applying generalized slip boundary conditions at the hydrophobic curved surface. Two kinds of channels are explored with the glass channel and the heterogeneous channel consisting of glass and polydimethylsiloxane, covering thin to thick electric double layer (EDL) problem. Due to a sufficiently low Dean number, an inward skewness in the streamwise velocity profile is observed at the turn. The electrokinetic effect gets higher contribution in the velocity profile, with increasing EDL thickness. Simulation results regarding the variations of streamwise velocity depending on electrokinetic parameters and fluid slippage show consistency with the predictions in the literature [Joly et al., J. Chem. Phys. 125, 204715, 2006]. Secondary flows arise due to a mismatch of streamline velocity between fluid in the channel center and near-wall regions [Yun et al., Phys Fluids 22, 052004, 2010]. Strengthened secondary flow results from increasing the EDL thickness and the contribution of fluid inertia (i.e., electric field and curvature), providing a scaling relation with the slope. The particle streak velocimetry is performed by using an inverted epi-fluorescence microscope with tracer particle, which provides experimental verifications and optimum selection in applications such as stronger secondary motion for mixing.
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