The geometry effect on steady electrokinetic flows in curved rectangular microchannels

Abstract

Microfluidic designs require the effort to understand the flow pattern depending on the channel geometry. An in-depth analysis based on the theoretical model is presented for the pressure-driven electrokinetic microflows in curved rectangular channels by applying the finite volume scheme with a SIMPLE (semi-implicit method for pressure-linked equations) algorithm. The external body force originated from between the nonlinear Poisson-Boltzmann field around the channel wall and the flow-induced electric field is employed in the Navier-Stokes equation, and the Nernst-Planck equation is taken into further consideration. Unknown pressure terms of the momentum equation are solved by using the continuity equation as the pressure-velocity coupling achieves convergence. Attention is focused on the geometry effect on the fluid velocity profile at the turn of charged rectangular channels with ranging complementary channel aspect ratios (i.e., H/W=0.2-5.0). Simulation results exhibit that the streamwise axial velocity at the turn skews the profile to the inner region of the microchannel. This is due to the stronger effect of spanwise pressure gradient arising from a sufficiently low Dean number. The skewed pattern in the velocity profile becomes greater with decreasing channel aspect ratio as well as degree of the channel curvature. Quantitative predictions for the decreasing velocity due to the electrokinetic interaction were also provided in both cases of shallow and deep microchannels. (C) 2010 American Institute of Physics. [doi:10.1063/1.3427572]