Electroosmotic flows in an electric double layer overlapped channel with rectangle-waved surface roughness

Abstract

To further understand the wall-roughness effect, the present study has performed numerical simulations, by employing the Poisson–Nernst–Planck model, on the two-dimensional electroosmotic flow in a plane channel with dielectric walls of rectangle-waved surface roughness where the two electric double layers (EDLs) are overlapped. Results show that the steady electroosmotic flow and ionic-species transport depend significantly on the shape of the surface roughness such as the amplitude and periodic length of wall wave, but their characteristics are basically different from those in the case where the EDLs are not overlapped at all (Kang and Suh in Microfluid Nanofluid, doi:10.1007/s10404-008-0321-5, 2008). It is found that the fluid flows over the waved wall (or wall roughness) with involving a separation or recirculation of flow in the cavity, which resembles much the traditional pressure-driven flow. In addition, the flow characteristics are determined chiefly by the level of the electric-charge density in the bulk region above the waved wall. As a result, with increasing wall-wave amplitude (0.01 ≤ h/H ≤ 0.2), the flow rate increases due to the enhanced amount of electric charges released from the enlarged wet surface at low amplitudes and then decreases due to the reduced flow-passage area at high amplitudes above a certain critical value. With increasing periodic length (0.2 ≤ L/H ≤ 1.2), on the other hand, the flow rate decreases in a hyperbolic fashion due to the reduced amount of electric charges.