Electroosmotic entry flow in a microchannel

The entry flow induced by an applied electrical potential through microchan nels between two parallel plates is analyzed in this work. A nonlinear, two -dimensional Poisson equation governing the applied electrical potential an d the zeta potential of the solid-liquid boundary and the Nernst-Planck equ ation governing the ionic concentration distribution are numerically solved using a finite-difference method. The applied electrical potential and zet a potential are unified in the Poisson equation without using linear superp osition. A body force caused by the interaction between the charge density and the applied electrical potential field is included in the full Navier-S tokes equations. The effects of the entrance region on the fluid velocity d istribution, charge density boundary layer, entrance length, and shear stre ss are discussed. The entrance length of the electroosmotic flow is longer than that of classical pressure-driven flow. The thickness of the electrica l double layer (EDL) in the entry region is thinner than that in the fully developed region. The change of velocity profile is apparent in the entranc e region, and the axial velocity profile is no longer flat across the chann el height when the Reynolds number is large. (C) 2001 Academic Press.