Electroosmotic flow in microchannels

The electroosmotic flow induced by an applied electrostatic potential field through microchannels between two parallel plates and a 90° bend is analyzed in this work. A nonlinear, two-dimensional Poisson-Boltzmann equation governing the electrical double-layer field and the Laplace equation governing the electrostatic field distribution in microchannels are numerically solved using a finite-difference method. A body force caused by the interaction between the electrical double-layer field and the applied electrostatic field is included in the full Navier-Stokes equations. The effects of the electrical double-layer field and the applied electrostatic field on the fluid velocity distribution, pressure drop, and skin friction are discussed. A small pressure drop along the parallel plates is detected, although it is always neglected in the literature. Pressure is not a constant across the channel height. The axial velocity profile is no longer flat across the channel height when the Reynolds number is large. A separation bubble is detected near the 90° junction when the Reynolds number is large.