Geometry effects in electroosmotic flow in micro- and nano-channels

Ramirez, J.C.1, Conlisk, A.T.2
1 Los Alamos National Laboratory, Materials Science and Technology Division
2 The Ohio State University

We present a model for electro-osmotic flow and apply it to examine the effect of complicated geometries on the flow behavior along micro and nano-channels connecting two reservoirs. We perform two and three dimensional simulations. The model consists of the Navier-Stokes equation for the fluid momentum and pressure, species conservation equations for the concentrations of multiple ionic species dissolved in the solution and an equation for the electric potential.

We observe that a sudden expansion or contraction in the channel cross-section area causes two effects: First, a “pinchoff” effect that causes a fraction of the fluid to return to its original reservoir without ever reaching the other reservoir and second, the formation of a flow separation region adjacent to the sudden expansion or contraction. This separation region is interesting because it is formed at the extremely low Reynolds number typical of electro-osmotic flows.