Formation of vortices near abrupt nano-channel height changes in electro-osmotic flow of aqueous solutions

Abstract

We perform computational fluid dynamics simulations of electro-osmotic flow in nano-channels and examine the effects of sudden changes in channel cross-section area (e.g., channels with a backward-facing step) which may be a simple model of one type of fabrication flaw. When the width of the electric double layers is large enough, we observe the formation of vortices or recirculation regions near the step face. On the other hand, flows with thin electric double layers are less likely to exhibit recirculation regions. We also simulate the formation of vortices and recirculation regions for flows with asymmetrical boundary conditions for charge and concentrations.