Rheology effects on cross-stream diffusion in a Y-shaped micromixer

Micromixers are one of the essential components of modern bio-microfluidic devices. Since most bio-fluids are complex and their rheological behavior usually cannot be described by the Newtonʹs law of viscosity, it is vital to take into account the non-linear behavior of the fluids being manipulated in these devices in the pertinent simulations. In this paper, the non-Newtonian rheology effects on mass transport in an electrokinetically driven Y-shaped micromixer of rectangular cross section are being investigated. The fluid rheological behavior is assumed to be efficiently described by the power-law viscosity model. The governing equations are solved in dimensionless form through a finite difference based numerical procedure for non-uniform grid. The results show that the deviations of the fluid rheological behavior from the predictions of the Newtonʹs law of viscosity may result in significant alteration of the species concentration field, especially for thick EDLs. In this respect, a higher value of the flow behavior index gives rise to a thicker diffusion layer in the presence of a purely electroosmotic flow. Whereas the same is observed for a pressure assisted flow, the opposite is right in the presence of an adverse pressure gradient. Moreover, the diffusion layer extent is an increasing function of EDL thickness. The relevant functionality is pronounced by increasing the flow behavior index. In addition, the effect of decreasing both Péclet number and the rectangular geometry aspect ratio is to enhance the mixing efficiency.