Study of Slip Effect on Electro-osmotic Micromixer Performance Based on Entropy Index

In this article electrokinetic mixing through heterogeneous microchannels has been studied and the effects of slip coefficient, zeta-potential, Debye-Huckel parameter and Reynolds number on mixing efficiency have been investigated. The microchannels have homogenous surface properties except for zeta-potential. In order to study the electro-osmotic mixing, the Navier-Stokes, Nernst–Planck, electric potential and concentration equations have been solved numerically. In order to evaluate the mixing efficiency, entropy of concentration has been used as a quantitative index. The results show that the behavior of electro-osmotic micromixers is highly depended to amount and distribution of wall zeta-potential. Furthermore, mixing efficiency increases with reduction of slip coefficient and Debye-Huckel and Reynolds number parameters in most cases. It is seen that slip coefficient can decrease or increase mixing efficiency dependent on the Reynolds number. Furthermore the accuracy of Helmholtz-Smoluchowski approximate model is also investigated and it is found that in high wall zeta-potential cases or low values of Debye- Huckel parameter, results of this model have significant error compared to Nernst Planckmodel. It is also found that the mixing performance increases when as the charge pattern of micromixer is more asymmetric so that the certain mixing value can be obtained in shorter length which is importance in micromixers design.