Electroosmotic mixing of non-Newtonian fluid in an optimized geometry connected with a modulated microchamber

Abstract

The main objective of this work is to enhance the micromixing of different species transported through the electrokinetic mechanism applicable in lab-on-a-chip devices used in BioMEMS. In this process, it is essential to predict the efficiency and precision of the micromixture for the quick and correct mixing. In this paper, a numerical study is conducted to investigate the mixing quantification of the electroosmotic micromixer with a nozzle–diffuser shaped channel connected to reservoirs located at both ends of the channel with a microchamber located in the middle of the channel modulated with an inner rectangular obstacle. Since enhancing mixing quality is the paramount factor, this study examines how the design of the mixing chamber (circular and triangular), the size of the inner obstacle, the conical angle of the nozzle–diffuser channel, and the electric double layer height influence the flow inside the electroosmotic micromixer. Numerical simulations have been performed by using the Poisson–Nernst–Planck based Cauchy momentum equations for a non-Newtonian power-law fluid. This study focuses on both the mixing enhancement and the performance evaluation factor by lowering the pressure drop with variation of geometric modulation. The reservoir end wall effects are considered for the flow rate and mixing of the power-law fluids with variation of different flow parameters. After obtaining the optimal values of the effective parameters used in the micromixers for the experiments, regardless of the geometry of the obstacles, the present model is formulated and validated, and the results are presented. According to the findings, it is observed that the height and width of the inner obstacle, Debye–Hückel parameter, and the slope of the channel have a significant role in the overall mixing quality. The mixing efficiency is improved up to 90% for Newtonian fluid and 96% for shear thickening fluid by using obstacle fitted in the microchamber of the system. In addition, the results demonstrate that shear thickening fluids have better mixing performance than shear thinning fluids, which can be helpful in the fabrication of advanced micromixers.