Enhanced electroosmotic mixing of non-Newtonian fluids in a heterogeneous surface charged micromixer with obstacles

Abstract

We investigate the mixing and hydrodynamic characteristics computationally for a pure electroosmotic flow of non-Newtonian fluid through a nonuniformly charged micromixer with obstacles arranged in staggered and inline orders. The constitutive behavior of the fluids is described by the power-law model. We present the results by varying the dimensionless zeta potential (|ζ|), Debye parameter (κ), and power-law index (n) in the range of 1 ≤ |ζ| ≤ 8, 0.5 ≤ κ ≤ 100 and 0.5 ≤ n ≤ 1.5, respectively. The mixing is strongly influenced by the rheology of the fluids and the formation of the recirculatory zones. For the overlapped EDL (κ = 0.5), mixing efficiency (ME) decreases with n for lower |ζ| values, while ME increases with n for higher |ζ| values for both the orientation of obstacles. When the obstacles are arranged in a staggered manner, the variation of ME with n follows a decreasing-increasing trend for the intermediate values of |ζ|. The value of ME is higher for the inline arrangement with overlapped EDL (κ = 0.5) and is close to 100%. For thinner EDL (κ = 100), the value of ME is higher for inline arrangement only for |ζ|= 1 and 0.5 ≤ n ≤ 0.6, and for all other cases, it is higher for staggered arrangement. The presence of heterogeneous charged surface always enhances the mixing and the enhancement is always higher for shear-thickening fluid and for the staggered order of the obstacles. The present design of electroosmotic micromixer handling with non-Newtonian fluids provides a higher mixing efficiency as compared to most of the existing designs available in the literature. The values of n, κ and |ζ| are identified for the micromixer with two orientations of the obstacles for quick and efficient mixing and the findings may be helpful to design an efficient micromixer for the point-on care diagnostic applications handling with of non-Newtonian fluids.