Analysis of micromixing of non-Newtonian fluids driven by alternating current electrothermal flow

Biochemical applications pertaining to chip scale mixing often deal with fluids which exhibit non-Newtonian behavior. This paper presents numerical investigations on the characterization of the effect of shear dependent apparent viscosity of non-Newtonian fluids on the mixing efficiency and volume flow rate in an alternating current electrothermal micromixer driven by electrothermal micropump. The micromixer consists of thin film asymmetric pairs of electrodes on a microgrooved channel floor and an array of electrode pairs on the top wall. The results show that mixing quality and flow rate have a strong dependence on shear dependent viscosity of the non-Newtonian fluid. Using a power law based constitutive model, it is found that for specific design parameters, more uniform and homogeneous mixing is achieved with increasing flow behavior index. Thus, electrothermal mixing in a microfluidic device has higher efficiency and effectiveness in the regime of dilatant fluids compared to Newtonian and pseudoplastic fluids. Our results also demonstrate that an optimal voltage for maximum mixing efficiency progressively reduces, while the flow rate continues to increase monotonically, with enhancements in the applied AC potential. These results hold practical implications in several emerging applications, including chemical analysis of biological fluids in general, and biomedical diagnostics in particular.