Mixing and flow transition in an optimized electrokinetic turbulent micromixer

TL;DR

This study systematically optimizes an electrokinetic turbulent micromixer, revealing key parameters for maximum mixing efficiency and highlighting the need for turbulence modeling over linear instability analysis.

Contribution

It provides the first comprehensive analysis of how electric field, frequency, conductivity ratio, and channel width influence EK turbulence and mixing in a Y-type micromixer.

Findings

Maximum mixedness of 0.93 achieved at 84 μm from entrance

Optimal mixing conditions: 350 μm width, 100 kHz, 1.14×10^5 V/m electric field

Most unstable EK flow does not coincide with optimal mixing conditions

Abstract

Micromixer is a key element in lab on a chip for broad applications in the analysis and measurement of chemistry and engineering. Previous investigations reported electrokinetic (EK) turbulence could be realized in a Y-type micromixer with a cross-sectional dimension of 100 ${\mu}$m order. Although the ultrafast turbulent mixing can be generated at a bulk flow Reynolds number of O(1), the micromixer has not been optimized. In this investigation, we systematically investigated the influence of electric field intensity, AC frequency, electric conductivity ratio, and channel width at the entrance on the mixing effect and transition electric Rayleigh number in the "Y" type electrokinetic micromixer. It is found the optimal mixing is realized in a 350 ${\mu}$m wide micromixer, under 100 kHz and 1.14*10^5 V/m AC electric field, with an electric conductivity ratio of 1:3000. Under the conditions, a maximum degree of mixedness of 0.93 can be achieved at 84 ${\mu}$m from the entrance and 100 ms. A further investigation of the critical electric field and the critical electric Rayleigh number indicates the most unstable condition of EK flow instability is inconsistent with that of the optimal mixing in EK turbulence. To predict the evolution of EK flow under high $Ra_{e}$, it is necessary to apply a computational turbulence model, instead of linear instability analysis.