Analysis of different shapes of cross-sections and obstacles in variable-radius spiral micromixers on mixing efficiency

Spiral micromixers are one of the most widely used passive micromixers, but their mixing efficiency in the medium Reynolds number range (0.5∼50) is not ideal. To enhance the mixing efficiency of variable-radius spiral micromixers, VSR-C,VSR-T,VSR-H micromixers were designed by inserting cylindrical,triangular and hexagonal obstacles into the microchannel, and VSE, VST micromixers were designed by turning the cross section of the microchannel into triangle and ellipse. All micromixers were fabricated by LCD 3D printing. Simulation analysis and mixing experiments indicate that variable-radius spiral micromixers with obstacles can only increase mixing efficiency at high Reynolds number, while micromixers with triangular or elliptical cross sections can improve the mixing efficiency not only at high Reynolds number (Re > 5), but also at low and medium Reynolds number (Re < 3). The results suggest more Dean vortexes could be generated in spiral micromixer with an elliptical cross section (VSE) at the same Dean number,and the effective action area of Dean flow is enlarged simultaneously. As compared to VSR micromixer, the mixing efficiency of VSE exhibited 28% improvement on average, which implys the optimization of cross-section shape provides a potential way to improve the performance of spiral micromixers.