Optimization of Serpentine Micromixers with Non-Rectangular Cross-Sections

Serpentine or spiral-shaped microchannels have been popular choices for microfluidic mixers due to their relatively easy fabrication and possibility for re-use. The technique used in these types of microchannels aims to utilize the cross-sectional transversal (Dean) flows experienced by the fluids as they round a curved channel. Because of the reliance on centrifugal forces the mixing quality is strongly Reynolds number-dependent, with quality mixing occuring only at Re>100. It has been shown that the use of channels with non-rectangular cross-sections can be used as an effective strategy in this type of design to induce mixing at much lower flow rates. In this work, we seek to optimize the geometrical parameters of these channels to maximize their overall mixing performance. The results of the optimization process were obtained numerically through computational solutions of the flow fields and fluid concentration. Experimental results are also included showcasing the increase in mixing quality. We found that our optimized designs substantially outperformed standard serpentine geometries with rapid mixing being achievable down to Re~20.