Design and numerical investigations of mixing enhancement for single-layer SAR micromixer with localized offsets and slots

The present work focuses on developing a single-layer separation and recombination (SAR) based micromixer to enhance the mixing process of two miscible fluids. As in recent findings, separation and recombination type micromixers demonstrate their outstanding mixing efficiency in diverse flow scenarios. An accurate and stable platform, OpenFOAM V21 is used to perform the numerical investigations. We propose the four noteworthy SAR-based micromixers, which are designed by integrating the offsets and slots in selected micromixers. The first micromixer is without offset and slots, while the offsets are provided in the second, and slots are integrated into the third variant. The final design comprises both offset and slots by superimposing the above mentioned micromixers. We critically analyze the flow physics in these micromixers by detailing the concentration contours, streamlines, and velocity vectors. The results indicate that the inclusion of the offset promotes the twisting flow, while slots are responsible for stretching and folding phenomena. We found micromixer with offsets and slots provides the highest mixing index than the other proposed designs. Furthermore, it achieves 99.99% mixing efficiency across a wide range of Reynolds numbers, including low values ($Re\ge 20$), and we also provide data on pressure drop and mixing cost to facilitate optimal design selection. At last, the present obtained results are compared with the existing two-layer micromixers which are found to be on par or even superior for a wide range of Reynolds numbers.