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As an essential component of chip laboratories and microfluidic systems, micromixers are widely used in fields such as chemical and biological analysis. In this work, a square cavity micromixer with multiple structural parameters (baffles, obstacles, and gaps) has been proposed to further improve the mixing performance of micromixers. This study examines the comprehensive effects of various structural parameters on mixing performance. The impact of baffle length, obstacle length-to-width ratio, gap width, and obstacle shape on the mixing index and pressure drop were numerically studied at different Reynolds numbers (Re). The results show that the mixing index increases with baffle length and obstacle length-to-width ratio and decreases with gap width at Re = 0.1, 1, 10, 20, 40, and 60. The mixing index can reach more than 0.98 in the range of Re ≥ 20 when the baffle length is 150 μm, the obstacle length-to-width ratio is 600/100, and the gap width is 200 μm. The pressure drop of the microchannel is proportional to baffle length and obstacle length-to-width ratio. Combining baffles and obstacles can further improve the mixing performance of square cavity micromixers. A longer baffle length, larger obstacle length-to-width ratio, narrower gap width, and a more symmetrical structure are conducive to improving the mixing index. However, the impact of pressure drop must also be considered comprehensively. The research results provide references and new ideas for passive micromixer structural design.

As an important part of lab-on-a-chip and micro-total analysis systems, micromixers have a wide range of applications in biochemical analysis, pharmaceutical preparation and material synthesis. In the work, a novel rhombic separation and recombination micromixer with baffles was presented to further improve the performance of the micromixer and study the effect of multiple structural parameters on mixing. The effects of the rhombic angle, the width ratio of sub-channel and the size and relative positions of baffles on the mixing index were studied numerically at different Reynolds numbers (Re), and the sensitivity of the mixing index to various structures was also investigated. The results showed that the mixing index increased with the subchannel’s width ratio and slowly decreased after reaching the peak value in the range of Re from 0.1 to 60. The maximum mixing index appeared when the width ratio was 6.5. The pressure drops in the microchannel were proportional to the width ratio. The mixing effect can be further improved by adding baffle structure to asymmetric rhombus micromixer, and more baffle quantity and larger baffle height were beneficial to the improvement of the mixing index. The research results can provide reference and new ideas for the structure design of passive micromixers.