Numerical Investigation of Vortex-Induced Enhancement in the Mixing Characteristics of Double-Spiral and Serpentine Microchannels

To enhance passive mixing in microchannels, T-shaped double-spiral and serpentine microchannels with identical curvature radii were designed and numerically analyzed across a Reynolds number (<i>Re</i>) range of 1 to 300. The double-spiral microchannel exhibited superior mixing performance at <i>Re</i> ≤ 200, which is primarily attributed to the efficient utilization of Dean vortices. In contrast, the serpentine microchannel showed better performance at <i>Re</i> ≥ 250, benefiting from the early formation of four-vortex structures induced by periodic curvature reversals. To further enhance the performance of the serpentine microchannel at low <i>Re</i>, groove structures with varying orientation angles were incorporated. The introduction of the groove structures generated lateral secondary flows that not only increased flow disturbances but also disrupted the symmetry of the Dean vortices. Among these configurations, Structure 2, with a 45° angle between the groove direction and centrifugal force, exhibited the most pronounced enhancement in vortex intensity, as the secondary flows induced by the grooves synergistically interacted with the Dean vortices. This configuration resulted in the highest mixing enhancement (>50%). This study provides valuable insights into geometry-driven mixing mechanisms and offers design guidelines for high-efficiency micromixers across a wide range of <i>Re</i>.