Mixing in a split-and-recombined multi-helical microchannel: A numerical study

Efficient mixing in microfluidic systems at low Reynolds numbers is fundamentally limited by laminar flow, where molecular diffusion governs inter-stream transport. To address this constraint, we present a comprehensive three-dimensional numerical study of a novel split-and-recombined multihelical (SRMH) micromixer that combines curvature- and torsion-induced secondary flows. The SRMH design leverages the formation of Dean vortices and torsional swirl to intensify transverse advection and stretch fluid interfaces, enabling rapid homogenization even in diffusion-limited regimes. This can further help in shrinking microfluidic devices and creating multi-functional gadgets for numerous applications. Using finite element simulations, we systematically vary the Reynolds number (Re=1–450), helix angle, and shape deformation index (SDI) to evaluate mixing efficiency (η), velocity fields, and pressure drop. Compared to standard triple multihelical designs, the SRMH architecture exhibits markedly higher mixing efficiency (eta), particularly in the intermediate and high-Re regimes. A unified power-law scaling relation, η∼Re(βm−αm)( sin2θ cos θ)βm, captures the interplay between inertial suppression (αm) and curvature- and torsion-driven enhancement (βm).Our results reveal that secondary flow strength, quantified via Dean and Germano-type effects, increases with both Reynolds number and SDI, promoting strong radial and tangential velocity components. However, at very high Re and low SDI, a decline in βm is observed, indicating that excessive overlap and transition toward circular cross-sectional geometry suppress asymmetric vortex generation. These findings underscore the importance of geometric modulation in sustaining secondary flow structures and establish the SRMH micromixer as a robust and scalable platform for enhanced mixing in laminar microfluidic systems.