Document Type : Original Article
Authors
1 University of Bonab
2 University of Tabriz
Abstract
This study numerically investigates mixing performance in an active micromixer combining geometric modification and oscillating wall excitation. The proposed design features two variable-angle inlets (45°, 60°, 90°, and 180°), a circular mixing chamber (R = 10 and 12.5 mm), and a flexible oscillating outlet section (2-8 Hz, 1-3.5 mm amplitude). A two-way fluid-structure interaction (FSI) approach in COMSOL Multiphysics captures the mutual effects between fluid flow and the elastic wall. Water enters at 20°C and 80°C with Reynolds numbers of 100-825 in laminar flow regime, with average outlet temperature serving as the mixing indicator.
Results show that increasing oscillation frequency and amplitude enhances mixing, with 8 Hz and 3 mm identified as optimal. The 60° Y-configuration outperforms the conventional T-mixer (90°) and parallel inlet (180°). While the mixing chamber generally improves performance, its effect is less pronounced at the optimal 60° angle. Unequal inlet velocities generate Kelvin-Helmholtz instability, creating shear-induced vortices that further enhance mixing.
The optimal configuration—60° inlet angle, 10 mm chamber radius, and 8 Hz, 3 mm wall oscillation—achieves a 92% mixing index at Re = 825, a 58% improvement over the base T-mixer. Estimated Nusselt numbers range from 9.2 to 13.8, with friction coefficients of 0.42-0.52. All configurations reach steady mixing within 6 seconds. These findings provide valuable insights for designing high-efficiency active micromixers for microfluidic applications requiring rapid homogenization of non-isothermal fluids.
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