Abstract Summary (Max 250 words)
Laminar mixing is critically important in industries dealing with high‑viscosity materials, food, and cosmetics, yet conventional anchor impellers operating at very low Reynolds numbers inevitably generate distinct poorly mixed regions between the blades and the central shaft. To address this long-standing limitation, we examined whether rotational reciprocation could induce chaotic mixing and thereby enhance mixing performance. Chaotic mixing was successfully achieved when the Reynolds number was not excessively low, although isolated mixed regions still appeared, with their positions and shapes varying dynamically with the impeller motion. To eliminate these regions, we further investigated asymmetric anchor geometries and found that circumferential asymmetry, achieved by unequally spacing the blade attachment angles, was effective in suppressing poorly mixed regions. CFD analysis revealed that excessively narrow inter‑blade angle produced stagnation near the shaft, and that overly large reciprocation amplitudes weakened chaotic mixing. Finally, we demonstrated that a three‑blade anchor impeller with a 120‑degree inter‑blade angle, reciprocated at an amplitude of 90 degrees, could completely eliminate poor mixing while maintaining unsteady chaotic flow. Chaotic mixing induced by rotational reciprocation has rarely been explored in previous anchor‑impeller studies, and the use of symmetry breaking to improve mixing performance provides a new and practical design guideline.
