Rotating ellipsoids in viscous fluids: Shape-driven hydrodynamics around the spinners enhances transport efficiency

Rotating microparticles offer a promising approach for generating tunable local fluid motion and enhancing mass transport in applications such as lab-on-a-chip platforms, microfluidic tissue engineering, and advanced biotechnologies. Here, we quantify how the shape of a rotating particle governs the hydrodynamics and reactive transport in confined viscous fluids. Using fully three-dimensional Stokes simulations for oblate, spherical, and prolate ellipsoids of fixed volume, we evaluate a hydrodynamic factor Q(γ) derived from far-field scaling, the total kinetic energy integrated over the fluid domain E/Es, and the normalized solute flux J/Js for a model surface reaction. Prolate (elongated) particles generate stronger near-field entrainment and markedly higher flux enhancement than spheres, while oblate particles confine vorticity to a more localized region, yet can still increase the total flux under confinement. Within the explored parameter range, particle shape—rather than rotation rate—is the dominant parameter controlling transport performance. We further compare different geometries in terms of an energy-efficiency metric defined as the solute flux per unit input power, which reveals that, under the fixed-volume constraint, spheres maximize efficiency even though prolate particles provide the largest absolute flux. These results provide quantitative design guidelines for geometry-tunable micromixers and catalytic micromachines operating under confinement and establish a direct link between particle morphology, hydrodynamic response, and reactive transport in microreactors and lab-on-a-chip systems.