Effects of acoustic resonance intensification on micromixing performance in a heart-shaped microreactor

Overcoming the inherent mass-transfer limitations of laminar microfluidics is critical for optimizing fast chemical reactions. In this study, low-frequency acoustic resonance was introduced as an active external excitation strategy to intensify micromixing within a custom-designed heart-shaped microreactor. The micromixing performance was quantitatively evaluated using the standardized Villermaux–Dushman parallel competitive reaction system and characterized via the segregation index (XS), micromixing time (tm), and Damköhler number (Da). Hydrodynamic analyses demonstrate that acoustic resonance induces secondary flows, periodic vortex shedding, and chaotic advection, which disrupt the diffusion-limited boundary layers within the microchannel. Consequently, compared to baseline vibration-free conditions, the application of acoustic resonance reduced the segregation index by 11.3% to 84.5%. Furthermore, the characteristic micromixing time was decreased from 1.94 × 10⁻⁴ – 7.27 × 10⁻⁴ s to 0.55 × 10⁻⁴ – 1.08 × 10⁻⁴ s. Under optimal acoustic excitation, the Damköhler number was maintained below 1.0 across all operating conditions, reaching a minimum of 0.12. This indicates that the system transitions into a reaction-kinetics-controlled regime, mitigating fluid mixing as the primary rate-limiting step. These findings provide experimental evidence and mechanistic insights for the design of microreactors.