A stable high mixing performance of Koch fractal array obstacle-based micromixer

Passive micromixers are essential components in microfluidic systems, enabling efficient fluid mixing under laminar flow conditions without external energy input. This study numerically investigates the mixing performance and flow mechanisms of passive micromixers incorporating Koch fractal obstacle arrays. Four fractal geometries—Secondary Snowflakes Fractal (SSF), Tertiary Snowflakes Fractal (TSF), Rounded Secondary Snowflakes Fractal (RSSF), and Rounded Tertiary Snowflakes Fractal (RTSF) are analyzed in both same-side and different-side configurations using COMSOL Multiphysics over a wide Reynolds number range (Re = 0.1–100). Model validation against benchmark obstacle-based micromixers from the literature shows good agreement in mixing efficiency and pressure drop, confirming the reliability of the numerical framework. The results demonstrate that Koch fractal obstacles enhance mixing through flow splitting, stretching, and chaotic advection. Among all configurations, the different-side rounded tertiary snowflake fractal (DSRTSF) exhibits the most stable and consistently high mixing performance, achieving a maximum mixing efficiency of 97.70% at a Reynolds number (Re) of 0.1. Performance index analysis further reveals that rounded fractal geometries provide a favorable balance between mixing efficiency and pressure drop. These findings offer practical design guidelines for high-performance fractal obstacle-based passive micromixers in lab-on-a-chip and microfluidic applications.