Investigation of configuration parameters and geometry in microball micromixers based on fluid–structure interaction analysis: A numerical study for enhancing mass transfer

Micromixers are vital components of microfluidic systems, enabling precise fluid manipulation and rapid reactions at the microscale. Active micromixers are valued for their remarkable controllability and rapid mixing. However, those with rotating magnetic actuators often produce oscillations in their mixing results, and the present work suppresses these fluctuations actuator-geometry manipulation, and targeted micromixer design modifications to achieve more stable mixing by employing fluid–structure interaction analysis. This study develops and validates a numerical model of a magnetically actuated microball micromixer and confirms its accuracy through comparison with experimental measurements. Furthermore, the time-dependent effect of variations in microball diameter, number, angular spacing, angular velocity, dimensionless ring radius, and Reynolds number on mixing quality, pressure drop, and mixing energy cost is quantitatively evaluated. Incorporating a second ring with an extra microball outside the main ring notably enhanced mixing, achieving an impressive 97% mixing index at Reynolds 5 by increasing the fluid residence time. While increasing each parameter except Reynolds number improves mixing quality, the associated variations in pressure drop across configurations necessitate assessing the mixing energy cost to identify the ideal design. Computational simulations show that four microballs arranged at 90° angular spacing, operating at Reynolds 15 and angular velocity 530 rpm, achieve optimal performance with a mixing index of 96% and a minimum mixing energy cost of 1.11 Pa, while also reducing mixing fluctuations to 0.5%. These findings offer valuable insights into the design principles of microball-based micromixers and provide practical guidance for developing high-efficiency micromixers for chemical and biological applications.