Inertial particle focusing in microfluidic systems: Role of particle size, surface slip, and flow regime

Inertial particle focusing is a key mechanism in microfluidic systems, enabling enhanced particle alignment and separation for applications such as drug delivery, biosensing, and diagnostics. However, a comprehensive understanding of this phenomenon remains challenging due to the intricate coupling between suspended particles and the surrounding fluid, particularly in capturing lift forces, interfacial slip effects, and long-distance particle migration. In this study, we present a direct numerical simulation framework based on a diffuse interface method, incorporating parallel solution algorithms to accurately and efficiently capture fluid–particle interactions. The proposed method is straightforward to implement and demonstrates improved accuracy compared with existing approaches at comparable mesh resolutions. The numerical approach is validated through convergence tests and comparison with previously reported results. We systematically explore the influence of key physical parameters such as Reynolds number and particle size on inertial focusing behavior. For the first time, the influence of particle surface slip on equilibrium focusing positions is quantified, showing good agreement with available experimental observations, and the method is further extended to study multi-particle inertial focusing and size-based separation in complex microchannel geometries, benefiting from high parallel scalability.