Predicting particle migration in helical microchannels via a lift-drag model incorporating secondary flow torsion effects

Helical microchannels induce stable secondary flow for high-precision particle manipulation. However, current studies neglect the effect of flow torsion on particle migration, resulting in an unclear understanding of the particle evolution in helical microchannels. This study develops a helical channel-based microfluidic platform and establishes a lift-drag particle migration model in the helical orthogonal coordinate system to clarify the particle migration mechanism under torsion effect. This model combines inertial lift from direct numerical simulation results with secondary flow drag based on the velocity field and simplifies the particle force in the helical channel to a two-dimensional rotating coupled force field. Using the lift-drag model and microfluidic particle-tracking experiments, we identified attractors (points and limit cycles), particle migration patterns, and bifurcation behaviors under various torsion levels, blockage ratios, and Reynolds numbers. This work reveals the migration mechanism of particles in helical microchannels and provides design guidance for predicting particle manipulation in inertial microfluidic devices.