Inertial particle dynamics in the presence of a secondary flow

The manipulation of particles using inertial lift forces has broad implications in the separation, concentration and sorting of particles. In this work, we show that in the presence of a secondary flow, equilibrium locations of particles subject to inertial lift can be spatially varying. Using a well-defined microfabricated straight microfluidic channel with perpendicular permeate channels, we perform experiments over a range of particle sizes and inlet and outlet flow rates to highlight different focusing regimes. We show that a permeate flow can control the equilibrium location of particles and can be used to interrogate the balance between inertial and permeate forces.