Transient inertial flows: A new degree of freedom for particle focusing in microfluidic channels

This paper reports a new inertial particle focusing approach using a rapidly changing flow rate in microfluidic channels. The transient flow rate effects manipulates the relative velocity between the particles and the main flow, therefore changes the balance between the (inertial) hydrodynamic forces acting on the particle. A comparative analysis was conducted with a theoretical basis in inertial flow phenomena for both constant and transient flow rates in straight rectangular channels. Results found using an apparent size correlation (ASC) three-dimensional particle tracking method indicate that particles focus in different equilibrium positions depending on whether a constant or changing flow rate is applied.