Inertial focusing in two dimensional flows with sharp viscosity stratification in a microchannel

Recent experimental studies have shown that lateral particle migration can be controlled passively using stratified flows of co-flowing streams. In this study, we numerically analyze particle migration in a stratified Poiseuille flow of two liquids of different viscosities. A novel numerical approach using immersed boundary method is employed to perform 2D simulations in moving frame of reference. The effect of viscosity ratio, flowrate ratio, Reynolds number and particle size on focusing position is analyzed to identify conditions under which particle migration occurs from one fluid to the other. It is shown that the particle migrates to the low viscous fluid beyond a critical flowrate ratio which increases with particle size. The results of the present study can be used to select suitable flowrate ratio to enable separation of particles of different sizes in membrane less separators.