Particle migration of suspensions in a pressure-driven flow over and through a porous structure

Laboratory experiments were conducted to study particle migration and flow properties of non-Brownian, noncolloidal suspensions ranging from 10% to 40% particle volume fraction in a pressure-driven flow over and through a porous structure at a low Reynolds number. Particle concentration maps, velocity maps, and corresponding profiles were acquired using a magnetic resonance imaging technique. The model porous medium consists of square arrays of circular rods oriented across the flow in a rectangular microchannel. It was observed that the square arrays of the circular rods modify the velocity profiles and result in heterogeneous concentration fields for various suspensions. As the bulk particle volume fraction of the suspension increases, particles tend to concentrate in the free channel relative to the porous medium while the centerline velocity profile along the lateral direction becomes increasingly blunted. Within the porous structure, concentrated suspensions exhibit smaller periodic axial velocity variations due to the geometry compared to semidilute suspensions (bulk volume fraction ranges from 10% to 20%) and show periodic concentration variations, where the average particle concentration is slightly greater between the rods than on top of the rods. For concentrated systems, high particle concentration pathways aligned with the flow direction are observed in regions that correspond to gaps between rods within the porous medium.