  Laboratory experiments were conducted to study particle migration and flow
properties of non- Brownian, non-colloidal suspensions ranging from 10% to 40%
particle volume fraction in a pressure-driven flow over and through a porous
structure at low Reynolds number. Particle concentration maps, velocity maps
and corresponding profiles were acquired using a magnetic resonance imaging
(MRI) 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 semi-dilute
suspensions (bulk volume fraction ranges from 10% to 20%) and show periodic
concentration variations, where 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.
