Miscible displacements of a non-colloidal suspension in a tube

Understanding of the dynamics of particle suspensions in a confined geometry is relevant to many natural and industrial processes, including oil recovery, filtration, and hydrology. In this talk, we experimentally investigate the displacement of a neutrally buoyant, non-colloidal particle suspension by the same suspending fluid inside a cylindrical tube. Refractive index matching and fluorescence are applied to simultaneously visualize the shape of the invading fluid and particles on the central axial plane of the tube. This canonical flow configuration is expected to resemble the miscible displacement of pure liquids in the continuum limit. However, our preliminary experimental observations paint a rather different picture. Our experiments reveal that the shape of the invading oil changes dramatically for different volume fractions of the suspension, while the suspended particles do not mix with the invading oil. At high volume fractions, the invading fluid flows around the suspended particles, forming surprisingly complex interfacial structures. We will discuss our new experimental results and offer new physical insight in comparison to the pure liquid miscible displacement case.