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Flow of Non-Brownian Suspension in Pipe
Suspensions are ubiquitous in nature and are encountered in many applications : cement and concrete technology, ceramic processing, coating and pigment technology, propellants and explosives, mineral processing, soil science, composite processing and various slurry flow technologies. The rheological properties of suspensions are highly dependent on the concentration. In the very dilute regime, the particles follow streamlines and have a limited impact on the flow properties. Only the viscosity is slightly increased. In the concentrated regime, these systems exhibit a jamming transition, at a volume fraction of the order or above 60%. In between, the flow is governed by the spatial organization of the particles. The difficulty in modeling the flow of suspensions arises from the coupling between the velocity field and the solid fraction profile. This problem is tricky since shocks or interactions between particles give rise to concentration heterogeneities and thus to rheological properties that are not understood at this stage. The particles migrate from low to high shear zones in non-homogeneous flows such as Couette flows or pressure driven tube flows. This migration comes from the hydrodynamics forces and interaction between particles that are badly characterized.
In this seminar, I will provide an experimental investigation on two different systems that are solid rigid particles and highly viscous droplets. Using microfluidic devices, confocal microscopy and fluorescence photobleaching, I will display the measurement of volume fraction profiles, but also of the relative velocity between the particles and the suspending liquid. The comparison between viscous droplets and rigid particles will enable us to get some insight on the amplitude of the contact or interaction forces as compared to purely hydrodynamic forces.