On the Sedimentation of a Blob of Particles Suspended in a Viscous Fluid

Wilber Cerqueira¹; Rafael Gabler Gontijo¹; Sara Malvar Mauá¹; Francisco Ricardo Cunha¹

¹ UnB

doi:10.20906/CPS/COB-2015-0264

Resumo

This work explores the sedimentation process of an approximately initially spherical blob of dense particles immersed in a Newtonian fluid. We develop an experimental and numerical approach. For our experiments we designed a sedimentation column with super high viscosity silicon oil as the surrounding fluid. The particles are made of iron and sediment due to the action of gravity. The flow induced by the motion of the particles is in the Creeping flow regime, so we can reccur to fundamental laws of microhydrodynamics in order to compute numerically hydrodynamic interactions. We film the sedimentation process with a high definition camera and perform an image treatment analysis to count the main physical quantities of the problem. In this sense we account for the instant sedimentation velocity of the aggregate center of mass, the rate of particles escaping in the wake of the blob and the anisotropy ratio of the blob as a function of time. We also show some results obtained from numerical simulations developed by the authors with a non commercial academic research code called SIMS. For this purpose we use a sophisticated technique of Ewald sums in oder to account for particle hydrodynamic interactions in low Reynolds number flows. All the results obtained are interpreted from a physical perspective using scaling arguments and microstructural modifications to justify the alterations on the suspension transport properties. A good agreement is observed between our experiments, numerical simulations and scaling laws.

Palavras-chave: Sedimentation; Hydrodynamic interactions; Particle wake; Ewald summation; Particulate system