Sedimentation of Fractal Aggregates in Shear-Thinning Fluids

Abstract

Solid–liquid separation is a key unit operation in the wastewater treatment, generally consisting of coagulation and flocculation steps to promote aggregation and increase the particle size, followed by sedimentation, where the particles settle due to the effect of gravity. The sedimentation efficiency is related to the hydrodynamic behavior of the suspended particles that, in turn, depends on the aggregate morphology. In addition, the non-Newtonian rheology of sludges strongly affects the drag coefficient of the suspended particles, leading to deviations from the known settling behavior in Newtonian fluids. In this work, we use direct numerical simulations to study the hydrodynamic drag of fractal-shaped particles suspended in a shear-thinning fluid modeled by the power-law constitutive equation. The fluid dynamics governing equations are solved for an applied force with different orientations uniformly distributed over the unit sphere. The resulting particle velocities are interpolated to compute the aggregate dynamics and the drag correction coefficient. A remarkable effect of the detailed microstructure of the aggregate on the sedimentation process is observed. The orientational dynamics shows a rich behavior characterized by steady-state, bistable, and periodic regimes. In qualitative agreement with spherical particles, shear-thinning increases the drag correction coefficient. Elongated aggregates sediment more slowly than sphere-like particles, with a lower terminal velocity as the aspect ratio increases.

Evaluating the influence of particle morphology and density on the viscosity and injectability of a novel long-acting local anesthetic suspension

“…It has been shown that for suspension systems, an increase in suspension zeroshear viscosity lengthens suspension sedimentation time. [32][33][34] Additionally, there is evidence that an increase in viscosity of the suspension allows for slower degradation in vivo, allowing the formulation to stay at the administration site for longer than traditional local anesthetic solutions. [16][17][18][19] The rheological properties of the suspension were analyzed to characterize how particle density and HA hydrogel concentration play a role in the material behavior and viscosity.…”

Sustainable Environmental Solutions

“…The efficiency improvement of simple and economical processes such as solid-liquid separation (a key operation in wastewater treatment) can be promoted through the optimization of the hydrodynamic behavior of suspended particles and the rheology of sludge [2].…”

Experimental Study and Analytical model of Shear Thinning in 3D Bioprinting of Gelatin

“…Assuming negligible fluid and particle inertia, the fluid dynamics of the investigated system is governed by the following mass and momentum balance equations [10,[14][15][16], as given in equations 7-10, where u -velocity; τ -shear stress tensor; p -pressure; I -unit tensor (3x3); η -viscosity; σ -strain rate tensor, and T means that velocity vector is transposed.…”