Weheliye, WH; Meridiano, G; Mazzei, L; Angeli, P; (2020) Experimental investigation of the solid-liquid separation in a stirred tank owing to viscoelasticity. Physical Review Fluids , 5 (6) , Article 063302. 10.1103/physrevfluids.5.063302.

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Abstract

In this study, we investigated the motion of solid particles dispersed in highly viscous complex fluids agitated in a stirred vessel. We used a refractive index matching method and a combination of planar laser- induced fluorescence (PLIF), particle image velocimetry (PIV), and particle-tracking velocimetry (PTV) techniques to measure the velocity fields of the solid and fluid phases simultaneously along with the spatiotemporal distribution of the solids in the tank. The experimental data show that in a Newtonian ambient fluid, particles disperse uniformly in the plane of measurement, while in a strongly shear-thinning viscoelastic ambient fluid they tend to accumulate in the core of the vortices formed in the flow domain. We found that the solids migrate to the core of the vortices also when the ambient fluid is a Boger fluid, i.e., viscoelastic but not shear thinning. The effect of the first normal stress difference, N1, on the vortex sizes and circulation intensities was also examined, with both properties decreasing for increasing N1. Finally, we observed that the clustering time of the solids in the vessel for viscoelasticity-induced migration was at least three orders of magnitude lower than that obtained from the literature for inertia-induced migration.

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