Numerical Investigation of Particle Suspensions in a Liquid–Solid Stirred Tank with Baffles

Abstract

Stirred vessels have been widely used in the chemical and process industries, while particle suspensions in a liquid−solid stirred tank with baffles have little been studied. In this work, a particle suspension in a standard stirred tank driven by a Rushton turbine was simulated using large eddy simulation coupled with the Lagrangian particle tracking technique. The rotation speed was N = 313 rpm, and three particle sizes ranging from 200 to 2500 μm (St = 0.24−37.3) were considered. The simulation results including the flow field and particle concentration showed good agreement with the experimental data. Turbulent flows were found in the wake region formed by the impeller sweep, and double trailing vortices behind the impeller blades were visualized. Three particle suspension states were found as quasi-homogeneous, complete, and incomplete suspensions. Impeller rotation produced strong turbulence and vortex to promote particle dispersion and particle mixing, where the dual circulated flow drove the particles to suspend in the tank. Small particles (St = 0.24) and medium particles (St = 2.6) tended to have a large drag force that caused preferential concentration around the trailing vortex, while large particles (St = 37.3) were hardly driven by the circulated flow, so their concentration gradient varied from 0 to 2 orders of magnitude.

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“…10 Turbulence and vortices are important characteristics of fluid flow. Using the large eddy simulation method, Wang et al 11 discussed the flow state in a liquid−solid stirred tank with baffles. They found that the strong turbulence and vortex generated by the impeller rotation promoted the mixing of particles and the double trailing vortices appeared behind the impeller blades.…”