Numerical Simulation of Solids Suspension in a Stirred Tank

Large-eddy simulations of the turbulent flow dri®en by a Rushton turbine ha®e been coupled to a Lagrangian description of spherical, solid particles immersed in the flow. The working fluid was water, whereas the solid particles had the properties of glass ( y 23 ) beads. Simulations were restricted to a lab-scale tank ®olume 10 m , and relati®ely () low solids ®olume fractions up to 3.6% . Two sets of particles were considered with particle dia. of 0.30 mm and 0.47 mm, respecti®ely. It has been in®estigated to what le®el of detail the particle motion needs to be modeled in order to meet Zwietering’s just suspended criterion. It appeared to be essential to take particle-particle collisions into account, mainly because of their exclusion effect that pre®ents unrealistic buildup of particle concentrations closely abo®e the bottom. The simulations gi®e detailed insight in the beha®ior of the particles, and in the way that the liquid flow is altered by the presence of the particles. The frequency and intensity of particle-particle collisions, and particle-impeller collisions, ha®e been in®estigated. Furthermore, it will be demonstrated () that the rotational Reynolds numbers of the big 0.47 mm particles were of the same order of magnitude as their translational counterparts.

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