Experimental Assessment and CFD Simulations of Local Solid Concentration Profiles in a Pilot-Scale Stirred Tank

An experimental assessment of solid particle distribution in a stirred vessel was performed by conductivity measurements, and for the same solid-liquid system, the capabilities of the Computational Fluid Dynamics (CFD) simulation were investigated. A detailed particle distribution measurement of a solid-liquid suspension at the just-suspended state was carried out in a pilot-plant stirred vessel of one meter in diameter. This baffled stirred tank was agitated with a pitched blade turbine, which generates an axial-flow pattern in the tank. The water suspension of glass beads of diameter 0.35 mm was studied. Average particle concentration was 5 vol. %. In this mode of experimental arrangement, a particle-filled layer of suspension was observed. Axial and radial particle concentration gradients and their standard deviations were determined. CFD simulations were performed using a two-phase model implemented in the commercial code Fluent 6.2. The Eulerian-Eulerian multiphase model was adopted in conjunction with the Multiple Reference Frames and the “mixture” k-e turbulence model. Computational results are compared with the experimental data and critically discussed. The simulation results are in agreement with experiment, but the drag coefficient for particles settling in a stagnant fluid needs to be corrected in order to obtain acceptable results for a turbulent flow regime.