CFD simulation of precipitation in the sliding-surface mixing device

Abstract

Steady-state precipitation of pseudo-boehmite is studied in the sliding-surface mixing device, both experimentally and using a commercially available CFD package (FLUENT ® 4.5). A 3-D description of the reactor geometry is employed. Solutions of the Navier–Stokes equations along with the standard two-equation k– ε turbulence model provide both the velocity and energy dissipation fields, while generation and development of the solid crystal phase are described by the moment equations of the population balance. These equations and the precipitation kinetics have been implemented directly in the CFD code using Fortran User-Defined Subroutines. A size-dependent growth rate model is used to describe the crystal growth of pseudo-boehmite crystallites. Local quantities are calculated, such as species concentrations, supersaturation and mean particle size. A good agreement is obtained between experimental and predicted crystal properties. The influence of feed point location, rotating speed of the spinning disk and reagent concentrations on the quality of the precipitate is also investigated.