A PDF MODELLING OF PRECIPITATION REACTORS

摘要

Efforts to model precipitation processes in chemical reactors need to combine fluid mechanics with precipitation processes description. The main difficulty is to consider together micromixing phenomena, which is known to play an important role, with complex reactions kinetics and particles size distribution in the flow. In the present study, a Probability Density Function (PDF) method is presented to calculate the evolution of the particles size distribution. The main advantage of the method is to include a micromixing model based on a lagrangian frame where chemical reactions are treated without modelling and which requires minimal computational resources. The considered micromixing model is the Interaction and Exchange with the Mean (IEM). Because of the nature of the used powerful numerical technique, based on Monte-Carlo simulations, the method is able to produce, at any point in the flow, reactants concentration and supersaturation fields, and the fields of moments of the particles size distribution. The main advantage of the method over traditional population balance solvers is its capability to treat multidimensional (e.g. size, crystal morphology, chemical properties, etc.) population balances just as efficiently as it treats high-dimensional PDF. The PDF code is coupled with the commercial CFD package FLUENT which is used for the turbulent calculation of the flow (classical k-e turbulence model), where the presence of the solid phase is assumed not to affect the flow field. Examples are presented in the case of silica aggregation.