Turbulent precipitation in micromixers: CFD simulation and flow field validation

The object of this work is the investigation of the process of nanoparticles turbulent precipitation in a micromixer, the Confined Impinging Jets Mixer. This study is motivated by the increasing importance that nanoparticulate systems have for applications in several fields and by the consequent necessity of developing an economical and reliable process for the production of nanoparticles with the desired qualities, in terms of size, morphology and composition. The precipitation process is among the most promising processes for this purpose, and micromixers, such as the CIJM, are employed because they provide high mixing rates and efficiencies, which are needed because the process is highly mixing sensitive. Here a precipitation model based on classical precipitation theory and Computational Fluid Dynamics was developed and tested on barium sulphate precipitation, which is often employed as a mixing sensitive test reaction alternative to parallel competitive reactions. The use of barium sulphate precipitation also allows to assess the capability of the CIJM of producing very fine particulate systems. The flow field is modelled with a RANS approach, and validated through comparison with experimental data, obtained with the microscopic Particle Image Velocimetry. Model predictions on barium sulphate mean particles size were compared with experimental data and good agreement was found.