Chapter 5 - Characterisation and modelling of a two impinging jet mixer for precipitation processes using laser induced fluorescence

Abstract

This chapter focuses on a two impinging jet mixer that is used for precipitation processes highlighting its components and process mechanism by the means of the laser induced fluorescent technique. Neutralization reactions with a fluorescent pH-indicator are used to reveal the mixing process up to the molecular level. On the basis of the experimental results, a phenomenological mixing model is derived. The mixing model involves a macrodilution process and a coalescence-redispersion process through which the fluids are contacted at the molecular level. The mixing model is applied to the precipitation of barium sulfate, and it is found that its predictions are very close to experimental results. The mathematical description of the mixing process relies on the coalescence-redispersion model, which predicts very realistic distributions of concentration. The mixing model is easy to perform. Besides, it provides a global dynamical description of the process, from which the influence of the operating parameters becomes transparent. This phenomenological approach is an alternative to computational fluid dynamics (CFD) simulation, as, due to instabilities of the flow, this latter approach can provide less accurate results. The mixing model can be advantageously used to investigate the capabilities of the TIJ mixer when applied to precipitation processes, and it can serves as a basis for the design.