This thesis provides an original contribution to knowledge of fluid mixing in agitated vessels. This flow application has a critical importance in the manufacture of a wide range of intermediates and products in Johnson Matthey. The novelty of the research undertaken is twofold. Firstly, it presents quantitative investigations of the agitation of Newtonian and non-Newtonian fluids under transitional flow conditions. Despite the fact that transitional mixing is very common in industry, particularly for formulated products showing non-Newtonian rheology, most studies in the literature focus on fully laminar or fully turbulent mixing. Secondly, with the development of a methodology for 3D Particle Tracking Velocimetry measurements in laboratory scale vessels, this thesis has taken a step towards more accessible flow visualisation capabilities in industry. Numerical simulations have also been carried out to cross-validate the 3D-PTV data and provide additional information that could not be obtained
experimentally.
Experiments and simulations have been conducted for many combinations of fluid rheology and impeller speed and at two vessel sizes. The hydrodynamics of transitional flows have been shown to depend significantly on the Reynolds number and fluid rheological behaviour. Non-Newtonian fluids showed smaller values of shear rate, Lagrangian acceleration and flow numbers, compared to the Newtonian ones. For
Newtonian fluids, the local energy dissipation rate scaled differently depending on the position relative to the impeller. Non-Newtonian fluids did not follow the same scaling.
The information obtained in this thesis will help the design, optimisation and scale-up of mixing operations within Johnson Matthey.