Mixing non-Newtonian Fluids in the Transitional Regime

EPSRC supported EngD Mixing non-Newtonian Fluids in the Transitional Regime

Tax free bursary of £19,500 p.a. plus fees paid

Johnson Matthey: Dr Li Liu, Prof Hugh Stitt
University of Birmingham: Dr Federico Alberini, Prof Mark Simmons

Fluid mixing in stirred vessels is widely encountered in the formulation of catalytic and battery materials. An important example is washcoats for the manufacture of vehicle emission catalysts. Commonly, the fluids are dense suspensions and thus are non-Newtonian, typically shear thinning. Fluid mixing in stirred vessels has been classified into three groups: laminar regime (Re < 100), transitional regime (100 < Re 10,000). Mixing of non-Newtonian fluids in practice is generally under the transitional regime where the viscous and inertial effects are both significant. Due to the complexity of the transition between the viscous and inertial flow, there is very little basic understanding of mixing in the transitional regime; particularly for non-Newtonian fluid mixing. Therefore, achieving a good scale up of mixing for these systems is challenging. So far, there are no satisfactory general rules for the design and scale-up for non-Newtonian fluid mixing in the transient regime. Although the traditional scale-up strategy of maintaining constant power per volume has been used widely for the scale-up of fluid mixing in the turbulence regime, it is not proven to be sufficient for the scale-up of fluid mixing in the transitional regime. A new scale-up strategy is thus desired. A key parameter in the mixing and scaling of dense solid liquid suspensions and structured liquids is the shear rate; maximum and average values. While the impact of shear rate on the formulated fluid can be measured at the laboratory scale, it is not currently possible to predict these values at pilot and manufacturing scales.

The objective of this project is thus to build an alternative method for mixing design and develop a new strategy for the scale-up of fluid mixing in the transitional regime. Different techniques including both experimental and numerical approaches will be applied in this project. Flow visualisation techniques such as Particle Imaging Velocimetry (PIV), 3D-PTV (Particle Tracking Velocimetry) and the like, will be used to provide information pertaining to both the macro- and micro-scale. Computational Fluid Dynamics (CFD) modelling, will also be used as it gives access to information not easily measurable experimentally. Comparison of experimental and modelled results will be a key element of this project. These will work towards providing an improved understanding of the distributions of shear rates and energy dissipation in non-Newtonian fluids in the transitional regime that will be used to provide a new basis for design and scale up. Experiments at different scales using commercially relevant formulations will be used to assess the effectiveness of the new approach.