The objective of this thesis is the investigation of the behaviour of solid particles suspended in a viscoelastic liquid and subjected to mixing in a stirred vessel. In particular, the well-known phenomenon of viscoelasticity-induced particle migration, was observed for the first time in the flow field generated in stirred vessel. This thesis is divided in three parts.

First, we performed an experimental campaign aimed at the study of the mixing of a non-Newtonian liquid-solid suspension in a cylindrical vessel equipped with a dual-blade impeller. The experiments were performed with liquids with different rheological behaviours. Particle image velocimetry (PIV) was used to measure the velocity filed of the liquid while particle tracking velocimetry (PTV) was employed to measure velocity and concentration fields of the solids. We show that in the presence of viscoelasticity, the particles accumulate at the centre of the vortices created by the impeller.

We then focused on the viscoelasticity-induced migration in the flow field created by a Rushton turbine in an unbaffled vessel. We propose a scaling law for predicting the migration time as a function of the Weissenberg number ($Wi$). The experimental campaign shows that the particles migrate in the radial direction driven by the presence of gradients of shear-rate. Finally, the scaling law is validated against experimental data obtained at different $Wi$.

The third part, describes the development of CFD tool, based on the volume of fluid (VOF) framework, for the simulation of particles in viscoelastic fluids. The objectives were, (i) to use the VOF model to simulate a solid sphere in flow, and (ii) to simulate the rotational velocity of a sphere in a viscoelastic fluid. Although, the model was capable of simulating a solid sphere with good accuracy in the Newtonian case, the viscoelastic case failed to reproduce the results available in the literature