Gaetano D'Avino  

Computational Rheology of Solid Suspensions

Tesi di Dottorato in Ingegneria Chimica (XX Ciclo)

Recently, an increasing interest in materials filled with solid particles is observed. Addition of rigid particles to a liquid alters the flow field and hydrodynamic effects lead to strong variations in the rheological properties. In several applications, the suspending fluid shows a non-Newtonian behaviour, further complicating the overall rheological response of such materials. Aim of the present thesis is to analyze the rheology and the dynamic of a suspension of solid particles dispersed in a viscoelastic medium through numerical simulations. In the first part, the rotation of a single sphere in a sheared viscoelastic medium and the resulting rheology are studied. The results show a slowing down effect of the particle rotation rate related to the fluid viscoelasticity. In the second part, solid concentrated suspensions in planar elongational flows are investigated. A new efficient method to take into account the boundary conditions is devised. For a viscoelastic suspending fluid, the bulk elongational viscosity is found to be an increasing function of solid area fraction and fluid viscoelasticity. Nevertheless, a less and less pronounced strain hardening is found as the solid concentration increases. The simulations successfully predict the experimental observations reported in literature.