(3do) Flow Behavior in Complex Fluids and Particulate Systems

Experimental and modeling of flow in particulate systems, e.g. colloidal dispersions, solid handling systems, composites and filled polymers, polymer solutions, and hydrogels.

During my Ph.D., I focused on the flow behavior of particulate systems and specifically on flow in colloidal dispersions, polymer melts and solutions, hydrogels, and solid handling systems.

During my first project, I investigated the mechanism controlling shear thickening in colloidal silica slurries. Shear thickening in colloidal dispersions often seriously limits formulations for coating and spraying operations, as well as flow rates for pumping concentrated dispersions. Besides, controlling shear thickening occurrence is critical in modern cement formulations, oil field extractions, and semiconductor polishing applications as well. The current study seeks ways to modify shear thickening in particulate systems and to investigate the underlying mechanisms controlling the shear thickening phenomena. Commercially available fumed silica suspensions exhibiting irreversible shear thickening at shear rates above 10,000 s-1 were used in this study as the base material. Using a specialized experimental protocol, the impact of spherical silica particles on shear thickening of fumed silica suspensions was investigated. It was shown that spherical particles can increase the critical shear rate when thickening occurs. In addition, rheo-Small-Angle-Light-Scattering (SALS) patterns also confirm the shift in shear thickening of fumed silica suspensions by applying spherical silica particles.

In my second project, I studied the flow of biomass and the problems associated with biomass handling and feeding from both experimental and modeling standpoints. The goals here is to develop physics-based computational methods which will be able to capture interactions between particles and their environment as imposed by the process. To experimentally validate the physics-based models, the impact of feedstock characteristics including particles size and size distribution, moisture content, and the screw feeder operating conditions such as screw speed on the flow characteristics of terrestrial biomass feedstock was investigated. Then, the experimental results were validated by Computational Fluid Dynamics (CFD) simulations using OpenFOAM software package for a simple pipe flow case. We found that at higher screw speeds and moisture contents, the material flows easier. In addition, the viscosity of biomass in the microcompounder falls within the shear thinning region of a Cross model fit. Moreover, the impact of particle size distribution on the flow behavior of compressed biomass is insignificant. For the modeling and simulation efforts, density-dependent Bingham and Cross models were developed and validated for biomass pipe flow under pressure. Rheological values obtained from pipe flow simulations showed that the models developed are able to capture the flow behavior of compressed biomass under pressure.