Colloquia

Samenvatting

Segregation during mixing is a common issue when processing granular materials. This applies to a myriad of different industries like pharmaceutical, agriculture and construction. It can cause faults in the distribution of chemical components for medicine or soil enrichment, or cause uneven distribution of granular material in concrete thereby affecting the strength of the material.

While evenly mixed bi-dispersed mixtures are relatively well understood, both in simulation and theory, the same does not apply for more complex mixtures. Diluted bi-dispersed mixtures, with a small number of particles deviating in size from the vast majority, are poorly understood in comparison. Neither theory or simulation allow for accurate prediction of behavior during mixing. Even less is known about multi-dispersed systems, where the presence of more than two particle sizes adds further complexity.

In previous research a theoretical and numerical model was proposed focusing on a single intruder particle, to research the forces causing segregation. These forces are understood as a combination of a buoyancy force, resulting from packing effects and a lift force, induced by the velocity field of the surrounding bulk particles. While both theory and simulation for this model have shown consistent result, it awaits experimental validation.

In this study, a novel experimental setup was developed to directly observe the dynamics of a single intruder particle in a bulk of smaller particles. The setup consists of a transparent drum with a horizontal axis of rotation and transparent hydro-gel particles, whose refractive index is matched to that of the surrounding fluid. This enables visual tracking of the intruder particle throughout the entire bulk volume with a camera. This eliminates the need for hazardous and complex methods, used in previous research, like lasers, X-rays, or radioactive particles. The setup provides a means to gather reliable experimental data to validate theoretical models. Moreover it offers a simple and repeatable method for future research into more complex segregation behavior. The hydro-gel particles used can be customized in size, making the system adaptable for studying a wide range of particle size distributions.