Abstract
In this paper we present a model to predict the onset and evolution of segregation during the discharge of binary mixtures of granular materials. The model accounts for the multi-phase and multi-component nature of the granular mixtures, to simulate the main flow regimes occurring in the discharge of silos (funnel and mass flow) and how they affect segregation. The new comprehensive model for segregation follows a continuum Eulerian approach and results from the coupling between an ad-hoc rheology for granular flow and a percolation model for multi-component mixtures. Predictions are compared with independent literature experimental data, for short and tall silos and prove to be quite accurate, after a tuning of the percolation flux sub-model. The larger segregation in short flow paths with smaller amount of fines reported by the experiments is quantitatively predicted. The model also predicts the three phases observed in experiments during the discharge of tall silos.
Highlights
Several industries process granular materials routinely, including chemical, food and pharmaceutical to mention a few
The simulation of bi-dispersed granular flows, allowing for a free, moving surface was achieved by an Eulerian, continuum approach to the two phase flow
It could be observed that at the end of any funnel flow discharge, an increase of fines was observed at the outlet, more evident in the experimental data; this was not the case in the mass flow. It was an expected consequence of the first in-last out nature of funnel flow; the residual portion of fines accumulated at the wall left the hopper towards the end of the discharge
Summary
Several industries process granular materials routinely, including chemical, food and pharmaceutical to mention a few. The model is based on a simple percolation idea, in which the segregation velocity is explicitly dependent on gravity and Marks et al (2011) include a time dependent shear rate contribution These models predict a minimum distance from the feeding point beyond which a complete separation of small particles from large particles occurs. The experiments by Ketterhagen et al (2007) and Arteaga and Tüzün (1990) nicely prove that the funnel flow regime promotes segregation, at the discharge point, whereas mass flow regime keeps segregation bounded These experiments were used to critically evaluate our model predictions and to assess its reliability on different scales and geometries
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