Prediction of segregation in funnel and mass flow discharge

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

Collapse of quasi-two-dimensional wet granular columns

This paper deals with the experimental characterization of the collapse of wet granular columns in the pendular state, with the purpose of collecting data on triggering and jamming phenomena in wet granular media. The final deposit shape and the runout dynamics were studied for samples of glass beads, varying particle diameter, liquid surface tension, and liquid amount. We show how the runout distance decreases with increasing water amount (reaching a plateau for $w>1 \%$) and increases with increasing Bond number, while the top and toe angles and the final deposit height increase with increasing water amount and decrease with decreasing Bond number. Dimensional analysis allowed to discuss possible scalings for the runout length and the top and toe angles: a satisfying scaling was found, based on the combination of Bond number and liquid amount.Comment: 8 pages, 14 figure

Texture analysis as a tool to study the kinetics of wet agglomeration processes

In this work wet granulation experiments were carried out in a planetary mixer with the aim to develop a novel analytical tool based on surface texture analysis. The evolution of a simple formulation (300 g of microcrystalline cellulose with a solid binders pre-dispersed in water) was monitored from the very beginning up to the end point and information on the kinetics of granulation as well as on the effect of liquid binder amount were collected. Agreement between texture analysis and granules particle size distribution obtained by sieving analysis was always found. The method proved to be robust enough to easily monitor the process and its use for more refined analyses on the different rate processes occurring during granulation is also suggested

Influence of process variables on the properties of simvastatin self-emulsifying granules obtained through high shear wet granulation

Improvements of the oral bioavailability of lipophilic drugs can be obtained using lipidic formulations such as the self-emulsifying drug delivery systems. The high shear wet granulation (HSWG), using microemulsions as binder, is a viable process to produce self-emulsifying granules. However only few information are present in the literature on the effect of process variables on the properties of the granules obtained with these binders. Consequently, this article compares the effects of some relevant experimental variables (impeller speed and massing time) on thefinal technological and pharmaceutical properties of the granules produced using simple water, or alternatively, a microemulsion as binder and containing simvastatin (SV) as model drug. The effects of the variables were determined by evaluating the granule median diameter, their particle size distribution, roundness, disintegration time and dissolution rate of SV. Results clearly demonstrated that the microemulsion-based process was less sensitive tooperating conditions than the water-based process. With microemulsion the nucleation process and growth regimes were more difficult to control, resulting in products with broader PSDs. At the same operatingconditions microemulsion-based granules were more brittle but rounder and showed smaller median diameter compared to water-based granules. The dissolution rate of simvastatin was not significantly affected by the operating conditions

Collapse of wet granular columns: experiments and discrete element simulations

This work aims at investigating the effect of triggering and jamming due to the addition of a small quantity of fluid to the material. Collapse of dry and wet granular columns is studied both from the experimental and the numerical point of view. Wet samples of glass beads of different grain-sizes in the pendular state were packed in a rectangular box and then allowed to flow by removing a lateral wall. The dependence of the kinematics and the final state of the system on grain size and water content was particularly investigated. DEM numerical simulations were carried out in a 1:1 scale. A good qualitative agreement between experiments and DEM simulations was found with respect to the kinematic and the final slope profile. In particular, both the techniques highlight the strong effect of the liquid which decreases the run-out distance and time even for small liquid contents. This work demonstrates the suitability of the DEM approach also for the study of wet granular materials in static as well as in dynamic conditions, however it highlights that the water redistribution model is critical for the model outcome

Effective boundary conditions for dense granular flows

We derive an effective boundary condition for granular flow taking into account the effect of the heterogeneity of the force network on sliding friction dynamics. This yields an intermediate boundary condition which lies in the limit between no-slip and Coulomb friction; two simple functions relating wall stress, velocity, and velocity variance are found from numerical simulations. Moreover, we show that this effective boundary condition corresponds to Navier slip condition when GDR MiDi's model is assumed to be valid, and that the slip length depends on the length scale that characterises the system, \emph{viz} the particle diameter.Comment: 4 pages, 5 figure

formulation design and experiment interpretation through torque measurements in high shear wet granulation

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