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    Determination of the angle of repose and coefficient of rolling friction for wood pellets
    (2022-02-08) Madrid, Marcos A.; Fuentes., José María; Ayuga, Francisco; Gallego Vazquez, Eutiquio
    The determination of the angle of repose for granular materials is indispensable for their handling and the design of containers and technological processing equipment. On the other hand, computational simulations have become an essential tool to understand the micro-behavior of the granular material and to relate it with the macro-behavior. The experimental determination of the angle of repose has a fundamental role when defining the required parameters to perform realistic simulations. However, there is a lack of a standard that allows the reproducibility of the experiments when using granular materials of equivalent spherical radius greater than 2 mm, such as corn, soybeans, wheat and PLA pellets, among others. In particular, a product of growing importance in the global strategy of decarbonization of the economy is biomass pellets, whose handling operations are one of the main components for the total cost of pellets supplied to the final user. In the present work, with the aim of determining the rolling friction coefficient, the variations in the angle of repose with the drop height for biomass pellets were studied both experimentally and with simulations, and an optimal procedure for its determination was found. Then, a calibration of the coefficient of rolling friction was performed through computational simulations using the discrete element method. The accuracy of the model under different configurations was checked.
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    Effect of bevelled silo outlet in the flow rate during discharge
    (2023-07-29) Gago, Paula; Madrid, Marcos A.; Boettcher, Stefan; Blumenfeld, Raphael; King, Peter
    We investigate the effect of a bevelled (or slanted) outlet on the discharge rate of mono-sized spheres from a quasi-two-dimensional silo, using the discrete element method. In contrast to hopper discharges, where the bevelling is across the entire base of the container, we study a bevelled opening that is significantly smaller than the silo width and in which the slanting is limited to half a sphere diameter at the boundary of the outlet. We show that the bevelling increases the flow rate comparably to the inclination in hopper walls. Using Beverloo’s model, we relate this increase in rate to what we define as the ‘effective opening’ of the silo and analyse the velocity profiles associated with the discharges. We show that different openings, having effectively the same discharge rates, give rise to distinctly different internal dynamics in the silo. These results have the potential to aid industrial processes by fine-tuning and improving control of silo discharges, with a minimal impact on silo design, thus significantly reducing production and handling costs.