بررسي تاثير شكل دانه بر ساختار بستر و خصوصيات جريان خروجي از سيلوها با استفاده از شبيه سازي عددي به روش المان هاي مجزا (DEM)

Effect of Particle Shape on Bed Structure and Flow Characteristics of Materials Discharged from a Hopper Using a DE Model

Particle discharge from a flat bottom hopper has been performed employing a Discrete Element Model with Multi-sphere particles. A flat bottom hopper of 100cm width has been prepared using 3dimensional particles in a vertical layer. Particulate assemblies comprising 5000 particles of equal volume but different aspect ratios ranging from I to 4 have been created using some non-overlapping spheres in order to investigate the effect of particle shape on bed structure and flow characteristics of particles. The particles all generated and deposited in an upper section with almost the same hight and flow started by removing the orifice. The results showed a distribution of solid fraction within each bed, with the closest distribution to the normal distribution for the beds of elongated particles. The localised densely packed areas have been separated by voids caused by bridging of particles in the beds. Simulation results on silo discharge showed that the behaviour of beds of spherical particles was quite different from that of non-spherical particles. Spherical particles moved individually during flow and rolled over each other, resulting in a lower resistance to shear with a fluid-like flow, whereas elongated particles exhibited a stronger shear due to interlocking between particles, resulting in a flow, like a breaking continuum. This unique behaviour of spherical particles caused a higher flow rate than non-spherical particles. The formation of arching has been also simulated by the DE model. A qualitative correlation between the frequency of arching and aspect ratio has been recognised. More arching occurred as the aspect ratio of particles increased. Due to this behaviour of non spherical particles their observed flow rate was less than that of spherical particles. It can therefore be concluded that the results obtained from the OEM models with spherical particles cannot be generalised to real material comprising non-spherical particles.