Discharge of rapeseeds from a model silo: Physical testing and discrete element method simulations

Laboratory tests and discrete element method simulations were conducted to evaluate regions of validity of two basic contact models to describe flow rate of rapeseeds through horizontal orifice. Rectangular container of 50 by 50mm cross section, 50mm high, having hopper of 30^o in inclination was used to hold seeds. Bedding of 10,000 seeds was generated in preparatory container and then discharged through square orifice of 12, 14 or 16mm side to similar lower container. This was equipped with independent floor supported on load cell to measure the weight of seeds during discharge of the upper container. Rapeseeds of moisture content of 5.5% and 15% were used for testing. DEM simulations were performed in geometrical setup similar to laboratory equipment using spherical particles with material parameters of rapeseeds. Two contact models were used in simulations that were previously found to adequately represent impact of dry and wet seeds against flat surface. In laboratory testing mass flow rates of dry rapeseeds (5.5% M.C.) through the orifices were higher than that of wet (15% M.C.) seeds. In the simulations no difference in mass flow rates of dry and wet seeds was found if the mass flow rates were calculated as a sum of masses of particles falling into the receiving container per time unit. However, difference in the mass flow rates was observed if they were calculated using sum of vertical forces exerted by particles on walls and floor of receiving container. Simulations revealed that proposed contact models reproduced well experimental results for slow particle flow but for higher flow rates the models need to be improved by inclusion of dissipative term.