A CFD-DEM study of the behaviour of single-solid and binary mixtures in a pyramidal spouted bed
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We simulated a lab-scale cold-flow spouted bed through Computational Fluid Dynamics (CFD), coupled with the Discrete Element Method (DEM) for the solid phase, with the commercial CFD program ANSYS FLUENT 18.0. To limit the computational expense, we tested both a simplified pseudo-2D geometry and a complete 3D geometry. We found that the Haider and Levenspiel drag model is suitable for the pseudo-2D geometry, while it does not correctly predict the fluidisation in the 3D geometry. The Gidaspow drag model, instead, behaves accurately in the 3D geometry, but overestimates the motion of particles in the pseudo-2D geometry. We studied several single-solid and binary mixtures to assess the reproducibility of segregation phenomena. The pseudo-2D model was able to predict the onset and minimum spouting flow rates of all mixtures with good accuracy. An analysis of the volume fraction contours of binary mixtures permitted to confirm that segregation phenomena were correctly predicted at low gas velocity. Segregation was proved to be reduced with an increase of the inlet gas flow rate. Calculations performed in the complete 3D geometry were preliminarily assessed as more reliable but required almost four times the computational time needed with the pseudo 2D geometry.