Spontaneous structures in three-dimensional bubbling gas-fluidized bed by parallel DEM–CFD coupling simulation

Flow structures induced by bubbles formed in three-dimensional shallow rectangular gas-fluidized beds are investigated by the DEM–CFD coupling simulation. A numerical code is parallelized and more than 4.5million particles are tracked in the maximum by using 16 CPUs. To investigate the domain-size dependency, the cross-sectional area of beds is enlarged by the factors up to 82 and the results are compared. Under the ideal uniform inflow condition, multiple bubbles are spontaneously formed in large cross-section cases. The dependency of bubble size on the cross-section size is not so clear under the same bed height condition. Clear circulation patterns are observed in the time-averaged data. Down-flows of particles exist in low void fraction portions selectively with particle up-flows dominating in the high void fraction regions. Three-dimensional visualization of bubble shape is also conducted. Bubbles that have complex structures such as worm-like one exist in addition to the conventional spherical cap.