Visualization on the meso-scale particle flow in turbulent fluidized bed reactors with lower H₀/D ratios via image processing

A two-step Otsu's method was applied to process the images of gas-solids flow field at multiple axial levels in a TFB with a H₀/D ratio from 0.5 to 2.0. The flow field was segmented to a discrete particle phase, a dense particle phase, and a cluster core and a cluster cloud phases. The solids holdup, volume and mass fractions, and the velocity vector field of each phase were analyzed by postprocessing. The frequency, size, shape, and velocity of the cluster cores were also extracted. The increasing H₀/D ratio results in an increase in solids holdup in each phase and a decrease in the mass and volume fraction of cluster clouds. A strong disturbance in the local flow field was resulted from the formation and movement of cluster cores and a more dynamic velocity change was found inside cluster clouds. The clusters were found to travel downwardly and with equal chances to move towards the center and the wall of the TFB at a low H₀/D ratio with a high U_g.