Structured Bubbling Dynamics in Granular Media Induced by Oscillatory Gas Injection

Gas bubbling dynamics in fluidized beds significantly affect particle mixing with chaotic behaviors posing challenges for system scale-up and optimization. Structured bubbling, induced through oscillating gas flow, offers a solution by stabilizing bubble patterns; however, it often restricts horizontal mixing. Using two-fluid modeling (TFM) simulations, we replicate the structured bubbling behavior and explore how varying the gas injection offset phase at a 7Hz frequency in different distributor sections affects bubble lattice formation and particle mixing rates. A parametric study, varying the number of gas injection slices and their phase offsets, further reveals optimal configurations for maximizing horizontal mixing. We divided the injection surface into various parts, ranging from 2 to 10 slices, with constant phase differences between consecutive slices. As we increase the phase difference between slices from π/4 to π, we observe an increase in the number of bubbles in the bed and a consequent decrease in both the size of the bubbles and the vertical distances between them. For a constant phase of π/4, as the number of slices increases from 4 to 10 at the bottom, the structure pattern modifies, and the number of bubbles in the pattern increases, while the size of the bubbles decreases. The results also demonstrate improved mixing efficiency via oscillatory gas injection. Cases with fewer slices, like 2 and 4, showed better mixing, and the optimum phase offset for mixing, in the range of 0 to π, was found to be π/2.