Experimental study on the discharge characteristics with downward moving bubbles in a two-dimensional aerated hopper

The characteristics of bubble behaviors during powder discharge process in a two-dimensional aerated hopper were studied by a high-speed camera system. The experimental results show that there are three typical discharge states with the rise of the aeration gas velocity. Correspondingly, three critical aeration gas velocities were all tested including the minimum bubbling, the maximum discharge rate and the minimum bubbling for downward moving to the outlet. The downward moving bubble formation frequency increases with the growth of gas velocity, and its proportion finally stabilizes at about 90%. This tendency is similar with that of the discharge rate. Resultantly, the bubble formed in the powder bed can promote the discharge by provide the interstitial gas to the powder bed, but plays a negative role as it gets larger and substantially moves downward. (C) 2020 Elsevier Ltd. All rights reserved.