The hydrodynamics of gas and liquid flow through a granular bed were
proposed in this work. A high-speed camera was used to capture bubbles
at different heights in a granular bed. The effect of bubble size on the
rising velocity and stagnation of single bubble and multiple bubbles was
investigated. The results showed that a single bubble rose along a
non-uniform trajectory. The average rising velocity increased
nonlinearly with the increase of the initial bubble diameter. This work
also provides a visual verification that multiple bubbles stagnation
occurs. The results show that the rising velocity and bubble size were
the two key factors, which dominate the stagnation probability. The
rising velocity of multiple bubbles is expressed by the overall
velocity, and the bubble size is expressed by the projected area, which
is found the bubble projection area and the overall velocity of the
bubbles were negatively correlated with the stagnation.