  The fluid dynamics video show a gas stream which is injected into a packed
bed immersed in water and fluid dynamcis video present the dynamics involved.
The refractive index of the water an the packed bed are quite similar and the
edges of the spherical particles can be seen. Two distinctive regimens can be
observed. The first one, for low air flow rates, which is characterized by the
percolation of the air thought the interstitial space among particles. And the
second one, for high air flow rates, which is characterized by the accumulation
of air inside the packed bed without percolation, it can be observed that the
bubble pull apart the particles apart. Furthermore, for the first case the
position of the particles remains constant while for the second one a
circulation of particles is induced by the bubbles flow.
