The evolution of the volume of a fluidized bed solid-gas over time is measured by the oscillation of its surface. It is assumed that the system is governed by the pressure gradient between the plenum and the surface; the latter is considered as the reference. The surface oscillation is measured with a laterally located CCD video camera such that it monitors the flattest portion of the surface and records its coordinates. Simultaneously obtain all the phenomena that regulate the hydrodynamics of the bed, the entering bubbles, coalesce, split, increase their volume adiabatically, and explode on the surface. The gas flow and the weight of fluidized material are studied. The time series of the surface oscillation is analysed in the frequency domain and the phase space. The frequencies obtained are approximately between 0.6 Hz and 1.8 Hz. The entropy values behaves linearly proportional to the total number of bubbles. (C) 2019 Elsevier B.V. All rights reserved.