Effects of gas velocity on nonequilibrium characteristics of fluidization

The gas velocity is a key factor of the macroscale operating conditions, affecting the nonequilibrium behavior and regime transitions of fluidization, but the mechanism of its effects remains unclear, resulting in a deterioration of the accuracy of the two-fluid model (TFM) simulation with the increase of the gas velocity. To seek its underlying mechanism, we performed time-resolved, particle-tracking velocimetry (PTV) measurements of a fluidized bed operated under bubbling to turbulent states, thereon the analysis of the probability density distribution of particle velocity, and hydrodynamic parameters. It is found that a stronger nonequilibrium exists with the increase of the gas velocity, in the sense that the bimodal distribution of particle velocity is more significant at turbulent fluidization. The total fluctuating energy and stress show a scale separation, suggesting that a reasonable continuum modeling should take into account the whole range of fluctuation.