Investigating the hydrodynamics of gas–solid bubbling fluidization using recurrence plot

Hydrodynamics of gas–solid fluidized bed was investigated using time series of pressure fluctuations by evaluation of the corresponding recurrence plot (RP). Patterns within RP of the fluidized bed were classified into two groups of local white areas (LWA), showing macro structures, and local bold areas (LBA), showing meso and micro structures. These patterns showed that the fluidized bed system has three different hydrodynamic behaviors as superficial gas velocity increases; at low gas velocities, macro structures become more dominant, further increase in gas velocity empowers influence of finer structures on the hydrodynamic and finally the fluidization regime changes. Additionally, these results were confirmed by recurrence rate (RR) and average cycle frequency. Comparison of RP of the fluidized bed with Lorenz and complete stochastic systems showed that the fluidized bed is more complex than Lorenz system, however, it’s hydrodynamic has not stochastic nature.