Recurrence plots to characterize gas-solid fluidization regimes

Recurrence plots have been used to analyze and characterize the investigated fluidization regimes: bubbling, slugging and turbulent. Recurrence plots can be qualitatively analyzed considering the distribution of their local white areas (LWA) and local bold areas (LBA). The LWA reflect the macro-scale structure in the bed and appreciably increase for slugging regime because of the increase of the bubble phase contribution to the fluidization dynamics. On the other hand, the LBA, reflecting meso-scale and micro-scale structures, decreases. Several recurrence quantification analysis parameters (RQA) have been computed for the different regimes analyzed and the most appropriate ones have been chosen to characterize and classify the fluidization regimes. It has been found out that the determinism (DET), the average diagonal length (L), the laminarity (LAM), the trapping time (TT) and the recurrence time of type 2 (RET2) detect the evolution from bubbling to slugging regime. The evolution from bubbling to turbulent regime can be detected with all the investigated RQA parameters. A combination of two RQA parameters gives an excellent classification map which distinguishes the slugging from the bubbling regime.