Figure 10. Box plots of local
segregation data in terms of percentage mass of the more massive species
for binary mixtures and broad PSDs. The fast fluidized bed had 324
datasets 14, while the turbulent fluidized bed had 190
datasets 21.
Figure 11 presents the random forest analyses of the relative influence
of the variables on segregation extents. While both axial and radial
segregation are well acknowledged for risers14,21,33-36, two interesting observations are made
with respect to the contrast between the fast and turbulent fluidized
beds. Firstly, while r/R was the most influential in the fast
fluidized bed, it was the least in the turbulent bed. This is because
the core-annulus profile is generally more significant in the fast
fluidized bed relative to that in the turbulent one, and the radial
profiles of chaotic parameters have been reported to be flatter for the
turbulent bed 11. Notably, this is in contrast to that
for local mass flux (Figure 7), in which r/R was the most
dominant influence for both regimes. More studies are needed to
understand why r/R has such significant effect on the local mass
flux but not segregation in the turbulent fluidization regime. Secondly,
while h/H had a negligible influence in the fast fluidized bed,
it was more significant in the turbulent bed. This is to be expected as
the particle concentration gradient is more significant than that of the
fast fluidized bed. Therefore, although Figure 10 shows the two
segregation datasets from the two fluidization regimes were
statistically similar, Figure 11 suggests that different mechanisms
govern the segregation behaviors.