Figure 2. Box plots of local
cluster characteristics. The left column corresponds to 1188 datasets
from a fast fluidized bed 16,17, while the right
column corresponds to 378 datasets from a turbulent fluidized bed20.
To understand the relative influence of the various variables, Figure 3
displays the random forest analysis results. The variables include
particle properties (namely, dave andρp ), riser position (namely, radial position
normalized with respect to the riser radius (r/R ), and axial
position normalized with respect to the riser height (h/H )) and
operating condition (namely, Ug andGs ). Regarding cluster probability, the
similarity between the fast and turbulent fluidized beds lies inh/H being the most dominant and Ug being
least dominant in both fluidization regimes. For the cluster duration
and frequency, the relative influences were different for the two
fluidized beds. For the fast fluidized bed, four of the six variables
(namely, dave , ρp ,r/R, and Gs ) were approximately similar in
influencing cluster duration, while dave was the
most influential on cluster frequency. The lack of a more distinctively
dominant variable among the six evaluated here is because the single
most influential factor has been reported earlier to be whether the
particle system was monodisperse or not (Figure 4) 26.
As for cluster duration and frequency in the turbulent fluidized bed,h/H was by far the most dominant, which is tied to the steep
particle concentration drop with height typical of this regime2, while r/R was the least important, which is
consistent with the relatively flat radial profiles of chaotic
parameters reported earlier 11. The different
variables governing the cluster duration and frequency suggest that the
underlying mechanisms leading to cluster formation were different in the
different regimes.