  In this work, we assess the internal dynamics of particles in liquid-solid
fluidized beds using an unresolved CFD-DEM model. We use the Nearest Neighbors
Method (NNM) and the mixing index based on the principal component analysis
proposed by Doucet et al. [1] to quantify the bed mixing for several flow
regimes and particle properties. Discussions on the advantages and drawbacks of
each method are provided. Using results for several inlet flow rates, we show
that the dimensionless mixing time reaches a plateau and does not increase
significantly with the inlet velocity. The principal component analysis shows
that the studied fluidized bed has no preferential mixing component.
Additionally, we show that, except for the sliding friction coefficient, the
collision properties have almost negligible influence on the mixing behavior.
