Conclusion
To enhance the understanding of the difference between the fast and turbulent fluidization regimes, the cluster, mass flux, and segregation datasets of Geldart Group B particles were comparatively analyzed. While the fluidized beds were of different sizes, the measurement instruments used were the same, specifically, fiber optic probes for clusters, extraction probes for local mass flux and sieve for segregation. The particle systems investigated in both regimes included narrow PSDs, binary mixtures, and broad PSDs.
Regarding clusters, all three characteristics (namely, probability, duration, and frequency) were statistically different between the two regimes. Relative to the fast fluidized bed, the turbulent bed gave higher cluster probability and frequency due to higher bed density, and lower duration due to more chaotic hydrodynamics. For cluster probability, the relative dominance of the variables was similar for both fast and turbulent fluidized beds, with h/H being most dominant and Ug least. The mechanisms underlying cluster formation appeared to be different in the two regimes, because (i) the relative influences on cluster duration and frequency were different for the two fluidized beds; and (ii) although the monodisperse (i.e., narrow PSD) systems gave distinctly larger clusters than the non-monodisperse (i.e., binary mixtures and broad PSDs) ones in the fast fluidized bed, the different dispersity of the particle systems gave similar cluster durations in the turbulent bed.
Regarding local mass flux, the data from the fast and turbulent fluidized beds were statistically different, with the latter giving a lower median. Although the median values were of the same order of magnitude, the prevalence of downflow was much greater for the turbulent bed. While an earlier study has shown that particle-related properties had little influence on the overall mass flux in the fast fluidized bed, it was shown here that particle-related properties played a more significant role in the turbulent bed.
Regarding segregation, although the segregation extents were expected to be different in the two fluidization regime to the much greater dissipation and collisional stress in fast fluidization, the segregation datasets from the two fluidized beds were found to be statistically similar. Radial position (r/R ) was the most influential variable on segregation in the fast fluidized bed, but the least in the turbulent one, because of the more pronounced core-annulus profiles in the former. While h/H had a negligible influence in the fast fluidized bed, it was more significant in the turbulent bed.
The comparative analysis of the two fluidization regimes here, therefore, provides more insights into the differences in flow phenomena. Further studies recommended include investigation of whether and under what circumstances does the core-annulus profile exist for the turbulent regime, and why radial position influences local mass flux but not segregation in the turbulent bed.