Bed collapse experiments provide vital information about fluidized bed hydrodynamics. In this study, the region-wise bed collapse dynamics of glass beads, titania (TiO2), and hydrophilic nanosilica (SiO2) particles with widely different voidages (ε) of 0.38, 0.80, and 0.98, respectively, were carefully investigated. These particles belonged to different Geldart groups and exhibited varied hysteresis phenomena and fluidization indices. The local collapse dynamics in the lower, lower-middle, upper-middle, and upper regions were carefully monitored in addition to the distributor pressure drop to obtain greater insight into the deaeration behavior of the bed. While the collapse dynamics of glass beads revealed high bed homogeneity, the upper middle region controlled the collapse process in the case of titania due to the size-based segregation along the bed height. The segregation behavior was very strong for nanosilica, with the slow settling fine agglomerates in the upper bed regions controlling its collapse dynamics. The collapse time of the upper region was 25 times slower than that of the lower region containing mainly large agglomerates. The spectral analysis confirmed the trend that was observed in the pressure transients. The clear presence of high frequency events at 20 and 40 Hz was observed in the nanosilica due to agglomerate movements. The residual air exiting the plenum was strongly affected by the bed voidage, being lowest for the nanosilica and highest for the glass beads.

The use of fluidization assistance can greatly enhance the fluidization hydrodynamics of powders that exhibit poor fluidization behavior. Compared to other assistance techniques, pulsed flow assistance is a promising technique for improving conventional fluidization because of its energy efficiency and ease of process implementation. However, the inlet flow configuration of pulsed flow can significantly affect the bed hydrodynamics. In this study, the conventional single drainage (SD) flow strategy was modified to purge the primary flow during the non-flow period of the pulse to eliminate pressure buildup in the inlet flow line while providing a second drainage path to the residual gas. The bed dynamics for both cases, namely, single drainage (SD) and modified double drainage (MDD), were carefully monitored by recording the overall and local pressure drop transients in different bed regions at two widely different pulsation frequencies of 0.05 and 0.25 Hz. The MDD strategy led to substantially faster bed dynamics and greater frictional pressure drop in lower bed regions with significantly mitigated segregation behavior. The spectral analysis of the local and global pressure transient data in the frequency domain revealed a pronounced difference between the two flow strategies. The application of the MDD inlet flow strategy eliminated the disturbances from the pulsed fluidized bed irrespective of the pulsation frequency.