Abstract
Deagglomeration of ultrafine powders poses an important challenge towards their efficient and effective utilization. In the present study, we investigate the effect of frequency on the hydrodynamics of pulsed fluidized beds of ultrafine powders that show strong agglomeration behavior. We have carefully selected square waves of three different frequencies: 0.05 Hz, 0.10 Hz, and 0.25 Hz. The lowest frequency used here allowed the fluidized bed to settle completely before another pulse was introduced whilst the highest frequency ensured that the bed remained in a state of continuous turbulence between occurrences of consecutive pulses. On the other hand, the intermediate frequency pulse was just sufficient to complete the process of bed collapse before the start of the next pulse. Both local and global bed dynamics in all the three cases were rigorously monitored using fast response pressure transducers. The pressure transient data during the bed collapse were processed using the bed collapse model reported in the literature to compute the effective hydrodynamic diameter of agglomerates. Though there was substantial decrease in the agglomerate size, the effect of the frequency appeared to be rather insignificant as the global pressure transients remained rather insensitive to the change of the fluidization velocity.
Highlights
Due to strong interparticle van der Waals forces, ultrafine powders tend to agglomerate
Pulsed fluidized beds have lately attracted a lot of attention towards this end. This belongs to a class of assisted fluidization techniques, whereby the fluidized bed technology is further assisted with a technique to improve the fluidization quality, enhance the bed homogeneity, and promote the deagglomeration [1,2,3,4]
The focus of the present study is to investigate the effect of the pulsation frequency on the hydrodynamics of pulsed fluidized beds containing hydrophilic nanoparticles that show strong agglomeration behavior during their contacting with the gas phase
Summary
Due to strong interparticle van der Waals forces, ultrafine powders tend to agglomerate. Liu et al pointed out that bed collapse experiments can give valuable insight into the fluidization behavior [2] Their experimental minimum fluidization velocity for a superfine powder was found to be much higher than the corresponding theoretical value. The focus of the present study is to investigate the effect of the pulsation frequency on the hydrodynamics of pulsed fluidized beds containing hydrophilic nanoparticles that show strong agglomeration behavior during their contacting with the gas phase. Extending our earlier work [12] that used local pressure transients to determine the minimum fluidization velocities, global pressure transient data are processed here for the three different cases of pulsation frequencies in conjunction with the bed collapse model of Nie and Liu to obtain the effective hydrodynamic diameter of nanopowder present in the bed [14]
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