Dynamics of partially collapsing pulsed fluidized bed

Abstract

The use of flow pulsation as an effective assisted fluidization technique has been suggested in a number of applications, such as drying of food and pharmaceutical products, dry beneficiation of coal, and deagglomeration of nanopowders, owing mainly to its cost‐effectiveness and ease of implementation. The efficacy of this technique is, however, greatly affected by the frequency of pulsation since it controls the collapse dynamics of the fluidized bed. In this study, using ultrafine hydrophilic nanosilica with strong agglomeration tendencies, the pulsation frequency was controlled to allow only partial collapse of the bed between two successive pulsations while the global and local dynamics in different bed regions were carefully monitored. Besides the usual advantages associated with assisted fluidization techniques, such as lower minimum fluidization velocity, higher bed expansion, and elimination of bed non‐homogeneities, the continuous and intense solid motion imparted by the partial bed collapse caused a more substantial increase in the overall pressure drop than the one obtained with the conventional unassisted fluidization. The results of the frequency domain analysis highlighted the fact that the effect of pulsation event was felt differently in different regions of the bed depending upon the amplitude of the pulsation. These results were further corroborated by the similarity analysis.

Pulsed Fluidization of Nanosilica: Rigorous Evaluation of the Efficacy of Pulsation Frequency

“…During the square-wave pulsed flow, the flow stoppage initiated the collapse, thereby causing a simultaneous decline in the pressure drop as well. However, for the evaluation of the average pressure drop, the pressure drop magnitudes for the fully developed were considered [24]. The variation in the local pressure drop in the upper region of the fluidized bed with the velocity is shown in Figure 4 for various pulsed flows.…”

“…Given that the transition of the fixed bed to the fluidized bed mode of gas-solid contact occurs at the U mf , it is therefore considered a critical fluidization parameter. Similarly, a pulsation of the inlet flow promotes deagglomeration, reduces the U mf , and suppresses the hysteresis phenomenon [13][14][15][16][17][18][19][20][21][22][23][24]. Another assisted fluidization strategy widely reported in the literature utilizes the acoustics perturbations generated from a sound source.…”

“…Pulsation frequency can be adjusted to cause either partial or total collapse of the bed between two successive pulsation events. Further lowering the pulsations frequency beyond that required for complete collapse would provide additional time for the adjustment of solid particles before the next pulsation event [14,17,24].…”

Effect of Voidage on the Collapsing Bed Dynamics of Fine Particles: A Detailed Region-Wise Study

“…An important tool for analyzing the fluidized bed hydrodynamics is the collapse bed study, which can provide meaningful insight into the bed's dynamic behavior. The fluid flow is instantly stopped in a steady fluidized bed, and the solid particles are allowed free fall under gravity, until the bed attains complete rest [22,[25][26][27][28][29][30]. During the first phase of the collapse process, the residual air escapes as bubbles followed by the free fall of the particles.…”

“…The deaeration of the residual air during the collapse process critically governs the collapse process. The residual air moves upward during a bed collapse in a conventional fluidized bed [22,28,29,31,33]. However, other deaeration strategies have also been suggested in the literature [24,26,34,35].…”