(189y) Nanofluidization as Affected by Vibration and Electrostatic Fields

Pfeffer, R., Arizona State University
Valverde, J. M., University of Seville
Sanchez Quintanilla, M. A., University of Seville
Castellanos, A., University of Seville

The behavior of a fluidized bed of silica nanoparticles under the influence of externally applied vibrations and electrostatic field will be presented. It has been observed that the application of these fields separately has opposite effects on bed expansion. On one hand, vertical vibrations enhances bed expansion as the vibration intensity is increased up to a critical value. On the other hand, an electrostatic field applied in the horizontal direction, hinders bed expansion. In previous research papers, it has been suggested that the size of nanoparticle agglomerates could be affected either by vibration or by the action of the electric field. Using the modified Richardson-Zaki method to analyze our experimental data, we find that vertical vibration tends to decrease the average agglomerate size in agreement with previous research. However, in this work we look further into the physical mechanisms which affect the response of the fluidized bed. Our results suggest that both vibration and the electric field produce a significant perturbation to the flow of agglomerates on the fluidized bed. Vibration transmits a vertical motion to the agglomerates that enhances bed expansion until vibration velocity becomes of the order of the expected rising velocity of macroscopic bubbles. At this critical point, bubbles growth is stimulated by vibration. A horizontal electrostatic field produces a drift of the charged agglomerates towards the walls that gives rise to fluidization heterogeneity and bed collapse. When both fields are jointly applied these opposed effects can be practically compensated.