Effect of vibrational modes on fluidization characteristics and solid distribution of cohesive micro- and nano-silica powders

Fluidization of powders with small particle sizes is typically troublesome due to their cohesive nature. These powders to not transition from a packed bed into a homogeneous fluidizing one upon the introduction of a gas flow. Rather, they tend to stay mostly stationary, forming vertical channels through which the gas can escape. 

Several methods have been studied to overcome this behaviour and initiate fluidization, one of which is vertical vibration. We hypothesized that a horizontal component of the vibration would be more effective in disrupting the channelling, since the vibration would work perpendicular to the channel direction. In our work we compared the fluidization quality of beds of micro- and nano-particles, subjected vertical and elliptical (a combination of vertical and horizontal) vibration.

In contrast to our expectations, we found that adding a horizontal component mitigated the effect of the vibrations, to the point that channels mostly remained present in the bed, whereas solely vertically vibrated beds showed full fluidization. Additionally, utilizing sectional pressure drop measurements, we showed improvements in fluidization behaviour with respect to the superficial gas velocity, which could not be acquired through conventional indicators of fluidization. Finally, we confirmed our results by X-ray imaging, where the presence or absence of channels could easily be demonstrated. 

Rens Kamphorst, Kaiqiao Wu, Matthijs van Baarlen, Gabrie M.H. Meesters, J. Ruud van Ommen