Fluidization of nanoparticles: A simple equation for estimating the size of agglomerates

In this work, we revise data published in the last decade on the size of agglomerates in gas-fluidized beds of nanoparticles. Experimental measurements reviewed are based on non-invasive techniques, mainly consisting of laser-based planar visualization of agglomerates in the splash zone and indirect derivation from the fit of bed expansion, settling, and/or minimum fluidization velocity data to empirical correlations. Special attention is focused on the effect of fluidization aids such as vibration, magnetic assistance, sound excitation or centrifugation. Independent measurements performed by diverse authors or by the same authors using different techniques are confronted. Empirical models proposed to predict agglomerate size are also reviewed. Most of these models are difficult to apply in practice because they rely on parameters that need to be measured in the fluidization experiment or assumed.We propose a simple equation to estimate agglomerate size derived from the balance between the local shear force on the particle attached at the outer layer of the agglomerate and the interparticle adhesion force. In general, the results predicted by this equation are in satisfactory agreement with the reviewed experimental data.