Fluidization of nano-size particles

Fluidization and collapsing bed experiments were performed with 'Tullanox', 10 nm diameter fumed silica. The minimum fluidization velocity was determined to be 0.0115 m/s at the unusually low volume fraction of solids of 0.0077. The solids volume fraction was measured using gamma-ray densitometer. Fluidization was without large bubbles, with a high bed expansion ratio. The highest granular temperature was of the order of that of Geldart B particles, as measured by Cody et al. (1996). The sedimentation process was simulated using a two-fluid hydrodynamic model. The input into the model was a measured solids stress modulus and an agglomerate size determined from the settling curves. With these two rheological parameters, there was good agreement between the sedimentation theory and the experiment. This study shows that the standard collapse bed experiment used in industry is a good test of rheological properties of particles.