Numerical evaluation of the wall effect on the hydrodynamic behavior of a fluidized nanoparticle agglomerate

In this study, the wall effect of the reaction tube on the hydrodynamic behavior of a fluidized nanoparticle agglomerate is examined with varying fractal dimension and agglomerate-to-tube radius ratio at intermediate Reynolds numbers from 1 to 40. A radially varying permeability model is adopted to account for the porous, hierarchical and fractal structure nature of the fluidized nanoparticle agglomerates. Simulation results reveal that the wall forces more fluid to flow through the agglomerate, and a fluid velocity peak inside the agglomerate is observed in most cases. The fluid flow inside agglomerates is significantly affected by the Reynolds number and fractal dimension, nevertheless, the wall constrains the deformation of streamlines. The fluid passes through the agglomerate almost parallel to the wall, and the wake in the rear region of an agglomerate is depressed, with no flow separation observed. The wall effect brings in additional drag for the agglomerate, and the drag coefficient decreases with the Reynolds number and increases with the radius ratio.