CHARACTERIZATION OF AGGLOMERATE DISPERSION BY EROSION IN SIMPLE SHEAR FLOWS

The extent of dispersion of solid agglomerates in hydrodynamic flow fields is believed to depend on the material properties as well as flow conditions. The purpose of this study has been to investigate the mechanism of agglomerate breakup in simple shear flows and to correlate the various parameters affecting the dispersion process. Experiments were performed in a transparent cone and plate device. Two distinct breakup mechanisms, denoted as "rupture" and "erosion", were observed. The rupture process is characterized by an abrupt breakage of the agglomerate into a few large pieces. The erosion process is more gradual and initiates at lower applied shear stresses than rupture. The erosion process is characterized by the detachment of small fragments from the outer surface of the agglomerate. For the erosion of carbon black agglomerates suspended in Newtonian fluids, it was found that the kinetics of the process follows a first order rate equation and the size of the eroded fragments obeys a normal distribution. The strength of the flow field does affect the kinetics of the dispersion process, and a parameter alpha, scaling the applied shear stress with the cohesive strength of the agglomerate, is characteristic for the erosion process.