Investigation of the dispersion of carbon black agglomerates of various sizes in simple-shear flows

• Published in: Chemical engineering science 2003-05, Vol.58 (9), p.1859-1865
• Main Authors: Pomchaitaward, C., Manas-Zloczower, I., Feke, D.L.
• Format: Article
• Language: English
• Subjects: Agglomerate; Carbon black; Dispersion; Exact sciences and technology; Fluid dynamics; Fluid mechanics; Fundamental areas of phenomenology (including applications); Multiphase and particle-laden flows; Nonhomogeneous flows; Particle processing; Physics; Transport processes
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/S0009-2509(03)00012-5

The dispersion of spherical carbon black agglomerates suspended in polydimethyl siloxane liquid and subjected to simple shear flows has been studied in a cone-and-plate shearing device. Sets of dispersion experiments were carried out for agglomerates of various size and packing density. For agglomerates of equal density and under conditions of equivalent cone rotation rates, the dispersion rates of small agglomerates were smaller than those observed for larger agglomerates. Since the agglomerates occupy a significant fraction of the flow domain, the magnitude and distribution of shear stress acting on the agglomerate at a fixed cone rotation rate depends on the ratio of agglomerate size relative to the size of the gap between the cone and plate. To investigate whether this effect could cause the observed variation in dispersion behavior, we performed three-dimensional simulations of the flow fields within the cone-and-plate device and calculated the resulting stress fields acting on spherical agglomerates. These results helped guide additional experiments in which the peak stress acting on agglomerates of various sizes was matched. However, even under matched stress conditions, the dispersion kinetics was found to vary according to the agglomerate size. In addition, the dispersion kinetics for identical sized agglomerates was found to depend on their processing history. Both of these results lead to the conclusion that some other effect, likely the infiltration of the processing fluid within the agglomerate structure, also influences the dispersion behavior.