STRUCTURE OF THE AGGREGATES DURING THE PROCESS OF AGGREGATION AND BREAKUP UNDER A SHEER FLOW

A particle size analyzer together with a video camera has been used to investigate the structure of the aggregates during the process of agg regation and breakup of particles in a shear flow induced by means of a Couette-flow system. Three different values for the shear rate have been used (25, 32, and 50 s(-1)). The initial volume fraction of the p articles was phi(o) = 5.0 x 10(-5). Different fractal dimensions (D-3) , D-2, D-1, and D-pf), the shape factor (xi(2)), and the aspect ratio (AR) have been used to characterize the structure of the aggregates. D uring the process of aggregation, no significant changes in the fracta l dimensions, shape factor, and aspect ratio were found. The high valu es obtained for D-3 (D-3 = 2.2) and D-2 (D-2) = 1.98) show us the high compactness of the flocs. Also, values of the fractal dimension and s hape factor have been found to not depend on the shear rate. (C) 1998 Academic Press.