SECTIONAL AND DISCRETE REPRESENTATIONS OF FLOC BREAKAGE IN AGITATED SUSPENSIONS

The destruction of large aggregates plays several important roles in t he sea, yet a rigorous method for incorporating this process into comm only applied models of aggregate dynamics has not been available. To f ill this void the statistical, population-balance approach to modellin g flee breakage developed most formally and completely by Pandya and S pielman (Journal of Colloid and Interface Science, 90(2) (1982) 517-53 1) is cast into geometric sectional and discrete forms popular for mod elling the effect of aggregation on particle-size distributions. Two b reakup mechanisms are considered. Flee erosion occurs when small parti cles are removed from the surface of larger flocs. Flee splitting is t he rupture of flocs into roughly equal-sized daughter fragments. The r ate of change of mass in a size class due to these mechanisms is best represented by six terms: loss due to diminution by erosion of fines, loss due to erosion of fines, gain from diminution of larger flocs, ga in from production of erosion fines, loss due to splitting and gain fr om splitting. Comparisons of the sectional and discrete equations are made with inputs that are consistent with observations of flocs in the marine environment. A simple, new model of particle-disaggregation ra te that emphasizes the importance of dissipative eddies in disrupting flocs is proposed. It suggests that splitting dominates the breakup of flocs of all sizes. Copyright (C) 1996 Elsevier Science Ltd