An attempt was made to study the aggregate dispersion process in three different flow fields namely; steady shear, elongation flow, and combined shear and elongational flows using the discrete element method. The simulation was performed on two aggregate structures characterized by their fractal dimensions. The predicted results showed that the aggregate break-up process evaluated in terms of weighted average fragment size < w > follows a power-law type relation as < w > = kt(-m) in all the three flow fields. The dispersion performance of different flow fields evaluated by dispersing rate and a final steady-state fragment size was found to be dependent upon the extent of applied stress and flow fields such that at low applied stress levels much smaller steady state values Of (W) Could be obtained for the elongational flow. The aggregate structure, characterized by its fractal dimension, was found to have different effects on the aggregate dispersion process depending on the flow field and applied stress level. The results predicted from this simulation could be explained in terms of ability of flow fields in rotating the aggregates and fragments in appropriate position to be broken up and the fractal dimensions of aggregates. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 3303-3310, 2010