An orthokinetic coagulation model including the effects of agglomeration and local stress-induced aggregate breakup was developed, This model was used to simulate coagulation in the flow between two eccentrically located and rotating cylinders. Four methods of modeling coagulation in the flow system were examined. The first technique used a volume-weighted average of the local strain rates, while a second method used an equivalent volume-weighted power ((G) over bar). A third method treated each volume element as a separate batch reactor and determined a final volume-averaged flee population. The final modeling technique applied mass transfer between each of the elements. Results indicated that substantial differences in average particle diameters and populations were generated with each of the methods, especially where mass transfer between the elements was considered. It was concluded that mass transfer between regions of varying how strain rate and/or velocity gradient should be included in accurate coagulation modeling.