Polymer Engineering Faculty Research


A time-scale approach for analysis of coalescence in processing flows

Document Type


Publication Date

Fall 2004


Coalescence of droplets in flow through capillary dies and in the filling of strip molds was investigated using experiments and time-scale analysis. The time scales of droplet approach, droplet-droplet interactions, and fluid drainage were compared with the time scales of flow in order to predict the extent of coalescence in each case. In the case of capillary dies, coalescence took place predominantly in the zones away from the die wall and away from the die axis, and the expanse of the coalescence zone increased with blend composition and decreased with mean shear rate. In the case of mold filling, droplet coalescence took place after the polymer flowed a characteristic distance along the mold. A semiquantitative agreement was found between the predictions and the experimental results obtained using blends of polypropylene and polystyrene. In addition to larger-diameter droplets, long fibrils, formed by stringing of coalescing droplets, were observed. Polym. Eng. Sci. 44:2254–2265, 2004. © 2004 Society of Plastics Engineers.



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