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Dynamic Wetting and the Encapsulation of Voids in Free Surface Flows

Lisa A. Mondy1, Alan L. Graham2, Rekha R. Rao1, Carlton F. Brooks1, Kathryn A. Berchtold2, Amy Sun1, Thomas A. Baer3, and David R. Noble1. (1) Sandia National Laboratories, PO Box 5800, Albuquerque, NM 87185-0834, (2) Materials Science & Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, (3) Gram Inc., 8500 Menaul Blvd NE, Suite B-335, Albuquerque, NM 87112

During processes such as mold filling, viscous Newtonian fluids flow around obstacles potentially trapping voids in corners and as knit lines come together. Furthermore, voids can be trapped when the flow front crosses depressions in the bounding surface such as machine marks. The size and distribution of voids can be a function of geometry and dimensionless groups such as the capillary number, Reynolds number, and Bond number. In this coupled numerical and experimental study, the role of dynamic wetting and the surface condition is examined. A series of careful experiments are performed to determine both the dynamic and static wetting properties of the materials. This information is combined with computational modeling using a finite element code to predict the trapping of voids in a variety of flow geometries. The finite element code, developed at Sandia National Laboratories, is massively parallel, two- and three-dimensional, and excels in analyses of manufacturing processes in which there are complex material rheology and evolving interfaces with free surfaces. The evolution of the free surface is captured with a level set method. These numerical predictions are compared to experimental flow validation studies. We find that dynamic wetting characteristics can have a significant, and under some conditions, a dominant role in the formation of voids in these flows. In other cases the geometry plays the dominant role.