(83f) Multi-Scale, Multi-Physics Modeling for the Design and Scale-up of a Novel Microchannel Cast Film Die

A novel flexible plastic film structure has been developed, which incorporates a series of hollow microchannels oriented along the machine direction of the extruded plastic sheet. Numerous applications that can exploit the unique properties of these microchannel films are being explored, such as light-weighting opportunities, water purification membranes, and squeeze pouch structures. The cast film die geometry to create the microchannel films includes an array of air pins located near the die outlet to generate microcapillary openings. The die has been scaled up from the original 51 mm wide lab die to a large production scale die. One of the scale-up challenges is gauge (i.e. film thickness) uniformity. Standard die design techniques for maintaining uniform film gauge are not applicable with this technology, requiring novel approaches to control film thickness. Modeling has been an integral part of the die design methodology being used to improve flow uniformity across the die. The modeling tools include numerical methods such as computational fluid dynamics (CFD) and finite element analysis (FEA), as well as a spreadsheet-based flow profile optimization tool. The large variation in scale, from the upstream distribution manifold and die land regions to the numerous very small microcapillaries in the die lip region, make it impractical to perform CFD simulations over the entire die that include all of the geometric details. Instead, micro-scale flow modeling was performed around a single microcapillary channel in the die lip region to determine the associated pressure drop versus flow rate relationship. The flow geometry associated with the comb-like structure of the air pin region in the macro-scale model was then replaced by a porous medium with an equivalent viscous resistance. The large pressure drops coupled with very wide dies also create challenges with potential clam shelling of the die body leading to additional flow non-uniformity issues. FEA structural analysis, based on pressure prediction from CFD, were used to develop solutions to the clam-shelling issues. This talk will focus on the various modeling techniques used in the design of these dies.