(553g) Modeling Methodology for the Design and Scale up of a Microcapillary 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 microcapillary films are being explored, such as light weighting opportunities, water purification membranes, and squeeze pouch structures. The cast film die geometry to create the hollow microcapillary films includes an array of air pins located near the die outlet to generate the microcapillary openings. The die has been scaled up from the original 51 mm wide lab die to a 610 mm application development 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 structural 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. This talk will focus on the various modeling techniques used in the design of these dies.