Optimizing modeling the multilayer coextrusion flow of non-newtonian fluids through rectangular ducts: appropriate shear rate definition for a local power law formulation

The accuracy of viscosity predictions is a crucial aspect of polymer melt flow model-ing and essential for the design of coextrusion die systems. In the field of non-Newtonian fluidmodeling for coextrusion flows through rectangular ducts, significant progress has been madein understanding multilayer flow dynamics. Our fundamental research, employing numericaltechniques such as the shooting method, finite element method, and finite difference methodfor flow evaluation, has established a critical base for the field. Our current research advancesfluid dynamics by refining our existing numerical solver, specifically developed for multilayercoextrusion flows. We aim to enhance the solver’s performance by implementing more sophis-ticated calculations of shear rates that go beyond the traditional approach. The traditionalapproach often relies on average flow velocities and channel heights, which can underrepresentthe complexity of experimentally studied polymer multilayer flows. Our study systematicallycompares various definitions for characteristic shear rates to describe the local shear ratedependent viscosity behavior using, for instance, a local power law model. A thorough erroranalysis quantifies the accuracy of each model and its predictive limitations for industriallyrelevant material combinations and operating conditions. This includes CFD simulations andexperimental data comparisons, employing methods aligned with our fundamental research in this area. Furthermore, our work paves the way for integrating these advanced fluid dynamicsmodels into the evolving field of process digitalization, thereby contributing to the developmentof more efficient, digitally integrated manufacturing processes.