Comparison of the Dynamic Thin Shell and Quasi-cylindrical Models for Blown Film Extrusion

Most models of blown film extrusion are based on thin shell theory, which was first applied to these processes by Pearson and Petrie. There has been some contention in the literature as to the suitability of the thin shell model. More recently, Liu and coworkers presented an alternative quasi-cylindrical model that neglects longitudinal curvature but was reported to agree more closely with experiments. In later studies, other researchers used the quasi-cylindrical model to investigate flow-induced crystallization. The current paper presents finite difference solutions of the quasi-cylindrical model and quantifies the differences in the steady-state behavior, dynamics, and stability between the quasi-cylindrical and the thin shell models. The differences in the steady-state and dynamic behavior between the thin shell and quasi-cylindrical models are found to be significant, both qualitatively and quantitatively. This study should aid future researchers in developing dynamic simulation models that include more sophisticated descriptions of the underlying polymer physics. Polym. Eng. Sci. 44:1267–1276, 2004. © 2004 Society of Plastics Engineers.