Convective linear stability analysis of two-layer coextrusion flow for molten polymers |
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| Affiliation: | 1. Centre de Mise Forme des Matériaux, Ecole Nationale Supérieure des Mines de Paris, UMR 7635 CNRS, 06904 Sophia Antipolis, France;2. Institut Non-Linéaire de Nice, Université de Nice Sophia Antipolis, UMR 6618 CNRS, 06560 Valbonne, France;1. St Vincent''s Clinic, Sydney, Australia;2. University of New South Wales, Sydney, Australia;3. Victor Chang Cardiac Research Institute, Sydney, Australia;4. Department of Biomedical Engineering, FMHS, Macquarie University, Sydney, Australia;5. Department of Cardiovascular Medicine, University of Florida, Gainesville, USA;6. 1st Department of Cardiology, University of Athens Medical School, Athens, Greece;7. Health Sciences and Technology, MIT, Cambridge, USA;8. Harvard Medical School, MIT, Cambridge, USA;1. Department of Mathematics, Faculty of Science, University of Jeddah, Jeddah 21589, Saudi Arabia;2. Department of Mathematics, Faculty of Education, Ain Shams University, Roxy, Cairo 11757, Egypt;3. Department of Mathematics, Faculty of Sciences, Taibah University, Yanbu, Saudi Arabia;1. Max Planck Institute of Colloids and Interfaces, Potsdam, Germany;2. Sharif University of Technology, Tehran, Iran;3. University of Tehran, Tehran, Iran;1. Department of Mechanical Engineering, University of Colorado, Boulder, CO 80309-0427, USA;2. School of Mathematical Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia;1. Department of Chemical Engineering and Biotechnology, Cambridge University, Cambridge CB2 3RA, United Kingdom;2. Department of Chemical Engineering, Jeju National University, Jeju 63243, Republic of Korea |
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| Abstract: | The interface instability of the coextrusion flow of a polyethylene and a polystyrene is studied both experimentally and theoretically in a slit geometry. For prototype industrial conditions, we have found a stable/unstable transition which bounds the occurrence of stable/unstable sheets at die exit. By investigating a large range of processing conditions, we have shown that this transition is controlled by both temperature and flow rate ratios. Close to the transition, we used a transparent die to measure spatial amplification of different controlled perturbations at die inlet and pointed out the convective nature of the instability which exhibits a dominant mode (for which the instability is the most severe). We have then found that a convective stability analysis, using the White–Metzner constitutive equation, is able to account for the spatial amplification rate experimentally measured on controlled perturbation experiments. By considering that the instability is controlled by its dominant mode, we performed a convective stability analysis for all studied prototype industrial conditions and showed that such an analysis is able to forecast the occurrence of defects at die exit. |
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