eng URI http://hdl.handle.net/10795/3389 physical sciences applied research university research It is well-known that, increasing the flow rate in polymer extrusion, the flow becomes unstable and the smooth extrudate surface becomes wavy and disordered to an increasing degree. In order to investigate the mechanisms responsible for these instabilities we perform a linear stability analysis of the steady extrusion of a viscoelastic fluid flowing through a planar die under creeping flow conditions. We consider the Phan-Thien-Tanner (PTT) model to account for the viscoelasticity of the material. We employ the mixed finite element method combined with an elliptic grid generator to account for the deformable shape of the interface. The generalized eigenvalue problem is solved using Arnoldi’s algorithm. We perform a thorough parametric study in order to determine the effects of all material properties and rheological parameters. We investigate in detail the effect of the interfacial tension and the presence of a deformable interface. It is found that the presence of a finite surface tension destabilizes the flow as compared to the case of the stick-slip flow. We recognize two modes, which become unstable beyond a critical value of the Weissenberg number and perform an energy analysis to examine the mechanisms responsible for the destabilization of the flow and compare against the mechanisms that have been suggested in the literature. 39 pp. LOMv1.0 creator LOMv1.0 publisher LOMv1.0 Project Executing Organisation 2015 Digital Library of the Operational Programme "Education and Lifelong Learning" abstract types Text extrusion instabilities polymer melts sharkskin stability analysis viscoelastic elastic extrudate swell surface tension PTT 3055113 application/pdf http://repository.edulll.gr/edulll/bitstream/10795/3389/2/3389_JNNFM_paper2.pdf Πανεπιστήμιο Θεσσαλίας. Τμήμα Μηχανολόγων Μηχανικών. - Δημοσιεύσεις. URI http://hdl.handle.net/10795/3389 LOMv1.0creator 2016-05-25T08:02:01Z LOMv1.0validator 2016-05-25T08:02:01Z LOMv1.0 gre no no Copyright EYD-EPEDBM (Operational Programme "Education and Lifelong Learning")