Flow visualisation of polymer melts in abrupt contraction extrusion dies : quantification of melt recirculation and flow patterns
การทำให้มองเห็นภาพการไหลของพอลิเมอร์หลอมในดายเอกซ์ทรูดที่มีการเปลี่ยนขนาดอย่าง ทันทีทันใด : การวิเคราะห์รูปแบบการไหลวนในเชิงปริมาณ

Charoen Nakason, Asst. Prof., D. of Rubber Tech. and Polymer Sci., F. of Sci. and Tech., PSU.
Martyn, M. T., D. of Mechanical and Medical Eng., IRC in Polymer Sci. and Tech., U. of Bradford, England
Coates, P.D., D. of Mechanical and Medical Eng., IRC in Polymer Sci. and Tech., U. of Bradford, England
Corresponding e-mail : ncharoen@bunga.pn.psu.ac.th

Grant : Government Budget, PSU., ESRC Council and University of Bradford
Published : J of Non-Newtonian Fluid Mechanics 2000, 91 : 109-122
Key words : branched polyolefins, linear polyolefins, natural flow profile, screw-driven flow, abrupt contraction geometry

This paper is the first part of a series of three in which we present experimental and analytical data covering the development of entry profiles, normal and shear stress fields and the in-process extensional viscosity measurement of branched and linear polyolefins. Here, we report accurate in-process measurements of the natural flow profiles of selected branched and linear polyolefins obtained from screw-driven extrusion flows through an abrupt contraction geometry. Recirculation areas, vortex centres and detachment lengths were quantified and their dependence on flow rate and process temperature studied. Significant recirculation areas were observed for the branced melts. Both the size and the development of these features were dependent on flow rate and temperature. Recirculation areas of the linear polymers were less prominent and independent of flow conditions, Correlation has been observed between rheological characteristics of the low density polyethylenes and their entry behaviour.

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