Etude transfert de chaleur dans un écoulement de polymère fondu en régime non stationnaire

Abstract

Extrusion is a shaping process that is widely used in various industries such as plastics, metallurgy, ceramics, and the food industry. The materials, however, must be subjected to high pressure and stress levels to be extruded at sufficient flow rates. The objective of this study is to determine the rheological characteristics of LDPE (Lower Density Polyethylene) polymer extrusion through a single, axisymmetric matrix. This polymer is considered a generalized Newtonian fluid. The numerical simulation was carried out thanks to the software "POLYFLOW" developed by the firm ANSYS, this calculation code is based on the finite element method; it is specially designed for the flows of polymers. The "POLYFLOW" software requires the GAMBIT code as a preprocessor for the finite element mesh. The calculation parameters provided by the « Polyflow” code are velocity, shear rate, pressure and dynamic viscosity, and current cloths. This study clearly shows us that for sufficiently low flow rates, the extrudate is smooth, transparent and free of defects. As the flow increases, the surface of the extrudate becomes matte and cracks on the surface increasingly pronounced gradually appear at the exit of the die. Currently, it is known that this cracking of the extrudate is a surface defect due to the singularity, and the associated stress concentration present at the die exit where the polymer passes from a confined flow to a free surface jet.