Flow geometries and experiments

Two types of flows were investigated. At CEMEF, experiments on a plane geometry were carried out. Birefringence measurements were performed, the results of which are presented in Section III-l. Comparison with computed results will be presented in paragraph 6.2. At LRMP, flows in axisymmetric contractions were studied. We present in the next pages the experimental results obtained for presstire drops, entrance pressure losses and die swell. 

In addition, entrance pressure losses were estimated using Bagley s procedime. The set of vEdues presented in Figs. 5 and 6 were obtained from flow measurements with two different rheometers, one eqxoipped with a load sensor, the 

The polymer melt was extruded at 160°C downwards directly into air. The diameter of the passing extrudate was then measured at 6.5 mm fi om the die exit, using an electro-optical device ZIMMER OGH. All measurements were made approximately 5 mm back from the lower end so that sagging under gravity could be neglected [46]. 

In order to get complementary information on the evolution of the shape of the extrudate at the die exit, photographs were taken simultaneously for each flow condition. Examples of free surfaces build establishments are presented in Figs. 7 and 8, respectively for smooth (long dies and low shear rate) and for stronger flow conditions (short die and high shear rate). It is clear that strong flow conditions enhance the differences between LLDPE and LDPE. While LLDPE exhibits rapid evolution towards a constant diameter, instabilities occur for LDPE, which correspond to the onset of melt fracture. 

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