| Abstract: | It is of importance to estimate the pressure drop of polymeric materials in a converging die with an abrupt change in geometry for many polymer processes. In the present study, experiments have been conducted with an extruder and conical dies of four different converging angles for two different polymeric melts under various processing conditions. As part of the analysis, numerical calculations have been carried out using a finite element method (FEM) for a power-law fluid model, A simple formula for estimating pressure drops has also been derived based on a power-law fluid model with normal-stress effects incorporated. In particular, the formula with the normal-stress term excluded underpredicts pressure drops systematically at high flow rates, giving very similar results to those by the FEM calculation. When the normal-stress term is included, the formula is in bettor agreement with the experimental data, confirming that the normal stress effect is important at high flow rates. Other formulae in the literature have been also compared with the present experimental data. |
