THE HYBRID FEM FDM COMPUTER-MODEL FOR ANALYSIS OF THE METERING SECTION OF A SINGLE-SCREW EXTRUDER/

A hybrid FEM/FDM computer model was employed in this study for simulat ing the non-Newtonian, nonisothermal polymer melt felt in the metering section of a single-screw extruder. The pressure distribution in the screw surface was obtained by solving the generalized Reynolds equatio n. Instead of using the energy equation in Eulerian frame, a Lagrangia n expression was involved for stabilizing the numerical scheme. The te mperature profiles were obtained by finite difference discretization f or the energy equation in such element. The screw surface with the scr ew channels and the flight lands could be modeled as a surface divided into small shell elements. To demonstrate applicability, the results provided by the hybrid FEM/FDM were found to be similar to those of th e 2D FDM for the thermally developing flow, through Fenner's example. It can also illustrate the leakage flow and the cross-channel effect i n the screw pumping problem. The results from the Hybrid FEM/FDM revea led that if the clearance becomes too large, the volumetric flow rate would considerably decrease and the exist melt temperature would incre ase. In addition, when the clearance is close to the normal design cle arance, the leakage flow through the flight lands was found to be smal l. These computational results were observed to correlate with those o f other experimental studies. Finally, the hybrid FEM/FDM approach can in principle be extended to the non-Newtonian, nonisothermal flow in a complex screw surface such as the barrier screw and the Maddock mixi ng head.