Abstract: Three-dimensional isothermal flows of polymer melt in the screw assemblies of a modular(intermeshing) co-rotating twin-screw extruder ZSK60 are simulated using the finite element package POLYFLOW.Melt pumping characteristics,velocity and shear rate distribution profiles of the screw assemblies are analyzed and discussed.According to the quasi-steady assumption and the rotational(periodicity) of twin screws,flow fields corresponding to the 180°screw rotations are calculated.On this basis,flow patterns and dynamic mixing processes in the screw assemblies are visualized using particle tracking technique(PTA).Numerical results agree with previous experiments.This work presented some methodological suggestions for the numerical simulation of flow in modular twin-screw extruders.It also indicates that,compared with experimental methods,numerical simulation could provide deeper insight into the complex flow patterns of polymer melt in screw assemblies.