Three-Dimensional Modeling of Non-Newtonian Fluids Flow in the Mixing Section of Extruder Using the Two-Relaxation-Time Lattice Boltzmann Method

The properties of polymer products are closely related to the mixing quality of the polymer melt in extruders and injection molding machines. The mixing quality of polymer melts depends on the geometric parameters of the screw, the rotation speed of the screw, the back pressure, and the rheological properties of the material. The lattice Boltzmann method can calculate shear rate tensor locally without calculating the velocity gradient and is easy parallelizable. In this paper, a three-dimensional model of non-Newtonian fluid flow in the mixing section of an extrusion screw is established by using the two-relaxation-time lattice Boltzmann method. The effects of non-Newtonian properties and dimensionless pressure gradient on the flow patterns, the trajectories of fluid particles, the throughput of the extruder, and the metering time of the injection molding machine have been studied. The effects of the non-Newtonian properties of a fluid and dimensionless pressure gradient on the residence time and the average total strain of fluid particles have been studied. The effects of the initial position of fluid particles on the movement trajectory, residence time, and average total strain of fluid particles have been studied. This study can provide a theoretical basis for the optimization of screw geometric parameters and operating parameters so as to improve the mixing quality of a polymer melt.