Numerical Simulation Of Mixing Performance In The Miniature Conical Twin Screw Extruder

With the development of polymer industry, the miniature conical twin screw extruder(MCTSE) is increasingly applied for the blending of new polymer nanocomposites. But atpresent, limited attention has been paid to theoretical analysis of mixing performance in theMCTSE. It is very significant to research on the experiment and fundamental theory about themixing performance of MCTSE. The advantage of MCTSE is able to switch between the batchmixing and continuous extrusion. In this paper, the mixing performance of MCTSE wasevaluated under the condition of batch mixing and continuous extrusion.Under the condition of continuous extrusion, the inlet pressure and outlet pressure are set tozero in order to be more correct to evaluate the conveying capacity of MCTSE itself. A studywas firstly done on the numerical simulation of polypropylene (PP) melt flow in the MCTSE,then the three-dimensional flow field, pressure field and shear stress field were obtained. Theeffects of screw speeds and screw configuration on the conveying capacity of MCTSE and meanpressure distribution along the axial distance were theoretically analyzed. Then a number ofparticles were randomly distributed in an inlet vertical plane and their trajectories between theinlet and outlet were calculated from the velocity profiles. The mixing index and mixingefficiency along the axial distance were calculated, and the influences of screw speed and screwconfiguration on the mixing performance of MCTSE were also discussed. Meanwhile, alongeach trajectory, the residence time was computed. The residence time distribution (RTD) wasthen obtained based on the residence time of each of these particles. This provided a numericaltool to assess point-by-point information on the dispersing, distributive and axial mixing ofpolymer melt along the axial distance in the MCTSE.Under the condition of continuous extrusion, there exists the pressure gap between the inletand outlet in order to better research of the mixing performance of MCTSE. Also a study wasdone on the numerical simulation of PP melt flow in the MCTSE, then the velocity field andshear stress field were obtained. A large number of particles were randomly distributed in an inletvertical plane and their trajectories between the inlet and outlet were calculated from the velocity profiles. The shear ability and mixing efficiency along the axial distance were calculated, and theeffects of feed rate, screw speed and screw configuration on the mixing performance of MCTSEwere also discussed. Afterwards the RTD was then obtained based on the residence time of eachof these particles.Under the condition of batch mixing, the flow of PP in the MCTSE was also simulatedusing finite element method (FEM) with mesh superposition technology (MST), then thevelocity field and shear stress field were obtained. A mass of particles were randomly distributedin an inlet vertical plane and their trajectories between the inlet and outlet were calculated fromthe velocity profiles. The dispersive, distributive mixing and stretching over time were analyzed,and the influences of screw speed and screw configuration on the mixing performance ofMCTSE were also discussed.