Numerical Simulation Of Flow And Mixing In Assmbly Tri-scrw Extruder

During the process of extrusion by tri-screw extruder, the combination of mixing components in tri-screw extruder has an important impact on extrusion properties. Kneading blocks are the major mixing components in tri-screw extruder.When simulating an individual kneading block, simplified entry and exit boundary conditions caused deviations between the simulation and the actual extrusion at some extent. Screw elements were included in simulation in upstream and downstream flow field would solve the deviations problem at some extent. At the same time, changed processing condition and types of screw elements in upstream and downstream during simulation has a guiding significance on research of how processing condition and screw element influencing the flow field of kneading blocks.Meshes of the numerical simulation in tri-screw extruder have an important impact on accuracy of the simulation conclusions. Appropriate principles and mesh accuracy have been determined by experiment verification of residence time distribution in co-rotating intermeshing twin screw extruder. Impact on flow field and mixing capability in tri-screw extruder arranged in the horizontal line by the changes of kneading block's type, screw speed and screw element's type in downstream has been analyzed based on experiment verification , orthogonal experiment design and variance analysis.The axial pressure building capability, distributive mixing capability and dispersive mixing capability of assembly tri-screw extruder have been quantitative examined by analyzing average pressure, back flow, back flow coefficient and average shear rate. The results were that the average pressure were mainly impacted by screw element in downstream, the back flow and shear rate of forward and neutral kneading blocks were mainly impacted by screw speed and they were improved with the increase in screw speed. The back flow and shear rate of reverse kneading blocks were mainly impacted by screw element in downstream, the back flow and shear rate of reverse kneading blocks were improved by the screw element in downstream.On the basis of quantitive analysis of flow field of assembly tri-screw extruder, it concluded that the mixing capability of neutral and reverse screw extruder were better than forward kneading blocks. Furthermore, by the analysis of simulation on residence time distribution, average logarithm of stretching(ln? ) and distribution of ln? of neutral and reverse kneading blocks, conclusion has been drawn that the mixing capability of neutral kneading in tri-screw extruder have been slightly impacted by screw element in downstream, it improved with the increase in the volumetric flow rate or screw speed. The mixing capability of reverse kneading block were better than neutral kneading block, it impacted slightly by the volumetric flow rate, and improved with the increase in screw speed.