Tip-clearance Effect on Mixing Performance of Twin Screw Extruders

Abstract

In order to evaluate the tip-clearance effect on mixing, 3-D numerical simulations were applied to kneading block section of co-rotating twin screw extruders. The software we used was originally developed for non-Newtonian and non-isothermal flow analysis based on the finite element technique. The marker-particle tracking analysis was also developed in order to estimate the particle path, residence time distribution, stress and strain history, and so on.The stress distribution obtained by the above-mentioned simulations suggested the following mixing mechanisms. The kneading block with the small tip-clearance (TC) caused the bimodal stress distribution which had peaks in both high and low stress level. The marker-particles which overpassed the TC formed the peak at the high stress level and the other particles contributed to the peak at the low stress level. In other words, a large number of particles evaded the TC and it caused heterogeneous stress induced mixing. On the other hand, the large tip-clearance caused the narrow and sharp stress distribution because most of the particles passed over the TC. The stress level was not high, however, homogeneous stress induced mixing was expected. Since the tip-clearance applied a significant effect to the dispersive mixing, it should be optimised in accordance with the material design.

Extension‐dominated improved dispersive mixing in single‐screw extrusion. Part 1: Computational and experimental validation

“…Several numerical studies have examined mixing and flow analysis in the extruders via three-dimensional non-Newtonian finite-element modeling. [57][58][59][60][61] Kim et al 62 performed three-dimensional, nonsteady, and nonisothermal simulations on metering section of screw elements to investigate the flow field and the effect of processing parameters. Computational validation on EME for TSE have been performed using ANSYS Polyflow simulations.…”

“…The basic idea is to design an element which has hyperbolic C‐D channels. Several numerical studies have examined mixing and flow analysis in the extruders via three‐dimensional non‐Newtonian finite‐element modeling 57–61 . Kim et al 62 performed three‐dimensional, nonsteady, and nonisothermal simulations on metering section of screw elements to investigate the flow field and the effect of processing parameters.…”

Comparative computational analysis of dispersive mixing in extension‐dominated mixers for single‐screw extruders

“…Various computational studies have examined mixing and flow analysis in the extruders by means of threedimensional finite-element modeling (FEM) for non-Newtonian fluids (see, eg, [24][25][26][27][28] ). CFD simulations of the KB region in a TSE have also been performed.…”

Effects of Pitched Tips of Novel Kneading Disks on Melt Mixing in Twin-Screw Extrusion

“…Among various types of mixing elements [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] , kneading disks (KD) are the most commonly used due to their mixing efficiency. In order to tune the mixing characteristics of conventional KD for application to various purposes, a modified type of KD has been proposed, called "pitched-tip kneading disks" (ptKD).…”