Improving mixing characteristics with a pitched tip in kneading elements in twin‐screw extrusion

Abstract

In twin‐screw extrusion, the geometry of a mixing element mainly determines the basic flow pattern, which eventually affects the mixing ability as well as the dispersive ability of the mixing element. The effects of geometrical modification, with both forward and backward pitched tips, of a conventional forward kneading disks element (FKD) in the pitched‐tip kneading disks element on the flow pattern and mixing characteristics are discussed. Numerical simulations of fully filled, nonisothermal polymer melt flow in the melt‐mixing zone were performed, and the flow pattern structure and the tracer trajectories were investigated. The pitched tips largely affect the inter‐disk fluid transport, which is mainly responsible for mixing. These changes in the local flow pattern are analyzed by the distribution of the strain‐rate state. The distribution of the finite‐time Lyapunov exponent reveals a large inhomogeneity of the mixing in FKD is suppressed both by the forward and backward tips. By the forward tips on FKD, the mixing ability is relatively suppressed compared to FKD, whereas for the backward tips on FKD, the mixing ability is enhanced while maintaining the same level of dispersion efficiency as FKD. From these results, the pitched tips on the conventional KD turn out to be effective at reducing the inhomogeneity of the mixing and tuning the overall mixing performance. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1424–1434, 2018

Fundamentals of Global Modeling for Polymer Extrusion

“…The 3D simulation method was found to be more accurate to describe flows in kneading discs, but the 1D model provided very satisfactory results for flows in screw elements. Several recent papers on modeling of co-rotating twin-screw extrusion may also be cited in this case [185][186][187][188][189][190][191].…”

Flow Classification and Its Application to Fluid Processing

“…The multiaxiality of flow at a spatial point is quantified by the strain-rate state. The strain-rate state has been used to analyze the relation between the channel geometry and non-Newtonian flow (Nakayama et al, 2016(Nakayama et al, , 2018, and discuss the elongational flow distribution in turbulence (Lund and Rogers, 1994;den Toonder et al, 1996).…”

A Review on Transport Phenomena of Entangled Polymeric Liquids

“…99) For the mixing process, Nakayama and coworkers analyzed this process using a shear thinning fluid. 100,101) For flow properties, since the contraction-expansion channel (schematically shown in Fig. 4 (b)) can be considered one of the model geometries in the injection molding process, flows in this geometry have been extensively examined using phenomenological or molecular-based constitutive equations, including the Oldroyd-B model, 102) the pom-pom model, [103][104][105] and the Rolie-Poly model.…”