Parametric Study of the Mixing Efficiency in a Kneading Block Section of a Twin-screw Extruder

Alsteens, Bernard; Legat, Vincent; Avalosse, T

doi:10.3139/217.1836

Cited by 49 publications

(30 citation statements)

References 28 publications

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“…This is common for the conveying screw of extruders and many types of kneading elements, such as kneading disks, rotor elements, screw mixing elements, and so on. [5][6][7][8][9][10][11]15,[17][18][19][20]22,28,34,37,38 To observe this, Figure 2 shows the distribution of the magnitude of the strain rate, ffiffiffiffiffiffiffiffiffiffiffi D : D p , at the cross section B indicated in Figure 1. At the clearances between the screw-tips and the barrel surface, and the gap between two screws, ffiffiffiffiffiffiffiffiffiffiffi D : D p takes values larger than 600 (1/s), which is consistent with the circumferential shear rate of 460 (1/s) estimated from the screw rotation speed of 200 rpm.…”

Section: Resultsmentioning

confidence: 95%

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Strain mode of general flow: Characterization and implications for flow pattern structures

2016

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in Wiley Online Library (wileyonlinelibrary.com) Understanding the mixing capability of mixing devices based on their geometric shape is an important issue both for predicting mixing processes and for designing new mixers. The flow patterns in mixers are directly connected with the modes of the local strain rate, which is generally a combination of elongational flow and planar shear flow. We develop a measure to characterize the modes of the strain rate for general flow occurring in mixers. The spatial distribution of the volumetric strain rate (or non-planar strain rate) in connection with the flow pattern plays an essential role in understanding distributive mixing. With our measure, flows with different types of screw elements in a twin-screw extruder are numerically analyzed. The difference in flow pattern structure between conveying screws and kneading disks is successfully characterized by the distribution of the volumetric strain rate. The results suggest that the distribution of the strain rate mode offers an essential and convenient way for characterization of the relation between flow pattern structure and the mixer geometry.

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Section: Resultsmentioning

confidence: 95%

“…8,9,[17][18][19][20][21][22] In mixing devices for highly viscous fluids, like polymers, the largest strain rate is achieved in narrow gap regions, which are the clearance between the screw/rotor tips and the barrel surface, and the gap between two screws/rotors in twin-shaft machines. Thus, it is usually the case the condition (1) is satisfied.…”

Section: Theorymentioning

confidence: 99%

Strain mode of general flow: Characterization and implications for flow pattern structures

2016

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“…With the recent advances in computational fluid dynamics to solve the problems related to rotational fluid mechanics ( ), a large number of studies on the flow and mixing mechanism in the kneading disks of the twin-screw extruders use finite element method (FEM) and finite volume method (FVM) (For example, Alsteens et al,2004;Bravo et al, 2004;Ishikawa et al, 2001;Ghoreishy et al, 2005;Nakayama et al, 2011;Rafei et al, 2009;Sobhani et al, 2010;Yoshinaga et al, 2000;Zhang et al,2009.). In a way, although similar in structure and design to the twin-screw extruder, the tri-screw extruder is different from the twin-screw extruder in the flow and mixing mechanisms.…”

Section: Introductionsmentioning

confidence: 99%

Evaluations of Flow and Mixing Efficiency in the Kneading Disks of a Novel Tri-Screw Extruder

Zhu¹,

Wang²,

Wang³

2016

JAFM

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The forward or backward stagger angles of the kneading disks have great effects on configures of the special center region along axial length in a novel tri-screw extruder. In this paper, the flow and mixing of a nonNewtonian polyethylene in kneading disks of a tri-screw extruder were simulated using three-dimensional finite element modeling based on mesh superposition technique. Three types of kneading disks, neutral stagger, staggered 30° forward and staggered 30° reverse were considered for the tri-screw extruder. The effects of stagger angles of kneading disks on the flow pattern in the tri-screw extruder were investigated. Moreover, at different stagger angles, the dispersive and distributive mixing efficiencies in the kneading disks of the tri-screw extruder and the twin-screw extruder were calculated and compared by means of mean shear rate, stretching rates, maximal stress magnitudes, mixing index, residence time distribution (RTD) and logarithm of area stretch. It is found that increasing the stagger angles decreases the axial velocities of polymer melt in the center region for the tri-screw extruder. The staggered 30° reverse is relatively reasonable for the tri-screw extruder and neutral stagger for the twin-screw extruder for the mixing efficiency. In comparison, the kneading disks in the tri-screw extruder have higher distributive and dispersive mixing efficiencies than those in the twin-screw extruder with the same stagger angles.

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“…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).…”

Section: Introductionmentioning

confidence: 99%

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

Nakayama

Nishihira

Kajiwara

et al. 2017

J. Soc. Rheol., Jpn

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In mixing highly viscous materials, like polymers, foods, and rubbers, the geometric structure of the mixing device is a determining factor for the quality of the mixing process. In pitched-tip kneading disks (ptKD), a novel type of mixing element, based on conventional kneading disks (KD), the tip angle is modified to change the channel geometry as well as the drag ability of KD. We discuss the effects of the tip angle in ptKD on mixing characteristics based on numerical simulation of the flow in the melt-mixing zone under different feed rates and a screw rotation speed. It turns out that the passage of fluid through the high-stress regions increases in ptKD compared to conventional KD regardless of the directions and sizes of the tip angle, while the fluctuation in residence time stays at the same level as the conventional KD. Furthermore, pitched tips of backward direction increase the mean applied stress on the fluid elements during its residence in the melt-mixing zone, suggesting the enhancement of dispersive mixing quality in ptKD. These understandings of the role of the tip angle on KD can give a basic guide in selecting and designing suitable angle parameters of ptKD for different mixing purposes.

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Parametric Study of the Mixing Efficiency in a Kneading Block Section of a Twin-screw Extruder

Cited by 49 publications

References 28 publications

Strain mode of general flow: Characterization and implications for flow pattern structures

Strain mode of general flow: Characterization and implications for flow pattern structures

Evaluations of Flow and Mixing Efficiency in the Kneading Disks of a Novel Tri-Screw Extruder

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

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