Mixing in a partially-filled screw channel of a baffled non-twin screw using the moving-particle semi-implicit method

doi:10.11949/0438-1157.20240673

Abstract

Abstract:

In order to improve the mixing ability of traditional twin-screw extruders, a new type of baffled twin-screw extruder is proposed. The unique baffle structure can act on the mixing of materials, but the flow and mixing characteristics under the non-filled state are still unclear. The two-phase interface between the viscous fluid and air in the partially filled transport state is investigated by using the moving-particle semi-implicit method (MPS). The corresponding visualization experiments are conducted by using self-developed extrusion equipment with a totally transparent barrel. The distributions of velocity and pressure of the viscoelastic fluid were solved, and a self-programmed procedure are utilized to calculate the Euclidean spacing and finite time Lyapunov exponents (FTLE) of the particles to characterize the distributive mixing of the baffled non-twin screw (BTSE). The results show that the numerically simulated free interfaces are consistent with the experimental results, confirming the validity of the MPS. The particle tracking results show that in TSE the fluid particles far away from the intermeshing zone are obviously prone to aggregate together, resulting in a larger mean value of the Euclidean spacing and smaller average FTLE. Compared to the traditional TSE, BTSE generates larger values of Euclidean spacing and average FTLE, indicating that the latter is superior in distributive mixing.

Key words: baffled non-twin screw, moving-particle semi-implicit method, non-Newtonian fluids, Euclidean spacing, mixing, PIV

摘要：

为提升传统双螺杆的混合能力，提出一种新型折流板双螺杆，独特的折流板结构可作用于物料的混合，但非充满状态下的流动和混合特性尚不明确。采用移动粒子半隐式方法（MPS）求解了黏性流体非充满输送状态下的两相界面，基于自主研制的全程可视化折流板挤出装备进行非充满输送实验。求解了黏性流体在非充满状态下的速度和压力分布，结合自编程序计算了粒子欧氏距离及有限时间的Lyapunov指数，表征折流板双螺杆的分布混合。结果表明数值模拟自由界面与实验结果保持一致，验证了半隐式方法求解的有效性。粒子示踪结果显示传统双螺杆远离啮合区存在明显的粒子聚并区域及较小平均有限时间的Lyapunov指数。而相对传统双螺杆，折流板双螺杆内欧氏距离和有限时间的Lyapunov指数的平均值较大，分布混合能力优于传统双螺杆。

关键词: 折流板双螺杆, 移动粒子半隐式方法, 非牛顿流体, 欧氏距离, 混合, 粒子图像测速

CLC Number:

TQ 315

Peizhou DONG, Huiwen YU, Lingcao TAN, Baiping XU, Fang YANG. Mixing in a partially-filled screw channel of a baffled non-twin screw using the moving-particle semi-implicit method[J]. CIESC Journal, 2025, 76(1): 198-207.

董沛洲, 喻慧文, 谈灵操, 徐百平, 杨芳. 基于移动粒子半隐式方法的非充满折流板双螺杆流道内混合[J]. 化工学报, 2025, 76(1): 198-207.

Figures/Tables 9

Fig.1 Geometrical configuration of the screw

Table 1 Geometrical parameters of the screw

螺杆型号	$D_{0}$ /mm	$D_{i}$ /mm	C/mm	$D_{e}$ /mm	$D_{f}$ /mm	$L_{1}$ /mm	L/mm	$D_{g}$ /mm	$D_{h}$ /mm
BTSE	35	25	30	15.5	17.5	5	96	0.5	1
TSE	35	25	30	—	—	5	96	0.5	1

Table 1 Geometrical parameters of the screw

螺杆型号	$D_{0}$ /mm	$D_{i}$ /mm	C/mm	$D_{e}$ /mm	$D_{f}$ /mm	$L_{1}$ /mm	L/mm	$D_{g}$ /mm	$D_{h}$ /mm
BTSE	35	25	30	15.5	17.5	5	96	0.5	1
TSE	35	25	30	—	—	5	96	0.5	1

Fig.2 Relationship between viscosity and shear rate of CMC-Na aqueous solution

Fig.3 Schematic diagram of the experiment

Fig.4 Velocity distribution in XZ direction for TSE

Fig.5 Two-phase interface: (a) TSE, Top; (b) TSE, Bottom; (c) BTSE, Top; (d) BTSE, Bottom

Fig.6 Euclidean spacing

Fig.7 Euclidean spacing of fluid particles with different initial positions

Fig.8 Three-dimensional finite time Lyapunov index

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