Film formation and surface renewal characteristics of co-rotating horizontal twin-shaft kneading devolatilizer

doi:10.11949/0438-1157.20250389

Abstract

Abstract:

The horizontal twin-shaft kneading devolatilizer has a complex structure and its blades are interlaced in the overlapping area, and its flow film-forming characteristics are still lacking in-depth understanding. This paper establishes a facile numerical simulation method using the overset mesh method combined with VOF model, and reports the film formation and surface renewal characteristics of the kneading devolatilizers at viscosities of 50—1000 Pa∙s and rotating speeds of 1—5 r·min^-1 at periodic steady state. The simulated film thickness data agree well with experimental measurements using a visualization device. An asymmetric liquid level is formed within the reactor, and the asymmetry is affected by both the viscosity and the rotating speed. The film area generally increases with increasing the rotating speed. At a given speed, the film area firstly increases significantly and then levels off with increasing the viscosity. Shear-stretching between the kneading rods creates a localized high-speed zone, which helps to enhance the mixing efficiency. Surface renewal mainly occurs in the kneading rods drag-out, kneading, front and back sides of the E-shaped rods, and drag-in regions. The average surface renewal frequency is linearly related to the rotating speed. The findings above could be of guidance in the rational design and process optimization of kneading reactors.

Key words: twin-shaft kneading reactor, computational fluid dynamics(CFD), two-phase flow, hydrodynamics, film flow

摘要：

卧式双轴捏合脱挥器结构复杂，桨叶在重叠区域相互交错，对其流动成膜特性尚缺乏深入认识。采用基于重叠网格和VOF模型的数值模拟方法，系统研究了捏合脱挥器在黏度为50~1000 Pa∙s、转速为1~5 r·min^-1下达到周期性稳态的成膜和表面更新特性。膜厚模拟数据与可视化装置测试结果吻合度高。脱挥器内形成不对称液位，不对称度受黏度和转速的综合影响。成膜面积随转速增加而增大，恒定转速下的成膜面积随黏度升高先迅速增加，后趋于平缓。捏合杆间的剪切拉伸作用显著，局部形成高速流体区域，有助于提高混合效率。表面更新主要发生在捏合杆抽出、捏合、“E”字形前后侧及进入区域，平均表面更新频率与搅拌转速呈线性关系。研究结果可为捏合脱挥器结构设计和工艺参数优化提供理论依据。

关键词: 双轴捏合反应器, 计算流体力学, 两相流, 流体动力学, 流动成膜

CLC Number:

TQ 315

Pinhan JIN, Xinchong WEI, Min YAO, Jintang DUAN, Xueping GU, Cailiang ZHANG, Lianfang FENG. Film formation and surface renewal characteristics of co-rotating horizontal twin-shaft kneading devolatilizer[J]. CIESC Journal, 2025, 76(10): 5024-5034.

金聘涵, 魏新崇, 姚敏, 段金汤, 顾雪萍, 张才亮, 冯连芳. 同向旋转卧式双轴捏合脱挥器的成膜和表面更新特性[J]. 化工学报, 2025, 76(10): 5024-5034.

Figures/Tables 13

Fig.1 Geometry and its cold mold experimental setup of horizontal twin-shaft kneading devolatilizer

Fig.2 Overset meshing

Fig.3 Effect of the grid number on the film area (N = 1 r·min-1, μ = 100 Pa∙s)

Fig.4 Spatial distribution of the gas-liquid interface at μ = 100 Pa∙s, N = 1 r·min-1

Fig.5 Methods for film thickness determination (μ = 100 Pa∙s, N = 5 r·min-1)

Fig.6 Comparison of simulated and experimental measured film thickness distribution

Fig.7 Spatial distribution of liquid bulk and liquid film at steady state

Fig.8 Effect of viscosity and rotating speed on the ratio of liquid hold-up on the left and right side

Fig.9 Kneading process in one kneading cycle (μ = 500 Pa∙s, N = 3 r·min-1)

Fig.10 Effect of viscosity and rotating speed on film area

Fig.11 Velocity vectors (μ = 200 Pa∙s, N = 2 r·min-1)

Fig.12 Distribution of surface renewal frequency at film surface

Fig.13 Effect of fluid viscosity and rotating speed on the averaged surface renewal frequency

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