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Thesis Advisor陈飞国 ; 杨宁
Degree Grantor中国科学院研究生院
Place of Conferral北京
Degree Discipline化学工程
Keyword气液体系 软球模型 聚并 破碎 气泡粒径分布

随着计算机运算能力的提高,气液体系欧拉-拉格朗日模拟的应用逐渐广泛。气液体系的欧拉-拉格朗日模拟中,把液相看为连续相,其运动用NS方程求解;而气相被作为离散相处理,应用牛顿运动定律跟踪每个气泡的运动。在传统的气液体系欧拉-拉格朗日模拟中,气泡碰撞通常采用硬球模型 (hard-sphere model) 处理,即假设气泡在碰撞过程中不发生形变,并且碰撞在瞬间完成。本文尝试将软球模型 (soft-sphere model) 应用到气泡碰撞计算中,考虑气泡在碰撞过程中的形变以及接触时间,从而更准确反映气泡的动力学特性。进一步,本文建立基于软球模型的气泡破碎聚并模型,来预测鼓泡塔中气泡的粒径分布 (Bubble size distribution, BSD)。本文由以下部分组成: 第一章综述了气液体系的模拟方法、研究现状、气泡的聚并和破碎理论。同时讨论了各种模拟方法的特点,以及本文选取离散颗粒模型 (discrete particle model, DPM) 的原因。 第二章介绍本文的研究工具──开源流体力学计算软件包OpenFOAM。其基于C++风格写成,我们能够添加气液作用力模型以及气泡的聚并和破碎模型等,实现气液的欧拉-拉格朗日模拟。 第三章通过模拟计算一个拟二维的气固流化床,验证了DPM求解器对于最小流化速度,颗粒床层高度等物理量的计算能力。 第四章选取两个常用的气液体系例子,即Becker case和Deen case进行模拟,暂时不考虑气泡的聚并和破碎,证实了软球模型能够成功应用于此类低气含率的鼓泡体系,并初步确定了气泡刚度系数 (stiffness coefficient) 的取值范围。 第五章将软球模型与液膜排干模型结合用于处理气泡的聚并,同时气泡的破碎也加以考虑,从而建立一套完整的气液模拟程序。本章模拟了带有聚并破碎的Deen case体系,得到了鼓泡塔的BSD,与实验结果进行了对比,并进一步分析了气泡刚度系数的选择。

Other Abstract

Eulerian-Lagrangian method is becoming more and more popular for the simulation of dispersed multiphase flow as the computational ability grows. In this method, the liquid is regarded as continuum and solved by the NS equations. The gas phase is treated as discrete bubbles, and each bubble is tracked by the Newton’s second law of motion. The collision between two bubbles is generally handled by the hard-sphere model which neglects the deformation and contact time of bubbles during the collision processes. We tried to apply the soft-sphere model into the Eulerian-Lagrangian simulation of gas-liquid systems, and the deformation and contact time were also considered, resulting in better description of bubble properties. Furthermore, based on the soft-sphere model we established a completed coalescence and break-up model to predict the bubble size distribution. In chapter 1, we summarize the CFD simulation methods and give an overview of the coalescence and break-up theory. A discussion about the applicability of different methods is also made, then we decide to select the DPM method. In chapter 2, the open source CFD package OpenFOAM is introduced. Owing to its C++ code style, we are able to add new gas-liquid force model and bubble coalescence and break-up model to perform Eulerian-Lagrangian simulation in gas-liquid systems. In chapter 3, we simulate a pseudo 2D gas-solid fluidized bed, and find the DPM solver able to reproduce the minimum fluidization velocity and the bed height. In chapter 4, two bubble column systems, the Becker case and Deen case are selected to perform simulations. The bubble coalescence and break-up are not considered. The soft-sphere model is found to be successful in such low gas holdup systems, and an investigation of the bubble stiffness coefficients is also included. Finally, in chapter 5, the soft-sphere model is combined with the film drainage model to handle bubble coalescence, and the bubble break-up is incorporated. The predicted BSD is compared to the experimental data, and further discussion on the stiffness coefficient is presented. 

Document Type学位论文
Recommended Citation
GB/T 7714
薛靖. 气液欧拉-拉格朗日模拟中软球模型的应用研究[D]. 北京. 中国科学院研究生院,2016.
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