QQ客服 官方微博 反馈留言

题名	鼓泡塔反应器内气液（固）流动多尺度模型分析和计算
作者	陈建华
学位类别	博士
答辩日期	2011-05-31
授予单位	中国科学院研究生院
导师	李静海 ; 杨宁
关键词	能量最小多尺度 鼓泡塔 气液两相流 流型过渡 浆态床
其他题名	Multi-scale Modeling and Simulation of Gas-Liquid(Solid) Flow in Bubble Column Reactors
学位专业	化学工程
中文摘要	鼓泡塔反应器在能源、化工、环保等领域有广泛的应用。这类反应器内的流动是典型的多尺度问题。液体在气相驱动下产生显著的湍流脉动，相界面由于气泡聚并、破碎而发生动态变化。本文的主要研究目标是将能量最小多尺度模型应用到气液泡状流体系，研究气液体系内的多尺度结构与稳定性条件。第1章综述了鼓泡塔反应器流型过渡的实验研究与理论研究成果，以及近年来计算流体力学方法(CFD)在鼓泡塔反应器和浆态床中的研究进展。第2章对单气泡尺寸模型(SBS)和双气泡尺寸模型(DBS)进行了系统的研究。将气液体系划分为宏尺度能量输运、介尺度能量输运+耗散和微尺度能量耗散过程，在此基础上本文认为气液、气固、单相湍流体系的稳定性条件可以统一表述为：微尺度能耗取最小值，介尺度能耗取最大值。应用DBS模型对鼓泡塔内的流型过渡进行了研究，在空气–水体系中预测到气含率在表观气速Ug=0.128~0.129 m/s之间发生跳变，分析认为该跳变代表了流型过渡的第二转变点，即由过渡流转变为湍动流。研究发现DBS模型还可以反映物性对流型过渡的双重影响。为了研究能量最小多尺度方法对不同体系的共性特征，第3章对气固与气液体系的EMMS模型进行了类比。基于模型解空间的分析，二者的类比揭示了两相流流型过渡与结构参数分支的内在关系：流型过渡发生时系统的状态在两条分支之间发生切换，EMMS模型定义的微尺度能耗是连续的，而气含率存在突变。实现了气固EMMS模型的GPU求解，模型求解速度提高了60~100倍。推动了该模型的应用。鼓泡塔反应器的CFD模拟具有重要意义，第4章提出DBS整体曳力模型并与双流体模型耦合，对鼓泡塔进行了模拟。均匀进气时预测的气含率径向分布和液速径向分布与实验值吻合较好。不过在单孔进气的情形，由于中间气泡集中且较大，DBS曳力模型高估了气液相间作用，需要建立局部曳力模型加以改进。浆态床是鼓泡塔反应器的重要应用形式(如浆态床费托合成技术)，第5章研究了浆态床的轴向浆液浓度分布，基于对颗粒团聚的分析提出一种液固相间作用模型，预测到液固之间微弱的滑移速度，轴向浆液浓度分布的模拟结果与实验结果一致。
英文摘要	Bubble column is widely used in energy conversion, chemical production and environmental protection and so on. The flow in bubble columns is a typical multi-scale problem. A large part of turbulent fluctuation in liquid is generated by the buoyancy-driven bubbly flow, and the bubble interfaces change dynamically due to bubble coalescence and break-up. The objective of this study is to extend the Energy-Minimization Multi-Scale (EMMS) method to gas-liquid bubbly flow, and analyze the multi-scale dynamic structure and the stability condition. Chapter 1 reviews the experimental and theoretical findings of regime transitions in bubble columns and the recent progress of CFD simulation of bubble columns and slurry bubble columns in literature. In chapter 2, the Single-Bubble-Size (SBS)model and Dual-Bubble-Size (DBS)model are investigated. The gas-liquid system is divided into three sub-systems: macro-scale energy transport, meso-scale transport and dissipation, and micro-scale dissipation. Recognizing the similarity among gas-liquid flow, gas-solid flow and single-phase turbulence, the stability conditions for these three systems could be unified into the minimization of micro-scale energy dissipation or the maximization of meso-scale energy dissipation. It is found that regime transition in bubble column can be resonably captured by the DBS model. Jump change on the gas hold-up occurs within the range of 0.128 and 0.129 m/s of superficial gas velocity for air-water system. The jump change reflects the second regime transition, i.e., the shift from transitional flow to churn-turbulent flow. The dual-effects of liquid properties on regime transition can also be predicted by the DBS model. To further understand the features of the energy-minimization multi-scale method, chapter 3 compares the EMMS models for gas-solid system with that for gas-liquid system. Based on the analysis of the solution spaces, the two systems are found to bear some analogy, that is, there does exist some relationship between regime transition and bifurcation of structual parameters: the system state shifts between the two branches when the transition happens. At this point, the micro-scale energy dissipation is still continuous but the gas hold-up exhibits jump change. At the end of this chapter, the EMMS model for gas-solid system is re-programmed and implemented on GPU, and the acceleration of 60~100 times faster than solving it on the CPU is obtained. This work promotes the application of the EMMS model. It is important to investigate the CFD simulation of bubble columns. In chapter 4, the DBS drag model is proposed on the basis of the aforementioned global analysis and coupled with the two-fluid model to simulate the flow in bubble column. With uniform aeration, the simulated gas hold-up distribution and axial liquid velocity distribution fit well with the experiments. But the DBS drag model over-estimated the phase interaction in the case of single-orifice aeration due to the large bubbles in the core, calling for further improvement on the drag model by considering local parameters. Slurry bubble column is another important type of bubble column reactors(e.g., the slurry bubble column for Fischer-Tropsch synthesis). Chapter 5 investigated the axial slurry concentration in slurry bubble column and proposed a modified liquid-solid drag model based on the particle agglomeration analysis. Three phase flow is simulated and the weak slip velocity between liquid and solid phase is captured. The simulated axial slurry concentration agrees well with the experimental data.
语种	中文
公开日期	2013-09-23
页码	124
内容类型	学位论文
源URL	[http://ir.ipe.ac.cn/handle/122111/1687]
专题	过程工程研究所_研究所（批量导入）
推荐引用方式 GB/T 7714	陈建华. 鼓泡塔反应器内气液（固）流动多尺度模型分析和计算[D]. 中国科学院研究生院. 2011.

个性服务

查看访问统计

相关权益政策

暂无数据

收藏/分享

除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。