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Alternative TitleInfluence of DBS Drag Model and Turbulence Models on CFD Simulation of Gas-Liquid Flow
Thesis Advisor杨宁
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword曳力模型   气液两相流   多尺度   鼓泡塔   内环流反应器
Abstract气液两相流是工业界常见的一种多相流动现象。鼓泡塔和内环流反应器是气液两相进行质量、动量和能量传递与化学反应的重要设备,广泛用于能源、化工、环保等领域,其内部流动是典型的多尺度问题。流体力学特性研究对于气液多相反应器的内部结构设计、尺寸放大、操作条件优化等都具有重要的意义。本文的主要研究目标是研究湍流模型对鼓泡塔内气液CFD模拟结果的影响,以及气液双气泡尺寸(Dual-Bubble-Size,DBS)模型在内环流反应器中的应用。 第1章综述了鼓泡塔反应器和内环流反应器的实验与理论研究成果,以及近年来计算流体动力学(Computational Fluid Dynamics,CFD)在鼓泡塔反应器和内环流反应器中的研究进展。 第2章简要介绍DBS模型,研究了曳力模型对CFD模拟鼓泡塔内总体气含率、气含率径向分布、轴向液速径向分布的影响。分析发现表观气速在一定范围内,DBS曳力模型均可以模拟出与实验值吻合的气含率径向分布结果,但是低估了轴向液速,需要考虑采用湍流模型。 为了研究湍流模型对鼓泡塔内气液CFD模拟结果的影响,第3章中选取了层流模型与三种湍流模型模拟鼓泡塔内气液两相流,并将其结果进行对比。研究发现重整化群(RNG)k-ε湍流模型对轴向液速的模拟结果有很大的改善作用。RNG k-ε湍流模型与DBS曳力模型组合下模拟的气含率以及轴向液速模拟值与实验值吻合较好。 由于内部导流管的作用,内环流反应器的流动状态呈现较为复杂的介尺度结构。第4章中研究发现基于网格的DBS(DBS-local)曳力模型对内环流反应器中提升管和下降管内气含率的模拟精度有很大的提高。DBS-local曳力模型可以模拟出气泡随液体被带入下降管中的现象,而传统的曳力模型模拟的下降管内的气含率几乎为零。这显示出基于网格的DBS模型运用在内环流反应器中的优势和潜力。最后,第5章对本论文进行了总结并对未来工作进行了展望。
Other AbstractGas-liquid two-phase flow is commonly encountered in chemical industry. Bubble column and internal-loop airlift reactors are widely used in energy conversion, chemical production and environmental protection and so on. Understanding the hydrodynamics of the multiphase flow is very helpful on the design and optimization of reactor. The objective of this study is to analyze the influence of different drag and turbulence models on the simulation of gas-liquid flow in bubble columns and to extend the Dual-Bubble-Size (DBS) drag model to internal-loop airlift reactors. Chapter 1 outlines the experimental and theoretical studies of bubble column reactors and internal-loop airlift reactors and the recent progress of CFD simulation of multiphase reactors in literature. In chapter 2, several simulations have been implemented to analyze the influence of drag models on the simulation of total, local gas hold-up profiles and local axial liquid velocity profiles in bubble columns. The simulated gas hold-up distribution of DBS drag model fits well with the experiments. But the DBS drag model under-estimates the axial liquid velocity, requiring further study on the effect of turbulence models. To study the influence of turbulence models on gas-liquid flow in bubble columns, chapter 3 compares the simulation results of laminar model with three turbulence models. The RNG k-ε model can improve the simulation results of axial liquid velocity. Both the simulated gas hold-up and axial velocity using RNG k-ε model and DBS drag model agree well with the experimental data. Simulation of internal-loop airlift reactors is challenging due to the complex meso-scale structures in different sections separated by the draft tube. Chapter 4 employs a new DBS model (DBS-local) which can greatly improve the simulation of gas-holdup in the riser and downcomer. In particular, the gas holdup and circulation of two-phase flow can be successfully captured by the new model, whereas traditional drag models such as the Schiller-Naumann correlation show the absence of gas in the downcomer. The simulation demonstrates the advantage and potential of this new model for internal-loop airlift reactors. Finally, chapter 5 summarizes the main results in this thesis.
Document Type学位论文
Recommended Citation
GB/T 7714
许婷婷. DBS曳力模型与湍流模型对气液CFD模拟的影响[D]. 中国科学院研究生院,2014.
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