基于介尺度结构的EMMS模型的改进、扩展及应用

发布时间：2018-03-12 16:06

本文选题：气固系统　切入点：EMMS　出处：《中国科学院大学(中国科学院过程工程研究所)》2017年博士论文　论文类型：学位论文

【摘要】：气固两相流是具有多尺度复杂结构的非线性非平衡系统,往往在介于微尺度单颗粒与宏尺度反应器之间呈现诸如团聚物或气泡等介尺度结构特征,从而对系统的反应和传递性能产生重要影响。为了对这种复杂系统进行描述,人们基于平均假设建立了各种经验或半经验的关联模型,但在适用性和准确性方面都有较大的局限性。因此,从理论上实现对介尺度结构的表征以及对流动参数非均匀分布的预测成为量化调控气固反应系统的关键问题。在考虑气固系统中的多尺度相互作用并建立介尺度稳定性条件的基础上,能量最小多尺度(Energy-Minimization Multi-Scale,EMMS)模型合理预测了气固系统中诸如介尺度结构和噎塞等本征流动特征。本论文以气固两相流控制机制相互协调所产生的介尺度非均匀结构及其加减速动态演化特征为切入点,进一步解决气固系统中介尺度结构的定量表征、相间耗散的表达、以及宏尺度非均匀分布的求解等问题。建立了气固系统的团聚物动态演化方程,并在边界条件等约束下实现了气固EMMS模型的轴径向二维扩展,最终形成了气固反应器的全系统多尺度稳态建模的统一方法和工业应用软件包。各章主要内容安排如下:第一章介绍了气固两相系统的研究进展,首先对气固系统的多尺度研究现状进行了综述,并进一步介绍了 EMMS模型及其工业应用。在此基础上详细介绍了气固系统的经验性全循环建模方法和虚拟过程工程技术。第二章分析了颗粒团聚物在循环流化床提升管过渡段的动态演化机理,并进一步考虑颗粒加速度,建立了轴向EMMS模型,在模型中通过引入颗粒团聚物体积平均数密度的概念和变量分离的方法,实现了对模型的数值求解。轴向模型在无需借助经验关联式的情况下实现了对循环流化床提升管轴向非均匀分布的预测。计算结果和实验对比基本一致。第三章根据固相颗粒在局部稀密两相之间相互传递关系建立了团聚物动态演化方程,并用此方程替换原团聚物尺寸方程,改进了 EMMS单元模型。改进模型不仅可以应用于CFD数值模拟网格内的结构非均匀曳力计算,还避免了原团聚物尺寸方程无法直接应用到顺重力场或低固体通量工况的计算问题。第四章通过考虑壁面效应和界面剪切作用对提升管径向动力学的影响,完善了径向EMMS模型。采用团聚物动态演化方程来定量表征局部微元的非均匀结构,从而有效的解决了原团聚物方程不适用于近壁面处颗粒速度为负时的计算问题。另外,针对径向模型方程非线性强、难以直接数值求解的特点,采用了函数逼近的方法实现了模型的近似求解。只要给定截面平均空隙率和气固表观速度,模型就可对其径向环核结构和壁面处颗粒向下运动等典型动力学特征进行预测。模型的计算结果和实验体现了很好的一致性。第五章将EMMS模型和相关拓展模型应用于气固反应器系统的各离散单元,发展和完善了基于EMMS模型的复杂气固系统全循环稳态建模方法,并以此为基础初步实现了稳态虚拟过程工程(VPE)的示范。第六章开发了基于EMMS理论的可视化虚拟流态化软件包Virtual Fluidization(?)。利用该软件可以对大型工业反应器内的全局稳态动力学进行准实时的快速预测。本研究工作发展和完善了 "先整体分布、后局部模拟、再细节演化"的EMMS多尺度计算模式,打下了以工业过程的实时模拟为特征的虚拟过程工程的基础,而且还拓展了 EMMS模型直接工业应用新领域,为化工工艺过程的设计和放大提供了定量参考。
[Abstract]:Gas solid two-phase flow is a complex structure with multi-scale nonlinear non-equilibrium systems often appear as clusters or in between bubble and meso scale structure characteristics between micro scale and macro scale single particle reactor, which has an important effect on the system response and transfer performance. As described in this complex system, based on the people the average hypothesis to establish the correlation model of various empirical or semi empirical, but there are limitations in applicability and accuracy. Therefore, the characterization of meso scale structure and the key problems of non uniform distribution of flow parameters prediction become quantitative regulation of gas-solid reaction system theoretically. Based on the consideration of many the scale of gas solid interactions in the system and the establishment of meso scale stability conditions, energy minimization multi-scale (Energy-Minimization Multi-Scale, EMMS) model to predict reasonably the gas-solid system In the system, such as meso scale structure and choking intrinsic flow characteristics. In this paper, the gas-solid two-phase flow control coordination mechanism produced by the meso scale heterogeneous structure and dynamic evolution characteristics of acceleration and deceleration as the starting point, to further solve the gas-solid system of medium scale structure and quantitative characterization, expression of dissipation, and macro the scale for solving non uniform distribution. Established the evolution equation of agglomerate dynamic gas-solid system, and boundary conditions are realized under the constraints of axial radial gas-solid the extension of EMMS model, and eventually formed a unified method of gas-solid reaction system for multi scale steady state modeling and industrial application software. The main content each chapter is as follows: the first chapter introduces the research progress of gas-solid two-phase flow system, this paper summarizes the status quo of multi-scale of gas-solid system, and further introduces the EMMS model and its industry . based on the detailed empirical technology of gas-solid system full cycle modeling and virtual process engineering. The second chapter analyzes the agglomeration of particles in circulating fluidized bed to enhance the dynamic evolution mechanism of the transition section, and further considering particle acceleration, establishes axial EMMS model by introducing aggregates volume average number density the separation of concepts and variables in the model, the numerical solution of the model. In the axial model without the help of empirical correlation under the condition of the tube axial circulating fluidized bed to enhance the non uniform distribution prediction. The result of calculation and experiment are consistent. The third chapter according to the comparison between the local density of solid particles in two-phase interaction transfer relationship established dynamic agglomeration evolution equation, and this equation is used to replace the original agglomerate size equation, improved EMMS element model. The improved model not only CFD can be applied to numerical simulation of non uniform drag calculation structure within the grid, but also avoids the original agglomerate size equation cannot be applied directly to the calculation of gravity magnetic field or low solid flux conditions. In the fourth chapter, by considering the wall effect and shear effect to improve the effect of radial dynamics, improve the radial EMMS model. The cluster's dynamic evolution equation to characterize local micro inhomogeneous structure, which effectively solves the original cluster equation is not suitable for the near wall particle velocity for calculation of negative. In addition, the radial model equation of nonlinear characteristics of strong, difficult to direct numerical solution, using the method of function approximation the approximate solution of the model. As long as the given section average voidage and gas-solid apparent velocity model can be on the radial ring core structure and wall particles and other typical downward movement The kinetic characteristics were predicted. The model calculation results and experiment shows good agreement. The fifth chapter of the discrete element model of EMMS and the related development model is applied to the gas-solid reactor system, the development and improvement of the EMMS model of complex gas solid system modeling method based on cyclic steady state, and on the basis of preliminary the steady state of virtual process engineering (VPE) demonstration. The sixth chapter developed the visualization software EMMS virtual fluidization theory based on Fluidization package Virtual (?). The software can be used for the large-scale industrial global steady state reactor dynamics of quasi real-time rapid prediction. The development of this research work and improve the overall after the local distribution, simulation, calculation model of multi-scale EMMS and detailed evolution ", laid the foundation of virtual engineering process to real-time simulation of industrial process characteristics, but also expand the EMMS mode The new field of direct industrial application provides a quantitative reference for the design and enlargement of chemical process.

【学位授予单位】：中国科学院大学(中国科学院过程工程研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ018

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