气固反应流的格子气自动机模型与仿真

发布时间：2018-07-12 09:59

本文选题：气固反应流 + 格子气自动机　；参考：《重庆大学》2015年硕士论文

【摘要】：气固反应流是石油、化工以及冶金工业中常见的现象。由于大多数反应是一个复杂的非线性过程,其中包含了流动、传热、传质及化学反应等环节,易受体系波动的影响,因此这一过程很难用标准方法从理论上加以有效分析。研究气固反应流的方法包括实验方法和数值模拟方法两大类。由于实验方法成本较高,且受到检测手段的限制而难以获得反应中的细节数据,加之近些年来计算机技术的飞速发展,使得数值模拟方法开始成为与实验方法同等重要的技术手段。气固反应流数值模拟问题对反应器设计有重要作用,但由于研究问题的复杂性而成为反应器理论及应用研究的难点。目前,气固反应流数值模拟方法通常从宏观层面出发,基于流动、传质、传热及反应相关过程的耦合建立数理模型或半经验模型,采用计算流体动力学(Computational Fluid Dynamics,CFD)中的有限差分、有限体积等方法对模型求解,涉及到流动、传质、传热以及反应等环节的复杂耦合,并且在边界处理、算法设计以及并行处理上较为困难。而格子气自动机(Lattice Gas Automata,LGA)是一种在介观层面上基于时间、空间以及流体离散的简化分子动力学模型,既具有微观方法下假设条件较少的特点,又具有宏观方法难以涉及分子或粒子层次微观细节的优势,并可通过模型演化和统计而得到体系在宏观上的非线性行为,整个过程以离散粒子的一系列自组织演化规则替代了对机理模型的复杂求解,并且在处理复杂边界以及反应流中各环节的耦合方面也显得更为高效。为模拟气固相反应流问题,本文根据固体颗粒的未反应核理论,基于格子气自动机方法,构建了包含多物质、多能量状态的气固反应流LGA模型。通过对不同组分、不同能量状态的气体粒子的属性标记,根据物质组分的浓度梯度设计了碰撞方式选择概率表达式,以控制多种物质粒子间的扩散迁移,并引入了热交换过程的能量传递规则;参照反应速率方程结构,设计了气固反应的概率表达式,并依照热力学原理进行了反应热效应的量化描述。以Visual Studio 2005为平台开发了气固反应流模型的仿真软件,实现了反应过程的人机交互以及模拟结果的可视化,为模拟结果的定量分析提供了帮助。根据文献中Bohna等人的实验条件,分别在等温和非等温条件下,利用所建立的气固反应流LGA模型模拟了CO与Fe2O3颗粒还原生成Fe3O4的过程,结果表明:在同一时刻,与等温条件相比,非等温条件下反应转化率平均提高了约6.92%,且模拟结果位于Bohna实验结果的误差上下限范围内,所建立的反应流模型有效;同时,反应流模型能够有效地描述出反应过程中的速度场、温度场以及浓度场的变化细节。此外,在此基础上还分别模拟了不同反应条件下CO与Fe2O3颗粒的还原反应过程,结果表明:气体温度、浓度、颗粒粒径以及孔隙率对颗粒反应过程均有显著性影响。构造具有不同空隙率的Fe2O3多颗粒体系,利用反应流模型模拟了CO与Fe2O3多颗粒体系的还原反应过程,并对体系中的速度场、温度场以及浓度场分布情况进行了研究分析。结果表明:反应流模型可以有效地捕捉到多颗粒体系中的流动、传质、传热以及反应等细节;多颗粒体系中的反应过程具有不均匀性,增大流体流速以及空隙率有利于提高整个体系的反应效率,这与客观规律是相一致的。构造填充床反应器,床中采用随机方法生成一系列大小不一、位置分布不均匀的Fe2O3固体颗粒群体,采用反应流模型模拟了床中的反应过程。结果表明:受壁面效应、固体颗粒体系分布以及传热、热效应规则的影响,床层中的速度场、温度场以及浓度场的分布呈现出不均匀性。此外,在此基础上,根据实际冶金填充床中的黑白像素图,模拟了填充床中局部的反应过程,并成功得到了其中反应流现象。
[Abstract]:Gas-solid reaction flow is a common phenomenon in petroleum, chemical and metallurgical industries. Because most reactions are a complex nonlinear process, including flow, heat transfer, mass transfer and chemical reactions, it is easily affected by the fluctuation of the system. Therefore, it is difficult to analyze the gas solid reaction in theory by the standard method. The method of flow includes two kinds of methods: the experimental method and the numerical simulation method. Because of the high cost of the experiment method and the restriction of the detection means, it is difficult to obtain the detailed data in the reaction. In addition, the rapid development of computer technology in recent years makes the numerical simulation method become the same important technical means as the experimental method. The problem of flow numerical simulation plays an important role in the design of reactor. However, due to the complexity of the research problems, it has become a difficult problem in the theoretical and applied research of the reactor. At present, the numerical simulation method of gas solid reaction flow is usually based on the macro level, based on the coupling of flow, mass transfer, heat transfer and reaction related processes to establish a mathematical model or a semi empirical model. The model is solved by finite difference and finite volume method in Computational Fluid Dynamics (CFD). It involves complex coupling of flow, mass transfer, heat transfer and reaction, and it is difficult to deal with boundary processing, algorithm design and parallel processing. The lattice gas automata (Lattice Gas Automata, L) GA) is a simplified molecular dynamics model based on time, space and fluid dispersion at the mesoscopic level. It has the characteristics of less hypothetical conditions under the microscopic method, but also has the advantage that macro methods are difficult to involve the microcosmic details of molecular or particle levels, and can be obtained by model evolution and statistics. The whole process takes a series of self organized evolution rules of discrete particles to replace the complex solution of the mechanism model, and is more efficient in dealing with complex boundary and coupling of each link in the reaction flow. The LGA model of gas solid reaction flow including multi matter and multi energy state is constructed. By marking the properties of different components and energy states, the probability expression of the selection probability is designed according to the concentration gradient of the material components to control the diffusion and transfer between various material particles, and the heat exchange process is introduced. According to the reaction rate equation structure, the probability expression of gas solid reaction is designed, and the quantitative description of the reaction heat effect is described in accordance with the principle of thermodynamics. The simulation software of the gas solid reaction flow model is developed with Visual Studio 2005 as the platform. The human-computer interaction and the visualization of the simulation results are realized. According to the experimental conditions of Bohna et al. In the literature, the LGA model of gas solid reaction flow is used to simulate the reduction of CO and Fe2O3 particles by the established gas solid reaction flow model under the conditions of the isothermal and non isothermal conditions. The results show that, at the same moment, the reaction is compared with the isothermal condition in the same temperature condition. The average increase of the rate is about 6.92%, and the simulation results are within the range of the error of the Bohna experiment. The model of the reaction flow is effective. At the same time, the reaction flow model can describe the velocity field, the temperature field and the concentration field in the reaction process effectively. In addition, the different reaction strips are simulated on this basis. The reduction reaction process of CO and Fe2O3 particles shows that the gas temperature, concentration, particle size and porosity have significant effects on the reaction process. The structure has a Fe2O3 multi particle system with different void fraction, and the reaction flow model is used to simulate the reduction reaction process of CO and Fe2O3 multiple grain systems, and the velocity in the system is also simulated. The field, the temperature field and the distribution of the concentration field have been studied and analyzed. The results show that the reaction flow model can effectively capture the details of flow, mass transfer, heat transfer and reaction in the multi particle system, and the reaction process in the multi particle system is inhomogeneity, and the increase of the flow velocity and the void ratio is beneficial to the improvement of the reaction of the whole system. Efficiency, this is in accordance with the objective law. In a packed bed reactor, a random method is used to generate a series of Fe2O3 solid particle groups with different size and uneven distribution. The reaction flow model is used to simulate the reaction process in the bed. The results show that the effect of wall surface effect, the distribution of solid particle system and heat transfer, the rule of heat effect. The velocity field, the temperature field and the distribution of the concentration field in the bed are not uniform. On the basis of this, according to the black and white pixels in the actual metallurgical packed bed, the local reaction process in the packed bed is simulated, and the reaction flow phenomenon is successfully obtained.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ052

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