快速反应体系中流体微观混合机理的研究
发布时间：2018-12-24 10:13
【摘要】：微观混合主要是指物料从经湍流分散后的最小粘性涡尺度即Kolomogrov尺度到分子尺度的均匀化混合过程。这种微尺度上的混合对于快速反应体系(如丙烯高温氯化反应、环己酮肟重排反应等)有着非常重要的影响,反应体系的物料浓度分布、产品质量及系统操作稳定性等均与微观混合过程有着紧密联系。由于这类体系的反应速率极快,在物料混合尚未达到分子尺度均匀化之前,反应有可能已经或者接近完成。因此,研究快速反应体系中流体微观混合的机理并建立相应的理论模型对于设计和优化反应器、提升目标产物选择性、避免混合不均匀而形成的物料局部过浓现象以及抑制由此产生的深度副反应等具有重要意义。已有文献中的微观混合模型主要有经验模型和结构模型两种。经验模型主要有聚并-扩散模型、双/多环境模型、IEM模型等,结构模型主要有层状结构模型、薄层片状/片状结构模型、涡旋卷吸模型等。经验模型大都引入了一个或者多个模型参数,且这些参数常无实际物理意义、缺乏流体力学基础。现有的结构模型大都仅考虑物料微团的一维压缩变形,并将模型简化为相邻物料富集区局部微元内的混合过程。由于这类模型过于简化,导致其所描述的混合过程与实际情形存在一定偏差。本文针对前人模型存在的不足,提出了一个新的微观混合机理模型。本文模型考虑了湍流场结构的复杂性和尺度裂变动力学,考虑了物料富集区在多维对流和扩散协同作用下的混合过程,即引入了物料富集区微元的切向、法向变形和分子扩散,构建了一个耦合拉伸、剪切、挤压、卷吸等多种机制的微观混合模型。基于物料浓度的对流、扩散方程,构建了耦合物料浓度输运以及化学反应的数学方程,并推导出了涡旋速度分布。并引入了代表性的快速反应体系即串联-竞争反应体系(?-萘酚与苯磺酸重氮盐生成偶氮染料的反应系统),分析了物料的摩尔体积比、粘度、分子扩散系数、物料的初始浓度对反应选择性的影响及其对微观混合均匀程度的影响。然后,以快速强放热的反应体系(即丙烯高温氯化反应体系)为例分析了温度瞬态分布及其对混合过程的影响。研究表明,当物料的摩尔体积比不同时,物料富集区之间的卷吸厚度和层数均不同;当粘度不同时,反应的选择性随着粘度的增加而增大;当分子扩散系数不同时,反应的选择性随着扩散系数的增加而减小,且在一定范围内这种趋势较明显;同时反应选择性随着物料初始浓度的增加而增大;当考虑温度影响时,局部反应区域内存在温度梯度。上述工作对于实际反应中微观混合的过程调控具有一定的指导意义。
[Abstract]:Microscopic mixing mainly refers to the homogenization of materials from the minimum viscous vortex scale (Kolomogrov scale) to the molecular scale. This microscale mixing plays an important role in rapid reaction systems such as propene chlorination reaction, cyclohexanone oxime rearrangement reaction and so on. Product quality and system operation stability are closely related to micro mixing process. Because the reaction rate of this kind of system is very fast, it is possible that the reaction has been completed or nearly completed before the material mixing reaches molecular scale homogenization. Therefore, the mechanism of micro fluid mixing in the rapid reaction system is studied and the corresponding theoretical model is established for the design and optimization of the reactor to enhance the selectivity of the target product. It is of great significance to avoid the local overconcentration of materials caused by uneven mixing and to suppress the depth side effects. There are two kinds of microcosmic mixed models in the literature: empirical model and structural model. The empirical models mainly include the aggregation and diffusion model, the double / multi-environment model, the IEM model and so on. The structure models mainly include the layered structure model, the thin lamellar / flake structure model, the vortex entrainment model and so on. Most empirical models introduce one or more model parameters, and these parameters often have no physical significance and lack of hydrodynamic foundation. Most of the existing structural models only consider the one-dimensional compression deformation of the material microclusters, and the model is simplified as the mixing process of local microelements in adjacent material enrichment areas. Due to the simplification of the model, the mixing process described by the model deviates from the actual situation. In this paper, a new microscopic mixing mechanism model is proposed to overcome the shortcomings of previous models. In this paper, the complexity of turbulent field structure and the scale fission dynamics are considered, and the mixing process of material enrichment region under the interaction of multi-dimensional convection and diffusion is considered, that is, the tangential, normal deformation and molecular diffusion of the micro-elements in the material enrichment region are introduced. A micro-mixing model of coupling stretching, shearing, extrusion and entrainment is constructed. Based on the convection and diffusion equations of material concentration, the mathematical equations of coupling mass concentration transport and chemical reaction are established, and the vortex velocity distribution is derived. The representative rapid reaction system, that is, the series competition reaction system (the reaction system of naphthol and benzenesulfonic acid diazo salt to form azo dyes) was introduced. The molar volume ratio, viscosity, molecular diffusion coefficient of the materials were analyzed. The effect of the initial concentration of the material on the selectivity of the reaction and its effect on the microcosmic mixing uniformity. Then, the transient distribution of temperature and its influence on the mixing process were analyzed by taking the reaction system of rapid and intense exothermic reaction (i.e. propylene high temperature chlorination reaction system) as an example. The results show that when the molar volume ratio of the material is different, the entrainment thickness and the number of layers are different among the rich regions of the material, and the selectivity of the reaction increases with the increase of the viscosity when the viscosity is different. When the molecular diffusion coefficient is different, the selectivity of the reaction decreases with the increase of the diffusion coefficient, and the tendency is obvious in a certain range, and the selectivity increases with the increase of the initial concentration of the material. When considering the influence of temperature, there is a temperature gradient in the local reaction region. The above work has certain guiding significance for the process regulation of micro mixing in actual reaction.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ027.1
本文编号：2390497
[Abstract]:Microscopic mixing mainly refers to the homogenization of materials from the minimum viscous vortex scale (Kolomogrov scale) to the molecular scale. This microscale mixing plays an important role in rapid reaction systems such as propene chlorination reaction, cyclohexanone oxime rearrangement reaction and so on. Product quality and system operation stability are closely related to micro mixing process. Because the reaction rate of this kind of system is very fast, it is possible that the reaction has been completed or nearly completed before the material mixing reaches molecular scale homogenization. Therefore, the mechanism of micro fluid mixing in the rapid reaction system is studied and the corresponding theoretical model is established for the design and optimization of the reactor to enhance the selectivity of the target product. It is of great significance to avoid the local overconcentration of materials caused by uneven mixing and to suppress the depth side effects. There are two kinds of microcosmic mixed models in the literature: empirical model and structural model. The empirical models mainly include the aggregation and diffusion model, the double / multi-environment model, the IEM model and so on. The structure models mainly include the layered structure model, the thin lamellar / flake structure model, the vortex entrainment model and so on. Most empirical models introduce one or more model parameters, and these parameters often have no physical significance and lack of hydrodynamic foundation. Most of the existing structural models only consider the one-dimensional compression deformation of the material microclusters, and the model is simplified as the mixing process of local microelements in adjacent material enrichment areas. Due to the simplification of the model, the mixing process described by the model deviates from the actual situation. In this paper, a new microscopic mixing mechanism model is proposed to overcome the shortcomings of previous models. In this paper, the complexity of turbulent field structure and the scale fission dynamics are considered, and the mixing process of material enrichment region under the interaction of multi-dimensional convection and diffusion is considered, that is, the tangential, normal deformation and molecular diffusion of the micro-elements in the material enrichment region are introduced. A micro-mixing model of coupling stretching, shearing, extrusion and entrainment is constructed. Based on the convection and diffusion equations of material concentration, the mathematical equations of coupling mass concentration transport and chemical reaction are established, and the vortex velocity distribution is derived. The representative rapid reaction system, that is, the series competition reaction system (the reaction system of naphthol and benzenesulfonic acid diazo salt to form azo dyes) was introduced. The molar volume ratio, viscosity, molecular diffusion coefficient of the materials were analyzed. The effect of the initial concentration of the material on the selectivity of the reaction and its effect on the microcosmic mixing uniformity. Then, the transient distribution of temperature and its influence on the mixing process were analyzed by taking the reaction system of rapid and intense exothermic reaction (i.e. propylene high temperature chlorination reaction system) as an example. The results show that when the molar volume ratio of the material is different, the entrainment thickness and the number of layers are different among the rich regions of the material, and the selectivity of the reaction increases with the increase of the viscosity when the viscosity is different. When the molecular diffusion coefficient is different, the selectivity of the reaction decreases with the increase of the diffusion coefficient, and the tendency is obvious in a certain range, and the selectivity increases with the increase of the initial concentration of the material. When considering the influence of temperature, there is a temperature gradient in the local reaction region. The above work has certain guiding significance for the process regulation of micro mixing in actual reaction.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ027.1
【参考文献】
相关期刊论文 前1条
1 李希;陈甘棠;戎顺熙;;微观混和问题的研究——(Ⅲ)物质的细观分布形态与变形规律[J];化学反应工程与工艺;1990年04期
，本文编号：2390497
本文链接：https://www.wllwen.com/kejilunwen/huaxuehuagong/2390497.html
