搅拌槽内宏观混合和微观混合的实验研究与数值模拟
文献类型：学位论文
| 作者 | 张庆华 |
| 学位类别 | 博士 |
| 答辩日期 | 2009-06-02 |
| 授予单位 | 中国科学院过程工程研究所 |
| 授予地点 | 过程工程研究所 |
| 导师 | 毛在砂 |
| 关键词 | 搅拌槽 混合时间 微观混合 沉淀过程 k-ε湍流模型 气－液两相流 |
| 其他题名 | Experimental and Numerical Study of Macro-mixing and Micro-mixing in a Stirred Tank |
| 学位专业 | 化学工程 |
| 中文摘要 | 由于相际接触面积大、传热传质效率高、操作弹性大、使用范围广、操作稳定等优点，搅拌槽广泛应用于石油、化工、食品、医药、能源、废水处理等领域，因此对搅拌槽反应器内的流体力学和混合传递特性进行研究，对于反应器的设计、放大、操作和优化具有重要意义。虽然有关搅拌槽内流体力学特性和混合特性已有众多报道，但研究体系大多是单相体系。基于此，本文从实验和数值模拟两个方面对多相搅拌槽内的流体力学和混合特性进行了研究。 基于对混合时间定义的思考，本文提出了一种新的定义方法，即体积分数来表征搅拌槽内整体的混合状况，将混合时间定义为示踪实验中示踪剂浓度达到最终平均浓度的流场体积达到一定体积分数所需的时间。在湍流流场数值计算的基础上，求解示踪实验的溶质对流－扩散方程，得到了搅拌槽中示踪剂浓度达到混合均匀标准的体积分数随时间的变化，从而得到了混合时间的数值。主要考察了不同进料位置、不同转速和搅拌桨安装位置以及导流筒对混合时间的影响。本文定义的混合时间避免了主观性的影响，能够很好地表征搅拌槽内整体的混合状况。 沉淀过程是一个非常重要的化工生产过程，因其是一个快速反应过程，所以受微观混合的影响较大。本文首次将CFD-PDF模型用于研究连续搅拌槽内的沉淀过程，系统地考察了搅拌转速、反应物浓度和停留时间等参数对沉淀过程的影响，并与文献实验数据进行了比较，二者吻合很好。 由于气液两相流动的复杂特性，目前研究者对于气液两相混合时间的数值研究主要集中在结构较为简单的反应器。本文首次利用CFD方法研究了气液两相搅拌槽内的混合过程。利用k-ε湍流模型，通过求解两流体模型和浓度输运方程，计算得到了混合时间。主要考察了搅拌转速、进料位置和通气流率对混合时间的影响，通过与实验数据进行比较发现，二者吻合很好。 考虑到微观混合特性对高分子聚合、化工、精细化工、制药等工业过程中涉及的快速复杂反应体系的产物分布、产品质量及操作稳定性等均有非常重要的影响, 而目前针对反应器内气液两相体系的微观混合报道非常少。本文首次以酸碱中和与氯乙酸乙酯的平行竞争反应和空气作为工作体系，对气液两相搅拌槽内的微观混合特性进行了研究，考察了进料方式、搅拌转速、通气流率等因素对离集指数的影响。 |
| 英文摘要 | Stirred tanks are widely used in the process industry for petroleum processing, chemical, food and pharmaceutical processes, energy and waste water treatment because of their large contacting area, high mass and heat transferring efficiency, better operating flexibility and stability, and wide range of usage . It is important to study the fluid flow, mixing, and transport characteristics for the design, scale-up, operation and optimization of stirred tanks. There are many reports of hydrodynamics and mixing characteristics on stirred tanks, but most of them are on single phase systems. So the hydrodynamics and mixing characteristics for multiple-phase systems are experimentally studied and numerically simulated in this dissertation. A new definition of mixing time was proposed based on scrutiny of the traditional definition of mixing time: the fraction of volume of homogenized space was used to index the mixing status in the stirred tank. The new definition of mixing time was that by which the fraction of liquid volume with the tracer concentration entering a narrow band around the final average concentration reaches a certain value. The mixing process in the stirred tank was examined by solving the transport equation of the tracer based on the numerical results of the whole flow field, and then the mixing time was determined. The effects of feed position, impeller speed, impeller clearance and draft tube were investigated. Unlike the traditional mixing time definition, the new definition of mixing time can avoid the subjectivity and reflect accurately the overal mixing status in the stirred tank. Precipitation is an extraordinarily important chemical process involved with a fast reaction thus the micromixing affects significantly the reaction process. The CFD-PDF model was used to investigate the precipitation process in a stirred tank for the first time in this dissertation, and the effects of impeller speed, reactant concentration and residence time were considered. The simulation results were compared with the reported experimental data and good agreement is observed. Due to the complexity of gas-liquid two-phase systems, the simulation study of mixing time of gas-liquid two phase reactors was just concentrated on simple configure reactors. The CFD method was used to investigate the mixing time in a gas-liquid stirred tank for the first time. The effects of impeller speed, feed position and gas flow rate on mixing time were considered and compared with the experimental dada, and good agreement was achieved. The micromixing characteristics are so important to fast reactions in macromolecule polymerization, chemical industry and pharmacy etc. and affect the product distribution, quality and operating stability, but there are only a few reports of micromixing in gas-liquid two phase systems. A pair of competitive parallel reactions, the neutralization of sodium hydroxide by hydrochloric acid and the alkaline hydrolysis of ethyl chloracetate, were used as the test reactions to investigate the micro-mixing in a gas-liquid stirred tank. The effects of feed mode, impeller speed and gas flow rate on segregation index were experimentally examined. |
| 语种 | 中文 |
| 公开日期 | 2013-09-13 |
| 页码 | 155 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1193]  |
| 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 | 张庆华. 搅拌槽内宏观混合和微观混合的实验研究与数值模拟[D]. 过程工程研究所. 中国科学院过程工程研究所. 2009. |
入库方式： OAI收割
来源：过程工程研究所
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