Direct numerical simulation of multi-physics reactive mass transfer at single and multiple bubbles

单气泡和多气泡多物理反应传质的直接数值模拟

• 批准号: 256739956
• 负责人: Professor Dr. Dieter Bothe
• 金额: --
• 依托单位: Arbeitsbereich Mathematische Modellierung und Analysis (MMA)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2014
• 资助国家: 德国
• 起止时间: 2013-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/256739956?language=en
• 关键词: Direct; numerical; simulation; multi; physics

Reactive mass transfer from rising gas bubbles is the basis for many chemical processes of industrial importance. The necessary process intensification leads to faster process steps and highly concentrated systems. In such two-phase flows with complex local interaction between mass transfer, transport and chemical reactions, additional multi-physics becomes relevant. This includes: volume effects for dissolving bubbles; partly immobilized bubble surfaces due to contamination or additives; ionic species with strong coupling of diffusive fluxes by the intrinsic electrical field, typically leading to local electro-neutrality of the mixture away from the interface; cross-diffusion effects as well as non-idealities in systems of higher concentrations. These complexities add to the multi-scale nature of reactive mass transfer with extremely thin concentration boundary layers due to convection-dominated transport. Besides experimental investigations, a thorough understanding of the local interplay of elementary sub-processes requires numerical simulations based on rigorous mathematical modeling. Our approach employs continuum physics based on the two-phase balances of mass, momentum and species mass. Based on the Volume of Fluid (VOF)-method, we built on our two-scalar approach for 3D Direct Numerical Simulations of mass transfer at gas bubbles. The approach employs a subgrid-scale model which has been strongly improved in the first funding period to allow for realistic Schmidt numbers. In the second funding period, the method will be extended and applied to groups of several bubbles, rising in a computational box with periodic boundary conditions, thus simulation an infinite bubble swarm. Moreover, the existing approach to account for contamination effects will be improved by including a variable Gibbs elasticity to model a partly immobilized bubble interface. Detailed numerical simulations will yield deep insights into reactive mass transfer processes and bulk mixing around bubbles under swarm-like conditions. Within the network of the priority program, these techniques allow to simulate the mass transfer in bubbly flows with different model chemistry, developed in other projects. In particular, the oxidation of iron complexes in methanol and the nitration of iron complexes in water will be considered. In addition to local Sherwood numbers and enhancement, the influence of system parameters on yield and selectivity will be studied. Besides the investigation of freely rising bubble groups/chains, the project will contribute to the guiding measure of Taylor bubbles/flow with simulations including bubble shrinkage and conjugate mass transfer. Finally, the influence of electro-migration of ionic species due to the inherent electrical field will be analyzed. All simulation results for experimental setups will be discussed with the cooperating colleagues. Improved correlations for a scale-reduced modeling will be developed in cooperation within the SPP.

上升气泡的反应传质是许多具有工业重要性的化学过程的基础。必要的工艺强化导致更快的工艺步骤和高度集中的系统。在这样的两相流与复杂的局部相互作用之间的质量传递，运输和化学反应，额外的多物理变得相关。这包括：溶解气泡的体积效应;由于污染或添加剂而部分固定的气泡表面;通过固有电场与扩散通量强耦合的离子物质，通常导致远离界面的混合物的局部电中性;交叉扩散效应以及较高浓度系统中的非理想性。这些复杂性增加了反应传质的多尺度性质，由于对流占主导地位的运输具有极薄的浓度边界层。除了实验研究，深入了解当地的相互作用的基本子过程需要严格的数学建模的基础上的数值模拟。我们的方法采用连续物理的基础上的质量，动量和物种质量的两相平衡。基于VOF方法，我们建立了一个三维气泡传质的直接数值模拟的双标量方法。这一方法采用了一个次网格规模模型，该模型在第一个供资期得到了大力改进，以考虑到现实的施密特数字。在第二个资助期，该方法将被扩展并应用于多个气泡的群体，在具有周期性边界条件的计算箱中上升，从而模拟无限气泡群。此外，现有的方法来考虑污染的影响将得到改善，包括一个可变的吉布斯弹性模型的部分固定的气泡界面。详细的数值模拟将产生深刻的见解反应传质过程和批量混合周围的气泡在蜂群条件下。在优先计划的网络中，这些技术允许用其他项目中开发的不同模型化学模拟气泡流中的传质。特别地，将考虑铁络合物在甲醇中的氧化和铁络合物在水中的硝化。除了局部舍伍德数和增强，系统参数对产率和选择性的影响将被研究。除了自由上升的气泡群/链的调查，该项目将有助于泰勒气泡/流的模拟，包括气泡收缩和共轭传质的指导措施。最后，将分析由于固有电场的离子物种的电迁移的影响。所有实验装置的模拟结果将与合作的同事讨论。将在SPP内部合作开发用于缩小规模建模的改进相关性。