Development and Application of a Direct Numerical Method for Reactive Transport Processes in Bubble Systems

本研究计划的最初目标包括开发和应用一种直接数值模拟方法，用于多泡系统动态变形界面的反应性传质。为了在可接受的计算成本下解决这一多尺度问题，申请人在第一个资助期内开发了两种混合方法。在第二个资助期，重点将放在一种专门的混合方法的应用上，以便研究反应工程方面的问题。其基本思想依赖于气泡流体动力学和物质输运的离散输运方程，以获得更高的分辨率，特别是在浓度边界层内。这种混合方法能够解决边界层中的浓度梯度，而边界层中的浓度梯度在高p<s:1> - （Reynolds-和Schmidt-）和hhatta数下通常会变得非常陡峭，而两相流体动力学求解的计算成本仍然是现实的。这种新方法的开发和应用是在OpenFOAM上完成的，OpenFOAM是一个免费的开源c++计算连续介质力学库。在重点项目的第二个资助期采用该方法，即通过直接数值模拟的方法，解决两个中心问题：(i)对两相流体动力学、输运过程和化学反应之间复杂的相互作用获得详细的知识和透彻的理解；（ii）分析和澄清定性机制以及这些过程在质传递增强、液相利用以及产品分布和选择性方面的定量影响——包括竞争性（混合敏感）原型反应和具体测试反应；并进行了实验研究。为了实现这些目标，与化学和工艺工程方面的同事密切合作是必不可少的。此外，申请人应进一步与其他参与模拟小组共同阐述数值基准，特别是提供使用OpenFOAM进行Taylor气泡反应传质的本地反应工程数据。

The original objectives of this research proposal consist of both the development and application of a method for Direct Numerical Simulation for reactive mass transfer at dynamically deforming interfaces of multiple bubble systems. In order to resolve this multiscale problem, which stems from the significantly different resolution requirements in the boundary layer region, at acceptable computational costs, the applicant has developed two hybrid methods within the first funding period. In the second funding period the focus shall be set on the application of one specialised hybrid method so as to examine reaction engineering aspects. The basic idea relies on discretising transport equations for bubble hydrodynamics and species transport separately in order to allow a higher resolution particularly within the concentration boundary layer. Such a hybrid method enables to resolve the concentration gradient in the boundary layer, which become typically very steep for high Péclet- (Reynolds- and Schmidt-) and Hatta numbers, while computational costs for the solution of two-phase hydrodynamics remain realistic. Development and application of the novel method has been accomplished using OpenFOAM, a free open source C++ library for computational continuum mechanics.By employing the method in the second funding period of the priority program, i.e. by means of Direct Numerical Simulations, two central aspects shall be addressed: (i) gain of detailed knowledge and thorough understanding of the complex interplay among two-phase hydrodynamics, transport processes and chemical reactions, and (ii) analysis and clarification of the qualitative mechanisms and of the quantitative influence of these processes with respect to mass transfer enhancement, liquid phase utilisation as well as product distribution and selectivity - for both competitive (mixing sensitive) prototype reactions and concrete test reactions, which are additionally studied experimentally. In order to achieve these goals intensive joint collaboration with colleagues from chemistry and process engineering is imparative. Moreover, the applicant shall further jointly elaborate on the numerical benchmark with the other participating simulation groups, in particular providing local reaction engineering data for reactive mass transfer at Taylor bubbles using OpenFOAM.