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

本研究方案的最初目标是开发和应用多个气泡系统动态变形界面上反应传质的直接数值模拟方法。为了以可接受的计算费用解决边界层区域分辨率要求明显不同造成的这一多尺度问题，申请人在第一个供资期间制定了两种混合方法。在第二个资助期，重点应放在一种专门的混合方法的应用上，以便审查反应工程方面。基本思想依赖于将气泡流体力学的输运方程和物质的输运方程分开，以便实现更高的分辨率，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，在高Péclet-(Reynolds-and Schmidt-)和Hatta数时，浓度梯度通常变得非常陡峭，而求解两相流体动力学的计算成本仍然是现实的。新方法的开发和应用是使用OpenFOAM，一个免费的开源C++计算连续介质力学库。通过在优先程序的第二个资助期使用该方法，即通过直接数值模拟，将解决两个中心方面：(I)获得详细的知识和对两相流体力学、传输过程和化学反应之间的复杂相互作用的透彻理解，以及(Ii)分析和澄清这些过程关于传质强化的定性机理和定量影响，对于竞争性(对混合敏感的)原型反应和混凝土测试反应，液体的利用率以及产品分布和选择性都进行了额外的实验研究。为了实现这些目标，与化学和过程工程的同事进行密集的联合合作是至关重要的。此外，申请人应与其他参与模拟小组进一步共同阐述数值基准，特别是使用OpenFOAM为泰勒气泡的反应性传质提供本地反应工程数据。

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.