Euler-Euler-Modeling of reactive flow in bubble columns

在本项目中，化学反应的闭合模型以及相关的质量传输将包括在泡状流的欧拉-欧拉描述中。这种方法可以捕捉气泡数密度和气泡大小的不均匀分布，以及鼓泡塔尺度上浓度和流场的局部差异。通过这种方式，直到工业设备或其部件的尺寸的计算成为可能。为了实现这一点，闭合模型必须考虑单个气泡尺度上的输运过程和化学反应。针对纯流体动力学过程，HZDR定义了一套闭合模型，其中包括气泡与周围液体之间的动量交换、气泡诱导的湍流以及气泡的合并和破裂。通过与包括鼓泡塔实验在内的多个实验数据集的比较，验证了完整的模型，从而为预测鼓泡塔的流体动力学行为提供了一个强大的模型。在此基础上，物质从气泡进入液体的闭合模型现在将以类似的方式进行验证。为此，对不同模型变量的模拟结果与合适的实验数据进行了比较。这方面的一个重要参数是化学反应的时间尺度：快速反应主要发生在气泡周围的边界层，而慢反应主要发生在液体内部。此外，反应的类型也起着重要作用。考虑到这些影响的充分验证的闭合模型目前还不存在。传质和流体动力学耦合在一起，因为吸收的结果是气泡尺寸的减小，而气泡尺寸又是决定流动的重要因素。通过这种耦合，可能会产生有趣的、但很少被探索的现象。例如，如果气泡尺寸沿鼓泡塔的高度下降到某一值以下，则可能发生从非均相鼓泡塔到均相鼓泡塔的转变。伴随而来的是气体分布和流型的质的变化。对这种相互关系的研究扩展了对反应性气泡流动的基本理解。SPP1740的框架为实现这些目标提供了极好的可能性，因为在没有或有同时化学反应的情况下，气泡上发生的传质模型可以从SPP中其他小组的工作中提取出来。同样，可以使用对SPP中合作伙伴的实验室规模实验调查来验证模型，而反过来模拟可能有助于规划未来的实验。

In the present project closure models for chemical reaction as well as the associated mass transport will be included in the Euler-Euler description of bubbly flows. This approach allows to capture inhomogeneous distributions of bubble number density and bubble size as well as local differences in concentration and flow fields on the scale of the bubble column. In this way calculations up to the size of industrial equipment or components thereof become feasible. Transport processes and chemical reactions on the scale of individual bubbles have to be taken into account by closure models to achieve this.Concerning purely fluid dynamical processes, a set of closure models has been defined at HZDR which encompasses the exchange of momentum between the bubbles and the surrounding liquid, the bubble-induced turbulence as well as bubble-coalescence and -breakup. The complete model was validated by comparison to a number of experimental data sets, including also bubble column experiments, so that a powerful model for the prediction of the fluid dynamical behavior of bubble columns is available.On this basis, closure models for the transfer of matter from the gas bubbles into the liquid shall now be qualified in an analogous way. To this end, simulation results obtained for different model variants are compared to suitable experimental data. An important parameter in this respect is the time scale of the chemical reaction: fast reactions take place mostly in the boundary layer around the bubbles, slow reactions in contrast mostly in the interior of the liquid phase. In addition, the type of the reaction plays an important role. Sufficiently validated closure models taking into account these kind of effects are not available yet.Mass transfer and fluid dynamics are coupled together, because a consequence of the absorption is a decrease of bubble size, which in turn is substantial in determining the flow. From this coupling interesting and yet only little explored phenomena may result. If for example the bubble size falls below a certain value along the height of the bubble column, a transition from the heterogeneous to the homogeneous bubble column regime may occur. This is accompanied by a qualitative change of both the distribution of gas and the flow pattern. Investigation of this kind of interrelations extends the fundamental understanding of reactive bubbly flows.The frame of the SPP1740 offers excellent possibilities to reach these goals since models for the mass transfer taking place at bubbles without or with simultaneous chemical reaction can be extracted from the work of other groups in the SPP. In a similar vein, lab scale experimental investigations of partners in the SPP can be used to validate the models, while the other way round simulations may aid the planning of future experiments.