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输运将包括在泡状流的欧拉-欧拉描述中。这种方法允许捕获气泡数密度和气泡尺寸的不均匀分布，以及在鼓泡塔的尺度上的浓度和流场的局部差异。以这种方式，直到工业设备或其部件的尺寸的计算变得可行。运输过程和化学反应的规模上的单个气泡必须考虑到封闭models.Concerning纯流体动力学过程，一组封闭模型已被定义在HZDR，其中包括交换的气泡和周围的液体，气泡引起的湍流以及气泡聚结和破裂之间的动量。通过与大量实验数据集（包括鼓泡塔实验）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，物质从气泡转移到液体中的封闭模型现在将以类似的方式进行验证。为此，不同的模型变量获得的模拟结果进行比较，以适当的实验数据。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中，相反，缓慢反应主要发生在液相内部。 此外，反应的类型也起着重要的作用。考虑到这些影响的封闭模型还没有得到充分验证。质量传递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，这反过来又是决定流量的重要因素。从这种耦合中可能会产生有趣但很少探索的现象。如果例如气泡尺寸福尔斯沿泡罩塔的高度下降到沿着某一值以下，则可能发生从非均相到均相泡罩塔状态的转变。这伴随着气体分布和流动模式的质的变化。这种相互关系的研究扩展了对反应性泡状流的基本理解。SPP 1740的框架为实现这些目标提供了很好的可能性，因为气泡中发生的传质模型可以从SPP中其他小组的工作中提取出来，无论是否同时发生化学反应。在类似的静脉，实验室规模的实验研究合作伙伴在SPP可以用来验证模型，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.