Mixing structures in bubble wakes of single bubbles and bubble swarms and their influence on gas-liquid mass transfer and chemical reactions

单气泡和气泡群气泡尾流的混合结构及其对气液传质和化学反应的影响

• 批准号: 517064495
• 负责人: Professorin Dr. Alexandra von Kameke
• 金额: --
• 依托单位: Institut für Mehrphasenströmungen V-5
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/517064495?language=en
• 关键词: Mixing; structures; bubble; wakes; single

The main objective of this proposal is to unveil how mixing structures in the wakes of freely rising single bubbles and in bubble swarms can be incorporated into compact mass transfer correlations for process engineering. In this way the impact of the wakes on chemical reactions can be estimated more easily. The knowledge about the detailed mass transfer is crucial to produce a vast proportion of bulk chemicals used in everyday life that are synthesized in gas-liquid reactions like hydrogenation, oxidation, or chlorination. Furthermore, contained high gas concentrations in bubble wakes can also be potentially harmful to microorganisms and enzymes in gassed reactors leading to a substrate inhibition. To predict how much gas is transferred from a bubble to a surrounding liquid the mass transfer coefficient (or the nondimensionalized Sherwood number )has to be determined. Todays mass transfer models (Sherwood correlations) either build on the two-film theory, on the penetration theory, or on the surface-renewal theory with varying parameters in dependence on bubble relative velocity to the surrounding liquid and laminar or turbulent surrounding flow conditions. Adapted models exist to account for the effect of surfactants onto the mass transfer. All theories assume, however, that once the gas is dissolved in the liquid phase it gets immediately well mixed and that all fluid parcels passing the bubble interface experience the same conditions in the bubble wake once they leave the bubble surface. This picture neglects effects of a heterogeneous concentration wake that will likely influence a reaction taking place close to the bubble interface and in the bubble wake for small to intermediate Hatta numbers as according to Levenspiel. So far, the details of the structure of the mixing in the bubble wake are not considered for mass transfer correlations. In this research proposal, the Lagrangian coherent structures (LCS) in the bubble wake of 3D freely rising bubbles and bubble swarms in stagnant liquid will be analyzed by evaluating 4D-PTV measurements using recently developed mathematical tools stemming from dynamical systems theory. Additionally, a quantitative evaluation of the concentration of the dissolved gas will be obtained using Time Resolved Laser Induced Fluorescence (TRS-LIF). The LCS will be compared to the concentration wakes and both measurements supply input for the development of new Sherwood correlations that incorporate the effect of coherent flow structures in bubble wakes.

该提案的主要目标是揭示如何将自由上升的单个气泡和气泡群中的混合结构纳入过程工程的紧凑传质关联中。通过这种方式，可以更容易地估计尾流对化学反应的影响。有关详细传质的知识对于生产日常生活中使用的大量化学品至关重要，这些化学品是在氢化、氧化或氯化等气液反应中合成的。此外，气泡尾流中含有的高浓度气体也可能对充气反应器中的微生物和酶有害，导致底物抑制。为了预测有多少气体从气泡转移到周围液体，必须确定传质系数（或无量纲舍伍德数）。当今的传质模型（舍伍德相关性）要么建立在两膜理论、渗透理论或表面更新理论的基础上，其参数取决于气泡与周围液体的相对速度以及层流或湍流的周围流动条件。存在适应模型来解释表面活性剂对传质的影响。然而，所有理论都假设，一旦气体溶解在液相中，它就会立即充分混合，并且一旦离开气泡表面，穿过气泡界面的所有流体块都会在气泡尾流中经历相同的条件。根据 Levenspiel 的说法，这张图片忽略了异质浓度尾流的影响，这种效应可能会影响气泡界面附近以及小到中等哈塔数的气泡尾流中发生的反应。到目前为止，气泡尾流中混合结构的细节尚未考虑到传质相关性。在本研究提案中，将通过使用最近开发的源于动力系统理论的数学工具评估 4D-PTV 测量来分析静止液体中 3D 自由上升气泡和气泡群的气泡尾流中的拉格朗日相干结构 (LCS)。此外，将使用时间分辨激光诱导荧光（TRS-LIF）对溶解气体的浓度进行定量评估。 LCS 将与浓度尾流进行比较，两种测量结果都为新舍伍德关联式的开发提供了输入，该关联式结合了气泡尾流中相干流结构的影响。