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.

该提案的主要目的是揭示如何将单个气泡和气泡群中的混合结构纳入工艺工程的紧凑型传质相关性中。这样，唤醒对化学反应的影响就可以更容易估计。关于详细传质的知识对于在日常生活中生产大量的大量化学物质至关重要，这些化学物质是在氢化，氧化或氯化等气体液体反应中合成的。此外，气泡唤醒中的气体浓度很高也可能对导致底物抑制的气体反应器中的微生物和酶有害。为了预测多少气体从气泡转移到周围的液体，必须确定传质系数（或非量化的舍伍德数）。今天的传质模型（Sherwood相关性）要么建立在两膜理论，穿透理论的基础上，要么基于表面续订理论，具有不同参数，以依赖于气泡相对速度与周围液体和层流或湍流周围流动条件的相对速度。存在改编的模型，以说明表面活性剂对传质的影响。但是，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，并且所有流体包裹经过气泡界面后，一旦它们离开气泡表面，就会在气泡唤醒中经历相同的条件。这张图片忽略了异质浓度唤醒的影响，这可能会影响靠近气泡界面的反应，并且在气泡唤醒中，对于levenspiel的说法，对于中间的hatta数字，对小气泡的唤醒。到目前为止，对于传质相关性，气泡唤醒中混合的结构的细节尚未考虑。在这项研究建议中，将通过使用最新开发的数学工具来评估来自动力学系统理论的新近开发的数学工具，通过评估4D-PTV测量值，通过评估4D-PTV测量值，通过评估4D-PTV测量值来分析Lagrangian连贯结构（LCS（LCS）和停滞液体中的气泡群。另外，将使用时间分辨激光诱导的荧光（TRS-LIF）获得对溶解气体浓度的定量评估。 LCS将与浓度唤醒和两个测量供应输入进行比较，以开发新的Sherwood相关性，这些相关性结合了气泡唤醒中相干流量结构的影响。