Chen Michael A, Lee Sang Hyun, Kang Peter K
Department of Earth and Environmental Sciences, College of Science and Engineering, University of Minnesota, Minneapolis, MN 55455.
Saint Anthony Falls Laboratory, College of Science and Engineering, University of Minnesota, Minneapolis, MN 55414.
Proc Natl Acad Sci U S A. 2024 Dec 10;121(50):e2407145121. doi: 10.1073/pnas.2407145121. Epub 2024 Dec 5.
Solute transport and biogeochemical reactions in porous and fractured media flows are controlled by mixing, as are subsurface engineering operations such as contaminant remediation, geothermal energy production, and carbon sequestration. Porous media flows are generally regarded as slow, so the effects of fluid inertia on mixing and reaction are typically ignored. Here, we demonstrate through microfluidic experiments and numerical simulations of mixing-induced reaction that inertial recirculating flows readily emerge in laminar porous media flows and dramatically alter mixing and reaction dynamics. An optimal Reynolds number that maximizes the reaction rate is observed for individual pore throats of different sizes. This reaction maximization is attributed to the effects of recirculation flows on reactant availability, mixing, and reaction completion, which depend on the topology of recirculation relative to the boundary of the reactants or mixing interface. Recirculation enhances mixing and reactant availability, but a further increase in flow velocity reduces the residence time in recirculation, leading to a decrease in reaction rate. The reaction maximization is also confirmed in a flow channel with grain inclusions and randomized porous media. Interestingly, the domain-wide reaction rate shows a dramatic increase with increasing Re in the randomized porous media case. This is because fluid inertia induces complex three-dimensional flows in randomized porous media, which significantly increases transverse spreading and mixing. This study shows how inertial flows control reaction dynamics at the pore scale and beyond, thus having major implications for a wide range of environmental systems.
多孔和裂隙介质流中的溶质输运和生物地球化学反应受混合作用控制，诸如污染物修复、地热能生产和碳封存等地下工程作业也是如此。多孔介质流通常被认为是缓慢的，因此流体惯性对混合和反应的影响通常被忽略。在此，我们通过微流体实验以及对混合诱导反应的数值模拟表明，惯性再循环流很容易在层流多孔介质流中出现，并显著改变混合和反应动力学。对于不同尺寸的单个孔隙喉道，观察到存在一个使反应速率最大化的最佳雷诺数。这种反应最大化归因于再循环流对反应物可用性、混合和反应完成的影响，这取决于再循环相对于反应物边界或混合界面的拓扑结构。再循环增强了混合和反应物可用性，但流速的进一步增加会减少再循环中的停留时间，导致反应速率降低。在具有颗粒夹杂物的流道和随机多孔介质中也证实了反应最大化。有趣的是，在随机多孔介质的情况下，全区域反应速率随雷诺数增加而显著增加。这是因为流体惯性在随机多孔介质中诱导了复杂的三维流动，这显著增加了横向扩散和混合。本研究展示了惯性流如何在孔隙尺度及更大尺度上控制反应动力学，从而对广泛的环境系统具有重要意义。
