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arXiv 2306.05018physics.flu-dyn
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孔隙尺度混沌混合对 Darcy 尺度反应速率的影响

Impact of pore-scale chaotic mixing on Darcy-scale reaction rates

Satoshi Izumoto, Gauthier Rousseau, Tanguy Le Borgne, Joris Heyman

AI总结:

本文通过折射率匹配三维多孔介质的化学发光实验,揭示孔隙尺度混沌混合与 Darcy 尺度加速度共同影响反应速率,并提出含薄层折叠和浓度梯度的机制模型。

摘要:

当孔隙尺度不完全混合起作用时,多孔介质中反应性输运的预测仍然具有挑战性。以往的实验研究主要通过在均匀流场中可视化反应产物或反应物来考察多孔介质中的化学反应。然而,如果不考虑反应产物和反应物的输运,就无法获得推断孔隙空间中反应机制所必需的局部反应速率。因此,相关解释一直难以明确。我们在零加速度和恒定加速度流场下,利用折射率匹配的三维多孔介质中的化学发光对反应速率场进行可视化,以研究孔隙尺度混沌混合和 Darcy 尺度流体加速度如何校正反应性输运。我们发现,在恒定加速度场中,反应速率从上游到下游持续增加;而在零加速度场中,反应速率仅在上游区域增加。弥散速率与混合界面尺寸之比决定了加速度的这种效应。此外,实验结果表明,与假设孔隙空间中完全混合的数值模拟相比,反应速率对速度具有更强的依赖性。为解释这一点,我们提出了一个机制模型,其中包含由混沌混合导致的孔隙尺度薄层折叠,以及抵抗压缩的孔隙尺度浓度梯度。这种孔隙尺度机制与实验观察到的反应速率在空间上的变化相一致。这些结果为认识多孔介质中反应性输运的潜在机制提供了新的见解。

英文摘要:

Prediction of reactive transport in porous media remains challenging when pore scale incomplete mixing is at play. Previous experimental studies investigated chemical reactions in porous media by visualizing reaction product or reactants mostly in uniform flow. However, the local reaction rate, which is necessary to infer mechanisms of reaction in pore space, could not be obtained without considering transport of reaction products and reactants. Thus, the interpretation remained elusive. We visualized the reaction rate field using chemiluminescnece within index-matched 3D porous media under zero acceleration and constant acceleration flow fields to investigate how pore scale chaotic mixing and Darcy scale fluid acceleration rectify reactive transport. We found that the reaction rate kept increasing from upstream to downstream in constant acceleration field, whereas it increased only at the upstream zone in zero acceleration field. The ratio of dispersion rate and size of the mixing interface determined such an effect of acceleration. Moreover, the experimental results showed stronger dependency of reaction rate on velocity compared to the numerical simulations that assume complete mixing in pore space. To explain this, we suggested the mechanistic model that includes the pore scale folding of lamellae due to chaotic mixing and the pore scale concentration gradients against compression. Such a pore scale mechanism was consistent with the experimentally observed change in reaction rate over the space. These results give new insights on underlying mechanisms of reactive transport in porous media.

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