Mixing and Reaction Kinetics in Porous Media: An Experimental Pore Scale Quantification
Mixing and Reaction Kinetics in Porous Media: An Experimental Pore Scale Quantification
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DOI：
10.1021/es403105b
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发表时间：
2014-01-07
影响因子：
11.4
通讯作者：
Meheust, Yves
中科院分区：
文献类型：
--
作者：
de Anna, Pietro;Jimenez-Martinez, Joaquin;Meheust, Yves
我们提出了一个新的实验设置，以表征混合和反应在多孔介质中的传输具有高空间分辨率在孔隙尺度。类似的多孔介质由一个He le-Shaw单元组成，该单元包含由软光刻构建的单层圆柱形固体颗粒。一方面，使用荧光示踪剂进行局部、孔内、保守浓度场的测量。另一方面，考虑到当A取代B时发生的快速双分子反应A + B -> C，我们使用荧光反应从孔尺度反应速率的空间分辨测量来量化产物形成速率。该设置提供了一个动态测量的局部浓度场超过3个数量级，并允许调查范围广泛的Peclet和Damkohler数通过改变细胞内的流速和局部反应速率。我们用它来研究A和B之间的反应前沿的动力学。虽然对流扩散（菲克）理论，应用在连续尺度，预测的累积质量的产品C的M-C α根t的缩放，实验表现出两个不同的制度，其中产生的质量M-C演变速度比菲克行为。在这两个制度的前端速率的产品形成的反应物之间的混合界面的几何形状控制。最初，入侵的溶质组织在拉伸薄片和反应是有限的质量传递通过薄片边界。在较长的时间前演变成第二个制度，在那里lamebrases合并，形成一个混合区，其时间演变控制的产品形成的速度。在第二种情况下，C的产生质量与由保守物种限定的混合区的体积成正比。这个有趣的属性确实是从反应和保守的数据的比较验证。因此，对于这两个制度，直接测量的空间分布的孔尺度反应速率和保守的组分浓度被证明是至关重要的，以了解偏离的Fickian缩放以及量化的基本机制，管理的混合和反应动力学在孔尺度。
We propose a new experimental set up to characterize mixing and reactive transport in porous media with a high spatial resolution at the pore scale. The analogous porous medium consists of a He le-Shaw cell containing a single layer of cylindrical solid grains built by soft lithography. On the one hand, the measurement of the local, intrapore, conservative concentration field is done using a fluorescent tracer. On the other hand, considering a fast bimolecular reaction A + B -> C occurring as A displaces B, we quantify the rate of product formation from the spatially resolved measurement of the pore scale reaction rate, using a chemiluminescent reaction. The setup provides a dynamical measurement of the local concentration field over 3 orders of magnitude and allows investigating a wide range of Peclet and Damkohler numbers by varying the flow rate within the cell and the local reaction rate. We use it to study the kinetics of the reaction front between A and B. While the advection-dispersion (Fickian) theory, applied at the continuum scale, predicts a scaling of the cumulative mass of product C as M-C alpha root t, the experiments exhibit two distinct regimes in which the produced mass M-C evolves faster than the Fickian behavior. In both regimes the front rate of product formation is controlled by the geometry of the mixing interface between the reactants. Initially, the invading solute is organized in stretched lamellae and the reaction is limited by mass transfer across the lamella boundaries. At longer times the front evolves into a second regime where lamellae coalesce and form a mixing zone whose temporal evolution controls the rate of product formation. In this second regime, the produced mass of C is directly proportional to the volume of the mixing zone defined from conservative species. This interesting property is indeed verified from a comparison of the reactive and conservative data. Hence, for both regimes, the direct measurement of the spatial distribution of the pore scale reaction rate and conservative component concentration is shown to be crucial to understanding the departure from the Fickian scaling as well as quantifying the basic mechanisms that govern the mixing and reaction dynamics at the pore scale.