Contributions of Pore‐Scale Mixing and Mechanical Dispersion to Reaction During Active Spreading by Radial Groundwater Flow
Contributions of Pore‐Scale Mixing and Mechanical Dispersion to Reaction During Active Spreading by Radial Groundwater Flow
复制标题
DOI：
10.1029/2019wr026276
复制
发表时间：
2020-07
影响因子：
5.4
通讯作者：
R. Neupauer;L. J. Sather;D. Mays;J. Crimaldi;E. J. Roth
中科院分区：
文献类型：
--
作者：
R. Neupauer;L. J. Sather;D. Mays;J. Crimaldi;E. J. Roth
扩散和混合是互补的过程，促进地下水中连续羽流中存在的两种反应性水溶质的反应。扩散重新配置了羽流的几何形状，拉长了羽流之间的界面，而混合则增加了每个羽流占据的含水层的体积，使溶质分子聚集在一起发生反应。由于反应仅发生在两个溶质羽流相互接触的地方，因此驱动羽流之间界面附近的流动和传输的局部机制控制着反应量。这项工作利用羽流的局部特征和羽流界面附近的流场来分析孔隙尺度混合和机械分散对均质含水层中瞬时、不可逆、双分子反应的相对贡献，该含水层由来自井的径向流引起主动扩散。将两种溶质依次引入孔中，形成同心圆形羽流。通过将孔隙空间建模为隔离室和混合室，并在两个室之间进行一级传质，我们允许孔隙空间中溶质的不完全混合。我们开发了两个隔室中溶质浓度的半解析表达式。我们发现，机械分散对反应的相对贡献随着时间的推移而增加，并且由于佩克莱特数、追逐溶质的相对源浓度以及从孔隙空间的隔离室到混合室的传质速率的增加而增加。
Spreading and mixing are complementary processes that promote reaction of two reactive aqueous solutes present in contiguous plumes in groundwater. Spreading reconfigures the plume geometry, elongating the interface between the plumes, while mixing increases the volume of aquifer occupied by each plume, bringing the solute molecules together to react. Since reaction only occurs where the two solute plumes are in contact with each other, local mechanisms that drive flow and transport near the interface between the plumes control the amount of reaction. This work uses local characteristics of the plumes and the flow field near the plume interface to analyze the relative contributions of pore‐scale mixing and mechanical dispersion to instantaneous, irreversible, bimolecular reaction in a homogeneous aquifer with active spreading caused by radial flow from a well. Two solutes are introduced in sequence at the well, creating concentric circular plumes. We allow for incomplete mixing of the solutes in the pore space, by modeling the pore space as a segregated compartment and a mixed compartment with first‐order mass transfer between the two compartments. We develop semi‐analytical expressions for concentrations of the solutes in both compartments. We found that the relative contribution of mechanical dispersion to reaction increases over time and also increases due to increases in the Peclet number, in the relative source concentration of the chasing solute, and in the mass transfer rate from the segregated compartment to the mixed compartment of the pore space.