Effects of Pore-Scale Heterogeneity on Macroscopic NAPL Dissolution Efficiency: A Two-Scale Numerical Simulation Study
Effects of Pore-Scale Heterogeneity on Macroscopic NAPL Dissolution Efficiency: A Two-Scale Numerical Simulation Study
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DOI：
10.1029/2019wr026035
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发表时间：
2019-11-10
影响因子：
5.4
通讯作者：
Babaei, Masoud
中科院分区：
文献类型：
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作者：
Aminnaji, Morteza;Rabbani, Arash;Babaei, Masoud
非水相液体（NAPL）的相间传质系数是预测污染物在多孔介质中迁移的重要参数。虽然文献提供了关于该系数在连续尺度上对不同参数的依赖性的有价值的见解（例如，污染物饱和度和达西速度），孔隙尺度非均质性对宏观溶解系数的影响很少受到关注。在这项工作中，一个三维孔隙尺度模型的开发，以模拟不同的合成孔网络结构与各种孔径相关长度的相间传质。孔隙网络模型模拟了固定的NAPL通过水-NAPL界面的扩散喉道溶解到水中（单相）。研究了孔隙网络空间相关非均匀性、NAPL饱和度/分布和水相流速对NAPL传质系数和水-NAPL界面表面积的影响。这些宏观性质，然后在二维连续尺度域中使用，所述二维连续尺度域通过在x和y方向上连接20 × 20孔网络形成。结果突出了孔隙尺度异质性对NAPL分布的影响，并随后对溶解速率的影响（即，溶解系数）。孔隙半径的不相关分布始终导致更高的NAPL溶解系数比空间相关的异质性。连续介质模拟的结果表明，只有在很高的流速和达西速度下，相关和非相关孔隙网络形成的区域之间的NAPL溶解速率不同。然而，对于地下水系统中的达西速度的典型值，由于孔隙尺度的非均匀性的传质系数的变化是最小的有效质量去除。
Interphase mass transfer or dissolution coefficient of nonaqueous phase liquids (NAPL) is an important parameter in predicting the transport of contaminant species in porous media. While the literature offers valuable insights into the dependence of this coefficient on different parameters at the continuum scale (e.g., contaminant saturation and Darcy velocity), effects of pore-scale heterogeneity on macroscopic dissolution coefficient have received little attention. In this work a three-dimensional pore-scale model is developed to simulate interphase mass transfer over different synthetic pore network structures with various pore radii correlation lengths. The pore network modeling simulates dissolution of immobile NAPL into water (single phase) through diffusive throats for the water-NAPL interface. The impacts of pore network spatially correlated heterogeneities, NAPL saturation/distribution, and aqueous phase velocity on NAPL mass transfer coefficient and water-NAPL interfacial surface area are studied. These macroscopic properties are then employed in two-dimensional continuum-scale domains formed by concatenating 20 by 20 pore networks in x and y directions. The results highlight the impact of pore-scale heterogeneity on the distribution of NAPL and subsequently on the dissolution rate (i.e., dissolution coefficient). An uncorrelated distribution of pore radii consistently leads to higher NAPL dissolution coefficient than spatially correlated heterogeneity. The results of continuum modeling show that NAPL dissolution rates are only different between domains formed by correlated and uncorrelated pore networks at very high flow rates and Darcy velocities. However, for typical values of Darcy velocity in groundwater systems, variation in mass transfer coefficient due to pore-scale heterogeneity is minimal for efficient mass removal.