Effect of NAPL film stability on the dissolution of residual wetting NAPL in porous media: A pore-scale modeling study
Effect of NAPL film stability on the dissolution of residual wetting NAPL in porous media: A pore-scale modeling study
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DOI：
10.1016/j.advwatres.2005.03.025
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发表时间：
2007-02
影响因子：
4.7
通讯作者：
Weishu Zhao;M. Ioannidis
中科院分区：
文献类型：
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作者：
Weishu Zhao;M. Ioannidis
干旱不仅深刻影响天然土壤中残留NAPL污染物的初始分布，而且影响其随后在流动水相中的溶解。在NAPL优先润湿的条件下，残余NAPL相存在于较小的孔隙内，并以连续的角丝和孔壁上的厚膜的形式存在。这样的膜暴露出比由相同量的非润湿NAPL暴露的大得多的用于传质的界面面积。重要的是，毛细管和水力连续性的NAPL长丝和厚膜是必不可少的维持NAPL-水逆流过程中的NAPL溶解在流动的地下水的机制，保持，甚至增加传质的界面面积。持续溶解导致NAPL膜逐渐变薄，其可能变得不稳定并破裂，从而导致以簇形式的残留NAPL断开。使用孔隙网络模拟器，我们证明，NAPL膜的不稳定性大大修改残余NAPL的微观配置，因此，局部流体动力学条件和界面面积的传质，与宏观上可观察到的量，如水的流出物浓度和分数NAPL恢复随时间的伴随效应。这些结果强烈表明，NAPL膜的分离压力可能会产生一个重要的，迄今为止未解释的，控制在油湿系统中的残留NAPL相的溶解行为。
Wettability profoundly affects not only the initial distribution of residual NAPL contaminants in natural soils, but also their subsequent dissolution in a flowing aqueous phase. Under conditions of preferential NAPL wettability, the residual NAPL phase is found within the smaller pores and in the form of continuous corner filaments and thick films on pore walls. Such films expose a much greater interfacial area for mass transfer than would be exposed by the same amount of non-wetting NAPL. Importantly, capillary and hydraulic continuity of NAPL filaments and thick films is essential for sustaining NAPL–water counterflow during the course of NAPL dissolution in flowing groundwater—a mechanism which maintains and even increases the interfacial area for mass transfer. Continued dissolution results in gradual thinning of the NAPL films, which may become unstable and rupture causing disconnection of the residual NAPL in the form of clusters. Using a pore network simulator, we demonstrate that NAPL film instability drastically modifies the microscopic configuration of residual NAPL, and hence the local hydrodynamic conditions and interfacial area for mass transfer, with concomitant effects on macroscopically observable quantities, such as the aqueous effluent concentration and the fractional NAPL recovery with time. These results strongly suggest that the disjoining pressure of NAPL films may exert an important, and hitherto unaccounted, control on the dissolution behaviour of a residual NAPL phase in oil wet systems.