Kneafsey Timothy J, Hunt James R
Earth Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720, USA.
J Contam Hydrol. 2004 Feb;68(3-4):143-64. doi: 10.1016/S0169-7722(03)00147-5.
Many non-aqueous phase liquids (NAPLs) are expected to spread at the air-water interface, particularly under non-equilibrium conditions. In the vadose zone, this spreading should increase the surface area for mass transfer and the efficiency of volatile NAPL recovery by soil vapor extraction (SVE). Observations of spreading on water wet surfaces led to a conceptual model of oil spreading vertically above a NAPL pool in the vadose zone. Analysis of this model predicts that spreading can enhance the SVE contaminant recovery compared to conditions where the liquid does not spread. Experiments were conducted with spreading volatile oils hexane and heptane in wet porous media and capillary tubes, where spreading was observed at the scale of centimeters. Within porous medium columns up to a meter in height containing stagnant gas, spreading was less than ten centimeters and did not contribute significantly to hexane volatilization. Water film thinning and oil film pinning may have prevented significant oil film spreading, and thus did not enhance SVE at the scale of a meter. The experiments performed indicate that volatile oil spreading at the field scale is unlikely to contribute significantly to the efficiency of SVE.
许多非水相液体（NAPLs）预计会在空气-水界面处扩散，尤其是在非平衡条件下。在包气带中，这种扩散应会增加传质的表面积以及通过土壤气相抽提（SVE）回收挥发性NAPL的效率。对在水湿表面上扩散的观察得出了一个概念模型，即油在包气带中的NAPL池上方垂直扩散。对该模型的分析预测，与液体不扩散的情况相比，扩散可提高SVE对污染物的回收率。在湿多孔介质和毛细管中对挥发性油己烷和庚烷的扩散进行了实验，在厘米尺度上观察到了扩散现象。在高度达一米且含有停滞气体的多孔介质柱内，扩散小于十厘米，对己烷挥发的贡献不大。水膜变薄和油膜钉扎可能阻止了油膜的显著扩散，因此在一米尺度上并未提高SVE效率。所进行的实验表明，挥发性油在现场尺度上的扩散不太可能对SVE效率有显著贡献。
