Yoon Hongkyu, Kim Joong Hoon, Liljestrand Howard M, Khim Jeehyeong
Department of Civil and Environmental Engineering, Korea University, Sungbuk-gu, Seoul, South Korea.
J Contam Hydrol. 2002 Jan;54(1-2):1-18. doi: 10.1016/s0169-7722(01)00164-4.
The effect of water content on the volatilization of nonaqueous phase liquid (NAPL) in unsaturated soils was characterized by one-dimensional venting experiments conducted to evaluate the lumped mass transfer coefficient. An empirical correlation based upon the modified Sherwood number, Peclet number, and normalized mean grain size was used to estimate initial lumped mass transfer coefficients over a range of water content. The effects of water content on the soil vapor extraction SVE process have been investigated through experimentation and mathematical modeling. The experimental results indicated that a rate-limited NAPL-gas mass transfer occurred in water-wet soils. A severe mass transfer limitation was observed at 61.0% water saturation where the normalized effluent gas concentrations fell below 1.0 almost immediately, declined exponentially from the initiation of venting, and showed long tailing. This result was attributed to the reduction of interfacial area between the NAPL and mobile gas phases due to the increased water content. A transient mathematical model describing the change of the lumped mass transfer coefficient was used. Simulations showed that the nonequilibrium mass transfer process could be characterized by the exponent beta, a parameter which described the reduction of the specific area available for NAPL volatilization. The nonequilibrium mass transfer limitations were controlled by the soil mean grain size and pore gas velocity, were well described by beta values below 1.0 at low water saturation, and were well predicted with beta values greater than 1.0 at high water saturation.
通过进行一维通风实验来评估集总传质系数，从而表征含水量对非饱和土壤中非水相液体（NAPL）挥发的影响。基于修正的舍伍德数、佩克莱数和归一化平均粒径的经验关联式，用于估算一系列含水量范围内的初始集总传质系数。通过实验和数学建模研究了含水量对土壤气相抽提（SVE）过程的影响。实验结果表明，在水湿土壤中发生了速率受限的NAPL-气体传质。在水饱和度为61.0%时观察到严重的传质限制，此时归一化废气浓度几乎立即降至1.0以下，从通风开始呈指数下降，并呈现长拖尾现象。该结果归因于含水量增加导致NAPL与流动气相之间的界面面积减小。使用了一个描述集总传质系数变化的瞬态数学模型。模拟表明，非平衡传质过程可以用指数β来表征，β是一个描述可用于NAPL挥发的比表面积减小的参数。非平衡传质限制受土壤平均粒径和孔隙气体速度控制，在低水饱和度下β值低于1.0时能很好地描述，在高水饱和度下β值大于1.0时能很好地预测。
