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首页> 外文期刊>Journal of Contaminant Hydrology >The effect of multicomponent diffusion on NAPL dissolution from spherical ternary mixtures
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The effect of multicomponent diffusion on NAPL dissolution from spherical ternary mixtures

机译：多组分扩散对NAPL从球形三元混合物中溶解的影响

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This paper investigates the dissolution characteristics of ternary nonaqueous phase liquid (NAPL) mixtures with the goal of comparing the relative contributions of multicomponent (inira-NAPL) diffusion, film transfer and thermodynamic nonideality. These contributions are compared at the pore scale and intermediate scale (several centimeters downstream from the source). Trichloroethene (TCE), tetrachloroethene (PCE) and 1,1,1 -trichloroethane (TCA) were selected to model a reasonably ideal mixture; TCE, PCE and octanol were selected as a relevant nonideal mixture. A multicomponent diffusion-based dissolution model incorporating hydrodynamic theory was formulated to estimate intra-NAPL concentration gradients and associated aqueous interfacial concentrations for ideally shaped (spherical) NAPL blobs. Pore scale dissolution times for this model were compared to those generated using the conventional well-mixed NAPL dissolution model, applying the same film transfer boundary condition in both cases. Activity coefficients (spatially and temporally variable for the diffusion model, temporally variable for the well-mixed model) were estimated using UNIFAC. NAPL interfacial concentration histories generated using the pore scale models were used as input in a three-dimensional groundwater transport model (MT3DMS) to compare downstream concentration distributions. For the relatively large NAPL bodies simulated (r = 0.6 cm), intra-NAPL diffusion effects were found to be significant at the pore scale and were strongly impacted by the mixture's thermodynamic ideality. At the intermediate scale, and for the conditions tested, modest differences in the simulations suggested that intra-NAPL diffusion effects would be negligible compared to those associated with mixture composition uncertainty, dissolution rate processes related to NAPL-induced permeability effects and hydrodynamic issues associated with flow field heterogeneity.
机译：本文研究了三元非水相液体（NAPL）混合物的溶解特性，目的是比较多组分（inira-NAPL）扩散，薄膜转移和热力学非理想性的相对贡献。这些贡献在孔尺度和中等尺度（源下游几厘米）处进行比较。选择三氯乙烯（TCE），四氯乙烯（PCE）和1,1,1-三氯乙烷（TCA）来模拟合理理想的混合物；选择TCE，PCE和辛醇作为相关的非理想混合物。制定了一个基于流体动力学理论的基于多组分扩散的溶出模型，以估算理想形状（球形）NAPL斑点的NAPL浓度梯度和相关的水界面浓度。在两种情况下，采用相同的膜转移边界条件，将该模型的孔尺度溶出时间与使用常规充分混合的NAPL溶出模型产生的溶出时间进行比较。使用UNIFAC估算活动系数（扩散模型的时空变化，充分混合模型的时空变化）。使用孔隙尺度模型生成的NAPL界面浓度历史记录被用作三维地下水传输模型（MT3DMS）的输入，以比较下游浓度分布。对于模拟的相对较大的NAPL体（r = 0.6 cm），发现NAPL内的扩散效应在孔尺度上很显着，并且受到混合物热力学理想性的强烈影响。在中等规模和测试条件下，模拟中的适度差异表明，与混合物成分不确定性，与NAPL引起的渗透性效应有关的溶出速率过程以及与NAPL相关的流体力学问题有关的NAPL扩散效应相比，可以忽略不计。流场异质性。

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