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Transverse dispersion of non-reactive tracers in porous media: A new nonlinear relationship to predict dispersion coefficients

机译:非反应示踪剂在多孔介质中的横向弥散:预测弥散系数的新非线性关系

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Assessing the potential of natural attenuation in groundwater relies on the ability to predict and quantify the processes that occur in contaminant plumes. Transverse dispersion is a significant mass transfer mechanism for mixing of electron acceptors and donors and thus may control the lengths of steady state plumes.rnLaboratory experiments were carried out using a 2-dimensional acrylic glass tank filled with glass beads, quartz sand and field site material as porous media. Flow velocities and grain sizes were varied in order to cover a large range of Peclet numbers including typical field scenarios. The laboratory study was extended by a comprehensive literature search to compare the new results with earlier work. As a result we propose a new empirical relationship for prediction of transverse dispersion coefficients (D_t) which is based on the Peclet number (Pe). This new relationship indicates a nonlinear dependency on the flow velocity (v_a) and grain size (d), namely a relative decrease of the dispersion coefficient with increasing flow velocity in relatively fast flowing water: D_t/D_(aq)=D_p/D_(aq) + 0.28(Pe)~(0.72) (with Pe = v_ad/D_(aq); D_(aq) and D_p denote the aqueous and pore diffusion coefficients, resp.).
机译:评估地下水中自然衰减的潜力取决于预测和量化污染物羽流中过程的能力。横向分散是电子受体和供体混合的重要传质机理,因此可以控制稳态羽流的长度。使用填充有玻璃珠,石英砂和现场材料的二维丙烯酸玻璃罐进行实验室实验。作为多孔介质。流速和晶粒尺寸各不相同,以涵盖大范围的佩克利特数,包括典型的现场情况。通过全面的文献检索扩展了实验室研究,以将新结果与早期工作进行比较。结果,我们提出了一个新的经验关系,用于基于Peclet数(Pe)预测横向色散系数(D_t)。这种新的关系表明了对流速(v_a)和晶粒尺寸(d)的非线性依赖性,即在相对快速流动的水中,分散系数随流速的增加而相对降低:D_t / D_(aq)= D_p / D_( aq)+ 0.28(Pe)〜(0.72)(其中Pe = v_ad / D_(aq); D_(aq)和D_p分别表示水和孔扩散系数)。

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