Collaborative Research: Upscaled Mass Transfer Coefficients for Modeling Dissolution of Nonaqueous Phase Liquids in Homogeneous and Heterogeneous Porous Media in the Field

非水相液体(NAPLS)污染地下经常发生。影响NAPL污染场地风险评估和环境管理决策的最重要过程之一是NAPL溶解到地下水中的速度。NAPL溶解控制污染物向下梯度受体的流动，是影响监测系统设计、人类和生态风险评估以及补救策略选择的重要过程。虽然我们对NAPL溶解在这种尺度上的理解相对成熟，但这种理解并不能转化为可靠的场尺度模型，原因有两个：(1)如果试图解决厘米尺度的已知对场尺度模拟很重要的特征，那么使用当前的技术很难解决计算问题；(2)NAPL溶解的放大模型在计算上容易处理，还处于发展阶段。我们在以前的工作中已经证明，溶解过程会导致溶解手指的形成，而溶解手指的形成对溶解速度有很大的影响。由于这些手指在某些情况下可以影响传质速率两个或更多个数量级，因此在场级模拟器中表示这种机制的效果是至关重要的，我们还没有听说过这样的情况。本工作的目标是扩展一种新的基于分形的放大方法，以产生一个适合于更真实的场级模拟的非线性、多尺度传质模型。多尺度模型是地下科学的圣杯，实际上是许多一般科学的圣杯。到目前为止，我们在这方面的努力已经取得了相当大的成功，但影响NAPL溶解指进的几个关键悬而未决的问题仍然存在：NAPL的润湿性、多孔介质的非均质性、溶解开始时NAPL污染的初始空间分布，以及现实的场尺度非均质性模式对手指的发展和演化以及NAPL总体溶解的影响。这项工作将结合创造性的理论、新颖的实验和先进的计算方法来解决这些问题。更广泛的影响：在这项工作中，将开发一个数值模型，并将其用于研究非线性过程，并将条件的范围从实验室可以轻松研究的范围扩展到复杂自然系统的典型条件。实验和计算方法之间的协同作用提供了一个独特的机会，可以吸引高中和本科的工程和理科学生进入令人兴奋的地下水水文学和计算科学世界。为此，我们将根据我们的工作创建两个基于问题的学习(PBL)模块，这两个模块将在特拉华大学(UD)和北卡罗来纳大学(UNC)的本科生中进行测试，并用于一个旨在吸引有天赋的高中生进入工程和科学领域的项目。PBL是以学生为中心或主动学习的成功范例，其优势已被教育心理学的研究牢牢确立。UD已经形成了对PBL的机构关注，并已成为全国和国际PBL的领导者，他们将向全美的教师传播这些PBL教育模块。此外，这项研究将直接涉及来自活跃的研究小组的本科生和研究生，这些研究小组对科学和工程领域中代表性不足的群体有着强烈的承诺和代表性。

0440236ImhoffSubsurface contamination by nonaqueous phase liquids (NAPLs) is a frequent occurrence. One of the most important process influencing risk assessment and environmental management decisions at NAPLcontaminated sites is the rate at which NAPLs dissolve into groundwater. NAPL dissolution controls fluxes of contaminants to down-gradient receptors, and is a significant process affecting the design of monitoring systems, the assessment of human and ecological risk, and the selection of remediation strategies.Intellectual Merit: Numerous models for NAPL dissolution have been developed based upon and intended to describe centimeter-scale laboratory columns. While our understanding of NAPL dissolution at this scale is relatively mature, this understanding does not translate to reliable field-scale models for two reasons: (1) the computational problem is intractable with current technology if one endeavors to resolve centimeter-scale features known to be important for field-scale simulations; and (2) upscaled models of NAPL dissolution, which are computationally tractable, are in their developmental infancy. We have shown in previous work that the dissolution process leads to the formation of dissolution fingers, which have aprofound effect on the rate of dissolution. Because these fingers can affect the rate of mass transfer by two or more orders of magnitude in some cases, it is essential that the effect of this mechanism be represented in field-scale simulators, and we know of no case in which this has been done.The goal of this proposed work is to extend a novel fractal-based upscaling approach to produce a nonlinear, multiscale mass transfer model suitable for more realistic field-scale simulation. Multiscale models are the holy grail of subsurface science, indeed much of science in general. Our efforts to date in this regard have met with considerable success, but several key unresolved issues that influence NAPL dissolution fingering remain: NAPL wettability, porous medium heterogeneity, the initial spatial distribution of NAPL contamination at the onset of dissolution, and the effect of realistic patterns of field-scale heterogeneity on the development and evolution of fingers and NAPL dissolution in general. A combination of creative theoretical, novel experimental, and advanced computational approaches will be used to address these issues.Broader Impacts: In this work, a numerical model will be developed and used to investigate a nonlinear process and to extend the range of conditions beyond what can be easily studied in the laboratory to those typical of complex natural systems. The synergy between the experimental and computational approaches provides a unique opportunity to draw high school and undergraduate engineering and science students into the exciting world of subsurface hydrology and computational science. To that end, we will create two Problem-Based Learning (PBL) modules based on our work that will be tested with undergraduate students at the University of Delaware (UD) and the University of North Carolina (UNC) and used in a programintended to attract gifted high school students into engineering and science. PBL is a successful example of student-centered or active learning, the strengths of which have been firmly established by research in educational psychology. UD has developed an institutional focus on PBL and has become a national and international PBL leader, and they will disseminate these PBL educational modules to instructors throughout the US. In addition, this research will involve directly both undergraduate and graduate students from active research groups that have both a strong commitment to and representation of under-represented groups in science and engineering.1