Nonequilibrium Transport and Transport-Controlled Reactions

非平衡传递和传递控制反应

• 批准号: 0738772
• 负责人: Peter Kitanidis
• 金额: $ 38万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-08-01 至 2012-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0738772&HistoricalAwards=false
• 关键词: Nonequilibrium; Transport; Controlled; Reactions

Porous media are extremely important, not only because they contain most of accessible freshwater, but also because of their biological significance, e.g., hyporheic zones (below rivers or estuaries). Dilution and biochemical reactions control the quality of water in the subsurface, in the sediment of beaches or riverbeds, at groundwater recharge basins, etc. For example, a contaminant plume emanating from a source is gradually diminished through dilution and through chemical reactions in the interior or at the edges of the plume. The success of projects of engineered in-situ remediation often depends on the effectiveness of chemical delivery and mixing of additives, which stimulate native microorganisms to break down contaminants. Equally important to the mixing of reactants may be the removal of reaction products which, if they remain, inhibit reactions because they are deleterious to the microorganisms. Many biochemical reactions that are important in the study of environmental processes are very fast in comparison to transport processes, like advection, diffusion, and mass exchange between aqueous and solid zones. Mixing in porous media is very slow and, thus, is usually the mechanism that controls rates. Reaction rates at scales of interest in practical applications are usually controlled by the rates of transport and mixing within geologic formations, rather than by the rates measured in small and completely mixed reactors. Numerical transport-reaction simulation models are invaluable in describing field-scale processes but there are widespread concerns about their effectiveness, the physical significance of the mathematical expressions and parameters that they employ to describe reaction kinetics, or the extent that these expressions or parameters can be transferred to other sites, or be scaled to sites of different size. This research is a critical reexamination of the fundamentals of transport-limited reactions in order to identify underlying mechanisms and to develop insights into the applicability of commonly used mathematical expressions, appropriate values of parameters, and the importance of scale effects. Existing approaches are revisited and novel approaches are proposed and tested. A new approach is proposed based on the premise that existing parameters like dispersion coefficients or mass-transfer coefficients are inadequate, and occasionally ill-suited, for describing the kinetics of reactions that are controlled by hydrologic transport. Alternative quantities need to be considered, measured, and studied with respect to changes in scale. One approach, which constitutes a drastic departure from available procedures, is based on a rigorous derivation of mixing potentials, which quantify transport-controlled reactions and determine their rates. Critical questions include: what practical tests to perform in the field, how to interpret the results, what accuracy or reliability are practically feasible, and risk-assessment implications. The applicability of various approached is evaluated by examining specific problems from recently completed field studies and experiments and by performing laboratory experiments and detailed numerical simulations.

多孔介质极其重要，不仅因为它们含有大部分可利用的淡水，而且还因为它们具有生物学意义，例如潜水带(在河流或河口以下)。稀释和生化反应控制着地下水、海滩或河床沉积物、地下水补给盆地等中的水质。例如，从源头发出的污染物羽流通过稀释和羽流内部或边缘的化学反应逐渐减少。工程就地修复项目的成功往往取决于化学品输送和添加剂混合的有效性，这些添加剂刺激本地微生物分解污染物。对于反应物的混合来说，同样重要的是反应产物的去除，如果它们保留下来，就会抑制反应，因为它们对微生物有害。在环境过程研究中很重要的许多生化反应比传输过程要快得多，如平流、扩散以及水和固体区之间的质量交换。多孔介质中的混合非常缓慢，因此通常是控制速率的机制。在实际应用中，在感兴趣的规模上的反应速率通常由地质地层中的输送和混合速率控制，而不是由在小型和完全混合的反应堆中测量的速率控制。数值输运-反应模拟模型在描述现场尺度的过程方面非常有价值，但人们普遍关注它们的有效性、它们用来描述反应动力学的数学表达式和参数的物理意义，或者这些表达式或参数可以转移到其他位置的程度，或者这些表达式或参数可以缩放到不同大小的位置的程度。这项研究是对运输受限反应的基本原理的批判性重新审视，以确定潜在的机制，并深入了解常用数学表达式的适用性、参数的适当值以及尺度效应的重要性。对现有方法进行了重新审查，并提出了新的方法并进行了测试。提出了一种新的方法，其前提是现有的弥散系数或传质系数等参数不足以，甚至有时不适合描述受水文输运控制的反应动力学。需要考虑、测量和研究与尺度变化相关的替代量。一种方法是基于对混合势的严格推导，这种方法严重偏离了现有的程序，混合势量化了运输控制的反应并确定了它们的速率。关键问题包括：在现场进行什么实际测试，如何解释结果，实际可行的准确性或可靠性，以及风险评估的影响。各种方法的适用性是通过检查最近完成的实地研究和实验中的具体问题以及进行实验室实验和详细的数值模拟来评估的。