A Comprehensive Multi-Scale Study of the Impact of Capillary-Held Water Films on Fluid Motion, Transport and Mass Transfer in the Unsaturated Zone

毛细管持水膜对非饱和区流体运动、传输和传质影响的多尺度综合研究该项目所获得的知识可能最终导致对广泛的非饱和现象的改进模型，这些非饱和现象对实际的水文、农业和环境应用非常重要，包括预测土壤中的水分渗透和暴雨期间的洪水、修复受污染的土壤和地下水以及化肥、农药等。当水从多孔介质中排出时，水膜仍然留在固体颗粒表面。因此，在干燥条件下，水膜在非饱和带中无处不在，并在许多现象中起着中心作用。尽管水膜面积很大，但空气-水界面上的持续传质取决于固体表面的膜在多大程度上通过水力连接和移动性，足以从大量孔隙水中补充。最近的信息表明，固体颗粒表面的水膜可能比之前认为的要厚几个数量级，它们的形状和厚度由固体颗粒表面的粗糙度决定。这一发现的含义是，固体颗粒表面的水膜中的流动和传输可能比之前认为的要大得多。然而，关于颗粒表面相关水膜中的流动和传输如何发生的定量信息很少。该项目旨在解决这一关键的知识差距。这项拟议的工作将把跨越一系列尖端技术的实验工作与建模工作结合起来，以达到对非饱和区毛细管水膜行为的定量、预测性理解。实验和模拟将在纳米尺度到颗粒团簇尺度上进行。立体扫描电子显微镜将被用来创建真实颗粒和颗粒团的非常详细的表面粗糙度图，而共焦显微镜技术将被用来研究外部输入(毛细压力、蒸发)对动态膜结构、流动和平流输送的影响。工作将集中于四个紧密耦合的任务，旨在测试工作的假设，然后探索观察到的亚孔尺度薄膜现象对REV和场尺度行为的影响。

A Comprehensive Multi-Scale Study of the Impact of Capillary-Held Water Films on Fluid Motion, Transport and Mass Transfer in the Unsaturated ZoneThe knowledge resulting from the project could ultimately lead to improved models for a wide range of unsaturated phenomena important to practical hydrologic, agricultural, and environmental applications, including prediction of water infiltration into soils and flooding during heavy rainfalls, remediating polluted soils and groundwaters, and movement of fertilizers, pesticides, etc. When water drains out of a porous medium, films of water remain behind on solid grain surfaces. For this reason, water films are ubiquitous in the unsaturated zone under dry conditions, and they play a central role in a wide range of phenomena. Although the magnitude of water film area is substantial, sustained mass transfer at air-water interfaces depends on the extent to which films on solid surfaces are hydraulically connected and mobile enough to be replenished from bulk porewater. Recent information has shown that water films on solid grain surfaces are likely orders of magnitude thicker than previously thought, and that their configuration and thickness are dominated by the roughness of solid grain surfaces. The implication of this finding is that flow and transport in water films on solid grain surfaces are likely far greater than previously thought. However, very little quantitative information is available on how flow and transport occur in grain surface-associated water films. This project is aimed at addressing this critical knowledge gap. The proposed work will combine experimental work spanning a range of cutting-edge techniques with a modeling effort to arrive at a quantitative, predictive understanding of the behavior of capillary-held water films in the unsaturated zone. Experiments and simulations will be conducted at scales ranging from the nanoscale to the grain cluster scale. Stereoscopic SEM will be used to create highly detailed surface roughness maps of real grains and grain clusters, and confocal microscopy techniques will be used to study the impact of external inputs (capillary pressure, evaporation) on dynamic film configuration, flow, and advective transport. Work will be focused around four tightly-coupled tasks designed to test the hypotheses of the work, and then explore the implications of the observed sub-pore-scale film phenomena on REV and field scale behaviors.