Local thermal equilibrium or not? Reconciling the groundwater heat transport mechanisms in heterogeneous sediments at different scales

局部热平衡与否？

• 批准号: 468464290
• 负责人: Professor Dr. Peter Bayer
• 金额: --
• 依托单位: Abteilung Ingenieurgeologie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/468464290?language=en
• 关键词: Local; thermal; equilibrium; Reconciling; groundwater

Shallow sedimentary aquifers in Central Europe are important freshwater reservoirs while also gaining attention for their ability to store enormous amounts of thermal energy. Understanding and controlling the thermal conditions in such aquifers is vital for quantifying flow regimes, estimating the potential for geothermal use and maintaining groundwater quality. While the fundamental heat transport mechanisms (i.e., diffusion and advection) are well established, interpreting their combined effects under the influence of scale-dependent heterogeneity remains unresolved. Natural materials are inherently heterogeneous at scales from small (e.g., grain size mixtures) to large (e.g., hydraulic conductivity distribution). In hydrogeology, a volume-averaging approach assuming local thermal equilibrium (LTE) between grains and the surrounding liquid has traditionally been applied to describe heat transport, yet this approach has neither been verified nor have conditions for its validity been defined. Further, this state-of-the-art approach ignores the variable effects of heterogeneities on heat transport at different scales. Such effects include local thermal non-equilibrium (LTNE) and an apparent scaling of macroscopic thermal dispersion. This project aims to reconcile the heat transport mechanisms at scales from grain (millimetres) to geological heterogeneity (tens of metres) by combining laboratory, field, analytical and numerical methods. At the small scale, specific flow-through column experiments will be conducted to investigate the influences of natural grain size distributions on LTNE and thermal dispersion. At the large scale, real aquifer analogues will be tested in heat transport models to scrutinize the role of sedimentary structures. At an established test site with well-known subsurface heterogeneity, field experiments will reveal the occurrence and intensity of LTNE and quantify thermal dispersion as a function of geological scale heterogeneity. Both laboratory and field experiments will be used to validate detailed numerical heat transport simulations. These will subsequently be deployed to elucidate advanced aspects, such as the relationship between mixtures of grain sizes and heat transfer coefficient as well as the influence of geological heterogeneity on LTNE and thermal dispersion. Finally, the findings will be jointly interpreted to reconcile heat transport mechanisms at different scales. The outcome will provide a novel and universal framework for modelling heat transport in sediments with natural heterogeneities. It is anticipated that the developed knowledge will advance standards in theory and practice and support improved planning and management, for example of heat tracing in groundwater and shallow geothermal systems.

中欧的浅沉积含水层是重要的淡水储层，同时也因其存储大量热能的能力而引起人们的关注。理解和控制此类含水层中的热条件对于量化流动状态至关重要，估计地热使用的潜力和维持地下水质量至关重要。尽管基本的热传输机制（即扩散和对流）已经确定，但在依赖规模依赖性异质性的影响下解释其联合效应仍未解决。天然材料本质上是从小（例如晶粒尺寸混合物）到大（例如液压电导率分布）的尺度上的异质。在水文地质学中，传统上使用了谷物和周围液体之间局部热平衡（LTE）的体积平衡方法来描述热传输，但是这种方法既未得到证实，也没有定义其有效性的条件。此外，这种最先进的方法忽略了异质性在不同尺度下热传输的可变影响。这种影响包括局部热非平衡（LTNE）和宏观热分散的明显缩放。该项目旨在通过结合实验室，现场，分析和数值方法来调和从谷物（毫米）到地质异质性（数十米）的尺度的热传输机制。在小规模上，将进行特定的流通柱实验，以研究自然晶粒尺寸分布对LTNE和热分散体的影响。在大规模上，将在热传输模型中测试真正的含水层类似物，以仔细检查沉积结构的作用。在具有众所周知的地下异质性的已建立的测试位置，现场实验将揭示LTNE的发生和强度，并量化热分散体作为地质尺度异质性的函数。实验室和现场实验都将用于验证详细的数值热传输模拟。这些将随后部署以阐明高级方面，例如晶粒大小与传热系数的混合物之间的关系以及地质异质性对LTNE和热分散体的影响。最后，将共同解释这些发现，以调和不同尺度的热传输机制。该结果将为自然异质性的沉积物中的热传输建模提供新颖而通用的框架。可以预料，发达的知识将提高理论和实践的标准，并支持改进的计划和管理，例如在地下水和浅地热系统中进行热追踪。