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.

中欧的浅层沉积含水层是重要的淡水水库，同时也因其储存大量热能的能力而受到关注。了解和控制这些含水层的热条件对于量化水流状况、估计地热利用潜力和保持地下水质量至关重要。虽然基本的热传输机制（即，扩散和平流）是很好地建立，解释其组合效应的影响下，尺度依赖的异质性仍然没有解决。天然材料在从小到大的尺度上本质上是异质的（例如，粒度混合物）到大（例如，水力传导率分布）。在水文地质学中，假设颗粒和周围液体之间的局部热平衡（LTE）的体积平均方法传统上被应用于描述热传输，但这种方法既没有得到验证，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在不同尺度上热传输的非均匀性的可变影响。这种效应包括局部热非平衡（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，协调从颗粒（毫米）到地质异质性（数十米）尺度上的热传输机制。在小规模下，将进行特定的流通柱实验，以研究天然粒度分布对LTNE和热分散的影响。在大尺度上，将在热传输模型中测试真实的含水层模拟物，以仔细研究沉积结构的作用。在一个具有众所周知的地下非均匀性的既定试验场地，现场实验将揭示LTNE的发生和强度，并将热扩散量化为地质尺度非均匀性的函数。实验室和现场实验将用于验证详细的数值热传输模拟。这些将随后部署，以阐明先进的方面，如混合物的粒度和传热系数之间的关系，以及地质异质性对LTNE和热扩散的影响。最后，研究结果将被共同解释，以协调不同尺度的热传输机制。这一结果将为模拟具有天然非均质性的沉积物中的热传输提供一个新颖而通用的框架。预计所积累的知识将提高理论和实践标准，并支持改进规划和管理，例如地下水和浅层地热系统的伴热。