A novel description of heat transfer between fluid and rough-walled fractures in porous rock

裂隙多孔介质中的传热是地球系统中的一个基本过程。它是间歇泉、热液和火山系统等自然现象以及岩崩和地震等地质灾害的驱动机制。此外，它是地热系统等多种工业应用的基础。存在广泛的方法，包括连续介质力学，多个域和明确的断裂定义。然而，关于传热，最近的模型有两个主要缺点：它们通常只考虑固相和液相之间的热平衡，并且它们缺乏传热过程中裂缝的适当表示。这两个障碍是密切相关的，因为高流速的裂缝往往会导致局部热不平衡，但没有合适的描述岩石基质和裂缝流体之间的传热。在这个项目中，将开发一个新的模型来描述裂缝中的传热，包括微观裂缝表面形态。最近的实验室实验允许研究这些过程的准确性未知到现在为止，并使深入的比较与理论和数值模型。裂缝孔径，表面粗糙度，和接触面积显着影响不仅流体流动，而且传热。此外，温度影响流体性质，而应力又取决于温度和流体压力，影响裂缝表面形态。因此，一个合适的传热模型需要结合水力和机械过程，从而形成一个完全耦合的热-水力-机械模型。模型开发将从实验室规模的简化几何形状开始，以便与外部项目合作伙伴在厘米级的实验结果进行良好的比较。该模型将被扩展到复杂的裂缝网络。然而，为了适用于数百米范围的大规模应用，该模型将使用统计方法进行升级，并改变其参数化，以纳入合适的参数，如裂缝密度。通过与实际案例的比较和应用，保证了模型的准确性。计划将开发的模型纳入科学数值流体流动求解器的广泛选择中。这种创新的方法可以实现到现有的各种建模方法，独立于所选择的fracture representation.The建议的模型关闭了长期以来的差距，考虑动态和静态参数的跨尺度的传热裂缝多孔介质中的一致的描述。第一次的影响和相互作用的边界条件和约束的传热和运输可以详细研究。在自然和工业应用中的传热计算将显着改善与新模型。

Heat transfer in fractured porous media is an essential process in the earth system. It is driving mechanism in natural phenomena like geysers, hydrothermal and volcanic systems, as well as in geo-hazards like rockfalls and earthquakes. Further, it is the base for several industrial applications like geothermal systems.Fluid flow in fractured porous media is quite well understood. A broad range of approaches exists including continuum mechanics, multiple domains and an explicit definition of fractures. However, with respect to heat transfer recent models have two major drawbacks: They often only consider thermal equilibrium between the solid and fluid phase and they lack a suitable representation of fractures in the heat transfer process. Both obstacles are strongly connected, as fractures with high flow velocities often cause local thermal non-equilibrium but there is no suitable description for heat transfer between rock matrix and fracture fluid.In this project, a novel model will be developed to describe heat transfer in fractures including microscopic fracture surface morphology. Recent laboratory experiments permit a study of these processes in an accuracy unknown up until now and enable an in-depth comparison with theoretical and numerical models. Fracture aperture, surface roughness, and contact area significantly influence not only fluid flow but also heat transfer. Furthermore, temperature affects fluid properties and stress, which again depends on temperature and fluid pressure, affects the fracture surface morphology. Therefore, a suitable heat transfer model needs to incorporate hydraulic and mechanical processes, resulting in a fully coupled thermo-hydraulic-mechanical model.Model development will start with simplified geometries on laboratory scale to enable a good comparison with experimental results of external project partners at centimeter- scale. The model will be extended to complex fracture networks. However, to be suitable for large scale applications with an extent of hundreds of meters, the model will be upscaled using statistical methods and changed in its parameterization to incorporate suitable parameters, like fracture density. Comparison and application to field cases will ensure the accuracy of the developed model. Incorporation of the developed model into a broad selection of scientific numerical fluid flow solvers is planned. This innovative approach can be implemented into diverse existing modeling approaches, independent of the chosen fracture representation.The proposed model closes the long-standing gap of a consistent description of heat transfer across scales in fractured porous media considering dynamic as well as static parameters. For the first time influence and interaction of boundary conditions and constraints for heat transfer and transport can be studied in detail. Calculation of transferred heat in natural and industrial applications will significantly improve with the new model.