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

裂缝性多孔介质中的传热是地球系统中必不可少的过程。它是间歇泉、热液和火山系统等自然现象的驱动机制，也是落石和地震等地质灾害的驱动机制。此外，它还是地热系统等几种工业应用的基础。裂缝性多孔介质中的流体流动已经被很好地理解了。现有的方法范围很广，包括连续介质力学、多域和裂缝的明确定义。然而，就传热而言，最近的模型有两个主要缺点：它们通常只考虑固相和流体之间的热平衡，并且它们缺乏传热过程中裂缝的适当表示。这两个障碍是紧密联系在一起的，因为高流速裂缝往往造成局部热不平衡，但岩石基质与裂缝流体之间的传热没有合适的描述。在这个项目中，将开发一个新的模型来描述裂缝中的传热，包括微观断裂表面形貌。最近的实验室实验允许以迄今为止未知的精度研究这些过程，并能够与理论和数值模型进行深入比较。断裂孔径、表面粗糙度和接触面积不仅对流体流动有显著影响，而且对传热也有显著影响。此外，温度会影响流体性质和应力，而应力又取决于温度和流体压力，从而影响裂缝表面形态。因此，一个合适的传热模型需要结合水力和力学过程，从而形成一个完全耦合的热-水-力学模型。模型开发将从实验室尺度上的简化几何开始，以便与外部项目伙伴在厘米尺度上的实验结果进行良好的比较。该模型将推广到复杂的裂缝网络。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。通过对现场实例的比较和应用，可以保证所建立模型的准确性。计划将开发的模型纳入广泛选择的科学数值流体流动求解器。这种创新的方法可以应用到各种现有的建模方法中，与选择的裂缝表示无关。所提出的模型填补了长期以来在考虑动态和静态参数的裂隙多孔介质中跨尺度传热一致描述的空白。首次详细地研究了边界条件和约束对传热和输运的影响和相互作用。在自然和工业应用中传热计算的新模型将显著改善。

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.