Abstract Understanding the process of heat transfer in fractures and the influence of fracture surface morphology is crucial for optimized heat mining. In this work, we investigated transient heat transfer behavior at high flow rates, ranging from 80 to 350 mm/s, at various inflow temperatures. A split sandstone core was installed in an experimental setup that allowed the fluid to be circulated, cooled and reheated. Water was circulated through the fracture and a temperature step was induced with the help of a heat exchanger upstream to the core. Thermocouples before and after the core enabled the measurement and evaluation of transient cooling and heating curves. The thermal breakthrough curves reveal the capacity of the rock to maintain maximum outflow temperature for a substantial amount of time. Thermal and mass dispersion coefficients are comparable but analytical solutions for heat transport can only be used with strong limitations. Heat transfer coefficients were determined using the stationary state. The evaluation of the surface roughness identifies its substantial influence on the heat transfer coefficient. Our experiments show that flow velocities beyond 200 mm/s lead to cold outflow temperatures, causing undesired cooling and prolonged heat transfer processes in the reservoir. These effects should not be underestimated in terms of the efficiency of geothermal energy generation.

中文翻译：

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高流速下单个岩石裂缝中的瞬态传热过程

摘要 了解裂缝中的传热过程和裂缝表面形态的影响对于优化热采至关重要。在这项工作中，我们研究了不同流入温度下高流速下的瞬态传热行为，范围从 80 到 350 mm/s。一个分裂砂岩岩心安装在一个实验装置中，允许流体循环、冷却和再加热。水通过裂缝循环，并在岩心上游的热交换器的帮助下引发温度变化。核心前后的热电偶能够测量和评估瞬态冷却和加热曲线。热穿透曲线揭示了岩石在相当长的时间内保持最高流出温度的能力。热扩散系数和质量扩散系数相当，但热传输的解析解只能在有很大限制的情况下使用。使用静止状态确定传热系数。表面粗糙度的评估确定了它对传热系数的重大影响。我们的实验表明，超过 200 毫米/秒的流速会导致冷流出温度，从而导致不希望的冷却和储层中延长的传热过程。就地热能发电效率而言，不应低估这些影响。表面粗糙度的评估确定了它对传热系数的重大影响。我们的实验表明，超过 200 毫米/秒的流速会导致冷流出温度，从而导致水库中不希望的冷却和延长的传热过程。就地热能发电效率而言，不应低估这些影响。表面粗糙度的评估确定了它对传热系数的重大影响。我们的实验表明，超过 200 毫米/秒的流速会导致冷流出温度，从而导致水库中不希望的冷却和延长的传热过程。就地热能发电效率而言，不应低估这些影响。