Abstract: The development, utilization and storage of thermal energy in deep rock masses generally involve fracture seepage and heat transfer problems, and the geometry of rough fractures has an important effect on the seepage and heat transfer characteristics. The geometric models of rough fractures with different fractal dimensions and standard deviations were constructed by successive random accumulation method. Combined with Navier-Stokes equations, momentum and energy conservation equations, the dynamic process of seepage and heat transfer in rough fractures was simulated. The rock fracture seepage and heat transfer test system was developed and the granite fracture seepage and heat transfer test was performed to verify the reliability of the numerical method. Then the variations of seepage and heat transfer characteristics in rough fracture were analyzed under different fractal dimensions and standard deviation conditions. The results show that the water-rock heat exchange effect gradually decreases with time and enters the thermal equilibrium stage after the heat front penetration. As the fractal dimension increases and the standard deviation decreases, the average convective heat transfer coefficient gradually decreases due to the significant enhancement of the dominant flow effect and the weakening of the overall heat transfer characteristics. The local convective heat transfer coefficient is positively correlated with the average fracture opening and the maximum elevation difference of the center line. The local Nusselt number increases with the increase of fractal dimension and reaches its peak at the exit.

Key words: rock fracture, convective heat transfer, fractal dimension, standard deviation