岩体裂隙几何结构对其渗流传热特性的影响

Effect of rock fracture geometry on its seepage and heat transfer characteristics

深部岩体热能开发、利用及存储过程中普遍涉及裂隙渗流传热问题,粗糙裂隙几何结构对其渗流传热特性具有重要影响。通过逐次随机累加法,构建不同分形维数和标准差的粗糙裂隙几何模型;结合Navier-Stokes方程、动量和能量守恒方程,模拟粗糙裂隙渗流传热动态过程;研发岩体裂隙渗流传热试验系统,开展花岗岩裂隙渗流传热试验验证数值方法的可靠性;然后分析不同分形维数与标准差条件下粗糙裂隙渗流传热特性的变化规律。结果表明:水岩换热作用随着时间推移逐步下降,热锋面贯通后进入热平衡阶段;随着分形维数的增大和标准差的减小,由于优势流效应显著增强,总体换热特性减弱,因此平均对流换热系数逐步减小;局部对流换热系数与裂隙的平均开度和中线最大高程差值呈正相关关系;局部努塞尔数随分形维数增大而增大,在出口处达到峰值。

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.