考虑流体热物理性质动态演化的高温岩石粗糙裂隙渗流传热效应研究

Study on the seepage and heat transfer effect of rough fractures in hot matrix considering dynamic thermophysical properties of fluid

为了研究高温岩体粗糙裂隙渗流-传热耦合作用机制,提高地热能的开采效率,基于格子Boltzmann方法采用双分布函数分别模拟渗流速度场及传热温度场的演化过程,考虑流体温度对其运动黏度及热扩散系数的影响,建立模拟粗糙岩石裂隙渗流-传热过程的数值计算模型,并结合经典算例验证计算模型的准确性。最后,基于该模型研究裂隙壁面粗糙程度、流体热物理参数动态演化等因素对其渗流-传热耦合作用机制的影响,并讨论裂隙壁面粗糙程度与地热提取性能指标之间的联系。研究表明:粗糙裂隙壁面的阻碍作用会增大惯性压降,降低渗流流速,使得流体与岩石基质间的传热更充分,出口处的流体温度更高。忽略流体温度对其运动黏度的影响,将会严重高估裂隙内的渗流流速,并低估其热突破时间。随着裂隙壁面粗糙程度的加剧,其热突破时间逐渐增加,而采热速率则呈减小的趋势。当裂隙壁面分形维数为1.0798时,其热突破时间比光滑裂隙增加了191.49%;而采热速率则仅为44.36%。此外,在裂隙两端压降相同的情况下,其壁面越光滑,在相同时间内获得的热回收率越高,但由于其热突破时间较短,使得在热突破时刻的热回收率显著降低。

To study the coupling mechanism of seepage and heat transfer in high-temperature rough rock fracture and to improve the efficiency of geothermal energy extraction,lattice Boltzmann method the double distribution functions were applied to deal with the evolution of seepage velocity field and heat transfer temperature field separately.Considering the effects of fluid temperature on its kinematic viscosity and thermal diffusion,a numerical model was proposed to simulate the coupled process of seepage and heat transfer in rough rock fracture.And the accuracy of the model was verified according to a classic example.Based on the proposed model,the effects of rough fracture surface and dynamic evolution of fluid physical parameters on the coupling mechanism of seepage and heat transfer were analyzed,and the relationship between the roughness of fracture surface and the performance indicators of geothermal extraction was discussed.The results show that the obstruction effect of the rough fracture surface increases the inertial pressure drop and reduces its seepage velocity,which makes the heat transfer between water and rock more sufficient,and the water temperature is higher at the outlet.Neglecting the influence of fluid temperature on its kinematic viscosity seriously overestimates the flow velocity,and significantly underestimates the thermal breakthrough time.As the roughness of the fracture surface intensifies,its thermal breakthrough time gradually increases,while the heat production power shows a decreasing trend.When the fractal dimension of fracture surface is 1.0798,its thermal breakthrough time increases by 191.49%compared to the smooth fracture,and the heat production power is only 44.36%of that of smooth fracture.In addition,when the pressure drops are the same,the smoother the fracture surface is,the higher the heat recovery rate obtained within the same time.However,due to its shorter heat breakthrough time,the heat recovery rate is significantly reduced when the thermal breakthrough occurs.