填砂裂隙岩体渗流传热模型试验与数值模拟

Model experiment and numerical simulation of flow and heat transfer for sand-filled fractured rock model

选取中国高放射核废物地下处置库重要预选场区——甘肃北山地区的花岗岩,加工组合成规则裂隙岩体,将垂直裂隙用粒径为0.5～0.63 mm的砂土填充,进行了裂隙水渗流传热试验;对模型试验进行了数值模拟,进而计算分析了热源温度、裂隙水流速和裂隙开度变化对裂隙岩体模型稳态温度场的影响。模型试验表明,当热源温度维持在120℃时,裂隙水仍无相变,裂隙岩体模型稳态温度场分布规律与热源温度为95℃时一致;热源温度越高,热源的水平影响距离越大,模型达到稳态需要的时间越长;裂隙填砂加强了裂隙两侧岩石之间的热传导,热源的水平影响距离和模型到达稳态需要的时间均明显大于无填充裂隙岩体模型的情况。模型试验得到的岩体模型温度场与数值计算得到的岩体模型温度场规律一致。试验过程中裂隙岩体模型在边界上存在一些热量散失,无法与数值计算中的绝热边界条件等同,致使试验数据低于数值计算值,并且热源温度越高,两者之间的差异越大。模型试验和数值计算均表明,邻近热源侧的裂隙水渗流对模型的温度场分布起控制作用,而远离热源侧的裂隙水渗流则主要影响该侧的边界温度和模型达到稳态所需要的时间。数值参数敏感性分析表明,裂隙水流速与裂隙开度越大,裂隙水对水平传热的阻滞作用越明显。

With the vertical fractures filled with sands of grain diameters 0.5-0.63 mm,a fractured rock model is fabricated by using granite rock blocks taken from the Beishan area in Gansu province,which is being investigated as potential site for the high-level radioactive nuclear waste repository in China.Fluid flow and heat transfer experiments and numerical simulations are conducted for the model;and the influences of heat source temperature,the water velocity and aperture of the vertical fractures on the steady-state temperature of the model are also parametrically analyzed.The experiment results reveal that for a 120 ℃ heat source temperature,there is no phase change in the fracture water,and the steady-state temperature field is similar in pattern to that for 95 ℃ heat source temperature;the range of influence of the heat source and the time for asymptotic steady-state temperature field increased with the heat source temperature;sands filled in the fractures enhanced the heat conduction of neighboring rock matrix,making the range of influence of the heat source and the time for asymptotic steady-state both larger than the unfilled fracture model.The temperature field from the experiment is similar in pattern to that from the numerical simulation;however,since some degree of boundary heat loss in the experiment is unavoidable,the measured temperatures are smaller than the numerical simulation results for adiabatic boundary conditions;and the differences increased with the heat source temperature.Numerical parametric sensitivity analyses reveal that the fracture water flow adjacent to the heat source controlled the temperature field of the model,while the vertical fracture water flow further away from the heat source mainly affected the time for the model temperature approaching steady-state and the far side boundary temperature,the retardation of the horizontal heat transfer due to vertical fracture flow is more significant for higher water velocities and larger vertical fracture apertures.