岩石导热热阻对裂隙对流换热的影响机制

增强型地热系统(EGS)中高温岩石与流体之间的对流换热特征一直以来是干热岩(HDR)研究的重要基础内容。岩石导热热阻对裂隙对流换热特征具有重要影响。为研究其具体影响，综合运用理论解析与数值模拟2种研究方法，通过对解析解讨论以及建立数值模型，研究两平行光滑平板之间的换热规律。结果表明：流体速度、传热边界层充分发展时，局部努塞尔特准数Nu_x为定值，与其他因素无关；局部对流换热系数h_x仅与流体热导率k和裂隙开度e有关，与其他因素无关。上下平板壁面热流恒定时，Nu_x为8.235；温度恒定时，Nu_x为7.54。然后建立多组导热热阻不同的岩石裂隙对流换热数值模型，发现岩石导热热阻增大，温度场进口段延长，对流换热系数h增大。岩石长度显著影响进口段占比，进而影响h的大小。h随着长度增大而减小；当岩石长度足够长时，进口段占比足够小，此时除k与e之外的参数对h基本没影响。并且发现实验室常用岩石长度为100 mm，而典型EGS工程中裂隙长度是米级的，建议室内实验重视岩石长度对裂隙对流换热特征的影响。

Influencing mechanism of rock thermal resistance on convective heat transfer of fracture

The convective heat transfer characteristics between high temperature rocks and fluids in Enhanced Geothermal Systems (EGS) have been an important fundamental element of research on Hot Dry Rock (HDR). The thermal resistance of rock has an important influence on the convective heat transfer characteristics of fracture. In order to study its specific influence, two research methods, i.e., the theoretical analysis and the numerical simulation, were used in combination to study the heat transfer law between two parallel smooth flat plates by discussing the analytical solution and establishing the numerical model. The results show that the local Nusselt number Nu_x is constant and unrelated to other factors when the fluid velocity and the heat transfer boundary layer are fully developed. The local convective heat transfer coefficient h_x is only related to the fluid thermal conductivity k and the fracture opening e, but independent of other factors. Nu_x is 8.235 when the heat flux at the upper and lower flat wall is constant, and 7.54 when the wall temperature is constant. Then, several sets of convective heat transfer models of rock fissure with different thermal resistance were constructed. Thereby, it is found that the convective heat transfer coefficient h increases when the thermal resistance of the rock increases and the inlet section of the temperature field are extended. The length of the rock significantly affects the portion of the inlet section, which in turn affects the magnitude of h. Besides, h decreases with the increasing length. When the rock is long enough, the portion of the inlet section is small enough, and the parameters other than k and e have little effect on h. The rock commonly used in the laboratory is 100 mm in length, while the length of fractures in typical EGS is of the meter level. Therefore, it is recommended that special attention should be paid in the lab experiments to the influence of rock length on the convective heat transfer characteristics of fractures.