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| Study on the seepage and heat transfer effect in rough fracture with hot matrix considering the dynamic thermophysical properties of fluid |
| SHEN Linfang1，SU Wei 1，ZHANG Jiaming1，WANG Zhiliang1，LI Shaojun2，XU Zemin1 |
(1. Faculty of Civil Engineering and Mechanics，Kunming University of Science and Technology，Kunming，Yunnan 650500，China；
2. State Key Laboratory of Geomechanics and Geotechnical Engineering，Institute of Rock and Soil Mechanics，
Chinese Academy of Sciences，Wuhan，Hubei 470071，China) |
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Abstract To study the coupling mechanism of seepage and heat transfer in high-temperature rough rock fracture and improve the efficiency of geothermal energy extraction，based on 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 was 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 1.079 8，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.
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