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An accurate understanding of the heat transfer of water flow through rough fractures is important for geothermal energy extraction and utilization. In this study, we used 3D printing to manufacture ten samples with joint roughness coefficient (JRC) values of the fracture surface ranging from 0–2 to 18–20 and conducted experimental investigations of the heat transfer characteristics of the water flow through the ten samples. The effects of the volumetric flow rate, the outer wall surface temperature, the JRC, and the fracture apertures on the heat transfer characteristics were determined. The results showed that a rougher fracture surface resulted in greater heat removal during the flow of the fluid through the rock surface.

Seepage characteristics and heat transfer efficiency in rough fracture are indispensable to evaluate thermal reservoir lifetime and production performance. This study presents the seepage experiment, experiment and simulation on convective heat transfer in rough fracture for two artificial specimens. The repeatable artificial specimens are prepared by cement mortar. The roughness on the fracture surface is manufactured based on JRC profiles and 3D printing technology. The effects of fracture surface property (including proppant) and specimen temperature on seepage characteristics under confining pressure of 30 MPa are obtained. The convective heat transfer performance is evaluated considering roughness, multiple flow rates and specimen temperatures. Moreover, the effects of roughness on temperature distribution, local heat transfer and flow velocity in two specimens are analyzed and discussed. The main results indicate that the proppant and higher specimen temperature can improve hydraulic aperture and be conducive to seepage in rough fracture. The higher specimen temperature can strengthen thermal convection and conduction. The higher flow rate can extract more heat to develop thermal breakthrough. Furthermore, the anisotropy of roughness can affect heat transfer efficiency by reducing effective heat transfer area. The bulge and groove on rough fracture can interfere with temperature distribution and local heat transfer by controlling retention time of fluid.