Abstract: Convection heat transfer in a single granite fracture was experimentally investigated in this work. Distilled water was used as working medium for heat transfer in manmade smooth and rough fractures of granite samples. The influence of fracture roughness on heat transfer intensity was analyzed. The evolution of external surface temperatures of rock samples was monitored using resistance temperature detectors during seepage heat transfer to study the local heat transfer characteristics along the seepage path. Subsequently, the heat transfer correlations were summarized on the basis of the experimental results. Main conclusions are as follows: (1) under a given temperature level, the convection heat transfer coefficient features a positive correlation with flow rates. The increase rate of heat transfer coefficient is greater than the flow rates. Under a given flow rate, the convection heat transfer coefficient increases with the increase of experimental temperature. (2) the roughness of rock fracture increases the local heat transfer intensity to a certain extent, but the enlargement is not big. (3) the external surface temperatures exhibit nonlinear characteristic with multiple peaks, the temperature evolution history of rough fracture are more complicated than smooth fracture. For both smooth and rough fracture, the heat transfer intensity decreases with the distance to the inlet. (4) the quotient of Nusselt number and the 1/3 power of Prandtl number is close to a power function of Reynolds number under the experimental conditions in this work. With the increase of experimental temperature, the relationship gradually tends to be linear.

Key words: convection heat transfer, rock fracture, joint roughness, heat transfer correlation, local heat transfer intensity