Heat transfer by water flowing through rough fractures and distribution of local heat transfer coefficient along the flow direction

•Local heat transfer coefficients (LHTC) in rough fracture flow passage were obtained.•The value of JRC was used to evaluate the roughness of fractures.•The 3D printing technique was adopted to produce different rough fractures.•The effect of fracture surface tortuosity on the distribution of LHTC were discussed. Heat transfer coefficient is a significant parameter that can describe the characteristics of the heat transfer process of fluid through fracture surface and can be used to predict hot water production from an enhanced geothermal reservoir and conventional geothermal systems. This study adopted numerical and experimental approaches that produce specimen with different rough surfaces through a 3D printing technique to improve the understanding of the heat transfer characteristics of water flowing through rough fractures and the distribution of local heat transfer coefficient along the flow direction. Results indicate that the local heat transfer coefficient increases to the maximum at the inlet and then decreases to a relatively constant value further along the flow direction. In addition, fracture surface tortuosity influences the local fluctuations.