Experimental research on the convection heat transfer characteristics of distilled water in manmade smooth and rough rock fractures

Convection heat transfer characteristics in a single rock fracture was experimentally investigated in this work. Distilled water was used as working medium for heat transfer in manmade smooth and rough fractures of sandstone and granite samples. The influence of fracture surface roughness on heat transfer intensity was analyzed. During seepage heat transfer process, evolution of samples external surface temperatures was monitored using six resistance temperature detectors to study the local heat transfer characteristics along the flow direction. Subsequently, heat transfer correlations were proposed on the basis of the experimental results. The results indicate that the roughness of rock fracture surface improves the overall heat transfer intensity to a certain extent, whereas lithology has little influence on the heat transfer intensity. For smooth fractures, the local heat transfer intensity decreases with the increase of the distance from the inlet. For rough fractures, evolution of sample external temperatures along the flow direction exhibits strong nonlinear characteristics with multiple peaks. Nu/Pr1/3 is close to a power function of Re under the experimental conditions in this work. With the increase of experimental temperature, the relationship gradually tends to be linear.