Fluid friction and heat transfer through a single rough fracture in granitic rock under confining pressure

To better understand flow and heat transfer in the fractured rock in enhanced geothermal systems (EGS), experiments were conducted to investigate the single-phase convective heat transfer and pressure drop of water flowing through a single fracture in a cylindrical granite rock. Dimensionless correlations for the Poiseuille number (Po) and the average Nusselt number (Nu) with the Reynolds number (Re) were obtained from the experimental data. It was found that the experimental results significantly deviated from those of rectangular macrochannel flows, and the flow friction is raised and the heat transfer is weakened significantly due to the large relative roughness. As confining pressure is applied, reduction of the aperture raises both Po and Nu. A roughness-viscosity model (RVM) was employed to account for the effects of the surface condition, and a satisfactory agreement between the numerical results based on RVM and the experimental data was achieved.