Effect of fracture structure on heat transfer in heat pipes in a submarine hydrothermal reservoir

Complex geological structures like pores, fractures and faults in submarine hydrothermal reservoirs have significant but unclear effects on internal hydrothermal flow and heat transfer, which hinders reservoir exploitation. This study establishes a heat transfer model of a buried pipe coupled in fracture-porous media based on the reservoir characteristics. The model is verified through experiments using fractured porous media test rigs and computational fluid dynamics simulations. Simulations are performed to investigate the effects of fracture flow velocity, width, cornerstone porosity on the heat transfer efficiency of the buried pipe. Results show that optimizing fracture flow velocity, fracture width and cornerstone porosity can substantially improve the heat transfer performance of the buried pipe. Increasing fracture flow velocity from 10^–4 m/s to 10^–3 m/s, results in a 161.92% increase of Nusselt number. When the fracture width increases to 5 times the pipe diameter, Nusselt number rises by 35.52%. The heat transfer is optimal at a porosity of 0.3. This study provides theoretical guidance for exploiting submarine hydrothermal resources and designing fracture-porous couplings to enhance buried pipe heat transfer.