Numerical simulation study on heat transfer enhancement performance of annular inner ribbed tube of geothermal wellbore

As a kind of clean and renewable energy, geothermal energy has the advantages of high reserves, safety and stability. In order to strengthen the heat extraction capacity of wellbore for geothermal energy, the numerical calculation models of triangular, rectangular and fan-shaped inner rib tubes are established in this paper. The temperature field, velocity field and pressure field f them and smooth circular tube in wellbore geothermal heat transfer are compared and analyzed. The results show that the inner rib tube destroys the boundary layer through the rib disturbance, enhances the fluid mixing, and enhances the heat transfer. The heat transfer effect of the rectangular inner rib tube is the best. The flow diversion effect of the rib leads to the change of the flow velocity, forming a stagnant area, which further strengthens the heat transfer, and the rectangular inner rib tube has a larger retention area. In terms of heat transfer efficiency and resistance performance, the Nu number of rectangular inner rib tube is the highest, and the f number increases significantly. At low mass flow rate, the comprehensive performance evaluation factor η of the fan-shaped inner ribbed tube is better. When the flow rate is greater than 10kg/s, the performance of the three inner ribbed tubes is not much different, and the influence of the rib shape can be ignored.