Numerical analysis on heat transfer enhancement of sCO2 in the tube with twisted tape

Supercritical carbon dioxide (sCO2) has the advantages of easy to reach critical conditions, inactive chemical properties and good safety, which can be used as reactor coolant. However, the thermophysical properties of sCO2 change drastically near the pseudo-critical point. The resulting buoyancy and flow acceleration effects may cause local heat transfer deterioration in the coolant channel. Twisted tape is a good structure for heat transfer enhancement in tube. It can enhance turbulence, generate secondary flow, and disturb fluid flow boundary layer and thermal boundary layer, which can effectively mitigate the heat transfer deterioration of sCO2. The numerical analysis of sCO2 heat transfer deterioration and the heat transfer enhancement of twisted tape is presented in the article using ANSYS Fluent. The default turbulent Prandtl number model was modified to improve the calculation of turbulence generation and diffusion. The heat transfer enhancement characteristic of sCO2 with twisted tape under different working conditions was considered, and the effects of geometric characteristics were also discussed. The results indicate that when the flow rate is low and the heat flux is high, adding twisted tape can effectively suppress the heat transfer deterioration by reducing the viscous sublayer thickness and enhancing the turbulence intensity near the wall. The smaller the twist ratio, the more obvious the enhancement of heat transfer.