Study On Heat Transfer Performance Enhancement Of A Solar Tower Supercritical Carbon Dioxide Receiver Tube

Tower solar thermal power generation technology has promising application prospects.Among them,the receiver is the key component for absorbing external heat energy and realizing system power conversion,which has the characteristics of high temperature,high pressure and non-uniform heat flux distribution.However,traditional molten salts are prone to decomposition and degradation at high temperatures,causing corrosion of the absorber wall.Supercritical CO₂ has a higher circulation efficiency than traditional heat transfer mediums,which can effectively reduce the volume of heat transfer equipment and cut the investment cost of solar thermal power generation systems.Therefore,it is of great application value to study the flow and heat transfer performance of supercritical CO₂ in the heat absorber.This thesis carries out the performance study and structural enhancement of the tower solar supercritical CO₂ absorber under non-uniform heat flux.The main research contents include.（1）A numerical simulation of supercritical CO₂ convection and heat transfer under non-uniform heat flux were realized.The HFCAL model was used to define the non-uniform heat flux boundary conditions on the surface of the tower solar receiver.A material model for the temperature dependence of supercritical CO ₂ thermal property parameters was developed.The reliability of the numerical simulation method is verified by comparison with experimental data.（2）The effect of the absorber arrangement on the heat transfer performance of supercritical CO₂ was investigated.The heat transfer performance of supercritical CO₂ in horizontal and vertical absorbers was compared and analyzed.The results show that the longitudinal vortex in the horizontal absorber effectively enhances the heat transfer performance of supercritical CO₂ and reduces the circumferential temperature difference in the absorber.However,no vortex is generated in the vertical absorber,so the heat transfer performance of supercritical CO₂ is poor.（3）The enhanced heat transfer structure arrangement in the absorber is proposed by the field synergy principle and the performance analysis of the enhanced absorber is carried out.The distribution of the local field synergy angle in the horizontal and vertical absorbers was determined through numerical simulations,and the enhanced heat transfer structure was arranged at the locations with large field synergy angles by using the field synergy principle,and the effect of the enhanced heat transfer structure on the heat transfer performance of supercritical CO₂ was further analyzed.The results show that the heat transfer performance of the absorber can be significantly improved according to the arrangement scheme given in this thesis,and the Nusselt number can be increased by up to 163%.（4）The effect of the type of the absorber on the heat transfer performance of supercritical CO₂ was studied and a novel alternative elliptical twisted tube was designed.The flow and heat transfer performance of supercritical CO ₂ in five typical absorbers were analyzed,and the effects of different types of the absorber on the flow and heat transfer performance of supercritical CO₂ were compared.Based on this,a novel alternative elliptical twisted tube was designed.The results of the study show that the flow and heat transfer of supercritical CO₂ in other absorbers are better than those of the smooth tube.In the horizontal arrangement,the heat transfer coefficient of the novel alternative elliptical twisted tube is increased by 92%compared to that of the smooth tube.In the vertical arrangement,the heat transfer coefficient of t he novel alternative elliptical twisted tube is increased by 100%compared to that of the smooth tube.The results of this thesis can provide a reference for the design and structural enhancement of supercritical CO₂ absorbers in tower solar thermal power systems.