Thermal-Fluid-Mechanical Analyses Of Supercritical CO₂ Solar Receiver

In the tower solar thermal power generation system,the solar receiver is the core component to realize solar thermal conversion,and its performance affects the efficiency and economy of the entire solar system.Using supercritical CO₂as the heat transfer fluid in the solar receiver can not only achieve higher operating temperature and improve the thermal performance,but also directly use the heating supercritical CO₂to drive a supercritical CO₂Bryton cycle,has gradually become a research focus.In this paper,the two most promising categories—tubular and compact receiver in direct supercritical CO₂heat receivers are taken as the research objects,and their thermal-fluid-mechanical coupling characteristics of supercritical CO₂and the stress distribution on the wall under different working conditions and structures are analyzed.The main work and conclusions are as follows:（1）A coupled thermal-fluid-mechanical model is developed for the solar tube of the tubular receiver using supercritical CO₂as heat transfer fluid,and the law of wall temperature and stress distribution of the solar tube are analyzed.The effects of wall thickness and tube diameter on the heat transfer performance and stress distribution of the solar tube are also discussed.The results indicate that:the temperature difference between the inner/outer wall of the heat-absorbing side is larger,and the thermal stress is greater.Reducing the wall thickness and increasing the tube diameter lead to higher comprehensive heat transfer performance,smaller temperature difference wall stress of the soar tube.（2）A coupled thermal-fluid-mechanical model is developed for the tubular receiver panels using supercritical CO₂as heat transfer fluid where the flow maldistribution phenomenon is taken into account.The effects of solar flux distribution and flow arrangements on the thermal and mechanical performances of the receiver panel are discussed with emphasis,and the effects of working conditions are also analyzed.The results indicate that:non-uniform solar flux distribution leads to larger temperature difference,more thermal loss,and greater stress and deformation of the receiver panel,and the maximum equivalent stress occurs on the junction of the outlet and the solar tubes in the receiver panel.Different arrangements of inlet and outlet affect the uniformity of mass flow and temperature distribution of the receiver panel.The type of flow arrangement that leads to a better uniformity of mass flow and temperature distribution can results in less thermal loss and smaller stress.Increasing mass flow and reducing solar flux can improve the thermal performance and reduce wall stress of the receiver panel.（3）A coupled thermal-fluid-mechanical model is developed for the compact receiver unit using supercritical CO₂as heat transfer fluid.The effects of different channel shapes on the heat transfer performance and stress distribution of the receiver unit were discussed,and the receiver units obtained from different channel layers were also analyzed.Finally,the performance of the receiver units with different channel structures was compared.The results indicate that:The downward semicircular channel has the lowest heat loss,the best heat absorption performance.The circular channel leads to the best comprehensive heat transfer performance.The maximum stress value of the both channels appear on the lower surface.When the number of channel layers is increased to more than three layers,the outer wall temperature and heat absorption performance will no longer change,and the position of the maximum stress shifts to tips from the middle bottom of the channel.The airfoil channel has the smaller flow resistance,and the best comprehensive heat transfer performance.