Study On Optical-thermal Performance And Safety Of Supercritical Carbon Dioxide High Temperature Solar Cavity Receiver

Integrating supercritical CO₂（s CO₂）Brayton cycle with tower or dish solar thermal power generation technology to establish s CO₂ solar thermal power generation system,a promising development direction of the concentrating solar power technology（CSP）,can effectively improve the working temperature and power generation efficiency.The solar receiver is a critical component of this system,and its performance determines whether the system can run safely and efficiently.In this dissertation,the s CO₂ conical cavity receiver is selected as the research object,and the receiver’s optical-thermal conversion performance and safety are studied.The optical model of the receiver is established based on the Monte Carlo ray tracing method,and the effects of the relative distance of focus,angle ratio,and aspect ratio on the optical efficiency and heat flux distribution of the receiver are studied.The results show that the relative distance of focus has a more significant effect on the optical performance.Given the optical efficiency and working reliability,it is recommended that the relative distance of the focus should be within 0～30 mm,the angle ratio should be within 0.25～0.75,and the aspect ratio should be within 1.5～2.0.According to the heat flux distribution characteristics of the receiver,a heat flux loading method is proposed.The receiver is divided into different regions,and the optical results are applied to each region as the boundary conditions for thermal analysis.Based on this method,the coupled optical-thermal-fluid model is constructed,and the influence of critical geometric parameters（aspect ratio and angle ratio）and operation parameters（mass flow rate,inlet temperature,and direct normal irradiance（DNI））on thermal performance of the receiver under different flow directions（up-flow and down-flow）are investigated.The results demonstrate that the thermal performance under up-flow is better than the case of down-flow.The optimum thermal performance is achieved when the aspect ratio and angle ratio are 1.5 and 0.25,respectively.The results also show that increasing the flow rate can improve thermal performance,and an opposite trend is observed when the inlet temperature increases,when the DNI>800 W/m²,the thermal performance will deteriorate.Based on the coupled optical-thermal-fluid model and the theory of thermoelasticity,a coupled thermal-mechanical model of the receiver is established,and the effects of critical geometric parameters and operating parameters on the static characteristics under different flow directions are studied.The results show that the stress level of the receiver is higher under up-flow;The increase of angle ratio will increase the stress,and the increase of aspect ratio will reduce the stress,among which the effect of angle ratio is more significant;The increase of mass flow or DNI will increase the stress,and an opposite trend is observed when the inlet temperature increase.According to the damage accumulation theory,the damage model of the receiver is established,and a fatigue-creep damage calculation method is proposed to predict the damage of the receiver.Based on the damage allowable region,the comprehensive damage coefficient K_D,which can reflect the interaction between fatigue and creep,is proposed to assess the safety margin of the receiver.Based on this method,the effects of flow direction,geometric parameters,and operating parameters on damage and K_Dare investigated.The results demonstrate that the damage and K_D are smaller,and the safety margin of receiver is larger under up-flow;The smaller the angle ratio and the larger the aspect ratio,the greater the safety margin of the receiver;Higher inlet temperature and DNI will lead to damage and K_D increase,the safety margin is smaller,and the impact of mass flow shows the opposite trend.Based on the above research,the experimental prototype of the receiver is manufactured,the s CO₂ parabolic dish collector experimental system is built,and the thermal performance of the receiver is experimentally studied.According to the experimental results,the influence of operating parameters on the thermal performance of the receiver is analyzed,and the numerical model is verified by comparison.