Investigation Of Natural Convection With Curved Surface Heating From Below In A Rectangular Enclosure

In the design of a certain small modular reactor(SMR),the upper head of containment vessel(CV)is immersed in external water tank.After a severe accident,the residual heat inside CV is removed by the natural convection above the upper head,thereby maintaining the long term effective cooling of the reactor and improving its inherent safety.Investigation the phenomena and characteristics of natural convection heat transfer above the upper head of CV is very important for safety analysis of reactor core under severe accidents.Based on the research background of the natural convection above upper head of CV,the natural convection induced by curved surface heating from below in a rectangular enclosure has been taken as the research object,and experimental research has been carried out.The temperature distribution of curved heating section was measured using high-precision thermocouples,while an L-shape temperature measurement structure was utilized for obtaining the thermal stratification characteristics inside the rectangular enclosure.At the same time,the local flow field visualization was performed using particle image velocimetry technique,and the influence of curved structure on the flow structure of natural convection was analyzed.Through the analysis and processing of the thermal experimental data of natural convection,the effect of curved heating section on the heat transfer characteristics was studied and one existing correlation was analyzed and evaluated.By employing the standard analysis procedure of visualization data,the distributions of velocity and turbulence kinetic energy near the curved heating surface were obtained.Based on the measurement results of temperature and velocity,the influence mechanism of curved heating surface on natural convection heat transfer was identified,and a correlation suitable for describing the heat transfer characteristics of curved heating section was fitted.Based on numerical simulation method,by considering the heat transfer between solid domain and fluid domain,the two-dimensional natural convection heat transfer problem under the same conditions as experiments has been investigated.The heat transfer characteristics of curved heating section with different turbulence models and turbulent heat flux models were evaluated and analyzed.Based on the experimental data,the turbulent heat flux model was optimized and improved.The modified turbulent heat flux model can effectively improve the prediction accuracy of natural convection heat transfer characteristics generated by the curved heating section in a rectangular enclosure.Based on the parameters optimized model,the characteristics of fluid flow and heat transfer induce by curved heating section in the rectangular enclosure were simulated and analyzed.The experimental and numerical results of this paper could be utilized in reactor thermal-hydraulic analysis and numerical model development.It is of great significance to improve the reliability of reactor under accident conditions.