Numerical Simulation Of Multi-tube Flow Boiling Heat Transfer Under Coupled Heat Transfer Conditions

In the actual operation of the once-through steam generator,the primary working fluid conducts coupling heat transfer with the secondary working fluid through the tube wall,and the secondary working fluid undergoes whole process of flow boiling from subcooled to superheated.The "dry out" phenomenon that occurs somewhere in the tube will cause the wall temperature to rise sharply,which may cause problems such as uneven stress and rupture of the heat transfer tube.In addition,the number of heat exchange tubes of the steam generator is large,and the temperature distribution and flow field characteristics of different heat exchange tubes also greatly affect the heat transfer performance of the steam generator.At present,the numerical simulation method under the coupled heat transfer condition of the primary and secondary side is not mature enough,and the numerical simulation method and thermal engineering of the full flow pattern boiling and phase change heat under the coupled heat transfer condition of the steam generator are carried out.The study of hydraulic characteristics is of great significance to steam generator thermal hydraulic design,safety analysis,structural design,and heat transfer tube material selection.Firstly,this paper uses the Becker experiment,based on the Euler two-fluid multiphase flow model,couples the wall boiling model(RPI)and the improved wall boiling model(CHF),respectively,to verify the reliability of the two-phase flow boiling numerical model and verify the CHF model Predict the rationality and reliability of the heat transfer characteristics after "dry out" and "post dry-out".The thermal-hydraulic characteristics of single-tube two-phase flow boiling(including pressure drop,velocity,temperature,steam content,etc.)are numerically analyzed,and the law of two-phase flow and boiling heat transfer on the secondary side of the once-through steam generator is clarified.Then,taking the minimum periodic unit tube of the steam generator as the research object,based on the verified full flow pattern boiling numerical simulation method,the applicability of the numerical simulation under the sodium-water coupled heat transfer condition is analyzed,and the analysis is performed under the coupled condition The regular characteristics of the secondary side wall temperature,wall heat flux distribution,dry out position and other parameters,and the sensitivity analysis of the interphase force model and parameters,and the influence of interphase force on flow boiling is obtained.Finally,with the 19-tube PFBR model steam generator as the research object,a 19-tube grid model was established,and the application research of multi-tube flow boiling under coupled conditions was carried out.The position of the “dry out” point on the secondary side was obtained,and the secondary side Key thermal parameters such as side wall temperature,cavitation share,heat flux distribution,and pipe temperature at different locations are analyzed to further clarify the application characteristics of the verified numerical method under multi-tube coupling heat transfer conditions.The calculation results show that the improved wall boiling model(CHF)can better simulate the flow boiling and heat transfer process of the secondary side of the once-through steam generator;the temperature field of the multi-tube under the coupled heat transfer condition and the "dry out" position documentary The working conditions of the heat flux density on the fixed wall of the tube are quite different,and the results of the coupling calculation on both sides have little error with the experimental value,which can more accurately predict the laws of the secondary side temperature field,flow field,and heat transfer;model sensitivity analysis found The drag force model has little effect on the radial parameter distribution,and has a certain effect on the axial parameters.The non-drag force model has basically no effect on the axial parameters.The turbulent dissipation force and lift force have an effect on the distribution of radial cavitation and the wall void The peak value of the bubble share has a significant impact.The wall lubrication force has a smaller effect on the radial cavitation share than the lift force,and the virtual mass force can be ignored in the calculation.According to the simulation results of 19 pipes,the temperature of the outer pipe is greater than the temperature of the inner pipe,and In the case of the same peripheral pipe,the temperature of the pipe closer to the shell side is relatively low.