Investigation On Flow And Heat Transfer Models Of A LBE Cooled Fast Reactor Helical Coiled Tube Once Through Steam Generator Based On Two-fluid Model

Helical coiled tube Once Through Steam Generator(HOTSG)has been applicated in some Lead Bismuth Eutectic(LBE)cooled fast reactor heat exchangers because of its compact structure design,advanced heat transfer coefficient and free thermal expansion.As the key heat exchanger of primary and secondary sides in LBE cooled fast reactor,the stability and reliability of HOTSG affect the economy and safety of reactor system.The thermal hydraulic characteristics are the input conditions for the structural design and optimization of steam generator,the distribution of key parameters under steady and transient states,and the analysis of safety characteristics.Therefore,the thermal hydraulic models are the basis of steam generator design and analysis.In this study,thermal hydraulic models of LBE cooled fast reactor HOTSG is analyzed.The coupled flow and heat transfer model of primary and secondary sides based on two fluid structure is established.The distribution characteristics of thermal hydraulic parameters and flow field information are obtained by combining one-dimensional code calculation with threedimensional numerical analysis.What’s more,through the comparison of BREST-OD-300 and MRX experimental data,the correctness of the model system is verified.Last but not least,according to the results of three-dimensional numerical calculation,the influence of cross mixing and other three-dimensional effects on heat transfer is revealed.The main work of this thesis includes:(1)Based on the structural characteristics of HOTSG of LBE cooled fast reactor,the one-dimensional physical model of primary and secondary side is simplified.The thermal hydraulic system of three-phase fluid based on two fluid structure is mainly developed,and the boiling phase flow pattern in helical tube is divided.According to the sensitivity analysis of the mesh,the size of one-dimensional control volume is determined.What’s more,through the sensitivity analysis of the model,the phase wall,phase to phase friction and heat transfer models coupled with the primary and secondary sides are evaluated and confirmed.The flow field is discretized by finite volume method and the governing equations are solved by SIMPLEC algorithm.(2)The experimental data of BREST-OD-300 and MRX steam generators are used,the calculation results are carefully analyzed and compared with thermal hydraulic characteristics of steady state and transient state respectively.The maximal relative error between the primary side outlet temperature and the experimental data is 5.94%,and the secondary side outlet temperature error is only 0.69%.The thermal hydraulic parameters are in good agreement with the experimental data,which verifies the accuracy of the models on both sides.Then,the model application calculation of the steam generator of LBE fast reactor are carried out,and the distribution characteristics of thermal hydraulic parameters along the tube length are obtained.The calculated results are in good agreement with the design values.Through the uncertainty analysis,the primary side temperature change has a great impact on the operation of steam generator,resulting in the outlet steam temperature uncertainty of 40.96℃.The changing process of the thermal hydraulic parameters of helically coiled steam generator conforms to the qualitative mechanism analysis results of thermal hydraulic analysis.(3)By using established and validated models,three-dimensional numerical simulation based on porous media model is investigated.The three-dimensional independent characteristics of the model are verified by comparing the one-dimensional results with the three-dimensional numerical results.The relative errors of outlet steam temperature and design value calculated by one-dimensional program and threedimensional numerical calculation are 0.55% and 0.81% respectively,and the relative errors of LBE outlet temperature are 1.20% and 0.33%,both of which have small errors.Three dimensional effects such as cross mixing have limited influence on heat transfer.In addition,the three-dimensional characteristics of the overall flow field and temperature field of the steam generator are obtained,and the influence of the radial velocity and cross flow of LBE in the inlet chamber on the overall flow field is clarified.In conclusion,based on two fluid structure,friction and heat transfer model of HOTSG is developed in this study.The correctness of the model is verified by experimental data and three-dimensional numerical simulation,which provides input conditions for the subsequent structural design optimization and safety characteristics analysis of LBE cooled fast reactor.Moreover,the research is of great significance to ensure the safety of steam generator.