棒束通道两相流相界面浓度输运机理研究

The interfacial structure of the two-phase flow is the basis for prediction of the interfacial heat and mass transfer, the interfacial drag between the gas and liquid phases, and closure relations for two-fluid model. The traditional flow regime-based method usually selects correlations for the interfacial area concentration and heat transfer prediction based on the flow regime determined from the flow regime map. This method encounters difficulties when applying to the rod bundle channel geometry due to the complex channel structure. Determination of the correct flow regime and prediction correlations is challenging, and the method cannot accurately predict the dynamic evolution of the two-phase flow parameters. This directly affects the performance and safety of the advance nuclear fuel... This project intends to combine the miniatured conductivity probe and the Particle Image Velocimetry to form joint two-phase flow measurement technique. The distribution of the interfacial two-phase parameters across the entire cross-section and its evolution characteristics along the axial direction will be obtained through experiment. By analyzing the experimental data, the effects of two-phase flow pressure drop, turbulence, bubble breakup and coalescence on the interfacial transport will be obtained. From the microscopic interfacial structure point of view, the interfacial area transport equation (IATE) can be established based on the Boltzmann transport equation and the experimental results, and the mechanism of the interfacial transport will be revealed. This can solve the basic technical problem of continuous and dynamic prediction of the interface area concentration variation, provide closure relation for two-fluid model, and promote the nuclear system analysis code autonomy. On this basis, the effects of the spacer grid on the interfacial transport will be studied and be modeled as source terms to the IATE, which can promote the development and optimization of the advanced fuel and spacer grid.

相界面结构输运是气液两相流相间传热传质、阻力预测及两流体模型封闭的基础。传统方法通常在确定流型的基础上选择经验关联式计算相界面浓度及流动传热，应用到复杂结构棒束通道时，确定正确的流型及关联式较困难，不能获得准确、动态的预测结果，直接影响反应堆先进燃料的性能和安全性。.本项目拟结合微型电导探针和粒子图像测速，突破两相流参数联合测量技术。试验获得带定位格架棒束通道相界面结构参数的截面分布及轴向演化特征，分析给出两相压降、湍流、气泡破裂与聚并等因素对相界面浓度输运的影响规律。进而从微观相界面结构出发，基于玻尔兹曼输运方程，结合实验研究结果，构建棒束通道相界面浓度输运方程，揭示相界面输运机理。解决连续、动态预测相界面浓度变化这一基础问题，为两流体模型提供封闭关系，推动核电软件自主化。在此基础上研究定位格架的影响并建立相界面浓度输运定位格架源项模型，促进先进燃料及定位格架的研发与优化。

准确预测棒束通道内的两相流动与传热特性是燃料组件设计的关键，也是开发系统分析程序的难点。传统的热工水力计算方法通常采用针对不同流型构建的空泡份额及相界面浓度等参数的经验公式，虽能保守的满足工程计算需求，但存在预测较为保守、流型转换边界偏差大等问题。.本项目以掌握棒束道两相流相界面结构特性、建立相界面预测模型为目标，结合实验及模型构建方法，针对棒束通道内两相流相界面结构输运特性及定位格架对相界面结构的影响机理开展研究，主要包括：（1）棒束通道两相流相界面结构输运特性实验研究；（2）棒束通道两相流相界面结构参数输运模型建模及模拟；（3）定位格架对两相流相界面结构输运特性的影响研究。.针对棒束道两相流相界面输运特性，设计搭建了棒束通道两相流相界面参数精细化测量实验系统及二维探针移动测量系统，在此基础上开展了棒束通道两相流实验，建立了精细化两相流相界面结构参数数据库。从宏观相界面特性角度，基于可视化方法进行了流型划分与流型图构建，基于机器学习建立了流型分类与预测模型；从微观相界面特性角度，构建了两相流相界面浓度输运方程，编程实现了棒束通道内相界面浓度等参数的动态预测。最后，评价了定位格架对棒束通道两相流流型图、流型转换边界以及对两相流相界面参数演化的影响。.本项目建立的相界面浓度输运方程，可准确、动态地预测两相流参数，为两流体模型提供封闭关系，提高核电系统分析程序的可靠性；所获得的精细化实验数据，可为模型研发及验证提供全面数据支持，也可用于两相流CFD、系统分析程序验证。研究成果对燃料组件及定位格架设计与基准事故工况分析与评价具有重要意义。