瞬变外力场下棒束通道过冷流动沸腾汽泡迁移行为研究

The mechanism of bubble dynamic characteristics and bubble migration behaviors in rod bundle under transient forces is considered to be very complex, which will affect the safe heat transfer boundary of nuclear reactor. The bubble growth characteristic, departure parameters, bubble velocity and bubble trajectory in rod bundle under transient forces induced by rolling and heaving motions will be obtained using the visualization method in this project, and the correlation of bubble velocities and bubble equivalent diameters will be established. The statistical law of bubble number density, bubble equivalent diameters and bubble velocity distribution will be acquired through digital image processing. Combined with the visualization experiment and bubble force analysis, the mathematical physics models related to bubble dynamics and the migration behavior will be achieved, and using two-fluid model as the basic framework, numerical simulation work of subcooled flow boiling in rod bundle under transient forces will be conducted with the help of CFD software platform. The effect of transient forces on bubble migration behavior will be evaluated quantitatively and the influence of bubble migration behavior on mixing characteristic and macro heat transfer ability will be explored, by setting different sources of transient forces in the UDF code module. The research results are expected to be helpful to deeply understand the mechanism of two-phase flow and boiling heat transfer in complex channel under transient forces, also can be reference for reactor thermal hydraulics analyzing under marine conditions.

瞬变外力场下棒束通道汽泡动力学特性及汽泡迁移行为作用机制十分复杂，并直接关系到核反应堆的安全传热边界。本项目基于可视化方法，获得起伏和摇摆运动引起的瞬变外力场下棒束通道内汽泡生长特性、脱离参数、运动速度和轨迹，建立运动速度与汽泡等价直径的关联式。通过数字图像处理，获得瞬变外力场下子通道汽泡数密度、汽泡等价直径和汽泡速度分布的统计学规律。结合可视化实验和汽泡受力分析，构建瞬变外力场下汽泡动力学和汽泡群迁移行为相关数学物理模型，以两流体模型为基本框架，借助于CFD软件平台开展瞬变外力场下棒束通道过冷沸腾数值模拟。通过在UDF程序模块中设置不同的瞬变外力场源项，量化评价瞬变外力场对汽泡迁移行为的影响机制，探索汽泡迁移行为对子通道交混特性和宏观流动传热特性的影响规律。研究成果将有助于深入认识瞬变外力场下复杂通道内两相流动和沸腾换热机理，亦可为海洋条件下反应堆热工水力学分析提供参考。

鉴于海洋运动条件下棒束通道过冷流动沸腾的复杂性及工程应用重要性，本基金通过汽泡可视化实验获得瞬变外力场下3×3棒束通道汽泡动力学特性及汽泡运动特性实验数据，借助于Fluent软件对运动条件下棒束流道内的过冷沸腾进行数值模拟，通过在UDF程序模块中设置不同的瞬变外力场源项，评价倾斜、起伏运动、摇摆运动对汽泡迁移行为的影响规律。基于现有实验结果，从局部空泡分布和瞬态宏观参数波动两方面验证了数值模型。从二次流和浮力分量两方面分析倾斜对汽泡迁移行为的影响；从附加力、二次流、流量波动三方面分析起伏的影响；从附加力、二次流、浮力分量、流量波动四方面分析摇摆运动的影响，数值模拟和实验研究工作基本实现预期目标。本基金研究成果有望应用于船舶蒸汽动力系统设计及海洋运动条件下反应堆热工水力分析。