过冷流动沸腾相界面演变过程的非均匀特性研究

The subcooled flow boiling in the hot channel and the outlet of the nuclear reactor core is helpful to improve the natural circulation and the safety performance of the system. The research on the phase interface evolution characteristics in subcooled flow boiling can support the precise design of the nuclear reactor. Most of the previous researches are limited by the uniform hypothesis in the understanding of the subcooled flow boiling for the limitation of the experimental technology and theory. In this project, the flow boiling visualization technology and laser diagnose technology are introduced to acquire the variation of the phase interface shape, the microlayer and the flow field in the subcooled flow boiling. Furthermore, the nonuniform features of phase interface evolution can be obtained. The effects of the thermal and fluid parameters on phase interface evolution are analyzed based on the experimental data and the statistical theory. The models to describe the nonuniform characteristics of the phase interface evolution are proposed by integrate the nonuniform factors generated in the subcooled boiling. At last, the relations and the impacts between the phase interface, heated wall and the surrounding fluid field are analyzed based on the obtained experimental results and models. The potential effect of the nonuniform characteristics of the phase interface evolution on heat transfer is analyzed to reveal the mechanism of the phase interface evolution under this multi-physical field. It is believed that the conduction of this project will provide new insight of the unsteady condition, random characteristics and the combined wall affections to understand the subcooled flow boiling phenomena.

核反应堆堆芯热通道和出口处的过冷流动沸腾能够显著增强系统的自然循环能力和安全裕度，开展过冷流动沸腾条件下的相界面演变特性研究可为反应堆的精细化设计提供理论依据。受实验技术和理论水平的限制，目前很多研究受困于均匀化假设，在深入理解过冷流动沸腾方面尚有不足。本项目引入可视流动沸腾技术和激光诊断技术获取过冷流动沸腾相界面形态、微液膜以及流场的瞬时变化规律，掌握过冷流动沸腾下的相界面演变过程的非均匀特性。基于获取的实验数据和概率分析方法研究局部参数条件对相界面演变过程的影响，综合考虑过冷流动沸腾中的非均匀因素，构建描述相界面演变过程的非均匀特性的模型。结合实验结果和理论模型研究相界面、加热壁面以及周围流场之间的耦合响应关系，分析相界面演变过程的非均匀特征的潜在影响，揭示多物理场耦合作用下相界面演变机理。通过本项目的研究，可以从非定常条件、随机特征以及耦合壁面效应等新的视角认识过冷流动沸腾现象。

过冷流动沸腾是指在加热通道中主流流体温度处在饱和温度以下时在壁面的加热作用下发生沸腾的现象，广泛存在于核反应堆和电子元器件等设备的冷却中。本项目通过沸腾条件下汽泡行为可视化实验获得汽泡动力学特性和汽泡统计分布特性，在此基础上研究不同表面特性下的沸腾行为及汽泡核化规律，在流动沸腾条件下，实验中观察到了两类特征完全不同的汽泡行为，基于实验数据获得了汽泡行为分类特性预测模型，通过对沸腾条件下汽泡可视化图像数据处理掌握了汽泡最大直径随机分布特性，并对不同条件下的汽泡最大直径进行了理论分析，进一步考虑流场特性对于气泡运动特性的影响，分析气泡生长过程中流场不均匀性对气泡的作用机制，构建更为精细的过冷流动沸腾非均匀相变数值模型，得到了可以预测汽泡最大直径的分析模型。