开式自然循环系统出口排热管内流型演化研究

开式自然循环系统作为新型非能动余排系统最终热阱排放回路，其安全稳定运行对于事故工况下堆芯余热安全导出至关重要，本研究通过可视化实验方法观察了开式自然循环系统出口排热管内流型演化特性，发现随着加热功率增加，开式自然循环逐步建立，该系统出口排热管内依次出现单相流、间歇性汽泡流、弥散泡状流、弹状流和间歇喷射流5种典型流型，分析了出口排热管内流型与系统稳定运行之间的关系，发现了开式自然循环系统剧烈振荡的根源，为提高开式自然循环系统流动稳定性提供了参考。 

Study on Flow Pattern Evolution in Outlet Heat Removal Pipe of Open Natural Circulation System

As the ultimate heat sink discharge loop of the new passive residual heat removal system, the safe and stable operation of the open natural circulation system is very important for removing the residual heat of the reactor core under accident conditions. In this paper, the flow pattern evolution in the outlet heat removal pipe of the open natural circulation system is observed by visual experiment. It was found that with the increase of heating power, the open natural circulation is gradually established. There are five typical flow patterns in the heat removal pipe at the outlet of the system: single-phase flow, intermittent bubble flow, dispersed bubble flow, slug flow and intermittent jet flow. The relationship between the flow pattern in the outlet heat removal pipe and the stable operation of the system is analyzed, and the source of the violent oscillation of the open natural circulation system is found, which provides reference for improving the flow stability of the open natural circulation system.