开式自然循环系统启动特性实验研究

Experimental study on start-up characteristics of open natural circulation system

对开式自然循环系统的启动过程进行了实验研究,并详细分析了不同加热功率和不同入口过冷度条件下系统出现的实验现象和流动特性,最后给出了自然循环系统在启动过程中的流动不稳定性边界图。结果如下:在低加热功率下,随着入口过冷度的减小系统会依次经历单相稳定、两相振荡和两相稳定流动;增大加热功率会使系统的两相流动不稳定范围增大,甚至很难形成稳定的两相流动。在两相振荡阶段,系统会出现由闪蒸诱发的不稳定流动以及由沸腾喷发和闪蒸共同诱发的不稳定流动两种模式,这两种不同模式的流动不稳定性均属于密度波不稳定性。

Background： The open natural circulation system has been used gradually in the passive safety system after severe accidents such as passive containment cooling system. Purpose： The aim is to investigate the start-up process of the open natural circulation system, and analyze the experimental phenomena and flow characteristics under different heating power and inlet subcooling conditions in detail. Finally, the map of the instability boundary during the startup of the natural circulation system is given. Methods： Experimental facility was set up and numbers of experiments under different conditions were conducted. The flow characteristics and mechanisms with different flow phenomena are analyzed in detail combining with the measurement results of the fluid temperature, pressure and mass flow rate. Finally, all the flow behaviors were classified under different conditions. Results： The results are as follows： the system which operates under low-power conditions will experience the stable single-phase, two-phase oscillation and stable two-phase flow sequentially with the inlet subcooling increasing. During the two-phase oscillation phase, two flow modes including the flashing-induced instability and the combination of the boiling eruption and flashing-induced instability occur. Conclusion： The instability region of the system enlarges with the increase of the heating power, which even makes it difficult to form the stable two-phase flow. During the two-phase oscillation phase, both the flashing-induced instability and the combination of the boiling eruption with flashing-induced instability belong to the density wave instability.