Abstract As nuclear power plants tend to be miniaturized and integrated, equal-height-difference natural circulation systems (EHDNCSs) have potential applications in floating nuclear power plants. This work experimentally investigated the flow modes of an EHDNCS at low pressure. It has observed four quintessential flow modes in the experiments. The transient characteristics of each flow mode were analyzed by the visualization results. In addition, the dispersion and amplitude characteristics of flow rate were compared in different flow modes based on 134 experimental cases. The experimental results reveal that the flow oscillation is related to unsteady flow pattern for intermittent and condensation oscillations. The condensation induced water hammer (CIWH) is found in the condensation oscillation. According to the stability map, it is found that the regions of stability and CIWH can be well divided by equilibrium quality of −0.23% and 0.47%, and the unstable range is enlarged by increasing the inlet temperature and resistance.

中文翻译：

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低压等高差自然循环系统流动模式及瞬态特性试验研究

摘要 随着核电站趋于小型化和集成化，等高差自然循环系统（EHDNCS）在浮动核电站中具有潜在的应用。这项工作通过实验研究了 EHDNCS 在低压下的流动模式。它在实验中观察到四种典型的流动模式。通过可视化结果分析了每种流动模式的瞬态特性。此外，基于134个实验案例，比较了不同流动模式下流速的弥散和幅度特性。实验结果表明，流动振荡与间歇振荡和冷凝振荡的非定常流动模式有关。在冷凝振荡中发现了冷凝引起的水锤（CIWH）。根据稳定性图，