加热功率对低压低高差自然循环系统两相流动特性影响研究

对浮动式核电站中一类具有倾斜热管段的低压低高差自然循环系统的两相流动特性进行了实验研究，分析了加热功率对两相流动特性的影响。结果表明，不同功率条件下系统存在两相稳定冷凝和伴随蒸汽冷凝诱发水锤两相振荡2种流动模式，热管段内过冷水倒流和蒸汽与低温过冷水直接接触冷凝是导致2种流动模式的内在机制。此外，蒸汽冷凝诱发水锤的发生会产生较大压力脉冲，并导致过冷水倒流长度显著增加，进而加剧系统流动不稳定。进一步研究表明，加热段出口含气率可以作为流动不稳定判断依据。 

Research on Influence of Heating Power on Two-Phase Flow Characteristics in Natural Circulation System with Low Height Difference at Low Pressure

Two-phase flow characteristics of a kind of natural circulation system with low height difference and inclined heat pipe section in floating nuclear power plants are experimentally studied at low pressure. The influences of heating power on the two-phase flow characteristics are analyzed. The results show that there are two flow modes in the system under different power conditions: two-phase stable condensation and two-phase oscillation along with steam condensation induced water hammer. The backflow of subcooled water in the heat pipe section and the direct contact condensation of steam and low-temperature subcooled water are the internal mechanisms resulting in the two flow modes. In addition, the occurrence of steam condensation induced water hammer will generate large pressure pulses and cause a significant increase in the backflow length of subcooled water, which further aggravates flow instability. Further research shows that the gas content at the outlet of the heating section can be used as a basis for judging the flow instability.