A study on Flashing Phenomenon of Cryogenic Liquid

在与本研究项目相关的以前的研究中，指出当液体受到快速降压，如低温储罐或管道破裂时，在极高降压率的情况下，容器液体表面会形成更稠密的雾层，这对之后发生的沸腾行为有很大的影响。因此，在本研究中，利用最初一年购买的高速摄像机，对雾化和沸腾现象之间的关系进行了闪光实验。并对快速降压过程中气泡形成的开始条件进行了尝试。此外，将这些结果应用于与数值模拟模型相比较的估计它们的压力下冲量和由于液体沸腾而产生的水蒸气的压力恢复。通过本研究项目得到的结果是…主要内容如下：1.采用两种不同壁面粗糙度的容器进行了实验研究。结果表明，即使在相同的条件下，压力瞬变和雾滴生长速度也有显著差异。这是由于预暴露的核位置的数量对壁面的影响。2.由于热渗透(导热、对流和辐射等)引起的不完善绝热壁面，在低温液体中形成热层状，使壁面温度升高是不可避免的。从周围环境看，与常温或高温液体相比，气泡形成初期的壁面特性对气泡形成的初始条件有很强的依赖性。3.容器内压力欠冲和随后的恢复压力的瞬变压力变化可由通过孔板的蒸汽传输率(对应于容器和管道的破裂和泄漏区域)与其降压后的爆炸性蒸汽产生率之间的质量平衡决定。较少

In the former study related to this research projects, it was pointed out that when liquid was subjected to a rapid reduction of pressure such as a breakdown of cryogenic storage tanks or pipes, a denser mist layr was formed over the liquid surface of vessel in case of extremely high depressurization rates, and that gave a strong influence to a boiling behavior to occur after that. So, in this study, flashing experiments on the relationship between the mist formation and boiling phenomenon was conducted by using the high speed video-camera being purchased during an initial year. And also an attempt have been made to clear the condition of inception of bubble formation under the rapid depressurization processes. In addition, these results are applied to the estimation of their quantities of pressure undershoot and pressure recovery due to the vapor generation along with the liquid boiling in comparison with the numerical simulation model.Results obtained through this research project ar … More e summarized as follows1.Experiments were carried out by using two kinds of vessel having the state of different wall roughness. As its result, it was observed that there are remarkable differences in both of pressure transients and mist growth rates even though the same condition. This can be considered due to the effects of the amount of preexsting nuclear sites on the wall surface.2.As a formation of thermal stratification in cryogenic liquid and making a high temperature of wall surface has not been avoidable because of the imperfect adiabatic wall caused by heat penetration (heat conduction, convection and radiation etc.) from the surroundings, a dependency of the wall charatevistics on the incipient condition of bubble formation appears strongly in comparison with those of normal or high temperature liquid in stored state.3.The transient pressure changes of the pressure-undershoot and the recovery pressure followed after that within the container may be determined by the mass balance between the vapor delivery rates through the orifice (corresponds to the breakdown and leakage area of vessel and pipes) and the explosive vapor generation rate after its depressurization process. Less