A study on Flashing Phenomenon of Cryogenic Liquid

在与该研究项目相关的以往研究中，指出了在低温储罐或配管破裂等液体急剧减压时，在减压率极高的情况下，在容器的液面上形成了较浓的雾层，对之后的沸腾行为产生了很大的影响。因此，本研究利用一年前购置的高速摄影机，进行了喷雾与沸腾现象的闪烁实验。并对快速降压过程中气泡形成的起始条件进行了探讨。此外，将这些结果应用于估算它们的压力下冲量和压力恢复量，并与数值模拟模型进行比较。 关于我们 1.采用两种不同壁面粗糙度状态的容器进行了实验研究。其结果是，它被观察到，即使在相同的条件下，在压力瞬变和雾增长率有显着的差异。2.由于热渗透（热传导、对流和辐射等）造成绝热壁面不完善，在低温液体中形成热分层，使壁面温度升高已不可避免。从周围环境中，与常温或高温储存状态相比，壁面特性对气泡形成的初始条件有很强的依赖性; 3.容器内压力下冲和随后的恢复压力的瞬态压力变化可以由通过孔板的蒸汽输送速率之间的质量平衡决定（对应于容器和管道的破裂和泄漏面积）和其降压过程后的爆炸性蒸汽产生率。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