Study On Leakage Model Of Two-phase Critical Flow And Its Application

In chemical industry process, almost all the liquefied gases must be stored and transported in pressure vessels and piping. If some through-wall cracks exist in these vessels and piping, the mediums will leak through the cracks and the two-phase critical flow may occur. Generally, leakage accident will result in fire hazards or explosion disasters, which will lead to enormous pecuniary loss, personal injury and environment pollution. The study on the leakage model can help to describe the dynamic process of the leakage occurrence and development and to analyze the accident consequence and seriousness. The calculation of leakage rates of mediums has guiding significance on evaluating the design and improvement of some equipment and technical processes, and it is also important to assess the safety of the current process systems. Two-phase critical flow has been widely studied theoretically and experimentally for the last 40 years and some valuable results have been obtained. However, the prediction model accurately calculating critical mass flux does not exist up to now. The non-equilibrium and non-homogeneity of the medium and the non-continuity of the thermodynamic character make the research on the two-phase critical flow be more complex. It is the divergence on solving these problems that leads to the variance of the research results. Study on leakage model of two-phase critical flow and its application is a sub-project of the project "Fundamental Research on Disastrous Accidents Prevention and Control Techniques in Typical Chemical Industry Process" (No. 29936110), which is sponsored by the National Natural Science Foundation of P. R. China. In this study, a leakage model of two-phase critical flow is developed by mathematical method and applied to the leak-before-break (LBB) analysis of pressure vessels and piping.In this paper, a leakage model of two-phase critical flow is established on the basis of Fauske's model of two-phase critical flow and Levy's formula of the void fraction. The test device for two-phase critical mass flux is developed and the experimental investigation on the leakage model carried out. The experimental data are in good agreement with the calculation results of the leakage model. The leakage model of two-phase critical flow established already is applied to theleak-before-break analysis of pressure vessels and piping. A new leakage rate calculation method for mediums flowing through through-wall cracks is derived. A computer program for two-phase critical leakage analysis is compiled. By means of this software, the two-phase critical mass flux and the two-phase critical leakage rate through the through-wall crack can be calculated easily, and the thermodynamic parameters of water or vapor can also be queried quickly. Based on the results obtained in this paper, the two-phase critical mass flux can be calculated satisfactorily, which has important significance on predicting the leakage rate of the flammable, explosive, noxious and corrosive mediums and assessing the safety of the in-service process equipment. The research results are helpful for ensuring the LBB failure of pressure vessels and piping so as to prevent the occurrence of disastrous accidents.