Yuanzineng kexue jishu (Jul 2023)
Characteristic Analysis and Model Validation of Supercritical Carbon Dioxide Ejection in Pressure Vessel
Abstract
When the pressure vessel of supercritical carbon dioxide energy conversion system breaks, very complex ejection phenomena will occur, and its critical flow characteristics need to be studied urgently. Based on Moody’s and Henry-Fauske’s two-phase critical flow analysis method for one-component mixture, SCRSAP-LOCA program was opened in Modelica language. This program was divided into simple vessel module, phase judgment module, break injection calculation module and physical property query module according to the calculation function. Then, the flow phenomena in different stages of supercritical carbon dioxide injection process were modeled and analyzed, and compared with the existing experimental data to verify, and the effects of different initial conditions in the vessel on the injection process were analyzed. The results show that the program calculation results agree well with the experimental data. The error between flow rate and pressure is within 23%. The mass flow rate at the fracture calculated by Moody’s model is closest to the experimental value. The flow rate calculated by Henry-Fauske’s model is about 15%-25% higher than the experimental value. The emission of carbon dioxide in pressure vessel can be roughly divided into three stages: Fast pressure relief stage with high mass flow, stable pressure relief stage with medium mass flow and uniform pressure relief stage with low mass flow. The break flow and pressure curve of the vessel show a stepped decrease. The emission behavior of supercritical carbon dioxide in vessels varies greatly at different initial temperatures and pressures. When the initial temperature in the pressure vessel is 297 K and the initial pressure increases from 10 to 20 MPa, the initial ejection mass flow in the first stage is larger, the pressure in the vessel is lower at the beginning of the second stage and the critical two-phase ejection duration is longer. When the pressure in the pressure vessel is 15 MPa, the increase of the initial temperature will significantly reduce the fluid density, accelerate the decrease of the free liquid level and shorten the critical discharge time of two-phase. As the initial temperature increases further, the flow and pressure curves become smoother as supercritical carbon dioxide approaches the gaslike region. In addition, phase transitions occur in the vessel during the ejection process and liquefied carbon dioxide deposits at the bottom of the vessel due to the difference in density. The research results can provide reference for the analysis of supercritical carbon dioxide emission characteristics in pressure vessel, and provide support for the research of leakage accident process and safety analysis and evaluation of supercritical carbon dioxide energy conversion system.
