超临界二氧化碳破口喷放特性数值分析

Numerical analysis of break ejection characteristics in supercritical carbon dioxide

超临界二氧化碳布雷顿循环系统在发生小破口事故时破口位置处因系统内外压差出现的复杂喷放现象尚未研究清楚。为探究不同上游滞止参数与管道长径比对喷放特性的影响,本文采用数值模拟方法开展三维压力容器小破口喷放现象研究。研究结果表明:上游滞止压力升高或滞止温度降低引起质量流量增加,长径比增加时质量流量减少。上游滞止参数对流量的影响机理主要是参数变化引起密度发生较大改变从而影响喷放质量流量,管道长径比对流量的影响主要因为直径的变化。滞止压力升高时3组工况流量增加值相差5.3%,滞止温度降低时3组工况流量增加值相差90.7%,相比于压力对喷放流量的影响,温度对流量增加速率影响更为显著。

When a small break accident occurs at the break location in a supercritical carbon dioxide(S-CO2)Brayton cycle system,a complex ejection phenomenon occurs owing to the significant pressure difference between the inside and outside of the system.However,this ejection phenomenon remains unclear.This paper investigates the effects of different upstream stagnation parameters and the length-to-diameter ratio(L/D ratio)of the pipe on the spray characteristics.The ejection phenomenon of a three-dimensional pressure vessel at the small break location was studied through numerical simulation methods.The research results show that an increase in upstream stagnation pressure or a decrease in stagnation temperature leads to an increase in mass flow rate,while an increase in the L/D ratio results in a decrease in mass flow rate.The upstream stagnation parameters mainly affect the flow rate because changes in these parameters cause significant variations in density,thereby influencing the mass flow rate of the discharge.In contrast,the L/D ratio of the pipe affects the flow rate mainly because of changes in diameter.When the stagnation pressure increases,the difference in the flow increase value among the three sets of conditions is 5.3%.Conversely,when the stagnation temperature decreases,the difference in the flow increase value among the three sets of conditions is 90.7%.This indicates that temperature has a more significant impact on the discharge flow rate compared with pressure.