钠滴着火特性和预燃模型综述

Characteristics and Model Development of Sodium Droplet Pre-ignition

与碳氢化合物燃料液滴着火特性不同,液态钠滴在常温空气中会自发着火,钠滴着火延迟时间及着火极限受着火前的预燃阶段控制。预燃阶段钠滴主要发生表面氧化反应,该阶段的特性及表面氧化的速率模型是钠滴燃烧研究的一个重点。目前国内用于快堆雾状钠火安全分析程序的预燃模型是通过氧气向钠滴表面传输来控制表面氧化反应速率,着火延迟时间由钠滴温度升高到沸点(1156 K)进行计算。基于温度的化学动力学控制模型以及传质与化学动力学组合控制模型被开发出来用于描述钠滴的预燃阶段,通过不同模型对不同初始条件钠滴着火特性的数值计算和分析对比,这两种模型可以预测不同条件下的钠滴着火极限,计算结果更加符合钠滴实际着火特性。

Usually,the liquid sodium droplet can ignite spontaneously when it appears in normal temperature air,which is different from the ignition characteristics of hydrocarbon fuel droplets.The ignition delay time and ignition limit of sodium droplets are controlled by the pre-ignition stage before gas phase combustion.In the pre-ignition stage,surface oxidation is the main process.The characteristics and physical model of this stage is a key point in the study of sodium droplet combustion.At present,the pre-ignition model used in the safety analysis program of the spray sodium fire of fast reactor in China controls the surface oxidation reaction rate by the rate of oxygen transfer to the surface of sodium drops,and the ignition delay time is calculated from the temperature of the sodium drop to the boiling point(1156 k).The temperature based chemical kinetic control model and the combined mass transfer/reaction kinetic control model have been developed to describe the pre-ignition stage of sodium droplet.Through the comparison of the calculation and analysis results of different models for different initial conditions of sodium droplet ignition,the latter two models can predict the ignition limit of sodium droplet under different conditions and more in line with the actual ignition characteristics of sodium droplets.