水平填充床中纤维质燃料正向阴燃数值模拟研究

Numerical simulation study of forward smoldering propagation of cellulosic material in a horizontally packed bed

根据多孔燃料三步反应动力学过程,建立了2D非稳态纤维质材料填充床阴燃的数学模型.阴燃的化学动力过程包括燃料热解、燃料放热氧化及焦炭的放热氧化.该模型既考虑了固-气之间的热交换,也考虑到气体在多孔介质内的扩散系数变化.数值模拟了来流速度对阴燃速度及平均最高温度的影响,结果表明:阴燃传播速度与来流速度基本上呈线性关系,来流速度对阴燃最高温度影响不大.同时也模拟了燃料阴燃过程中气体组分(O2、CO、CO2及H2O)的变化.通过改变3个反应指前频率因子发现:增大A2(燃料氧化频率因子)会加速阴燃,增大A1(燃料热解频率因子)和A3(焦炭氧化频率因子)均会减小燃料阴燃传播速度.

Based on a three-step kinetic mechanism, a two-dimensional, time-dependent numerical model is presented for the smoldering propagation of cellulosic material in a horizontally packed bed. The kinetic processes include pyrolysis and oxidation degradation of fuel and oxidation of char. Heat transfer between solid and gas is taken into account, and the diffusion coefficient varies with the temperature. The effects of airflow velocity is numerically simulated on spread rate and average maximum temperature of smoldering fuel. The results indicate that the spread rate linearly varies with the increasing of airflow velocity, airflow velocity has little effect on maximum temperature of smoldering fuel. The evolution of gas species （including O2, CO, CO2 and H2O） are predicted. By varying separately the pre-exponential frequency factors, the simulations show that smoldering spread rate increases with the increasing of A2 （fuel oxidation）, but decreases with A1 （fuel pyrolysis） and A3 （char oxidation）.