Effect of oxygen on flame spread over liquids
Effect of oxygen on flame spread over liquids
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DOI：
10.1016/j.proci.2006.07.196
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
K. Takahashi;Y. Kodaira;Y. Kudo;A. Ito;K. Saito
中科院分区：
文献类型：
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作者：
K. Takahashi;Y. Kodaira;Y. Kudo;A. Ito;K. Saito
利用窄宽度矩形开顶塔板，在不同氧气浓度下，对几种不同液体进行了火焰蔓延实验。在所有实验情况下，初始液体温度都保持在闪点以下，因此在火焰传播过程中形成了亚表面液体循环。用粒子径迹激光测温仪(PTLS)结合高速摄像机测量了流场结构，用扩散光阴影技术(DLSG)测量了流场的温度结构。XO2=0.175的正常重力下的火焰传播速率与XO2=0.21时的微重力(10-5g)火焰传播速率相当。次表层液体对流形成的热边界层和动量边界层的尺寸随着氧气浓度和重力的降低而增大。动量边界层的深度是热边界层深度的两倍。通过标度分析发现，对于浅液池，无因次火焰传播速率与(mA·Pr)−1相关，而对于深液池，无因次火焰传播速率与(mA·Pr)−1.5相关。这里Ma是Marangoni数，Pr是Prandtl数。我们预测了(mA·Pr)−1随重力的降低而减小，实验发现(mA·Pr)−1随环境氧浓度的降低而减小。(mA·Pr)−1与重力和环境氧浓度的依赖关系相似，表明微重力火焰在液体上的传播可以在正常重力下低氧浓度环境下进行研究。
Using a narrow width rectangular open top tray, we performed flame spread experiments over several different liquids under various oxygen concentrations. The initial liquid temperature was kept below the flash point for all experimental cases, therefore, sub-surface liquid circulation was formed during the flame spread. We measured the flow structure by a particle-track laser-sheet (PTLS) combined with a high-speed video camera and the temperature structure by a diffusion light shadowgraph (DLSG) technique. The flame spread rate in normal gravity with XO2=0.175 matched that in microgravity (10–5g) with XO2=0.21. The size of thermal and momentum boundary layers created by a sub-surface liquid convection increased with a decrease in both oxygen concentration and gravity. The depth of the momentum boundary layer was found twice larger than the depth of the thermal boundary layer. Scaling analysis was conducted and found that the non-dimensional flame spread rate can be correlated with (Ma·Pr)−1for the shallow liquid pool and with (Ma·Pr)−1.5for the deep liquid pool. Here Ma is Marangoni number and Pr is Prandtl number. We predicted that (Ma·Pr)−1decreases with a decrease in gravity and experimentally found that (Ma·Pr)−1decreases with a decrease in the ambient oxygen concentration. A similarity was found between the dependency of (Ma·Pr)−1with gravity and that with the ambient oxygen concentration, indicating that the microgravity flame spread over liquid can be studied under normal gravity with a reduced oxygen concentration ambient.