Effect of blockage ratios on the characteristics of methane/air explosions suppressed by dry chemicals
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摘要: 为了研究开口阻塞比φ对粉体抑爆特性的影响,采用质量浓度C为0、80、160、240 g/m3的Al (OH)3和NaHCO3粉体,分别抑制具有不同φ(0、0.2、0.4、0.6、0.7、1.0)值的5 L管道内甲烷/空气预混气爆炸。实验结果表明:火焰的破碎度随粉体抑爆效率的增大而增大;最大超压峰值pmax、爆燃指数Kst由燃烧速率和泄爆速率共同决定。φ=0.7是每条爆炸特征参数曲线的拐点。随着φ值增加,超压峰值下降率δ先增大后减小,在0.4和0.6之间达到最大;总体上,Al (OH)3和NaHCO3两种粉体的抑爆效率相近。但在某些阻塞比下,阻塞比引起的低湍流影响着粉体颗粒的沉降行为,使得Al (OH)3抑爆效率优于NaHCO3。当粉体质量浓度从80 g/m3增加到240 g/m3时,热阻增加,火焰的热量不能扩散到粒子云的中心,不利于内部粒子的吸热分解,致使浓度效应越来越弱。Abstract: To investigate the effect of blockage ratios (φ) on the inhibited flame, an experimental study was performed to suppress the methane-air explosions in a 5 L duct with the blockage ratios φ = 0, 0.2, 0.4, 0.6, 0.7, 1.0 under BC and Al(OH)3 inhibitors with the mass concentrations C = 0 g/m3, 80 g/m3, 160 g/m3 and 240 g/m3. The results indicated that the flame fragmentation increased with the improvement of the suppression efficiency. The maximum explosion pressure (pmax) and the deflagration index of the explosion (Kst) were dominated by the combustion rate and the discharge rate. Furthermore, φ = 0.7 was the inflection point of pmax and Kst curves. The drop rate in the Pmax (δ) firstly increased and then decreased as the blockage ratio increased. And the maximum δmax was achieved at the blockage ratio between 0.4 with 0.6. In general, the suppression efficiency of Al(OH)3 and NaHCO3 powders was comparable. However, the low turbulence caused by certain blocking ratios impacted the sedimentation of inhibitor particles, which made the suppression efficiency of Al(OH)3 better than that of NaHCO3. There was an increasing heat resistance as the powder concentration increased from 80 g/m3 to 240 g/m3, which blocked the penetration of heat from the flame into the interior of particle cloud and disabled interior particles’ thermal decomposition, leading to a weakening concentration effect.
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Key words:
- blockage ratios /
- powder concentration /
- explosion suppression /
- methane explosion
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表 1 不同工况下超压峰值下降率增值的比较
Table 1. Comparison of the increment in the drop rate of pmax with different experimental conditions
粉体 φ (δ|C=160−δ|C=80)/% (δ|C=240−δ|C=160)/% NaHCO3 0 9.4 3.5 0.2 12.3 7.3 0.4 15.7 2.1 0.6 13.9 11.2 0.7 18.3 13.9 1.0 3.7 2.7 Al(OH)3 0 5.1 9.5 0.2 10.1 16.8 0.4 16.2 1.1 0.6 9.6 3.1 0.7 12.1 8.7 1.0 3.5 1.3 -
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