Effect of sodium bicarbonate powder on the process of ducted venting
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摘要:
为了研究惰性粉体对导管泄爆过程的影响,采用质量浓度C为0、40、80、120、160、200 、240 g/m3的碳酸氢钠(NaHCO3)粉体,分别抑制连接不同长度(250 mm、500 mm、750 mm)泄爆导管的5 L容器内甲烷/空气预混气爆炸。对火焰传播特性分析结果表明:容器内添加NaHCO3粉体可以极大地削弱导管内二次爆炸,且合适质量浓度的NaHCO3粉体可以消除二次爆炸。随着NaHCO3粉体质量浓度增加,容器内火焰结构逐渐不规则化,火焰到达容器末端时间延长,导管内火焰经历弱化到熄灭过程,不同质量浓度NaHCO3粉体导致3种火焰速度发展模式。对压力特性分析得知,导管内爆炸超压上升机理依赖于NaHCO3粉体质量浓度,粉体质量浓度较低时,容器中最大爆炸超压取决于二次爆炸产生的第二压力峰值,反之取决于火焰在容器触壁时产生的第一压力峰值。随着NaHCO3粉体质量浓度增加,超压峰值下降率先增加然后趋于稳定,表明质量浓度效应逐渐减弱。最后定量分析了导管-容器配置中火焰传播速度与爆炸超压的关系。
Abstract:To investigate the effect of sodium bicarbonate on the process of ducted venting, an experimental study was performed to suppress the methane-air explosions in a 5 L vessel connected with different duct length (250, 500, 750 mm) under NaHCO3 dry powder with the mass concentration C=0, 40, 80, 120, 160, 200, 240 g/m3. The flame front propagation and explosion overpressure waveform were analyzed. The results show that NaHCO3 powder greatly weakened the secondary explosion in the discharge duct, and the appropriate mass concentration of NaHCO3 powder eliminated the secondary explosion. As the NaHCO3 powder mass concentration increased, the flame structure in the vessel was gradually irregular, and the flame in the discharge duct went through the process of weakening to extinguishing. Moreover, the time for the flame to reach the end of the vessel was prolonged with the increase of powder mass concentration. Different mass concentration of NaHCO3 dry powder led to three development modes of flame velocity. The mechanism for the pressure rise in the vessel depended on the NaHCO3 powder mass concentration. The maximum pressure in the vessel was mainly dominated by the second pressure peak for the low powder mass concentration, but by the first pressure peak for the high powder mass concentration. The drop rate of overpressure increased at first and then leveled off with the increase of NaHCO3 powder mass concentration, which indicates that the mass concentration effect gradually weaken. Finally, the relationship between flame propagation velocity and explosion overpressure in the ducted vented vessel was quantitatively analyzed.
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Key words:
- methane explosion /
- ducted venting /
- explosion suppression /
- powder mass concentration
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