Experiments on the effects of venting and nitrogen inerting on hydrogen-air explosions
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摘要: 为了解受限空间内不同氮气体积分数φ对氢-空气泄爆的影响，在高1 m的顶部开口容器中进行了实验。结果表明：当φ≤40%时，容器内部的最大压力峰值由外部爆炸造成；而当φ>40%时，内部最大压力峰值则由泄爆膜破裂引起；在所有实验中，都观察到内部压力的亥姆霍兹振荡，其振荡频率随φ的增加而降低；声学振荡仅出现在φ=25%, 30%时；容器内3个不同压力监测点（靠近泄爆口、容器中心和接近容器底端）的最大爆炸超压pmax都随着φ的增加而降低，且整体上最大的pmax始终在爆炸容器底部附近出现。但当φ>40%时，3个监测点间pmax的差异可忽略不计；外部最大爆炸超压也随φ的增加而减小，且不论其大小如何，均对内部压力曲线有显著影响。Abstract: Explosion venting and inerting are two commonly used explosion protective measures in hydrogen-based industries, both of them are effective in reducing the maximum explosion overpressure when used alone. However, the coupling effects of venting and inerting on hydrogen deflagrations have not been well understood. To this end, experiments were carried out in a 1 m high top-vented vessel with a cross-section area of 0.3 m×0.3 m to investigate the effects of nitrogen volume fraction (φ) in the range of 0 to 50% by volume on vented hydrogen-air explosions with a fixed equivalence ratio. The premixed hydrogen-nitrogen-air mixtures obtained according to Dolton’s law of partial pressure were ignited in the center of the vented container by an electric spark with an energy of about 500 mJ. A 0.75-m long transparent window was installed in the center of the vented container, through which the flame images in the container were recorded by a high-speed camera at 2 000 frames per second. The pressure-time histories within and outside the vented container were measured by four piezoresistive pressure sensors with a measuring range of 0–150 kPa. The experimental results reveal that φ significantly affects the vented deflagration of hydrogen-air mixtures. The pressure peak owing to the external explosion dominates the internal pressure-time histories when φ≤40% and that resulting from the rupture of vent cover becomes dominant for higher values of φ. Under the current experimental conditions, Helmholtz-type oscillations with a frequency decreasing with φ are always observed, and acoustic oscillations appear in the tests only for φ=25%, 30%. The maximum internal explosion overpressures (pmax) near the vent, at the center of the vessel, and near the bottom of the vessel decrease with increasing φ. Moreover, the highest overall pmax is obtained always near the bottom of the vessel. However, the difference of pmax between the three measuring points is negligible when φ is larger than 40%. The maximum external explosion overpressure decreases with increasing φ. In addition, significant effects of the external explosion on the internal pressure-time histories are observed in all tests, regardless of its explosion overpressure.
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Key words:
- hydrogen /
- explosion venting /
- nitrogen inerting /
- overpressure /
- flame
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图 2 当φ=20%时容器内外火焰演化过程
Figure 2. Flame evolution inside and outside the vessel for φ=20%
图 3 当φ=0%时点火后火焰锋面的位置和速度
Figure 3. Flame front locations and velocities after ignition for φ=0%
图 5 容器最大内部超压和氮气体积分数的关系
Figure 5. Relations between maximum internal overpressures of the vessel and nitrogen addition ratios
图 6 当φ=0%时容器内外压力曲线
Figure 6. Internal and external pressure curves of the vessel for φ=0
图 7 当φ=20%, 40%时容器外部压力曲线
Figure 7. External pressure curves of the vessel for φ=20%, 40%
图 9 容器最大外部超压与氮气体积分数的关系
Figure 9. Relations between maximum external overpressures of the vessel and nitrogen addition ratios
图 10 不同氮气体积分数下最大外部超压峰值时的火球
Figure 10. Fireballs at maximum external overpressure under different nitrogen addition ratios
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