Effect of sodium bicarbonate powder on the process of ducted venting

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 mm、500 mm、750 mm) under NaHCO3 dry powder with the mass fraction C=0 g/m3, 40 g/m3, 80 g/m3, 120 g/m3, 160 g/m3, 200 g/m3, 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 fraction of NaHCO3 powder eliminated the secondary explosion. As the NaHCO3 powder mass fraction 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 fraction. Different mass fraction 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 fraction. The maximum pressure in the vessel (pv, max) was mainly dominated by the second pressure peak (p2) for the low powder mass fraction, but by the first pressure peak (p1) for the high powder mass fraction. The drop rate of overpressure increased at first and then leveled off with the increase of NaHCO3 powder mass fraction, which indicating that the mass fraction effect gradually weaken. Finally, the relationship between flame propagation velocity and explosion overpressure in the ducted vented vessel was quantitatively analyzed.