Secondary Explosions in Relief Duct During Aluminum Dust Explosion Venting

Experiments of aluminum dust explosion venting were conducted with a cylindrical vessel of 68 mm internal diameter and 305 mm height connected with a relief duct of 25 mm internal diameter. The relief duct length and the dust concentration could be adjusted. Four piezoelectric pressure transducers were used to record the pressure characteristics in both the vessel and relief duct. The results indicate that, secondary explosion occurs when the relief duct and dust concentration are no less than 1 500 mm and 500 gám-3, respectively. The occurrence of secondary explosion is probabilistic, with probability ranging from 17% to 50%. The second pressure peak appears in the duct because of secondary explosion. The residual unburnt combustible mixture in vessel re-reacts due to the disturbance of secondary explosion and hence the secondary pressure peak also appears in the vessel.