The influence of hydrogen concentration on the characteristic of explosion venting: Explosion pressure, venting flame and flow field microstructure

Hydrogen explosions happen occasionally, resulting in heavy casualties and huge property losses. Explosion venting as an effective method of explosion protection need to be further studied. In this work, the influence of hydrogen concentration (20%–60%) on the explosion venting was investigated. It was indicated that the maximum explosion pressure (Pmax) inside the vessel and in the vent pipe first increased and then decreased with the increase of hydrogen concentration. The Pmax in the vent pipe was always much larger than that inside the vessel. However, the Pmax outside the vessel increased gradually with increasing hydrogen concentration. The propagation characteristic and the temperature field distribution of the explosion venting flame were also analyzed. There was no obvious venting flame for 20% hydrogen concentration, because of the exhaustion of hydrogen inside the vessel. The change of the concentration affected the occurrence of secondary explosion, which affected the flame morphology, propagation velocity and flame temperature field distribution. The maximum temperatures were 1164 °C and 1207 °C for 50% and 60% hydrogen concentrations. Furthermore, changes of hydrogen concentration resulted in changes of the explosion intensity inside the vessel, thus affecting the flow field microstructure inside the vessel and near vent port. The stronger the explosion intensity, the more unstable the flow field microstructure and the shorter the time required to reach stability inside the vessel.