Effect of vent size on explosion overpressure and flame behavior during vented hydrogen-air mixture deflagrations

In this study, the effects of vent size on the internal overpressure and flame behavior within and outside a 1 m(3) cuboid test chamber with 30 vol% hydrogen-air mixtures were investigated. Different pressure peaks and the corresponding mechanisms were presented. Two regions of pressure oscillation were found in the pressure-time histories. The oscillation frequency of one region was independent of the nondimensional vent coefficient- K-V, and that of the other increased considerably with KV. The maximum overpressures increased slightly when the vent sizes were large (K-V <= 12.50) and increased significantly as the vent sizes were decreased (K-V > 12.50). Two empirical correlations-Molkov's best-fit model and a modified version of NFPA 68 (2013) by Fakandu et al.- relating the vent sizes to overpressure were found to be appropriate for the present study. A Mach disk was identified for the smallest vent size (K-V = 25.00) in the external flame, and a constant-pressure jet flame was observed.