Investigation of vented hydrogen-air deflagrations in a congested vessel.

• The maximum overpressure increased when more obstacles were added. • Low and high frequency spectra of vessel vibration were observed. • A close relation between the pressure oscillation and vessel vibration was found. Experiments were conducted in a 1-m3 rectangular vessel with a 700 mm × 400 mm top vent to investigate the effects of cylinders placed parallel to the venting direction on vented hydrogen-air deflagrations and the structural response of the vessel wall to an explosion. Three pressure peaks, which corresponded to the opening of the vent cover, venting of the burnt gas mixtures, and the occurrence of the external explosion, respectively, were observed. The pressure peak corresponding to the external explosion always dominated the pressure-time histories, and the maximum internal overpressure was reached at the bottom of the vessel. The presence of cylinders in the vessel affected the explosion venting significantly. When more cylinders were placed, the maximum internal and external overpressure increased, whereas the amplitude of pressure oscillation and the time needed to reach the maximum overpressure decreased. A close relation between the pressure oscillation and vessel vibration was found. Low and high dominant frequency spectra of vessel vibration were observed in all tests. The former resulted from the acoustic oscillation of the internal pressure, and the latter corresponded to the resonance of the vessel, which may react against the flame and result in pressure oscillation with a frequency comparable with the natural frequency of the vessel. [ABSTRACT FROM AUTHOR]