Effects of equivalence ratio, thickness of rupture membrane and vent area on vented hydrogen–air deflagrations in an end-vented duct with an obstacle

Abstract

Experiments were conducted in an obstructed 3-m-long duct to investigate the effects of equivalence ratio, thickness of rupture membrane, and vent area on vented hydrogen–air deflagrations. Shockwave-induced pressure peaks were observed inside and outside the duct in some tests. In the tests with one end of the duct totally opened, the location at which the overall maximum internal overpressure is achieved depends on the thickness of the rupture membrane for a given equivalence ratio; however, it is independent of equivalence ratio for a given thickness of rupture membrane. The pressure peak resulting from an external explosion always dominates the pressure–time histories 1.5 m downstream of the duct exit. The maximum internal and external overpressures first increase and then decrease as the equivalence ratio increases from 0.26 to 3.57, unexpectedly; none of these increase monotonically with an increase in the thickness of the rupture membrane. Two explosion venting regimes, namely sonic and subsonic, are observed. During sonic venting, the maximum internal overpressure increases exponentially with a decrease in vent area; it is nearly independent of the vent area during subsonic venting when the vent area is larger than approximately 19% of the cross-sectional area of the duct.