Scaling effects of vented deflagrations for near lean flammability limit hydrogen-air mixtures in large scale rectangular volumes

Combustion-generated overpressures in nuclear containment buildings during a severe accident may be relieved by venting gases to adjacent compartments through relief panels or existing openings to avoid compromising a containment breach. Experimental studies on the dynamics of vented hydrogen-air combustion were extensively performed using vessels varied in shape and size at the Canadian Nuclear Laboratories. In this paper, the scaling effects are examined for near lean flammability hydrogen-air mixtures (6-12 vol.% H2) with tests performed in rectangular volumes (25, 57 and 120 m3) with a scaled vent area (Av/V2/3) of 0.02-0.05 under both initially quiescent and fan-induced turbulent conditions. This study has found that the maximum peak overpressure of all quiescent tests are dominated by the acoustic coupled effect for the hydrogen concentration greater than 8 vol.%, and the acoustic effect becomes insignificant under turbulent conditions. The measured peak over-pressures are generally over-predicted for the quiescent tests and better predicted for the turbulent tests by the well-known Bradley-Mitcheson and Molkov correlations.