Hydrogen-air deflagrations: Vent sizing correlation for low-strength equipment and buildings

This paper aims to improve prediction capability of the vent sizing correlation presented inthe form of functional dependence of the dimensionless deflagration overpressure on theturbulent Bradley number similar to our previous studies. The correlation is essentiallyupgraded based on recent advancements in understanding and modelling of combustionphenomena relevant to hydrogeneair vented deflagrations and unique large-scale testscarried out by different research groups. The focus is on hydrogeneair deflagrations inlow-strength equipment and buildings when the reduced pressure is accepted to be below0.1 MPa. The combustion phenomena accounted for by the correlation include: turbulencegenerated by the flame front itself; leading point mechanism stemming from the preferentialdiffusion of hydrogen in air in stretched flames; growth of the fractal area of theturbulent flame surface; initial turbulence in the flammable mixture; as well as effects ofenclosure aspect ratio and presence of obstacles. The correlation is validated against thewidest range of experimental conditions available to date (76 experimental points). Thevalidation covers a wide range of test conditions: different shape enclosures of volume upto 120 m3; initially quiescent and turbulent hydrogeneair mixtures; hydrogen concentrationin air from 6% to 30% by volume; ignition source location at enclosure centre, near andfar from a vent; empty enclosures and enclosures with obstacles.