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

Abstract

a b s t r a c t This paper aims to improve prediction capability of the vent sizing correlation presented in the form of functional dependence of the dimensionless deflagration overpressure on the turbulent Bradley number similar to our previous studies. The correlation is essentially upgraded based on recent advancements in understanding and modelling of combustion phenomena relevant to hydrogeneair vented deflagrations and unique large-scale tests carried out by different research groups. The focus is on hydrogeneair deflagrations in low-strength equipment and buildings when the reduced pressure is accepted to be below 0.1 MPa. The combustion phenomena accounted for by the correlation include: turbulence generated by the flame front itself; leading point mechanism stemming from the preferential diffusion of hydrogen in air in stretched flames; growth of the fractal area of the turbulent flame surface; initial turbulence in the flammable mixture; as well as effects of enclosure aspect ratio and presence of obstacles. The correlation is validated against the widest range of experimental conditions available to date (76 experimental points). The validation covers a wide range of test conditions: different shape enclosures of volume up to 120 m 3 ; initially quiescent and turbulent hydrogeneair mixtures; hydrogen concentration in air from 6% to 30% by volume; ignition source location at enclosure centre, near and far from a vent; empty enclosures and enclosures with obstacles.

Performance evaluation of empirical models for vented lean hydrogen explosions

“…Four models are discussed in this section. They include the statutory standards -(i) EN-14994 [2], (ii) NFPA-68 [3], and other empirical models (iii) FM Global model [1,[4][5][6], and (iv) Molkov model [13].…”

“…However, the detailed model is used for the present study. [13] is based on a novel concept of turbulent Bradley number, and it is based on previous versions of the same model and several numerical studies by the author and his group on vented deflagrations [14][15][16][17][18][19]. Bradley number can be defines as:…”

Dynamics of Explosions in Cylindrical Vented Enclosures: Validation of a Computational Model by Experiments

“…In particular, it has been suggested that external explosion, flame-acoustic interaction, and the flame wrinkling caused by obstacles are responsible for the multiple peak overpressures noticed in the pressure history. Molkov and Bragin [10] also developed a model predicting peak overpressure for vented hydrogen-air explosion based on the turbulent Bradley number, which was presumed to correlate with the overpressure in an enclosure. Sinha et al [11] have developed another model predicting vented hydrogen-air explosion, based on the external cloud formation and explosion.…”

Explosion venting of rich hydrogen-air mixtures in a small cylindrical vessel with two symmetrical vents

“…In addition to the experimental investigations, numerical works about the effect of vent area on explosion venting have also been conducted to describe pressure buildup and flame propagation [12,[16][17][18][19][20]. In the model given by Molkov et al [21][22][23][24], the ratio of turbulence factor to discharge coefficient was introduced to account for the pressure buildup. Based on the extensive experimental and numerical works, NFPA 68 [25] and EN 14994 [26] provide the correlations for calculating vent area.…”