A method to characterize mixing and flammability of hydrogen–air mixtures in enclosures

Since the use of hydrogen as energy carrier is likely to increase in the future, the associated safety concerns have to be addressed. It is necessary that the mixing characteristics of hydrogen gas released into an enclosure be quantified with the help of numerical indices that qualitatively and quantitatively reflect the overall mixing process and hazard of formation of flammable cloud in the enclosure. Four indices meant to characterize mixing and flammability of hydrogen in enclosures, namely, Average mole fraction, Non-uniformity index, Deflagration Volume Fraction and Deflagration Pressure Ratio are proposed in this paper. Significance and utility of these indices in providing useful information on mixing and flammability have been demonstrated through numerical studies of hydrogen distribution in enclosures containing air. These indices can serve as useful tools in studies of hydrogen distribution in enclosures.

► A method to characterize mixing and flammability of H2–air mixture is developed. ► Four numerical indices are used to depict mixing and flammability of hydrogen. ► Theoretical basis and significance of these indices are explained. ► Three case studies are used to demonstrate the utility of these indices.