Russian Federation: Physics-Based Approach For Reduction Uncertainties In Concentration Limits Of "Slow-To-Fast" Flame Transition in Hydrogen-Air Gas Mixtures

Limits (concentration and geometrical) for effective flame acceleration is of vital importance for hydrogen safety of nuclear power plants. In prior empirical studies it was revealed a substantial difference in potential for effective flame acceleration for the "weak" combustible hydrogen-air mixtures, where unstable/quench and unstable/slow combustion regimes can exist and for the "strong" ones, where choked flames and quasi-detonations can occur. In order to reduce the uncertainties in empirical-based estimation of the flame acceleration concentration limits, an alternative, model-based framework is presented. It was assumed that fundamental concentration limits for deflagration flames are ultimate edges for empirical concentration limits for flame acceleration. Non-empirical engineering method for quantitative estimation of the concentration limits for plane deflagration flame is described. It was obtained, that theoretical estimation provides a more conservative estimation of lower concentration limit then the empirical one. Targets for the future the physical or computational experiments, focused on understanding of nature and further refining of the lower concentration limit for "deflagration-to-flame-ball" transition is proposed. (author)