A mechanistic analysis of H 2 O and CO 2 diluent effect on hydrogen fl ammability limit considering flame extinction mechanism

• Published in: Nuclear engineering and technology 2021, 53(10), , pp.3286-3297
• Main Authors: 전준구, 김연수, 정회철, 김성중
• Format: Article
• Language: English
• Subjects: 원자력공학
• ISSN: 1738-5733; 2234-358X
• DOI: 10.1016/j.net.2021.05.004

The released hydrogen can be ignited even with weak ignition sources. This emphasizes the importanceof the hydrogen flammability evaluation to prevent catastrophic failure in hydrogen related facilitiesincluding a nuclear power plant. Historically numerous attempts have been made to determine theflammability limit of hydrogen mixtures including several diluents. However, no analytical model hasbeen developed to accurately predict the limit concentration for mixtures containing radiating gases. Inthis study, the effect of H2O and CO2 on flammability limit was investigated through a numericalsimulation of lean limit hydrogen flames. The previous flammability limit model was improved based onthe mechanistic investigation, with which the amount of indirect radiation heat loss could be estimatedby the optically thin approximation. As a result, the sharp increase in limit concentration by H2O could beexplained by high thermal diffusivity and radiation rate. Despite the high radiation rate, however, CO2with the lower thermal diffusivity than the threshold cannot produce a noticeable increase in heat lossand ultimately limit concentration. We concluded that the proposed mechanistic analysis successfullyexplained the experimental results even including radiating gases. The accuracy of the improved modelwas verified through several flammability experiments for H2-air-diluent. KCI Citation Count: 0