The mechanisms controlling the heat release growth rate and its dependency on time are studied in this work for cases of a high-rack storage facility and a single large-scale vertical PMMA slab. The latter case is considered to be a simplified set-up to get a deeper understanding of transient dynamics of the HRR growth rate and studied both theoretically and numerically. First, we modify and apply the simplified analytical model based on the classical approach, in which combustible surface is divided into the inert heating zone and the pyrolysis zone. The relationship for the flame spread is based on empirical correlations for turbulent flame length and HRR. In this work we set the turbulent flame height to be equal to the inert heating zone height and, thus, an accelerating flame spread can be predicted. Assuming that a pyrolysis front is flat and normal to the direction of propagation, the HRR growth rate for this scenario can be described using the t3 dependence, which over-predicts the published measured values. Overall, a reasonable agreement is achieved. Secondly, we address the same scenario with CFD simulations using FDS with finite-rate pyrolysis model. The transient HRR rate is predicted and favourably agrees the published measured data. This and and the predicted distribution of the burning rate over the burning surface justify that the pyrolysis front is in fact curviliniar. Finally, the simplified approach is applied to predict the fire growth in the rack storage configuration. We show that a dramatically fast HRR growth rate can be observed for a large-scale scenario. A t-cube dependency of HRR growth rate is in a better agreement with FDS results than a conventional t-squared fire curve for the fast and ultrafast growth rate recommended by NFPA 204, etc. The predicted fire dynamics is analysed and the influence of the ignitor position is found to be substantial only for the initial stages of fire growth.
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International Seminar on Fire and Explosion Hazards (9; 2019; Saint Petersburg, Russia). Proceedings of the Ninth International Seminar on Fire and Explosion Hazards [Электронный ресурс]. Vol. 2: 21-26 April 2019, Saint Petersburg, Russia / Peter the Great St. Petersburg Polytechnic University, Autonomous Non-Profit Organization "Fire and Explosion Safety", Gefest Holding Ltd ; [edited by A. Snegirev [et al.]. — Электрон. текстовые дан. (1 файл : 98,7 Мб). — Saint Petersburg, 2019. — Загл. с титул. экрана. — Свободный доступ из сети Интернет (чтение, печать, копирование). — Adobe Acrobat Reader 7.0. — <URL:http://elib.spbstu.ru/dl/2/k19-97.pdf>. — <URL:http://doi.org/10.18720/SPBPU/2/k19-97>.
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