A fully coupled fluid/solid model for open air combustion of horizontally-oriented PMMA samples
A fully coupled fluid/solid model for open air combustion of horizontally-oriented PMMA samples
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DOI：
10.1016/j.combustflame.2016.04.009
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发表时间：
2016-08
影响因子：
4.4
通讯作者：
A. Kacem;M. Mense;Y. Pizzo;G. Boyer;S. Suard;P. Boulet;G. Parent;B. Porterie
中科院分区：
文献类型：
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作者：
A. Kacem;M. Mense;Y. Pizzo;G. Boyer;S. Suard;P. Boulet;G. Parent;B. Porterie
计算流体动力学 (CFD) 火灾模型的预测能力高度依赖于确定燃料热解源项的准确性。热解速率是控制燃烧行为的关键参数，进而驱动热量从火焰反馈到燃料表面。本研究的主要目标是双重的。首先，将具有深度辐射和移动气/固界面的半透明固体燃料（此处为透明聚甲基丙烯酸甲酯或 PMMA）的深度热解模型与包括气相湍流、燃烧和辐射的 CFD 代码相结合。其次，进行实验以验证耦合模型的结果。将遗传算法/热解组合模型与来自非燃烧热解实验的锥形量热仪数据结合使用，以估计 PMMA 热解的一组独特的动力学参数。燃烧实验在边尺寸为 10、20 和 40 厘米的 PMMA 方形板上进行。从板中心收集的数据发现，i) 对于任何样本大小，实验回归率随时间几乎保持恒定，对于边长为 10、20 和 40 cm 的 PMMA 板，实验回归率的平均值分别为 5.8、8.6 和 10.9 µm s−1；ii) 尽管辐射和总传热随样本大小显着增加，但辐射对总热通量的贡献几乎保持恒定（～80%）。耦合模型结果显示与文献以及板中心热通量、气体温度和回归表面速率的当前测量结果相当吻合。发现基于阈值温度标准的预测火焰高度与从 Heskestad 相关性推导出的火焰高度接近。然而，观察到预测和测量的总热解速率之间存在差异，这是由于低估了板边缘的火焰热反馈，这一点通过燃烧样品的预测和观察到的形貌之间的比较得到证实。
The predictive capability of computational fluid dynamics (CFD) fire models is highly dependent on the accuracy with which the source term due to fuel pyrolysis can be determined. The pyrolysis rate is a key parameter controlling fire behavior, which in turn drives the heat feedback from the flame to the fuel surface. The main objectives of the present study were twofold. First, an in-depth pyrolysis model of a semi-transparent solid fuel (here, clear poly-methyl-methacrylate or PMMA) with in-depth radiation and a moving gas/solid interface was coupled with a CFD code which included turbulence, combustion and radiation for the gas phase. Second, experiments were conducted in order to validate coupled model results. A combined genetic algorithm/pyrolysis model was used with Cone Calorimeter data from a non-flaming pyrolysis experiment to estimate a unique set of kinetic parameters for PMMA pyrolysis. Flaming experiments were conducted on square slabs of PMMA with side dimensions of 10, 20 and 40 cm. From data collected at the center of the slabs, it was found that i) for any sample size, the experimental regression rate remains almost constant with time, with average values of 5.8, 8.6 and 10.9 µm s−1for the PMMA slabs with side lengths of 10, 20 and 40 cm respectively, and ii) although the radiative and total heat transfers increase significantly with sample size, the radiative contribution to the total heat flux remains almost constant (∼80%). Coupled model results show a fairly good agreement with the literature and with current measurements of the heat fluxes, gas temperature and regressing surface rate at the center of the slabs. Predicted flame heights based on a threshold temperature criterion were found to be close to those deduced from the correlation of Heskestad. However, discrepancies between predicted and measured total pyrolysis rates are observed, which result from the underestimation of the flame heat feedback at the edges of the slab, as confirmed by the comparison between predicted and observed topography of burned samples.