Abstract This contribution experimentally investigates the heat transfer and the consequent auto-ignition of thermally thick PMMA (polymethyl methacrylate) exposed to linearly declining heat flux (HF) coupling with a theoretically derived model. Thermal decomposition in solid was ignored and critical temperature was utilized. Both scenarios neglecting and considering surface heat loss were studied in the proposed model. An asymptotic solution, extending the derivation method from constant to time-declining heat flux, was obtained to explicitly estimate the surface temperature and ignition time. The credibility of the established model was validated through comparison with experimental data and a previously developed numerical model. The results show that in both considered scenarios ignition is confined in a region where the decreasing rate of heat flux is lower than a critical value. No ignition occurs if the decreasing rate increases beyond this region. The newly developed model is compatible with the correlations of constant heat flux, and it provides identical accuracy in predicting ignition time when compared with other existing models in the literature. A constant surface heat loss coefficient was used in the model, and it was found little error is introduced by invoking this approximation. Also, a parametric study was implemented, indicating that the critical temperature affects the ignition time prediction significantly. Meanwhile, the effects of surface heat loss on surface temperature and ignition time were quantitatively evaluated.

中文翻译：

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暴露于线性减少的热辐射的热厚 PMMA 的自燃

摘要 本论文通过实验研究了暴露于线性下降热通量 (HF) 的热厚 PMMA（聚甲基丙烯酸甲酯）的传热和随之而来的自燃，并结合了一个理论推导模型。忽略固体中的热分解并利用临界温度。在所提出的模型中研究了忽略和考虑表面热损失的两种情况。获得了一种渐近解，将推导方法从恒定热通量扩展到随时间下降的热通量，以明确估计表面温度和点火时间。通过与实验数据和先前开发的数值模型进行比较，验证了所建立模型的可信度。结果表明，在两种考虑的情况下，点火都被限制在热通量下降率低于临界值的区域。如果下降率增加超过该区域，则不会发生点火。新开发的模型与恒定热通量的相关性兼容，并且与文献中的其他现有模型相比，它在预测点火时间方面提供了相同的精度。在模型中使用了一个恒定的表面热损失系数，并且发现通过调用这个近似值引入的误差很小。此外，还进行了参数研究，表明临界温度显着影响着火时间预测。同时，定量评估了表面热损失对表面温度和点火时间的影响。