复杂边界下炭层拓扑形态、内部渗流及热氧屏障动力学特性研究

Char layer acts as a crucial heat and oxygen barrier during fires while it also forms the paths for pyrolysis gases. Therefore, it is worthwhile studying the morphology, internal flow of char layer and thus quantifying the effects of heat and oxygen blockages for safety evaluations. The morphology and internal flow of char layer determine the blockage effects of heat and oxygen which affects the safety level of virgin material. However, the formational and developmental mechanisms of morphology and internal flow of char layer are still unknown so far. The current project studies the char layer morphology and internal flow under varying boundary conditions using relatively homogenous charring materials including engineering board and polymers. The char layer will be examined with high resolution X-ray scanning and analyzed using subsequent mass-density autocorrelation method, etc. The project aims to reveal the mechanism of formation of char layer morphology and the fluid dynamics of internal flow as well as the interaction between them. The morphology will be experimentally measured and then correlated with incident heat flux, ambient pressure, flaming condition and so on to develop a non-linear dynamic model expressing the overall developing process of char layer formation. The effects of morphology on thermo-physical properties of char layer are determined. Then, the internal flow pattern and pressure field inside the char layer are measured and profiled during the pyrolysis process. Based on the results, an analytical model is built expressing the behaviors of internal flow using Darcy’s law and filtration theory, which also identifies the driving effects of internal flow on the morphology of char layer. Finally, the project quantifies the blockage effects of heat and oxygen by combining the findings in morphology and internal flow of char layer, and reveals how the blockage effects are realized while furthermore improves the theories and mathematics of evaluating the combustion processes of charring materials.

炭层是材料燃烧过程中的重要热氧屏障及内部热解气流动通道，解析其拓扑形态、内部流及热氧屏障的动力学特性具有重要的科学意义与应用价值。炭层的拓扑形态和内部流动特征决定了其热氧屏障特性，但目前二者的产生和发展机理尚未得到系统揭示。本项目以均质（木质及高分子）成炭材料为对象，开展多种边界条件下的热解实验，利用X射线断层成像及质量-密度自相关分析等方法，重点解决两个科学问题：①炭层拓扑形态的发生机理，②内部流的潜在动力学机制。通过本项目的研究，可望得到复杂热压边界条件下炭层拓扑形态的演变规律；构建拓扑形态发展全过程随压力、辐射强度、燃烧条件等变化的非线性动力学模型，明确拓扑形态对物化特性的影响；获取炭层内部流动特征及气压场变化规律，结合渗流理论建立内部流的动力学模型，揭示内部流对拓扑形态成形的驱动作用；定量炭层的热氧屏障能力，揭示热氧屏障作用的产生机理，发展评估成炭材料燃烧特性的理论及计算方法。

炭层是材料燃烧过程中的重要热氧屏障及内部热解气流动通道，解析炭层的拓扑形态、内部流及热氧屏障的动力学特性具有重要的科学意义与应用价值。本项目以成炭材料为对象，重点解决两个科学问题：①炭层拓扑形态的发生机理，②内部流的潜在动力学机制。截止目前为止，研究小组已按照项目研究计划，实施并完成具体研究任务，实现了项目的既定目标。在炭层拓扑形态方面，项目组利用自行设计的变氧压量热仪等仪器开展多种边界条件实验，揭示了拓扑形态形成机理，量化了炭层在不同方向的收缩比，提出了炭层裂纹形成的屈缩理论，获取了高聚物及阻燃炭层的物化特性。在内部流的流动传热特性方面，项目组自主研发了高温渗透-孔隙率测试仪等实验装置，通过开展变氧压热解及不同温度渗透实验等，结合现存最大尺度的火蔓延过程数值模拟，提出了炭层表面裂隙火焰融合判据及融合概率预测模型，建立了“虚拟热流场”技术，大幅缓解火蔓延过程模拟的实现难度，并发现了“开裂将导致表面炭层分离，弱化裂块间的关联性传热，导致表观导热系数降低”的裂纹热效应。.本项目共发表论文18篇，其中SCI收录16篇，高区12篇，第一作者5篇，通讯作者13篇，国际会议论文5篇，会议特邀报告5次，授权发明专利2项。共发表国际合作论文12篇，获批国际合作交流基金1项，国际论文奖励2次。依托本项目共培养学生16人，其中在读博士3人，毕业硕士6人，在读硕士9人。部分成果写入FDS源程序，并应用到多个实际火场的数值重构工作中。项目负责人受邀出任国务院特别重大火灾事故调查组技术组专家及第39届国际燃烧学大会火灾分论坛共同主席。自主研发“大型燃烧量热室”和“高温渗透-孔隙率测试仪”两套实验仪器。协办“全国消防科学传播专家系列论坛”第一期“火灾调查”论坛。建立用于成果推荐及消防科普公众号一个。本项目的研究成果，将进一步推进科学界对材料炭层的认知，积累基础数据，提升成炭材料燃烧过程数值模拟技术，并推动火灾调查领域的技术迭代。