【作者】 郭再富；

【导师】 范维澄； 杨立中；

【作者基本信息】 中国科学技术大学 ， 安全技术及工程， 2006， 博士

【摘要】 固体可燃物受热时，达到一定温度后会发生热解，并生成炭及可燃挥发分，可燃气体从固体表面逸出后与环境中的氧气混合，当达到点燃的临界条件时即可点燃形成气相火焰并开始蔓延。因此在火灾发生的早期，能否准确预测固体可燃物的热解行为决定了能否较好的模拟火灾的发生和发展过程。炭化材料燃烧后会留下相当数量的残余物，主要是炭，其典型代表是木材。木材是火灾中最常见的可燃物之一，能否准确预测木材在火灾的发生和发展阶段的燃烧特性对火灾安全设计有着极其重要的作用。 热辐射是室内火灾中热传递的主要方式，并且决定着火灾的蔓延和发展。国内外学者的实验和模型工作基本都是在外部辐射热流保持恒定的情况下进行的，而对于通常的室内火灾过程，可燃物接受到的辐射热流随着火灾的发展而不断变化，因此，有必要对变化热流下木材的燃烧特性进行研究。 在前人工作的基础上，本文研究了木材在变化热流条件下的热解，炭化及点燃过程中的现象和规律，研究工作主要包括以下几个方面： 利用火灾早期特性实验台研究了随时间线性上升辐射热流下不同种类木材的热解和点燃过程，分析了热流变化率及木材密度对点燃时间、表面温度及内部温度分布等关键参数的影响。研究表明热流变化率及木材密度对木材的点燃时间都有很大影响，点燃时间随着热流变化率的增加而减小，利用点燃时间和热流变化率之间的乘幂函数关系推导得到的变化热流下木材点燃所需的临界热流变化率为0.02kW·m^-2·s^-1，点燃时间和木材密度之间的线性函数关系表明，点燃时间随着密度的增加而增加，这分别是由其外部和内部热传递速率决定的。对于同种木材，其温升速率随着热流变化率的上升而增加，而在相同的外部辐射条件下，密度较小的木材样品表面附近升温较快。点燃时刻的表面温度随着热流变化率的上升而降低，而密度对其影响不大，温度值在340℃—520℃范围内。 在实验研究的基础上，建立了变化热流下木材热解的偏微分模型并利用模型进行计算分析。研究了不同热流变化率下木材的温度分布，并与实验结果进行了比较，发现模型可以较好的预测热解过程中的温升。对比了不同热流条件下木材更多还原

【Abstract】 When subjected to external heating, solid combustible start to decompose, giving a mixture of volatile species and, sometimes, char as products. The mixture of the volatiles emitting from the solid surface and the ambient oxygen will be ignited when the criteria of ignition are achieved. Charring material will product large amount of solid carbonaceous residual, mainly char, after combustion. Wood is to be considered as the most representative of charring materials and is one of the most popular combustibles in a fire. So the capability to predict the combustion characteristics of wood is quite important to fire safety engineering.Thermal radiation is the main method of heat transfer in a compartment fire. The previous experimental and theoretical studies were almost conducted with the external heat flux imposed on the specimen is fixed and is not varied with time. While, in a common compartment fire, the external heat flux imposed on the combustibles will vary continuously with the growth of fire. So it is necessary to examine the combustion characteristics of wood exposed to variable heat fluxes.Based on the former work, this paper experimentally and theoretically examines the pyrolysis, charring and ignition process of wood exposed to variable heat fluxes, as following:The radiation platform for studying the fire behavior of combustibles is utilized to research the pyrolysis and ignition of different wood species under heat fluxes linearly increasing with time. The influences of increasing rate of heat flux and wood density on the ignition time, surface temperature and internal temperature distribution are examined. It is found that both of them will affect the ignition time. The ignition time will decrease with a larger increasing rate of heat flux and a smaller wood density. This is determined by the external and internal heat transfer respectively. The critical increasing rate of heat flux for wood ignition under variable heat flux, with the value of 0.02 kW·m^-2·s^-1, can be estimated from the power function of ignition time and increasing rate of heat flux. The rate of temperature rise will increase with a larger increasing rate of heat flux and a smaller wood density. The surface temperature at ignition will decrease with a larger increasing rate of heat flux, and in the region of 340更多还原