【作者】 宗若雯；

【导师】 廖光煊；

【作者基本信息】 中国科学技术大学 ， 安全技术及工程， 2008， 博士

【摘要】 火灾调查作为火灾科学研究的一个重要分支,集成多学科交叉,正在取得越来越广泛的关注。而火灾重构正是依据科学方法确定火灾中最真实的发生发展过程。轰燃是室内火灾过程中的一个瞬间,但却是特别重要的阶段。在空间狭小,通风不畅的特殊受限空间内很容易发生轰燃。在火灾调查中,轰燃分析的应用可以提供很多的有价值的信息,包括揭示火灾起源和蔓延的信息,提供判断的理论依据。本文基于火灾重构的角度对轰燃现象进行重构研究。火灾重构研究中材料的分析是建立重构模型的基础,尤其是固态可燃物的热解过程是火灾轰燃发生和发展的重要因素。首先对典型的固体可燃性材料的热解过程进行了研究,采用热重分析和热分析动力学方法,分别对尼龙和胶合板材料进行了研究。通过所得到的动力学参数可以用以预测不同温度下材料热解产物的百分含量,推测在特定条件下的轰燃发生的可能性,同时为轰燃的数值模拟重构提供了基础数据。建立了不同尺寸的轰燃模拟实验台,通过实验模拟重构,改变实验中的各种工况,包括顶棚高度的变化、火源位置、补风条件、火源半径的变化等因素,研究了腔室内发生轰燃的临界条件;利用区域模拟的两层结构模型,非线性动力学模型中的热增益和热损失的变化解释了腔室火灾的发展:壁面温度的无量纲数U_c与火源半径是决定轰燃发生与否的主要影响因素:利用修正后的非线性动力学模型,可以较好判断腔室内能否发生轰燃,同时预测烟气层最高稳定温度。研究了轰燃过程中的尺度模拟准则。建立了无量纲的腔室油池火的控制方程及无量纲组合数组,结合经验羽流的速度与热释放速率的关系,认为无量纲的能量产生速率为主导控制作用,根据无量纲能量产生速率恒定,确立了腔室油池火的尺度准则,并将该尺度关系用于模拟实验的设计。通过对受限空间火灾轰燃的数值实验重构,比较了CFAST和FDS的数值模拟结果与实验值的差别。CFAST在模拟火源热解和燃烧反应上存在不足,使其在火场重构中的应用受到限制;它模拟的烟气层温度普遍高于实验值。但是CFAST在轰燃理论的研究上可以起到辅助作用;FDS能模拟火源的热解和燃烧过程,进而较好预测腔室火灾的发展过程。通过全尺寸房间的轰燃实验,分析了轰燃的经验模型、BFD参数曲线估计法和FDS场模拟软件在火场重构的实际应用中的可行性。结果表明FDS模拟具有较广的适用性。BFD曲线对房间内发生轰燃的过程中烟气层温度曲线的预测以及最高温度的判断强于FDS。通过McCaffrey的模型来估算房间内的最大热释放速率,进而确定FDS模拟所需的网格密度,是一套有效的方法。更多还原

【Abstract】 Fire investigation, an important branch in the fire science research, is obtaining more and more attention in the world as an interdisciplinary research. Fire reconstruction is used to determine the most likely development of a fire using a scientifically based methodology. Flashover is a rapidly occurring transitional event in the development of a compartment fire. It can be easily occurred in the specially confined compartment, where ventilation is poor in such limited space. In fire investigation, proper application of flashover analysis can be very valuable tool in unraveling the mysteries of a fire’s origin and development, and presenting the theoretical basis for judgment. In this paper flashover is under research from the point of fire reconstruction.The basement of construction of fire reconstruction model is the analysis of material. Especially the thermal degradation of combustible material in solid phase related with the occurrence and development of flashover. First the thermogravimetric evaluation of typical solid combustible material, including nylon and plywood, was studied with thermogravimetric analysis and thermal kintiecs . The kinetics parameters obtained could be used to predict the percentage composition of pyrolysis product under different temperatures, which might indicate the possibility of flashover under certain circumstances. Meanwhile the study could provide the basic data for numerical simulation for flashover reconstruction.The model compartments of different scales were constructed. The experimental reconstruction was done under various experimental conditions, including the height of ceiling, the location of fire source, the ventilation condition, the radius of fire, etc. The critical conditions of occurrence of flashover were studied in such compartment. With the help of two-layer zone model, the change of heat gain and heat loss in the nonlinear dynamics could well explain the development of compartment fire. The wall temperature parameter U_c and the radius of fire were the primary factors in the development flashover. The nonlinear dynamics model could judge the occurrence of flashover and predict the highest stable temperature in the smoke layer.The scale modeling in the process of flashover was studied.The dimensionless control equations of pool fire in compartment were established .Under the analysis of the relation of the plume velocity and the heat release rate, the dimensionless variable of heat release rate was considered to take the leading control effect. This induced the establishment of the scaling rule for the pool fire in a compartment by this constant rate variable of heat release, which could be applied in the design of model experiment.The numerical simulation results in CFAST and FDS were compared with the experimental results by the numerical experiment reconstruction of the flashover in this confined compartment. CFAST was weak in modeling the thermal degradation of fire source and the combustion reaction, which would limit the application of CFAST in fire scene reconstruction. FDS could well predict the development process of compartment fire by modeling the thermal degradation of fire source and the combustion process properly.The feasibility of the application of the empirical model of flashover, the BFD curve method and FDS modeling in the fire scene reconstruction were studied by the full scale flashover test. It showed that the FDS modeling had wide applicability, and BFD’s ability to predict the temperature curve of smoke layer and the judgment of the highest temperature for the flashover in compartment were better than FDS. It could be an effective way to estimate the highest heat release rate by McCaffrey’s model, resulting in the judgment of the mesh dimension in FDS.更多还原