典型非碳化聚合物材料热解及逆流火蔓延实验和理论研究

发布时间：2018-01-17 15:23

本文关键词：典型非碳化聚合物材料热解及逆流火蔓延实验和理论研究　出处：《中国科学技术大学》2014年博士论文　论文类型：学位论文

【摘要】：固体可燃物热解及火蔓延是火灾初始和发展阶段的重要分过程,决定着后续火灾的发展,因此一直是国内外众多学者重点研究的对象。热解又是火蔓延的子过程,两者有着密切的关系。非碳化聚合物材料作为现代建筑中广泛应用的装饰材料,其在火灾中表现出的诸多特殊蔓延行为越来越多地受到研究者的关注。在外部热流作用下,非碳化聚合物材料受热后发生热解反应,热解产生的可燃气通过形成气泡等方式从材料内部传输到材料表面进而析出到外界空气中。热解释放出可燃性气体与空气混合形成可燃预混气,经点燃后会在材料表面发生燃烧化学反应形成火焰。燃烧产生的热量一部分用来加热燃烧产物,一部分通过辐射散失到环境中,剩下的一部分则通过对流、辐射和热传导的方式反馈回材料表面形成反馈热流而对未燃材料进行预加热,当未燃材料被加热后发生热解又进一步释放出热解可燃气以维持气相燃烧,如此不断的循环进而形成材料表面持续的火蔓延过程。与传统的碳化材料(如纸张、木材等)不同,非碳化材料在热解的过程中基本没有碳层形成,不会阻碍外部热流对材料的预加热,因此其热解速率要远大于碳化材料的热解。此外,材料的熔融和流动特性也会增加材料的蔓延速率。本文首先在锥型量热仪氮气气氛下对PMMA (Poly(methyl methacrylate))、 ABS(Poly(acrylonitrile butadiene styrene))和HIPS(High Impact Polystyren)三种典型非碳化聚合物材料进行了不同热流下的热解实验研究,在此基础上对非碳化聚合物材料有限尺寸自然条件下逆流火蔓延过程进行了实验和理论研究,其中包括材料厚度、宽度、环境压力和三维效应等参数对逆流火蔓延过程的影响。具体内容概括如下：热解方面,在低、中、高三种热流下对PMMA、ABS和HIPS的一维热解过程进行了实验研究。通过对比热电偶和红外热像仪材料背面温度的测量结果,验证了非接触测温方法的可行性。利用实验所测得的材料背面温度和质量损失速率,并结合Stanislav I. Stoliarov的ThermoKin模型得到材料的导热系数与温度的分段线性关系。进而在实验的基础上建立了一个考虑材料表面热流吸收方式和热解化学反应的非碳化聚合物材料的一维热解模型,模型对文献中广泛采用的深度吸收和表面吸收这两种假设分别进行了研究和对比,结果表明不同吸收方式对材料表面温度和热穿透层内温度分布有较大影响,这种不同在空气气氛下体现在着火时间的明显差异。而在宏观热解方面,即不考虑材料内部热解细节的情况下,两者的模拟结果均在可接受的范围之内。通过对比失重速率和背面温度的实验和模拟结果验证了此一维热解模型的正确性。火蔓延方面,在热解研究的基础上对自然对流和不同环境压力下的逆流火蔓延过程进行了实验和理论分析。结果表明在材料宽度较小的情况下,逆流火蔓延速率随厚度的增大而增加,这与二维无限宽条件下的结论有较大差别。主要原因是有限尺寸条件下,材料两侧的燃烧过程加速了蔓延速率。在厚度固定情况下,火蔓延速率反比于材料宽度。在合肥、西宁和拉萨不同环境压力条件下,失重速率、火焰高度和火蔓延速率均随压力的增大而增大。在低压条件下,气相化学反应动力学和火焰反馈热流是影响火蔓延速率的主要因素,当表征气相化学反应的Damkohler数小于一个临界值会产生熄火现象。本文还从传热和传质角度出发对火蔓延过程进行了理论分析并得到简化模型,模型中材料的火蔓延速率是材料尺寸、火焰前沿角度和材料热物理参数的函数。另外此模型还提供了通过测量火蔓延速率估算热解区和预热区火焰反馈热流大小的方法。同样,模型与实验结果较好的一致性说明了简化模型的正确性。
[Abstract]:Solid combustible pyrolysis and fire spread is an important branch of fire and initial stage of development, determines the development of subsequent fire, so it has been the focus of the study of many scholars at home and abroad. The pyrolysis is the fire spreading process, the relationship between them. The non carbide polymer material is widely used in modern architecture the decoration materials, which exhibit in the fire spread many special behavior more and more attention of researchers. In the external heat flux under non carbide were pyrolyzed polymer material after heating, the pyrolysis of combustible gas through the formation of bubbles from inside the material transfer to the material surface and precipitation to the outside air. Thermal release of flammable gas pre mixed with air to form combustible mixed gas, the formation of flame combustion chemical reaction on the surface of the material will ignite after combustion heat. A part is used to heat the combustion products, part of a loss to the environment by radiation, the remaining part is by convection, radiation and conduction of the way back to the surface of materials and heat feedback to pre heat the unburned material, when unburned after pyrolysis and pyrolysis gas can be further released to maintain gas phase combustion the material is heated, this constant cycle and the formation of continuous material surface fire spread process. With the traditional carbon materials (such as paper, wood, etc.), non carbide materials in the pyrolysis process of no carbon layer is formed, will not hinder the external heat flux of pre heating of the material, so it should be far greater than the pyrolysis rate of pyrolysis carbide materials. In addition, the melt flow characteristics of materials and materials will also increase the rate of spread.
Firstly, in the cone calorimeter under nitrogen atmosphere of PMMA (Poly (methyl methacrylate) (Poly), ABS (acrylonitrile butadiene styrene)) and HIPS (High Impact Polystyren) three kinds of non carbonized polymer materials were studied under different thermal pyrolysis experiments, on the basis of non carbonized polymer material Co. the size of the fire spread process under natural conditions countercurrent experiments and theoretical research, which includes material thickness, width, ambient pressure and three-dimensional effects of parameters such as the spread of countercurrent fire. The specific contents are summarized as follows:
The pyrolysis, in low, high heat flux of PMMA, ABS and HIPS in the process of one-dimensional pyrolysis was studied. By measuring the results of thermocouple and infrared camera on the back of the material temperature, verify the feasibility of the non-contact temperature measurement method. By using the experimental material on the temperature and mass loss rate. Combined with ThermoKin model Stanislav I. Stoliarov are piecewise linear relation between thermal conductivity and temperature of the material. Then on the basis of experiment established a one-dimensional model of heat absorption material surface pyrolysis and pyrolysis reactions of non carbonized polymer materials, the absorption depth and surface model is widely used in the literature of the two absorption the hypothesis were studied and compared, the results showed that different absorption layer temperature distribution have great effect on the material surface temperature and thermal penetration, this kind of Different in the atmosphere is reflected in the difference in ignition time. In the macro aspect that is not considered material pyrolysis, pyrolysis and internal details of the case, the simulation results of both were in the acceptable range. By comparing the experimental and simulated weightlessness rate and the temperature of the results validate the correctness of the one-dimensional pyrolysis model.
The fire spread, based on the research on the pyrolysis of natural convection and different environment under the pressure of the counter current fire spread processes are analyzed theoretically and experimentally. The results show that the width of material under the condition of low increase rate increases with the thickness of the fire spread countercurrent increased, and the two-dimensional unconditional width limit the conclusion has great difference the main reason is that the finite size conditions, the combustion process of material on both sides of the spread rate. In the case of fixed thickness, the fire spread rate is inversely proportional to the width of material. In Hefei, Xining and Lhasa under different environmental stress conditions, the weight loss rate, flame height and fire spread rate increases along with the pressure increases at low pressure. Under the condition of gas phase chemical reaction kinetics and flame heat feedback are the main factors influence the fire spread rate, the number of Damkohler when the characterization of gas phase chemical reaction is less than a critical value will have stalled This phenomenon. From the view of the heat and mass transfer of fire spread process is analyzed and simplified model, the model of material fire spread rate is the size of the material, the function of flame front angle and thermal physical parameters. In addition, this model also provides by measuring the fire spread rate estimation method of flux flame pyrolysis zone and preheating zone feedback. Also, the models and experimental results illustrate the validity of the simplified model is in good agreement.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU564

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