环境压强对固体可燃物火蔓延的影响研究
发布时间：2018-11-15 08:51
【摘要】：固体可燃物火蔓延作为火灾科学领域的重要研究对象之一,受到了火灾科学研究者的广泛关注。通过开展实验,进行理论分析和数值模拟,人们加深了对不同可燃物性质和蔓延条件情况下火蔓延过程的控制机制和影响因素的认识。固体可燃物火蔓延的影响因素包括可燃物性质和环境特征等多个方面,其中一个重要的影响因素是环境压强。从文献回顾情况来看,当前关于环境压强对固体可燃物火蔓延行为的影响的研究尚存在几个方面的不足：1)针对顺流火蔓延的研究非常少；2)由于实验条件等的限制,绝大部分研究者采用的可燃物尺寸均非常小这些研究结果是否适用于较大尺寸的火蔓延仍然值得探讨；3)不同研究者给出的结论有所不同,而对导致这些差异的原因尚没有给出系统性的解释。基于以上考虑,本文通过在合肥(海拔高度29.8m,环境压强约100.1kPa)和拉萨地区(海拔高度3658.0m,环境压强约65.2kPa)开展对比实验,研究了环境压强对沿PMMA平板和墙角火蔓延的影响。实验测量结果表明,拉萨地区火蔓延速率远小于合肥地区；在沿竖直平板向上和沿墙角向上火蔓延情况下,拉萨地区火蔓延速率接近为合肥地区的1/2。通过两地火蔓延过程中预热区大小和火焰向固体壁面的热流强度的对比发现,导致拉萨地区火蔓延速率较小的原因是由于低压条件下,固体表面接受的对流热流减小,并且火焰区内的碳烟颗粒浓度降低,从而火焰发射率减小,向固体壁面的辐射热流减小。本文另外研究了墙角火蔓延的特殊行为,通过对比不同环境压强和壁面夹角条件下热解前锋形状的差异,并结合墙角火燃烧模拟结果,指出墙角火蔓延过程中“M”型热解前锋的形成是由于在靠近墙角中心线位置,氧气供应不充分,燃烧不能维持。其次,本文利用FDS(直接数值模拟方式)模拟了自然对流条件下沿不同厚度PMMA材料的竖直向上火蔓延,研究了蔓延速率随环境压强的变化特点。结果表明,当压强P≥55kPa时,对于热薄型材料,竖直向上火蔓延速率与环境压强的1/2次方成正比；而对于热厚型材料,竖直向上火蔓延速率则近似随压强呈线性变化。最后,在前人理论模型的基础上,本文通过进一步分析讨论,建立了不同可燃物类型和火蔓延形式情况下,蔓延速率与环境压强之间的定量关系,并且利用文献中以及本文的实验和数值模拟结果对这些关系式进行了验证。这些关系式可以应用于一定压强范围内固体可燃物火蔓延速率的预测。
[Abstract]:As one of the important research objects in the field of fire science, the spread of solid combustible fire has been paid more and more attention by fire science researchers. Through experiments, theoretical analysis and numerical simulation, people have a deeper understanding of the control mechanism and influencing factors of the fire spread process under different flammable properties and spreading conditions. The factors influencing the spread of solid combustible fire include the properties of combustible materials and the environmental characteristics, among which the environmental pressure is one of the most important factors. According to the literature review, there are still several deficiencies in the current research on the influence of environmental pressure on the spread behavior of solid combustible fire: 1) there are very few studies on the downstream fire spread; 2) due to the limitation of experimental conditions, most of the fuel sizes used by researchers are very small. 3) the conclusions of different researchers are different, but there is no systematic explanation for the causes of these differences. Based on the above considerations, a comparative experiment was carried out in Hefei (29.8m above sea level, 100.1kPa) and Lhasa (3658.0 m, 65.2kPa). The effect of ambient pressure on fire spread along PMMA plate and corner is studied. The experimental results show that the fire spread rate in Lhasa is much smaller than that in Hefei, and that the fire spread rate in Lhasa is nearly 1 / 2 of that in Hefei under the condition of fire spreading up the vertical plate and along the corner of the wall. By comparing the size of preheating zone and the heat flux from flame to solid wall during fire spread between the two places, it is found that the reason for the low fire spread rate in Lhasa is that the convection heat flux accepted by solid surface decreases under low pressure. The concentration of soot particles in the flame region decreases, thus the flame emissivity decreases and the radiation heat flux toward the solid wall decreases. In addition, the special behavior of corner fire spread is studied in this paper. The difference of pyrolysis front shape under different ambient pressure and wall angle is compared, and the simulation results of corner fire combustion are combined. It is pointed out that the formation of the "M" pyrolysis front in the spreading process of corner fire is due to the insufficient oxygen supply near the center line of the wall corner, and the combustion can not be maintained. Secondly, the vertical fire propagation along different thickness of PMMA materials under natural convection is simulated by FDS (direct numerical simulation), and the variation of propagation rate with ambient pressure is studied. The results show that when the pressure P 鈮，
本文编号：2332815
[Abstract]:As one of the important research objects in the field of fire science, the spread of solid combustible fire has been paid more and more attention by fire science researchers. Through experiments, theoretical analysis and numerical simulation, people have a deeper understanding of the control mechanism and influencing factors of the fire spread process under different flammable properties and spreading conditions. The factors influencing the spread of solid combustible fire include the properties of combustible materials and the environmental characteristics, among which the environmental pressure is one of the most important factors. According to the literature review, there are still several deficiencies in the current research on the influence of environmental pressure on the spread behavior of solid combustible fire: 1) there are very few studies on the downstream fire spread; 2) due to the limitation of experimental conditions, most of the fuel sizes used by researchers are very small. 3) the conclusions of different researchers are different, but there is no systematic explanation for the causes of these differences. Based on the above considerations, a comparative experiment was carried out in Hefei (29.8m above sea level, 100.1kPa) and Lhasa (3658.0 m, 65.2kPa). The effect of ambient pressure on fire spread along PMMA plate and corner is studied. The experimental results show that the fire spread rate in Lhasa is much smaller than that in Hefei, and that the fire spread rate in Lhasa is nearly 1 / 2 of that in Hefei under the condition of fire spreading up the vertical plate and along the corner of the wall. By comparing the size of preheating zone and the heat flux from flame to solid wall during fire spread between the two places, it is found that the reason for the low fire spread rate in Lhasa is that the convection heat flux accepted by solid surface decreases under low pressure. The concentration of soot particles in the flame region decreases, thus the flame emissivity decreases and the radiation heat flux toward the solid wall decreases. In addition, the special behavior of corner fire spread is studied in this paper. The difference of pyrolysis front shape under different ambient pressure and wall angle is compared, and the simulation results of corner fire combustion are combined. It is pointed out that the formation of the "M" pyrolysis front in the spreading process of corner fire is due to the insufficient oxygen supply near the center line of the wall corner, and the combustion can not be maintained. Secondly, the vertical fire propagation along different thickness of PMMA materials under natural convection is simulated by FDS (direct numerical simulation), and the variation of propagation rate with ambient pressure is studied. The results show that when the pressure P 鈮，
本文编号：2332815
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