【摘要】：固體可燃物火蔓延作為火災科學領域的重要研究對象之一,受到了火災科學研究者的廣泛關注。通過開展實驗,進行理論分析和數(shù)值模擬,人們加深了對不同可燃物性質和蔓延條件情況下火蔓延過程的控制機制和影響因素的認識。固體可燃物火蔓延的影響因素包括可燃物性質和環(huán)境特征等多個方面,其中一個重要的影響因素是環(huán)境壓強。從文獻回顧情況來看,當前關于環(huán)境壓強對固體可燃物火蔓延行為的影響的研究尚存在幾個方面的不足：1)針對順流火蔓延的研究非常少；2)由于實驗條件等的限制,絕大部分研究者采用的可燃物尺寸均非常小這些研究結果是否適用于較大尺寸的火蔓延仍然值得探討；3)不同研究者給出的結論有所不同,而對導致這些差異的原因尚沒有給出系統(tǒng)性的解釋。基于以上考慮,本文通過在合肥(海拔高度29.8m,環(huán)境壓強約100.1kPa)和拉薩地區(qū)(海拔高度3658.0m,環(huán)境壓強約65.2kPa)開展對比實驗,研究了環(huán)境壓強對沿PMMA平板和墻角火蔓延的影響。實驗測量結果表明,拉薩地區(qū)火蔓延速率遠小于合肥地區(qū)；在沿豎直平板向上和沿墻角向上火蔓延情況下,拉薩地區(qū)火蔓延速率接近為合肥地區(qū)的1/2。通過兩地火蔓延過程中預熱區(qū)大小和火焰向固體壁面的熱流強度的對比發(fā)現(xiàn),導致拉薩地區(qū)火蔓延速率較小的原因是由于低壓條件下,固體表面接受的對流熱流減小,并且火焰區(qū)內的碳煙顆粒濃度降低,從而火焰發(fā)射率減小,向固體壁面的輻射熱流減小。本文另外研究了墻角火蔓延的特殊行為,通過對比不同環(huán)境壓強和壁面夾角條件下熱解前鋒形狀的差異,并結合墻角火燃燒模擬結果,指出墻角火蔓延過程中“M”型熱解前鋒的形成是由于在靠近墻角中心線位置,氧氣供應不充分,燃燒不能維持。其次,本文利用FDS(直接數(shù)值模擬方式)模擬了自然對流條件下沿不同厚度PMMA材料的豎直向上火蔓延,研究了蔓延速率隨環(huán)境壓強的變化特點。結果表明,當壓強P≥55kPa時,對于熱薄型材料,豎直向上火蔓延速率與環(huán)境壓強的1/2次方成正比；而對于熱厚型材料,豎直向上火蔓延速率則近似隨壓強呈線性變化。最后,在前人理論模型的基礎上,本文通過進一步分析討論,建立了不同可燃物類型和火蔓延形式情況下,蔓延速率與環(huán)境壓強之間的定量關系,并且利用文獻中以及本文的實驗和數(shù)值模擬結果對這些關系式進行了驗證。這些關系式可以應用于一定壓強范圍內固體可燃物火蔓延速率的預測。
[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，

本文編號：2332815