環(huán)境壓強(qiáng)對(duì)固體可燃物火蔓延的影響研究
發(fā)布時(shí)間：2018-11-15 08:51
【摘要】：固體可燃物火蔓延作為火災(zāi)科學(xué)領(lǐng)域的重要研究對(duì)象之一,受到了火災(zāi)科學(xué)研究者的廣泛關(guān)注。通過開展實(shí)驗(yàn),進(jìn)行理論分析和數(shù)值模擬,人們加深了對(duì)不同可燃物性質(zhì)和蔓延條件情況下火蔓延過程的控制機(jī)制和影響因素的認(rèn)識(shí)。固體可燃物火蔓延的影響因素包括可燃物性質(zhì)和環(huán)境特征等多個(gè)方面,其中一個(gè)重要的影響因素是環(huán)境壓強(qiáng)。從文獻(xiàn)回顧情況來看,當(dāng)前關(guān)于環(huán)境壓強(qiáng)對(duì)固體可燃物火蔓延行為的影響的研究尚存在幾個(gè)方面的不足：1)針對(duì)順流火蔓延的研究非常少；2)由于實(shí)驗(yàn)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(jié)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(jié)論有所不同,而對(duì)導(dǎo)致這些差異的原因尚沒有給出系統(tǒng)性的解釋�；谝陨峡紤],本文通過在合肥(海拔高度29.8m,環(huán)境壓強(qiáng)約100.1kPa)和拉薩地區(qū)(海拔高度3658.0m,環(huán)境壓強(qiáng)約65.2kPa)開展對(duì)比實(shí)驗(yàn),研究了環(huán)境壓強(qiáng)對(duì)沿PMMA平板和墻角火蔓延的影響。實(shí)驗(yàn)測(cè)量結(jié)果表明,拉薩地區(qū)火蔓延速率遠(yuǎn)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(yù)熱區(qū)大小和火焰向固體壁面的熱流強(qiáng)度的對(duì)比發(fā)現(xiàn),導(dǎo)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(duì)流熱流減小,并且火焰區(qū)內(nèi)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(duì)比不同環(huán)境壓強(qiáng)和壁面夾角條件下熱解前鋒形狀的差異,并結(jié)合墻角火燃燒模擬結(jié)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(yīng)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(duì)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(qiáng)的變化特點(diǎn)。結(jié)果表明,當(dāng)壓強(qiáng)P≥55kPa時(shí),對(duì)于熱薄型材料,豎直向上火蔓延速率與環(huán)境壓強(qiáng)的1/2次方成正比；而對(duì)于熱厚型材料,豎直向上火蔓延速率則近似隨壓強(qiáng)呈線性變化。最后,在前人理論模型的基礎(chǔ)上,本文通過進(jìn)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(qiáng)之間的定量關(guān)系,并且利用文獻(xiàn)中以及本文的實(shí)驗(yàn)和數(shù)值模擬結(jié)果對(duì)這些關(guān)系式進(jìn)行了驗(yàn)證。這些關(guān)系式可以應(yīng)用于一定壓強(qiáng)范圍內(nèi)固體可燃物火蔓延速率的預(yù)測(cè)。
[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(hào)：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，
本文編號(hào)：2332815
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