不同宽度和角度下木材表面火蔓延特性的实验研究

选取宽2～11 cm、厚3 mm的樟木、杉木和白木试样进行了一系列实验,测量了火蔓延速度、火焰高度、火焰温度和试样表面温度。结果表明,火焰高度随试样宽度增加而增大,并在宽度增加至某个值后不再增大;同宽度下,密度大的试样火焰高度大。放置角度为负时,不同密度试样的火蔓延速度差较小,角度为正时,火蔓延速度随角度增加而增大,且不同密度试样的火蔓延速度差变大.     

不同收光角度下煤粉颗粒流的LIBS光谱特性研究

将激光诱导击穿光谱技术(LIBS)应用于煤粉颗粒流的直接检测,利用自行搭建的颗粒流实验台架重点研究不同收光角度下煤粉颗粒的等离子体光谱特性,分析煤中具有代表性的C,Si和Al三种元素原子谱线的强度及其相对标准偏差的变化规律,结果表明收光角度在30°～45°区间时收集到的等离子体信号强且稳定。     

晶体几何结构及入射角度对自抽运相位共轭特性影响的研究

基于两块不同尺寸的Cu∶KNSBN晶体自抽运相位共轭实验,研究了光折变晶体的几何结构及入射角度对自抽运相位共轭特性的影响,得到在入射位置不变化的情况下,随着入射角度的变化相位共轭光输出有最大值,几何结构不同对应的最大值不同。并从理论上分析了晶体结构及入射角度在双作用区自抽运相位共轭机理中的作用,指出几何结构、入射角度与自抽运光通道、耦合系数的关系,及在自抽运相位共轭效应中存在一个最佳入射角度,这时相位共轭光输出最大。最后,对理论上的相位共轭反射率公式进行了修正。对自抽运相位共轭实际应用中,选择最佳入射角度提供了理论和实验依据。     

一种改善红光顶发射OLED色纯度及角度依赖特性的方法研究

在Si/SiO₂衬底上生长金属银作为阳极,4,4,4-tris(3-methylphenylpheny-lamino)-triphenylamine(m-MTDATA):MoOx/m-MTDATA/N,N-bis-(1-naphthyl)-N,N-diphenyl-1,1-biphenyl-4,4-diamine(NPB)作为空穴注入及传输层,发光层采用4,4-N,N-dicarbazole-biphenyl(CBP)掺杂磷光染料(1-(phenyl)isoquinoline)iridium(III) acetylanetonate(Ir(piq)₂(acac))的结构,4,7-di-phenyl-1,10-phenanthroline(BPhen)作为空穴阻挡层及电子传输层,阴极为LiF(1 nm)/Al(2 nm)/Ag(20 nm)复合阴极结构.通过在光取出的复合阴极上方生长一层CBP光学覆盖层,有效地改善了复合阴极膜系的透射率,从而改善了顶发射结构的光学耦合输出特性,在提高器件的正向发光效率的同时还使色坐标往深红光区移动.并且生长光学覆盖层结构的器件角度依赖特性明显得到改善,这对于制作高显示质量的显示器件具有重要意义.在原有结构的基础上增加20 nm的NPB掺杂磷光染料Ir(piq)₂(acac)作发光层,从而得到双发光层结构为NPB:Ir(piq)₂(acac)(1%,20 nm)/CBP:Ir(piq)₂(acac)(1%, 20 nm).由于NPB具有较高的空穴迁移率,避免了由于光学厚度的增加而引起器件工作电压的大幅升高,而双发光层的结构有利于增大激子复合区域,提高辐射复合几率,减少非辐射损耗,实现主客体之间高效的三线态能量传递,相对单发光层顶发射结构,双发光层结构不仅提高了器件的发光效率,而且改善了器件的色坐标.     

窄通道内热薄燃料表面火焰传播特性研究

利用实验和数值模拟对微重力和常重力条件下高度为14mm和10mm的窄通道内热薄纸张表面火焰传播特性进行了研究。不同重力条件下窄通道内火焰传播速度随气流速度变化的规律符合得较好,说明地面窄通道实验能够模拟微重力条件下材料表面火焰传播的主要特征。地面窄通道中浮力流动速度的最大值约为5cm／s,与常规实验通道（高度较大）相比...     

Thermal Analysis of Vertical Upward Flame Spread and Dripping Behaviors of Polystyrene Foams at Different Altitudes

In order to reveal the effect of altitude on the flame spread and dripping behaviors of PS foams a series of upward flame spread experiments was carried out on the plateau area of Lhasa and the plain area of Hefei. It was found that, during the flame spread process, extinction occurred on the plateau for expanded polystyrene (EPS) and extruded polystyrene (XPS) foams while, on the plain, the flame spread could be well sustained and, at longer times, even acceleration was observed. Due to the increase of smoke generation, resulting in decreases of the flame heat flux and oxygen concentration in air entrainment on the plateau, the burning and heat transfer were not efficient in Lhasa, making extinction occur. A larger angle for the pyrolysis front of EPS and XPS on the plateau was another important factor promoting extinction. The mass of dripping PS in the pool fire zone was also studied for different thicknesses of PS at the two altitudes. The maximum dripping mass of EPS or XPS was much larger for thicknesses of 4 cm and 5 cm than for 2 cm and 3 cm, attributed to the melting PS dripping to the pool fire zone directly making the effect of attaching to the wall weaken.     

Flame structure and flame spread rate over a solid fuel in partially premixed atmospheres

We have investigated the downward flame spread over a thin solid fuel. Hydrogen, methane, or propane, included in the gaseous product of pyrolysis reaction, is added in the ambient air. The fuel concentration is kept below the lean flammability limit to observe the partially premixing effect. Both experimental and numerical studies have been conducted. Results show that, in partially premixed atmospheres, both blue flame and luminous flame regions are enlarged, and the flame spread rate is increased. Based on the flame index, a so-called triple flame is observed. The heat release rate ahead of the original diffusion flame is increased by adding the fuel, and its profile is moved upstream. Here, we focus on the heat input by adding the fuel in the opposed air, which could be a direct factor to intensify the combustion reaction. The dependence of the flame spread rate on the heat input is almost the same for methane and propane/air mixtures, but larger effect is observed for hydrogen/air mixture. Since the deficient reactant in lean mixture is fuel, the larger effect of hydrogen could be explained based on the Lewis number consideration. That is, the combustion is surely intensified for all cases, but this effect is larger for lean hydrogen/air mixture (Le < 1), because more fuel diffuses toward the lean premixed flame ahead of the original diffusion flame. Resultantly, the pyrolysis reaction is promoted to support the higher flame spread rate.     

Flame spread and interactions in an array of thin solids in low-speed concurrent flows

Flame spread in an array of thin solids in low-speed concurrent flows was investigated and numerical solved. A previous steady, two-dimensional flame-spread model with flame radiation was employed and adapted in this work. The flame structures of spreading flames between parallel solids were demonstrated and some of the features were presented, including flow channelling effect and flame radiation interactions. The channelling effect is caused by flow confinement by the presence of the other solids; the flows through the hot combustion gases are accelerated downstream drastically. Radiation interactions between flames and solids contributed to a less heat-loss system, and radiation re-absorption by flames resulted in a larger flame with higher temperature, which increased the conductive heat fluxes to the solids and flame spread rate. Consequently, the extinction limit for the interacting flames is extended beyond the low-speed quenching limit for a single flame. The influence of the separation distance on the flame spread rate was also studied, which exhibits a non-monotonic behaviour. At larger separation distance, the flame spread rate increases with decreasing the separation distance owing to the channelling effect and radiation interactions. However, at very small separation distance, the flame spreading rate decreases with decreasing the distance because of the limited space for thermal expansion and flow résistance between solids.     

边条翼后掠角对钝头细长旋成体非对称流动的影响

为探究大迎角时边条翼前缘后掠角对钝头细长旋成体导弹绕流特性的影响,开展了模型表面测压和粒子图像测速的风洞实验,研究了亚临界Reynolds数Re=150000、迎角α=50°条件下不同前缘后掠角固定边条翼的钝头细长旋成体非对称绕流特性.结果表明,在边条翼上游区,后掠角增大使边条涡涡位更靠近前体物面且对称性更好,导致前体...     

Influence of edge propagation on downward flame spread over three-dimensional PMMA samples

This systematic experimental study measures the effect of flame propagation along vertical edges on the overall downward spread of flames using Polymethyl Methacrylate (PMMA). Samples with a wide range of regular cross-sections – from triangular through octagonal – as well as irregular ones, have been used to test a large variation of internal angles. A MATLAB-based tool was used to calculate instantaneous spread rate for central and edge flames. The edge flame is shown to significantly enhance the spread rate, as much as five times, in respect to samples with no edges. This amplification is shown to depend primarily on the internal angle at the edge (the smaller the angle, the faster the flame) and fuel thickness, and not on other factors such as aspect ratio or cross-sectional area. Using a phenomenological argument, the edge propagation rate is correlated to the spread rate over an equivalent cylindrical fuel (the limiting shape with infinite edges) with an effective radius obtained from the geometry of the edges and the diffusion length scale of the solid phase. A formula for flame spread over cylindrical fuel from the literature is used to link the new results to existing models. Both thick and thin limits are shown to encompass the wide range of three-dimensional spread rate data within the effective radius (the independent variable), which can be determined from the known parameters. Based on these results, different types of cross-sectional areas can be sorted in the order of their inherent fire safety characteristics.     

表面粗糙度对点扩散函数影响的研究

建立了粗糙波面点扩散函数。所建立的点扩散函数，包括“核”和“晕圈”两部份，前者随粗糙度的增加而减少，后者随粗糙度的增加而增加。     

Effect of Polyborosiloxane on the Flame Retardancy and Thermal Degradation of Intumescent Flame Retardant Polypropylene

A novel synergistic flame retardant agent containing boron and silicon, namely polyborosiloxane (PBSil), was prepared via the condensation reaction of boric acid (BA), tetraethoxysilane (TEOS), and octamethyl cyclotetrasiloxane (OMCTS). The obtained PBSil was then combined with an intumescent flame retardant (IFR) to flame retard polypropylene (PP), and the effects of PBSil on the flame retardancy and thermal degradation of the PP/IFR composite were investigated. It was found that PBSil could improve the compatibility between the IFR and the PP matrix, thereby improving the mechanical properties of the composite. Compared with zinc borate, zeolite, and nano-silica, PBSil showed much better flame retardancy and smoke suppression in the PP/IFR composite. When the content of PBSil was 3.0 wt%, the limiting oxygen index (LOI) value of the flame retardant PP was increased from 29.0% to 35.0%, and the UL-94 rating was improved from V-1 to V-0 rating. Simultaneously, the heat release rate (HRR) and smoke production rate (SPR) of the composite were decreased dramatically. The thermogravimetric (TG) analysis, Fourier transform infrared (FTIR), and thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR) results showed that, PBSil could enhance the thermostability of the IFR, and promote the char formation. Furthermore, the compactness and thermostability of the intumescent char were significantly improved, contributing to the improvement of the flame retardancy of the composite.     

沟渠内杨木三合板架空燃烧的火灾行为的研究

建立了缩尺寸沟渠火灾试验模型,测量了沟渠以及平台入口附近的温度分布,研究了沟渠内杨木三合板架空燃烧的位置和沟渠的倾斜角度对火蔓延行为的影响,分析了火焰传播特征和火蔓延速率.试验结果表明:在沟渠效应和烟囱效应的综合作用下,火焰先从杨木三合板与沟渠底板之间的狭长空间传播到沟渠顶部,在入口处形成喷射状火焰;狭长空间内的温度先...     

On the role of radiation and dimensionality in predicting flow opposed flame spread over thin fuels

In this work a flame-spread model is formulated in three dimensions to simulate opposed flow flame spread over thin solid fuels. The flame-spread model is coupled to a three-dimensional gas radiation model. The experiments [1] on downward spread and zero gravity quiescent spread over finite width thin fuel are simulated by flame-spread models in both two and three dimensions to assess the role of radiation and effect of dimensionality on the prediction of the flame-spread phenomena. It is observed that while radiation plays only a minor role in normal gravity downward spread, in zero gravity quiescent spread surface radiation loss holds the key to correct prediction of low oxygen flame spread rate and quenching limit. The present three-dimensional simulations show that even in zero gravity gas radiation affects flame spread rate only moderately (as much as 20% at 100% oxygen) as the heat feedback effect exceeds the radiation loss effect only moderately. However, the two-dimensional model with the gas radiation model badly over-predicts the zero gravity flame spread rate due to under estimation of gas radiation loss to the ambient surrounding. The two-dimensional model was also found to be inadequate for predicting the zero gravity flame attributes, like the flame length and the flame width, correctly. The need for a three-dimensional model was found to be indispensable for consistently describing the zero gravity flame-spread experiments [1] (including flame spread rate and flame size) especially at high oxygen levels (>30%). On the other hand it was observed that for the normal gravity downward flame spread for oxygen levels up to 60%, the two-dimensional model was sufficient to predict flame spread rate and flame size reasonably well. Gas radiation is seen to increase the three-dimensional effect especially at elevated oxygen levels (>30% for zero gravity and >60% for normal gravity flames).