电焊熔珠对棉布和聚氨酯泡沫的引燃能力研究

研究了加载电压对电焊熔珠数目和粒径分布的影响,在模拟装置上实验了电焊对棉布、聚氨酯泡沫和纸张的引燃性能.结果表明,随着加载电压升高,电焊熔珠的数目逐渐减少,熔珠粒径逐渐增大,引燃能力逐渐增强.固体材料性质对电焊熔珠引燃能力也有很大影响,表面粗糙,易蓄热材料容易被点燃.电焊熔珠引燃棉布、聚氨酯泡沫和纸张的临界电压为37.5V、40V和45V.     

火灾中摩擦火花和热表面引燃能力的研究

用摄影和热点偶等方法在一个有磨削轮的容器中研究了机械摩擦火花和热表面的引燃能力。在本研究中发现,对于某些材料,如碳钢等,由摩擦产生的磨屑可以被周围空气中的氧氧化而放出大量的热,从而使屑粒温度升高,达到白热程度。通常我们把一簇这样的颗粒中做“摩擦火花”。     

外界辐射热对浸油沙层着火特性影响研究

通过实验研究了施加辐射热后浸油沙层的着火特性.实验中使用柴油为燃料,沙层为多孔介质,自制的施加辐射热测量闪点和燃点的设备,研究了施加辐射热后,沙油质量比、沙粒直径以及外界辐射热通量对浸油沙层着火特性的影响.结果表明,沙粒直径及沙油质量比不变,随着辐射热通量的增大,浸油沙层的闪点、燃点降低到某一值后不再变化;施加辐射热通量,浸油沙层的闪点、燃点随沙油质量比的增加而升高,不再出现闪点和燃点的最小值点;沙粒直径对浸油沙层的闪点和燃点有影响.     

膨胀型防火涂料对高压电力电缆引燃特性影响的实验研究

膨胀型防火涂料在电缆防火工程中有较广泛的应用,在使用过程中确保电缆涂料的效果与经济性具有重要意义。对喷涂不同厚度膨胀型高氯化聚乙烯防火涂料的高压电力电缆开展了在典型强度外加辐射热流条件的着火引燃实验,分析了电力电缆点燃时间、受热期间涂层对电缆外护套的保护与涂层受热后的形态变化。结果表明,电缆的着火行为与涂层厚度紧密相关。相比于未喷涂防火涂料的电缆,覆有膨胀型高氯化聚乙烯防火涂料的电缆在加热过程中明显膨胀,生成较软的泡沫状碳质层,且引燃时间较长,电缆起火后火势较弱。随着涂层厚度的增加,该涂料对电缆的阻燃和保护效果更为显著,研究结果表明,电缆表面喷涂1.0 mm厚度的防火涂料较为适宜。     

膨胀型防火涂料对高压电力电缆引燃特性影响的实验研究

膨胀型防火涂料在电缆防火工程中有较广泛的应用,在使用过程中确保电缆涂料的效果与经济性具有重要意义.对喷涂不同厚度膨胀型高氯化聚乙烯防火涂料的高压电力电缆开展了在典型强度外加辐射热流条件的着火引燃实验,分析了电力电缆点燃时间、受热期间涂层对电缆外护套的保护与涂层受热后的形态变化.结果表明,电缆的着火行为与涂层厚度紧密相关...     

着床后引燃对电弧迸溅熔珠组织特征的影响

为探究迸溅熔珠着床后的热交换过程对其组织特征的影响,建立基于着床后高温迸溅熔珠的动态测温方法,从而揭示迸溅熔珠着床后引燃与否对其组织特征形成的影响规律。研究结果表明：引燃可燃物的熔珠受火焰热反馈和铜氧化放热的共同作用,着床后其温度出现反复波动,延长迸溅熔珠的冷却凝固时间,组织呈等轴状;无法引燃可燃物的熔珠在可测范围内,短暂升温后降温速率持续上升,组织更易呈现树枝状或胞状。研究结果可为准确认定电气故障电弧迸溅熔珠引发火灾提供技术支持。     

含水率及燃烧性能等级对中密度纤维板点燃行为及安全性能影响的研究

采用锥形量热仪,在不同辐射热流强度下,对三种燃烧性能等级(B级、C级和非阻燃)的中密度纤维板在不同相对湿度(0%、50%和98%)形成的含水率条件下进行了辐射引燃实验,测得点燃时间和热释放速率等参数。利用点燃理论中热厚型积分模型,推导了不同含水率不同燃烧性能等级(防火等级)纤维板的临界辐射热通量。通过对比发现,点燃时间随着板材含水率的增加而明显增大,而临界辐射热通量则几乎不受环境相对湿度(即含水率)的影响。添加阻燃剂可延长点燃时间,使板材临界辐射热通量增加,并能有效地降低纤维板材燃烧时的热释放速率。阻燃纤维板的临界辐射热通量要明显高于非阻燃纤维板,但是阻燃纤维板材之间相比,临界辐射热通量差别不大。因而,从本质安全的角度对材料的安全性进行评价,不能将临界辐射热通量作为单一的标准,必须综合多个参数进行全面评价。     

阻燃剂对棉布和地毯热解燃烧性能的影响研究

研究了氢氧化铝和三聚氰胺氰尿酸盐对棉布和地毯热解和燃烧行为,考察了阻燃剂添加量对棉布和地毯点燃时间、热解速度和火焰持续时间的影响,并利用锥形量热仪测定了添加阻燃剂前后材料在点燃时间、热释放速率、质量损失速率和CO释放速率的变化,结果表明海水中添加10%的Al(OH)3和MCA可显著降低棉布和地毯的热解速度及热释放速率.     

悬浮填料对曝气池充氧能力影响的试验研究

通过清水曝气充氧试验测定在不同填充率情况下水中溶解氧量的变化,分析悬浮填料能否增加曝气池溶解氧的转移速率。试验结果表明：悬浮填料对微孔曝气充氧速率无明显加速作用。     

Effect of particle size and dust layer size on ignition characteristics of PMMA dust layer on hot surface

Deposition of combustible dust on a hot surface is a hidden danger of fire. In this work, polymethylmethacrylate (PMMA) dust was selected to analyse the influence of dust layer diameter, dust particle size and dust layer thickness on the ignition characteristics of PMMA dust layer. Critical heating temperatures and ignition time had been measured. The STA-GC/MS-FTIR analysis was used to determine that the main products of PMMA pyrolysis were MMA, CO, CO₂, and C₂H₄, of which CO and C₂H₄ were transported to the ambient to cause gas phase combustion on the surface of the dust layer. For 10 mm thick dust layer, the critical heating temperatures of 5 μm PMMA, 100 nm PMMA, and 30 μm PMMA were 300 °C, 330 °C, and 320 °C. As the thickness of the dust layer increased, the gas transport path became longer, the critical heating temperature and ignition time increased. The characteristic particle size (D [3,2]) was utilized to represent the true particle size, and the ignition time increased with the increase of the characteristic particle size. The increase in the diameter of the dust layer had a slight effect on the temperature history and ignition time of the dust layer.     

Effect of ignition position on the run-up distance to DDT for hydrogen-air explosions

The method described in this paper enabled reliable and accurate positioning of an overdriven detonation by calculation of shock wave velocities (detonation and retonation) for hydrogen explosions in a closed 18 m long horizontal DN150 pipe. This enabled an empirical correlation between the ignition position and the run-up distance to DDT to be determined. It was shown that the initial ability of the flame to expand unobstructed and the piston-like effect of burnt gas expanding against the closed end of the tube contributed to initial flame acceleration and hence were able to affect the run-up distance to overdriven detonation. Flame speeds and rates of initial pressure rise were also used to explain how these two competing effects were able to produce a minimum in the run-up distance to DDT. The shortest run-up distance to DDT, relative to the ignition position, for this pipe and gas configuration was found when the ignition position was placed 5.6 pipe diameters (or 0.9 m) from the closed pipe end. The shortest run-up distance to DDT relative to the end of the pipe was recorded when the ignition source was placed 4.4 pipe diameters or 0.7 m from the pipe end.     

Effect of ignition delay on explosion parameters of corn dust/air in confined chamber

This paper presents the explosion parameters of corn dust/air mixtures in confined chamber. The measurements were conducted in a setup which comprises a 5 L explosion chamber, a dust dispersion sub-system, and a transient pressure measurement sub-system. The influences of the ignition delay on the pressure and the rate of pressure rise for the dust/air explosion have been discussed based on the experimental data. It is found that at the lower concentrations, the explosion pressure and the rate of pressure rise of corn dust/air mixtures decrease as the ignition delay increases from 60 ms; But at the higher concentrations, the explosion pressure and the rate of pressure rise increase slightly as the ignition delay increases from 60 ms to 80 ms, and decrease beyond 80 ms. The maximum explosion pressure of corn dust/air mixtures reaches its highest value equal to 0.79 MPa at the concentration of 1000 gm⁻³.     

龙柏树冠火对相邻建筑的辐射特性研究

我国城市绿化覆盖率快速增长,带来了植被与建筑混合区域的火灾隐患。以常见城市绿化树种龙柏为研究对象,开展了单树树冠火对其相邻建筑的热辐射规律实验研究,测量了不同间距情况下建筑物一层和二层窗户位置的辐射热流密度,并在圆柱火焰模型的基础上,将圆柱火焰分为下层的稳定火焰区和上层的间歇火焰区,提出了分层圆柱火焰模型。结果表明,分层圆柱火焰模型可以准确描述树冠火辐射热流密度最大值随高度和距离的增加而递减的变化趋势。单一圆柱火焰模型理论的结果表明竖直方向上热流密度随高度变化不大,未能准确描述辐射热流密度竖向变化规律;分层圆柱火焰模型计算的辐射热流密度比单一圆柱火焰模型更符合实验结果,能更好地预测安全距离。     

导热性能对浸油沙层闪点、燃点的影响研究

研究了浸油沙层的导热性能对浸油沙层闪点和燃点的影响。选用柴油作为燃料液体,铜粉和沙子的混合物代表沙层,浸油沙层的导热系数由混合物中的沙子和铜粉比例控制。实验结果表明,浸油沙层的导热性能对其着火特性有重要影响。不加铜粉时,存在一个使混合物的闪点与燃点最小的沙油质量比。随着铜粉添加量的增加,闪点与燃点的最小值点逐渐消失。这可能是加入细铜粉使混合物的表面平整造成的。在最小点后,随铜粉添加量的增加,也就是随混合物的导热性能的改善,混合物的闪点与燃点增大。但当沙子与铜粉的质量比达到1：1时,闪点与燃点随沙油质量比的变化出现了一个最大值,之后闪点和燃点随沙油质量比的增加而降低。这些现象的出现可能是导热能力、毛细现象和混合物内部的空隙三者共同作用的结果。     

Effect of transient heat transfer on ignition of solid particles

Ignition and combustion of solid particles are the issues of interest for many industrial applications. When simulating ignition and combustion of solid particles using available standard (ST) models, a number of simplifying assumptions are usually adopted, which are not always justified. For example, for calculating heat flux to particle surface, the Newton law is often applied with the heat flux proportional to the difference between the gas temperature and the mean particle temperature. However, Newton law is known to be valid only for steady-state heat transfer. Moreover, the actual heat flux is determined by the particle surface temperature rather than its mean temperature. The objective of this work is to develop a new particle-heating model with the correction factors to the Newton law taking into account transient heat transfer to a particle and nonuniform temperature distribution inside the particle. It was shown that the new particle-heating model correlates much better with detailed numerical calculations than the ST model. The transient heating effects were shown to be important for the problem of solid particle ignition in the oxidizer gas.     

Effect of initial temperature on the explosion pressure of various liquid fuels and their blends

In this work, the effect of initial temperature on the explosion pressure, P_ex, of various liquid fuels (isooctane, toluene and methanol) and their blends (isooctane-toluene and methanol-toluene, with three different fuel-fuel ratios) was investigated by performing experiments in a 20-l sphere at different concentrations of vaporized fuel in air. The initial temperature was varied from 333 K to 413 K.Results show that, as the fuel-air equivalence ratio, Φ, is increased, a transition occurs from a “thermodynamics-driven” explosion regime to a “radiant heat losses-driven” explosion regime. The maximum pressure, P_max, is found in the former regime (Φ < 3), which is characterized by a trend of decreasing P_ex with increasing initial temperature. This trend has been explained by thermodynamics. In the latter regime (Φ > 3), P_ex increases with increasing initial temperature. This trend has been addressed to the decrease in emissivity (and, thus, radiant heat losses) with the increase in temperature.