侧向风对挑檐防火阻隔作用的影响

建立了简易全尺寸建筑模型,采用FDS进行火灾模拟。选取火源功率为4 MW,设置0~10 m/s的侧向风,研究不同风速条件下挑檐临界特征尺寸以及火焰最大侧向蔓延距离的变化规律。研究结果表明:侧向风速较低时,溢出火焰主要为向上层蔓延,表现为热浮力主控;侧向风速较高时,溢出火焰表现为风速主控,挑檐最大临界长度为3.6 m;侧向风速继续增加时,溢出火焰不再接触挑檐,向邻侧蔓延,临界风速为6 m/s;溢出火焰侧向蔓延距离随风速增大先增大后缓慢减小,临界风速为8 m/s,溢出火焰的最大侧向蔓延距离为4.4 m。     

净化颗粒物用空气过滤材料性能测试与对比

针对修订的《采暖通风与空气调节设计规范》中PM10浓度小于0．15mg／m^3的要求，设计了空气净化材料过滤性能测试台。采用环境气溶胶中颗粒物PM10、PM25、PM18为过滤对象，存0．2m／s、0．8m／s、1．2m／s过滤风速下，对熔喷类、针刺类、复合类过滤材料的过滤性能进行了测试。测试结果表明，荷电纤维滤料具有低阻高效性能。荷电针刺纤维滤料阻力在200Pa以下，过滤效率在70％以上，低风速时可以达到95％，但不带荷电的针刺纤维过滤效率在20％-40％以下。熔喷纤维滤料的过滤效率在50％～80％之间，随着过滤风速的提高阻力增加较快。     

纵向通风风速对锯末正向阴燃过程的影响

为探讨通风条件对阴燃过程的影响,笔者利用小型阴燃试验炉,研究了纵向通风风速对落叶松锯末正向阴燃过程中的阴燃建立时间、阴燃速度、阴燃温度和质量损失的影响。结果表明,在不同的通风风速下,阴燃的建立时间差别不大,但总平均阴燃速度随着通风风速的增加而明显增大;沿阴燃传播方向,不同位置处的平均阴燃速度均呈现先增大后减小的趋势,阴燃温度均依次出现先升高后下降的变化趋势;当通风风速 v=0 m/s 时,阴燃最高温度达 451.9 ℃;锯末阴燃质量损失速率和最终剩余质量均随通风风速的增加而增大。研究结果可以为阴燃火灾事故预防提供一定参考。     

柔性光伏系统颤振性能的节段模型试验研究

柔性光伏支架的频率低、质量轻,极易在风荷载作用下发生大幅振动。以某实际柔性光伏项目为工程背景,借鉴桥梁抗风的研究经验,对该柔性光伏支架的颤振性能进行研究。首先,考虑严格的相似比关系,设计并制作了弹性悬挂节段模型系统,并对其动力特性进行了测试;然后,进行不同光伏组件倾角(-39°～+39°)下的弹性悬挂节段模型测振风洞试验,研究光伏组件风致响应随风速的变化规律,得到各倾角下柔性光伏节段模型的颤振临界风速值,探讨2种气动措施对提高柔性光伏支架颤振稳定性的效果。结果表明：在0°～39°的正倾角工况下,柔性光伏支架的颤振临界风速随光伏组件倾角的增大,呈现先减小后增大的趋势,最小颤振临界风速出现在12°～21°光伏组件倾角范围内,折算成实际风速为9.6m/s;在-39°～0°的负倾角工况下,颤振临界风速随光伏组件倾角的增大,也呈现先减小后增大的趋势,最小颤振临界风速出现在-21°～-12°光伏组件倾角范围内,折算成实际风速为10.1m/s;设置中央稳定板的气动措施难以有效提高柔性光伏支架的颤振临界风速。     

森林腐殖质阴燃向明火转变实验研究

以树木凋落物形成的腐殖质为实验材料,利用自主设置的实验装置进行阴燃实验,分析不同空气流速、阴燃传播方向、外界热交换条件、含水率和粒径尺寸对森林腐殖质阴燃向明火转变的影响。结果表明:森林腐殖质阴燃稳定后,空气流速越大,阴燃传播速率越大,转变为明火的时间越短;与正向阴燃相比,反向阴燃不易向明火转变,且风速越大越容易熄灭,反向阴燃具有更大的安全性;外界温度对阴燃向明火转变的影响较大,外界温度越高,阴燃越容易向明火转变;森林腐殖质含水率大于20%(包括20%)时,阴燃不能产生明火,且无法自维持传播,逐渐熄灭;粒径尺寸对森林腐殖质阴燃向明火转变的影响较小。     

钢桁梁斜拉桥抗风稳定性数值模拟分析

以金塘大桥为研究对象,基于弹簧悬挂系统,采用Starccm+软件为研究工具,利用微分方程的数值解法和动网格技术,研究不同风攻角下桥梁的颤振临界风速、涡振扭转和竖弯振幅。结果显示:风攻角为3°时颤振临界风速区间为81～83m/s,风攻角为0°时颤振临界风速区间为87～89m/s,风攻角为-3°时颤振临界风速区间为95～98m/s,而规范公式计算的弯扭耦合颤振临界风速为90.44m/s,均大于检验风速76.3m/s;金塘公铁两用大桥的竖向弯曲振动和扭转振动涡振的共振振幅分别为102mm和0.253 86°,均小于规范的容许值201.3mm和0.289 8°;主梁颤振及涡激振动性能满足要求。研究结果表明金塘公铁两用大桥设计抗风稳定性满足规范要求,研究方法对大跨度桥梁的抗风设计具有参考价值和实际意义。     

逆向阴燃传播过程和模型

为了解逆向阴燃传播的过程和特点,用聚氨酯泡沫材料在绝热封闭的装置中进行了实验.实验过程用热电偶进行温度的测量,通过调节气体流量观测风速对逆向阴燃的影响.聚氨酯泡沫材料的逆向阴燃可分为两个阶段,第一阶段泡沫材料阴燃变成多孔炭,材料的透过率很小,能进入材料内部参与反应的氧气量也少,气流增大,在增加氧气的同时也带走更多的热量,阴燃传播速度随风速先增大后减小.第二阶段多孔炭的燃烧,空气很容易进入到材料内部,传播速度随风速线性增大,燃烧达到的最高温度值也随风速增大.在第一阶段中逆向阴燃的传播是匀速的,以此建立了一维传播模型,模型模拟结果同实验的结果具有很好的一致性.     

太阳能采暖水箱温度分层的仿真分析

本文通过对太阳能采暖系统的理论分析,建立了采暖水箱模型,利用CFD软件在有无辅助加热的两种工况下,模拟水箱内部流动、换热、温度分层过程,结果表明,太阳能集热器管路水流速在0．01～0．05m／s时,水箱内部分层非常明显,水箱运行内部扰流小;流速0．09～0．35m／s,随着流速增大,水箱分层越来越不明显,水箱顶端的高温层被破坏。     

樟子松凋落物阴燃测温精度研究

采用红外热像仪探测樟子松凋落物阴燃温度,并通过温度拟合提高红外热像仪的使用精度,为阴燃火灾的探测提供精确的温度数据基础。设置风速0~3 m/s、探测距离1~10 m、探测角度30°~60°的工况,分别采用红外热像仪和热电偶进行测温,以热电偶测温为基准温度,研究红外热像仪探测阴燃的使用精度和误差。实验得出:红外热像仪的有效探测距离为8 m,测温的相对误差随着探测距离、探测角度以及森林风速的增大而升高。利用MATLAB得出不同风速的工况下红外热像仪测温的相对误差与探测距离、探测角度的二元二次非线性拟合方程,为森林阴燃火灾探测提供数据基础。     

改良型氧化沟活性污泥循环系统的改进

采用氧化沟工艺的污水厂在运行初期因其MLSS偏低，致使除污效果不够理想。在水下推进器和转碟的作用下，氧化沟中上、中、下三层的水流速度不同：上层为0．15～0．2m／s、中层为0．05～0．15m／s、下层为0．001～0．005m／s，导致MLSS也不同：上层为500～800mg／L、中层为1000ms／L左右、下层为4000～4500mg／L。当下层MLSS高而水流速度偏低时，活性污泥易发生沉降，不仅使系统中的MLSS提高得很慢或得不到提高，而且沉降的活性污泥多为老龄化活性污泥，＂-3堆积超过一定量时易发生“翻池”现象。由此可见，传统工艺中的活性污泥循环系统存在一定缺陷。     

少量聚氨酯泡沫样品从阴燃到有焰燃烧的变化研究

试验主要观察处于阴燃状态的少量聚氨酯泡沫样品的流速、氧气浓度和辐射热通量对气／固界面的影响。因为此试验研究对象是少量聚氨酯汽沫，所以阴燃蔓延以厦转化到有焰燃烧时必须借助于降低热损失并同时增加其氧气浓度。试验中，我们把呈平行六面体的样品竖向放置在风道中。样品的其中三个侧边处在高温状态，第四边暴露在上升气流和辐射中。结果发现，随着气流流速的降低以度氧气浓度的增加，或者增加辐射通量，都会加快其变成有焰燃烧的过程，减少这种变化的延误时间。试验结果表明，炭化部位内部的有焰变化因阴燃作用而出现滞后，这已经通过超声波穿透样品内部得到了证实。笔者这里给出了简化了的分析，证明这种变化可以作为一个气相燃烧程序进行处理。     

聚氨酯和聚苯乙烯热解前后的结构演变

以软质聚氨酯泡沫和聚苯乙烯泡沫颗粒两种典型多孔材料为试验对象,对其孔隙率、孔径分布、表观密度和堆积密度等结构特性参数及表面微观形貌进行了测算和表面扫描电镜(SEM)表征,研究不同热解程度材料结构特性演变与阴燃建立和传播趋势之间的关系。结果表明:软质聚氨酯泡沫结构尺寸更大,整体更为疏松,受热成炭后呈现轮廓清晰的细削骨架,孔隙硕大且畅通,氧气完全自由输运,热量传递更直接,更易建立阴燃、维持传播并实现向明火的转化;相对而言,聚苯乙烯泡沫颗粒孔径较为细小,受热后成炭显著,孔径尺寸减小,空气气流量和氧气容纳量大大减少,不易建立阴燃过程。     

Persistence of Sonic Deposition on Smoke Alarms in Forensic Fire Investigations

Smoke alarms have been shown to develop sonically-deposited regions of acoustically agglomerated soot particles when they sound in smoke-filled air. These sonic depositions can be examined forensically post-fire to determine if the smoke alarm sounded during the incident. However, it is not clear how these sonic depositions are affected by common firefighting and post-fire actions. To determine the effects of post-fire forensic smoke alarm testing and environmental conditions on the persistence of the existing sonic deposition of soot on the horns of a smoke alarm, sixty (60) smoke alarms were subjected to smoke from fires of several different fuel types and common post-fire conditions or actions. Initially, each alarm was exposed to smoke in a small-scale experimental fire to develop sonic deposition around the horn. The fuel types for the fires were smoldering wood, flaming toluene–heptane, smoldering polyurethane foam, flaming polyurethane foam, and a combination of smoldering and flaming polyurethane foam. The alarms were then subjected to four common post-fire actions: pressing the test button, exposure to synthetic canned smoke, exposure to standing water, and exposure to running water. Each detector was visually inspected before and after the post-fire action. Results varied from no soot removed to almost all soot removed depending on the fuel type and post-fire test. An objective evaluation system was used to rank the degree to which soot was removed from the alarm horns: 0 (no soot removed), 1 (some soot removed), and 2 (all soot removed) based on visual inspection. The smoldering wood and smoldering polyurethane foam fires left behind a sticky resin that was essentially unaffected by any of the post-tests. The flaming foam and flaming toluene–heptane fires left powdery soot on the horn which could be easily wiped off. This soot was almost completely washed off by running water (1.067 average degree of removal) while the canned smoke and standing water post-tests removed a significant portion of the soot (0.533 and 1.000 average degrees of removal, respectively), which could lead an investigator to an errant sounding determination. Pressing the test-button appeared to make minimal impact on the amount of soot around the alarms horns regardless of the fuel type (0.067 average degree of removal).     

柔性聚氨酯泡沫燃烧产物毒性评估

介绍了对弹性聚氨酯泡沫燃烧产物毒性的相关研究,并对其是否能用于毒性危害分析进行了评估。研究显示,暴露到聚氨酯燃烧产物中的人会导致中毒。窒息气体氮气有效剂量法能有效预测受害人因暴露于聚氨酯燃烧产物而导致的行为能力丧失情况。同时,也证明有效剂量法不能正确预测聚氨酯阴燃时情况。该方法不适用于热分解。研究发现,目前很多经验方法具有很大的局限性,对毒性危害研究造成了很多负面的影响。烟气粒子携带毒物的吸入和传播以及化学合成复杂的毒物,研究和考虑得很少。因此,很有必要对复杂毒性有机体的火灾燃烧产物进行更深入的物理和化学分析研究以及动物模型研究。     

Results from a Full-Scale Smoke Alarm Sensitivity Study

A series of 24 full-scale experiments was conducted to examine the effects of alarm type (photoelectric, ionization, and dual sensor), alarm location, fabric type (100% cotton and 100% polyester), polyurethane foam density, ignition scenario, and room configuration, on smoke alarm performance. A two-level, fractional factorial design of eight experimental configurations was developed around the five factors: fabric type, foam density, fire location, ventilation, and ignition scenario. A structure, designed to represent a single-story home or apartment, was constructed inside the Large Fire Laboratory at the National Institute for Standards and Technology for the experiments. The fire source was a chair mockup consisting of a seat and back cushion of a specific cover fabric and foam density, weighing between 5.5 kg and 8.3 kg. It rested on a metal frame and was subjected to a small propane gas flame, or an electric cartridge heater to initiate smoldering. Each experimental configuration was replicated three times. Smoldering fires were allowed to progress until they naturally transitioned to flaming fires except for one test that was terminated early due to time constraints. The smoldering to flaming transition times ranged from (81 to 182) min. Each fire progressed for a time sufficient to produce multiple hazards (smoke, heat, and toxic gases). All alarms tested were purchased from retail outlets and activated at their preset levels. Photoelectric, ionization, and dual photoelectric/ionization alarms were co-located at multiple locations to facilitate comparisons of each alarm type, and different designs of the same type of alarm. For smoke alarms in the room of fire origin, it was observed that each of the five factors had an effect on the measured alarm times that was primarily a result of fire growth rate (fabric type, foam density, and ignition scenario), or smoke dilution and transport (fire location and ventilation). The photoelectric alarm responded quicker on average than ionization alarm in two of four smoldering fire configurations, responding before the ionization alarm in all 6 trials, while the ionization alarm responded before the photoelectric alarm in two of three trials for the other two configurations. The ionization alarm responded quicker on average than photoelectric alarm in all four flaming fire configurations, and responded before the photoelectric alarm in all 12 flaming fire trials. One dual alarm had the fastest average alarm time for all four smoldering fire configurations, and responded first in 11 of the 12 trials. It also yielded faster average alarm times than the other dual alarm in seven of eight configurations, and was the first dual alarm to respond in 22 out of 23 trials where dual alarms were present.     

Effect of Smoke Source and Horn Configuration on Enhanced Deposition, Acoustic Agglomeration, and Chladni Figures in Smoke Detectors

A series of UL/EN based test fires was conducted in a two room/corridor enclosure to investigate the viability of methods for determining whether a smoke detector sounded under a variety of smoke conditions and to see if this methodology could be applied to a detector with a different horn configuration. The presence of enhanced deposition in the form of a black or orange-brown ring and agglomerates around the central opening of a smoke detector horn was found to be a reliable indicator that the horn sounded when it was exposed to smoke from eight standardized, single-substrate fuel sources including hydrocarbon pool, flaming polyurethane foam, and smoldering polyurethane foam fires. Determinations could generally not be made for detectors exposed to white or gray smoke generated by flaming paper, smoldering paper, flaming wood, smoldering wood, and smoldering cotton wick due to a general lack of visible soot deposition within the detector. Therefore, it is not recommended to use the absence of a black or orange-brown ring of enhanced deposition, in and of itself, as an indicator that the horn did not sound. Nevertheless, this conclusion can be reached when the absence of enhanced deposition is combined with evidence supporting the presence of flaming fuels that produce black, sooty smoke. Test series were conducted using two different smoke detector brands, each having a different horn configuration. Findings suggest that the same type of methodology for determining whether the detector sounded is applicable to both models. Chladni figures were not found on any of the smoke detectors, whether they sounded or not; hence, the absence of a Chladni figure was not an indicator that the detector did not sound. A smoke flow visualization technique was used to determine the mechanism that caused the observed enhanced deposition and agglomerates on horns that sounded during a smoke exposure. Additionally, a smoke box test series showed that the extent of observed soot deposition increased with increasing smoke exposure.     

Impact of Air Velocity on the Detection of Fires in Conveyor Belt Haulageways

A series of large-scale experiments were conducted in an above-ground fire gallery using three different types of fire-resistant conveyor belts and four air velocities for each belt. The goal of the experiments was to understand and quantify the effects of air velocity on the detection of fires in underground conveyor belt haulageways and to determine the rates of generation of toxic gases and smoke as a fire progresses through the stages of smoldering coal, flaming coal, and finally a flaming conveyor belt. In the experiments, electrical strip heaters, imbedded approximately 5 cm below the top surface of a large mass of coal rubble, were used to ignite the coal, producing an open flame. The flaming coal mass subsequently ignited 1.83-m-wide conveyor belts located approximately 0.30 m above the coal surface. Gas samples were drawn through an averaging probe for continuous measurement of CO, CO₂, and O₂ as the fire progressed. Approximately 20 m from the fire origin and 0.5 m below the roof of the gallery, two commercially available smoke detectors, a light obscuration meter, and a sampling probe for measurement of total mass concentration of smoke particles were placed. Two video cameras were located upstream of the fire origin and along the gallery at about 14 m and 5 m in order to detect both smoke and flames from the fire. This paper discusses the impact of ventilation airflow on alarm times of the smoke detectors and video cameras, CO levels, smoke optical densities and smoke obscuration, total smoke mass concentrations, and fire heat release rates, examining how these various parameters depend upon air velocity and air quantity, the product of air velocity, and entry cross-section.     

棉被阴燃火灾实验研究

针对烟头引燃棉被的火灾案例,实验测量烟头的表面温度及热辐射强度,得到烟头表面最高温度可达289 ℃,很容易引燃棉被等可燃物.通过无被套棉被的阴燃实验和有被套棉被的阴燃转明火实验发现,在没有被套的情况下,棉絮间空隙较大,无法积聚热量,只能阴燃而无明火;有被套情况下,产生的热量大部分被阻隔在棉被内部,散热速度较慢,提供了棉被阴燃转明火所需的热量.     

Effect of Wind on Smoldering Combustion Limits of Moist Pine Needle Beds

We studied moist pine needle beds burning under the effect of wind, in order to determine the upper moisture limit for which there is fire propagation for different wind velocities. For this purpose we built a wind tunnel that allowed us to burn a 600 mm by 150 mm by 40 mm bed under wind velocities between 0.5 m/s and 5.0 m/s and controlled air temperature. Results show an increase in moisture limit from 54% to approximately 140%, for the velocity range indicated. Combustion at limiting conditions proceeds mainly by smoldering with some periods of flaming combustion. It was observed that, for conditions close to extinction, the smoldering front is not quenched at the surface. Additionally, it was also observed that a strong flow of hot gases exit from the fuel bed at the free surface. These two observations lead to the conclusion that the main heat sink is moisture evaporation and that heat losses to the surroundings is reduced by the blowing effect of the hot gases coming off the bed. A dimensional analysis suggests a correlation between moisture limit and wind velocity of the form M = A ? B/ \( {v} \) _w ² , where M is moisture limit for fire propagation, A and B are constants, and \( {v} \) _w is wind speed. Two dimensionless numbers helped to plot the smoldering temperature and fire propagation velocity in a more meaningful way. They are \( \Uppi_{1} = {{T_{sml} c_{p,g} } \mathord{\left/ {\vphantom {{T_{sml} c_{p,g} } {v_{w}^{2} }}} \right. \kern-0pt} {v_{w}^{2} }} \) and \( \Uppi_{2} = {{Mh_{fg} } \mathord{\left/ {\vphantom {{Mh_{fg} } {v_{w}^{2} }}} \right. \kern-0pt} {v_{w}^{2} }} \) , where T _sml is smoldering temperature, c _p,g is the gas specific heat, M is fuel moisture content and h _fg is the latent heat of water evaporation. A relatively high moisture limit at 5 m/s wind velocity is possible due to the relatively high air flow into the smoldering front and the efficient heat feedback produced in forward smoldering.     

Full-Scale Experimental Investigation to Quantify Building Component Ignition Vulnerability from Mulch Beds Attacked by Firebrand Showers

Structure ignition by wind-driven firebrand showers is an important fire spread mechanism in large outdoor fires. Experiments were conducted with three common mulch types (shredded hardwood mulch, Japanese Cypress wood chips, and pine bark nuggets) placed adjacent to realistic-scale re-entrant corners. In the first series of experiments, mulch beds were placed adjacent to a re-entrant corner constructed with wood studs and lined with oriented strand board (OSB) as the sheathing. The premise behind conducting experiments with no siding treatments applied was predicated on the notion that bare OSB mulch contact would be a worst-case scenario, and therefore, a wall assembly in the most vulnerable state to mulch ignition. In the second series of experiments, vinyl siding was applied to the re-entrant corner assemblies (wood studs/OSB/moisture barrier/vinyl siding), and the influence of vertical separation distance (102 mm or 203 mm) on wall ignition from adjacent mulch beds was determined. The vertical separation distance was maintained by applying gypsum board to the base of the re-entrant corner. The siding itself did not influence the ignition process for the mulch beds, as the mulch beds were the first to ignite from the firebrand showers. In all experiments, it was observed that firebrands produced smoldering ignition in the mulch beds, this transitioned to flaming ignition, and the re-entrant corner assembly was exposed to the flaming mulch beds. With no siding treatments applied, the flaming mulch beds ignited the re-entrant corner, and ignition was observed to propagate to the back side of re-entrant corner assembly under all wind speeds (6 m/s to 8 m/s). With respect to the re-entrant corners fitted with vinyl siding, the mulch type, vertical separation distance, and wind speed were important parameters as to whether flaming ignition was observed to propagate to the back-side of a re-entrant corner assembly. Mulches clearly pose an ignition hazard to structures in large outdoor fires.