顶棚水平开口对细水雾灭室内火的影响研究

对细水雾扑灭具有顶棚水平开口的室内池火进行了实验研究和理论分析.研究表明,池火热释放速率较大时,在高温烟气作用下,细水雾能快速蒸发产生大量的水蒸气.在水蒸气的稀释作用和燃烧耗氧作用下,燃烧区域的氧气浓度迅速下降到极限氧浓度,火焰因此而窒熄.在池火热释放速率较小时,水蒸气稀释和燃烧耗氧对燃烧区域内的氧气浓度影响较小.细水雾雾滴冷却火焰和销毁自由基可能成为灭火的主要机理.在以上两方面机理共同作用下,出现灭火时间随着池火热释放速率的增大而减小的实验现象.顶棚水平开口的位置和面积决定进入室内到达燃烧区域的空气流量,从而影响细水雾的灭火时间.实验表明,开口位置与火源的距离越大,灭火时间越短;而开口面积越大,灭火时间越长.     

细水雾灭火有效性的影响因素研究

介绍了国内外细水雾灭火技术的最新研究进展,分析了细水雾雾滴物理特性参数(雾滴粒径、雾滴动量和喷雾通量)、添加剂、喷头及其相对火源位置、障碍物及可燃物类型等因素对细水雾灭火效果的影响,探讨了细水雾灭火技术的研究发展方向。     

细水雾系统参数对有障碍物液体火灾灭火效果的影响

利用FDS 数值模拟软件，采取控制变量法设置4 组数值模拟，分别研究细水雾系统水滴粒径、雾化角度、喷水强度、喷头高度对火源周围存在无法燃烧或尚未开始燃烧的障碍物情况下灭火效果的影响。研究发现，当火源设置为乙醇池火时，存在障碍物条件下，细水雾系统水滴粒径设置在250~400 μm，雾化角度设为120°，喷水强度设为2.0~2.5 L/（min·m2），喷头高度距障碍物1 m 时灭火效果较为理想。     

高、中压细水雾灭火性能比较实验研究

从细水雾雾场特性参数分析出发,搭建实验平台研究高压细水雾和中压细水雾的灭火性能,得到高、中压细水雾灭火时的温度和烟气组分体积分数变化情况,以及雾场特性参数如雾通量、粒径分布和雾动量等和灭火性能的关系。结果表明由于工作压力不同,使得雾场特性参数有所差异,在实验火场开阔的情况下,由于中压细水雾在燃烧区域的雾通量和雾动量更大,其对于木垛火和柴油池火的灭火效果均优于高压细水雾。     

浅谈细水雾灭火系统

1 细水雾的灭火机理及应用水喷雾灭火系统的灭火机理主要为表面冷却,窒息,冲击乳化和稀释。从水雾喷头喷出的雾状水滴,粒径细小,表面积很大,遇火后迅速汽化,带走大量的热量,使燃烧表面温度迅速降到燃点以下,使燃烧体达到     

超细水雾影响小型火焰在固体可燃物上蔓延的数值模型

开发了CFD模型，用来预测细水雾中火焰沿固体燃料蔓延的特性。采用气体和固体燃料作为对比试验，利用不稳定两维保守公式描述自持性火焰蔓延情况。因为的分析重点主要放在火焰前锋火焰的熄灭机理（火焰前锋完全暴露在细水雾中），所以考虑了有限率（finite—rate）化学反应。火焰基本传播数据也可虑了用于细水雾和蒸气质量的公式，这包括水蒸发造成的能量消耗。还对在细水雾喷洒下聚合材料做成的厚燃料床上火焰的水平传播进行了试验。结果显示，火焰热释放区内自持性能量守恒对外部能量消耗非常敏感。在本试验中，主要是水滴蒸发造成的能量消耗。因此，在火焰前锋，火焰在细水雾的喷洒下挣扎着，要么按几乎相同的速度（没有水喷雾情况下）继续传播，要么被完全熄灭。本文还研究了水滴直径大于30μm细水雾的灭火特性。本文获得了在不同条件下火焰蔓延情况下，灭火需要的细水雾质量分率的关键浓度。     

富氧舱室环境火灾特性模拟

针对现代舰船通常装备供氧系统的现实情况,选取舱室中普遍使用的聚氯乙烯材料作为舱室固体可燃物的代表,开展氧气泄漏造成的富氧环境对舱室火灾特性影响的FDS仿真研究。设计舱室火灾系列实验和细水雾灭火效能系列实验,分析PVC火源的热释放速率、舱室温度、烟气能见度以及细水雾对火灾抑制作用,并提出这些变化是氧气浓度增加、氧气的冷却作用和舱室压力上升共同作用的结果。     

浅析微细水雾灭火系统的技术性能优势

阐述了微细水雾灭火系统的工作原理及组成。将微细水雾灭火系统与普通灭火系统进行比较。从喷嘴设计、喷雾强度、喷雾时间、水滴作用面积等多方面,介绍了微细水雾灭火系统的优势及应用前景。     

利用细水雾灭火系统扑救食用油火（续1）

(续上期)5·2细水雾对食用油火的灭火效果细水雾灭火主要靠物理方式:冷却火焰、湿润/冷却燃料、排除用于燃烧的氧和燃料蒸气以及减弱辐射热。食用油在深油锅中燃烧时,热通过对流和辐射从火焰传到油中。随着细水雾的应用,由于小水滴的蒸发,热从油中散失,由于热传递,热又传到油锅     

高压细水雾对城市地下管廊火灾的降温效果

为探究城市地下管廊火灾蔓延的有效控制方法,研究基于高压细水雾作用下的城市地下管廊火灾蔓延规律。建立尺寸为3.1 m×12.0 m×3.6 m的城市地下管廊模型,根据火源位置、喷头数量、平均粒径、喷头压力等的不同设置工况,研究高压细水雾的降温性能、粒径对降温效果的影响。研究结果表明,受地下管廊结构与壁面的影响,可燃物在燃烧时形成单侧燃烧并发生轰燃。高压细水雾喷头开启后轰燃次数减少,管廊内温度明显下降,燃烧时间缩短;雾滴粒径对高压细水雾的降温灭火性能起主要影响,粒径为100μm时降温效率最高。     

Study of Water Droplet Behavior in Hot Air Layer in Fire Extinguishment

Evaporation of water droplets while traveling in hot air layer will be studied. The air-droplet system is analyzed by solving the mass, momentum and energy conservation equations for each phase. The droplet phase is described by the Lagrangian approach. Two conditions of air flow in the smoke layer are assumed. Firstly, as commonly used in modeling fire suppression by water spray, the smoke layer is assumed to be quiescent. Secondly, both gas cooling effect and air entrainment in the water spray cone are included. The properties of gas phase related to evaporation are specific heat capacity, thermal conductivity and dynamic viscosity. All these are evaluated by the one-third rule. The Runge–Kutta algorithm is used to solve the ordinary differential equation group for the droplet motion with heat transfer. Droplet positions, velocities, temperatures and diameters are calculated while traveling in the hot air reservoir. The effects of air temperature, water vapor mass fraction, thickness of hot air reservoir, and initial diameter on the droplet behavior are analyzed. The quantity of heat absorbed by a single droplet is calculated. Results are then calculated for a water spray by taking it has many droplets. The cooling effect of the water vapor produced is considered. Water spray consisting of small droplets should absorb more heat while acting on the hot air layer. The ratio of the heat for vaporization to the total heat absorbed by water can go up to 0.9 when all the droplets are evaporated. Limited experimental data are selected to verify the mathematical model. Predicted results are useful for studying fire suppression by water mist system.     

Burning rate of a pool fire with downward-directed sprays

The present study investigates how water sprays affect fire intensity, the burning rate of fuel and the relationship between droplet size and degree of water penetration. Downward-directed sprays which interact with a small-scale opposed gasoline pool fire are experimentally investigated in an open environment. It is shown that the burning rate of fuel is always greater under this opposed spray-fire plume arrangement compared to the freely burning condition, i.e. without water sprays, when fire extinction does not arise. These results imply that water sprays are able to enhance an oil fire. Furthermore, very small droplets are shown to be ineffective for fire extinction by cooling because they do not reach the fuel surface through fire plumes. Therefore, within a small-scale gasoline pool fire in an open environment, the mechanism of the fire extinction by water sprays is concluded to act via the cooling of the fuel surface, which will lead to the suppression of fuel evaporation, rather than the cooling of the fire plume itself.     

Interaction between water spray and smoke in a fire event in a confined and mechanically ventilated enclosure

This work deals with the interaction between water droplet flows and smoke in a fire event in a confined and ventilated enclosure. The objective is to identify the specific effect of water spray in the specific environment of a confined and ventilated enclosure. The study is based on 17 large-scale fire tests performed in one room of 165 m³ ventilated at a renewal rate of 15.4 h⁻¹. The fire source is a propane gas burner with a heat release rate of between 140 and 290 kW. The water spray system consists of two Deluge nozzles with a nozzle coefficient of 26 l/min/bar^0.5. The test parameters are the fire heat release rate, the water flow rate, from 50 to 124 l/min, and the activation time. The study focuses on three topics, the interaction of the droplets with the smoke, the droplet evaporation process and the energy transferred to the droplets. The water spray significantly modifies the smoke stratification by mixing and cooling the gas phase. The rate of droplet evaporation has been determined from the water mass balance and is of the same order of magnitude as the rate of water vapor production by the combustion reaction. Heat transfer from the smoke to the droplets has been investigated using the energy balance equation. For a fire scenario in a confined and ventilated enclosure, the energy released by the fire is mainly transferred to the walls and extracted by the ventilation network. In the event of water spray activation, a significant share, up to 65%, is transferred to the droplet flows.     

Extinction condition of counterflow spray diffusion flame with polydisperse water spray

The effect of polydisperse water droplet size distribution on the burning behavior and extinction condition of counterflow spray diffusion flame was investigated experimentally in this study. N-heptane as liquid fuel spray and nitrogen as a carrier gas were introduced from the lower duct while water spray and oxidizer consisting of oxygen and nitrogen was issued from the upper duct. The burning behavior of spray flame for different fuel droplet size with and without water spray was observed and the extinction condition of counterflow spray diffusion flame was characterized by oxygen concentration at extinction. The results show that the minimum value of oxygen concentration at extinction for counterflow spray diffusion flame with water spray is similar to the extinction condition without water spray for higher mean droplet diameter of water. The minimum value of oxygen concentration at extinction shifts to the smaller fuel droplet size when decreasing the water droplet size. For fuel droplet size higher than 48 μm, the optimum of water droplet size for suppressing counterflow spray diffusion flame was smaller than gaseous flame. The explanation of optimum water droplet size based on the coupled effect of Stokes number and vaporization Damköhler number can be used for prediction of the effectiveness of water droplet on the suppression of counterflow spray diffusion flame.     

单、双喷头细水雾对正庚烷池火灾的抑制作用

为了研究单、双喷头细水雾抑灭正庚烷池火灾的效能和机理,在半体积飞机模拟货舱中开展了单、双喷头细水雾雾滴粒径测试和抑灭20 cm 正庚烷池火灾的实验研究。结果表明,双喷头细水雾协同工作会导致雾滴之间相互碰撞发生二次破碎,有助于雾化效果的提升。通过对燃料表面温度、火焰区平均温度和舱内氧气浓度的测量和计算,对比分析了单、双喷头细水雾抑灭火的主导机理。结果表明,单喷头细水雾灭火的平均时间为283.14 s,耗水量约为3.54 L,燃料表面冷却是其抑灭火的主导机理。双喷头细水雾灭火的平均时间为212.22 s,耗水量约为5.31L,火焰冷却是其抑灭火的主导机理。     

Experimental study on the extinction of liquid pool fire by water droplet streams and sprays

This paper provides evidence about the interaction between the water droplet stream and the flame, and explains how the interaction affects the suppression effectiveness. Two purpose-built gasoline pools were used to generate different open fires. The mono-disperse water droplet streams and water sprays were used as the flame suppressant. The first pool with a circular shape was equipped with a concentric pipe to allow the droplet stream to pass through the flame without impinging the gasoline. The second pool with a long narrow shape was equipped with expandable sides and allowed to extend the fire size. The passing ways of the droplet stream were systematically varied. The results clearly show two modes of flame inhibition; one is by blocking or interfering with the mixing of gasoline vapor and fresh air, and the other by cooling down the flames. For the stream case, the direction of the stream passing through the flame can affect the effectiveness of the suppression which increases as the angle is changed from vertical to horizontal. Also, there is an optimum distance between the stream axis and gasoline surface for flame inhibition. Moreover, the ability can be affected by the droplet size. On the same volume flow rate, the larger the droplet size, the more effective the flame suppression. For the water spray passing through the flame in the long groove pool, whenever the quantity of water vaporization reaches a critical value, the effectiveness of flame suppression by combining the obstructing and cooling effects becomes better.     

气液流量对低压双流体细水雾雾场特性的影响

由于对民机货舱中不同气液流量的低压双流体细水雾研究较少,且对单个喷头雾通量和雾动量的定量、定性分析不够完善,还需设计开展实验进行更深入的研究。参考美国联邦航空管理局（简称“FAA”）制定的相关标准,设计并搭建飞机货舱低压双流体细水雾实验平台,主要包括FAA全尺寸飞机货舱、低压双流体细水雾系统。采用的喷头与常规的喷头有所不同,喷出的细水雾是一个圆形平面,具有优良的弥散性和滞空性。实验中采用马尔文粒径分析仪结合Spraytec软件测量不同气液流量下的细水雾雾滴粒径,发现当气体流量从250 L/min增加至350 L/min、液体流量保持0.5 L/min不变时,细水雾雾滴粒径从130 μm降低至95 μm;当液体流量分别为0.75 L/min和1.0 L/min时,粒径大小分别从161 μm降至110 μm,从201 μm降至142 μm。根据美国防火协会的标准,采用量杯收集法测量得到不同气液流量下的雾通量,发现单独增加气体流量或液体流量,其雾通量都会增加。当气体流量为350 L/min、液体流量为1.0 L/min时,雾通量达到最大值,为0.255 L/（min·m2）。利用粒子图像测速仪的高速摄像机拍摄喷雾照片,测量雾滴速度,结果显示,在3种不同的液体流量工况下,随着气体流量从250 L/min增加至350 L/min,对应的雾滴速度均近似以0.04的增长率上升,最小值为8.5 m/s,最大值为16.0 m/s。在假设细水雾雾滴形状为球状时,雾动量关系式由雾滴质量与速度的乘积得到。选取雾滴速度最大值代入公式,得到单个雾滴在不同气液流量下的雾动量变化曲线,发现当气体流量为250 L/min、液体流量为1.0 L/min时,单个雾滴动量达到最大值,为3.6×10-8 kg·m/s。通过实验研究不同气液流量对低压双流体细水雾雾场特性的影响,得出以下结论：当液体流量不变,气体流量从250 L/min以25 L/min的变化率增加至350 L/min时,雾滴粒径和雾动量逐渐减小,而雾滴速度和雾通量逐渐增加;当气体流量不变,液体流量从0.5 L/min以0.25 L/min的变化率增加至1.0 L/min时,雾滴粒径、雾动量和雾通量均逐渐增大,而雾滴速度逐渐减小。对于单个雾滴,雾动量取决于雾滴粒径的大小;而对于喷头喷出的所有雾滴,雾滴速度决定了整体雾动量的大小。今后课题将进行细水雾灭火实验,探究达到最佳灭火效果的气液流量。结论可用于飞机货舱细水雾灭火系统的设计与改进,为飞机防火系统一些参数的设置提供了实验和理论基础。     

低压双流体细水雾抑制锂离子电池热失控研究

利用自主设计的实验平台,采用加热棒模拟锂电池外部过热场景,分别在95、80、60 kPa的环境压力下对18650型锂电池热失控表面温度和CO体积分数变化进行对比,探究低压双流体细水雾对锂电池热失控的抑制效果。结果表明：低压双流体细水雾可在低雾化压力下产生较小的雾滴粒径,并能有效抑制锂电池热失控与热传播,减少CO生成量;雾化压力为1.2 MPa时产生的细水雾雾滴粒径最小,冷却效果最好。随着环境压力降低,细水雾的抑制效果下降。可考虑使用惰性气体作为雾化气体,增强灭火效果。     

Extinction limit of a pool fire with a water mist

This work describes an experimental investigation of fire extinction limit and enhancement for a gasoline pool fire interacting with a water mist. A downward-directed nozzle produces a fine water spray over a small-scale opposed pool fire. The fire extinction limit is obtained from minimum nozzle injection pressure measured when the fire extinguish takes place. The burning rate of the fuel is also measured using a verified technique. For the conditions tested, it is shown that there are two distinct regions in the relationship between the distance from the nozzle to the fuel pan and the injection pressure, i.e. a fire extinction region and a fire enhanced region. The effective water flux is shown to be a more useful parameter than the injection pressure for the fire extinction limit. It is also revealed that the larger the spray thrust the larger the burning rate is in the fire enhanced region.