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。     

细水雾粒径对地下综合管廊电缆舱灭火效果的影响研究

基于理论推导,结合实体实验及FDS模拟实验,讨论不同粒径细水雾扑救电缆舱火灾的灭火有效性。自行设计电缆舱灭火研究实验台,以聚氯乙烯电缆为研究对象进行全尺寸实验。对比空烧实验与粒径为80、110、150μm细水雾作用下的火场参数,结合FDS模拟粒径为50～250μm的9种工况,分析火场温度、O_2体积分数及灭火时间变化规律。结果认为,在压力和流量满足一定条件的情况下,50～100μm细水雾扑救电缆舱的火灾效果较好;115～130μm是细水雾系统表面冷却机理过渡为隔氧窒息机理的临界粒径值;细水雾系统隔氧窒息作用的灭火效果优于表面冷却作用。     

通风与细水雾耦合灭火机理实验研究

分析细水雾与火灾的传热机制。在尺寸为6.0 m×1.5 m×2.0 m的隧道模型中部放置0.25 m×0.20 m×0.05 m的油盆,进行柴油池火灭火实验,分析排烟模式、工作压力、通风风速对细水雾灭火的影响。结果表明,细水雾+顶部排烟耦合系统的灭火时间最短,细水雾压力增加有利于抑制灭火初期的强化燃烧现象。6 MPa、12 L/min细水雾作用下,纵向排烟风速不宜超过0.5 m/s,其灭火机理主要为对热辐射的衰减作用;顶部排烟风速可以达到1.0 m/s,其灭火机理主要为对火焰的冷却作用。10MPa细水雾灭火时间受1.0 m/s以下风的影响可以忽略不计。15 MPa细水雾灭火时间受1.5 m/s以下风的影响可以忽略不计。10 MPa及以上压力细水雾耦合通风系统的灭火机理为火焰冷却及热辐射衰减的综合作用。     

侧向喷射条件下细水雾扑灭水平表面流淌火研究

为探讨侧向喷射条件下细水雾扑灭流淌火的技术可行性,针对水平表面流淌火,在考虑火焰辐射、燃料与垫层之间的对流换热基础上,建立细水雾在开敞空间扑灭流淌火理论模型,实验研究细水雾喷头排数、倾斜角度对火焰形状、火焰温度、灭火机理和灭火时间的影响。结果表明：细水雾冲击燃料加快其流淌时可以增强灭火能力;采用单排喷头水平喷射时可有效抑制一侧火焰且对火焰拉伸作用最强;采用双排喷头水平喷射时,可有效抑制两侧火焰且灭火速度最快;当喷头向上倾斜15°时,细水雾冷却燃料能力减弱并使灭火时间变长。     

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。     

细水雾在铁路隧道救援站的应用研究

为研究细水雾在铁路救援站内的灭火特性,在30 m×6 m×6 m的铁路救援站模型布置了细水雾灭火系统,开展火灾试验。在轮胎火工况下,分别在不同细水雾喷头高度的情况下,对管网末端压力、隧道内细水雾颗粒粒径分布以及细水雾的灭火效果进行试验。结果表明,管网高度对管网末端压力和细水雾颗粒粒径影响较小;压力越大,流量越大,细水雾浓度越大;细水雾能有效抑制轮胎火。     

细水雾抑制火灾蔓延的影响因素与灭火效率的实验分析

细水雾灭火系统是一种灭火效率高,对环境友好的灭火技术,其应用范围正逐步扩大。本文在整理分析相关研究资料的基础上,讨论了细水雾抑制火灾过程中的影响因素,并介绍了最近的研究成果。通过系列不同工况的实验,探讨了细水雾灭火过程中压力与喷射角度对灭火效率的影响因素。根据实验结果与分析,得出以下结论:细水雾的生成压力越高,速度越高,粒径越小,动量越大,灭火所需时间就越短,但是增大压力提高灭火效率存在极限值。     

双流体细水雾抑制熄灭油池火的实验研究

在3 m×3 m×3 m的受限空间内使用双流体细水雾喷头进行了灭油池火的有效性实验,实验所用的燃料试样为柴油,雾化气体为氮气.实验中使用热电偶测量火焰温度的变化,使用烟气成分分析仪测量气体组分体积分数的变化.实验结果表明:由于雾化气体的介入,双流体细水雾的灭火过程和灭火机理与单流体细水雾有所不同;双流体细水雾在一定的压力下存在最佳的灭火水流率,在此水流率下灭火时间最短.     

细水雾控制高层住宅烟道火灾的有效性及参数优化

为了有效控制高层住宅厨房烟道火灾,构建细水雾控制厨房食用油火和带分支烟道的高层住宅厨房烟道油垢火的FDS数值模型,分析高层住宅厨房烟道细水雾灭火系统有效性的影响因素及最佳设计参数。结果表明,如果未能即时扑灭高层住宅底层厨房食用油火,在强烈的烟囱效应作用下,高温火焰和烟气会引燃烟道内油垢,造成火势的迅速蔓延。本文所建的30 m高厨房烟道火模型中,最佳细水雾灭火系统运行模式为关闭厨房抽油烟机,即时开启厨房灶台上方和主烟道内分段设置的细水雾喷头,雾流量分别为0.6,10 L/min,细水雾最佳参数为喷射流速10 m/s、喷射角度60°、水雾粒径500 μm。     

细水雾对置障管内预混气体抑爆机理研究

为揭示细水雾对爆燃的抑制作用以及细水雾的释放位置对甲烷预混气体爆燃过程的影响,设计了4 种细水雾释放位置和3 种粒径（8、45、80 μm）的细水雾共13 种工况的实验。结果显示：8、45 和80 μm 细水雾在位置2 释放时管内压力分别降低36.59%、65.85%和31.7%。在位置3 释放时管内压力分别降低34.15%、56%和39.02%。8 μm 水雾对爆燃过程具有明显的抑制作用,且对火焰的结构和火焰面的影响较小;45 μm 水雾和80 μm 水雾对火焰结构和火焰面产生明显影响,火焰面出现褶皱,并呈现发散状向前扩展,随着水雾粒径的增大这种效果更加明显。细水雾对火焰主要有稀释预混气体、降低局部可燃气体浓度和气化吸热作用。在距点火点最近障碍物上方和两个障碍物之间释放水雾时对管内爆燃抑制效果最显著。     

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。     

Extinguishment of Cooking Oil Fires by Water Mist Fire Suppression Systems

A series of full-scale experiments were conducted in a mock-up commercial cooking area to study extinguishing mechanisms and effectiveness of water mist against cooking oil fires. The impact of water mist characteristics, such as spray angle, droplet size, flow rate, discharge pressure and type of nozzle, on the effectiveness of water mist against cooking oil fires was investigated. A series of oil splash experiments were also conducted to determine if the oil was splashed by water mist. In addition, the change in oil composition during heating and fire suppression was determined using Fourier Transform Infrared (FTIR) technique.The study showed that cooking oil fires were very difficult to extinguish, because they burned at high temperature and re-ignited easily due to changes in oil composition during heating and fire suppression. The water mist systems developed in the present work effectively extinguished cooking oil fires and prevented them from re-ignition. The spray angle, discharge pressure, and water flow rate were important factors to determine the effectiveness of water mist in extinguishing cooking oil fires.     

一种旋流式喷嘴的雾化实验研究

细水雾喷嘴是细水雾灭火系统的关键部件。本文主要采用激光多普勒测试仪（LDV）和相位多普勒粒子测量仪（PDPA）对一种旋流式喷嘴进行雾化实验研究。通过实验得到了不同测试压力下,喷嘴的流量、流量特性系数K、雾化锥角θ、水平射程、索特尔平均粒径（SMD）和粒子轴向速度的分布情况,最后得到了这几个参数随测试压力的变化关系。所测试的细水雾灭火喷头具有较大的轴向动量和径向动量,有利于扑灭深位火灾和扩大灭火范围。     

水喷雾与泡沫喷雾灭油池火实验特性对比研究

通过自主搭建实验平台开展灭换流变压器油池火实验,对采集到的雾流密度、温度、热流、热成像等数据进行分析,得到水喷雾和泡沫喷雾系统的灭火特性,对比得出两灭火系统的灭火效率差异。结果表明：水喷雾与泡沫喷雾灭火所用时间为190、100 s;水喷雾灭火系统与泡沫喷雾灭火系统最终热流值分别降低至0.005 9、0.004 7 W/m2;与水喷雾灭火相比,泡沫喷雾灭火时热量快速降低,灭火时间短,其在100 s 内基本将火源有效控制。在基本条件相同的前提下,泡沫喷雾灭火效率高于水喷雾灭火效率。     

Physical scaling of water mist fire extinguishment in industrial machinery enclosures

Froude-based scaling relationships had previously been theoretically extended to, and experimentally validated in the laboratory for, water mist suppression of fires in open environment and in enclosures, which were shown applicable to gas, liquid and solid combustible fires. Before applying these relationships to real-world settings, their applicability needs to be further evaluated for the intended protection. This paper presents such an evaluation on scaling water mist fire extinguishment in an industrial machinery enclosure. In this evaluation exercise, a full-scale water mist protection set-up tested for a 260-m³ machinery enclosure was selected as the benchmark. A ½-scale machinery enclosure test replica was then constructed, together with a ½-scale nozzle whose orifices were geometrically similar to those of the full-scale nozzle. Spray measurements indicated that the ½-scale spray closely met the scaling requirements, in terms of discharge K-factor, water mist flux, droplet velocity and droplet size distribution. Two spray fires and one pool fire, which were scaled with the respective full-scale fires, were used to challenge the water mist protection in the ½-scale enclosure. At least five replicated tests were conducted for each of the four tested fire scenarios. Overall, the instantaneous local gas temperature and oxygen concentration measured inside the ½-scale enclosure for each fire scenario agreed reasonably well with those measured at the corresponding locations inside the full-scale enclosure, meeting Froude modeling's requirement that scalar quantities be preserved in different scales. The fire extinguishment times obtained from the ½-scale tests for each fire scenario were also statistically consistent with that observed in the corresponding full-scale test. Based on the obtained results, it is concluded that, for machinery enclosures and other similar occupancies, the previously laboratory-validated scaling relationships for water mist fire suppression can be used to determine the fire extinguishing performance of a full-scale water mist protection in a ½-scale test facility.     

A quasi-steady-state model for predicting fire suppression in spaces protected by water mist systems

A quasi-steady-state model was developed to predict the effectiveness of a water mist system for extinguishing fuel spray and pool fires. The model was developed for obstructed fires where extinguishment primarily occurs as a result of a reduction in oxygen concentration due to the consumption of oxygen by the fire and due to dilution of the oxygen with water vapor. Interactions between the mist and the flame are neglected resulting in limiting case predictions. The model is based on conservation of energy and requires the following input parameters: fire size, compartment geometry, vent area, and water flow rate. The steady-state temperatures and oxygen concentrations predicted by the model can be used to determine the smallest fire that can be extinguished. The predictions made by the model compared favorably to the results of three full-scale test series conducted for the US Coast Guard. These tests were conducted in shipboard machinery spaces with compartment volumes ranging from 100 to 500 m³ with a wide range of ventilation rates and openings. The model was able to accurately predict the compartment temperatures during the tests where steady-state conditions were produced. The model was also able to accurately predict the extinguishment times for a wide range of fire sizes and was used to identify the smallest fire that could be extinguished for a given set of conditions.     

喷头安装角度对综合管廊细水雾灭火的影响

为研究综合管廊火灾中喷头安装角度对细水雾灭火效果的影响,搭建实体火灾实验平台,利用FDS 模拟分析7 种喷头安装角度下细水雾对烟气温度和烟气层高度的影响。结果表明：侧喷无线槽工况火场温度下降得更快,降温效果更好;喷头安装角度≤50̊ 时,灭火时间少,灭火效果好,当喷头安装角度＞50̊时,灭火时间增加,灭火效果变差;喷头安装角度与平均温度降低值有一定的关系,但不呈线性关系,结合降温效果与烟气层高度,建议细水雾喷头安装角度为50̊ 。     

Examination of the Extinguishment Performance of a Water Mist System Using Continuous and Cycling Discharges

We conducted a series of full-scale fire tests of a twin-fluid water mist system in an empty enclosure and in a simulated machinery space. During the tests, two water mist discharge modes, continuous and cycling, were used. We investigated the extinguishment performance of the water mist system using these two discharge modes under various fire scenarios, including different fire sizes, types, and locations, and different ventilation conditions. Test results showed that use of the cycling discharge substantially improved the effectiveness of the water mist system for fire suppression, in comparison to the continuous discharge. The corresponding extinguishing time and water requirement for fire suppression were significantly reduced, and some fires that could not be extinguished with the continuous discharge were extinguished with the cycling discharge. The improvement in fire suppression was attributed to high depletion and dilution rate of oxygen and the recurrent dynamic mixing generated by the cycling water mist discharge in the compartment.     

A computational and experimental study of ultra fine water mist as a total flooding agent

Computational fluid dynamics (CFD) calculations were carried out to design total flooding fire tests in a 28 m³ compartment for an ultra fine water mist (<10 μm). The exit momentum of the mist produced by a proprietary ultrasonic generator technology was extremely low with a mist discharge velocity below 1 m/s. The mist was discharged with multiple floor outlets equally spaced around the centrally located 120 kW pool-like gas fire. The transport of mist and its interaction with the fire was simulated by Fluent, a commercial CFD model. Lagrangian Discrete Phase Model (DPM) was used for droplets. Simulation predicted extinguishment within 10 s with a mist delivery rate of 1 l/min. However, in total flooding fire tests conducted, extinction times were more than 5 min. Additional computations approximating the ultra fine mist (UFM) as a dense gas agreed well with the observed transport timescales of minutes indicating that UFM behaves like a gas. Further, the mist–fire interaction needs a multi-phase Euler–Euler approach with a droplet vaporization model.