Implications of fine water mist environment on the post-detonation processes of a PE4 explosive charge in a semi-confined blast chamber

The effects of a fine water mist environment in a semi-confined blast chamber on the chemical and thermodynamic processes following detonation of a 20 g PE4 explosive charge have been investigated.The effects were quantified by the analysis of pressure profiles recorded where several parameters including arrival time of the shock at the sensors, peak overpressures, specific impulse of the positive phase, period of the negative phase and the specific impulse of the multiple reflections were quantified.The effect of the fine water mist on the arrival time, peak pressures and the specific impulse of the positive phase agrees with previous findings in literature. In this paper, the focus is on the implications of the fine water mist on the negative phase and the impulse of multiple pressure reflections. The period of the negative phase was found to have increased by 40% and with higher negative peak pressure in the mist condition compared to the atmospheric condition. The activities of the multiple pressure reflections were found to have decreased considerably, both in number and in amplitude leading to lower impulses(by about 60%) for the water mist conditions.

Combined effects of obstacle and fine water mist on gas explosion characteristics

Combined effects of obstacles and fine water mist on a methane-air explosion of a semi-closed pipe were investigated experimentally.In this study,the diameter of the water mist,the location,and the number of obstacles was considered.The results demonstrated that 5 μm water mist present a significant suppression affected while 45 μm shows a slight promotion effected on a gas explosion of the condition without obstacles.In the presence of an obstacle,however,the inhibitory effect of 5 μm water veils of mist dropped significantly during flame propagation,and the effect of 45 μm water veils of mist changed from the enhancement of inhibition,and its inhibitory effect was significant.The inhibitory effect of 45 μm water veils of mist on gas explosion weakened firstly and then enhanced with the increasing distance between obstacle location from the ignition location as well as in several obstacles.

Coal combustion restrained by ultra-fine water mist in confined space

In order to apply ultra-fine water mist technology on spontaneous coal combustion in the goaf of a coal mine, we built a small scale compartment with ultra-fine water mist for restraining coal combustion in a confined space and then investigated the restraining efficiency and related factors. The study obtained the following results: a descending rate of heat release, an increase in O2, the production of CO2 decreased gradually, while the production of CO increased dramatically and quickly and then decreased; ultimately it tended to become stable after the discharge of an ultra-fine water mist. The technology showed that the ultra-fine water mist can effectively reduce the heat release rate of coal and the rate to generate components. We found that the restraining effect relied on the mist flux, the discharge time and other factors. A sufficient amount of mist has a better effect compared to an insufficient amount of mist. To combat coal combustion, the greater the discharge time, the better coal flames are extinguished.

Research on the effect of the component proportion in the new water mist additive on firefighting performance

Water mist technology provides efficient firefighting performance while there is still room for improvement. So varieties of additives have been studied in recent years both at home and abroad. The self-made additives are used to compare the firefighting performance of diesel and heptane fire in open space. By adjusting the concentration of substance in the additives and conducting the experiment under the pressure of 0.3 MPa,0.5 MPa and 0.7 MPa,extinguish time and temperature are measured in the experiment. Through the experiments using different fuels,it can be found when the fuel is heptane that has a lower ignition point and a higher evaporation rate, the water mist additive can still significantly improve the firefighting performance. According to the data based on different concentrations of fluorinated surfactants,we find that fluorinated surfactants are the main substance to improve the performances by changing physical property of water mist. Optimal proportion of the additives for firefighting performance is found by experiment results.

Analysis of Water Mist Suppression with Foam Additive in Wind Generator

The study adopted a 20-foot long container to simulate the situation inside a turbine cabin. Water mist sprays were installed internally and used to perform fire extinguishing tests. Under these different scenarios, several operating factors were adjusted with the results of each adjustment subsequently measured. The operating factors studied included： operating pressures, foam concentrations, cabin opening issues, and obstacles. Each of the factors was compared with the others so as to find out which combinations would be most suitable for a water mist spray system installed inside a wind turbine cabin. The presence of obstructions hinders the direct impact of the mist spray on the fire source and in average an additional 2 to 3 minutes is required to put out the fire. This study found that the effect of the foam-water ratio is linear. Regardless of the scenario, the optimum mixture ratio is 3%. The line graph shows that the most unsuitable aqueous film-forming mixture ratio is 6%. This experiment found that the main fire extinguishing mechanism of water mist spray is the cooling of a large area via water droplets. This system is very effective in bringing down the temperature. The addition of foam in water mist spray, however, impaired the effectiveness of the cooling effect although the fire control mechanism via emulsification markedly reduced the time required to put out the fire. The increase in foam magnification will considerably enhance the fire extinguishing efficiency.

Study on fire extinguishing performance of ultrafine water mist in a cup burner

Two simplified models for predicting minimum extinguishing concentration(MEC) of ultrafine water mist(UFM)(<10 m) were developed based on limiting oxygen concentration(LOC) and combustion limit temperature(CLT),respectively.Experiment was conducted using a modified cup burner which can reduce the surface adsorption of UFM.Two typical liquid fuels,n-heptane and ethanol,were used in the experiment.Tests using the same scenario were repeated 20 times or 10 times according to the variance of extinguishing time.The average and the standard deviations of extinguishing time were used to evaluate the fire extinguishing performance of UFM.Experimental results agree well with the model based on LOC,and disagree with the model based on CLT.The disagreements were explained by analyzing flow behavior of UFM.It was concluded that the primary mechanism of fire extinguishment with UFM was oxygen dilution.

气凝胶灭火剂抑制锂离子储能电池热失控特性研究

通过对比试验探究了气凝胶灭火剂对锂离子储能电池热失控的抑制效果。研究满荷电状态下的100 Ah磷酸铁锂储能电池热失控演变过程特征参数,识别出3个灾害演变特征拐点作为灭火剂施加的指导节点。在相同节点分别施加灭火参数一致的气凝胶灭火剂与细水雾开展灭火对比测试。结果表明:触发明火前施加灭火剂均可有效阻断电池内部放热副反应,两者表现出相似的冷却效能;电池起火后,气凝胶灭火剂展现出更为出色的明火抑制效果,其接触电池表面形成的致密泡沫可有效阻隔氧气,实现快速灭火;对于已经触发热失控的情形,气凝胶灭火剂凭借预热覆盖效果,显著缩短电池射流火持续时间,可大幅降低电池火灾危害。

城市地下综合管廊电缆火灾低压细水雾灭火效能研究

为了研究城市地下综合管廊电缆火灾低压细水雾灭火的有效性、明确影响低压细水雾灭火效能的关键因素,搭建了缩尺寸综合管廊低压细水雾灭火试验平台并开展了灭火试验。试验结果表明,低压细水雾能够快速有效地扑灭综合管廊电缆火灾,灭火时间最快为7 s,在启动灭火系统后50 s即可将管廊内部最高温度从650℃降至40℃。压力与喷头流量系数的改变对低压细水雾灭火效能影响较大,灭火时间分别最多缩短75.0%和66.7%,平均降温速率最高为8.2℃/s和7.43℃/s;喷头间距的改变对灭火效能影响相对较小,灭火时间最多缩短47.3%,平均降温速率最高为6.1℃/s。

含添加剂水雾抑灭单基药火焰的小尺度实验研究

为探究含不同性质添加剂的水雾对单基火药燃烧抑灭性能的影响,在自主搭建的火药燃烧及灭火平台上开展纯水雾与含Na_(2)SO_(3)、FeCl_(2)、K_(2)CO_(3)、KHCO_(3)添加剂的水雾对单基火药燃烧抑灭性能的对比实验,研究灭火过程中温度、辐射热流、火焰形态等的变化。结果表明:含还原性(Na_(2)SO_(3)、FeCl_(2))和非还原性(K_(2)CO_(3)、KHCO_(3))添加剂的水雾抑灭性能明显优于纯水雾,灭火时间更短。含非还原性添加剂的水雾在低浓度下抑灭效果较差,当添加质量分数提升至3%以上时,抑灭效果显著提升;含还原性添加剂水雾对单基药的抑灭性能在各添加剂浓度下均优于含非还原性添加剂的水雾,且随着添加剂浓度的增大,抑灭性能表现出饱和性。

文物建筑内移动式高压细水雾灭火装置设计参数研究

为了研究移动式高压细水雾灭火装置在文物建筑内的设计参数,搭建了6A木垛火试验台,研究在不同喷射距离和模式下,该装置应对大规模火灾时适合的喷射流量与距离,并采用FDS,以北京某古建筑为模型进行模拟,从喷射强度、喷射距离、喷射时机、雾化粒径等方面验证并补充移动式高压细水雾灭火装置的设计参数。结果显示,喷射强度可设定为4.4~6.6 L/(min.m^(2));喷射距离可设定为5 m,尽可能采用近距离喷射策略;灭火时机应尽早,至少在起火后300 s内;雾化粒径的选择需根据具体情况权衡考虑。

细水雾抑制巷道火灾蔓延影响因素研究

为探索细水雾抑制矿井胶带蔓延火灾的影响因素,利用火灾动力学模拟器(FDS)构建矿井巷道火灾蔓延几何模型,使用控制变量法,通过设置不同火源功率、雾通量、喷头安装距离与风速模拟细水雾抑制巷道火灾,观察不同工况的火场温度与热释放速率变化特征,揭示不同因素对火灾发展的影响。结果表明,细水雾对矿井火灾蔓延有良好的抑制作用,通过优化设计各种影响参数,可以更好地发挥细水雾冷却降温的作用;合理增加风速、雾通量和喷雾有效范围,可以有效提高灭火效率,降低温度和热释放效率;火源初始功率的变化也对细水雾灭火有较大影响,在其他条件相同的情况下,初始功率由2 MW增加到4 MW时,温度下降率由72.7%下降到32.7%。

滑移装置协同气液两相流抑制受限空间甲烷爆炸试验研究

为探究不同气体驱动水雾喷洒对滑移装置下甲烷爆炸特性的影响规律,在方形管10 cm×10 cm×100 cm中开展爆炸试验,借助高速摄像技术和压力采集技术,通过改变滑移装置弹簧线径、水雾驱动气体类别,剖析不同工况对爆炸火焰结构演变行为和压力瞬态变化规律的影响。结果表明:N_(2)驱动细水雾与滑移装置对甲烷的协同抑爆灭火效果优于空气驱动水雾协同滑移装置作用,且预防细水雾抑爆失效情形下,N_(2)可起到冗余灭火作用和协同增效作用。对比空气驱动细水雾作用,N_(2)驱动细水雾可有效缩短火焰燃烧时间,延缓火焰锋面速度峰值出现,抑制火焰锋面形态演变,缩小压力振荡区间,衰减近一半超压峰值,将最大超压峰值有效控制在燃烧区内,减少未燃区二次爆炸的可能性。

气体灭火系统和细水雾灭火系统在医院建筑中的应用及对比分析

介绍了气体灭火系统和细水雾灭火系统的灭火原理;以重庆某大型综合医院为例,对医疗设备、电气机房等进行消防灭火设计和对比分析,研究气体灭火系统和细水雾灭火系统的适用性及经济性;通过对比分析,对两种系统的选用提出相关建议。

单相高压与两相雾化方式对地铁车厢火灾抑制效果的对比实验研究

目前地铁车厢内细水雾灭火系统以单相高压雾化方式为主,高压管路一旦破损可对乘客生命安全构成潜在威胁。以行李袋和汽油作为燃烧物开展了全尺寸实验研究。分别从冷却能力、热辐射衰减效果及烟气抑制效果方面分析对比了单相雾化和两相雾化方式对车厢内火灾的抑制效果。结果表明单相雾化和两相雾化冷却效果相当,但两相雾化在热辐射衰减、烟气洗消效果方面较高压单相雾化更优,且安全性更好。

超声波细水雾灭火技术试验研究

利用超声波技术产生的细水雾可作为一种灭火剂,通过冷却、窒息等作用实施灭火。搭建试验平台,分析超声波雾化装置产生细水雾的特性,并设计灭火试验,研究局部应用和全淹没两种形式的灭火有效性和影响因素。结果表明:利用超声波雾化技术产生细水雾并确保足够雾化量和适宜的喷射方向,实施局部应用灭火是可行的;采用全淹没灭火时,灭火效果取决于场所通风情况和空间大小,在相对封闭空间内灭火效果较好。

北京艺术中心自动灭火系统与装饰设计结合及实施的探讨

建筑物自动灭火系统作为消防设施的核心组成部分,起着至关重要的作用,其布置的恰当与否直接影响控火灭火效率。基于北京艺术中心项目,介绍如何将设计自动灭火系统与装饰设计结合及实施,以确保建筑物的安全性和可持续发展。

某火电厂集控室消防细水雾抑制火灾模拟分析

以某火电厂建设工程集控室消防系统设计为例,利用PyroSim火灾模拟软件建立试验模型,模拟研究在不同压力和角度下细水雾对T^(2)模式自由火的抑制过程,对比分析细水雾在喷头角度为45°、60°、90°和喷头压力为1 MPa、2 MPa、5 MPa时的火焰温度变化曲线,模拟空间内的CO、O_(2)浓度变化、灭火时间和灭火用水量等情况。结果表明:灭火过程可以分为喷雾初期的抑制阶段、火焰强化膨胀阶段和细水雾再次抑制阶段3个阶段;水雾压力越大,灭火效果越明显;喷射角度为90°的细水雾灭火过程中火焰温度变化平稳,适合作为集控室的自动灭火喷头参数;垂直布设的中压细水雾具有更好的实用价值。

电缆竖井细水雾灭火系统数值模拟研究

利用数值模拟技术研究了电缆竖井不同高度和通风条件对细水雾灭火效果的影响,按典型高低压电缆井断面情况,基于火灾动力学软件,模拟了细水雾灭火系统在电缆竖井中不同通风条件下的控火和灭火效果,同时对细水雾灭火系统在电缆竖井中的形式、喷头布置方式等进行说明,得到在限定条件下的火灾规律性结果和相应的应用边界条件等结论,为电缆竖井防火实验研究和工程设计提供参考。

某客滚船低压水雾灭火系统设计

本文以某客滚船为例,介绍低压水雾灭火系统的组成及保护分类、系统水量估算方法、系统满足客船安全返港要求的布置特点以及设计过程碰到的有关问题。

Experimental study on the interaction of fine water mist with solid pool fires

This paper describes experimental study of the interaction of fine water mists with solid pool fires. Fine water mist was generated by a single pressure nozzle and solid pool fires were produced from solid red pine or polymethyl methacrylate(PMMA). The LDV/APV system was em-ployed to determine the water mist characteristics. The water mist droplet sizes and velocities from the nozzle were measured under varying conditions and at different locations. The effects of solid type, water flow rate, and nozzle distance from the sample surface on extinguishments time were examined. At a given water flow rate, the extinguishment time is much longer for PMMA fires than for solid pine fires. The extinguishment time was found to decrease with increasing water flow rate. At very low water flow, the extinguishment time decreases when the nozzle is positioned further from the sample surface. On the contrary, at high water flow, the extinguishment time appears to be independent of the distance between the nozzle and the sample surface. The experimental re-sults show that flame extinguishments is due primarily to fuel surface cooling and wetting.