受限空间中细水雾灭火的准稳态模型

通过受限空间中大量细水雾灭火实验，总结出预测细水雾系统灭火效果的准稳态模型。该模型是针对细水雾扑灭有障碍火的情况而发展的，火焰的熄灭主要是由于燃料燃烧耗氧和细水雾汽化稀释造成氧气浓度的降低而导致的，忽略了细水雾与火焰的直接作用，模型基于能量守衡，要求输入以下参数：火源功率、受限空间的几何结构、通风口面积和细水雾施加流量，通过模型预测出稳态时受限空间的温度和氧气浓度，进而可以确定临界火源的尺度(功率大小)，同时能准确预测较大功率范围火的熄灭时间。     

细水雾扑灭油池火的临界条件

通过模拟灭火实验发现细水雾灭火过程中由于雾特性参数的变化而形成两种相异的灭火过程,进而通过理论分析与计算得到了细水雾通过火焰冷却扑灭油池火所需的临界条件,并通过实验室尺度实验与全尺度实验对计算结果进行了验证．在实验中还发现对于下喷式系统而言,细水雾能否穿透烟气羽流层对于细水雾系统能否灭火具有至关重要的影响,为此引入了烟气羽流与细水雾的推力比这一概念,并通过实验确定了采用下喷方式时,细水雾灭火的临界推力比大致为10．     

细水雾抑制气体扩散火焰的机理研究

应用三维LDV／APV系统和热成像方法，测量了细水雾和气体扩散火焰作用过程中的细水雾雾场、火焰温度场并研究了细水雾和气体扩散火焰的作用过程．探索了细水雾抑制火焰的机理和规律，比较了细水雾抑制气体扩散火焰时3种主要灭火机理，用数据定量表征了细水雾灭火时，水雾的蒸发潜热吸热作用、热容吸热作用以及稀释氧气作用对抑制气体扩散火焰所做的贡献，细水雾直接喷射或被卷吸进入火焰内部时，由于表面积大，吸收热量快，迅速汽化，体积扩大。大量的汽化潜热会降低火焰区及气相燃料的温度，细水雾及其蒸汽吸收部分热辐射，降低对燃料的热回馈，减少其汽化蒸发，从而降低反应区的可燃气体积分量。这些因素都会大大降低化学反应速度，抑制火灾的发展，直至扑灭火灾。     

洁净气体/细水雾联合灭木垛火实验研究

通过小尺寸实验研究了洁净气体灭火剂溴氟丙烯(BTP)和细水雾与木垛火相互作用的特性,发现BTP可以迅速地扑灭木垛表面明火,但是难以抑制其内部阴燃火;而细水雾可以有效地抑制木垛阴燃火,但灭木垛表面明火效率较低.为了克服两者灭木垛火的不足,进而对两者联合灭木垛火进行了研究,并比较了两种不同的联合方式:先喷BTP再喷细水雾以及BTP和细水雾同时喷.结果表明,溴氟丙烯和细水雾联用可以实现两者的优势互补,提高灭火效能,且先喷BTP后喷细水雾比同时喷灭火速度更快,抗复燃时间更长.     

细水雾与油雾火焰相互作用的实验及数值模拟研究

开展了细水雾抑制熄灭燃油油雾火的实验研究,并在试验研究的基础上,利用大型计算流体力学商业软件模拟研究细水雾与油雾火焰的相互作用。研究表明,细水雾熄灭油雾火的机理是降低可燃物与氧气混合浓度比和动力学效应、火焰冷却与衰减热辐射。在细水雾与油雾火焰相互作用动态过程中模拟计算与实验有一定程度的吻合;模拟计算表明细水雾有效灭火的前提是快速穿透火焰。     

细水雾抑制淬火油池火的小尺度实验

通过小尺度模拟实验对两种不同喷头所产生的细水雾抑制熄灭淬火油池火的研究发现,细水雾施加之初对淬火油池火有明显的强化作用,粒径和速度较大的细水雾强化燃烧的程度较大但持续的时间较短,且粒径和速度较大的细水雾抑制熄灭淬火油池火的效率较高.实验观测和分析表明,粒径和速度较小的细水雾主要通过卷吸空气强化燃烧,其灭火机理主要是火焰冷却和燃料表面冷却,粒径和速度较大的细水雾则主要通过共沸强化燃烧,其灭火机理主要是燃料表面冷却.     

受限空间内细水雾抑制熄灭火焰过程中一氧化碳的生成率

细水雾抑制熄灭火焰过程中一氧化碳的浓度是评价细水雾灭火系统安全可靠性的一个重要参数.本文通过受限空间内细水雾抑制熄灭障碍火的模拟实验研究,发现细水雾抑制熄灭火焰过程中一氧化碳生成率存在两种控制模式,即燃料控制模式和细水雾流量控制模式.实验结果表明,在燃料控制模式下,一氧化碳生成率随着燃料流量的增大而增大;在细水雾控制模式下,一氧化碳生成率随着细水雾流量的增大而增大.为了获得两种控制模式的临界转变条件,对燃料控制模式和细水雾控制模式的临界工况进行水蒸气含量分析.通过理论分析,得到一氧化碳生成率控制模式转变的水蒸气含量临界范围与 Suh and Atryeya 理论基本一致,即空气中水蒸气质量分数达到25%~65.5%时,水蒸气对火焰的作用从化学作用转为物理作用,一氧化碳生成率控制模式开始转变     

通风条件下细水雾灭火的临界水流率

临界水流率是细水雾系统的重要设计参数.为了研究通风条件对细水雾灭火临界水流率的影响,开展了一系列细水雾熄灭木垛火的模拟实验.实验结果表明,对于木垛火,细水雾的临界水流率同时受到热释放速率、有效喷嘴直径、高度、风速和雾化锥角的影响.基于Heskestad的临界水流率预测模型,利用量纲分析得到的指数关系式对实验数据进行拟合,对纳入通风风速后的模型各参数指数进行了修正,从而将其拓展至通风条件下.     

含NaCl添加剂细水雾对不同燃料池火灭火性能的实验研究

为了提高普通细水雾的灭火有效性，克服不足之处，研究了含NaCl灭火添加剂的细水雾与油池火相互作用的过程。重点研究了不同质量分数、不同工作压力、不同燃料条件下，细水雾的灭火有效性。研究结果表明，向细水雾中加入NaCl，显影响其灭火性能。细水雾的灭火对间与加入的NaCl质量分数间呈现出“W”形的关系曲线；细水雾喷头工作压力和燃料性质也影响细水雾的灭火性能：工作压力越高，平均熄灭时间越短；在相同的实验条件下，含NaCl添加剂的细水雾熄灭煤油火的时间小于酒精火的时间。含添加剂细水雾的灭火有效性，存在着细水雾与灭火添加剂的最优质量分数配比关系。     

基于横向射流的旋流燃烧器热声不稳定控制

为研究横向射流控制旋流燃烧器内自激热声不稳定的机理,搭建了旋流燃烧器热声不稳定控制试验台架,分别采用了横向射流(JICF)和横向火焰射流(JFCF)研究了空气流率为1.333.3 mL/s、化学当量比为0.9、旋流强度为0.77时旋流燃烧器的热声不稳定控制作用.试验发现横向射流能够大幅度降低旋流燃烧器的热声不稳定强度,而且横向射流所占用的空气流率比例小.当横向射流空气流率比例XJICF为6%时,热声不稳定的有效压力振幅从1.712.Pa降到185.Pa,降低了89.2%.另外,横向射流的控制作用远远优于横向火焰射流,横向火焰射流需要在燃料流率比例XJFCF50%,时才能获得大于32.5%的控制效果.     

A numerical simulation of the suppression of hydrogen jet fires on hydrogen fuel cell ships using a fine water mist

In this paper, in order to evaluate the reliability of a fine water mist for the suppression of fires on hydrogen fuel cell ships, the fire dynamics simulator (FDS) software was used to simulate the jet fire process and the action of a fine water mist on a fire caused by a hydrogen leakage in the hydrogen storage tank areas of hydrogen fuel cell ships. The fire scenario was classified into vertical or horizontal jet fires according to the location of the leakage in the hydrogen storage tank area, and the suppression effects of a fine water mist on hydrogen jet fires under a different droplet size, spray velocity, and ambient wind speed were compared and analyzed. The results indicate that a fine water mist is not effective in extinguishing hydrogen jet fires; however, by selecting suitable parameters (a spray velocity of 30 m/s and average droplet size of 30 μm), it can effectively reduce the fire field temperature of hydrogen jet fires and prevent the fire from developing further. Increasing the average droplet size of the fine water mist results in a gradual degradation of the suppression effect, while a higher spray velocity of the mist enhances the suppression effect to a certain extent. The ambient wind speed is an important factor that influences the suppression effect of a fine water mist on hydrogen jet fires, and when this speed is less than 4 m/s, a fine water mist with a higher spray velocity and smaller average droplet size is still a superior way of suppressing fires.     

Experimental study on the effect of fan-shaped water mist on horizontal under-expanded hydrogen jet flames

A series of experiments were performed on the fan-shaped water mist interaction with the horizontal under-expanded hydrogen jet flames. The effects of various water mist pressures and horizontal release positions were focused on flame length, temperature, and radiant heat flux. The results show that, water mist causes the flame to be tilted and the tilt angle of the flame increases with the water mist pressure, and the horizontal length of the flame is shortened. It is also found that water mist may lead to the radiation and temperature enhancement on the axis and downstream of the action position of water mist and flame, which is closely related to the configuration of water mist. However, this situation disappears and the temperature and radiation decrease with the increase of water mist pressure.     

Suppression effects of ultrafine water mist on hydrogen/methane mixture explosion in an obstructed chamber

The mitigation effects of ultrafine water mist on hydrogen/methane mixture explosions with hydrogen fraction (ϕ) of the range from 0% to 60% were experimentally studied in a vented chamber with obstacles. The spraying time, droplets size of water mist and the volume ratio of hydrogen were varied in the tests, and the key parameters that reflect the explosion characteristics such as the flame propagation imagines, flame propagation velocity, and explosion overpressure were obtained. The results show that the ultrafine water mist presents a significant mitigation effect on hydrogen/methane mixture explosions. The flame propagation structures are similar under the condition of without and with ultrafine water mist while the flame temperature is declined by the physical and chemical inhibition by ultrafine water mist. In addition, the mitigation effect increases with the increase of water mist flux. As a result, the maximum flame speed and overpressure of ϕ = 30% hydrogen/methane mixture explosion are declined by 33.3% and 58.4% under the condition of spraying for 2 min with 15 μm ultrafine water mist, respectively. Besides, the mitigation effects of ultrafine water mist on ϕ = 30% hydrogen/methane mixture explosion descends evidently with the increase of the droplets size of the range from 6 μm to 25 μm, which due to the easier evaporation and the greater total droplets surface area of the smaller water mist. However, the explosion mitigation effect of ultrafine water mist on the hydrogen/methane mixture actually descends with the increase hydrogen fraction.     

细水雾灭油池火过程中火焰强化现象的实验研究

细水雾灭火初期,在短时间内会观察到剧烈燃烧的火焰强化现象。设计了多组实验对比不同燃料在不同工况下的火焰强化现象,发现液滴通过撞击油盘燃料引起的液滴飞溅可以增大燃料与空气的接触面积,强化火焰燃烧。细水雾在燃料内发生扬沸也可能强化火焰,但增益效果不明显,同时燃料气化率对于火焰强化程度有很大关系。     

细水雾熄灭K类火灾的全尺寸模拟实验

利用ISO 9705全尺寸多功能热释放速率测试仪在开放空间研究了细水雾作用下K类火灾的发展过程,实验中对细水雾作用下食用油火的温度、热释放速率及烟气的主要特性参数变化规律进行了测量与研究,分析了预燃时间对灭火有效性的影响,系统地阐述了细水雾作用下K类火灾关键特性参数的变化规律．实验发现,细水雾可以有效地抑制K类火灾的发展,在其作用下火焰温度及热释放速率快速降低,并可以有效地冲刷烟气,降低一氧化碳及二氧化碳的浓度,提高氧气的浓度及火场能见度．同时利用稳定火源热释放速率模型计算了K类火灾发展阶段的热释放速率,与实验测量结果比较发现,模型可准确地预测K类火灾发展阶段的热释放速率的变化规律．     

Experiment and prediction of fire extinguishment with water mist in an enclosed room

The correlation between oxygen concentration and fire temperature when fire was extinguished with water mist was theoretically studied. The Semenov theory was applied to analyze the critical condition when fire was extinguished with water mist, from which the correlation could be obtained. The water mist experiments were carried out by varying the fire size, atomizer number, ceiling height, system pressure, and pre-burn time in an enclosed room. The oxygen concentration near the edge of the liquid pool and the fire temperature above the center of the liquid pool were measured. A comparison of the experimental data with the correlation was made under different conditions. The results showed that fire extinguishment was a stochastic process which could be affected by many factors. This theoretical model could predict the correlation between fire temperature and oxygen concentration when fire was extinguished with water mist in an enclosed room and it can also be treated as a critical condition for fire extinguishment.     

Experimental evaluation of water mist with metal chloride additives for suppressing CH4/air cup-burner flames

In order to investigate the fire suppression effectiveness of water mist with metal chloride additives, ultrafine water mists of these salts with diameters about 10μm were introduced into CH4 /air non-premixed flame in the cup burner. Results showed that these droplets hard to make itself to the flame front under the cup burner flow conditions functioned as a carrier of the vaporized solid particles or its decomposed materials. The metal chloride improved fire suppression efficacy of water mist which were affected by the type and concentration of metal chloride. On a mass basis, there is a fire suppression effectiveness relationship of MgCl2 相似文献   

细水雾对油池火热释放速率影响的初步研究

热释放速率是反映火场规模与发展的最重要的基础参数，利用ISO9705实验台进行细水雾灭火有效性的影响因素及相关机理研究，不仅能营造出一个真实的室内火灾环境，而且能够得到火场的热释放速率。对汽油池火的初步实验表明：热释放速率曲线能直接反映出细水雾对火源的作用；细水雾作用下燃烧总的热释放量减少很大；开启水雾的时间不同，细水雾对热释放速率峰值的削减程度不同。