共查询到19条相似文献,搜索用时 234 毫秒
1.
2.
3.
王晔 《消防技术与产品信息》2006,(2):62-67
(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 相似文献
4.
对细水雾近距离扑灭油盘火焰进行了实验和理论分析。实验结果表明:利用水雾近距离扑灭油盘火时,水雾射流对火焰的吹熄作用是火焰熄灭的主导机理;气流对火焰的拉伸冷却和细水雾对火焰的蒸发冷却能使火焰的蔓延速度降低,对吹熄起促进作用;而化学反应动力学特征对火焰抵抗吹熄的能力也有重要影响。 相似文献
5.
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。 相似文献
6.
不同工况下细水雾灭火效能影响的数值模拟 总被引:1,自引:0,他引:1
采用FDS对单室火灾中细水雾与火焰相互作用过程进行数值模拟分析,探讨细水雾与火焰相互作用过程中不同区域的细水雾灭火机理,分析粒径分布、速度和雾化角度对细水雾灭火产生的影响.模拟结果表明:在细水雾与火焰相互作用过程中粒径分布对灭火效能影响显著;细水雾在粒径小于100 μm时不能实现有效灭火;当粒径为200~400 μm时细水雾能有效抑制火焰发展并熄灭火源;在细水雾灭火机理中,相对于气相冷却和隔氧窒息,细水雾的表面冷却作用起到主导作用;细水雾喷射速度对灭火效果影响较大,细水雾动量不小于火羽流动量是火灾发展得到有效控制的重要前提;细水雾有效雾通量随着雾化角度增大而逐渐减小,雾化角度增大不利于细水雾灭火效能提高. 相似文献
7.
赵侠 《消防技术与产品信息》2013,(12):37-41
在开放空间细水雾与火焰相互作用研究实验的基础上,进行了细水雾从不同方向施加于竖直向上气体射流火的灭火对比性实验,进而进一步研究细水雾熄灭气体射流火的方法,并结合细水雾灭火实际案例,探讨应用细水雾科学有效的扑救天然气泄漏火灾问题. 相似文献
8.
细水雾与固体木垛火相互作用的实验研究 总被引:1,自引:0,他引:1
为了更好地研究细水雾熄灭固体火焰的机理及其有效性 ,建立了单流低压细水雾灭火模拟实验平台 ,在 3m× 3m× 3m的受限空间中开展了一系列的灭火实验。实验过程中采用了两种不同功率的木垛火源 ,利用热电偶和红外热像仪对细水雾施加前后的火焰的温度场进行了实时观察研究 ,结果表明当细水雾的压力低于 0 .2 MPa时 ,细水雾不能有效地扑灭木垛火 ,当细水雾的压力较低时 ,喷嘴距火焰表面的距离和细水雾施加的流量是影响细水雾灭火有效性的关键因素 ;同时 ,功率越大的木垛火 ,越易被细水雾扑灭。 相似文献
9.
10.
11.
《Fire Safety Journal》1999,33(3):185-212
The focus of this paper is on numerical modeling of methanol liquid pool fires and the suppression of these fires using water mist. A mathematical model is first developed to describe the evaporation and burning of liquid methanol. The complete set of unsteady, compressible Navier–Stokes equations are solved along with an Eulerian sectional water mist model. Heat transfer into the liquid pool and the metal container through conduction, convection and radiation are modeled by solving a modified form of the energy equation. Clausius–Clapeyron relationships are invoked to model the evaporation rate of a two-dimensional pool of pure liquid methanol.The interaction of water mist with pulsating fires stabilized above a liquid methanol pool and steady fires stabilized by a strong co-flowing air jet are simulated. Time-dependent heat release/absorption profiles indicate the location where the water droplets evaporate and absorb energy. The relative contribution of the various suppression mechanisms such as oxygen dilution, radiation and thermal cooling is investigated. Parametric studies are performed to determine the effect of mist density, injection velocity and droplet diameter on entrainment and suppression of pool fires. These results are reported in terms of reduction in peak temperature, effect on burning rate and changes in overall heat release rate. Numerical simulations indicate that small droplet diameters exhibit smaller characteristic time for decrease of relative velocity with respect to the gas phase, and therefore entrain more rapidly into the diffusion flame than larger droplet. Hence for the co-flow injection case, smaller diameter droplets produce maximum flame suppression for a fixed amount of water mist. 相似文献
12.
13.
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。 相似文献
14.
《Fire Safety Journal》2002,37(6):569-589
The focus of this paper is on simulating water mist suppression of fires in large enclosures. A two-continuum formulation is used in which the gas phase and the water-mist are both described by equations of the Eulerian form. The water-mist model is coupled with previously developed codes based on the multi- block Chimera technique for simulating fires. Computations are performed to understand the various physical processes that occur during the interaction of water-mist and fires in large enclosures. Droplet sectional density contours and velocity vectors are used to track the movement of water-mist and to identify the regions of the fire compartment where the droplets evaporate and absorb energy. Parametric studies are performed to optimize various water-mist injection characteristics for maximum suppression. The effects of droplet diameter, mist injection velocity, injection density, nozzle locations and injection orientation on mist entrainment and flame suppression are quantified. Numerical results indicate that for similar injection parameters such as mist injection density, injection velocity and droplet diameter, the time for suppression was smallest for the top injection configuration. Water-mist injection through the side walls, the front and rear walls and through the floor were found to be less efficient than the top injection configuration. These results are compared with our earlier predictions on water-mist suppression of small scale methanol pool fires and other experimental studies. 相似文献
15.
Colomba Di Blasi 《Fire Safety Journal》1995,25(4):287-304
The effects of solid thickness on the initial stages of concurrent flame spread are studied through numerical simulation. The two-dimensional mathematical formulation of the problem is based on the fully elliptic, reactive Navier-Stokes equations coupled to energy and mass conservation equations for a charring solid. For all fuel thicknesses, uniform burn-out, pyrolysis and flame propagation rates are approached after an accelerative stage. As with the opposed flow problem, three main regimes of spread rate are established based on the dependence on fuel thickness. The first (kinetic) regime, where spread rates increase with the thickness, is established for samples below 0.008 × 10−2 m. Both flame and pyrolysis lengths are very short. In the second (thermally thin) regime, the spread rates decrease as the solid thickness is increased while the flame and the pyrolysis regions become successively larger. Finally, as the fuel thickness is increased above 0.5 × 10−2 m, the thermally thick regime, signified by constant spread rates, is simulated. As no experimental measurements of spread rate dependency on the thickness of charring materials are available, numerical predictions are compared with a thermal theory to assess its validity limits. 相似文献
16.
17.
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. 相似文献
18.
Adam N. Friedman Peter I. Danis Gregory J. Fiola Christopher A. Barnes Stanislav I. Stoliarov 《Fire Technology》2018,54(6):1829-1840
Recent research has shown that acoustics can be used to suppress flames from a liquid fuel source. The results of these experiments indicated that acoustics alone are insufficient to control flames beyond the incipient stage. Recent research has also shown that variations in the delivery of water mist to a fire can enhance the mist’s efficiency. Therefore, the addition of acoustics to water mist may be an effective means of enhancing an established fire protection technology. For the first time, acoustics and water mist have been combined and studied as a flame suppression strategy. A series of experiments were conducted that explored the potential for coupling acoustics with water mist as means of flame suppression. Heptane fueled flames were created from two different sized ceramic fiber wicks: 30 mm?×?50 mm with 5 mL of fuel, and 60 mm?×?100 mm with 20 mL of fuel. The flames were then exposed to water mist delivered at a constant rate, which was found to be incapable of suppressing the flames. Next, low frequency sound waves at 62 Hz and 80 Hz were used to suppress flames from both wicks, with each frequency being generated by a different resonator. Finally, acoustics from both resonators were combined with water mist, and used to suppress flames from both wicks. The results showed that a combination of acoustic waves and water mist suppressed the flames more effectively than each individual technique on its own. This finding opens the possibility of developing more efficient ways to use water mist technology. 相似文献
19.
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. 相似文献