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Heat exhaust coefficient of transversal smoke extraction system in tunnel under fire is studied by experimental means with a 1:10 model tunnel using Froude scaling. Heat exhaust coefficient is defined as the proportion of the heat exhausted by individual exhaust inlet, smoke duct and exhaust fans in total heat released by the fire in the tunnel, respectively. Results of a series of fire tests in a model tunnel are presented. Heat exhaust coefficient of single exhaust inlet and the smoke duct are strongly influenced by the configuration of the exhaust inlets. Heat exhaust coefficient of the exhaust fans varies in the range of 13–20% and is smaller than the heat exhaust coefficient of the smoke duct which varies from 17% to 83% and tends to be about 35% with the increase of the total area of the exhaust inlets. Activating small number of the exhaust inlets is beneficial for enhancing the heat exhaust coefficient of the smoke duct. The heat exhaust coefficient of the smoke duct and exhaust fans is high when the exhaust inlets are set close to the fire. Due to the cooling effect of the solid boundaries on the smoke while traveling in the tunnel and smoke duct, the heat exhaust coefficient of the exhaust fans in unilateral exhaust mode is slightly smaller than that in bilateral exhaust mode. 相似文献
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In this work, a numerical model of tunnel fire is developed and aimed to investigate the influence of cross-sectional fire locations on critical velocity and smoke flow characteristic. It is shown that the critical velocity for a fire next to the wall is obviously higher than that for a fire in the middle or on the left/right lane. The ratio is estimated to be 1.12. The predictions of critical velocity from ‘small-fire’ models show a good agreement with that for a fire in the middle or on the left/right lane from CFD. The tunnel height at the fire location is proposed to be instead of the hydraulic tunnel height in the ‘big-fire’ model of Wu and Bakar for a fire next to the wall. The smoke moves backward in a tongue like form as the ventilation velocity is lower than the critical velocity. The back-layering length of a fire in the middle is shown to be approximate twice than that on the left/right lane under the same ventilation velocity, although they share the same critical velocity. Whereas a relatively short back-layering length for a fire next to the wall under the velocity of 2.6 and 2.7 m/s. In addition, a snaky high-temperature profile on the top wall at the initial downstream is observed for a fire on the left lane and next to the wall, and finally a steady and layered smoke flow. The likely cause of this phenomenon is subsequently explained in this study. 相似文献
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Simulation of temperature and smoke distribution of a tunnel fire based on modifications of multi-layer zone model 总被引:4,自引:0,他引:4
Chen Xiaojun 《Tunnelling and Underground Space Technology incorporating Trenchless Technology Research》2008,23(1):75-79
Some modifications on Suzuki’s multi-layer zone model (MLZ) have been done to predict temperature and smoke distribution of a tunnel fires, i.e., the radiation heat loss of fire source is taken into account and a four-surface radiation heat transfer model is introduced. Like Suzuki’s model, as a special long and narrow space, the tunnel space is also divided into a number of layers in vertical direction and regions in longitudinal direction. The physical properties like temperature and species (CO, CO2, etc.) are assumed uniform in every zone like two-zone model. However, the different heat transfer model is introduced. The MLZ model prediction is compared with the experiments of USTC and CFD model (FDS). It shows good agreement between the model prediction, experiments and CFD models (FDS). And the MLZ model needs less time than CFD model. 相似文献
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The Fire Dynamics Simulator code is used to investigate the smoke filling process in a large building. Initially, the model is used to simulate the smoke descending process in an atrium under fire scenarios. By comparing with experimental data, reasonable model constants of Cs and Prt are determined for simulating smoke movement in buildings with large space. The performance of different smoke exhaust methods in a real gymnasium is then studied. Smoke filling processes are investigated under different natural and enhanced smoke exhaust methods. Simulated results show that natural smoke exhaust method is preferred when the smoke exhaust vents are located at the ceiling of the gymnasium. On the other hand, when the smoke exhaust vents are located on the walls of the gymnasium, enhanced smoke exhaust methods are preferred. In addition, the influence of ceiling temperature in the gymnasium on the smoke spreading process is presented in this paper. Results indicate that high ceiling temperature slows down the so-called smoke ceiling jet moving horizontally at the ceiling, whereas low ceiling temperature accelerates such smoke ceiling jets. 相似文献
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Prediction of fire and smoke propagation in an underwater tunnel 总被引:1,自引:0,他引:1
Juan Abanto Marcelo Reggio Daniel Barrero Eddy Petro 《Tunnelling and Underground Space Technology incorporating Trenchless Technology Research》2007,22(1):90-95
Different models and solvers are used to calculate the spread of fire and smoke in a tunnel. The methodology for obtaining the numerical solution of this fire dynamics problem involves commercial software and a research program. Both can handle geometries described in three dimensions. Particular emphasis was placed on road tunnels in which vehicles are present. The specific application of this work is a study of a fire scenario in the Louis-Hippolyte-Lafontaine Tunnel which runs under a river in the Montreal area. Besides standard representation, visualization is also used, with elements which consider the optical properties of the phenomenon for a realistic rendering of smoke and fire. 相似文献
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Based on the entrainment rate of isothermal jet, an application method of the isothermal model in tunnel fire was presented through the more reasonable estimation of total smoke flow rate and its density at jet exit. Acetone LIF measurement was performed to identify the entrainment of ambient air qualitatively, and the entrainment constants were provided with the results of a previous study of which jet velocity corresponded to that of this study. The entrainment effect was more remarkable for the smaller fire, because the normalized axial distance to ceiling was increased with decreasing the fire size. These results suggested that the present model considering the jet entrainment might enhance the previous isothermal model in tunnel fire. 相似文献
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In this study, numerical simulation was carried out to analyze the effect of the aspect ratio on smoke movement in tunnel fires using FDS 3.0. Temperature distribution under the ceiling showed a relatively good agreement with experimental results within 10 °C. It confirmed the possibility of application of FDS code to tunnel fires. Results from varying of the aspect ratio showed good agreement with experimental data. Temperature near the fire source decreased with the increase of the aspect ratio. But, the rate of the temperature decrease was reduced by the decrease of the heat loss in the spanwise direction. Clear height of the simulation by the analysis of the velocity distribution was about 3% higher than that of the experimental result. Numerical results predicted the back-layering distance and the critical velocity reasonably. 相似文献
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侧向集中排烟隧道火灾烟气控制优化 总被引:1,自引:0,他引:1
针对某特长沉管公路隧道采用侧向集中排烟系统的实际,采用FDS对隧道内温度场分布、2 m高处能见度分布、烟气蔓延范围、排烟效率等指标进行定量分析,获得合理的烟气控制方案.结果表明:火源位于-3%坡度段内,火源功率50MW的合理纵向诱导风速为2.5 m/s,合理排烟口开启方案为上游开启1组/下游开启4组排烟口;0坡度段合理的烟控方案为两端排烟,上游开启2组/下游开启3组排烟口,并配合1.5m/s的纵向诱导风速;3%坡度段合理的烟控方案为下游端排烟,上游开启2组/下游开启3组排烟口,并配合1 m/s的纵向诱导风速. 相似文献
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长区间隧道的防排烟系统设计通常是设置中间风井,但中间风井的设置容易受到多方面因素制约,可采用拱顶排烟道代替部分中间风井。为验证并拓展拱顶排烟道代替方案可行性,通过理论分析了3种排烟道设置方案对应的烟气控制方式。基于广州某区间地铁,通过数值模拟对排烟道设置方式进行验证,得到不同条件下3种排烟道设置方式控制烟气效果对比,结果表明:单侧送风1.6 m/s且排烟量为140 m3/s时基本可以控制火灾位于中间通风区段时烟气的排出。当火灾位于靠近风井或排烟口下方时,送风风速1.4~1.6 m/s、排烟量140~150 m3/s可有效控制烟气。证明了排烟道代替部分中间风井的可靠性,拓展了该方案的适用性。 相似文献
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在双区模型的基础上,给出墙边羽流和轴对称羽流的排烟稳态方程,最终求得烟气层密度以及高度。通过FDS模拟,得出不同工况下的排烟效果,验证了理论计算结果。得出结论认为,同种火源条件下,墙边羽流模型由于烟气产生速率小于轴对称羽流模型,烟气层密度较大,高度较高。 相似文献
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双层隧道具有空间利用率高,通行量大等优点,但由于顶部空间有限,多采用侧向排烟的方式控制隧道火灾时烟气的蔓延.以某越江隧道为例,采用火灾动态模拟软件FDS,改变排烟口数量、面积、间距,设计6个火灾场景,定量分析侧向排烟口的设置对机械排烟效果的影响.分析各排烟口流量、流速,分析隧道内温度分布、能见度分布.结果表明:在火源功率20 MW、无纵向风条件下,排烟口面积、排烟口开启数量以及排烟口间距都在火灾发生初期对烟气的蔓延起控制作用;提出在排烟口面积为4 m2、排烟口间距为90 m、火灾时开启4个排烟口时,排烟效果更经济合理. 相似文献
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Three full-scale model experiments were conducted in a unidirectional tube, which is a part of a metro tunnel with one end connected to an underground metro station and the other end opened to outside in Chongqing, PR China. Three fire HRRs, 1.35 MW, 3 MW and 3.8 MW were produced by pool fires with different oil pan sizes in the experiments. Temperature distributions under the tunnel ceiling along the longitudinal direction were measured. At the same time, CFD simulations were conducted under the same boundary conditions with the experiments by FDS 5.5. In addition, more FDS simulation cases were conducted after the FDS simulation results agreed with the experimental results. The simulation results show that the smoke temperature and the decay rate of the temperature distribution under the tunnel ceiling along the longitudinal direction increase as HRR increases. The smoke exhausts effectively from the tunnel under mechanical ventilation system, whether the emergency vent is activated as a smoke exhaust or an air supply vent. The operation mode of the mechanical ventilation system depends on the evacuation route. 相似文献
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The characteristics of the spread of smoke were investigated for a fire occurring in a shallow urban road tunnel with roof openings in its ceiling. In this type of tunnel, the smoke produced by a fire is ventilated through the openings in the ceiling given the natural buoyancy of hot smoke. A fire experiment was conducted using a 1/12 scale model tunnel to ascertain whether natural ventilation via the roof openings was sufficient to maintain a safe evacuation environment for tunnel users. The distance from the fire to the tip position of the spreading smoke and the thickness of smoke layers along the ceiling were investigated by changing the heat release rate and using two types of median structure as experimental parameters. The two types of median structure dividing the tunnel into two road tubes were pillars and walls. It was clarified that the smoke spreading distance was constant and independent of the heat release rate of the fire under our experimental conditions. Moreover, it was confirmed that the thickness of the smoke layers in the tunnel thinned out quickly due to the natural ventilation. 相似文献
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国外关于火灾初期烟气在空间内扩散的研究 总被引:1,自引:1,他引:0
分析了火灾燃烧和烟气扩散的机理,介绍了国外对火灾初期烟气扩散的研究,以及Rudiger Detzer博士对疏散通道充烟过程的时间温度曲线所进行的计算验证。通过对购物商场的火灾模化实验,得出小规模、低能释放火灾,可能导致大空间内明显地充满烟气。 相似文献
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为了研究分岔隧道在采取纵向通风排烟系统时各匝道所需临界风速,设计合流型和分流型两种Y 字型分岔隧道。数值模拟设定30 MW 火灾规模,对比Y 字型隧道各匝道的临界风速与单坡坡度隧道临界风速的理论值,并分别对匝道内2 m 和6.2 m 处的纵向温度进行分析。结果表明,对于非着火匝道,当匝道内的临界通风风速与单坡度隧道的理论值相当时,能保证烟气不通过岔口蔓延到该匝道;对于合流型隧道的着火匝道,其临界风速小于单坡度隧道的临界风速理论值;分流型隧道的着火匝道所需临界风速大于同等单坡度隧道的临界风速理论值。 相似文献