The maximum temperature of buoyancy-driven smoke flow beneath the ceiling in tunnel fires

In order to detect a fire and provide adequate fire protection to a tunnel structure, the maximum gas temperature beneath the ceiling to which the structure is exposed needs to be estimated. Theoretical analysis of maximum gas temperature beneath a tunnel ceiling based on a plume theory is given. The heat release rate, longitudinal ventilation velocity and tunnel geometry are taken into account. Two series of model-scale experimental tests were also carried out. The results of both analysis and experiments show that the maximum excess gas temperature beneath the ceiling can be divided into two regions. When the dimensionless ventilation velocity is greater than 0.19, the maximum excess gas temperature beneath the tunnel ceiling increases linearly with the heat release rate and decreases linearly with the longitudinal ventilation velocity. When the dimensionless ventilation velocity is less than 0.19, the maximum excess gas temperature beneath the ceiling varies as the two-thirds power of the dimensionless heat release rate, independent of the longitudinal ventilation velocity. In both regions, the maximum excess gas temperature varies as the −5/3 power of the vertical distance between the fire source bottom and tunnel ceiling. The investigation presented here considers only the cases when the continuous flame region is lower than the ceiling height.     

大空间建筑喷淋对烟气层的影响

采用PHOENICS软件，研究了大空间建筑水喷淋对烟气控制系统的影响。未考虑燃烧过程以及喷淋对燃烧的影响。采用紊流k-ε双方程模型模拟烟气的运动，用Lagrangian方法模拟热烟气与喷淋水之间相互作用的动能和换热。用具有不同初始速度和直径的液滴来模拟喷淋水。探讨了喷淋流量、喷射角、水滴直径对烟气层的影响。     

A mathematical model on interaction of smoke layer with sprinkler spray

A mathematical model was developed for predicting the downward descending behavior of the buoyant smoke layer under sprinkler spray. The behavior of the smoke layer was determined by considering the interaction between the drag force of the sprinkler spray and the buoyancy force of the hot smoke layer itself in the spray region. The smoke layer may be pulled down with its thickness increased at the center of the spray region due to the cooling and drag effects of the sprinkler spray, thus to form a downward “smoke logging” plume. In the mathematical model developed in this paper, the critical condition under which the smoke layer lost its stability, as a serious concern, was predicted. Additionally, the length of the downward plume, which was rarely investigated before, was also further calculated. Full-scale experiments were carried out to validate the model. Results showed that the predictions, including the critical condition and the length of the plume, by the mathematical model agreed well with that observed and measured in the experiments. The length of the downward plume was shown to increase with the sprinkler operating pressure by an approximately linear correlation.     

喷淋的冷却作用对自然排烟影响的实验研究

通过实验.研究了火源功率一定的情况下,喷淋的冷却作用对自然排烟造成的影响.针对喷淋前后烟气层温度和自然排烟速度进行了分析,结果表明,喷淋的冷却作用会对烟气层温度、自然排烟速度产生较大的影响,对建筑工程进行自然排烟设计时要充分考虑喷淋对排烟的影响.     

The influence of a perforated false ceiling on the performance of smoke ventilation systems

Perforated false ceilings ougth not to interfere appreciably with the flows of hot smoky gases from a fire to smoke ventilation openings above the false ceiling. The Fire Research Station currently recommends that such false ceilings should have a minimum free area of 25 percent.

An experiment using a 1/10th scale model of a single-level enclosed shopping mall has examined the performance of five perforated false ceilings having different percentages of free area. For both powered and natural venting, it was found that minimum free areas of between 30 and 10 percent could be used depending on the depths of the shop fascia below the false ceiling, and on whether the shops were open- or glass-fronted. The previously recommended minimum of 25 percent has been confirmed as a generally useful ‘rule of thumb’ value for allowing safe escape, even though cool smoke can be expected to affect some nearby shops under some circumstances.     

关于装设网格、栅板类通透性吊顶场所闭式喷头设置的探讨

近年来 ,闭式自动喷水灭火系统在我国被广泛应用于建筑火灾的扑救和控制 ,成为建筑消防设施中最普遍、最重要的一种灭火系统 ,本文从闭式喷头布设位置的角度分析了闭式喷头在通透性吊顶部位安装存在的问题 ,提出了相应的解决方法     

Experimental studies on fire-induced buoyant smoke temperature distribution along tunnel ceiling

Twelve tests were conducted to study the distribution of smoke temperature along the tunnel ceiling in the one-dimensional spreading phase, two tests in a large-scale tunnel and the other ten in full scale vehicular tunnels. The fire size and the height above the floor, the tunnel section geometry and longitudinal ventilation velocity varied in these tests. Experimental results showed that when the fire size was larger, the smoke temperature below the ceiling was higher, but it decayed faster while traveling down the tunnel. The longitudinal ventilation velocity seemed to take much influence on the smoke temperature decay speed downstream. A “barrier effect” was shown for the smoke temperature distribution of the upstream back layering. The smoke temperatures measured were higher upstream than downstream before the “barrier”, and were much lower and decreased faster along the tunnel ceiling after the “barrier”. The temperature and the traveling velocity of the upstream smoke flow decreased largely when the longitudinal ventilation velocity increased a bit. The dimensionless excess smoke temperature distributions along the tunnel ceiling in all tests fell into good exponential decay. But the decay speed along the tunnel seemed to be much larger in the large-scale tunnel than that in full-scale tunnels. The measured data on ceiling jet temperature decay along the tunnel was compared with predictions of Delichatsios's model, a model built based on small-scale tests, with hydraulic diameter introduced. Results showed that Delichatsisos’ model over estimated the decay speed of ceiling jet temperature for the downstream flow. However, good agreement was achieved between the measured data and the model predictions for the upstream back layering. All the experimental data presented in this paper can be further applied for verification of numerical models, bench-scale results and building new models on ceiling jet temperature distribution.     

On the evaporation effect of a sprinkler water spray

A crude model for estimating the evaporation heat loss due to a sprinkler water spray in a smoke layer is reported. It is found that the evaporation heat loss lies below 11.2% of the convective loss when water travels through a hot gas layer 0.9 m thick and 160°C under normal sprinkler operating conditions. It is also found that the value may go up to 26% if the smoke layer reaches 1.5 m and 273°C.     

高净空场所洒水喷头动作性能的数值研究

采用数学计算的方法对高净空场所实体火灾羽流流场进行定量分析.在确定空间高度、灭火系统参数以及火灾发展过程的条件下,基于喷头热响应性能理论,通过数值计算研究高净空场所自动喷水灭火系统第一只喷头的动作性能.结果表明:流场对流热释放速率和喷头动作时间的计算值与试验值基本一致,计算模型合理可靠,但针对不同火灾模型计算模型中的经验参数仍有待进一步修正.     

在装有水喷淋的商场和中庭中开展烟气运动的研究

加拿大国家研究院建筑研究所 (IRC)和美国供热、制冷空调工程协会 (ASHRAE)联合对装有水喷淋的商场和中庭中火灾状态下的烟气运动进行了研究 ,研究的结果最终将提高顾客的安全。这个研究项目表明 ,建筑中的水喷淋系统可以使烟气冷却并向下流动 ,这将影响建筑中人员的安全疏散。但是研究的结果也表明 ,最初的烟气是热的 ,向上直冲通道的顶棚 ,在那里可被排烟系统排除。为了进行这项工作 ,研究组建立了大空间试验装置以模拟一些特殊的区域 :购物中心二层的出口和人行通道的一部分。北美的火灾统计表明 ,将近 90 %的情况下 ,4个或更少的喷…     

格栅式吊顶场所点型感烟火灾探测器安装技术研究

通过公安部消防局项目"格栅式吊顶场所火灾探测设计安装技术研究"的研究工作,描述了在不同格栅或不同镂空比格栅条件下,探测器的安装方式、安装部位及探测效果,最终形成了格栅式吊顶场所点型感烟探测器的设计安装准则,为我国相关规范的制(修)订提供借鉴和参考依据。     

The effect of false ceiling on the cooling capacity of passive chilled beams

Passive chilled beams are often used to provide cooling or additional cooling when the ventilation system cannot cope with the whole cooling load. The advantage of passive cooling is that it is a silent cooling. Often the chilled beams are installed above a false ceiling and thereby the room is subdivided into two compartments. From the chilled beam a plume is generated. Make-up air (return air) needs to flow into the upper compartment to substitute the airflow generated by the chilled beam. Therefore openings for this purpose are installed in the false ceiling. Small openings constitute a resistance to the flow and the locations of the openings affect the flow pattern. The overall performance was studied in a mock-up of a real office by changing both the size and position of the openings for the make-up air. A uniform heating source was arranged by covering the floor with a heating foil. The best location and size of the openings were explored by both recording the heat absorbed by the beam and the temperature in the room. Minimum temperature attained in the room is the signature of the most efficient cooling. To achieve efficient cooling with a uniform floor-based heating source, two conditions must be fulfilled: a) the return opening area must be at least equal to the horizontal area of the chilled beam; b) the return air openings must be located at the perimeter of the room.     

顶棚抹灰层脱落事故分析及处理

结合具体工程实例,介绍了顶棚抹灰层脱落事故的情况,对事故产生的原因进行了分析,并针对性地提出了具体的处理措施,得出了采用措施返工至今情况良好的结论,从而完善了建筑物顶棚抹灰施工工艺.     

Velocity pressure effect on sprinkler system discharge

After conducting a series of sprinkler discharge tests, the authors concluded that the use of velocity pressure in sprinkler system calculations will give a false picture of the ability of the system. Note: Mr. Kirkman is a registered Professional Engineer and a practicing consulting engineer. Mr. Campbell is Vice President and Chief Engineer of The Reliable Automatic Sprinkler Company.     

挡烟垂壁与排烟口设置对烟气层高度的影响

通过N百分比法,理论计算得到了挡烟垂壁与排烟口设置对商业建筑内相邻防火分区烟气层高度变化的影响.分析结果发现,挡烟垂壁凸出越多,烟气层下降速率更为缓慢,后期烟气层高度越高;排烟口距离火源越近,后期烟气层高度越高;排烟口朝向对烟气层高度的变化影响不大.     

底部残余淤泥层对围堰稳定性的影响研究

以某围海造陆工程围堰为研究对象,建立了三维数值模型,分析了淤泥层存在对围堰稳定性的影响,研究结果表明,底部残留淤泥层的存在使得围堰与地基的变形出现了明显的不协调;存在底部淤泥层的围堰横向变形明显较大,围堰有整体滑动破坏的趋势;底部残留淤泥的围堰坡脚变形随上覆荷载增大而增长的速率要明显高于底部无淤泥的围堰。     

自动喷水灭火系统对环境的影响

1执行摘要当前,人们提高可持续发展能力及减少生活碳排放的努力,主要通过提高房屋的能源效率和减少潜在碳排放量来实现。最近,一种新的计算方式应运而生。它扩展了生活碳排放的评估范围,加入了诸如火灾之类的风险因素。这种方法表明,对于不同用途的建筑,无论是民居住宅、写字楼,还是高危险性厂房,如果没有适当风险管理和有效的消防设备,例如自动喷水灭火系统,统计碳排放量就会在建筑的生命周期期间增加。     

模型车厢内火灾烟气层运动模拟分析

旅客列车车厢内发生火灾时，火灾烟气的运动状况直接影响旅客的人身安全，往往造成重大的人员伤亡和巨大的财产损失。采用模型实验、数值模拟的方法对运行的旅客列车经过隧道发生火灾时车厢内烟气层高度的特征进行了研究，将旅客列车卧铺车厢处理为多个受限空间的组合，研究了车厢内烟气层高度在开口不同状况下的变化规律。模型实验与数值模拟相结合为列车车厢火灾研究提供了理论分析模型和实验研究方法，研究成果为车厢防火设计提供了重要的技术依据。