在受限和通风防火分区内对燃烧速率特性的试验研究

在核安全研究框架内对在受限和通风防火分区内油池火燃烧速率进行了试验研究。在实体火灾试验基础上，此研究为在受限和通风火灾场景下的燃烧速率机理提供了新的信息。描述了在自由条件和空气受限条件下所进行的试验，对试验装置、仪器以及火源进行了详细叙述。在相同场景（0．4m^2TPH油池火）下，对自由条件和空气受限条件的试验情况下的燃烧速率进行了对比。在空气受限情况下，燃烧速率与时间的变化曲线显示出三个不同阶段：自由条件和受限燃烧速率相同；不稳定阶段，空气受限条件下燃烧速率高于自由条件下的燃烧速率;稳定阶段。从图像分析看，不稳定阶段显示，动荡和间歇火焰大大提高了燃烧速率。介绍了通风速率和油池面积对此现象的影响。试验结果为理解有限区域内燃烧速率提供了新的试验信息。     

变压器油池火非稳态燃烧特性实验研究

为研究变压器油的非稳态燃烧特性,搭建变压器油燃烧实验平台,开展不同油池直径的池火实验,系统分析油池直径对变压器油非稳态燃烧的影响,定性、定量研究不同油池直径对燃烧速率、火焰脉动频率等的影响。结果表明：变压器油池火燃烧过程可以划分为：初期增长阶段、充分发展阶段和衰减阶段。其中充分发展阶段又可以根据燃烧速率的变化特征分为准稳态燃烧阶段和沸腾燃烧阶段。燃烧速率随油池直径的增大而增大。准稳态燃烧阶段中,火焰脉动频率与油池直径呈负相关,油池直径越大,火焰脉动频率越小。     

基于CFD的开放空间油池火燃烧速率和热辐射研究

采用混合组分燃烧模型和有限体积辐射模型,通过液体表面蒸发模型对液态燃料和火羽流进行耦合,建立开放空间油池火模型.利用CFD方法分别对不同直径的庚烷油池火进行模拟,研究其燃烧速率、热释放速率随直径的变化以及火焰中轴上的温度和单位体积热释放速率(HRRPUV)分布,并得出油池表面的热辐射反馈以及油池外部水平和垂直方向的热辐射强度分布规律.部分模拟结果与实验进行对比,验证该模型的适用性和有效性.     

纵向通风下障碍物对隧道火灾燃烧速率的影响研究

采用模型隧道实验的方法,研究不同纵向通风速度和障碍物距离下池火燃烧速率的变化规律。结果表明,在纵向通风的条件下,障碍物的距离为5 cm时池火的燃烧速率最高。在障碍物距离一定时,池火的燃烧速率随纵向通风速度增加而增加。障碍物距离在一定范围内,池火的燃烧速率高于无障碍物的情况,而障碍物距离超出一定范围时,池火燃烧速率与无障碍物的情况相差不大。障碍物的存在对池火燃烧速率的影响主要归因于侧壁辐射效应和气流场的变化。纵向通风对池火燃烧的影响更为明显。当障碍物距离改变时,气流场会改变火焰的倾斜方向,进而改变侧壁辐射效应。这些发现对于深入理解隧道火灾特性、优化消防安全设计以及制定有效的火灾防控措施具有一定的指导意义。     

纵向通风及坡度对隧道池火燃烧速率影响实验研究

采用1∶15的缩尺模型隧道,隧道坡度范围为0～10%,进行纵向通风风速为0～2.5 m/s的乙醇和正庚烷池火实验,研究坡度与通风风速对油池火燃烧状态的影响。油池采用厚度1 mm的不锈钢板打造,边长为8 cm和10 cm。随着纵向通风风速的增加,乙醇池火的燃烧速率先下降后上升,正庚烷池火在水平隧道和坡度为5%的情况下,燃烧速率也呈现先下降后上升的趋势。但在隧道坡度为10%的情况下,正庚烷的燃烧速率单调增加。火焰倾斜角随风速的增大先迅速增加后缓慢增加。     

细水雾熄灭受限空间油池火主导机理分析

通过对细水雾熄灭油池火实验过程中温度场的分析，得出了池火火焰存在核心反应区、通风控制区和燃料控制区。通过对烟气成分和池火燃烧熄灭过程中的能量分析可知，细水雾吸热膨胀、稀释氧气和窒息对熄灭油池火所起的作用非常微弱。细水雾对油池火的作用过程可分为主导机理不同的两个阶段，初期主导机理为气相冷却和衰减热辐射，后期主导机理为表面冷却。     

小尺度环氧丙烷池火燃烧特性研究

为研究低沸点易燃液体池火燃烧特性,以环氧丙烷为燃料,利用自行搭建的小尺度池火燃烧试验平台开展不同直径池火燃烧试验。使用油盘直径分别为12、16、20 cm,通过电子天平、热电偶、辐射热流计、电子摄像机等测量燃料速率、火焰温度、火焰高度、热辐射等特性参数,并结合理论公式分析特征参数随直径变化的规律。结果表明,环氧丙烷池火稳定燃烧速率与油池直径成正比;平均火焰高度试验测量值与理论结果基本一致,在试验工况下约为3.2倍油池直径;火焰轴线平均温度随着高度增加呈现先递增后递减趋势,油池直径越大温度递减趋势越缓慢;通过数据拟合得到在实验工况下热辐射与油池直径的函数关系。     

水浴保护对甲醇池火燃烧速率的影响

试验研究了水浴对不同尺寸甲醇池火燃烧速率的影响.燃烧盘与水浴盆均为正方形.结果:在水浴条件下,在稳定燃烧阶段的池火燃烧速率曲线比较平滑;在快速上升阶段,池火燃烧速率与油池尺寸及有无水浴关系不大;在下降阶段,有水浴的条件下,燃烧时间有所延长;在稳定阶段,有水浴时燃烧速率小于无水浴时,一般不超过10%.     

受限空间正庚烷油池火火焰脉动频率研究

利用光电二极管接收火焰辐射光强,将光信号转换为电信号的原理,研究了受限空间内正庚烷油池火的火焰强度和脉动频率随时间的变化规律。结果表明：在一定的时间内,随着正庚烷油池火点燃后,开始一段时间内,受限空间内氧气充足,油池火燃烧强度迅速增大,当达到一定时间和强度后,由于燃料减少,受限空间内氧气不足,火焰强度开始逐渐减弱;从实验中观察到油池火燃烧前期阶段,火焰并未有波动,当燃烧一段时间后,受限空间内供氧不足,需要外界提供氧气,火焰开始波动,火焰脉动频率迅速增大,最大值达到1.5 Hz 左右,火焰脉动频率与油盘直径的拟合结果为f=1.06 D- 0.5。通过利用低成本的光电二极管实现监测受限空间内油池火火焰脉动频率,有利于受限空间内火灾探测技术发展。     

小尺度变压器油池火灾燃烧特性的实验研究

开展了直径20～50 cm 的圆形变压器油池火实验,分别测量并研究了火焰形态、燃烧速率、火焰轴心温度等燃烧特性。结果表明：在变压器油燃烧的3 个阶段中,稳定燃烧阶段持续时间最长,而衰减熄灭阶段要明显短于起始燃烧阶段。在燃烧速率方面,油池的直径越大,变压器油燃烧速率越快,燃烧时间越短,变压器油的液位下降速度也越快。变压器油的单位面积燃烧速率与经典辐射模型具有良好的一致性,单位面积燃烧速率与油池直径呈现幂函数形式。在火焰温度方面,油池中心线温度呈现距离液面的垂直高度越大其火焰温度越低的趋势,液面上方火焰温度最高可达700～800 ℃,同时油池火尺度对火焰最高温度的影响不大。     

Feuerstätten in Häusern mit mechanischen Lüftungsanlagen ndash; Anforderungen und Lösungen

Burning appliances in buildings with ventilation installation ndash; requirements and solutions. There are permission criteria of the building supervisory board for room air‐independent burning appliances for liquid and solid fuels. With solid fuel burning appliances, these refer to higher tightness requirements, lower CO emissions and the demand of a self‐closing door. When critically analysing the permission criteria, it can be found that the limit values of leakage flow rate and CO emission cause an exchange of air of over 1.5 h^‐1 in a medium size installation area. Intermittently heated storage stoves are favourable for such cases of application because waste gas accumulation in the living space outside of the heating phase of the burning appliances can be diminished by the ventilation system. Special attention has to be put on the combustion air guidance in parallel and concentric air‐waste gas‐systems. On winter conditions, circulation flows arise outside of the operation of the burning appliances if the flow path combustion air guidance / room heater / flue duct is not interrupted by shut off dampers. The consequences are lower deviation of the dew point and dampness formation with appearances of icing in the unheated storey below the roof as well as in the area of the roof and floor breakthrough. Regarding the leak test of installed facilities and their monitoring, requirements and solutions have to be specified.     

A compartment burning rate algorithm for a zone model

A model is presented that dynamically predicts the mass loss rate of fuel in a compartment as a function of ventilation, thermal feedback, fuel type and scale. Without a loss of generality, a floor-based fuel is considered. The effect of ventilation is included in the model through the ambient oxygen concentration in the ambient surrounding the fuel at the floor. A mixing model associated with the inlet airflow at the vent is developed to determine this oxygen concentration. An extinction criterion for the flame is based on a critical flame temperature for a diffusion flame associated with the ambient conditions surrounding the flame at the floor. The model is executed in BRI2002, a zone model, capable of computing species and thermal conditions in the upper and lower compartment gas layers. Computations show good agreement with small-scale compartment data for heptane pool fires. The results can accurately portray many regimes of burning including extinction, combustion oscillations, reduction in the flaming area, and quasi-steady burning.     

城市地下空间的自然光环境营造

在地下建筑中,自然采光可增加空间的开敞感,改善通风效果,并在视觉心理上大大减少地下空间所带来的封闭单调、方向不明、与世隔绝等负面影响.该文从被动式采光法和主动式采光法两方面,阐述了地下空间利用自然光线的技术手段,希望尽可能多地将自然光线引入地下,从而充分满足工作、生活在地下空间的人们对自然的渴望.     

Assessment of the Burning Rate of Liquid Fuels in Confined and Mechanically-Ventilated Compartments using a Well-Stirred Reactor Approach

The objective of this work is to provide a ‘support tool’ to assess the burning rate of a pool fire in a well-confined and mechanically-ventilated room using a single-zone model based on conservation equations for mass, energy and oxygen concentration. Such configurations are particularly relevant for nuclear facilities where compartments are generally sealed from one another and connected through a ventilation network. The burning rates are substantially affected by the dynamic interaction between the fuel mass loss rate and the rate of air supplied by mechanical ventilation. The fuel mass loss rate is controlled by (i) the amount of oxygen available in the room (i.e. vitiation oxygen effect) and (ii) the thermal enhancement via radiative feedback from the hot gas to the fuel surface. The steady-state burning rate is determined by the ‘interplay’ and balance between the limiting effect of oxygen vitiation and the enhancing effect of radiative feedback. An extensive sensitivity study over a wide range of fuel areas and mechanical ventilation rates shows that a maximum burning rate may be obtained. For the studied HTP (Hydrogenated Tetra-Propylene) pool fires, the maximum burning rate is up to 1.75 times the burning rate in open air conditions.     

An experimental study on the effect of ventilation velocity on burning rate in tunnel fires—heptane pool fire case

The 1/20 reduced-scale experiments using Froude scaling are conducted to investigate the effect of longitudinal ventilation velocity on the burning rate in tunnel fires. The n-heptane pool fires with heat release rate ranging from 3.71 to 15.6 kW are used in this study. A load cell is used to measure the mass loss rate of burning fuel and the temperature distributions are measured by K-type thermocouples in order to investigate smoke movement. The ventilation velocity in the reduced-scale tunnel is controlled by the wind tunnel through an inverter. The increases in ventilation velocity lead to enhance burning rate of n-heptane fuel. The reason is that the oxygen supply effect prevails rather than the cooling effect as the ventilation velocity increases. As a result, the heat release rates in experiment are larger than constant heat release rates by 4.45–11.3 times in the n-heptane pool fires. Also, it is found that non-dimensional critical ventilation velocity is proportional to one-third power of non-dimensional heat release rate.     

Wind tunnel experiments on wind-induced natural ventilation rate in residential basements with areaway space

In residential building design, areaways can act as an open subsurface space to help improve the living environment in adjacent basements for residential purposes, mainly by wind-induced natural ventilation. The accurate prediction of effective air change rate is quite important; nevertheless so far little is known about this kind of ventilation issue. In order to acquire more knowledge in this field and make accurate ventilation predictions, direct measurement of ventilation rate was performed in this study using small-scale wind tunnel models. In the experiment, considering ventilation induced only by the exterior wind, we applied the constant tracer gas flow technique to measure the time-averaged ventilation rate for nine wind directions for each case. Furthermore, the relationships between the ventilation rate and a variety of parameters including wind direction, opening type, plan area of the areaway space and building coverage ratio, etc. were investigated and analyzed in detail. The findings of the present study can provide fundamental data for the design of areaway space in the urban residential buildings.     

Critical velocity and burning rate in pool fire during longitudinal ventilation

Since the prediction of ‘critical velocity’ is important to control the smoke in tunnel fires, many researches have been carried out to predict critical velocity with various fire sizes, tunnel shape, tunnel slope, and so forth. But few researches have been conducted to estimate critical ventilation velocity for varied burning rate by longitudinal ventilation, although burning rate of fuel is influenced by ventilation conditions. Therefore, there is a need to investigate the difference of upstream smoke layer (e.g., backlayering) between naturally ventilated heat release rate and varied heat release rate by longitudinal ventilation.In this study, the 1/20 reduced-scale experiments using Froude scaling are conducted to examine the difference of backlayering between naturally ventilated heat release rate and varied heat release rate by longitudinal ventilation. And the experimental results obtained are compared with numerical ones. Three-dimensional simulations of smoke flow in the tunnel fire with the measured burning rates have been carried out using Fire Dynamics Simulator; Ver. 406 code, which is developed by National Institute of Standards and Technology. They show a good degree of agreement, even if some deviation in temperature downstream of the fire is evident. Since ventilation velocity had a greater enhancing effect on the burning rate of fuel due to oxygen supply effect, the critical ventilation velocity should be calculated on the basis of varied HRR by ventilation velocity.     

Simulating the effects of fuel type and geometry on post-flashover fire temperatures

This paper discusses the effect of fuel type and geometry on predicted compartment temperatures derived from computer modelling of post-flashover compartment fires. Many previous studies have investigated post-flashover fires with either wood crib or liquid pool fuels, but very few analytical or experimental studies have considered realistic wood-based fuels with different ratios of surface area to volume, combined with plastic-based fuels. A simple single zone fire model was used to calculate the temperatures in post-flashover compartment fires. The program includes a catalogue of furniture items, each with fuel mass loss rate evaluated on the basis of a constant regression rate on all exposed surfaces. The program also includes a pool-burning model and considers wood fuels and thermoplastic fuels burning together inside a compartment. Use of the model shows that the total fuels load alone is not sufficient to characterise a post-flashover fire. The fire temperature is highly dependent on the fuel type and geometry. For given ventilation and total fuel load, the resulting temperature depends greatly on the average thickness of the wood fuels and the presence of thermoplastic fuels. The ratio of the available fuel surface area to the ventilation opening is particularly important. Several fire scenarios involving different fuel types and characteristics are simulated and compared with Eurocode parametric fires.     

Heat feedback to the fuel surface of a pool fire in an enclosure

As a part of an effort to determine the energy balance at the pool fire surface in compartments, a series of fire experiments were conducted to study heat flux of the flame in a vitiated environment formed with air and combustion products gases. This paper presents experimental results of the burning behaviour of a heptane pool fire in a reduced scale compartment equipped with a mechanical ventilation network. Measurements of heat fluxes, fuel mass loss rate, oxygen concentration and temperature are performed for heptane fires of 0.26 and 0.3 m diameter pans at different ventilation flow rates. An original method to separate effects of the radiant heat flux of the flame and of the external heat feedback to the fuel surface is developed. This was achieved by using an additional heat flux measurement located under the pool fire. A correlation was also developed to determine the temperature rise on the plume centerline in the compartment as a function of the heat release rate. The results indicate a decrease in the fuel mass loss rate, flame temperature and heat fluxes to the fuel surface as the oxygen concentration measured near the fuel decreases by varying the air refresh rate of the compartment. The flame radiation fraction shows a similar behaviour, whereas the convective fraction of the flame heat flux increases when oxygen concentration decreases. Based on these experimental findings, it was discussed that any classification of the burning regime of a pool fire should consider both the effects of pan diameter and the burning response to vitiated air.