Measuring rate of heat release by oxygen consumption

This paper provides a comprehensive set of equations and guidelines to determine the rate of heat release in full-scale fire tests based on the O₂ consumption principle. The approach is different from other investigators as the enphasis is on full-scale fire test applications and the use of volumetric flow rates is avoided. Some general equations for flow rate (i.e., applicable irrespective of the configuration of the gas analysis system) are described first. In subsequent sections, distinctions are made between various gas analyzer combinations to derive the equations for rate of heat release. Procedures to calculate net rate of heat release from a specimen exposed to a gas burner or wood crib ignition source are also given. A summary at the end of the paper lists step by step procedures for all cases covered.     

Eulerian-Lagrangian model for traffic dynamics and its impact on operational ventilation of road tunnels

This contribution deals with a computational Eulerian-Lagrangian model that simulates movement of cars inside a road tunnel and its impact on operational ventilation. The model simulates moving cars as discrete objects that “fly” through the tunnel. The objects are treated with a Lagrangian momentum equation and their velocity is solved along their trajectories that are determined by the shape of the roadway. The flow of the ambient air is solved with a commercial CFD code StarCD. Due to drag force, the cars virtually change their velocity, but the latter is continuously re-set to its original value. The momentum equation for the continuous phase contains an additional source term that results from the net efflux of momentum of cars when they enter and leave a particular control volume of the solution domain. The model by Jicha et al. (Int. J. Environ. Monit. Asses. 65 (2000) 343) can simulate cars moving at different speeds and traffic rates in individual traffic lanes. As a result we obtain flow rate generated by moving vehicles as a function of traffic speed and traffic rates. Turbulence was modelled using standard k-ε model with three different formulas for extra sources of the kinetic energy of turbulence that account for additional turbulence generated by moving vehicles. The traffic-induced turbulence shows a non-negligible effect on the total flow rate inside the tunnel. The model was validated with experimental data from Chen et al. (Int. J. Wind Eng. Ind. Aerod. 73 (1998) 99), where the small-scale tunnel 1:20 was investigated. The experiments were carried out with a moving belt carrying small car-like objects. The tunnel length was 20 m, the height 36.5 cm and the tunnel had two parallel lanes. Several traffic densities and speeds were simulated, namely 10,000, 20,000 and 30,000 cars/h per lane with speeds of 20 km/h and 40 km/h.     

On the significance of transient heat release rate excursions above a set limit

When a heat release rate limit for a consumer product is set by a regulatory agency, it is of interest to know whether small excursions above that limit, such as may occur due to production line variability, represent a disproportionate increase in fire hazard. This paper presents a methodology to examine this issue. The heat release rate curve of the object is described by a Gaussian time variation; a perturbation peak, also Gaussian, is added to this main peak. The impacts of the perturbation peak on the build up of hazardous conditions in a room fire (where the object is the only item burning) and on the threat of ignition of secondary items are examined. For the peak heat release rate domain studied here, only the ignition threat is significantly affected by the perturbation peak. The results quantify the trade-off between the height of the perturbation peak and its duration for a fixed percentage of increase in the room area threatened by secondary object ignition. The results show that the increased threat is of the same order as the relative perturbation in heat release rate.     

倾斜隧道内可燃液体连续泄漏漫流特征及其潜在火灾热释放速率试验研究

摘 要：为研究倾斜隧道内可燃液体泄漏漫流引发的潜在火灾危险性,建立了双向坡度可调试验平台,对连续泄漏漫流形态、宽度、面积等特征随隧道坡度的变化规律进行了试验研究;同时开展火灾试验,研究燃料厚度对热释放速率的影响。结果表明：当隧道仅存在纵坡时,随着坡度的增加,液体漫流宽度及面积缩小;当同时存在横坡和纵坡时,液体流向隧道侧墙,漫流长度及面积缩小。液体漫流平均厚度为2 mm,该厚度下可燃液体热释放速率为经典模型计算值的30%~50%。结合上述试验研究,可对隧道内可燃液体连续泄漏漫流潜在火灾热释放速率进行估算。研究结果表明：隧道横坡由1%增加至2%,液体漫流面积可减少约50%,大幅降低潜在的热释放速率。     

Innovative experimental reduced scale model of road tunnel equipped with realistic longitudinal ventilation system

Road tunnels require ventilation system for different reasons in order to provide a good level of safety and effectiveness in ordinary service and, in case of fire, to prevent the upstream smoke flow (back-layering phenomena). To evaluate the ventilation system, full scale experiments are more expensive both in terms of the costs and time, and the CFD model has high uncertainty without experimental validation. In this paper the authors have made and characterized experimentally a reduced scale impulsive jet fan in order to carry out a scaled longitudinal road tunnel subsection equipped with a realistic ventilation system. This innovative reduced scale model of road tunnel could give more relevant information such as phenomenology and performance of full-scale tunnel using suitable similarity rules. It could be useful to do parametrical studies or to focus on particular physical aspects (i.e. smoke pattern of thermal plume behavior with respect to usual experimental sections reported in literature). The innovative reduced scale model presented in this paper can provide a useful alternative method with respect to the full-scale experiments.Moreover, the authors have simulated numerically, by means the CFD commercial software FLUENT®, the scaled road tunnel and have compared experimental and numerical results in terms of axial velocity.     

Effect of cross section and ventilation on heat release rates in tunnel fires

Model scale fire tests were performed in tunnels with varying tunnel widths and heights in order to study the effect of tunnel cross-section and ventilation velocity on the heat release rate (HRR) for both liquid pool fires and solid fuel fires. The results showed that for well ventilated heptane pool fires, the tunnel width nearly has no influence on the HRR whilst a lower tunnel height clearly increases the HRR. For well ventilated solid fuel fires, the HRR increases by approximately 25% relative to a free burn test but the HRR is not sensitive to either tunnel width, tunnel height or ventilation velocity. For solid fuel fires that were not well ventilated, the HRRs could be less than those in free burn laboratory tests. In the case of ventilation controlled fires the HRRs approximately lie at the same level as for cases with natural ventilation.     

风速对航空煤油池火热释放速率的影响

利用全尺寸多功能热释放速率综合实验平台,增加环境风速调节与控制模块,在不同环境风速的条件下进行航空煤油的油池火燃烧特性实验研究,实验所用圆形油盘的直径分别为0.2、0.34、0.5m,风速为0～3.78m/s。实验结果表明:热释放速率与风速影响因子之间存在较明显的函数关系。提出圆盘油池火燃烧热释放速率的表面风速影响因子,并给出了二者的函数关系。     

非稳态火源热释放速率在火灾网络模型中的应用

详细分析了目前常用的非稳态火源热释放速率计算式,并对其特点和参数范围进行了对比讨论;将各种非稳态火源热释放速率计算式嵌入建筑物火灾烟流性状预测软件并进行了算例验证。结果表明,加入非稳态火源的烟流性状预测软件计算结果与日本同类成功软件的计算结果吻合得很好,且曲线走势更平滑,并减轻了输入的工作量。结果证实了对烟流性状预测软件火源部分的改进是成功的。     

Estimation of chemical heat release rate in rack storage fires based on flame volume

Quantification of heat release rate is crucial to many fire research works. Under certain conditions, such as very large fires and fire tests with sprinklers, measurements of fire heat release rate can be a challenging problem. This study attempted to develop a methodology of estimating chemical heat release rate using flame volume. This method is based on the theory that heat release rate per unit flame volume is relatively invariant, as long as the combustion is controlled by diffusion in buoyant fires under well-ventilated conditions. Test data were examined from a variety of fire experimental conditions to evaluate the proposed method. The results demonstrate that the flame-volume based method can provide reasonable estimation of heat release rate compared to oxygen-consumption based method.     

超大断面水平隧道纵向通风临界风速CFD分析

首先介绍了临界风速研究的基本思路及国内外主要研究成果.结合国内某长大公路隧道设计,建立一长300m、水力高度10.64m的水平隧道模型,通过CFD模拟确定超大断面隧道临界风速的影响因子及相应的准则关联式.模拟表明:与火灾热释放速率相比,环境温度的影响可以忽略不计;与Atkinson(模型试验)及Buxton(大尺度试验)相似,临界风速随热释放速率的变化分为两个区域,与低热释放速率时不同,一旦热释放速率超过40MW,临界风速的变化明显趋于缓慢.     

单体燃烧热释放测试影响因素的探讨

GB/T 20284-2006《建筑材料或制品的单体燃烧试验》是评定建筑材料及制品燃烧性能等级的重要测试方法。通过阐释燃烧热释放测试原理及计算公式,描述设备选型和日常校准核查的重要性,并基于试验数据说明试样安装对检测结果的影响。     

Predicting the structural response of a compartment fire using full-field heat transfer measurements

Inverse heat transfer analysis (IHT) was used to measure the full-field heat fluxes on a small scale (0.9 m×0.9 m×0.9 m) stainless steel SS304 compartment exposed to a 100 kW diffusion flame. The measured heat fluxes were then used in a thermo-mechanical finite element model in Abaqus to predict the response of an aluminum 6061-T6 compartment to the same exposure. Coupled measurements of deflection and temperature using Thermographic Digital Image Correlation (TDIC) were obtained of an aluminum compartment tested until collapse. Two convective heat transfer coefficients, h =35 W/m²-K and h =10 W/m²-K were examined for the thermal model using the experimentally measured heat fluxes. Predictions of the thermal and structural response of the same compartment were generated by coupling Fire Dynamics Simulator (FDS) and Abaqus using the two values for h, h =35 W/m²-K and h from convection correlations. Predictions of deflection and temperature using heat fluxes from IHT and FDS with h=35 W/m²-K agreed with experimental measurements along the back wall. The temperature predictions from the IHT-Abaqus model were independent of h, whereas the temperature predictions from the FDS-Abaqus model were dependent on h.     

Effects of a transverse external wind on natural ventilation during fires in shallow urban road tunnels with roof openings

Fire experiments using a 1:12 scale model tunnel were conducted to evaluate effects of a transverse external wind on the performance of roof openings in a shallow urban road tunnel under fire conditions. A particular focus was placed on clarifying the characteristics of the spread of smoke in the tunnel under the condition of a transverse external wind blowing above the roof openings. Two types of median barriers, pillars and walls, were examined as dividing structures in the model tunnel, and the heat release rate was selected as the experimental parameter. The following conclusions were obtained. Compared to conditions with no external transverse wind, in the model tunnel with the pillar median structure, the smoke spreading distance was shortened when the transverse external wind was in the positive direction, and the distance remained the same when the wind was in the negative direction; in the model tunnel with the wall median structure, the smoke spreading distance was shortened when the wind was in the positive direction. Furthermore, the smoke spreading distance in each case was constant and independent of the heat release rate of the fire under the scope of the experimental conditions used in this study.     

Comparison of FDS predictions by different combustion models with measured data for enclosure fires

The performance of mixture fraction models FDS4 and FDS5 is investigated under different global equivalence ratios (GER). Predictions of heat release rate (HRR), upper-layer temperature, and CO yield are compared with measurements considering their sensitivities to the lower limit of fuel, mixing time scale, and turbulence model constants. When using FDS4, the inclusion of an extinction model can result in significant variations in both total and volumetric HRR prediction. When using FDS5, the mixing model constant has significant effects on volumetric HRR prediction. At low GER (<0.23), the prediction of upper-layer temperature shows dependency on both the lower fuel limit and the mixing model constant, but the predicted temperature is always lower than measured temperature, with deviations in excess of 30%. At higher GER (0.53<GER<0.81), the upper-layer temperature prediction shows significant dependency on the mixing model constant but can be over-predicted, with deviations up to 24%. The variations of CO yield prediction with lower fuel limit or with the mixing model constant show an opposite trend to that of upper-layer temperature. Furthermore, the prediction of CO yield shows a much greater dependency on the Smagorinsky constant and on the turbulent Schmidt number than do those of HRR and upper-layer temperature.     

阻塞效应下隧道火灾顶棚最高温度的实验分析

隧道火灾时拱顶最高烟气温度的预测对于隧道防火安全设计具有很重要的意义。通过1/10隧道火灾缩尺模型实验得到了不同火源热释放率、不同通风速度下隧道顶棚最高温度测试值,并与现有的温度模型预测值进行了对比,发现现有模型对于无风及风速较小的情况,或多或少存在缺陷。另外在实际情况中车辆通常占据一部分的隧道断面积,所形成的阻塞效应不可忽略。为此,进行了不同阻塞比情况下的实验,发现现有的温度模型与不同阻塞比下的实验数据相差较大。最后,基于本文实验数据对Kurioka温度模型进行了修正,所提出的修正模型与已有的其他实验数据吻合也较好。     

木垛暴露面积与其热释放速率关系的研究

介绍木垛暴露面积计算公式,计算了试验条件中木垛的暴露面积;利用ISO 9705标准试验房间火试验测试了木垛的热释放速率峰值、达到热释放速率峰值的时间和达到峰值前的热释放速率平均值;用线性拟合的方法分析木垛暴露面积与热释放速率值之间的关系,得到了拟合系数及拟合相关系数;利用线性拟合公式预测了在已知木垛暴露面积的条件下,木垛的热释放速率值,并与试验值进行了比较分析。     

Statistical characterization of the time to reach peak heat release rate for nuclear power plant electrical enclosure fires

Since publication of NUREG/CR-6850 (EPRI 1011989), EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities in 2005, phenomenological modeling of fire growth to peak heat release rate (HRR) for electrical enclosure fires in nuclear power plant probabilistic risk assessment (PRA) has typically assumed an average 12-min rise time [1]. One previous analysis using the data from NUREG/CR-6850 from which this estimate derived indicated this could be represented by a gamma distribution with alpha (shape) and beta (scale) parameters of 8.66 and 1.31, respectively [2]. Completion of the test program by the US Nuclear Regulatory Commission (USNRC) for electrical enclosure heat release rates, documented in NUREG/CR-7197, Heat Release Rates of Electrical Enclosure Fires (HELEN-FIRE) in 2016, has provided substantially more data from which to characterize this growth time to peak HRR [3]. From these, the author develops probabilistic distributions that enhance the original NUREG/CR-6850 results for both qualified and unqualified cables.² The mean times to peak HRR are 13.3 and 10.1 min, respectively, with a mean of 12.4 min when all data are combined, confirming that the original NUREG/CR-6850 estimate of 12 min was quite reasonable.Via statistical-probabilistic analysis, the author shows that the time to peak HRR for qualified and unqualified cables can again be well represented by gamma distributions with alpha and beta parameters of 1.88 and 7.07, and 3.86 and 2.62, respectively. Working with the gamma distribution for All cables given the two cable types, the author performs simulations demonstrating that non-suppression probabilities, on average, are 30% and 10% higher than the use of a 12-min point estimate when the fire is assumed to be detected at its start and halfway between its start and the time it reaches its peak, respectively. This suggests that adopting a probabilistic approach enables more realistic modeling of this particular fire phenomenon (growth time).     

Characteristics of smoke extraction by natural ventilation during a fire in a shallow urban road tunnel with roof openings

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.     

水压对盾构管片衬砌力学特征与破坏形态的影响模型试验研究

水压力作为一个重要因素,对盾构隧道管片衬砌结构的受力状态及长期安全性具有显著的影响。文中依托广深港客运专线狮子洋盾构隧道工程,采用模型试验的方法,比较分析了0m、30m、60m三种不同水压条件下管片衬砌结构的内力、变形、声发射数据及裂纹产生发展等试验数据信息,探讨水压对盾构隧道管片衬砌结构受力状态及破坏特征的影响规律。研究结果表明：在一定范围内,水压的增加,延长了管片衬砌结构的弹性受力阶段及塑性发展平台,延缓了结构内部出现损伤破坏的时间,提高了衬砌结构的极限载能力。随着水压的增加,管片临界失稳点的最大位移与隧道外半径之比由2.33%增大到2.77%,但是由局部损伤破坏出现到管片衬砌结构整体失稳的过程变得更短,发展速度变得更快,管片的主要破坏形式由以受拉破坏为主变为以压剪破坏为主。