Interaction effects of wind-blown flames from wood crib fires

In the past, the authors and their colleagues have studied the effects of wind-blown flames involving burning gases and liquid pool fires. It would seem logical to conduct a similar study with solid fuels. This the authors have done, and they report their observations here.     

Scale modeling of quasi-steady wood crib fires in enclosures

A scale modeling hypothesis for quasi-steady enclosure fires has been experimentally evaluated. The scheme utilizes geometric similarity and freeburn behavior of the source fuel to scale the source fuel element and the enclosure walls from one scale to another. The burning rate, gas and wall temperature rise, combustion product concentrations and radiative heat flux were measured in full, half and quarter-scale enclosures using wood cribs as the fuel. The good agreement of reduced data among different size enclosures strongly supported the modeling hypothesis. Relatively large scatters were observed with combustion product concentrations and radiative heat flux. In general, the scatters for the measured burning rate and gas and wall temperature rise in enclosure fires were within those observed in freeburn crib fires. The experimental results established that the modeling scheme can be used for predicting the burning rate and room environment in enclosure fires.     

细水雾与固体木垛火相互作用的实验研究

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。     

改性干水灭火剂灭木垛火试验研究

新型干水灭火剂因其高含水量和特殊核壳结构,具有良好的灭火效果。为探究干水对木垛火的灭火效果,自行制备磷酸二氢铵改性干水并开展小尺寸木垛火灭火试验。结果表明：干水灭火剂能够扑灭小尺寸木垛火且不发生复燃,改性干水的控火时间仅为8 s,控火过程中火焰高度持续快速下降,而干粉灭火剂的控火时间则为20 s,喷撒结束39 s后发生复燃;改性干水对火焰区及木垛的温度抑制效果均优于干粉灭火剂,控火时间内,改性干水作用下木垛表面的平均温降速率高达17.00℃/s,是干粉灭火剂作用下平均温降速率的1.94倍;改性干水能够有效降低木垛内部温度,在喷撒50 s内,木垛中心的平均温降速率为8.78℃/s,而干粉灭火剂缺乏冷却作用,木垛中心的平均温降速率仅为6.10℃/s,无法有效抑制阴燃。     

基于小尺寸抛沙装备的灭木垛火研究

基于小尺寸抛沙装备研究沙灭标准1-A 木垛火的灭火效果,利用K 型铠装热电偶、红外热成像仪等仪器测量抛沙灭火前后木垛火的变化特征。结果表明,抛撒沙料能有效抑制木垛表面明火,灭火初期木垛上方火焰被压制,抛沙灭火30 s 时木垛表面明火消失。沙料冲击下木垛不同位置的温度变化存在明显差异,温度下降幅度为：迎沙面最大、侧沙面次之、中心线最差。     

Heat of combustion in spreading wood crib fires with application to ceiling jets

Responding to a challenge raised with respect to a 1989 revision of a 1979 paper on the ceiling jet of t-squared fires, we have measured the heat of combustion in the growth phase of wood cribs made of sugar pine, the test fuel in the original work, needed to generalize the ceiling jet measurements to any combustible. The present determination of the chemical heat of combustion in the growth phase, 14.1 kJ/g, is a little higher than adopted in 1989 (12.5 kJ/g, from wood sample burning with diffusion flame) but still considerably lower than employed in 1979 (20.9 kJ/g, from oxygen bomb calorimetry). More importantly, the convective heat of combustion was measured as 11.5 kJ/g, which has been employed to update the ceiling jet equations for temperature and velocity in t-squared fires. An explanation is offered for the varying, and often higher than expected ceiling-level temperatures measured with thermocouples directly over the fire in the original experiments, suggesting that both plume lean and thermocouple insertion depth may have affected the indicated temperature.     

气力输送水泥粉体装置灭木垛火试验研究

为了研究水泥粉体扑灭木垛火灾的可行性,通过自行设计的气力输送水泥粉体装置开展木垛火的灭火试验研究,利用温度采集装置和摄像机等仪器测试水泥粉体灭火前后木垛火的变化规律.结果表明,气力输送水泥粉体能有效抑制木垛表面明火,显著降低木垛火的燃烧温度,其中水泥粉体主要通过堆积覆盖作用进行灭火,而过大的木垛高度和孔隙率对水泥粉体灭...     

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。     

基于ISO9705房间木垛火试验的FDS模拟预测研究

为了验证FDS模拟的有效性和可靠性,在ISO 9705试验房间内进行一定荷载的木垛火试验.利用火灾动力学模拟软件FDS针对同样的火灾场景进行模拟计算,比较不同网格配置对模拟结果的影响.结果表明:Multi-block 格点配置是最佳的格点配置形式,其模拟得到的木垛火热释放速率变化、烟气温度变化、CO2 体积分数变化的结果能够很好地与实测值吻合,但对CO体积分数不能准确模拟;Multi-block能够在不降低计算精度的前提下,降低格点数目,减少计算时间,节约计算成本.     

浅谈现浇井圈（梯形）施工技术

结合具体工程实例，介绍了现浇井圈（梯形）的施工技术方案及主要的技术参数，并对施工效果进行了检查，得出了平整度满足要求的结论，文中所述具体工艺可供类似工程借鉴。     

Modeling of dust air flames

This study analyzes a premixed dust–air flame, under conditions where a homogeneous gas-phase reaction front can exist. Discussion on four possible flame types is provided. A solution is obtained for the burning velocity of a flammable dust–air flame in both fuel and oxygen limiting cases. A sensitivity analysis is used to analyze the features controlling the dust burning. It is shown that vaporization is significant for fuel limiting conditions; however, does not play a major role in oxygen limiting cases. The calculated burning velocity shows good agreement with available experimental data for coal–dust–air flames.     

Investigation of the effect of tunnel ventilation on crib fires through small-scale experiments

This paper adopts a series of 1:20 scale tunnel experiments based on a series of large-scale tunnel experiments to study the influence of forced ventilation on fires. The small-scale tunnel has dimensions of 0.365 m (W)×0.26 m (H)×11.9 m (L). Cribs using a wood-based material provide the fuel source and forced ventilation velocities from 0.23 to 1.90 m/s are used. From the study of the measured heat release rate (HRR) and mass loss rate data it is found that the forced air velocity affects the fire spread rate and burning efficiency and further affects peak HRR values at different air velocities. A simple model to describe these influences is proposed. This model is used to reproduce the enhancement of peak HRR for cribs with different porosity factors noted by Ingason [1] and to assess the effects of using different length of cribs on peak HRR. The results from these analyses suggest that different porosity fuels result different involvement of burning surface area and result different changes in peak HRR. However, no significant difference to the enhancement on fire size is found when the burning surface area is similar. It is also found that the trend in the enhancement on fire size by using sufficiently long crib and available ventilation conditions matches the predictions of Carvel and Beard [2] for two-lane tunnel heavy goods vehicle fires.     

受限空间木垛火的热释放速率分析与研究

通过理论分析、试验研究以及拟合分析相结合的手段研究了木垛火在受限空间内的燃烧特性,着重总结了受限空间木垛火在不同阶段的燃烧特性及热释放速率的增长规律,并且讨论了热释放速率曲线的叠加问题,给出了热释放速率以一阶指数增长的数学关系,以及t2增长的火灾增长系数.     

Fire resistance performance of unprotected wood–wood–wood and wood–steel–wood connections: A literature review and new data correlations

This paper reviews fire resistance tests of double shear timber connections, including wood–wood–wood connections with nails, bolts and dowels and wood–steel–wood connections with bolts and dowels. Test data are used to assess the effects of the load ratio and the member geometry on the fire resistance of timber connections. New relationships are proposed and analysis results show good agreement with the test results. Design rules presented in Eurocode 5 are also discussed and compared with the proposed calculation method.     

Modeling pool-like gas flames of propane

Turbulent, buoyant pool-like propane flames with heat release rates of 15.8, 22.9 and 37.9 kW are numerically modeled. The model assumes a parabolic flow field, κ–ε turbulence model, and an eddy-dissipation concept for the interaction of the chemistry and turbulence. Radiative heat transfer is incorporated by the flux model with the absorption and emission coefficients evaluated using a temperature-weighted gray gas model. Predictions are made for the flame shapes, axial velocity, axial mean temperature and various scalar properties along the centerline, the radial distribution of temperature and velocity at various axial heights, and the air entrainment behavior. The overall agreement between the predicted and experimental flame behavior is seen to be good; however, the radial expansion of the flame is underestimated in the combustion zone.     

The effect of wind on flames

A simplified and improved correlation for the drag coefficient of windblown natural gas flames is given. Experimental results leading to the correlation were obtained in a low-speed wind tunnel specifically designed for such studies at the University of Oklahoma North Campus.     

Luminous heights of turbulent diffusion flames

A general analytical relation for predicting mean luminous heights of buoyancy-controlled, turbulent diffusion flames is established. The relationship is based on a plot of experimental flame heights in correlation coordinates proposed previously, including extensive data recently published.     

A phoenix from the flames

In this detailed account of an unusual project in Pondicherry, India, the celebrated Dutch ceramic artist and sculptor describes the building of a small, vaulted brick house. The house, however, was built with 'green' bricks; it was used as a kiln for the firing of a pile of other green bricks and tiles so that, after firing, the house itself would be transformed into a structure of hardened fired-clay bricks. The experiment took place at the Golden Bridge Pottery, established by American potters Ray Meeker and Deborah Smith some sixteen years ago. The author's consultancy role in the project was grant-aided by the Dutch government.     

Graybody radiation from conical flames

The spatial dependence of graybody radiation from a cone, the shape representative of small flames, has been computed. A comparison of the radiative heat flux from this model and experimental measurements of the total heat flux from a flame indicate that up to 74 percent of the total emitted intensity is radiative.     

A phoenix from the flames

In this detailed account of an unusual project in Pondicherry, India, the celebrated Dutch ceramic artist and sculptor describes the building of a small, vaulted brick house. The house, however, was built with ‘green’ bricks; it was used as a kiln for the firing of a pile of other green bricks and tiles so that, after firing, the house itself would be transformed into a structure of hardened fired‐clay bricks. The experiment took place at the Golden Bridge Pottery, established by American potters Ray Meeker and Deborah Smith some sixteen years ago. The author's consultancy role in the project was grant‐aided by the Dutch government.