含复合添加剂N2-双流体细水雾抑制乙醇火焰强化研究

细水雾扑灭油池火初期会出现火焰强化现象,这在一定程度上影响了细水雾灭火技术的安全性。本文研究了含复合添加剂N2-双流体细水雾对乙醇火的灭火有效性,从火焰温度、灭火时间和燃烧场流场结构特征三个方面,分析其对细水雾灭火火焰强化现象的抑制作用。实验结果表明:四种工况灭火效率从高到低分别为含KQ溶液N2-双流体细水雾>N2-双流体细水雾>含6%氟表面活性剂N2-双流体细水雾>Air-双流体细水雾;在含复合添加剂KQ溶液N2-双流体细水雾作用下,火焰强化现象几乎消失,同时表现出良好的控火效果,其原因是N2作为驱动气体则能预先稀释燃烧室内可燃气体浓度,降低火焰燃烧速率;而在氟表面活性剂与金属钾盐添加剂耦合作用下,有利于降低雾滴粒径,加快细水雾的蒸发与金属K离子的析出,从而提高了化学灭火和物理灭火作用。因此,KQ溶液N2-双流体细水雾灭火效率和控火能力大大提高。研究结果将为提高细水雾灭火技术的安全性提供指导。     

受限空间细水雾降温效果的实验研究

为研究细水雾在高温受限空间的降温效果,提出更广泛的细水雾系统应用范围,通过搭建小尺寸受限空间实验平台,开展大量水雾降温实验,研究细水雾在狭长受限空间内的降温特性,并重点分析影响水雾降温性能的主要参数。结果表明:随着纵向距离的增大,水雾降温效果逐渐减弱,降温幅度先急剧下降再缓慢降低,整个空间下层区域的降温效果优于上层区域。环境温度、喷头布置形式以及通风状况是影响水雾降温效果的重要因素:环境温度越高,降温范围越大,降温效果越明显;纵向喷头布置形式有利于水雾与周围环境更充分地热交换,提高降温效率;水雾-通风协同作用时,既能扩大水雾降温范围,又能显著提高降温效果,同时保持空间温度场稳定均匀。     

爆炸水雾扑灭油火过程的实验研究

爆炸水雾灭火是一种高效、快捷的新型灭火方式。为了研究爆炸水雾与油火的作用过程,采用CCD摄像机、微细热电偶、红外测温仪3种测试手段,获得了爆炸水雾与油火作用的图像以及灭火过程中温度的变化情况。实验结果表明:爆炸水雾在冲击油面后温度发生了突降,温度突降时间与CCD记录的水雾扑灭明火的时间一致;当水袋位于油盘正上方1.0m、炸药量为2.02g、水量为3kg时,灭火持续时间约为200ms;微细热电偶能够较准确地反映爆炸水雾灭火过程的温度变化,而红外测温仪可作为辅助测温手段定性分析灭火过程中的温度变化。     

黏弹性流体基铜纳米流体流动与传热实验研究

成功建立了流体流动阻力和换热性能测试实验台,在45℃的流体温度下,对不同铜粒子体积分数和基液浓度的纳米流体在湍流状态下的对流换热特性和流动阻力进行了实验测量。实验结果表明:黏弹性流体基液中添加纳米粒子后,在降低对应基液减阻率的同时能明显增强传热性能.例如,将1.0%体积分数的铜纳米粒子添加到质量分数为6×10~(-4)的基液中所形成的黏弹性流体基纳米流体其综合性能指数K=0.47,表现了很好的传热强化和减阻性能.     

纯PCBN高压烧结行为与工艺规律

采用粒度为10μm的纯cBN微粉在不同的高压烧结工艺参数(烧结压力、温度和时间)下制备了纯聚晶立方氮化硼(PCBN)烧结体。利用扫描电镜观察了PCBN烧结体的微结构,并测试了其耐磨性和抗压强度,进而讨论了压力、温度和烧结时间对纯PCBN烧结体性能的影响规律。结果表明:对纯PCBN烧结体性能影响最大的因素是烧结压力,其次是烧结温度和时间;在本实验条件下,当压力为9GPa、温度为1 700℃和烧结时间为240s时,高压烧结得到的纯PCBN烧结体样品性能最优,其磨耗比为10 200,抗压强度为2.52GPa。     

不同环境温度下工艺参数对扩散吸收式制冷机的性能影响

外界环境温度对扩散吸收制冷循环有重要影响,以四台相同结构的扩散吸收式制冷机为基础,用实验的手段研究了不同环境温度下,氨水溶液灌装浓度、充注压力、输入功率等工艺参数对扩散吸收式制冷机性能的影响。得出了实验样机在各工况下的最优工艺参数;研究发现随环境温度的升高,样机的最佳灌装浓度下降,而最佳输入功率和最适宜充注压力升高。可为扩散吸收式制冷机根据环境温度选择各工艺参数提供一定的依据。     

单螺杆发动机在不同进气压力下的实验研究

为了改善原有气动发动机的缺陷,提出了一种新型的气动发动机—单螺杆膨胀机,其具有容积效率高、结构控制简单、噪声低、寿命长等特点。为了测试单螺杆膨胀机的各项性能,建立了单螺杆膨胀机压缩空气动力系统,对膨胀机在不同进气压力下进行了实验研究.实验结果表明:随着进气压力升高膨胀机输出功率及总效率升高,而气耗率下降,即膨胀机在高进气压力下具有较好的动力性能、经济性能和较高的总效率。     

一种喷射式快速启动制冷器的研制

为了提高红外探测器用制冷器的启动时间,研究设计了一种新型喷射式快速启动制冷器。这种制冷器带有两级制冷,比传统的单级制冷器启动时间更短,采用多层换热管结构和多个节流孔技术,极大地提高了其换热效率和降温时间。对这种制冷器的工作原理进行了分析,确定了影响其启动时间的因素。设计了一系列试验,测试得出了这种制冷器在不同氮气压力下的启动时间。该实验结果表明,这种制冷器能在数秒内达到77K,实现了快速启动,并对更进一步提高其启动时间的方法提出了建议。     

细水雾协同滑动装置对甲烷/空气预混气体爆炸特性的影响

大量甲烷爆炸事故表明,甲烷/空气预混气体爆炸容易造成大量人员伤亡和巨大财产损失。利用10 cm×10 cm×100 cm透明实验管道,探究了细水雾协同滑动装置对甲烷爆炸特性的影响,并着重分析爆炸火焰和超压。结果表明:协同作用下,细水雾对燃烧区超压的影响较小,对未燃区超压峰值有明显衰减作用,甲烷体积分数为11.5%时衰减幅度最大,为44.71%。细水雾对指形火焰有冲毁作用,可加快火焰传播速度,甲烷体积分数为11.5%时,火焰传播速度的提升幅度最大,为62.50%。滑动装置反向压缩火焰至细水雾作用区,加速火焰焠熄。甲烷体积分数为9.5%和11.5%时,火焰焠熄时间明显下降,分别为20.76%和29.65%;甲烷体积分数为7.5%时,火焰焠熄时间下降3.5 ms。     

动力排气系统细水雾蒸发冷却试验研究

为了掌握设计的细水雾蒸发冷却器对发动机排气的喷雾降温性能,建立了喷雾降温试验台,用设计的屏蔽式气相测温装置和压力损失测量装置,准确测量了排气管内喷雾后的排气温度和压力损失。结果表明,细水雾蒸发冷却器向发动机排气内喷雾80 s,高温排气即可降至稳定温度,排气压力损失比喷雾前减小;雾化压力越大,喷雾流量越大,喷雾降温效果越好,压力损失越小;排气出口对应的液态水饱和温度可视为喷雾降温的极限温度。     

水雾与可燃多孔介质火焰相互作用的实验研究

采用非传播扩散火焰形式,研究了固体可燃多孔介质中水雾-火焰的相互作用,探讨了床层厚度、多孔介质粒度以及燃料预燃时间对水雾灭火效果的影响。结果表明,随着预燃时间增长,水雾停止后床层内部可能发生闷烧现象,随着燃料粒度的减小,这种闷烧几率反而降低。这表明,固体火焰与水雾的相互作用有其独特之处。     

Towards large eddy simulations of flame extinction and carbon monoxide emission in compartment fires

The general objective of this research is to adapt current combustion modeling capabilities used in computational fluid dynamics solvers to the treatment of under-ventilated compartment fires. More specifically, we consider in the present study two models proposed to describe: diffusion flame extinction due to air vitiation; and the emission of carbon monoxide (CO) and unburnt hydrocarbon (HC) mass in a compartment fire. The flame extinction model is based on a flammability diagram parametrized in terms of vitiated air properties. The CO/HC mass model is based on: a transport equation for fuel mass; a comparison of this fuel mass to a Burke–Schumann chemical-equilibrium expression; and an interpretation of the difference as a measure of incomplete combustion. Both models are implemented into a large eddy simulation solver developed by the National Institute of Standards and Technology, USA. The models performance is tested via detailed comparisons with an experimental database corresponding to reduced-scale compartment fires. The study considers two cases that correspond to different values of the fire room global equivalence ratio and are representative of strikingly different flame behaviors. The comparative tests serve to evaluate the general ability of the models to describe the transition from extinction-free conditions to conditions in which the flame experiences partial or total quenching, as well as the transition from fire regimes with no or little CO emission to regimes that emit hazardous levels.     

Experimental study of burning rates of cardboard box fires near sea level and at high altitude

To study the difference of solid fuel fire characteristics at different altitudes, two series of fire experiments of cardboard boxes filled with shredded office paper were conducted separately in Lhasa (altitude: 3650 m; air pressure: 65 kPa) and Hefei (altitude: 24 m, air pressure: 100.8 kPa), using a specially designed igniter. The measured parameters in the experiments include mass loss and flame axis temperature. Fuel load quantity and configuration were varied in the experiments. The results of the study indicate a likelihood that an ignition will result in smoldering fire at the high altitude. There is also likelihood that incipient phase may occur before the onset of full flaming combustion regardless of the altitude. The fuel mass loss fraction of flaming fires was found to follow a simple form of correlation with time when normalized over the half fuel consumption time, which was found to be inversely proportional to four-third power of the ambient pressure.     

油池火中雾卷吸现象的研究

细水雾与火焰相互作用中雾滴主要通过动量和雾卷吸进入火焰区,以达到抑制或扑灭火焰的效果。本文对细水雾与油池火相互作用时雾卷吸现象及其影响因素进行了初步研究,通过建立一个简单的模型,初步确定了雾卷吸量的计算方法。所进行的小尺度模拟实验也对理论分析的结果提供了验证。     

Simultaneous diode-laser-based in situ measurement of liquid water content and oxygen mole fraction in dense water mist environments

We performed what we believe are the first simultaneous in situ measurements of liquid water and oxygen concentrations in a dense water mist environment. Direct absorption tunable diode laser absorption spectroscopy was used to make oxygen concentrations and simultaneously quantify the liquid water via optical density measurements. This spectrometer with an absorption path length of only 36.8 cm was successfully tested during full-scale fire suppression tests with scattering losses up to 99.9%. The simultaneous oxygen and liquid water concentration measurements agree with fire suppression model calculations.     

基于傅里叶变换红外光谱探测的火灾早期过程特征信息研究

通过对火灾过程中各种特征参量进行分析,提出采用CO作为早期火灾探测的探测对象,并在此基础上建立起基于傅里叶变换红外光谱仪的完善试验系统。通过该实验系统进行了大量早期火灾加热阴燃及燃烧试验,经过光谱定量分析得到其各自CO浓度变化数据。在数据分析的基础上通过时间序列分析建模建立起CO浓度数据的二阶自回归模型,提取出表征火灾整体特性的过程特征信息参数1和2。通过相平面分析表明:真假火灾的过程特征信息参数具有明显的区域分布差异性,利用这种特性可以快速将真假火灾分辨出来。大量试验结果证实该探测方法能够在火灾发生早期及时对真假火灾进行有效辨别。     

Experimental study and large eddy simulation of effect of terrain slope on marginal burning in shrub fuel beds

This paper presents a combined study of laboratory scale fire spread experiments and a three-dimensional large eddy simulation (LES) to analyze the effect of terrain slope on marginal burning behavior in live chaparral shrub fuel beds. Line fire was initiated in single species fuel beds of four common chaparral plants under various fuel bed configurations and ambient conditions. An LES approach was developed to model fire spreading through a fuel bed with a subgrid scale turbulent combustion model based on a flame surface density concept. By examining two fuel bed slope configurations, it was found that upslope fire spread depends not only on the increased radiant heat transfer but also on the aerodynamic effect created by the interaction of the flame with the inclined surface. Under certain conditions, the convective heat transfer induced by this interaction becomes the dominant mechanism in determining fire spread success. Seventy-three (or 42%) of 173 experimental fires successfully propagated for slopes ranging from −70% to 70%. It was found there exists a critical slope above which fire spread in these live fuel beds was successful, and below which fire spread was unsuccessful. This critical slope for marginal burning varied widely with fuel moisture content and fuel loading. A stepwise logistic regression model was developed from experimental data to predict the probability of successful fire spread. It is expected that this model may be helpful in providing guidelines for prescribed fire application.     

Experimental measurements and numerical modeling of marginal burning in live chaparral fuel beds

An extensive experimental and numerical study was completed to analyze the marginal burning behavior of live chaparral shrub fuels that grow in the mountains of southern California. Laboratory fire spread experiments were carried out to determine the effects of wind, slope, moisture content, and fuel characteristics on marginal burning in fuel beds of common chaparral species. Four species (Manzanita sp., Ceanothus sp., Quercus sp., and Arctostaphylos sp.), two wind velocities (0 and 2 m/s), two fuel bed depths (20 and 40 cm), and three slope percents (0%, 40%, or 70%) were used. Oven-dry moisture content M of fine fuels (<6.25 mm diameter) ranged from 29% to 105%. Sixty-five of 115 fires successfully propagated the length (2.0 m) of the elevated fuel bed. A previously derived empirical marginal burning criterion was assessed, and a suitable modification was proposed for live chaparral fuels. Based on the experimental data, a stepwise logistic regression model was developed to predict the probability of successful fire spread. This procedure resulted in the selection of wind speed, slope percent, fuel loading, fuel moisture content, and relative humidity as the primary variables. It correctly classified 96% of 115 fires. Finally, a multidimensional numerical model for vegetation fire spread using a porous media sub-model was developed to simulate the laboratory fires. Results are used to analyze the internal heat transfer and combustion processes that determine fire spread success in shrub fuel bed.     

Thermal Radiation Modelling in Tunnel Fires

Modelling based on Computational Fluid Dynamics (CFD) is by now effectively used in fire research and hazard analysis. Depending on the scenario, radiative heat transfer can play a very important role in enclosure combustion events such as tunnel fires. In this work, the importance of radiation and the effect of the use of different approaches to account for it were assessed. Firstly, small-scale tunnel fire simulations were performed and the results compared with experimental data, then realistic full-scale scenarios were simulated. The results show up the capability of CFD modelling to reproduce with good approximation tunnel fires. Radiation proved to be noteworthy mainly when the scale of the fire is relatively large. Among the various approaches employed to simulate radiation, the use of the Discrete Transfer model gave the most accurate results, mainly when the absorption-emission characteristics of the combustion products were taken into account. Finally, the suitability of the use of CFD in quantitative Fire Hazard Analysis is discussed.