Numerical study on the spontaneous ignition of pressurized hydrogen during its sudden release into the tube with varying lengths and diameters

Fuel cell vehicles (FCV) and other hydrogen systems with pressurized hydrogen has a safety hazard of spontaneous ignition during its sudden release into the tube. Tube parameter is a key factor affecting the spontaneous ignition of pressurized hydrogen. In this paper, a numerical study on the spontaneous ignition of pressurized hydrogen during its sudden release into the tube with varying lengths and diameters is conducted. The models of Large Eddy Simulation (LES), Eddy Dissipation Concept (EDC), Renormalization Group (RNG), 10-step like opening process of burst disk and 18-step detailed hydrogen combustion mechanism are employed. 6 cases are simulated based on the previous experiments. Numerical results show that the possibility of spontaneous ignition of pressurized hydrogen increases inside the longer and thinner tubes, which agrees with the experimental results. The increasing of tube length has little influence on the shock wave formation and propagation inside the tube. However, there exists critical tube lengths for the generation of Mach disk and the normal shock wave: the maximum and minimum distances for the generation of the Mach disk in 10 mm diameter tube are 7.8 and 6.7 mm, respectively. As for the normal shock wave, these critical values are 22.1 and 19.4 mm, respectively. In addition, the formation times and initial positions of Mach disk and normal shock wave are delayed inside the thicker tube. Due to the shock-affected time increases with the increasing of tube length, the temperature could rise to the critical ignition temperature and triggers the spontaneous ignition due to the sufficient tube length even though the less hydrogen/air mixture and the contact surface with lower temperature is produced inside the thicker tube. Finally, a simple time scale analysis is conducted.     

Orientation behavior of homing pigeons at the Gernsheim anomaly

Pigeons were released at four release sites within the Gernsheim anomaly, a magnetic 'hill' with a peak 199 nT above the regional reference field and gentle 'slopes' to all sides, situated 44 km south of the Frankfurt loft. Local magnetic conditions at the sites differed in total intensity and in direction and steepness of the intensity gradient. At all sites, the pigeons were well oriented, showing counterclockwise deviations from the home directions that were most pronounced in the western part of the anomaly. There was no systematic difference in orientation behavior or homing performance between the sites within the anomaly and a control site outside. No effect of the local gradient direction was found, nor did the difference in intensity between home loft and the release site affect behavior. This argues against the use of magnetic navigational factors. However, pigeons released for the first time within the anomaly tended to have longer mean vectors with increasingly steeper gradients, which could mean that the birds might somehow have realized the anomalous nature of the local magnetic conditions and ignored them, relying on non-magnetic cues instead.Communicated by R. Gibson     

基于瑟利模型的社区火灾分析

随着我国城镇化速度的不断加快,我国城乡间社区的数量也不断提升,与此同时社区的消防安全隐患也开始逐渐显露。为了做好社区火灾的预防工作,本文有效的分析社区火灾发生发展过程中人的作用,把社区视为一个人、机和环境构成的完整系统,建立了社区火灾的瑟利模型,运用瑟利模型分析社区火灾发生、发展、防控过程中人的感知与响应因素,分析了社区火灾产生的部分原因,提出了针对火灾危险发生和释放阶段的预防措施和建议。     

金属有机骨架材料MIL-101用于气态碘单质的吸附与释放

目的研究金属有机骨架材料MIL-101对气态碘单质的吸附与释放。方法采用水热合成法合成金属有机骨架材料MIL-101,并利用X射线衍射(XRD)、扫描电子显微镜(SEM)、N2吸附脱附等温线等表征方法对合成的MIL-101样品进行表征。将制备的金属有机骨架材料MIL-101在75℃环境下对气态碘单质进行吸附,将吸附后的材料于无水乙醇溶液中进行碘单质的释放。结果随着吸附时间的推移,金属有机骨架材料MIL-101对气态碘单质的吸附量逐渐升高,并于8 h逐渐达到饱和吸附量2.61 g(I2)/g(MIL-101)。MIL-101在无水乙醇溶液中随着时间的延长,材料吸附的碘单质渐渐释放出来。结论 MIL-101对气态碘单质在较高温度下有着优异的吸附效果,并表现出良好的循环使用性能,适合用于核电站蒸汽中放射性气态碘的吸附。     

几种地板燃烧性能的实验研究

地板的燃烧性能对室内火灾的发展蔓延及火灾危害都有重要的影响,本文使用锥形量热仪对市场上常见几种地板(实木地板、竹制地板和复合地板)的燃烧性能进行试验研究。实验结果表明,地板的热释放速率具有两个峰,相同辐射功率下,竹地板和实木地板的比消光面积分别比复合地板高29．3％、42．5％,竹制地板点燃时间较小,复合地板火灾危险性要小于竹制地板和实木地板。     

辐射热流作用下树叶样品的燃烧特征研究

研究植物叶样在外部热辐射和值班火源作用下的燃烧现象特征并探索其成因和物理及化学本质。采用锥形量热仪开展实验,热辐射强度分别设定为35kW m-2、55kW m-2、70kW m-2和85kW m-2。实验样品为针阔叶树种共13种,其含水率在45%至79%间变化。实验表明,样品表现出不同的着火模式,有的为明火,有的则为阴燃,取决于树种和设定的辐射强度。样品出现有焰燃烧现象的最低热释放速率峰值(PHRR)在22.3kW m-2至35.6kW m-2之间,反映了形成气相火焰所需最低挥发分质量流率。气相产物CO2产生速率的峰值与PHRR呈高度线性性,表明了不同样品间气相燃烧或固相表面氧化(阴燃燃烧)反应的相似性。进一步分析表明,出现的独特热释放速率尖锐峰形是样品分层特性以及树叶的物理属性和热物性共同作用的结果。具有热薄特性的样品表层,在实验初期是接受外部辐射热的主体,其热解的产物是形成气相火焰的物质来源;在其转变为焦炭层后,对辐射热流向内层的渗透具有阻挡作用。建立起来的认识对于评估分层样品的燃烧性有一定的指导意义。     

情绪对新手驾驶员视觉特性的影响研究

为构建基于驾驶员生理特性情绪识别系统,采用眼动仪等设备对20名新手驾驶员开展不同情绪状态下的模拟驾驶试验,采集高兴、悲伤、愤怒3种情绪状态和无情绪下新手驾驶员的视觉数据,利用Matlab、SPSS软件统计分析新手驾驶员瞳孔变化、眼球扫视、注视点视觉数据.结果 表明:悲伤、愤怒情绪对新手驾驶员瞳孔尺寸分布频率及其变化差异...     

Concerns, dispositions and behaviors of aggressive drivers: what do self-identified aggressive drivers believe about traffic safety?

INTRODUCTION: The purpose of this investigation was to identify beliefs, driving personality dispositions, and behaviors that distinguish self-defined aggressive drivers from non-aggressive drivers. METHOD: Telephone surveys were used to identify self-reported aggressive drivers (n=305) who were compared to non-aggressive drivers (n=1,715) concerning their beliefs, driving behaviors, and self-described driving dispositions. RESULTS: Aggressive drivers, compared to non-aggressive drivers, were less concerned about speeding, aggressive driving, and cell phone use while driving, yet were more likely to have had an encounter with another aggressive driver. They were also more likely to report that they had driven when they knew they had too much to drink, yet they felt less likely that they would be stopped by the police. CONCLUSION: Aggressive drivers display many dispositions that define them as high risk drivers and public information/motivational campaigns alone will likely be ineffective with this group of drivers. Strategies that combine visible enforcement with widespread publicity campaigns appear to be necessary.     

Sorption-desorption of cadmium in aqueous palygorskite, sepiolite, and calcite suspensions: isotherm hysteresis

Sorption isotherms have been widely used to assess the heavy metal retention characteristics of soil particles. Desorption behavior of the retained metals, however, usually differ from that of sorption, leading to a lack of coincidence in the experimentally obtained sorption and desorption isotherms. In this study, we examine the nonsingularity of cadmium (Cd) sorption–desorption isotherms, to check the possible hysteresis and reversibility phenomena, in aqueous palygorskite, sepiolite and calcite systems. Sorption of Cd was carried out using a 24-h batch equilibration experiment with eight different Cd solution concentrations, equivalent to 20–100% of maximum sorption capacity of each mineral. Immediately after sorption, desorption took place using successive dilution method with five consecutive desorption steps. Both Cd sorption and desorption data were adequately described by Freundlich equation (0.81 < r² < 0.99). The sorption and desorption reactions, however, did not provide the same isotherms, indicating that hysteresis occurred in Cd sorption–desorption processes. The extent of hysteresis was quantified based on the differences obtained from sorption and desorption isotherms regarding the amount of Cd sorbed, the Freundlich exponent, and the Cd distribution coefficient. The results revealed that, sepiolite possessed the most hysteretic behavior among the minerals studied. Calcite showed much smaller hysteresis compared to the other two silicate clays at low Cd surface load, but its hysteresis indices significantly increased, and exceeded that of palygorskite, as the amount of Cd in the systems increased. The average amount of Cd released after five desorption steps, was 13.8%, 2.2% and 3.6% for the palygorskite, sepiolite and calcite, respectively, indicating that a large portion of Cd was irreversibly retained by the minerals.     

供电企业操作岗位员工安全胜任力模型的构建

为给供电企业的安全管理工作提供胜任力方面的理论依据和实践指导,通过采用系统编制的供电企业操作岗位员工安全胜任力调查问卷,对供电企业操作岗位员工进行整群随机抽样的问卷调查。对346份有效数据进行探索性因素分析,初步构建供电企业操作岗位员工安全胜任力的5因素模型;重新发放问卷,对141份有效数据进行的验证性因素分析支持了该模型因素结构的合理性;再次重新取样,对120份有效数据进行独立样本t检验和多层回归分析,检验5个安全胜任力因素对违章行为的影响。供电企业操作岗位员工安全胜任力模型以职业素养、安全意识、职业技能、身心健康和情绪稳定性5个因素为基本结构,其中,职业素养、安全意识、身心健康和情绪稳定性4个安全胜任力因素对违章行为具有显著负向影响。