采用绝热式自燃测试方法分析煤的自燃倾向

对煤的自燃倾向进行快速有效鉴别,有助于对煤的自燃倾向采取分级分类管理从而有效防治煤矿火灾,因而采用绝热式自燃测试方法对煤的自燃倾向进行准确分析很有必要。简要介绍绝热式自燃测试方法的测试原理及其仪器结构,模拟煤炭自燃的物理过程,通过采用包括反应器、气体预热铜管和跟踪温度控制方式等综合绝热措施以实现300 g煤样的自然发火实验,记录煤样从40℃上升到70℃的升温速率(或前30 h的升温速率),测试煤样的自燃特性曲线并分析曲线特征。即建立煤绝热氧化产热速率计算模型,结合实验数据计算所得的煤在绝热氧化条件下的升温速率和产热速率可鉴定煤自燃倾向性的强弱。采用绝热式自燃测试方法对不同煤的自燃倾向分析后表明,无烟煤和部分烟煤的自燃倾向较低,褐煤的自燃倾向较高,故而在煤矿开采时需特别注意褐煤的自燃倾向。     

Study of traffic characteristics based on internet web real-time traffic conditions by image identification technology

With the rapid development of Internet, it is increasingly convenient to obtain real-time traffic condition information, which has greatly stimulated the improvement of urban traffic guidance. Traffic conditions are generally divided into four grades in the existing network platform, which are expressed in different colours. The understanding of traffic condition is still at the level of abstract senses. Therefore, it is difficult to grasp the characteristics of urban traffic. To this end, a new idea is proposed in this paper, and the new idea is to study the urban traffic characteristics based on real-time traffic condition information extraction with image identification technology. With this method, we can not only quantify the abstract traffic condition information, but also solve the loss of traffic condition information. In addition, an instance is analysed in this paper, it shows that it can provide references for urban traffic organization management very well.     

下沟煤矿本煤层预抽钻孔合理封孔长度研究

封孔长度的合理性对于煤层预抽钻孔的抽采质量影响较大，当封孔长度较大时，不利于封孔段瓦斯的抽采，同时封孔成本增加，反之当封孔段长度较小时，若未封孔部分与煤壁裂隙导通，钻孔发生漏气又影响钻孔抽采质量。为确定合理的封孔长度，针对下沟煤矿302工作面特定的地质条件，采用单孔声波发射对巷道卸压区和应力集中区范围进行了研究，通过分析卸压区范围，确定了合理的封孔长度，并结合试验孔周边的预抽钻孔抽采数据，进行了验证分析，得出该工作面的合理封孔深度为8 m。     

考虑速度滑移的多孔质静压气体轴承静特性

对于多孔质材料内的气体流动,基于Darcy定律建立其理论模型,并建立气膜间隙流场的雷诺方程,考虑速度滑移修正方程;将上述2个区域的压力分布方程进行耦合,通过有限元方法对耦合后的压力分布方程进行离散化,用超松弛迭代求解出气膜内各节点的压力分布,分析速度滑移对多孔质静压气体轴承静特性的影响。结果表明,考虑速度滑移所计算的气膜压力分布变化平稳过渡,没有较大的突变。计算轴承的承载力及刚度,结果显示在气密间隙小于15μm时,随着气膜厚度的增大偏心导致的压差增大使承载力不断增大;且当速度滑移系数小于0.1时,速度滑移对轴承承载力及刚度有较大的影响。     

破碎带单孔循环注浆钻进工艺及应用

针对破碎带深孔施工存在的塌孔、卡钻问题,介绍了单孔循环钻进注浆工艺和新型无机注浆材料,并进行了效果考察。单孔循环注浆钻进工艺只采用一个钻孔,通过循环钻进、退钻、注浆工艺,对破碎带分别加固;新型无机双液注浆材料通过改变水灰比,实现浆液流动和凝结时间调整,解决了不同深度破碎带注浆后快速套孔问题。     

Statistics of ceramic strength: Use ordinary Weibull distribution function or Weibull statistical fracture theory?

“Weibull statistics” for strength distribution analysis refers to either the ordinary Weibull distribution function or the Weibull statistical fracture theory. The ordinary Weibull distribution function is an empirical distribution function on an equal footing with other type of classical empirical distributions such as normal and log-normal distributions for fitting the statistical data of various random variables nonexclusive to materials strength. It has no explicit physical meaning and cannot be used for size scaling and prediction of strength. The Weibull statistical fracture theory is a weakest-link statistical fracture model for a solid with the strength distribution of an elemental volume being described by the ordinary Weibull distribution function. It has the capability of size scaling and prediction of strength for specimens with different geometries and different loading modes. The three-parameter Weibull statistical fracture theory in uniaxial flexure of prismatic beams is reformulated and validated by both numerical and real strength experiments of different ceramics.     

Change and mechanism analysis of the softening-melting behavior of the iron-bearing burden in a hydrogen-rich blast furnace

The effect of hydrogen-rich smelting on the softening-melting behavior of the iron-bearing burden in a blast furnace (BF) was analyzed by simulating the actual burden structure of the BF and by studying the changes in the softening-melting behavior of the iron-bearing burden as well as the reaction behavior and interface characteristics of coke and slag-iron in the high-temperature zone. The influence mechanism of the softening-melting behavior of the iron-bearing burden after hydrogen-rich smelting in the BF was analyzed. The results show that after hydrogen-rich smelting in the BF, T_i decreases, T_10% and T_40% increase, ΔT increases when ϕ(CO) is 30%, ΔT decreases when ϕ(CO) is 40%, and the shrinkage rate decreases significantly at the same temperature. The assimilation of the burden is weakened, and the smelting reduction erosion of coke is decreased. T_s and T_d increase substantially, T_ds decreases, and ΔP_max and S decrease. An increase in ϕ(H₂) causes the softening-melting zone to move downward and become narrow, effectively improving the permeability. When 10% H₂ is used instead of 10% CO, the softening-melting zone becomes narrow and moves to the high-temperature zone, and the permeability of the burden improves, which shows that the influence of H₂ on the softening-melting zone is stronger than that of CO. After hydrogen-rich smelting, at 1673 K, the metallic iron phase gradually changes from a fragmental distribution to a flaky distribution, and the amount of molten slag and iron infiltrated into the pores of coke decreases. In addition, the amount of nonreduced wustite decreases substantially; the ash content on the coke surface is high; and hydrogen-rich smelting increases the temperature at which the slag phase and the ash on the coke surface fuse together. At 1713 K, a large amount of slag accumulates at the reaction interface of coke and hinders the carburization of iron.     

Tailoring electromagnetic absorption performances of TiO2/Co/carbon nanofibers through tuning graphitization degrees

Low density, high stability and strong dielectric loss capacity endow carbon-based nanocomposites with superb microwave dissipation performances. Different from grapheme or carbon nanotubes, the graphitization degrees of carbon-based composites derived from the organic precursor pyrolysis can be accurately regulated by controlling the carbonization temperature. As such, their electromagnetic properties can be easily tuned. In this work, we report the preparation of TiO₂/Co/Carbon nanofibers (CNFs) through a combined approach of electrospun and carbonization at different temperatures. The nanofibers with an average diameter of 300 nm were coated by a dense layer of TiO₂ and embedded by Co/CoO nanoparticles. The performance evaluation indicated the composite obtained at 700 °C exhibits remarkably strong absorption of −63.2 dB at 9.8 GHz and wide effective absorption bandwidth of 6.4 GHz with a pretty low filling rate of 15 wt%. Further analysis on the electromagnetic behaviors shows that the composite possesses regulable impedance matching characteristic and absorption performances, implying the huge application potential under various demand conditions.     

UHMWPE/HDPE/纳米SiO2共混体系的毛细管挤出流变行为

采用毛细管流变仪,研究了超高分子量聚乙烯(UHMWPE)/高密度聚乙烯(HDPE)/纳米二氧化硅(SiO2)共混体系,及其对照组的流变行为和挤出过程中的不稳定流动现象,分析了共混物发生鲨鱼皮畸变和整体破裂的临界剪切应力和临界剪切速率的变化情况。结果表明,经过偶联剂改性的纳米SiO2粒子,在PE基质的共混体系中存在一定的界面黏附作用,降低了纳米共混体系的挤出胀大比,弹性特征减轻。这种界面相互作用限制了纳米共混材料在口模区域的黏性流动以及分子链离开口模后的构象恢复,降低了发生流动不稳定现象的临界剪切速率,发生鲨鱼皮畸变的临界剪切应力增大,整体破裂后,形成交替出现"鲨鱼皮-破裂"的振荡性变化外观。     

Investigation of separation phenomenon in high-toughness X70 thick-walled linepipe steel

Separation is a commonly observed phenomenon during drop weight tear testing in high-toughness linepipe steels. Severe separation is harmful because it may cause fracturing or bursting of pipes. In this study,a quantitative measurement of separation was proposed,and using this new method,a relationship between the separation and microstructure was determined and discussed. The microstructures observed using optical and scanning electron microscopy revealed that the separation was related to the mixed ferritic and bainitic microstructures,or rather,it was related to the carbon enrichment in bainite.