温度及围护通风对独头巷道氡浓度分布的影响

根据计算流体力学以及氡的物理性质,建立具有硐室的独头巷道内氡的三维稳态传输模型,采用Fluent软件求解控制方程,使用UDF实现巷道内壁氡的析出和氡的衰变,得到独头巷道内的风场结构及氡的浓度分布。研究发现：通风量一定时,温度对氡的浓度影响显著,巷道内温度越高,巷道各处氡浓度越高。整个巷道硐室氡浓度最大,相比于修建防氡围护,对硐室采用局部通风,降氡效果更好。采用压入式通风时,巷道内氡浓度由内向外递增,提高巷道的通风率能够有效地降低巷道入口的氡浓度,但对硐室内氡浓度影响不大。     

煤矿掘进巷道内火灾所致继发性灾害分析

煤矿由于火灾所引起的继发性灾害已经处于非常严重的程度.本文采用数值分析方法研究井下掘进巷道内火灾所导致的继发性灾害发生的条件.得出:火灾所造成的通风阻力的变化随火灾强度增加而增加,山此造成通风量的减小.在本文所研究的火灾强度下(＜1.6 Mw),通风量的减少最大为2%,对矿片通风量不会产生较大影响.在掘进巷道风筒被烧断情况下,在风筒的前端容易形成瓦斯聚集区,易诱发瓦斯爆炸事故.     

通风瓦斯处理系统燃烧特性研究

本文设计了一种催化燃烧系统,利用天然气和空气来模拟通风瓦斯进行催化燃烧实验.实验结果证明,该系统能有效实现通风瓦斯浓度低至0.15%的稳定自持燃烧,几乎不生成NOx.循环周期、空速和气体浓度都是影响系统自持性和反应率的重要参数.通过合理的参数设计,能够在实现系统稳定运行的前提下,回收一定的热量.     

基于红外吸收光谱的瓦斯气体浓度检测技术

针对现有矿井瓦斯传感器的缺点,基于红外光谱吸收原理,采用差分吸收技术设计了红外瓦斯气体浓度探测系统.该系统采用单光路吸收气室和单光路双波长探测技术,利用差动放大电路为核心的微弱信号处理电路实现瓦斯浓度输出信号的检测,并采用线性关系式拟合瓦斯浓度和输出电压的关系曲线,实现了对瓦斯浓度的全量程精确探测.实验表明,该系统的测...     

高考物理试题中分压式与限流式的选择

分压式与限流式是滑动变阻器两种不同的连接方式,在近几年的高考中,曾多次重复考查滑动变阻器的这两种连接方式.从考生的答题的情况来看,失分率仍然较高.笔者从教学中发现原因主要有两个:一是与已形成的串联分压、并联分流的概念含义相混淆,对分压式与限流式的连接方式存在模糊认识.二是虽然知道分压式与限流式的连接方式,但遇到具体问题时根本不知道该选用哪种连接方式.为了使学生能正确选择分压式与限流式两种不同连接方式,有必要首先对两种连接方式的连接方法、特点作一个透彻的了解.     

超声速边界层中壁面抽吸对流动分离的抑制作用

当超声速或高超声速来流经过压缩折角时，由于壁面的位移效应，折角附近往往出现较强的逆压梯度，进而很可能导致流动分离，并伴随着激波与边界层干扰问题的出现.在工程应用中，流动分离会带来诸多不利因素.一个抑制流动分离的有效措施是在折角的上游引入定常的壁面抽吸单元.基于大Reynolds数渐近理论框架下的三层结构理论，文章研究了壁面抽吸抑制层流边界层分离的机理.研究发现，只要抽吸元被安置在折角上游O（R-3/8L）范围内，决定抑制效果的关键参数是抽吸的流量，而与抽吸元的位置无关；同时改变抽吸元的宽度和抽吸速度而保持抽吸流量不变并不影响其对分离区的抑制效果.      

地平式望远镜消旋K镜的设计

地平式望远镜在进行天体目标跟踪观测时会产生像旋,即视场中的星体会围绕视轴中心旋转,给实时目标识别和基于多帧积累的图像处理算法带来了诸多不便.本文针对地平式望远镜的Coude光路,设计了一种通光口径较大,由三面平面反射镜组成的K镜消旋机构来消除像旋.消旋K镜由三面反射镜组成,通光口径为42mm,第一面反射镜与第三面反射镜的夹角选择为120°,使K镜通光口径较大,能在全光谱波段范围内使用.入射光线绕光轴转动一定的角度,K镜相应的转动入射光线转角的一半,则出射光线不产生旋转.第一面反射镜和第三面反射镜由两面平面镜固定在金属三角架上组成,替代由三棱体磨制的反射镜面,利用自准直平行光管和高准确度转台装配各反射镜,使K镜光轴和回转轴同轴,并采用直流力矩电机直接驱动,使系统具有较快的响应速度.测角元件采用Renishaw圆光栅,细分后的角分辨率为0.072″.     

地平式望远镜消旋K镜的设计

地平式望远镜在进行天体目标跟踪观测时会产生像旋,即视场中的星体会围绕视轴中心旋转,给实时目标识别和基于多帧积累的图像处理算法带来了诸多不便.本文针对地平式望远镜的Coude光路,设计了一种通光口径较大,由三面平面反射镜组成的K镜消旋机构来消除像旋.消旋K镜由三面反射镜组成,通光口径为42 mm,第一面反射镜与第三面反射镜的夹角选择为120°,使K镜通光口径较大,能在全光谱波段范围内使用.入射光线绕光轴转动一定的角度,K镜相应的转动入射光线转角的一半,则出射光线不产生旋转.第一面反射镜和第三面反射镜由两面平面镜固定在金属三角架上组成,替代由三棱体磨制的反射镜面,利用自准直平行光管和高准确度转台装配各反射镜,使K镜光轴和回转轴同轴,并采用直流力矩电机直接驱动,使系统具有较快的响应速度.测角元件采用Renishaw圆光栅,细分后的角分辨率为0.072″.     

透射式负电子亲和势GaN光电阴极的光谱响应研究

利用金属有机化合物化学气相淀积(MOCVD)生长了发射层厚度为150 nm、掺杂浓度为1.6×10¹⁷ cm^-3的透射式GaN光电阴极,并在超高真空激活系统中对其进行了激活.通过多信息量测试系统进行了测试,发现透射式负电子亲和势(NEA)GaN光电阴极的量子效率曲线成一个"门"的形状,在255—355 nm波段有较大且平坦的响应,在290 nm处取得最大值为13%,由于AlN缓冲层对短波段光的吸收系数较大,在小于255 nm的波段量子效率出现了下降,当波长大于3 关键词： 透射式 NEA GaN光电阴极 量子效率     

低反动度附面层抽吸式压气机及其内部流动控制

本文进一步分析了低反动度附面层抽吸式压气机概念,并讨论了该压气机的设计要点和应用范围;分析了抽吸掉的附面层内的低能高熵流体的可能利用途径,以及对于不同的利用方式,效率的评估方法;基于上述概念设计了一台亚声速低反动度附面层抽吸式压气机,详细地分析了该压气机的气动参数选取与分布特点,以及该压气机内部的三维分离流动及其控制规律.     

溶剂萃取下构造煤的XRD结构演化特征

煤是一种短程有序、长程无序,且随着煤化程度的增加有序性增强、具有微晶或类晶态结构的沉积有机岩。在成煤过程中,地质构造的破坏作用使得煤发生不同程度的变形变质,引起煤的化学组成、微观结构发生变化,形成了不同煤体结构的构造煤。为了揭示构造破坏作用下,煤的微晶结构的变化特征,采用有机溶剂萃取的方法,对不同煤体结构的贫煤、气煤样进行了萃取。借助于X射线衍射(XRD)测试结果,探讨了煤样萃取前后的微晶结构的变化规律。研究发现：在溶剂萃取作用下,构造煤的萃取率所呈现的规律性变化并不因溶剂的种类、煤级的变化而改变,表现为溶剂萃取率均随着煤体破坏程度的增强而增大。室温条件下,溶剂的萃取并不足以改变高、低阶煤的微晶结构参数的对比关系,溶剂萃取前后均表现为贫煤的芳香层间距d₀₀₂小于气煤,堆砌度L_c和芳香层数N大于气煤。进一步研究发现构造的破坏作用下,萃取后d₀₀₂逐渐减小,L_c增大,而由于煤级的影响,以及溶剂的种类和渗入强弱不同,延展度L_a并没有表现出明显的规律性。     

In situ parametric study of alkali release in pulverized coal combustion: Effects of operating conditions and gas composition

This work concerns a parametric study of alkali release in a lab-scale, pulverized coal combustor (drop tube reactor) at atmospheric pressure. Measurements were made at steady reactor conditions using excimer laser fragmentation fluorescence (ELIF) and with direct optical access to the flue gas pipe. In this way, absolute gas-phase alkali species could be determined in situ, continuously, with sub-ppb sensitivity, directly in the flue gas. A hard coal was fired in the range 1000–1300 °C, for residence times in the range 3–5 s and for air numbers λ (air/fuel ratios) from 1.15 to 1.50. In addition, the amount of chlorine, water vapor and sulfur, respectively, was increased in known amounts by controlled dosing of HCl, H₂O and SO₂ into the combustion gas to determine effects of these components on release or capture of the alkali species. The experimental results are also compared with values calculated using ash/fuel analyses and sequential extraction to obtain a fuller picture of alkali release in pulverized fuel combustion.     

An in-situ method for time-resolved sodium release behaviour during coal combustion and its application in industrial coal-fired boilers

To mitigate the slagging, fouling and high-temperature corrosion problems caused by alkali metals during coal combustion process, measurement of time-resolved alkali metals release is very important. The paper proposed an in-situ approach for measuring sodium (Na) release in coal combustion by Flame Emission Spectroscopy (FES). Through the analysis of spontaneous emission spectra and a calibration procedure, the concentration of gas phase Na, temperature and thermal radiation can be obtained. Firstly, experimental measurement of Zhundong coal particles burning in a flat flame burner was done. Two kinds of Zhundong coal with similar proximate and ultimate analyses, but different ash composition were used. The Na-release history measured by FES was compared with that by LIBS. Results showed that the Na-release at the devolatilization, char, and ash stages can be distinguished by FES. The higher Si/Al content in ash can suppress the Na-release at the ash stage. Moreover, FES method was extended to the measurement of Na-release in four industrial boiler furnaces of two Zhundong coal-fired power plants. Results showed the Na-release measured by FES can reflect the change of fuel and load, and both temperature and thermal radiation play key roles in Na-release in coal combustion.     

光导管系统自然通风效果的CFD研究

本文利用CFD方法对光导管系统的自然通风进行模拟,综合分析了在不同大小和方向的室外风速下,风帽结构、通风管长、管道间距及光导管直径对自然通风效果的影响,结果表明,H型通风末端结构具有较好的通风效果,管长、管道间距与通风量之间存在最小风量极值点,通风量随着管道直径的增加而增大,这些结果为具有自然通风功能光导管系统实用化提供了理论指导.     

Ultrasonic coal-wash for de-sulfurization

Coal is the one of the world's most abundant fossil fuel resources. It is not a clean fuel, as it contains ash and sulfur. SOx as a pollutant are a real threat to both the ecosystem and to human health. There are numerous de-sulfurization methods to control SO(2) emissions. Nowadays, online flue gas de-sulfurization is being used as one such method to remove sulfur from coal during combustion. The biggest disadvantage associated with this method is formation of by-products (FGD gypsum). A way for effective usage of FGD gypsum has not yet been found. This will lead to acute and chronic effects to humans as well as plants. Power ultrasound can be used for the beneficiation of coal by the removal of sulfur from coal prior to coal combustion. The main effects of ultrasound in liquid medium are acoustic cavitation and acoustic streaming. The process of formation, growth and implosion of bubbles is called cavitation. Bulk fluid motion due to sound energy absorption is known as acoustic streaming. In addition, coupling of an acoustic field to water produces OH radicals, H(2)O(2), O(2), ozone and HO(2) that are strong oxidizing agents. Oxidation that occurs due to ultrasound is called Advanced Oxidation Process (AOP). It converts sulfur from coal to water-soluble sulphates. Conventional chemical-based soaking and stirring methods are compared here to ultrasonic methods of de-sulfurization. The main advantages of ultrasonic de-sulfurization over conventional methods, the mechanism involved in ultrasonic de-sulfurization and the difference between aqueous-based and solvent-based (2N HNO(3), 3-volume percentage H(2)O(2)) de-sulfurization are investigated experimentally.     

Reduction of nanoparticle exposure to welding aerosols by modification of the ventilation system in a workplace

Nanometer particle size distributions were measured in booths with two different ventilation patterns in an occupational environment with welding operations underway. The measurements were used to illustrate the impact of change of ventilation methods (existing – with ventilation ducts located at the top, modified – with ventilation ducts located below the weld bench) on the aerosol size distributions at different locations: close to the weld, in the vicinity of the welder’s face, and in the exhaust duct. Particle number concentrations measured in the vicinity of the welder’s face (mask) during a horizontal standard arc welding process in a booth with ventilation at the top was in the range of 7.78×10⁵ particles cm⁻³ with a geometric mean size of 181 nm and geometric standard deviation of 1.8. This reduced to 1.48×10⁴ particles cm⁻³ in the vicinity of the welder’s face with the modified ventilation system. The clearance of the welding aerosol was also faster in the modified booth (6 min compared to 11 min in a conventional booth). Particles were collected in the booth for the various test conditions, and analyzed to determine their composition and morphology. The particles were composed of hazardous heavy metals such as manganese, chromium and nickel, and had varying morphologies.     

基于光纤气体检测技术的煤矿自然发火预测预报系统

 分析了近红外光谱吸收式气体检测的基本原理以及煤矿采空区自然发火特征气体的选择,通过使用近红外激光光谱吸收式光纤气体传感器对采空区火灾特征气体浓度检测,报道实现了一套基于多种气体参数的火灾预测预报系统。系统使用分布反馈式半导体激光器（DFB LD）作为光源,光源驱动为低频锯齿波信号叠加高频正弦波信号,通过锁相放大器实现信号提取。根据采空区三带静态分布理论,给出了判断采空区自然发火危险程度的判定方法。该系统全部使用光纤进行井下信号传输和气体检测,使得检测精度更高,不带电工作,实时性更强,系统更加稳定可靠。     

Numerical study of coal particle ignition in air and oxy-atmosphere

The ignition and combustion of coal particles are investigated numerically under conventional and oxy-fuel atmospheres. Devolatilization is computed using the chemical percolation devolatilization (CPD) model. The CPD model is coupled with a Lagrangian particle tracking method in the framework of a multiphysics, multiscale Navier–Stokes solver. Combustion in the gas phase is described using finite rate chemistry. The numerical results for ignition are compared with available experimental data and a remarkably good agreement is observed. The effect on flame ignition of the different phases characterizing the release of volatile gases is assessed. These different phases manifest themselves in two distinct peaks in the devolatilization rate and it is observed that ignition can occur during the first volatile release or on the onset of the second, depending on the particle size and gas temperature. It is found that an increase of ignition delay time in oxy-atmosphere compared to the air case is related to the depletion of radicals that react with the abundant carbon dioxide of the oxy-atmosphere, while the increased heat capacity of the mixture does not play a role.     

An investigation of the effect of ultrasonic waves on the efficiency of silicon extraction from coal fly ash

Burning of coal accounts for an enormous proportion of the current energy supply, especially in developing countries. Burning of coal produces large amounts of coal fly ash, which causes serious environmental problems unless it is managed properly. Using chemical analysis, we found that coal fly ash could be a promising source of Si, Al, Ca and some rare earth elements, especially with the assistance of some measures such as ultrasound. In this study, we extracted silicon from coal fly ash using an alkaline dissolution strategy and investigated the effects of temperature and ultrasonic power on the efficiency of silicon extraction. During a 70 min reaction, the efficiency of silicon extraction increased markedly, from 9.41% to 34.96%, as the reaction temperature increased from 70 °C to 110 °C. With ultrasound assistance, ultrasonic waves enhanced the extraction of silicon at both 80 °C and 110 °C at 720 W ultrasound, increasing the efficiency of silicon extraction from 6.01% to 15.36% and from 34.96% to 54.42%, respectively. However, at 900 W ultrasonic power, extraction was slightly inhibited at both temperatures, causing a little decrease in efficiency.     

Molecular-beam mass spectrometry study of oxy-combustion in a novel coal-plate experiment

Oxy-fuel coal combustion could play a significant role in the foreseeable future for its application in carbon capture and storage (CSS) technologies. Therefore, detailed knowledge about the ongoing chemical kinetics in the combustion process is necessary. Here, we present an explorative approach to study volatile species gas phase kinetics in a novel coal-plate experiment probed with molecular-beam mass spectrometry. This coupling allows for time-resolved quantitative measurements of the gas-phase directly above the surface of solid fuels, which aid gaining more insight into the gas phase chemistry during coal combustion by detailed speciation information. Two coal samples, a rhenish lignite and a coal manufactured from hydrothermal carbonization, were chosen for this investigation due to their similar classification but different molecular structures. For both samples, our measurements show a two-stage devolatilization phase separated by a char-oxidation phase which can be attributed to the interaction of oxygen consumption in the gas phase and on the surface and the release of volatiles from deeper layers of the plate. Furthermore, detailed speciation data of light, oxygenated, and tar species allowed to identify fuel structure-specific decomposition patterns of the two different coal materials, thus providing comprehensive data that can be used for future model validation purposes.