N2 O-C2 H4预混气体火焰的传播特性

运用标准k-ε模型,对N₂O-C₂H₄预混气体在水平半封闭管道内火焰传播过程进行了数值模拟,得到了火焰锋面结构、传播速度、出口压力和燃烧区的气流速度随时间的变化规律。研究结果表明,管道内预混火焰传播过程分为3个阶段:点火初期的平面火焰传播阶段、Tulip火焰传播阶段和指形火焰传播阶段;火焰传播速度呈指数增长,管道出口处压力和气流速度均呈现出先增大后减小的趋势。同时,采用高速摄影系统、压力传感器、有机玻璃管等装置对预混气体的火焰加速进程和压力演变过程进行了验证,实验结果与数值模拟结果一致。     

燃烧管长度对煤粉火焰传播规律的影响

为评价煤粉爆炸的危险性,掌握煤粉爆炸过程中火焰传播的规律,实验采用垂直的哈特曼管,选择褐煤为研究对象,研究燃烧管长度对煤粉火焰传播的影响,并使用高速摄影机记录火焰的传播过程.结果表明:随着燃烧管长度的增加,煤粉火焰在传播过程中逐渐变细,同时煤粉火焰前锋阵面的最大高度、火焰传播的最大速度不断增加.火焰传播速度整体呈现先增大后减小的趋势.当燃烧管的长度分别为300 mm、 600 mm、 750 mm和900 mm时,煤粉云的火焰前锋阵面的最大高度分别达到649 mm、 808 mm、 1 003 mm和1 010 mm,煤粉云的火焰传播的最大速度分别为5.4 m/s、 12.09 m/s、 15.0 m/s和18.61 m/s.研究结果可以为保证煤炭的安全开采提供理论支撑.     

石松子粉爆炸过程中火焰传播特性研究

为了研究石松子粉火焰传播特征,采用哈特曼管装置对石松子粉在燃烧管中进行试验,利用高速摄影和红外热成像技术记录石松子粉火焰传播过程,并对石松子粉火焰传播速度和火焰温度变化情况进行了分析。结果表明:点火能量为200mJ,粉尘浓度在125⁵00g/m500g/m³范围内,火焰在燃烧管中向上传播所达到的最大速度随着粉尘浓度的增加先增大后减小;在石松子粉浓度为250g/m3范围内,火焰在燃烧管中向上传播所达到的最大速度随着粉尘浓度的增加先增大后减小;在石松子粉浓度为250g/m³时达到最大速度11.08m/s;火球的面积随着时间变化呈现先增大后减小的趋势,在60ms时达到最大,同时达到最高温度1100℃;随着火焰的向上传播,火焰的最高温度区域也随之向上移动。     

顶部点火下甲烷-空气预混泄爆特性研究

利用自主设计和搭建的1 m³矩形泄爆系统，开展了顶部点火条件下7%～13%浓度范围的甲烷-空气预混气体泄爆实验，研究甲烷浓度对泄爆过程中火焰演化和内部超压特性的影响规律，并结合压力时程曲线和火焰演化图像等进行机制分析，研究结果表明：浓度对甲烷-空气预混气体的泄爆特性有显著影响，在特定甲烷浓度下，容器内部超压出现双峰现象，在各浓度下均出现压力峰值P₁,而压力峰值P₂仅在浓度为9%出现。各浓度均出现的第一压力峰值P₁随着浓度的增加呈现先增大后减小的趋势，而该峰值出现时间的变化趋势却与之相反，两者均在甲烷浓度10%下取得极值。这一现象主要由初始火焰传播、外部爆炸、亥姆霍兹振荡和泰勒不稳定性等因素综合影响形成。仅在甲烷浓度9%出现由火焰与声波耦合作用诱发产生的声学峰值P₂,该峰值远大于压力峰值P₁;其主要由火焰和声压的相互促进与扰动触发热声耦合作用影响形成。火焰向下传播速度随浓度呈先增加后减小的趋势，在甲烷浓度10%时达到最大值，且稍富燃状态下燃烧速度总体较快。     

空气浴条件下三水醋酸钠相变材料的储热性能实验

三水醋酸钠（CH₃COONa3H₂O）作为一种无机相变储能材料,具有潜热值高、导热性能好等优点,但是其在凝固过程中过冷度大制约了CH₃COONa3H₂O的应用。为了调节CH₃COONa3H₂O在空气浴条件下的过冷度,本文选用Na₂HPO₄12H₂O、Na₂CO₃10H₂O、Na₄P₂O₇10H₂O、Na₃PO₄12H₂O、Na₂SiO₃9H₂O、Na₂S₂O₃9H₂O和Na₂B₄O₇10H₂O这7种无机水合盐材料作为成核剂,采用步冷曲线法在高低温试验箱中进行过冷度调节实验和热循环实验。结果表明：在空气浴条件下,质量分数为96% CH₃COONa3H₂O+2% Na₂HPO₄12H₂O+2%羧甲基纤维素的复合相变材料过冷度最小,为5.6℃;将复合相变材料进行25、50和75次热循环后,其相变点温度几乎维持不变,过冷度随循环次数增加而逐渐增大,相变潜热值随循环次数的增加逐渐减小。本研究丰富了CH₃COONa3H₂O相变材料的过冷度调节方案,为其工程化应用提供了参考。     

硬脂酸粉尘爆炸过程中火焰传播试验及数值模拟

采用试验和数值模拟相结合的方法研究了硬脂酸粉尘火焰在上端开口的圆柱形垂直燃烧管道的传播过程。试验利用高速摄影系统和红外热成像仪记录了火焰的传播过程和温度分布情况,结果表明:火焰传播速度和火焰温度均呈现先增大后减小的趋势。采用Fluent软件计算得到的模拟结果与试验值吻合较好,模拟结果揭示了硬脂酸粉尘爆炸过程中气流速度的变化情况,分析结果表明:在同一时刻,气流速度高于粉尘火焰传播速度,是造成粉尘二次扬尘,进而产生持续爆炸的重要因素之一。     

氧化亚氮基单元复合推进剂的燃烧热性能研究

为了研究氧化亚氮基单元复合推进剂的燃烧热性能,以几种典型推进剂配方为研究对象,利用Hess定律对燃烧热进行了理论计算。采用全自动绝热量热仪(氧弹)和恒温式爆热量热仪(爆热弹)对燃烧热进行了实验,探讨了不同添加剂与容器几何尺寸对部分配方燃烧热的影响规律。结果表明：相同条件下,N₂O/C₂H₄、N₂O/C₃H₈、N₂O/NH₃的燃烧热依次减小;随着CO₂含量的增加,N₂O/C₂H₄的燃烧热逐渐减小;随着C₃H₈含量的增加,爆热弹中N₂O/NH₃的燃烧热先增大、后减小,C₃H₈质量分数为3.8%时,燃烧热最大;容器几何尺寸增大,燃烧热呈增大趋势。     

碱式碳酸镁焙烧法制备多孔氧化镁晶体

【目的】实现多孔MgO晶体的可控制备。【方法】以菱镁矿为镁源,采用水化碳化-低温水溶液法,热解Mg(HCO₃)₂溶液合成平均直径为10.0μm、平均长度为50.0μm的多孔棒状碱式碳酸镁(4MgCO₃·Mg(OH)₂·4H₂O);通过焙烧法制备多孔MgO晶体,分别探讨焙烧温度、时间对前驱体4MgCO₃·Mg(OH)₂·4H₂O分解率、 MgO物相组成和形貌的影响,探究4MgCO₃·Mg(OH)₂·4H₂O热分解机制。【结果】在焙烧温度为700℃、时间为3.0 h时,制得平均直径为20.0μm、平均长度为50.0μm、比表面积为76.12 m²/g的介孔棒状MgO晶体;在4MgCO₃·Mg(OH)₂·4H₂O分解过程中,随着温度升高,结晶水失去,—OH的分离和C—...     

CaCl2·6H2O/膨胀石墨复合相变材料的制备及研究

以CaCl₂·6H₂O为相变材料、膨胀石墨(EG)为载体，采用多孔基质吸附法制备CaCl₂·6H₂O/EG复合相变材料。通过试验研究材料的性能和组成结构。结果表明EG对CaCl₂·6H₂O负载率可达90%,CaCl₂·6H₂O/EG的相变温度和相变潜热分别为29.78℃和128.43 J/g。EG的微孔隙表面对CaCl₂·6H₂O的约束作用，可提高热循环过程中CaCl₂·6H₂O结构的稳定，维持其相变温度和相变潜热的基本稳定。小室试验表明，采用CaCl₂·6H₂O/EG材料隔墙的试验小室可有效降低小室的最高温度，大大延缓小室达到最高温度的时间，减缓小室温度波动。因此，CaCl₂·6H₂O/EG复合相变材料对建筑节能具有重要意义。     

罐状空间内含尘甲烷爆炸流场变化试验研究

为了研究罐状空间内不同浓度的煤尘对含尘甲烷爆炸流场变化的影响,使用60 L的定容燃烧弹为试验装置,在试验装置的同一个断面上布置4个压力传感器,按照上、下、左、右位置命名为P_U、P_L、P_D、P_R,通过爆炸压力以及激光纹影系统拍摄的火焰图像,分析爆炸压力与火焰结构的变化情况。试验共设计6组工况,试验选用浓度为9.5%的甲烷空气预混气体,再分别往气体中加入0 g/m³、5 g/m³、10 g/m³、15 g/m³、20 g/m³、25 g/m³的煤尘进行试验。试验结果表明：单一甲烷爆炸时,爆炸压力变化共分为4个阶段：压力上升阶段,压力降低阶段,二次上升阶段以及持续降低阶段,其中P_U传感器压力峰值最大,上升速率最快。在含氧量恒定的情况下,含尘甲烷爆炸的压力峰值随煤尘浓度的增加呈现先增大后减小的规律,煤尘浓度为15 g/m³时,爆炸压力...     

粒径对煤粉云最低着火温度特性的影响

为了研究粒径对煤粉云最低着火温度特性的影响,采用粉尘云最低着火温度测试装置测试了不同粒径下煤粉云的最低着火温度,并结合ReaxFF分子动力学对其反应机理进行了微观层面的探讨。结果表明:当煤粉中位径在34 μm时,煤粉云的最佳着火质量浓度为750 g/m³,最低着火温度为550 ℃;随着煤粉粒径的增加,煤粉云最低着火温度逐渐增大,当煤粉中位径达到124 μm,煤粉云最低着火温度上升至650 ℃。通过ReaxFF分子动力学对煤粉热解过程的计算结果表明:随着反应的进行,大分子煤结构逐步分解,芳香环、C—C键、C—O键和C—H键等断裂,产生更小的分子结构,其中,H₂、H₂O、CO₂和CH₂O等小分子产生的数量逐渐增多;H·自由基和OH·自由基在反应初期有明显的数量变化,且其含量对于最终稳定产物有重要影响。     

Study on the preparation of green suppressors and their characteristics in coal dust flame propagation inhibition

The properties of a green waste molecular sieve-based powder suppressor in inhibiting the flame propagation of coal dust were studied. Waste molecular sieve (S) was pretreated and selected as the carrier, potassium oxalate (K) and ferric citrate (T) as the active components. The reverse dissolution crystallization method was adopted and S@K/T, S@T/K, S@T-K suppressors with different core–shell structure were prepared by different loading sequences. Their particle size, morphology and thermal pyrolysis behavior were compared. The results showed that the particle distribution of three powders is uniform and the dispersity of them is good. The active components of explosion suppression are evenly loaded on the waste molecular sieve carrier and they have different coating structure. The thermal desorption heat of them is 44.64 J/ g, 66.95 J/g and 92.9 J/g, respectively. Furthermore, the flame propagation characteristics of coal dust were tested by the Hartmann flame propagation device. The results showed that all powders had the effect of inhibiting the flame propagation of coal dust and the inhibition effect is S@T-K, S@T/K and S@K/T from strong to weak. Combined with characterization results, the influence mechanism of the difference in the flame propagation inhibition effect of three suppressants was investigated.     

Suppression mechanism of micron/nano PMMA dust flame based on thermal analysis

The suppression mechanism of NaHCO₃ on micron/nano PMMA dust cloud flame based on thermal analysis was investigated. The results showed that the pyrolysis oxidation processes of 30 μm and 100 nm PMMA dusts were suppressed by NaHCO₃, and the apparent activation energy E and pre-exponential factor A were increased. The flame combustion intensity and propagation velocity of both micro and nano PMMA dusts were decreased obviously. Compared with 30 μm PMMA, NaHCO₃ maintained an efficient suppression on 100 nm PMMA with the mass ratio of NaHCO₃ increased with no suppression saturation phenomenon appeared. And 100 nm PMMA were more sensitive to particle size of NaHCO₃. In the flame preheat zone, the suppression effect of NaHCO₃ was mainly dominated by physical suppression, including the cooling effect of both pyrolysis reaction and products and the dilution effect on the concentration of combustible reactant. In the combustion reaction zone, the suppression effect of NaHCO₃ was mainly dominated by chemical suppression. The free radicals were absorbed by the active groups NaOH, forming the Na?NaOH suppression cycle. The E of nano PMMA dust flame was sustainably increased in both preheat and combustion reaction zones, contributing to the continuous high efficiency suppression and the sensitiveness to the particle size of explosion suppressant.     

Suppression of methane/coal dust deflagration flame propagation by CO2/fly ash as a flue gas layer

To reveal the suppression characteristics of methane/coal dust deflagration flame propagation by the flue gas loading in local zones. The suppression experiments of flue gas layer (CO₂ and fly ash) with different thicknesses and fly ash concentrations were conducted in semi-open vertical combustion pipe. The flue gas layer was produced by self-designed flue gas layer generator. Flame propagation characteristics which including the flame image, velocity, the ion current and temperature were recorded by the high-speed photography, the ion current probe and the thermocouple. The residues after coal dust deflagration were characterized by FTIR (Fourier transform infrared spectroscopy). The results show that the flue gas layer has a significant suppression on deflagration flame propagation. With the increasing of flue gas layer thickness and fly ash concentration, the flame velocity, height, temperature and the ion current gradually decreases, and the suppression effect was enhanced. The asphyxiation of CO₂, heat absorption and insulation of fly ash were mainly methods for the suppression of coal dust deflagration flame.     

Flame spray synthesis of ZrO2 nano-particles using liquid precursors

This paper studies the feasibility of using flame spray to produce ZrO₂ nano-particles using a liquid precursor. The effects of varying precursor concentrations and ratio of diluting medium on the phase composition, size and morphology of ZrO₂ nano-particles are discussed. The morphology and size of the ZrO₂ nano-particles was very much dependent on the precursor concentration. The solvent ratio of H₂O:ethanol also played a part in determining the characteristics of the ZrO₂ nano-particles. The nano-particles had the best characteristics when the precursor concentration was low and ethanol (added as solvent) content was high. In particular, the best characteristics were obtained using precursor concentration of 0.25 M, H₂O:ethanol ratio of 0:1. The nano-particles had very small particle size (50 nm), relatively high specific surface area (28.6 m²/g) and high degree of crystallinity. However, particles synthesized tend to be agglomerated.     

一种新型球状纳米氧化铁的制备

以Fe(NO₃)₃·9H₂O为原料、以尿素为沉淀剂,用热解前驱体法制备出直径为40~60 nm的球状纳米氧化铁。使用XRD、SEM和EDS等手段对其表征,研究了Fe³⁺浓度、反应温度等因素对纳米氧化铁的粒径和形貌的影响、确定了球状纳米氧化铁的制备条件并分析了球状纳米氧化铁的形成机理。结果表明：随着Fe(NO₃)₃·9H₂O溶液温度的提高纳米氧化铁的结晶度随之提高、粒径增大。Fe(NO₃)₃·9H₂O的浓度对纳米氧化铁样品的粒度和形貌的影响不大。球状氧化铁纳米的形成机理是：铁源在水热条件下水解和结晶生成棕黄色絮状沉淀FeOOH,FeOOH在高温高压条件下溶解和再结晶生成了球状纳米氧化铁。     

基于不同共溶剂体系对于高电压正极材料LiCoPO4的形貌控制

水分别与乙醇、乙二醇、二乙二醇混合为共溶剂, 通过溶剂热法制备高电压锂离子电池正极材料LiCoPO₄, 研究不同醇类溶剂对于样品的微观形貌和颗粒尺寸的影响。借助X射线衍射、扫描电子显微镜和比表面积测试对样品的成分、晶型、微观形貌和颗粒尺寸进行分析。研究表明, 制备得到的LiCoPO₄颗粒平均尺寸大小与醇类溶剂对于前驱体的溶解度差异相一致, 而与溶剂粘度没有明显联系。通过乙二醇/水制备得到的LiCoPO₄颗粒呈六边形片状, 平均尺寸最小, 而通过乙醇/水和二乙二醇/水制备得到的LiCoPO₄颗粒呈菱形片状形态。此外, 前者结晶度较高且循环性能较好, 0.05C下首圈放电容量为130 mAh/g, 20圈后容量保留率为88%。     

Investigation of lag on ignition of coal dust clouds under varied experimental conditions

Lag on ignition (LOI) of coal dust cloud greatly influences the initiation and propagation of coal dust explosion. This paper investigates the effects of coal dust particle size, dust concentration, ignition temperature, and dust dispersion pressure on LOI of coal dust clouds using Godbert-Greenwald furnace along with a high-speed camera. LOI of coal dust cloud significantly decreased by 1/13 times from 959 to 77 ms with increase in the ignition temperature from 600 to 1000 °C, demonstrating greatest influence of ignition temperature on LOI. LOI increased by 60% with increase in dust concentration from 500 to 4000 g/m³. Optimum dust dispersion pressure at which LOI was found minimum is determined 70 kPa. Empirical relations are established between LOI of coal dust cloud and particle size, ignition temperature, dust concentration, and dispersion pressure. The results are analysed in terms of the occurring physical processes, which led to a better understanding of the variation of LOI, ignition behavior, and explosion propagation of coal dust clouds at varied experimental conditions.