粉尘浓度对20L球罐内硫磺粉尘分散过程流场特性的影响

为了解不同浓度的硫磺粉尘在20 L球罐内分散过程流场特性的变化规律,采用CFD数值模拟方法再现球罐内硫磺粉尘分散过程,揭示粉尘浓度与湍流动能、流场速度、粉尘云浓度、最佳点火延迟时间之间的关系。研究结果表明:在其他条件一定时,喷入的粉尘越少,球罐内湍流动能和流场速度的峰值越大,球心处的粉尘云等效浓度的峰值越小,粉尘颗粒滞留在球心处的时间越短,即粉尘浓度越小,最佳点火延迟时间段越小;粒径为163μm、浓度为0.15,0.3,0.45 kg/m3的硫磺粉尘对应的最佳点火延迟时间分别是50~60,50~85,50~105 ms。     

基于20 L球罐的多相混合物扩散模拟

为更好地探索多相混合物的爆炸特性，以铝粉、乙醚、空气为研究对象，基于20 L球型爆炸罐建立三维计算模型，对气固两相和气液固三相混合物的分散过程进行数值模拟，以分析不同多相混合物分散过程的差异，并为测量多相混合物爆炸下限时的点火延迟时间设定提供参考。监测分析铝粉浓度粒子分布、流场内部湍流动能以及液相体积百分数等的演化过程，讨论混合物分散效果的差异，并确定测量爆炸下限的点火延迟时间。研究结果表明:实验工况下，液相的存在会降低粉尘云团的湍流动能、降低其扩散速度，并使粉尘云内部浓度更均匀。测量多相混合物爆炸下限时，三相混合物的最佳点火延迟时间早于气固两相混合物10~20 ms。     

点火延迟时间对甘薯粉尘爆炸的影响研究

为了预防甘薯粉尘爆炸事故的发生,本文研究点火延迟时间对甘薯粉尘爆炸的影响规律,利用20 L球形爆炸仪研究甘薯粉尘的爆炸特性及其在200 g/m3,500 g/m3和800 g/m3质量浓度下通过改变点火延迟时间的爆炸规律。结果表明:粉尘的最佳点火延迟时间与浓度有关,在该点火时间下所测得的最大爆炸压力均高于在固定点火延迟时间下的测量值,60 ms的固定点火延迟时间不适用于甘薯粉尘爆炸测试。     

速生杨木粉尘最小点火能的实验研究

为防止木材加工中木质粉尘燃爆事故的发生,以纤维板生产中常见的原材料速生杨木粉尘作为研究对象,在分析粉尘粒径分布、元素分析、工业分析及形貌特征的基础上,采用1.2 L哈特曼管对3种不同粒径（0~50,＞50~96,＞96~180 μm）速生杨木粉尘进行最小点火能实验,探究点火延迟时间、喷粉压力、质量浓度和粒径分布对速生杨木粉尘最小点火能的影响及变化规律。研究结果表明:在质量浓度为500 g/m3时,分别增加点火延迟时间和喷粉压力,最小点火能都先减小后增大;最佳点火延迟时间和最佳喷粉压力分别为120 ms和120 kPa;粒径对最佳点火延迟时间和最佳喷粉压力无显著影响。在点火延迟和喷粉压力分别为120 ms和120 kPa条件下,最小点火能随质量浓度的增加先减小后增大。粉尘粒径与最小点火能呈正相关性,3种样品的最小点火能分别为1~3,1~3和7~13 mJ,对应的敏感质量浓度分别为500 ,750和1 250 g/m3,属于特别着火敏感性粉尘。     

蔗糖粉尘最小点火能实验研究

利用1.2 L哈特曼管研究广西区蔗糖粉尘的最小点火能,对3个主要影响因素:蔗糖粉尘质量、点火延迟时间和喷粉压力进行实验。实验结果表明:蔗糖粉尘质量对最小点火能的影响最为明显,随着蔗糖粉尘质量的增加,最小点火能先减小后增大,且在质量为0.5 g时,最小点火能最小;点火延迟时间不同,粉尘的分散程度不同,在最均匀的粉尘云状态时点火,即为最佳点火延迟时间,实验测得为90 ms;蔗糖粉尘的最小点火能随喷粉压力的增加先减小趋向平稳再明显增加。     

点火延迟时间对粉尘最大爆炸压力测定影响的研究

根据粉尘云形成时颗粒分散及沉降的时间效应,指出目前国际通行的球型爆炸装置采用固定点火延迟时间测定粉尘最大爆炸压力的方法具有不确定性,并以煤粉为介质在20 L标准爆炸球装置上进行系列爆炸实验,研究装置点火延迟时间对粉尘爆炸压力的影响。结果表明:点火延迟时间对粉尘爆炸压力测定有十分显著的影响,不同粒径粉尘的最大爆炸压力有不同点火延迟时间,目前仅以气相湍流度所确定的固定点火延迟时间下,所测粉尘最大爆炸压力可能严重偏离实际。     

基于多孔环形喷嘴的可燃爆粉尘分散特征的密度效应研究*

为了研究不同密度的可燃爆粉尘在内置多孔环形喷嘴的20 L爆炸特性测试装置中的分散特征,基于负载粒子流方法、耦合DPM动量平衡方程和时间平均 Navier Stokes控制方程组,实现3种不同密度的煤粉、铝粉和锆粉在20 L爆炸测试装置中粉尘分散全过程的数值模拟。研究结果表明:多孔环形喷嘴的分散较为均匀,但是约束管道末端存在局部粉尘残留区,致使爆炸仓内真实粉尘浓度远低于形式浓度;爆炸仓中心位置的最大湍动能随着粉尘密度的增加而减小,只有显著地变化粉尘密度才能展示区分度较高的浓度峰值和抵达浓度峰值的时间。     

铝粉分散过程中粒径效应的三维数值研究

为了研究不同粒径的铝粉在20 L爆炸测试装置中的分散规律,基于计算模型的非结构网格划分,耦合欧拉和拉格朗日方法,实现了描述可压缩气体演化的时间平均Navier-Stokes方程组和粒子运动的DPM动量平衡方程的求解,获得了不同粒径（25,50和100 μm）的铝粉在20 L爆炸仓内分散的三维时空演化规律。研究结果表明:铝粉粒径的差异对爆炸仓点火中心的湍动能和速度的演化过程影响不显著,但对粉尘浓度的变化率和峰值均具有重要影响;随着粒径的增大,峰值浓度越小,但均高于形式浓度0.25 kg/m3,达到峰值浓度的时间越滞后。     

三环唑粉尘爆炸特性研究

利用激光粒度仪对三环唑粉尘的粒径分布进行分析,并用20 L爆炸球测试装置、哈特曼管装置探讨了粉尘质量浓度、点火延迟时间、点火能量、粒径分布对粉尘爆炸的影响并总结了相关规律。实验结果表明:粉尘粒度是影响粉尘最小点火能和爆炸下限的单调因素,粉尘质量浓度是影响粉尘爆炸压力的极值因素,点火延迟时间是影响粉尘最小点火能的极值因素。     

敏感条件对粉尘云最小点火能的影响规律分析

为使粉尘云最小点火能实验测量更准确,从多个方面分析影响最小点火能的测量因素,并根据粉尘云状态、粉尘颗粒固有性质、点火电路等几个方面对影响粉尘云最小点火能的因素,即敏感条件进行了分类。在实验测量中,具体归纳为:粉尘浓度、粉尘湿度、粉尘粒度及其分布、粉尘挥发份含量、粉尘温度(环境温度)、粉尘云的湍流度、粉尘分散质量、粉尘云初始压力、环境氧浓度、电极材料、电极直径和电极末端曲率、电极间距、电火花持续时间、点火延迟时间、电火花能量密度、火花触发电路、可燃气体影响、实验次数等18个影响因素。重点分析了敏感条件对最小点火能的影响规律,从粉尘云点火机理和过程出发,着重分析一些敏感条件对最小点火能影响的内在原因和实质。     

CFD simulations of dust dispersion in the 1 m3 explosion vessel

According to standard procedures, flammability and explosion parameters for dusts and dust mixtures are evaluated in 20 L and/or 1 m³ vessels, with equivalent results provided a correct ignition delay time (60 ms in the 20 L vessel; 600 ms in the 1 m³ vessel). In this work, CFD simulations of flow field and dust concentration distribution in the 1 m³ spherical vessel are performed, and the results compared to the data previously obtained for the 20 L. It has been found that in the 1 m³ vessel, the spatial distribution of the turbulent kinetic energy is lower and much more uniform. Concerning the dust distribution, as in the case of the 20 L, dust is mainly concentrated at the outer zones of the vortices generated inside the vessel. Furthermore, an incomplete feeding is attained, with most of the dust trapped in the perforated annular nozzle. Starting from the maps of dust concentration and turbulent kinetic energy, the deflagration index K_St is calculated in both vessels. In the conditions of the present work, the K_St is found to be 2.4 times higher in the 20 L than in the 1 m³ vessel.     

基于正交实验的面粉爆炸特性研究

为探究面粉爆炸实验中粉尘质量浓度、点火能量、点火延迟时间对面粉爆炸的影响,采用正交实验法并利用20 L球形爆炸测试装置比较研究了粉尘质量浓度、点火延迟时间以及点火能对面粉爆炸的影响程度.结果表明:对最大爆炸压力影响最为显著的因素是点火延迟时间,对最大爆炸指数影响最为显著的因素是粉尘质量浓度;在实验浓度范围内,存在最佳实...     

Study of dust cloud behaviour in the modified Hartmann tube using the image subtraction method (ISM)

A dispersion of fine particles in the air is needed for a dust explosion to occur since an explosion is the fast combustion of particles in the air. When particles are poorly dispersed, agglomerated, or their concentration is low, the combustion velocity decreases, and deflagration would not occur. The combustion rate is strictly related to dust concentration. Therefore, the maximum explosion pressure rise occurs at dust concentration close to stoichiometric. Conversely, Minimum Explosion Concentration (MEC) is the lower limit at which self-sustained combustion and a pressure rise are possible. Dust explosion tests are designed to reproduce the dispersion and generation of dust clouds in industrial ambiences by using dispersion devices activated by pressurised air pulses. The resulting dust cloud, which has a marked transient character, is considered representative of real clouds by current standards. Over time, several studies have been carried out to optimise these devices (e.g. to reduce the inhomogeneity of the cloud in the 20 L sphere). The Minimum Ignition Energy (MIE) of dust is measured using the Mike3 modified Hartmann tube, where the ignition attempt is made 60–180 ms after dust dispersion regardless of dust characteristics.This work investigates the dust clouds’ actual behaviour inside the modified Hartmann tube before ignition using high-velocity video movies and a new image post-treatment method called Image Subtraction Method (ISM). Movies are recorded with high-speed cameras at a framerate of 2000 fps and elaborated with an on-purpose developed LabVIEW® code. Concentration (mass per volume) and dispersion pressure are varied to evaluate their effect on dust clouds. Maise starch, iron powder and silica powder are chosen to investigate the effect of particle density and size on the cloud structure and turbulence. This approach will help to investigate the structure of the dust cloud, the shape and size of the particle lumps and the change in dust concentration over time. In addition, information on the actual concentration and cloud turbulence at the ignition location and delay time were obtained, which may help identify the local turbulence scale and widen the characterisation of the cloud generated in the Hartmann tube.     

On the transient flow in the 20-liter explosion sphere

The turbulence level in the 20-l explosion sphere, equipped with the Perforated Dispersion Ring, was measured by means of laser Doppler anemometry. The spatial homogeneity of the turbulence was investigated by performing velocity measurements at various locations in the transient flow field. Directional isotropy was investigated by measuring two independent components of the instantaneous velocity. The transient turbulence level could be correlated by a decay law of the form

in which the exponent, n, assumes a constant value of 1.49±0.02 in the period between 60 and 200 ms after the start of the injection process. In this time interval the turbulence was also observed to be homogeneous and practically isotropic. The results of this investigation imply that the turbulence level in the 20-l explosion sphere at the prescribed ignition delay time of ms is not equal to the turbulence level in the 1 m³-vessel. Hence, these results call into question the widely held belief that the cube-root-law may be used to predict the severity of industrial dust explosions on the basis of dust explosion severities measured in laboratory test vessels.     

Effect of ignition delay on explosion parameters of corn dust/air in confined chamber

This paper presents the explosion parameters of corn dust/air mixtures in confined chamber. The measurements were conducted in a setup which comprises a 5 L explosion chamber, a dust dispersion sub-system, and a transient pressure measurement sub-system. The influences of the ignition delay on the pressure and the rate of pressure rise for the dust/air explosion have been discussed based on the experimental data. It is found that at the lower concentrations, the explosion pressure and the rate of pressure rise of corn dust/air mixtures decrease as the ignition delay increases from 60 ms; But at the higher concentrations, the explosion pressure and the rate of pressure rise increase slightly as the ignition delay increases from 60 ms to 80 ms, and decrease beyond 80 ms. The maximum explosion pressure of corn dust/air mixtures reaches its highest value equal to 0.79 MPa at the concentration of 1000 gm⁻³.     

超细聚苯乙烯微球粉体的燃爆特性研究

为研究超细聚苯乙烯微球粉体的燃爆特性,通过粉尘层最低着火温度测试装置、MIE-D1.2最小点火能测试装置、20 L球形爆炸测试装置,对其最低着火温度、最大爆炸压力、最小点火能量(MIE)等爆炸特性参数进行测定,探讨了加热温度、点火延滞时间、粉尘质量浓度、粉尘粒径对粉体燃爆特性的影响。结果表明:超细聚苯乙烯微球粉尘层在350℃左右时会发生无焰燃烧,且加热温度越高,粉体粒径越小,粉尘层发生着火时所需的时间越短;当粉体质量浓度为250 g/m3时,最大爆炸压力达到0.65 MPa,质量浓度为500 g/m3时,最大爆炸压力的上升速率达90 MPa/s以上;随点火延滞时间增加,最小点火能表现出先缓慢减小再急剧增大的规律;随粉尘质量浓度增加,最小点火能逐渐降低,当粉尘质量浓度超过500g/m3后逐渐趋于稳定。