Numerical Simulation for Particle Penetration Depth Distribution in Deep Bed Filtration

A two‐dimensional model has been developed to simulate particle penetration through porous media. The particle penetration depends on many parameters including the Reynolds number, particle drag coefficient, the ratio of the diameter of injected to filtered particles, fluid velocity, and pore size, etc. The numerical model for separation efficiency in periodic porous media was studied. Previous work has described the effects of injected particle size, Reynolds number and particle drag coefficient. In this study, the porous media flow is modeled (solution of the Navier‐Stokes equations) by using the finite element method, and the analysis is restricted to the case of two‐dimensional periodic porous media. The effects of these factors and particle depth distribution in porous media are investigated. It is noted that the results for the three Reynolds numbers 1, 16.56, and 100, are qualitatively similar, and about 40 % of particles are trapped in the top part of the filter.     

Relation of Structure,Properties and Performance of Fibrous Media for Gas Filtration

The relation between the structure, permeability and filtration performance of needled nonwoven filter media is reported. Surface treated and untreated fabrics were studied, including microporous coated, laminated e‐PTFE, heated calendered and surface singed materials. Surface treatments appear to impart higher packing densities, but mean pore size is governed by the type of treatment with microporous and PTFE having the smaller values. Filtration performance was determined from graphs of pressure drop with filtration duration, differences in filtration efficiencies and the dust concentrations in gas emissions. Except for the singed materials, the treated fabrics depicted surface filtration and the untreated depth filtration. The trend for singed fabrics showed initial depth followed by surface filtration. Markedly higher filtration efficiencies were obtained with surface filtration, which corresponded with higher rates of pressure drop. Surface treatments, giving smaller mean pore sizes, resulted in higher filter cake resistance owing to low particle penetration through the base fabric.     

Origination of Reaction Sites in the Front of Gasless Combustion under the Action of Heat Losses

A numerical study of combustion of a gasless mixture in a narrow cylindrical channel showed that conditions of intense heat removal involve waves passing on the reactionfront surface, which bring the influence of heat losses to deep layers of the filler and, reflecting from the axis, lead to formation of reaction sites near the shell.     

Filtration combustion characteristics of low calorific gas in SiC foams

This study investigated the combustion characteristics of low calorific gas in silicon carbide (SiC) foam. The temperature distribution, reaction zone, maximum temperature, and combustion wave propagation velocity were analysed at different inlet velocities, equivalence ratios of premixed gases, and pore densities. The temperature distribution near the reaction zone was determined by a time-based method. Super-adiabatic combustion was obtained in porous media under different conditions. The experimental results showed that higher temperatures were obtained in SiC foams of 30 pores per inch (PPI) than those measured for foam of 20 PPI. Increased equivalence ratio of premixed gases and pore density led to a thicker reaction zone and a higher preheating efficiency in the preheating zone. The combustion wave propagation velocity, which was less than 2 mm/s under these experimental conditions, was increased with increased inlet velocity and decreased equivalence ratio of premixed gases. The combustion wave propagation in foams of 20 PPI had the lowest velocity because of the good match of convection and radiation.     

可膨胀石墨阻燃EVA燃烧性能及热失重行为的研究

用粒径为37、48及75μm的可膨胀石墨(EG)阻燃EVA,用锥形量热仪探讨了不同粒径的EG对EVA的阻燃作用,利用热失重分析仪研究了EVA/EG体系的热稳定性。结果表明:经过锥形量热仪测试表明,EVA/EG的热释放速率曲线呈现前单峰型,体现了典型的凝聚相阻燃机理;30 g EG的加入可以明显降低热释放速率,且粒径越大,阻燃效果越好;通过TG考察EG/EVA阻燃体系的热降解行为,在空气气氛下,EG膨胀炭层负载催化EVA交联成炭;相比于75μm EG,48μmEG形成炭层紧密,成炭量超过2.2%,形成的炭层稳定,在850℃也不会分解。     

低燃速低燃温双基推进剂的催化燃烧

研究了含普通铅、铜盐催化剂的低燃速、低燃温双基推进剂的燃烧性能、热分解性能及熄火表面形貌特征和元素分布。观察到如下试验现象：(1)熄火试样表面元素分布不均匀,C元素和催化剂在熄火表面均有不同程度的积累;(2)含催化剂的试样燃烧熄火表面有大小不等的球体出现,催化剂不同,形成的球体直径分布不同,球体成分以Pb为主,兼有少量其它元素,各球体相互连接形成链状、短枝状;(3)含和不含催化剂的配方未燃表面无球体出现。结果表明,适用于普通双基推进剂的铅、铜盐催化剂在低燃速低燃温双基推进剂中同样具有催化作用,对热分解性能也有重要影响。     

含能材料燃烧过程中热分解化学的研究进展

从模拟燃烧条件、组分相互作用、组分物理状态、分析测试技术等几方面介绍了含能材料燃烧过程中热分解化学研究近几年来的最新进展。着重介绍燃烧热分解中的基元反应对建立推进剂燃烧新型模型的重要性、氧化剂和黏合剂及催化剂之间的相互作用、氧化剂的黏度和相态变化对燃烧和热分解过程的影响。     

防火金属复合板专用高阻燃芯材的燃烧与导热性能研究

针对防火金属复合板专用阻燃芯材的燃烧及导热性能进行了实验研究,以期为金属复合板行业在防火芯料的选择及推广应用提供参考,从而减少国际贸易摩擦与争端。     

Thermal Decomposition and Combustion of Ammonium Dinitramide (Review)

A comprehensive review of thermal decomposition and combustion of ammonium dinitramide (ADN) has been conducted. The basic thermal properties, chemical pathways, and reaction products in both the condensed and gas phases are analyzed over a broad range of ambient conditions. Detailed combustion-wave structures and burning-rate characteristics are discussed. Prominent features of ADN combustion are identified and compared with other types of energetic materials. In particular, the influence of various condensed- and gas-phase processes in dictating the pressure and temperature sensitivities of the burning rate is examined. In the condensed phase, decomposition proceeds through the mechanisms ADN → NH₄NO₃ + N₂O and ADN → NH₃ + HNO₃ + N₂O, the former mechanism being the basic one. In the gas phase, the mechanisms ADN → NH₃ + HDN and ADN → NH₃ + HNO₃ + N₂O are prevalent. The gas-phase combustion-wave structure in the range of 5–20 atm consists of a near-surface primary flame followed by a dark-zone temperature plateau at 600–1000°C and a secondary flame followed by another dark-zone temperature plateau at 1000–1400°C. At higher pressures (60 atm and above), a final flame is observed at about 1800°C without the existence of any dark-zone temperature plateau. ADN combustion is stable in the range of 5–20 atm and the pressure sensitivity of the burning rate has the form r _b = 20.72p ^0.604 [mm/sec] (p = 0.5–2.0 MPa). The burning characteristics are controlled by exothermic decomposition in the condensed phase. Above 100 atm, the burning rate is well correlated with pressure as r _b = 8.50p ^0.608 [mm/sec] (p = 10–36 MPa). Combustion is stable, and intensive heat feedback from the gas phase dictates the burning rate. The pressure dependence of the burning rate, however, becomes irregular in the range of 20–100 atm. This phenomenon may be attributed to the competing influence of the condensed-phase and gas-phase exothermic reactions in determining the propellant surface conditions and the associated burning rate. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 6, pp. 54–79, November–December, 2005.     

肋片对微小燃烧室内甲烷燃烧与传热特性影响

建立含有肋片的微小通道内甲烷/空气燃烧模型,研究了带肋片的导热壁面对微小尺度燃烧和传热特性的影响。结果表明,纵向肋片对于微小通道中的燃烧和传热过程有着非常重要的影响,与没有肋片的光滑通道相比,带有肋片的壁面起到了良好的导热作用,燃烧室内区域的温度分布梯度大幅降低;纵向肋片的数量对燃烧和传热特性的影响作用要优于肋片高度的影响;横向肋片的高度对火焰位置有着很大的影响,肋片高度增加火焰位置后移且流体区域的温度分布梯度加大;横向肋片宽度和肋片位置对微燃烧和传热过程的影响甚小;两个肋片及肋间距大的通道,其微燃烧和传热特性得到了较大的改善。     

Modes of gasless combustion and macrostructure of combustion Front (for the Ti-Si system as an example)

Gasless combustion of Ti+Si mixtures (taken as an example) was investigated by high-speed video recording followed by computer-assisted processing of stored still frames. The three-dimensional shape of the combustion front was reconstructed, and explanations were proposed for the combustion front propagation modes along the surface of cylindrical samples. The reconstructed front configuration was found to be nearly paraboloidal. The modes of unsteady combustion in T-rich and Si-rich mixtures turned out to be strongly different. The results were used to rationalize the available experimental data on unsteady combustion in terms of microheterogeneous theory. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 4, pp. 147–155, July–August, 2009.     

Network simulation for deep bed filtration of Brownian particles

The effect of different interaction energy curves of DLVO theory on the permeability reduction in a filter bed is investigated by using the Brownian dynamics simulation method and the modified square network model to track the individual particles movement through the filter bed. When energy barrier exists and both particle and pore size distributions are of the Raleigh type, it is found that particles with Brownian motion behavior are easier to get straining at small pores, and cause higher permeability reduction than those without considering the Brownian motion behavior. But, this result was not observed for the constant particle and pore sizes case. The permeability reduction for the Raleigh size distribution is higher than that of the constant size. Similar results are also obtained for the “barrierless” type interaction energy curve for the case of Raleigh type size distribution, with the exception that the decreasing rate of permeability reduction of Brownian particles is smaller than that without considering the Brownian motion behavior. When comparing with the permeability reduction experimental data, it is found that the present model shows fair agreement between the theory and the experimental results when the direct deposition mechanism is dominant.     

影响循环流化床锅炉燃烧热效率的因素和提高途径

为找出提高锅炉燃烧热效率的途径和措施,对循环流化床锅炉进行了燃烧调整试验,分析并总结了烟气氧含量、床层压差、床层温度、运行负荷、煤灰中的碳含量等因素对锅炉燃烧热效率的影响。通过试验数据,提出了提高锅炉燃烧热效率的途径、改进措施和建议。     

Effect of Initial Turbulence on Ignition, Combustion, and Flame Stabilization in a Gas-Suspension Flow

The influence of initial turbulence of an air flow with suspended aluminum particles and the aluminum-particle size on ignition, combustion, and flame stabilization in a combustor with sudden expansion is considered. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 1, pp. 39–48, January–February, 2006.     

新型高能聚合物GAP的热分解和燃烧

简要回顾了GAP的研究历程及应用情况，介绍了有关GAP的特点及研究现状，着重阐述了GAP热分解及燃烧过程的特点，给出了目前比较先进的实验方法及手段，如色谱—质谱联用、热解质谱、分子束质谱、红外激光、紫外激光、CO2激光诱导热解等，可供进一步研究GAP参考。     

Network simulation for deep bed filtration of Brownian particles—a supplement

The track of individual particles moving through a filter bed is simulated by applying the Brownian dynamics simulation method and the modified square network model. The effect of the Raleigh-type size distribution of particles and pores on the permeability reduction of porous media is also investigated. We find that the pore size distribution of porous media has a more profound effect on the reducing of the permeability ratio than that of the particle size distribution especially at the initial period of filtration. Straining is the main mechanism to reduce the permeability at the initial period of injection for the case of Raleigh distribution of the pore size, and vice versa for the case of unique size value where the direct deposition mechanism becomes dominant.     

多孔陶瓷热导率的影响因素及其有效热导率的数值计算方法

多孔陶瓷因具有孔隙率高、体积密度小、比表面积大等独特的表面物理特性而被广泛应用于保温材料、炉膛材料、热障涂层材料、高温烟气过滤材料等,研究多孔陶瓷导热机制并给出其有效热导率的计算方法既是重点又是难点。本文总结了国内外研究的多孔陶瓷热导率的影响因素,概述了多孔陶瓷有效热导率的计算方法,并重点分析了不同显微结构的不同计算方法。针对不同的应用领域对材料热导率的不同要求,提出通过控制显微结构控制热导率是今后多孔陶瓷热导率研究得发展趋势。     

Kinetic Analysis of the Chemical Structure of Waves of Filtration Combustion of Gases in Fuel-Rich Compositions

The structure of heat release and the dynamics of formation of radicals and methane oxidation in a wave of filtration combustion of gases in fuel-rich methane–air compositions is studied with the use of skeleton diagrams and sensitivity analysis. Depending on heat release, the wave is divided into a preheating zone, an exothermic zone characterized by partial oxidation of methane in the reaction CH₄ + 0.5O₂ = CO + 2H₂, and an endothermic zone with the conversion processes CO + H₂O = CO₂ + H₂ and CH₄ + H₂O = CO + 3H₂. It is shown that the composition of products in the wave front is essentially nonequilibrium. Several typical regions are also identified from the viewpoint of prevailing reactions of formation of the basic radicals in the wave. Thus, the dominating mechanism of chain branching is the reaction CH₃ + O₂ = CH₃O + O in the low-temperature region, H₂O₂(+M) = 2OH(+M) and HO₂ + CH₃ = CH₃O + OH in the transitional region, and H + O₂ = O + OH in the high-temperature region. Two former regions correspond to the preheating zone and the latter region corresponds to the exothermic peak of the wave of filtration combustion of gases.     

Transport analysis and model for the performance of an ultrasonically enhanced filtration process

This paper presents an analysis of a filtration technique that uses ultrasound to aid the collection of small particles (tens of microns in diameter) from suspension. In this method, particles are retained within a porous mesh that is subjected to a resonant ultrasonic field, even though the pore size of the mesh is two orders of magnitude greater than the particle diameter. The role of acoustic forces in driving the retention phenomena has previously been studied on a micro-scale, which included modeling and experimental verification of particle motion and trapping near a single element of the mesh. Here, we build on this work to develop an overall transport model to predict macroscopic performance criteria such as breakthrough times and the dynamics of the filtration performance. Results from this model compare favorably to experimental studies of the filtration phenomena; simulation results scale appropriately with experimental results in which inlet feed concentration and flow rate are varied.     

一种燃烧炉的内衬保温材料和烘炉的处理方法

燃烧炉是化工生产常用设备之一，而燃烧炉的筑炉方式又多种多样。本文介绍了硫化氢酸气燃烧炉的筑炉处理和该炉在安装前的早期强度烘炉的处理方法。