Mathematical Simulation of Three-Dimensional Spin Regimes of Gasless Combustion

A three-dimensional mathematical model is constructed for the gasless combustion of a solid circular cylindrical specimen. The steady-stated spin regimes obtained were studied by numerical methods. The structure and mechanism of spin combustion are illustrated and discussed. It is shown how the space–time pattern of spin-wave propagation is complicated as the radius of the cylinder increases. Spin propagation of the front can proceed in a regime in which the structure of the front does not change (for small radii of the sample) or in an unsteady regime, in which the structure of the front undergoes numerous changes over a period. In the second case, a synchronous or alternate flicker of the sites is observed on the surface of the cylinder. The nonuniqueness of the combustion regimes is detected. It is shown that the average velocity of propagation of the spin-combustion front is of the order of the velocity of steady front propagation under adiabatic conditions.     

Inert Additive Melting in a Gasless Combustion Wave

The effect of melting of an inert additive on the pattern of gasless combustion is analyzed for the case of a single-stage reaction. Stationary combustion regimes with a phase transition are studied analytically and numerically. The phase transition is shown to manifest itself differently in the dependences of the combustion velocity on the amount of the inert additive and the initial temperature. Combustion regimes are analyzed, where the front velocity in the model considered is independent of the inert additive amount. Making use of such regimes in studying the effect of structural factors on combustion is discussed. Key words: gasless combustion, low-melting inert component, phase transition.     

Relationship between Field Direction and Wave Propagation in Activated Combustion Synthesis

Using experimental and modeling studies, the effect of field direction on the field-activated combustion synthesis of SiC was investigated. Field application imposed in a direction perpendicular to wave propagation resulted in enhancement: the wave velocity increased linearly with an increase in field strength. For field application parallel to wave propagation, two cases were considered: confined and nonconfined areas of impacted energy from an ignition source. In the confined case both experimental (using laser ignition) and simulation studies were made. Both showed the establishment of a two-front combustion with waves moving to opposite sides in a direction perpendicular to the field. In the nonconfined case, initial waves propagated in a direction parallel to the field but were independent of field strength. The results are interpreted in terms of a model in which the current is confined to the combustion zone, adding another source of heat to the combustion process, at a rate of σE² (J·cm^-3·s^-1).     

Deformation Dynamics of a Reactive Medium During Gasless Combustion

Deformation during gasless combustion of 5Ti + 3Si and Ti + C samples was studied experimentally. The dynamics of motion of the material in a gasless combustion wave was studied using highspeed video recording (500 frames/sec) with a spatial resolution of the order of 10 m. It was shown that behind the combustion front, the medium was first expanded and then compressed. The dimensions of the expansion and compression zones were determined.     

Combustion of Granulated Gasless Mixtures in a Flow of Inert Gas

Combustion of granulated gasless mixtures in a flow of inert gas was numerically explored in terms of a two-temperature approximation to mathematical modeling of unsteady combustion. The regimes of combustion wave propagation were analyzed as a function of gas flow characteristics and parameters of interphase heat transfer.     

Gasless Combustion of a Model Multilayer System (Combustion of Disks without Gaps(

The mechanism of combustion in a multilayer system of disks pressed from a 5Ti–3Si mixture under compressive stresses was studied experimentally. In the examined range of process parameters, the existence of only the relay-race combustion regime is revealed. The times of combustion transfer between the disks are determined.     

Gasless Combustion of a Model Multilayer System (Combustion of Disks with a Gap)

The mechanism of combustion in a multilayer 5Ti+3Si system upon packing of disks with a gap is studied experimentally. The existence of a superadiabatic combustion regime is revealed. It is shown that only the relay–race combustion regime occurs at all the process parameters studied.     

Ionization in a Combustion Wave

The reaction mechanism and kinetics of self-propagating high-temperature synthesis in a Ti₅Si₃ system are experimentally studied. The Langmuir probe and optical spectroscopy are used to determine the composition and degree of ionization of the gas phase formed due to the combustion-induced degassing of impurities. The propagation of the combustion wave is shown to be accompanied by ionization of released gases, both the ion concentrations and electron temperatures being determined. Through a comparison between the data obtained and spectroscopic data, the ion species are identified. Key words: Combustion wave, gas phase, ionization, ion concentration, electron temperature.     

Effect of Kinetic Properties of a Mixture on Wave Macrocharacteristics of Filtration Combustion of Gases

On the basis of the latest experimental data using a detailed kinetic model, the influence of kinetic features of ultrarich methaneair mixtures (in comparison with ultralean ones) on the main characteristics of superadiabatic waves of filtration combustion of gases is considered. It is shown that substantially lower concentrations of O, OH, and H radicals are typical of ultrarich mixtures, which results from effective inhibition of atomic hydrogen participating in the chain branching reaction H + O₂ = OH + O by methane in the reaction H + CH₄ = CH₃ + H₂. Therefore, extension of the preheating zone and noticeable expansion of the heatrelease region are typical of rich compositions. A decrease in generation of the main radicals in ultrarich mixtures (as compared to ultralean compositions) leads to an increase in the maximum skeleton temperature by 300– 350 K and to a significant increase in velocity of wavefront propagation.     

窑炉燃烧室传热过程的数学模拟

本文对火焰传热过程中能量方程进行了离散发射处理及概率模拟计算,得出了窑炉燃烧室辐射传热过程的数学模型,并对所建立的数学模型进行了数字模拟且在计算机上实现.作为应用研究,文中对某实际窑炉燃烧室进行了理论计算及验证实验.验证结果表明:所建立的数学模型及其概率模拟的求解方法符合窑炉燃烧室实际传热过程,从而为窑炉燃烧室传热过程的数值计算指明了方向.     

Unsteady Combustion Regimes of Gasless Systems with a Low-Melting Inert Component

The paper studied the effect of temperature and heats of melting of an inert low-melting component of a mixture and its quantity on the regularities of ignition and unsteady combustion regimes of gasless systems.     

Numerical Simulation of Shock Wave Propagation n a Mixture of a Gas and Solid Particles

A numerical method based on the cubic interpolated polynomial (CIP) approach is applied for simulation of two-velocity two-temperature two-phase flow dynamics. Validation of the results is provided by numerical tests. A problem of shock wave propagation in a mixture of a viscous heat-conducting gas and solid particles of essential volume fractions is investigated as an application case. The influence of the particle size and drag coefficient formulation on the flow pattern, in particular, on the temperature behavior within the relaxation zone is revealed. A comparison with experimental dependences of the parameters behind the shock front on the Mach number is performed.     

Synthesis of Mullite Powders Through a Suspension Combustion Process

This work reports on the synthesis of mullite powders by a suspension combustion process. Aluminum nitrate, as a source of Al, and a colloidal silica suspension, as a source of Si, are used as reagents, and urea serves as the fuel. This colloidal suspension allows a complete mixing of the reactants, thus promoting a core-shell reaction to produce the mullite. The powders obtained need to be treated at a high temperature to form the mullite. However, when ammonium nitrate is also added as a combustion aid, the mullite phase is directly obtained without any further treatment. A chemical reaction involving all these compounds is proposed, and the thermodynamic parameters are calculated in order to predict the temperature reached during the combustion process. The addition of ammonium nitrate reduces the temperature of the reaction by ca. 150°C. Once the conditions for the combustion reaction are optimized, the Al/Si ratio is modified in an attempt to obtain monophasic mullite.     

Dynamic Features of Combustion of Polydisperse Aluminum Powders in a Gas

The results of a mesh analysis of aluminum powders are considered. It is shown that the particle mass distributions are nearly normal or lognormal. The differences in the combustion dynamics between powders consisting of polydisperse particles and particles of the same sizes are studied. It is established that these differences are manifested only in the late stage of combustion and are due to the presence of a coarse particle fraction in the powder.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 4, pp. 78–83, July–August, 2005.     

定容条件下火药实际燃烧规律的数值模拟

为研究火药的实际燃烧规律,建立了定容条件下火药燃烧的修正数学模型,分析了火药实际弧厚的分布及变化、点火不同步和燃速系数变化等因素对火药实际燃烧规律的影响.在此基础上,用考虑综合因素的修正数学模型对定容条件下火药的实际燃烧过程进行了模拟,计算值与实验结果具有较好的一致性,说明修正模型所建立的假设及处理方案是合理的.     

定容条件下火药实际燃烧规律的数值模拟

为研究火药的实际燃烧规律,建立了定容条件下火药燃烧的修正数学模型,分析了火药实际弧厚的分布及变化、点火不同步和燃速系数变化等因素对火药实际燃烧规律的影响。在此基础上,用考虑综合因素的修正数学模型对定容条件下火药的实际燃烧过程进行了模拟,计算值与实验结果具有较好的一致性,说明修正模型所建立的假设及处理方案是合理的。     

Metallochemical Analysis of the Reaction in a Mixture of Nickel and Aluminum Powders

Phaseformation processes are considered at the level of a mesocell of a mixture with the use of the state diagram for a binary system. Consecutive schemes of metallochemical reactions of formation and decomposition of intermetallide compounds in a mixture of nickel and aluminum powders are suggested. The problem of diffusion annealing of this mixture is numerically solved for two different conditions: at a constant temperature and at a temperature slowly increasing by a linear law.     

Combustion of Agglomerated Ultrafine Aluminum Powders in Air

It is shown experimentally that agglomeration of ultrafine aluminum powders decreases their reactivity during nonisothermal oxidation in air. Under normal and low pressures, the concentration of bound nitrogen in combustion products is lower for agglomerated powders than for unagglomerated powders, and under high pressures (>120 kPa), it is higher for agglomerated powders. Key words: ultrafine powder, aluminum, agglomeration, combustion, reactivity, aluminum nitride.     

Combustion of Mixtures of Commercial Aluminum Powders and Ultrafine Aluminum Powders and Aluminum Oxide in Air

The paper studies the combustion of mixtures of commercial aluminum powders (ASD-1 and ASD-4) and ultrafine powders of Al and -Al₂O₃ in air. It is shown that the combustion of coarsely dispersed commercial powders is accompanied by binding of air nitrogen with formation of AlN and AlON. The combustion of mixtures proceeds in two stages with the possible formation of intermediate gaseous and liquid products. The processes of sintering and incomplete combustion play an important role in the combustion of mixtures of commercial powders and ultrafine powders of aluminum.     

基于活性污泥数学模型的污水处理工艺动态模拟

以反应器动力学原理为基础,借助活性污泥数学模型,对污水处理工艺进行动态模拟实验,为增强实验结果的准确性,采用传统模型处理工艺作为对照。结果表明,基于活性污泥数学模型的污水处理工艺能够有效去除污水中的磷酸盐、氨氮化合物、硝态氮等污染介质,较传统模型处理工艺具有良好的污水处理能力。因此,该模型在污水处理工艺的优化设计与运行中具有较高的实用价值和良好的应用前景。