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.     

Ignition of Combustible Forest Materials by a Radiant Energy Flux

The paper reports results of experimental ignition of litter layers consisting of needles of cedar, pine, and fir-tree, birch leaves, lichen (Cladonia), and moss (Pleurozium shreberi). It is established that the moss is ignited faster than the other combustible forest materials. It is shown that with equal moisture contents, the ignition times of needle litter from different trees are identical within the experimental error, and for litter of birch leaves, the ignition time is shorter than that for litter of coniferous trees. This difference is found to be due to differences in the interaction of the radiant flux with litter layers of needles and leaves. Minimum values of the ignition heat pulses for needle and leaf litter layers are estimated for various heat-flux densities. These values tend to a minimum for a heat-flux density of 0.5–0.8 MW/m².     

Absolute and Convective Instability of an Oblique Flame Front in a Combustible Gas Mixture Flow

The influence of the velocity component u of a combustible gas mixture, tangent to the flame front, on the character of instability (absolute or convective) of the front in the presence of the force of gravity is considered. For u=0, the velocity v_* of expansion of the region occupied by flamefront perturbations increasing with time is numerically found, using Markstein's dispersion equation for different dimensionless parameters of the problem. Using the power expansions of (k), approximate analytical formulas for v_* are derived. The instability is convective if |u|>v_*; otherwise, it is absolute.     

Formulation and Solution of the Problem of Drying of a Layer of Combustible Forest Materials

The drying of combustible forest materials is the most important and least studied stage of the multiphase process of their burning under natural conditions. Physical and mathematical modeling of the drying of a layer of combustible forest materials is performed in a conjugate formulation by solving the equations of a binary boundary layer and the equations of heat and mass transfer in a layer of combustible forest materials with corresponding boundary and initial conditions. Solutions of this problem for diurnal and seasonal changes in environmental temperature are obtained for three scenarios of development of weather conditions. The data obtained are compared with experimental data on drying of needles of pine and some other coniferous trees. A rigorous physicomathematical basis for prediction of forest fires is given.     

Effect of Melting of Inert Components and Melt Flow on Nonstationary Combustion of Gasless Systems

The effect of the thermocapillary flow of melt of inert components of gasless mixtures on the spinning combustion regimes of cylindrical samples has been studied numerically. The change in the structure of the spinning combustion wave due to a change in the sample radius is discussed, and new spinning combustion regimes are found. Increasing the melt flow velocity leads to stabilization of the combustion, i.e., to the transition from spinning regimes to the stationary propagation of the combustion wave.     

氢火焰检测器气相色谱法测定空气中的可燃气体含量

详细描述了动火分析中用氢火焰气相色谱法测定空气中可燃气体含量的分析方法，利用该方法测定可燃气体含量。证明该测定方法灵敏度高、快速方便、简单易行，非常适用于动火分析。     

DBP对发射药燃烧可燃气体产物影响的理论研究

采用最小自由能算法理论研究了邻苯二甲酸二丁酯(DBP)对单基发射药燃烧生成可燃气体产物的影响规律,并利用定容燃烧试验对理论研究结果进行了验证.结果表明,配方中DBP含量超过某一临界值时,发射药燃烧会有固态游离碳生成;可燃气体的生成量随着DBP含量的升高先逐渐增加,并在DBP含量临界值时(生成游离碳)达到最大值,然后逐渐...     

Hot-Spot Ignition of a Reactive Gas in an Inert Porous Medium

The main stages of development of hot-spot ignition of a reactive gas in a high-porous medium with high values of the Peclet number under conditions of natural gas filtration and limited internal heat transfer between the phases are determined. Gas ignition in a U-shaped hot spot is considered within the framework of an asymptotic analysis with high values of the temperature difference and Frank-Kamenetskii parameter. The critical relation of parameters separating the regimes of gas ignition and gradual cooling of the hot spot is determined. The dependence of the ignition time on parameters of the process is found and analyzed. A strong effect of interphase heat transfer on the ignition limit and time is demonstrated. An example of calculating the critical parameters of hot-spot ignition of methane in processed rocks is given. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 41–48, September–October, 2005.     

Instability in Unsteady-State Evaporation of Binary Solutions into an Inert Gas

The critical time of transition to the convective mode of the unsteady-state evaporation of a horizontal layer of a binary solution into a stagnant gas is theoretically and experimentally determined. It is shown that the slow diffusion mode of evaporation can be destabilized and replaced by the convective mode if the molecular weight of one of the liquid components is higher than the molecular weight of the gas and the molecular weight of the other liquid components is lower than the molecular weight of the gas. The neutral stability curve of the diffusion mode is determined using the Navier-Stokes equation in the Boussinesq approximation, the continuity equation, and the convective diffusion equations of the evaporating components. The transition between the modes is faster than the molecular diffusion; therefore, the depth of penetration of the vapor of the light component into the gas in the diffusion mode can be taken as the linear scale of the phenomenon considered. By the Galerkin method, the neutral stability curve of the diffusion mode of evaporation is determined and the critical time of bifurcation of the mode is found as a function of the composition of an aqueous butanol solution. The theoretical and experimental data are in good agreement.     

Convective Regime of Filtration Combustion of Energetic Materials in a Cocurrent Flow of Their Combustion Products

The convective regime of filtration combustion of energetic materials in a cocurrent flow of their combustion products is studied using a model with extremely simplified kinetics and heat transfer, which shows instability of the process. It is shown that the more accurate twotemperature model describes a steadystate regime. In this regime, the gas temperature on the hot boundary of the heating zone is well below the combustion temperature, and the solidphase temperature is well below the temperature proposed in recent studies on this topic. It is pointed out that the twotemperature approach is unjustified and intragranular nonisothermicity must be taken into account for convective regimes. It is shown that the threetemperature model, which takes into account this effect, does not give a stable steadystate solution.     

Experimental Investigation of the Ignition of Combustible Gas Mixtures by Friction Sparks

This paper presents a method of testing structural materials for spark safety and the results of testing this method for several pairs of materials and samples of combustible gases and vapors. Hydrogen, acetylene, AI-92 gasoline vapor, methane and liquefied petroleum gas were used as combustible gases and vapor, and samples of various types of steel, aluminum, and brass as structural materials.     

Classification of Similarity Criteria in Combustion Theory and the Problem of Autoignition of a Combustible Mixture by Compression

The dynamic problems of the theory of combustion and explosion are classified from the point of view of competition of the characteristic times of bulk chemical reaction, frontal combustion, heat transfer, gas flow from the vessel, compression (motion of the piston), and heating (cooling) rate. We consider dynamic similarity criteria such as the ratio of the characteristic times in problems of classical thermal explosion, dynamic thermal explosion, flammability limits, combustion in communicating vessels, competition of frontal and volumetric combustion, autoignition by adiabatic compression, competition of frontal combustion and piston motion, as well as compound similarity criteria (such as functions of simple dynamic similarity criteria). The problem of autoignition of a mixture by compression is considered, and a method for obtaining an analytical solution of the problem and an algorithm for the approximate solution based on a special differential criterion are proposed.     

高炉滴下带气、液二相流的模拟研究

根据质量和动量的微分平衡,建立了描述高炉滴下带气、液二相流的三维数学模型.观察值与计算结果的一致性确认了本模型的合理性.应用本数学模型计算了首钢1号高炉干域区周围各参数,提出了高炉内焦炭流态化和渣溢流的判别图.     

空气和废气监测用氨溶液标准样品的制备与量值评价

对空气和废气监测用氨溶液标准样品进行了制备和定值分析;同时对不确定度进行了评定。分别从标准样品的定值、均匀性、长期和短期稳定性等方面论述了不确定度的来源和评定方法;介绍了各种因素产生的不确定度以及总合成不确定度的计算方法。     

Effect of Gas Mixture Pressure on the Ignition,Combustion, and Spontaneous Extinction of Chars of Coals of Different Polymorphisms

Combustion, Explosion, and Shock Waves - The dependence of the diameter of a porous carbon particle on stationary temperature at various gas mixture pressures is analyzed. The cases of particle...     

Filtration Combustion of an Energetic Material in a Cocurrent Flow of Its Combustion Products. Critical Combustion Conditions

The paper reports results of a numerical calculation using the threetemperature model developed previously by the authors. In addition to the temperature difference between the gas and the solid phase (skeleton), the model approximately takes into account the temperature distribution in skeleton elements. It is shown that quenching is possible (after burnout of part of the charge) with variation in a number of input parameters: the thermal conductivity of the charge, the ignition temperature, the weight of the igniter, the initial temperature, the porosity of the charge, and the local rate of its decomposition.     

铝电解惰性阳极材料选择的研究进展

论述了传统碳素阳极的缺点及使用惰性阳极的意义,提出了惰性阳极材料应符合的要求,重点阐述了国内外对金属氧化物陶瓷阳极、金属陶瓷阳极、金属阳极的研究成果并总结了以上三类惰性阳极有待进一步解决的主要问题。     

Preparation of Vanadium and Vanadium Oxide Clusters by Means of Inert Gas Aggregation

Vanadium clusters were prepared by the inert gas aggregation technique by evaporating V of high purity. Structural characterization was performed by high-resolution transmission electron microscopy. Apart from vanadium clusters of bcc structures in different orientations, crystalline VO clusters of NaCl structures were observed, which was attributed to the reaction with free oxygen present on the amorphous carbon substrates. The latter could be detected by electron energy-loss spectroscopy. The exposure of the samples to air caused a change to amorphous structures, which re-crystallized under the electron beam. This effect was interpreted as a reaction with water present in the air.     

燃天然气横焰玻璃熔窑火焰燃烧及玻璃液流动的三维CFD耦合分析

本文在全面考虑火焰空间的燃烧与玻璃液传热、流动的耦合的基础上,建立了燃天然气横焰玻璃熔窑火焰空间和玻璃液传热、流动过程的三维数学模型.然后以某燃天然气连通式横焰玻璃熔窑为对象,利用商用CFD软件进行了火焰燃烧和玻璃液传热、流动的耦合数值模拟,研究了该熔窖燃烧空间内气体流动和温度梯度分布以及熔池内玻璃液的流动和温度梯度分布,为提高玻璃窑炉的运行与设计水平提供理论依据,从而指导实际生产和玻璃熔窖设计.