Determination of the critical size of a particle cloud necessary for suppression of gas detonation

Conditions of detonation suppression by inserting inert particles into a reacting gas mixture through which a detonation wave propagates are considered. The pattern of the detonation flow and the scenario of its suppression are determined. The minimum length of the particle cloud that completely suppresses the detonation wave is calculated. The influence of the volume fraction of particles in the cloud on the detonation suppression efficiency is studied. The governing parameter is found to be the length of the cloud that ensures quenching of the ignition/combustion wave formed during detonation wave decomposition rather than the particle mass and the gradient of the volume fraction of particles. It is demonstrated that this length is approximately identical for different distributions of the volume fraction of particles in the cloud.     

Physicomathematical modeling of detonation suppression by inert particles in methane-oxygen and methane-hydrogen-oxygen mixtures

Based on the developed physicomathematical model of detonation attenuation and suppression in a methane-oxygen mixture by means of addition of a cloud of inert particles, the influence of the volume fraction of particles and their diameter on the detonation wave velocity is analyzed. Detonation limits in terms of the volume fraction of particles in methane-oxygen and methane-hydrogen-oxygen mixtures are found. A comparison with our previous data on suppression of detonation in a hydrogen-oxygen mixture shows that the critical volume fractions of particles resulting in detonation wave suppression in the methane-hydrogen-oxygen mixture are greater than those in the hydrogen-oxygen mixture.     

Modeling of propagation of shock and detonation waves in dusty media with allowance for particle collisions

Shock-wave and detonation flows in a two-phase medium consisting of a gas and incompressible particles are studied by methods of numerical simulation with allowance for the random motion and collisions of particles. Steady solutions corresponding to two previously predicted wave types are obtained for the problem of interaction of a plane shock wave with a cloud of particles. The influence of the mixture parameters on the corresponding solutions is determined. In considering the problem of propagation of cellular heterogeneous detonation in a mixture of reacting particles, oxidizer, and inert particles, it is found that the detonation flow structure and the cell size are retained in the mixture with particle collisions. However, smearing (dispersion) of the layers and inert phase structures formed in the far zone of cellular detonation occurs because of particle collisions.     

Numerical investigation of the process of interrupting the detonation wave propagation in monofuel gas suspensions using an inert particle layer

A numerical investigation was performed of the process of interrupting the propagation of a heterogenous detonation wave in a reacting dispersed mixture by means of a layer of inert particles located inside an atomized monofuel cloud. It was found that depending on the parameters of the monofuel and the inert particle suspension, regimes are possible of both interrupted, as well as of a continuous detonation wave propagation. An attempt was made to explain the mechanism of combustion wave suppression with an inert particle layer. An energy criterion is proposed for estimating the possibility of suppressing the detonation waves by means of an interrupter consisting of a suspension of inert particles.Tyumen'. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 2, pp. 90–98, March–April, 1993.     

惰性气体对氢气/空气爆轰传播的抑制作用

常温常压条件下,在内径52 mm的不锈钢管道中开展了惰性气体对氢气/空气（H₂/air）爆轰的抑制实验研究,通过改变当量比（0.6、0.8、1.0、1.2、1.4）和惰性气体种类（CO₂、N₂、Ar）探讨了三种惰性气体对爆轰火焰速度的影响。结果表明,H₂/air爆轰通过可燃气与惰性气体分界面后,爆轰波发生解耦,火焰速度大幅度下降。整个速度下降过程分为快速下降、波动缓慢衰减、火焰消失三个阶段。三种惰性气体中CO₂的抑制效果最明显,其次是Ar和N₂。相较比热容差异影响,Ar和N₂的分子量差异在爆轰抑制中起到主导性作用。贫燃和富燃条件下爆轰在惰性介质中衰减程度均比化学计量比工况下明显,其中富燃条件下爆轰在惰性介质中的衰减更为明显。     

Modeling of flame propagation in a mixture of combustible gases and particles

A physicomathematical model of flame propagation over a gas suspension composed of a mixture of gases (oxidizing, combustible, and inert components) and the particles of a condensed material that reacts heterogeneously with the oxidizing component is formulated. Numerical simulations are used to obtain a dependence of the flame velocity on the parameters related to the mass concentration of the particles, the particle size, the activation energy of a heterogeneous reaction on the particle surface, the heat of the heterogeneous reaction, and the mass exchange of the particles. Depending on the ratio of the dispersed-phase parameters, the flame velocity in this medium can increase severalfold in comparison with the flame velocity in a dust-free gas mixture or decrease. In the latter case, the effect of the particles is similar to the effect of the inert dispersed phase. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 2, pp. 3–9, March–April, 2000.     

Effect of Volume Fraction of Material on Separation by Density Difference in a Liquid‐Fluidized Bed of Inert Particles

A liquid‐fluidized bed was used to separate a pure material from a mixture. A quantity of relatively large sized material was immersed in an inert‐particle fluidized bed and the behavior of materials was examined for different liquid velocities. In particular, the volume fraction of the material was varied and its effect on the separation characteristics was examined. The material floats on the inert‐particle fluidized bed when the density of the material is lower than the apparent density of the bed, regardless of the volume fraction of the material. The apparent density of the bed can be adjusted by changing the liquid velocity. The materials in the upper portion of the bed affect the properties of the bed below them, i.e., the void fraction decreases and the apparent density increases in the inert‐particle suspension when materials are present in the upper portion of the bed. Therefore, the materials float on the bed although the apparent density of the inert‐particle suspension obtained from the case without material is less than the density of the material at a relatively high volume fraction of material. This phenomenon occurs more easily for lighter and smaller materials. This means that small inert particles and low liquid velocities are the optimum operating conditions for the separation.     

Effect of chemically inert particles on parameters and suppression of detonation in gases

An algorithm for calculating the parameters of a steady one-dimensional detonation wave in mixtures of a gas with chemically inert particles and estimating the detonation-cell size in such mixtures is proposed. The calculated detonation parameters and cell size in stoichiometric hydrogen-oxygen mixtures with W, Al₂O₃, and SiO₂ particles are used to analyze the method of suppression of multifront gas detonation by injecting chemically inert particles ahead of the leading wave front. The ratio between the channel diameter and the detonation-cell size is used to estimate the limit of heterogeneous detonation in the mixtures considered. The minimum mass of particles and the characteristic cloud size necessary for detonation suppression are calculated. The effect of thermodynamic parameters of particles on the detonation suppression process is analyzed for the first time. Particles with a high specific heat and (if melting occurs) a high phase-transition heat are found to exert the most pronounced effect. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 77–88, May–June, 2009.     

Prediction of the Behavior of a Liquid‐Fluidized Bed of Inert Particles Used for Separation by Density

A liquid‐fluidized bed of inert particles was used to separate a pure object from a mixture. One (binary solid‐liquid‐fluidized bed) or two (tertiary solid‐liquid‐fluidized bed) types of objects with relatively large‐sized particles were immersed in an inert‐particle bed, and the bed behavior was observed for different liquid velocities. The void fraction and apparent density of the inert‐particle suspension were predicted by considering the effect of the change in object position for different liquid velocities. The prediction method, which considers the change in the minimum fluidization velocity, accurately expressed the changes in the void fraction and the apparent density of the bed with the position of the objects in the bed. Using this method, the liquid velocity required to separate a certain kind of object from a mixture can be predicted.     

Ignition and combustion of disperse and nanodisperse gas suspensions under dynamic conditions

Results of mathematical modeling of propagation of heterogeneous detonation waves in a mixture of fine aluminum particles in oxygen and ignition of fine metal particles in reflected and transmitted shock waves and high-temperature gas flows, which were obtained at the Khristianovich Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences, are briefly reviewed. One-dimensional steady flows and one-dimensional and two-dimensional unsteady flows of reactive mixtures are considered. Flows in the form of weak and overdriven detonation waves and the Chapman-Jouguet detonation are found. Stability of the Chapman-Jouguet flow and weak detonation to interactions with rarefaction waves is demonstrated. Regimes of strong and weak initiation are determined; the calculated and experimental values of the initiation energy are found to be in reasonable agreement. Laminar detonation and cellular detonation for monodisperse and polydisperse mixtures are found within the framework of two-dimensional unsteady detonation flows. New numerical codes are developed for solving nonlinear-boundary-value problems of ignition of individual particles. Particular attention is paid to the accuracy of reproduction of integral parameters (burning time) of some experimental data, depending on the ambient temperature, etc. A solution of a single-phase Stefan problem of nanosized particle melting is described.     

水平圆管固液两相稳态流动特性数值模拟

水平井油水流动特性是设计产液剖面测井方法和建立解释模型的重要依据,当油水中携带沙颗粒时,其流动特性变得更为复杂。通过基于Eulerian描述方法的混合代数滑移模型（MASM）,建立挟沙水或油混合相控制方程和边界条件,并且使用有限差分方法和逐次超松弛（SOR）迭代法建立数值解,以模拟水平井挟沙水或油混合相的各运动特性参数分布。模拟结果表明,主流速度分布随着颗粒相体积分数增大有向下偏移特点,并随着压降值降低而减小。水平井圆截面上颗粒相体积分数分布特征主要与主流速度有关,随着速度降低,体积分数分布值向下向两侧增大。此外,挟沙油混合相主流速度大于挟沙水混合相速度。混合代数滑移模型不仅能够很好地模拟混合相各运动特性参数分布特征,而且计算效率比较高。     

Detonation Limits of Air Mixtures with Two-Component Gaseous Fuels

The problem of detonation limits for ternary mixtures of air with a two-component gaseous fuel is considered for a detonation region represented using the Le Chatelier rule. Examples are given of incorrect treatment of conditions for detonation suppression in hydrogen–air mixtures by the addition of hydrocarbons ignoring the overall composition of the mixture. It is suggested that the range of explosion hazard of lean hydrogen–air mixtures is extended by the addition of small amounts of hydrocarbon gases. Key words: detonation, detonation limits, multicomponent fuel mixtures, suppression and promotion of detonation.     

Interaction of a heterogeneous detonation wave propagating in a cellular regime with a cloud of inert particles

Interaction of heterogeneous cellular detonation propagating in a plane channel with a cloud of inert particles is numerically studied. It is demonstrated that the presence of inert particles alters the detonation wave structure and its velocity.     

Study of the Effect of Additive Particle Size on Non‐ideal Explosive Performance

Detonation performance of non‐ideal RDX‐based compositions was studied. Charges of phlegmatised RDX containing 30% of two types of aluminium powders, coarse aluminium oxide or fine lithium fluoride particles were tested. The research concerning influence of inert and reactive additives on the detonation velocity and quasi‐static pressure was carried out. To estimate the degree of afterburning of the detonation products and reactive particles, closed explosions were performed in a chamber filled with different atmospheres. Explosion residues were also analysed. Gasdynamical and thermochemical calculations were also performed for the tested explosive compositions.     

A comprehensive interpretation of solid layer inversion in liquid fluidised beds

Solid mixing and segregation in liquid fluidised beds containing binary mixtures of spherical particles of different density and size has been studied for a range of liquid velocities, bulk bed compositions and particle properties. It was shown that a bed of denser particles expands with liquid velocity independently of the presence of the lighter particles. When the bulk volume fraction of the lighter particles is high and the liquid velocity is relatively low, the bed forms two layers, i.e. the upper layer consisting almost entirely of the lighter and the lower mixed layer consisting of both components in which the volume of the lighter increases with liquid velocity. A completely mixed bed is obtained at a certain velocity and then a further increase of the velocity causes “layer inversion”. The liquid velocity at which complete mixing occurs depends on the bulk bed composition, and at that velocity the volume fraction of the lighter in the lower mixed layer is constant regardless of the bulk bed composition. It is shown that layer inversion occurs for a given particle mixture when the liquid velocity passes through a value at which the volume fraction of the lighter in the lower layer becomes equal to the bulk bed composition; or for a given velocity, when the bulk bed composition becomes equal to the fraction of the lighter component which exists in the lower layer. The dependency of the fraction on the liquid velocity and the particle properties is examined to some extent.     

Sedimentation of Binary Particle Mixtures

An equation is given, based on proposals of previous workers, for the slip velocity of each particle species within a polydisperse particle mixture moving vertically through a liquid. It is demonstrated how the initial settling velocity of each particle species may be determined when such a mixture undergoes sedimentation. A simplified graphical construction is developed for a binary particle mixture similar to that of Kynch, which was for a single species. It is shown how the zone boundary velocities and the sediment rise velocities may be determined using the proposed construction. The method is confirmed by experiments in which a mixture of particles consisting of two distinct sizes was allowed to settle to completion.     

An Analysis of the Influence of Detonator Parameters on the propagation of shock waves in an inert medium

The effect of mass, diameter and type of detonator on parameters of shock waves generated in plexiglas block is examined by experimental and theoretical means. The quantities connected with the shock wave, such as, the mean velocity of the shock wave front, the profile of mass velocity behind this front, and the mean velocity of free surface of the loaded block are measured. To perform an numerical analysis of the shock wave parameters mentioned above on type and size of detonator the problem is considered of acting of detonation products of an explosive charge on a block of inert material. In this goal, the active mass of charge is determined and, next, the model assumptions and mathematical formulation of the problem of penetration of pressure pulse into inert medium are presented. The results of computer simulation and experimental data are compared.     

Simulation and experiment of segregating/mixing of rice husk–sand mixture in a bubbling fluidized bed

The fluidization behavior of rice husk–sand mixture in the gas bubbling fluidized bed is experimentally and theoretically studied. The relevancy of the pressure drop profile of rice husk–sand mixture to the definition of its minimum fluidization velocity is discussed, and the minimum fluidization velocity of rice husk–sand binary mixture is determined. The distributions of mass fraction of rice husk particles along the bed height are measured, and the profiles of the mean particle diameter of mixture are determined. A multi-fluid gas–solid flow model is presented where equations are derived from the kinetic theory of granular flow. Separate transport equations are constructed for each of the particle classes, allowing for the interaction between particle classes, as well as the momentum and energy are exchanged between the respective classes and the carrier gas. The distributions of the mass fraction of rice husk particles and the mean particle diameter of binary mixture are predicted. The numerical results are analyzed, and compared with experimental data.     

Detonation characteristics of ammonium nitrate and activated fertilizer mixtures

To better understand the detonation characteristics of ammonium nitrate (AN) and activated additives mixtures, potassium chloride (KCl) and monoammonium phosphate (MAP) are mixed with AN by different mixing methods. The UN gap test and scanning electron microscopy are applied to study AN and AN-additive mixtures. For the mechanical mixing method, the detonation velocity of AN-additives decreases with increasing the additive proportion, while the detonation velocity of modified AN prepared by the solution mixing method shows the opposite tendency. It is proved that the sensitivity to shock waves increases as the size of AN particles decreases. The type of additives, the mixing methods, and the particle size distribution are important parameters that affect the detonation characteristics of AN.