Acceleration of solid particles during cumulation of detonation products in vacuum

The possibility of increasing the velocity of solid particles accelerated by an explosion of a long tubular charge of a high explosive (HE) in vacuum is analyzed. The experimental results obtained indicate that the acceleration velocity cannot be considerably increased. The probable causes are erosion of the material from the inner surface of the HE tube and a significant decrease in the mass flow velocity when the length of the HE tube exceeds the optimum length. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 4, pp. 102–105, July–August 1999.     

Parameters of an accelerating spherical deflagration

A numerical analysis of an accelerating spherical deflagration is performed. It is shown that the deviations of the deflagration parameters from steady values are determined by the degree of increase in velocity in the law of motion for the flame front rather than by the acceleration value. Maximum deviations are observed at a front velocity equal to ≈0.1 of the sound velocity in the starting mixture. Analytical relations are obtained for the main parameters of the resulting flow for velocities up to a front velocity a factor of1.5 higher than the sound velocity in the starting mixture. Bauman Moscow State Technical University, Moscow 107005. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 2, pp. 11–22, March–April, 1997.     

Explosive characteristics of aluminized HMX-based nanocomposites

The explosive characteristics of HMX compositions doped with 15% Al (by weight) were studied experimentally. The detonation velocity, pressure and temperature profiles, the velocity of endwise acceleration of plates, and the heat of explosion of dense pressed samples were measured. The results were compared for compositions based on mechanical mixtures of initial micron-size particles of HMX with aluminum powders of various sizes and for nanocomposites. The addition of nanoaluminum reduces the detonation velocity to a greater degree than the addition of micron-size aluminum. The mechanical mixtures have close detonation velocities, whereas in composites containing different types of nanoaluminum, they differ by almost 200 m/sec. For all compositions, except for the most homogeneous nanocomposite, two-peak pressure profiles are observed. For charges of a composite and a mechanical mixture with nanoaluminum of the same type, the second peak pressures almost coincide but are reached in different times. At the same time, the peak pressure increases with decreasing aluminum particle size. The temperature profiles agree qualitatively with the pressure profiles. The velocity of endwise acceleration of plates depends linearly on the activity of the aluminum powder used. Nanocomposites and mechanical mixtures containing the same aluminum powder have close heats of explosion. Nanoaluminum is almost completely oxidized during calorimeter bomb tests, and the major factor determining the heat of explosion of the compositions with nanoaluminum is also the content of active metal in the aluminum powder. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 85–100, March–April, 2008.     

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.     

The investigation of pressure drop in moving-beds

The pressure drop of a cross-flow moving-bed was investigated in a two-dimensional rectangular apparatus. The effects of the particle velocity, the superficial gas velocity, the formation and development of cavity/raceway and voidage of particles on the pressure drop were investigated experimentally under the operational conditions of 0.09–1.35 m/s of the superficial gas velocity and 0.95–9.68 cm/min of the particle velocity. The experimental results show that the particle velocity has little influence on the pressure drop, while the phenomena of cavity and pinning occur when the cross-flow velocity is high enough. The development of a cavity or a raceway can result in three types of variations of pressure drop with time: stabilization, slight fluctuation and severe fluctuation. A cavity appears in a process cycle of ‘formation-growing up-collapsing-fluidization’ at a high gas velocity. On the basis of experimental results, a model for calculating the pressure drop after a cavity occurs and a dimensionless relationship of cavity size is developed, which gives a good qualitative account of the experimental data. Translated from The Chinese Journal of Process Engineering, 2006, 6(5): 697–702 [译自: 过程工程学报]     

Propagation of spherical gas filtration combustion waves in inert porous media

The behavior of spherical combustion waves of gases in inert porous media is described in terms of one- and two-temperature models. Parametric dependences are obtained for the wave velocity and acceleration and for the temperature of the gas and porous medium in the wave. It is shown that in a diverging spherical gas flow, combustion waves initiated at different radii of the sphere converge to the standing wave coordinater ^*, and in a converging flow, on the other hand, they diverge from it. The experimentally observed propagation behavior of spherical combustion waves is well described by the proposed models. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 1, pp. 60–66, January–February 1999     

Formation of metal oxide nanoparticles in combustion of titanium and aluminum droplets

A study was performed of the formation of metal oxide nanoparticles during combustion of aluminum and titanium drops which moved in air at a velocity of up to 3 m/sec. The source of the burning particles was a pyrotechnic mixture which contained an oxidizer, a binder, and metal particles of size 4–350 μm. Transmission electron microscopic studies showed that the combustion products were 1–10 μm aggregates of fractal structure consisting of primary particles (spherules) of Al₂O₃/TiO₂ 5–150 nm in diameter. The Brownian diffusion of the aggregates and their motion in electric and gravitational fields were observed using videomicroscopic recording. The charge distribution of TiO₂ aggregates and the equivalent radius of Brownian mobility were determined. In Al combustion, the zone of nanoparticle formation is separated from the particle surface by a distance approximately equal to the particle radius, and in Ti combustion, this zone is located directly near the surface. Coagulation of the oxide aerosol in the track of a burning particle leads to aerogelation with the formation of huge aggregates. Analytical expressions for approximate calculation of the parameters of the oxide particles and zones of their formation are proposed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 6, pp. 33–47, November–December, 2006.     

Mathematical simulation of the ejection of a gas suspension from a shock-tube channel under the action of a compressed gas

Results are presented of a numerical calculation of an unsteady two-dimensional axisymmetric wave flow of an inert monodispersed gas suspension from the channel of a shock tube into the surrounding gaseous space under the action of a gas compressed in a high-pressure chamber. The acceleration of dispersed particles inside the tube and in the submerged space behind the diffracting air shock-wave front is analyzed. The effect of the formation of a vortex dispersed ring during dispersion of a particle cloud is discussed. The influence of the governing parameters of the ejected gas suspension layer and the driving gas on the distance of dispersion of a dispersed particle cloud is investigated. Translated fromFizika Goreniya i Vzryva,. Vol. 34, No. 3, pp. 107–116, May–June 1998.     

Solid-State Synthesis of ZnTe in Shock Waves

Shock front velocities in a heterogeneous stoichiometric zinc-tellurium mixture in cylindrical capsules were measured at normal and elevated temperatures. In the range of preheating temperatures of 150–300°C, the velocity of a strong shock wave was found to increase by 0.91 km/sec, which is attributed to the occurrence of an exothermic reaction in the zone of high dynamic pressures with an increase in the specific volume. The average velocity of a weak shock wave increased by 0.31 km/sec in the far region of the reaction cell as the preheating temperature of the stoichiometric Zn-Te mixture increased by 150°C. X-ray structure analysis of the shock-recovered products showed almost complete transformation of the reactants with the formation of the cubic ZnTe phase. Theoretical calculations of the acceleration of the shock front velocity due to the reaction in the Zn-Te mixture were conducted. The occurrence of solid-state detonation in the tested mixture is assumed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 1, pp. 130–137, January–February, 2006.     

Determination of nonideal self-sustained detonation regimes of aluminum particles in air

A two-velocity two-temperature model of detonation of aluminum particles suspended in oxygen is employed to study the problem of interaction of a plane detonation wave with an adjacent nonequilibrium rarefaction wave formed with instantaneous removal of the sustaining piston. It is confirmed that the Chapman-Jouguet regimes and weak regimes with a supersonic (with respect to the frozen sound velocity) final state are self-sustained. Stable propagation of the structure is shown for the weak regimes with subsonic (with respect to the frozen sound velocity) and supersonic (with respect to the equilibrium sound velocity) final states (which are unstable in a single-velocity approximation). Interaction of an overcompression wave with a rarefaction wave for relaxation-parameter values that fall into the region of existence of Chapman-Jouguet regimes, results in entry into a Chapman-Jouguet regime. A self-sustained regime of weak detonation that corresponds to the given relaxation parameters is realized outside this region. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 5, pp. 95–102, September–October 1998.     

Approximate computation of the projection of a massive body without a sealing liner by a two-phase medium flow

Within the framework of a single-velocity, two-phase medium, a method is proposed and calculations are performed for the projection of a massive body without a sealing liner by an unsteady flow of a gas-dispersed mixture., Qualitative and quantitative dependences of the velocity and kinetic energy of the projectile on its relative length and the density ratio of the projectile and the gas-dispersed medium are derived. The calculations are supported by experimental data. Translated fromFizika Goreniya i Vzryva, V. 34, No. 3, pp. 117–120, May–June 1998.     

Fireball during combustion of hydrocarbon fuel releases. I. Structure and lift dynamics

The formation, combustion, and thermal interaction of the fireballs which develop upon ignition of a cloud of hydrocarbon fuel near the Earth’s surface are simulated numerically. The axisymmetric nonstationary flow is described by a system of Favre averaged conservation equations invoking a (k−ε)-turbulence model, a model for turbulent combustion, and a global-kinetic scheme for formation and burnup of soot particles. The optical properties of the mixture of combustion products and soot are modeled by a weighted sum of gray gases. The radiation field is calculated using a combination of a volume emission approximation and a diffusion approximation. Calculations are done for fireballs formed during vertical releases of gaseous propane masses of 1 g to 10³ kg with ignition near the release point. The internal structure of a fireball is analyzed in detail at various stages of its evolution. The lift dynamics of a fireball is illustrated for release velocities corresponding to Froude numbers (defined as the square of the ratio of the linear outflow velocity to the characteristic velocity owing to buoyancy forces) ranging from 5–250. The temperature, concentrations, and reaction rates in the fireball are determined as functions of time. It is shown that for these ranges of fuel mass and release velocity, the dimensionless parameters introduced here can be used for scaling the results and using the calculated dependences obtained here in a unified fashion. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 3, pp. 7–19, May–June 1999.     

Numerical simulation of two-dimensional spouted bed with draft plates by discrete element method

A discrete element method (DEM)-computational fluid dynamics (CFD) two-way coupling method was employed to simulate the hydrodynamics in a two-dimensional spouted bed with draft plates. The motion of particles was modeled by the DEM and the gas flow was modeled by the Navier-Stokes equation. The interactions between gas and particles were considered using a twoway coupling method. The motion of particles in the spouted bed with complex geometry was solved by combining DEM and boundary element method (BEM). The minimal spouted velocity was obtained by the BEMDEM-CFD simulation and the variation of the flow pattern in the bed with different superficial gas velocity was studied. The relationship between the pressure drop of the spouted bed and the superficial gas velocity was achieved from the simulations. The radial profile of the averaged vertical velocities of particles and the profile of the averaged void fraction in the spout and the annulus were statistically analyzed. The flow characteristics of the gas-solid system in the two-dimensional spouted bed were clearly described by the simulation results. __________ Translated from Chemical Engineering (China), 2007, 35(6): 24–28 [译自: 化学工程]     

Interaction of rarefaction waves with a finite-thickness layer near a rigid boundary. Equilibrium approximation

Interaction of a rarefaction wave with a layer of solid particles near the end face of a shock tube is considered. A one-dimensional unsteady approximation of mechanics of heterogeneous media with identical pressures of the phases and with allowance for a finite volume concentration of particles in the layer is used as a mathematical model. The wave pattern of the flow and the mechanism of wave interaction with the layer, including the dynamics of the layer boundary depending on the layer thickness and rarefaction-wave width, are determined. The mathematical model proposed is verified against the dependence of the layer-boundary coordinate on time and also the dependence of the velocity of upward motion of the layer on the difference in pressures between the high-pressure and low-pressure chambers. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 126–135, September–October, 2007.     

Propellant performance of organic explosives and their energy output and detonation velocity limits

Methods for determining the propellant performance of high explosives (HEs) are considered. The common and distinguishing features of the techniques of end acceleration of plates and shell expansion are shown. Experimental data on the propellant performance of individual explosives are given. The influence of metal additives on the brisance (propellant performance) and blast effect of explosive compositions is considered. A theoretical method for estimating the propellant performance is proposed, and the propellant performance of hydrogen-free HEs is calculated using experimental data on the enthalpies of formation and densities of single crystals. The energy output and detonation velocity limits of organic HEs are considered and estimated. Promising directions in the investigation of the properties of HEs are considered. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 99–111, January–February, 2007.     

Velocities of acceleration of plates made of different materials by detonation products

Velocities of acceleration of plates made of different materials by explosion products from the end face of a small-thickness charge are measured. Velocities of acceleration of non-porous metal plates with an identical mass, made of aluminum, steel, copper, and tantalum differ by less than 5%. The difference in velocities of acceleration of porous plates made of the same materials and plates with an identical mass but made of several layers of different materials reaches 20%. Layered plates with aluminum layers of different porosities can be accelerated to higher velocities than solid plates. No decrease in velocity is observed in the case with a talcum layer placed under a steel plate of the same thickness, i.e., with an increased total mass. The effects observed can be explained by the wave approach to considering the process of plate acceleration. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 118-123, May–June, 2009.     

Detonation Velocity of Emulsion Explosives Containing Cenospheres

The detonation velocity of an emulsion explosive containing hollow alumosilicate microspheres (cenospheres) as the sensitizer is measured. The size of the microspheres is 50–250 μm. The relations between the detonation velocity and the charge density and diameter are compared for emulsion explosives containing cenospheres or glass microballoons as the sensitizer. It is shown that for a 55 mm diameter charge, the maximum detonation velocity of the composition with cenospheres of size 70–100 μm is 5.5–5.6 km/sec, as well as for 3M glass microballoons. The critical diameter for the emulsion explosive with cenosphere is 1.5–2 times larger than that for the emulsion explosive with glass microballoons and is 35–40 mm. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 119–127, September–October, 2005.     

Deformations inside burning specimens

The dynamics of particle motion inside burning specimens producing solid combustion products was studied by flash radiography. In the experiments, we used specimens of aTi+C+20% TiC mixture, inside which marks in the form of strips of a ofZr+WO ₃ mixture or a tantalum powder were placed. The specimens were burnt in a semiclosed rigid casing with exhaust of impurity gases through slags. It is established that, just behind the combustion front, particles of combustion products begin to move in the direction opposite to the direction of motion of the combustion front. In the central zone of specimens, the particle velocity reaches values comparable with the combustion velocity of the specimens (∼20 mm/sec), whereas, on the periphery, the particle velocity is close to zero. Institute of Experimental Physics, Sarov 607190. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 4, pp. 78–83, July–August, 1997.     

Method for calculating the combustion efficiency of aluminum in explosion products from a metallized composition

A method is proposed for calculating the dynamics of energy production in metallized explosive compositions based on constructing plots of the velocity and acceleration of radial expansion of a cylindrical shell and can be used to estimate the effective fraction of reacted aluminum. Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 5, pp. 99–101, September–October, 1993.     

Electrode gauge as an instrument for studying shock compression and metallization of the substance

An electrode gauge for particle velocity is used to study condensed substances that acquire high electrical conductivity under shock compression. Thin metallic electrodes are placed into the substance. A shock wave propagates over the substance along the electrodes in a transverse magnetic field. A moving conducting substance closes the electrodes and generates an electromotive force on them. To justify the operation principle of the electrode gauge, the electrical conductivity of selenium and aluminum powders is measured. The high electrical conductivity of the powders (up to ≈10⁴ Ω⁻¹ · cm⁻¹) allows the electrode gauge to be used for determining the kinematic characteristics of the shock wave. The voltage on the electrodes is proportional to the mean value of particle velocity in the probing conducting layer located directly behind the shock front. Introduction of additional electrodes into the measurement cell allows the wave velocity to be found. This technique is used to plot the shock adiabats of selenium and aluminum powders of different densities. The experimental data obtained are presented as linear dependences of wave velocity on particle velocity. For a powder with large particles, the thickness of the probing layer is commensurable with the shock-transition width. This offers a possibility of using the electrode gauge to study the structure of the shock transition and the phase of substance metallization. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 116–125, September–October, 2007.