Gas-detonation processing of particles

It is suggested to employ detonation waves for the processing of gas suspensions. Computational experiment is used for assessing the possibility of processing particles by detonation waves. The structure of detonation wave and its impact on solid particles are numerically calculated. The combined impact made by detonation wave and expansion wave on a particle is studied. The investigation results are used to demonstrate the possibility of processing particles in detonation tubes.     

Velocity Fluctuations in a Particle-Laden Turbulent Flow over a Backward-Facing Step

Dilute gas-particle turbulent flow over a backward-facing step is numerically simulated. Large Eddy Simulation (LES) is used for the continuous phase and a Lagrangian trajectory method is adopted for the particle phase. Four typical locations in the flow field are chosen to investigate the two-phase velocity fluctuations. Time-series velocities of the gas phase with particles of different sizes are obtained. Velocity of the small particles is found to be similar to that of the gas phase, while high frequency noise exists in the velocity of the large particles. While the mean and rms velocities of the gas phase and small particles are correlated, the rms velocities of large particles have no correlation with the gas phase. The frequency spectrum of the velocity of the gas phase and the small particle phase show the -5/3 decay for higher wave number, as expected in a turbulent flow. However, there is a "rising tail' in the high frequency end of the spectrum for larger particles. It is shown that large particles behave differently in the flow field, while small particles behave similarly and dominated by the local gas phase flow.     

A simple approach for determining detonation velocity of high explosive at any loading density

A simple empirical relationship is introduced between detonation velocity at any loading density and chemical composition of high explosive as well as its gas phase heat of formation, which is calculated by group additivity rules. The present work may be applied to any explosive that contains the elements of carbon, hydrogen, nitrogen and oxygen with no difficulties. The new correlation can easily be applied for determining detonation velocity of explosives with loading densities less than 1g/cm3 as well as greater than 1g/cm3. Calculated detonation velocities by this procedure for both pure and explosive formulations show good agreement with respect to measured detonation velocity over a wide range of loading density.     

An Euler–Lagrange particle approach for modeling fragments accelerated by explosive detonation

In this paper, a method is proposed for modeling explosive‐driven fragments as spherical particles with a point‐particle approach. Lagrangian particles are coupled with a multimaterial Eulerian solver that uses a three‐dimensional finite volume framework on unstructured grids. The Euler–Lagrange method provides a straightforward and inexpensive alternative to directly resolving particle surfaces or coupling with structural dynamics solvers. The importance of the drag and inviscid unsteady particle forces is shown through investigations of particles accelerated in shock tube experiments and in condensed phase explosive detonation. Numerical experiments are conducted to study the acceleration of isolated explosive‐driven particles at various locations relative to the explosive surface. The point‐particle method predicts fragment terminal velocities that are in good agreement with simulations where particles are fully resolved, while using a computational cell size that is eight times larger. It is determined that inviscid unsteady forces are dominating for particles sitting on, or embedded in, the explosive charge. The effect of explosive confinement, provided by multiple particles, is investigated through a numerical study with a cylindrical C4 charge. Decreasing particle spacing, until particles are touching, causes a 30–50% increase in particle terminal velocity and similar increase in gas impulse. Copyright © 2015 John Wiley & Sons, Ltd.     

爆轰合成用的乳化炸药制备工艺与爆轰特性

制备了一种用于爆轰合成纳米MnFe2O4颗粒的新型乳化炸药,并对其制备工艺及爆轰特性进行探讨,确定了其制备工艺参数,通过爆速测量实验及爆轰产物检测,获得了该炸药的爆速,并研究了其爆轰状态.结果表明,该乳化炸药的制备工艺比传统炸药要求更加严格.纯净乳化基质不具备爆轰感度,添加RDX后,其爆轰参数与传统乳化炸药相近(或略低...     

Detonation spraying behaviour of refractory metals: Case studies for Mo and Ta-based powders

In thermal spraying of refractory metal powders, two major issues need to be solved: particles of materials having high melting temperatures should be heated to reach a semi-molten/molten state or temperatures close to the melting point, while oxidation of the metals should be prevented. It has long been believed that it is rather difficult, if not impossible, to produce high-quality refractory metal coatings by detonation spraying. In this work, we demonstrated the capability of the detonation spraying method to produce tantalum-based and molybdenum coatings of low porosity. Using a computer-controlled detonation spray (CCDS2000) facility, the detonation spraying behaviour of a molybdenum powder and a partially oxidized tantalum powder was studied. Spraying was conducted onto steel substrates using an acetylene-oxygen mixture with O₂/C₂H₂?=?1.1. The spraying process was studied by means of analyzing the splat morphology and calculating the particle temperatures and velocities. According to the X-ray diffraction phase analysis, the metals did not experience oxidation during the deposition. Rather, partial reduction of the oxide phase contained in the Ta-based powder occurred during spraying.     

Effect of electrostatic charge of particles on hydrodynamics of gas-solid fluidized beds

The aim of this work was to investigate effect of electrostatic charge of particles on the fluidization hydrodynamics. Behavior of bubbles in beds of polyethylene particles was studied through analysis of pressure fluctuations in the frequency domain. Fluidized beds of uncharged, pre-charged and bed-charged particles were used in the experiments. Results revealed that in the bed of pre-charged particles, compared to uncharged experiments, particle-particle repulsive force increases the bed voidage and reduces equilibrium bubble size while the transition velocity to turbulent fluidization is decreased. In the case of bed-charged particles, at low gas velocities bubble fraction is greater compare to the other cases due to faster bubble coalescence in the presence of particle-wall attractive electrostatic force. Electrostatic charge of bulk increases by increasing the gas velocity. At high gas velocities, the repulsion force between highly charged particles overcomes the particle-wall effect on bubble formation and reduces the bubble size to less than in uncharged experiments. Accumulation of particles near the wall in the bed od bed-charged particles affects the hydrodynamics in two ways: first it accelerates bubble growth via bubble coalescence at low gas velocities, second it limits the bubble growth and reduces the transition velocity to turbulent regime to a value less than for pre-charged particles.     

Simulated pulsed flow of gas and particles in a horizontal oppose-pulsed gas jets of bubbling fluidized bed

Flow behavior of gas and particles with a horizontal oppose-pulsed gas jets are simulated by means of a three dimensional Computational Fluid Dynamics (CFD) model with the kinetic theory of granular flow in a gas-particles bubbling fluidized bed. The effects of amplitudes and frequencies on the hydrodynamics of gas and particles are analyzed. The simulation results are presented in terms of phase velocity vector plot, volume fraction of phases, granular temperature, power spectrum and Reynolds stresses in the bed. Results show that the impingement caused by the oppose-pulsed gas jets oscillates with the variation of pulsed gas velocity. The impingement zone with the high solid volume fraction reciprocates from the left side to the right side through the bed center with the variation of pulsed jet gas velocities. The lateral velocity and gas turbulent kinetic energy, granular temperature and Reynolds stresses of gas and particles are larger near the pulsed gas jets than that at the center of the bed. The large dispersion coefficients of particles using the horizontal oppose-pulsed gas jets enhance the mixing of particles in gas-solid fluidized bed.     

硝酸异丙酯与空气混合物的爆轰性能研究

采用立式激波管对硝酸异丙酯(IPN)与空气混合物的爆轰极限、起爆能、爆压和爆速进行了测定,同时从理论上对该燃料的爆轰参数作了计算,计算结果与实验值吻合较好.实验结果证明了IPN的临界起爆能与燃料当量比成"U"形曲线关系;该结果对防止意外事故有一定的指导意义.     

新型气源气相起爆系统实验研究

选择液化石油气加氧气为气相起爆系统新型混合气源，对其在细长管道内传爆性质进行实验研究。结果表明，新气源在内径３ｍｍ长度５００ｍ的细长塑料管道内，经激爆形成的爆轰波传爆可靠，爆速达２５００ｍ／ｓ，其尾部能可靠激爆多根分叉导爆管；爆轰淬熄直径为０７ｍｍ。气相起爆器采用气体配比、混合、反射增压、防爆等装置的系统设计是可行的。     

爆炸焊接条件下炸药爆速的探针法测定

用探针法测量了几种混合炸药的爆速 ,绘制了它们沿爆轰方向的分布曲线 ,分析和讨论了试验结果。指出 ,炸药的爆轰和它的传播 (爆速 )有一个发生、发展、持续和消亡的过程 ,研究这个过程对于爆炸焊接来说有重要的理论和实际意义     

爆炸焊接条件下炸药爆速的探针法测定

用探针法测量了几种混合炸药的爆速 ,绘制了它们沿爆轰方向的分布曲线 ,分析和讨论了试验结果。指出 ,炸药的爆轰和它的传播 (爆速 )有一个发生、发展、持续和消亡的过程 ,研究这个过程对于爆炸焊接来说有重要的理论和实际意义     

Plasma-assisted ignition and deflagration-to-detonation transition

Non-equilibrium plasma demonstrates great potential to control ultra-lean, ultra-fast, low-temperature flames and to become an extremely promising technology for a wide range of applications, including aviation gas turbine engines, piston engines, RAMjets, SCRAMjets and detonation initiation for pulsed detonation engines. The analysis of discharge processes shows that the discharge energy can be deposited into the desired internal degrees of freedom of molecules when varying the reduced electric field, E/n, at which the discharge is maintained. The amount of deposited energy is controlled by other discharge and gas parameters, including electric pulse duration, discharge current, gas number density, gas temperature, etc. As a rule, the dominant mechanism of the effect of non-equilibrium plasma on ignition and combustion is associated with the generation of active particles in the discharge plasma. For plasma-assisted ignition and combustion in mixtures containing air, the most promising active species are O atoms and, to a smaller extent, some other neutral atoms and radicals. These active particles are efficiently produced in high-voltage, nanosecond, pulse discharges owing to electron-impact dissociation of molecules and electron-impact excitation of N(2) electronic states, followed by collisional quenching of these states to dissociate the molecules. Mechanisms of deflagration-to-detonation transition (DDT) initiation by non-equilibrium plasma were analysed. For longitudinal discharges with a high power density in a plasma channel, two fast DDT mechanisms have been observed. When initiated by a spark or a transient discharge, the mixture ignited simultaneously over the volume of the discharge channel, producing a shock wave with a Mach number greater than 2 and a flame. A gradient mechanism of DDT similar to that proposed by Zeldovich has been observed experimentally under streamer initiation.     

Entrainment of particles and gas induced by draft fan over the particles bed

The draft fan is used to generate a controlled transportation of particles to enhance entrainment of gas and particles from the particles bed. Present investigations show the entrainment behavior of particles induced by an axial 4-blade draft fan hovering over the particles bed. The distributions of velocities and volume fractions of gas and particles are simulated using Euler-Euler two-fluid model (TFM) with kinetic theory of granular flow (KTGF) at different hovering heights and rotational speeds of the draft fan. The dense region with high solids volume fraction and low particles velocity and the dilute region with low solids volume fraction and high particles velocity exist beneath the draft fan along hovering heights. The entrainment of particles increases with the decrease of hovering height and increase of rotational speed of the draft fan. Present numerical simulations confirm that the gas-solid TFM with the kinetic theory of granular flow and multiple reference frame model can be effectively applied to analysis for entrainment of particles induced by draft fan.     

带壳炸药在高速运动炸药作用下殉爆效应研究

为研究带壳炸药在高速运动炸药作用下的殉爆效应,应用Lee-Tarver点火增长模型对三种不同运动速度的两种主发炸药作用下带壳炸药的临界殉爆距离进行数值模拟研究,获得了主发炸药运动速度对带壳炸药殉爆距离的影响规律。结果表明:主发炸药运动速度越快,动爆毁伤效能越强,被发带壳炸药临界殉爆距离越大;主发炸药运动速度越快,不同运动速度下被发带壳炸药临界殉爆距离差距越大;质量和运动速度均相同的TNT和PBX9404主发炸药,PBX9404炸药作用下被发带壳炸药临界殉爆距离较大,且两种主发炸药运动速度越快,这一差距越明显。     

Numerical Analysis of Powder Properties in Low Power Plasma Torch

A mathematical model was presented to describe the particle trajectory, velocity and temperature properties in the low power plasma spraying torch (3.6 kW)in which powder particles were directly injected into the region between the cathode and anode. The results show that the characteristics of the particles by low power plasma spraying are similar to that by traditional APS( Atmosphere plasma spraying) in 40 kW. The velocities of the particles increase with the increase of inlet gas flow rate, current and percentage of nitrogen and hydrogen, while the temperature of the powder increase with the decrease of the gas flow rate and with the increase of current and percentage of nitrogen and hydrogen.     

Velocity of detonation at any initial density without using heat of formation of explosives

The simplest method is introduced for reliable estimating the detonation velocity of large class of CHNO explosives based elemental composition and specific structural groups. There is no need to use heat of formation and the other experimental data for calculation of detonation velocity in the new procedure. Only elemental composition and the number of special structural groups without using heat of formation of explosive is sufficient for reliable desk calculation of detonation velocity. The results show good agreement with experimental values with respect to computed results obtained by complex computer code using BKWS and BKWR equations of state. Predicted velocities of detonation have root-mean-square (rms) percent deviation of 2.2, 5.9 and 5.3 from experimental data for new method, BKWS and BKWR equations of state, respectively.     

炮孔复合装药对爆破地震波影响的试验研究

利用炮孔复合装药进行了爆破试验。通过测定质点峰值振速,探索不同方向上地震波强度的差别。同时,与常规装药的爆破震动峰值振速进行了对比。试验结果表明,炮孔复合装药的爆轰波主传播方向上地震波强度最大,其反方向上地震波强度最小;与常规装药结构相比,炮孔复合装药爆轰波主传播方向的反方向上的爆破地震波强度降低30%以上。     

CPFD simulation on effects of louver baffles in a two-dimensional fluidized bed of Geldart A particles

Numerical simulation based on computational particle fluid dynamics (CPFD) model was carried out in a two-dimensional fluidized bed of Geldart A particles which was previously used by Zhang et al. (2009) to study the effects of louver baffles on bed hydrodynamics and gas mixing. With the help of bubble-based energy-minimization multi-scale (EMMS) drag model, the simulation successfully predicted most of the hydrodynamic results which were highly agreeable with experimental results. However, gas tracing simulation was found to depart far from experimental results due to lack of modeling of porous structure of FCC particles. A direct method to characterize solids back-mixing strength based on the simulated internal circulation fluxes was established. The results not only proved the strong suppression of solids back-mixing by louver baffles, but also validated the feasibility of the two indirect measures used in the previous experiment to characterize solids back-mixing strength. Louver baffles’ ability to break up bubbles was also proved. Under low superficial gas velocities, their vanes can split bubbles directly. However, it acts as a distributor under high superficial gas velocities.     

Liquid drop ejection from a membrane driven by gas detonation products

The process of jet formation from a liquid drop placed on a membrane and driven by detonation of hydrogen-air mixture in a thin tube behind the membrane has been studied. It is shown that a gas mixture capable of detonating can be used instead of a solid explosive in devices for ejecting solid particles and liquid drops-in particular, for needle-free injection of drug solutions.