共查询到20条相似文献,搜索用时 15 毫秒
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Michael A. Liberman Nathan Kleeorin Igor Rogachevskii Nils Erland L. Haugen 《Combustion Theory and Modelling》2013,17(6):1084-1102
Understanding the causes and mechanisms of large explosions, especially dust explosions, is essential for minimising devastating hazards in many industrial processes. It is known that unconfined dust explosions begin as primary (turbulent) deflagrations followed by a devastating secondary explosion. The secondary explosion may propagate with a speed of up to 1000 m/s producing overpressures of over 8–10 atm, which is comparable with overpressures produced in detonation. Since detonation is the only established theory that allows rapid burning producing a high pressure that can be sustained in open areas, the generally accepted view was that the mechanism explaining the high rate of combustion in dust explosions is deflagration-to-detonation transition. In the present work we propose a theoretical substantiation of an alternative mechanism explaining the origin of the secondary explosion producing high speeds of combustion and high overpressures in unconfined dust explosions. We show that the clustering of dust particles in a turbulent flow ahead of the advancing flame front gives rise to a significant increase of the thermal radiation absorption length. This effect ensures that clusters of dust particles are exposed to and heated by radiation from hot combustion products of dust explosions for a sufficiently long time to become multi-point ignition kernels in a large volume ahead of the advancing flame. The ignition times of a fuel–air mixture caused by radiatively heated clusters of particles is considerably reduced compared with the ignition time caused by an isolated particle. Radiation-induced multipoint ignitions of a large volume of fuel–air ahead of the primary flame efficiently increase the total flame area, giving rise to the secondary explosion, which results in the high rates of combustion and overpressures required to account for the observed level of overpressures and damage in unconfined dust explosions, such as for example the 2005 Buncefield explosion and several vapour cloud explosions of severity similar to that of the Buncefield incident. 相似文献
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An approximate solution of the problem of quenching and re-ignition of products/reactants pockets mixed by turbulence is presented. The approach is based on the analysis of thermal regimes of the pocket, but not on the concept of flame stretch. Critical conditions for quenching and re-ignition of the mixed pockets are obtained in a simplified analytical model, and applied to the problem of the sharp difference between the cases of weak and strong flame acceleration in gas explosions. The critical conditions of the mixed eddies in the turbulent flow are shown to depend on the size of the mixed eddies, mixture properties and turbulence intensity. The critical Karlovitz number, Ka, for thermal quenching is shown to increase with the ratio of densities between reactants and products, σ, and with the overall reaction order, n, and to decrease with the Zeldovich number β (dimensionless activation energy) and Lewis number, Le. For the smallest mixed pockets, which are about the size of the laminar flame thickness, the critical Ka-number defines the boundary of the domain of broken flamelets and distributed reaction zones. This number is shown to be of the same order of magnitude as that found from experiments and from direct numerical simulations. The critical conditions for thermal quenching of the largest pockets that can be mixed by turbulence are shown to be independent of the turbulent intensity and could be expressed as a function of σ on β, n, and Le. The mixture properties, thus, may prescribe certain types of flame behavior in turbulent flows. The corresponding critical conditions are linked to the sharp boundary between the cases of weak and strong flame acceleration, which was not satisfactorily explained in previous studies. These critical conditions are shown to have similar critical σ-values and general trends as the experimental data. 相似文献
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利用数值模拟程序模拟了不同高度核爆炸下大气的X射线电离及演化过程.结果表明: X射线电离产生的电子数密度在射线到达后约100 ns时刻达到峰值, 峰值数密度随着到裸核区距离的增加而减小;电子具有较长的寿命, 电子寿命随着到裸核区距离的增加而增大; X射线电离空气产生正离子O+, O2+, N2+,爆高为120 km情况下 O+的峰值数密度与O2+的相近,能维持约1 s. X射线对空气的电离影响范围在数十千米以内,在距裸核区较近的区域, 爆高为80 km时产生的电子峰值数密度比爆高为120 km时的电子峰值数密度高, 在距裸核区较远的区域则相反. 相似文献
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Confined and semi-closed explosions of new class of energetic composites as well as TNT and RDX charges were investigated using optical spectroscopy. These composites are considered as thermobarics when used in layered charges or enhanced blast explosives when pressed. Two methods to estimate fireball temperature histories of both homogeneous and metallized explosives from the spectroscopic data are also presented, compared and analyzed. Fireball temperature results of the charges detonated in a small explosion chamber under air and argon atmospheres, and detonated in a semi-closed bunker are presented and compared with theoretical ones calculated by a thermochemical code. Important conclusions about the fireball temperatures and the physical and chemical phenomena occurring after the detonation of homogeneous explosives and composite formulations are deduced. 相似文献
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Hohenberger M Symes DR Madison KW Sumeruk A Dyer G Edens A Grigsby W Hays G Teichmann M Ditmire T 《Physical review letters》2005,95(19):195003
Intense, femtosecond irradiation of atomic and molecular clusters can initiate Coulomb explosions, generating particle energies sufficient to drive nuclear fusion. Last and Jortner have proposed, based on particle dynamics simulations, that heteronuclear clusters with a mixture of heavy and light ions will not explode by the simple, equilibrium Coulomb model but that dynamic effects can lead to a boosting of energy of the lighter ejected ions [Phys. Rev. Lett. 87, 033401 (2001)]. We present experimental confirmation of this theoretically predicted ion energy enhancement in methane clusters. 相似文献
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The motion of an optically trapped sphere constrained by the vicinity of a wall is investigated at times where hydrodynamic memory is significant. First, we quantify, in bulk, the influence of confinement arising from the trapping potential on the sphere's velocity autocorrelation function C(t). Next, we study the splitting of C(t) into C_{parallel}(t) and C_{perpendicular}(t), when the sphere is approached towards a surface. Thereby, we monitor the crossover from a slow t{-3/2} long-time tail, away from the wall, to a faster t{-5/2} decay, due to the subtle interplay between hydrodynamic backflow and wall effects. Finally, we discuss the resulting asymmetric time-dependent diffusion coefficients. 相似文献
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Yojiro Ishino Ryuji Yamakita Norio Ohiwa 《Proceedings of the Combustion Institute》2007,31(2):2097-2105
Heating, gasifying and burning processes of a micro plastic-resin particle, which has a diameter of about 200 μm and is suddenly exposed to a hot oxidizing atmosphere, are observed and optically processed by combining a micro schlieren system with a high-speed CCD video camera. The following three devised approaches are introduced: the use of an oxidizing combustion gas downstream of a spark-ignited propane–air lean premixed flame as a sudden heat source, the use of a spherically reformed micro particle on a fine tungsten wire of 5 μm diameter, and the use of a simultaneous direct and schlieren optical system. The first technique realizes slow heating and enables a micro resin particle to undergo the same circumstances as those experienced by plastic-resin particles in the plastic-resin powder combustion. The second approach improves the accuracy and reproducibility of image processing, whereas the third optical system gives simultaneous pictures of the transparent visible image and the schlieren image around a micro resin particle of one heating process. The results show that there exists intense multiple internal bubbling, multiple micro explosions, multiple micro jets and micro diffusion flames, and that their existence exerts strong influences on gasification characteristics of a micro resin particle and results in a high burning rate constant. 相似文献
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R. Syrovatka Yu. Medvedev V. Filinov L. Vasilyak L. Deputatova V. Vladimirov V. Pecherkin 《Physics letters. A》2019,383(4):338-344
This paper demonstrates the possibility of generation of density waves in the form of individual humps in a long structure of the one-component Coulomb system of dust particles confined in the linear Paul traps in air under normal conditions Our numerical simulations by particle-in-cell method support this possibility. Physical possibility of analogous the hump density waves (caustics) is discussed by V.I. Arnold in his book ‘Catastrophe Theory’ and is caused by the nonuniform velocity distribution of dust particles. 相似文献
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研究了快速双原子分子离子在固体中穿行时,尾流效应对各离子电荷态以及库仑爆炸过程的影响.借助于线性介电响应理论和局域介电函数,离子之间的动力学相互作用势可以表示成对称的屏蔽库仑势和非对称的尾势.通过对分子离子上所有束缚电子的总能量进行变分和求解单个离子的运动方程,自洽地确定出分子离子中每个离子的电荷态.数值结果表明,由于尾流效应的影响,在初始穿行阶段,分子离子中导航离子的电荷数随穿行深度的增加而单调递增,而尾随离子的电荷数则随穿行深度的增加而振荡.但当穿行深度很大时,两个离子的电荷数都趋于具有相同速度的孤立离子的电荷数.此外,还发现分子轴的取向朝入射速度方向偏转 相似文献
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V. Crupi S. Magaz D. Majolino G. Maisano P. Migliardo 《Journal of Molecular Liquids》1999,80(2-3):133-147
An analysis of Rayleigh wing and Raman scattering data performed in water confined in a nanoporous GelSil matrix, is presented. In the restricted translational region, the results show a strong modification of the vibrational dynamics of water in the confined state, with the disappearance of the 60 cm−1 and 170 cm−1 lattice bands in the VDOS. Furthermore, the collective contribution to the polarised OH stretching band comes down indicating that the tetrabonded network is destroyed. 相似文献
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R.J. Giannaris F.P. Incropera 《Journal of Quantitative Spectroscopy & Radiative Transfer》1973,13(2):183-195
A comprehensive model has been developed for radiation emission and absorption in cylindrically confined plasmas, and calculations have been performed for the asymptotic region of an argon arc plasma. Radiation absorption is shown, in general, to have a negligible effect on bound level populations. The exception is for the near wall region of the 35 A arc, for which self-absorption in the lines of the 4s-4p array has a significant effect. For the 4s-4p array, absorption also significantly reduces the radiation flux to the constrictor wall. 相似文献
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Evgenij Zubko Yuriy Shkuratov Karri Muinonen Gorden Videen 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,100(1-3):489-495
We present an analysis of backscattered light by agglomerated debris particles whose size is comparable with the wavelength. We consider agglomerates that consist of one or two large central particles and a few relatively small fragments surrounding the particles. We find that for the particles we studied, the attachment of small fragments onto the particles leads to a decrease of the negative polarization branch (NPB) at small phase angles in comparison with the branch produced by the isolated particles. For relatively large agglomerates (with size parameters x about 25) the internal scatter in the agglomerates may produce a secondary minimum of the NPB. In this case the second order of scatter between constituents of aggregates plays the dominant role. 相似文献
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采用蒙特卡罗方法模拟了高空核爆炸瞬发辐射中子、γ射线、X射线电离大气的过程,给出了几种爆炸场景下瞬发辐射产生的附加电离电子密度空间分布.针对大气密度随高度非均匀连续变化的特性,采用质量距离抽样方法取代常用的步长抽样方法,无需根据大气密度随高度的变化进行分层处理,提高了计算效率.结果表明:对于不同的爆高,瞬发辐射电离分布存在显著的差异;随着爆高的增加,瞬发辐射附加电离区范围增大,但电子密度的峰值减小.
关键词:
高空核爆炸
瞬发辐射
大气电离
蒙特卡罗方法 相似文献
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Combustion of alane and aluminum with water for hydrogen and thermal energy generation 总被引:1,自引:0,他引:1
Terrence L. Connell Jr. Grant A. Risha Richard A. Yetter Gregory Young Dilip S. Sundaram Vigor Yang 《Proceedings of the Combustion Institute》2011,33(2):1957-1965
The combustion of alane and aluminum with water in its frozen state has been studied experimentally and theoretically. Both nano and micron-sized particles are considered over a broad range of pressure. The linear burning rate and chemical efficiency are obtained using a constant-pressure strand burner and constant-volume cell, respectively. The effect of replacing nano-Al particles by micron-sized Al and alane particles are examined systematically with the additive mass fraction up to 25%. The equivalence ratio is fixed at 0.943. The pressure dependence of the burning rate follows the power law, rb = aPn, with n ranging from 0.41 to 0.51 for all the materials considered. The burning rate decreases with increasing alane concentration, whereas it remains approximately constant with cases containing only Al particles. The chemical efficiency ranged from 32% to 83%, depending on the mixture composition and pressure. Thermo-chemical analyses are conducted to provide insight into underlying causes of the decreased burning rate of the alanized compositions. A theoretical model is also developed to explore the detailed flame structure and burning properties. Reasonably good agreement is achieved with experimental observations. 相似文献