Acceleration and Heating of Metal Particles in Condensed Matter Detonation

[摘要] For condensed explosives containing metal particle additives, interaction of thedetonation shock and reaction zone with the solid inclusions leads to non-ideal detonation phenomena. Features of this type of heterogeneous detonation are described and the behaviour is related to momentum loss and heat transfer due to this microscopic interaction.For light metal particles in liquid explosives, 60-100% of the post-shock velocity and 20-30% of the post-shock temperature are achieved during the timescale of the leadingdetonation shock crossing a particle. The length scales corresponding to particle diameterand detonation reaction-zone length are related to define the interaction into three classes,bound by the small particle limit where the shock is inert, and by the large particle limitdominated by thin-detonation-front diffraction. In particular, the intermediate case, wherethe particle diameter is of similar order of magnitude to the reaction-zone length, is mostcomplex due to two length scales, and is therefore evaluated in detail.Dimensional analysis and physical parameter evaluation are used to formalize thefactors affecting particle acceleration and heating. Examination of experimental evidence,analysis of flow parameters, and thermochemical equilibrium calculations are applied torefine the scope of the interaction regime. Timescales for drag acceleration and convectiveheating are compared to the detonation reaction time to define the interaction regimeas a hydrodynamic problem governed by inviscid shock mechanics. A computationalframework for studying shock and detonation interaction with particles is presented,including assumptions, models, numerics, and validation. One- and two-dimensionalmesoscale calculations are conducted to highlight the fundamental physics and determinethe limiting cases. Three-dimensional mesoscale calculations, with up to 32 million meshpoints, are conducted for spherical metal particles saturated with a liquid explosivefor various particle diameters and solid loading conditions. Diagnostic measurements,including gauges for pressure, temperature, and flow velocity, as well as mass-averagedparticle velocity and temperature, are recorded for analysis.Mesoscale results for particle acceleration and heating are quantified in terms of shockcompression velocity and temperature transmission factors. In addition to the density ratioof explosive to metal, the solid volume fraction and the ratio of detonation reaction-zonelength to the particle diameter are shown to significantly influence the particle accelerationand heating. A prototype heterogeneous explosive system, consisting of mono-disperse spherical aluminum particles saturated with liquid nitromethane explosive, is studied todevelop fitting functions describing the shock compression transmission factors.Results of the mesoscale calculations are formulated into a macroscopic physical modeldescribing an effective shock compression drag coefficient and Nusselt number. The novelmodels are explored analytically and are then applied to two challenging sets of test caseswith comparison to experiment. Heterogeneous detonation is considered for aluminumparticles saturated with liquid nitromethane, and inert particle dispersal is studied usinga spherical explosive charge containing steel beads saturated in nitromethane. Finally,discussion of practical considerations and future work is followed by concluding remarks.

[发布机构] University of Waterloo

[关键词] Mechanical Engineering