Explosive fragmentation of liquid shells

Abstract

International audienceThe forced radial expansion of a spherical liquid shell by an exothermic chemical reaction is a prototypical configuration for the explosion of cohesive materials in three dimensions. The shell is formed by the capillary pinch off of a thin liquid annular jet surrounding a jet of reactive gaseous mixture at ambient pressure. The encapsulated gas in the resulting liquid bubble is a mixture of hydrogen and oxygen in controlled relative proportions, which is ignited by a laser plasma aimed at the centre of the bubble. The strongly exothermic combustion of the mixture induces the expansion of the hot burnt gas, pushing the shell radially outwards in a violently accelerated motion. That motion triggers the instability of the shell, developing thickness modulations ultimately piercing it in a number of places. The capillary retraction of the holes concentrates the liquid constituting the shell into a web of ligaments, whose breakup leads to stable drops. We offer a comprehensive description of the overall process, from the kinematics of the shell initial expansion, to the final drop size distribution as a function of the composition of the gas mixture, the initial shell radius and thickness

Expansion Dynamics after Laser-Induced Cavitation in Liquid Tin Microdroplets

“…Imposing dynamic boundary conditions at the two liquid-vapor interfaces p(R−h) and p(R), and noting that the only force acting on the shell is the Laplace pressure, the net value of which is given by p = 4σ/R(t) (in contrast to Ref. [22], where this contribution was negligible), we find…”

“…The expansion of the shell can be described by the Rayleigh-Plesset equation, which in the limit of a thin shell reads [22]:…”

“…The expanding shell is subjected to Rayleigh-Taylor instabilities (RTI), here as instabilities of the liquid-vapor interface driven by the radial acceleration and deceleration of the liquid sheet [22]. Surface tension provides mode selection of the RTI [22,[24][25][26]. This phenomenon will lead to hole formation after which rapid hole opening and merging will lead to full fragmentation of the shell.…”

Drop fragmentation by laser-pulse impact

“…The qualitative analysis presented here underlines the difficulty of establishing in a non-ambiguous manner a drop size distribution arising from a non-trivial fragmentation process when the origin of each fragment cannot be traced back to a precisely identified intermediate mechanism. This is sometimes possible (Lhuissier & Villermaux 2013;Vledouts et al 2016) and when it is not, the analysis is often bounded to invoking general principles in lumped descriptions (see e.g. He et al (2017) in the context of laser-pulse fragmentation, and the other examples discussed in section 7 of Vledouts et al (2016)), a pitfall we conscientiously avoid here.…”

“…This is sometimes possible (Lhuissier & Villermaux 2013;Vledouts et al 2016) and when it is not, the analysis is often bounded to invoking general principles in lumped descriptions (see e.g. He et al (2017) in the context of laser-pulse fragmentation, and the other examples discussed in section 7 of Vledouts et al (2016)), a pitfall we conscientiously avoid here.…”