Implications of droplet breakup and formation of ultra fine mist in blast mitigation

Abstract

Blast-induced droplet breakup producing ultra fine water mist process was examined in view of assessing its implications on blast mitigation. An earlier review proposed that droplet breakup process, amongst other implications, may weaken the shock due to breakup energy absorption. In this work, droplet breakup energies for water droplets have been determined from the surface energies of both parent and child droplets. A breakup energy of 18 J/kg was required to fragment a 0.5 mm parent droplet into 10,000 mono-dispersed child droplets. Compared to the vaporization energy of 2.25 MJ/kg, the droplet breakup energy was found not significant in weakening the shock. While the droplet deformation energy and curvature effects could increase the breakup energy, its overall contribution to the total energy extraction was not as significant as the latent heat of vaporization. Further, the analysis shows about 22-fold increase in surface area of the child droplets. The study revealed the surface-to-volume ratio of the ultra fine droplets and their vaporization timescale should be well positioned for shock energy extraction.