FRAGMENTATION MECHANISMS BASED ON SINGLE DROP STEAM EXPLOSION EXPERIMENTS USING FLASH X-RAY RADIOGRAPHY

Flash X-ray and high-speed regular photography were used to investigat e the fragmentation processes during the vapor explosion of single dro ps of molten metal immersed in water. For relatively low ambient flow velocities (< 5 m/s), a comparison of the breakup of hot and cold drop s shows that whereas cold drops breakup due to the stripping of fragme nts by the relative flow, the fragmentation of a hot drop is dominated by the growth and collapse of a vapor bubble. X-ray radiographs show during the growth of the bubble, that fine filaments of metal protrude from the drop and the drop surface becomes highly convoluted. Using a simple model for the bubble dynamics, an estimate of the energy budge t shows that the majority (about 80%) of the thermal energy transfer o ccurs during bubble collapse. For hot drops at higher flow velocities (> 45 m/s), vapor bubble growth is diminished and high-speed motion of vapor within the bubble leads to an enhanced fragmentation rate.