Fragmentation of low-melting metals by collapsing steam bubbles

When a hot melt meets a vaporable liquid of lower temperature, explosive vaporisation of the cooler liquid may be the result. This is called a steam explosion if a substantial amount of thermal energy is converted into mechanical energy. One important step in understanding about steam explosions is to explain the surface increase of the hot melt. There are several competing fragmentation hypotheses, but so far there has been no model to describe fragmentation criteria as well as the time curve of surface increase on the basis of physical processes. An overall model is now given for one of the possible fragmentation mechanisms, i.e. the division of the melt by collapsing steam bubbles. The model estimates the surface increase of the melt on the basis of heavy supercooled boiling, the heat transfer connected with it, the transfer of mechanical energy during steam bubble collapse, and the solidification of the melt. The results of the calculations have shown that basic experimental observations, e.g. time and extent of fragmentation, are well presented in the model with regard to their order of magnitude. The model presents a qualitatively correct description of the effects of important influencing factors, e.g. supercooling of the coolant or initial temperature of the melt. (orig.)