Analysis of bubble dynamics in explosive boiling of droplet with fine fragmentation

If a high temperature liquid comes into contact with cold and volatile liquid, rapid (or explosive) evaporation may occur spontaneously or triggered by the impact of a pressure wave. This event generating a shock wave is called a steam explosion. It involves many multiphase flow and heat transfer phenomena. One of the more important phenomena in a steam explosion is the fine fragmentation of the hot liquid, which determines the explosive heat transfer from the hot liquid to the cold liquid and the vaporisation rate of the cold liquid. When a small hot single drop (∼1 mm) interacts with the coolant, a vapour bubble is formed around the drop. It was observed experimentally that these vapour bubbles grow and collapse. During this process, the small hot droplet fragments and generates finer particles. To understand the fine fragmentation process during a steam explosion, in this study, this phenomenon was examined by using non-linear stability analysis of vapour bubble dynamics based on a concept developed by Inoue et al. [Chem. Eng. Commun. 118 (1992) 189]. From the analysis, it was observed that higher spherical modes were very much unstable during collapse process, which decided the size of the fragmented particles. Vapour shell between molten metal and coolant was considered unstable if the amplitude of one of the spherical modes was greater than vapour shell thickness. In addition, the mass of fragmented particles during each cycle of vapour bubble dynamics was predicted from the analysis. The calculated results were found to be in reasonable agreement with the previously reported [J. Non-Equil. Thermodyn. 13 (1988) 27] experimental results.