Considerations and calculations on the breakup of jets and drops of melt related to premixing

Various descriptions of jet and drop breakup are applied in premixing codes, presently. The main task is to check these descriptions over a wide range of conditions in order to assure extrapolation capabilities for the codes. Jet breakup under non-boiling conditions is relatively well described by IKEJET, based on Conte/Miles (CM) instability description and a relatively detailed stripping model, in contrast to using Kelvin/Helmholtz (KH) theory. Remaining open questions are elaborated. Especially, thick jet behavior with dominance of stripping even at small relative velocities must be distinguished from thin jets with coarse breakup. The application of IKEJET to cases with jet breakup under strong film boiling yielded significantly too little fragmentation. As a possible explanation line, multiphase effects on the wave growth and stripping are considered, due to entrainment of melt and water. Parametric checking calculations are performed with a strongly simplified approach for PREMIX and FARO experiments in order to reveal main effects and the possible physical explanation features as a basis for extended modelling. The results indicate that jet breakup may be essentially sufficient to explain the experimental behavior. Rather coalescence than further drop breakup may be expected. This is also indicated by calculations with IKE drop breakup models. (author)