Numerical Analysis of Energy Conversion Ratio in Vapor Explosions Based on Different Fragmentation Mechanisms

A computer code PROVER-I is developed for propagation phase of vapor explosion. A new thermal fragmentation model is proposed with three kinds of time scale for modeling instant fragmentation, spontaneous nucleation fragmentation and normal boiling fragmentation. The propagation of pressure wave is simulated under different fragmentation mechanisms, and energy conversion ratio of ex-vessel vapor explosion is investigated. Much higher pressure peak is got by spontaneous nucleation fragmentation and the resulting energy conversion ratio is also much larger than that by hydrodynamic fragmentation. The instant fragmentation gives a slightly larger energy conversion ratio than spontaneous nucleation fragmentation. A smaller energy conversion ratio results from normal boiling fragmentation. When the delay time in thermal fragmentation model is longer, pressure attenuation occurs at the front of pressure peak. The high energy conversion ratio (>4%) is obtained in a small vapor volume fraction together with spontaneous nucleation fragmentation. In larger vapor volume fraction conditions (αv>0.3), the vapor explosion is weak. When the fragmentation rate takes both thermal and hydrodynamic fragmentation mechanisms into account, the propagation of pressure wave is dominated by hydrodynamic fragmentation. The energy conversion ratio is not enhanced. (authors)