Propagation in thermal explosions

In a number a small scale experiments the propagation phenomena in thermal explosions caused by contact of a molten metal with water were studied. To investigate the rapid vapor-blanket collapse a small amount of molten tin (800 deg C) was poured on to a crucible under water at decreased pressure. After pressurization to 1 bar the pressure rise in the vessel was measured and the occurring events were observed by cinephotography (8000ps-1). The experiment showed that explosion propagation by blanket collapse is energetically possible. Similar experiments were performed with a larger interacting surface in a through shaped and in a think tank shaped arrangement, which demonstrated that propagation actually occured; the propagation velocity could be estimated to about 5-103cm s-1. The findings favour the interpretation that the explosion is driven by fragmentation rather than by super heat. Fragmentation or mixing can occur through self-driven collapse and possibly by penetration of coolant jets formed by the collapse in the blanket. In a continuously propagation explosion, Taylor and Kelvin-Helmholtz instabilities may take part in the mixing process