Vapor explosion: heat transfer and fragmentation. VII. Molten-metal/ water interactions prior to a vapor explosion

Abstract

When a hot molten material comes into contact with a cool liquid, a violent explosion may occur. Based on prior laboratory observations of molten- metal/water interactions, fragmentation of the molten material is a necessary ingredient for the occurrence of an explosive incident. An analytical model is developed to describe the sequence of events associated with a hot molten sphere falling into a cool liquid, when a vapor blanket instantaneously surrounds the sphere. Energy and momentum considerations for each of the coupled regions (the molten-metal sphere, the vapor shell and the surrounding liquid coolant) provide the transient growth of the vapor-film thickness and the temperature distribution in ihe liquid coolant. When the vapor film collapses, the molten-metal/ liquidcoolant contact is initially a point rather than the entire vapor shell collapsing instantaneously. When the vapor film collapses locally, the liquid coolant is described by a semi-infinite model. The resulting limit-of-superheat temperature determination shows that the proposed limit-of-superheat explanation for the vapor explosion is inappropriate. Based on the predictions of the model, the mechanism of fragmentation of the molten material appears to result from cavitation following the rapid cooling associated with collapse of the vapor film. (auth)