EXPERIMENTAL STUDIES OF DIRECT-CONTACT BOILING AT THE SUPERHEAT LIMIT

The dynamic behavior of a single liquid butane droplet boiling explosi vely at its superheat limit has been experimentally and theoretically studied. A high speed photographic system and a fast response pressure transducer were employed in order to visualize and document the rapid (on the order of 10(-5) s) process. The phenomenon of dynamic instabi lity that distorts and roughens the evaporating surface has been confi rmed. The liquid-vapor interface is found to be wrinkled during most o f the vaporization process. The pressure obtained during the process s hows small-scale pressure oscillations at the initial stage of the exp losion. pressure reaches its maximum value as the vaporization consume s the entire liquid mass. As the ambient pressure increases, the maxim um pressure generated by the explosion decreases and is finally suppre ssed to a value that could not be detected. Such a phenomenon is signi ficant from the point of view of LMMHD (Liquid Metal MHD) power genera tion. The water in LMMHD systems is supposed to be injected into the h ot liquid metal in the riser under high pressure. This high ambient pr essure is expected to diminish the shock wave, which is produced by th e rapid evaporation explosion and thus reduces the possibility of pote ntial damage. The mathematical model employed to predict the evaporati on process is an improvement over the existing one (one of the few mod els published). The numerical predictions are in good agreement with e xperimental results.