Study on vapor film collapse behavior on high temperature particle surface. 1. Measurement of vapor film collapse pressure

In order to clarify the triggering condition for vapor explosion, experiments were conducted by passing pressure pulse through the film boiling on high temperature particle surface. The film collapse behavior was observed by a high speed video camera of maximum speed 40,500 fps. At the same time, time transient of the particle surface temperature and the pressure near the particle were simultaneously measured. As the results, the vapor film started to diminish just after the pressure pulse passing through the particle, then it was observed that many small splashes covered whole of the vapor film at the minimum vapor film thickness. Heat flux released from the particle surface increased with decreasing the vapor film thickness before the splashing and the heat flux kept almost constant after the splashing. It is supposed that the vapor film collapse can be judged by the visual information at the splashing. It was experimentally indicated that the measured pressure at the splashing is almost constant about 0.4 MPa independent on the initial particle surface temperature. (author)