Visualization of the Processes Occurring during Spontaneous Triggering of a Vapor Explosion

Abstract

The vapor explosion process is an explosive increase in the volume of vapor, accompanied by a sharp rise in pressure when a hot melt enters a cold liquid medium with a temperature above its limiting superheat temperature. This phenomenon incurs the threat of great destruction and human casualties in certain types of accidents in the nuclear, metallurgical, pulp and paper industries. Nevertheless, there are still many insufficiently studied aspects of this phenomenon, one of which is the initiation (triggering) of the process. There are a number of logically fairly consistent descriptions of the processes occurring at a given stage of a vapor explosion. However, almost all of them are based on experiments carried out with external (forced) triggering. The article describes the data obtained during spontaneous triggering, i.e. under conditions much closer to reality. In this paper, using high-speed video recording (with a frame rate of up to 180 kHz and an exposure time of up to 2 μs), the first visualization of the processes occurring during spontaneous triggering of a vapor explosion on molten NaCl salt drops in distilled water subcooled to saturation temperature is presented. It is shown that when several drops of the NaCl melt interact with water, the micro vapor explosion that occurred on one drop, with an interval of several tens of microseconds, causes explosive vaporization on neighboring drops as well. Thus, the logical descriptions of the processes received instrumental confirmation.