Experimental Studies of Phenomena Occurring during Vapor Explosion Triggering

Abstract

The work is devoted to an experimental study of individual poorly studied stages of vapor explosion triggering (a dangerous destructive phenomenon that occurs during certain emergency situations in nuclear energy, metallurgical, pulp and paper, and other industries). Experiments were carried out to study the propagation of the detonation front after spontaneous explosive boiling (triggering) of water on a molten drop of salt (NaCl) and a vapor explosion stimulated by it on closely spaced neighboring drops of salt and tin. The temperature of the melted drops in the experiments was 850–1100°C and water temperature was room temperature (22–24°C). The main research tool was high-speed video recording of the process (recording frequency up to 50 kHz, exposure up to 5 μs). In order to study the initial stage of triggering associated with local contact of the cooler with a hot substance, experiments were carried out using high-speed video footage of the process of the vapor film coming off on a hot solid sphere, synchronized with fixing the sphere-cooler contact electrically. The footage of the instantaneous (precipitous) mode of vapor film disappearance with a duration of 200–500 μs and gradual (progressive) mode lasting approximately 100 ms on spheres under similar experimental conditions. It is shown that the main influence on the regime of film melting and vapor explosion on molten tin drops is exerted by the pressure pulse from the vapor explosion on a nearby NaCl drop. The characteristic times of the triggering process have been determined: tens to hundreds of microseconds. The value of the primary pressure pulse in the liquid has been established. The decisive role in triggering fine fragmentation of centimeter-long drops of hot liquid by the first contact of cold liquid with their surface has been confirmed.