Initiation step of boiling liquid expanding vapour explosions

Abstract

Two sets of experiments have been performed to study the initiation of a BLEVE (Boiling Liquid Expanding Vapour Explosion). One litre tanks were caused to BLEVE while the pressure at the end of the tank was recorded. Experiments were then conducted in a shock tube equipped with windows. Liquid at the same conditions as the previous experiments was suddenly exposed to atmospheric pressure while a spark schlieren photograph was taken and the pressure response recorded. R12 and R22 were the fluids used in these experiments. Results show that the initial drop in pressure is followed by a rapid pressure rise, caused by the boiling of liquid. The initial depressurization results in superheated liquid in the vicinity of the break. The homogeneous nucleation of this liquid results in a local explosion. The blast wave from this explosion can be the cause for the catastrophic failure of the container. This study shows that a BLEVE is an explosion which can be initiated by the depressurization of a pressure-liquefied gas through a break. This depressurization causes the fluid near the break to be in a superheated state. There is a local explosion caused by a rapid, homogeneous boiling of this superheated fluid. Pressure records indicate that the local explosion near the break in the tank occurs before the expansion wave has propagated far from the break. The blast wave from the explosion eventually stops any further boiling. The volume of the fluid involved in the initial explosion determines the magnitude of the blast (pressure) wave. The blast wave is the cause for the catastrophic failure of the container as observed in many accidents.