An experimental study of water BLEVE

A BLEVE is a physical explosion characterized by the sudden expansion of a liquefied gas under pressure and the vapor space above it. In this work, the analysis of a set of water BLEVE experiments was carried out both in terms of data processing and numerical modelling. The main purpose of the project was to investigate safety implications of a pipe rupture containing superheated water that may affect a steam generation system in a nuclear or chemical plant. The experimental campaign consisted in 27 explosive tests in which an instantaneous depressurization of the content was enabled by the use of a calibrated rupture disk. A flange calibrated for different dimensions of the releasing orifice was incorporated in the prototype to replicate a pipe failure for various nominal sizes. The analysis primarily focused on the pressure field distribution generated in the surroundings, in the form of multiple shock waves. First observations came directly from high-speed pressure data recorded, showing a high directionality of the blast, stronger in the vertical direction, and the independence of the lead shock on the initial liquid fill level. The intensity of the overpressure of the lead shock was found to be increasingly correlated with the opening size. Available theoretical methods were used to preliminarily estimate the first overpressure peak. Models based on real gas behaviour and adiabatic irreversible expansion gave the best approximation of the vertical overpressure, providing an energy conversion factor (energy contributing to the blast overpressure over the total expansion energy) comparable with values found in the literature. A few CFD simulations were then performed under a shock tube configuration to validate the widely accepted assumption that the lead pressure peak is exclusively depending on the expansion of the pressurized vapor space.