Consequences of liquid jet breakup resulting from interaction with overpressure wave from domino effect

International audienceStorage tanks located on industrial sites are potential source term for leakages, followed by various consequences depending on the nature of the commodity: atmospheric dispersion, BLEVE, UVCE, toxic dispersion. Indeed, because of economic and security purposes, chemical substances are stored with different conditions of pressure, temperature and state. This study explores the consequences of a sudden opening of a storage tank due to an external aggression as a consequence from a previous event. Fragmentation of jets and droplets following the trigger event are thus evaluated. Indeed, increasing the exchange surface impacts the evaporation rate and can be an issue in case of toxic or flammable vapor. Laboratory experiments consisted in generating shockwave with an open ended shock tube to breakup liquid droplets with different viscosities. Size of fragmented droplets are optically measured by direct shadowgraphy. Shockwave is measured using both overpressure sensors and Edgerton retroreflective shadowgraphy. In these experiments, secondary breakups of a droplet into an important number of smaller droplets because of the shockwave induced flow are performed. Results are discussed in terms of velocity and size of droplets. Comparisons are made with existing fragmentation models such as Pilch and Erdman (1987) to provide up to date data with situations encountered in industrial risk evaluation

Natural background oriented schlieren and multiscale visualizations of overpressure wave resulting from vapor cloud explosion

International audienceConsiderable research efforts are focused to forecast consequences of aerial overpressure and impulse due to fuel-air explosions. Statistics indicate that some two-thirds of the financial loss is attributable to explosions. Previous work of the authors [1] was done on propane-oxygen stoichiometric clouds ignited by SEMTEX™ high explosives. In this second study, stoichiometric mixture of methane and oxygen filled a polyethylene envelope with a total volume of the mixture of 5.5 m3. Different image processing was performed to visualize simultaneously the propagation of combustion flame in the envelope and the overpressure in ambient air, outside the envelope. To represent realistic conditions, the shape of the gas envelope was elongated like the dispersion shape from an accidental leak with wind. An electric spark ignited the mixture gas volume on one side. Both flame propagation velocity and overpressure in open-air were recorded with direct visualization. Near field scene (10 m x 6.9 m i.e. about 1.7 times the envelope length and 6.2 times the envelope diameter) was recorded with direct illumination from the flame propagation through the use of a 20 kfps (fps, frame per second) camera. Far field scene (32.4 m x 17.3 m i.e. about 5 times the envelope length and about 16.8 times the envelope diameter) was recorded with direct lighting of the scene through the use of a 9.4 kfps camera. The mixture envelope and the camera were positioned in order to use far-field vegetation as contrasted natural background. In order to visualize the overpressure wave, natural Background Oriented Schlieren (BOS) was applied as image processing [2,3]. Because of the light fluctuation due to the explosion, the reference image for a frame corresponds to the previous frame. Direct visualization shows the combustion of the mixture with increasing velocity. A transition from deflagration to detonation is identified while the combustion front reaches the middle of the envelope. Analysis of the BOS images shows the presence of two overpressure waves of decreasing velocity outside the envelope. Evolution of the global dynamics of the phenomenon is achieved through the use of synchronization of near and far field in a composite image where RGB image layers are respectively set with the BOS image, the global view and the flame view scaled to fit the far field view