High-speed imaging optical techniques for shockwave and droplets atomization analysis
Résumé
Droplets atomization by shockwave can act as a consequence in domino effects on an industrial
facility: aggression of a storage tank (projectile from previous event, for example) can cause leakage of hazardous
material (toxic and flammable). As the accident goes on, a secondary event can cause blast generation,
impacting the droplets and resulting in their atomization. Therefore, exchange surface increase impacts the
evaporation rate. This can be an issue in case of dispersion of such a cloud. The experiments conducted in
the lab generate a shockwave with an open-ended shock tube to break up liquid droplets. As the expected
shockwave speed is about 400 m∕s (∼Mach 1.2), the interaction with falling drops is very short. High-speed
imaging is performed at about 20,000 fps. The shockwave is measured using both overpressure sensors:
particle image velocimetry and pure in line shadowgraphy. The size of fragmented droplets is optically measured
by direct shadowgraphy simultaneously in different directions. In these experiments, secondary breakups of a
droplet into an important number of smaller droplets from the shockwave-induced flow are shown. The results of
the optical characterizations are discussed in terms of shape, velocity, and size.
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