Time resolved digital holography applied to droplets fragmentation by shockwave

Droplets atomization by shockwave can occur in different issues commonly encountered in the industry such as leak, tank leakage or triple aggression (high speed impact, rupture and surrounded secondary explosion) of tanks. For the last case, shockwave can interact with liquid jets of drops and propagates the liquid far away from the container zone. Very fine secondary droplets can be produced in the worst case of atomization. These small particles can generate secondary effects like explosion in case of petrol derivatives in fire or toxic effects in case of direct breathing. High speed imaging is well suited to study transient phenomenon like explosions and shockwave. A dedicated shockwave generator has been designed to cope with interferometric measurement on holographic bench. This demonstrator is made of thick plastic tubes. The high pressure chamber is isolated from the guiding tube by domestic aluminum foils, the thickness and number of which drive the pressure rupture. Previous works have been carried on by time resolved shadowgraphy to characterize generated shockwave at the guiding tube outlet. This paper deals with time resolved digital holography to perform higher accuracy measurements and of course to reach 3D reconstruction of the whole phenomenon. Lensless in-line digital holography is carried on to improve the stability of the holographic set-up. Different Phantom high speed cameras have been tested as recording sensors, following pixel pitch, pixel size and of course the maximal throughput, from 7kfps (frame per second) up to 26kfps at full 1Mpixel resolution. Different regimes of droplet trains and droplet sizes have been tested. This has also been carried on for different liquids to show the effect of the physico-chemical properties of the liquid subjected to shockwave.

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