High power pulsed underwater electrical discharge can be used for different applications in medecine (destructions of kidney stones, decontamination of bacteria), industry (grinding of materials, forming, etc.) and recycling of multi-material wastes (separation and fragmentation of materials).
An electric arc between two electrodes creates a plasma channel generating a pressure wave which propagates into water. This wave is followed by expansion of a gaseous volume of water vapor. The amplitude of the shock wave depends on the electrical generator parameters, electrodes geometry, distance between them etc., and can be varied to obtain desired physical effects. Velocity measurements and Shlieren technique allow to visualize the waves propagation and characterize the shock waves and vapor bubble evolution. The experimental results are compared with corresponding RADIOSS numerical simulations in order to assess the code ability to physically reproduce this ultra-short high-intense phenomenon. After calibration, we utilized the series of simulations to analyze the mechanical and structural effects into objects placed in the water not far from the electrodes. The numerical modeling permit to design a new optimized concept for shock generation yielding to an improved efficiency in multi-material separation and fragmentation.
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Tests were carried out at the tank 60x60x53 cm (LxWxH). Gap between electrodes: 5 to 15 mm. Max stored energy - to 35 kJ. Time (shock risetime): 530 ns. 11
Model definition
• 2D axisymmetric
• QUAD elements 0.5x0.5 mm
• Gap is 15 mm
Material laws:
• water – law 26 SESAME #7150 ,
• discharge zone - law 26 SESAME #7150 with initial energy,
• outlet zone – law 11 type 3 (silent boundary).
For all 3 materials ALE description has been used.
SESAME law presentation 12
Pressure wave propagation
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Pressure max ~ 26 GPa
Interaction with aluminium foil
14 Pressure max ~ 2 GPa
Optimization: reflector
Possible mechanical amplification of shock waves – an ellipsoidal reflector.
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Pressure inside the foil
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Evolution of the bubble
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Conclusions and perspectives
• Ability of RADIOSS to simulate ultra-short high intense shock waves propagation in water.
• Satisfactory correlation between experiments and simulation.
• Improvements by correlation with new experiments (velocity measurements, structure effects…).
• Further optimization.
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Acknowledgements
The work supported by ADEME (AIDER project 2010-2013).
Thanks for Altair Engineering France for training seminars and online support.