Analytical Technologies Singapore

Supersonic Electrical Discharge in Water

Researchers at Loughborough University have been using a SIMX framing camera at frame rates up to 100 million frames / second to capture the initial stages of supersonic electrical discharges driven by nanosecond rise time, high-voltage ( 100 kV) impulses applied across a pair of electrodes mounted in water.

This research in high voltage breakdown in water, has progressed our understanding of how high-power ultrasound waves generated in a liquid by a high-voltage pulsed source can be used for industrial applications such as rock fracturing or in the medical or food industry domains to kill bacteria in a sterilisation process. The SIM camera was contained within a Faraday cage and viewed the electrodes mounted in a water tank. Pressure variation with different voltage rise times and interelectrode gaps were measured using a set of hydrophones placed 0.5m from the source.

This sequence shows results for an electrode gap of 3 mm and voltage rise time of 30 ns which corresponded to a streamer propagation speed of 63 Km/s and a peak pressure of 0.25 MPa.

Consistent peak pressures between 0.1 MPa and 1.1 MPa were found for inter-electrode gaps between 1 mm and 12 mm. The research concluded that the inter-electrode gap had a significantly greater effect on peak pressure than rise time for the same input energy.

The SIM camera’s nanosecond timing accuracy provided the flexible delays and exposure times required to capture and freeze the motion of these extremely fast events. To accommodate the different illumination conditions required to see both the source electrodes and the event, the camera control software “image merge” feature was used to overlay a static sequence, which used longer exposure times, with the dynamic sequence which used much shorter exposure times.

These merged images provide context and the relative positions of the event and electrode for all the tests.

Congratulations to Jessica Stobbs for receiving the EAPPC (Euro-Asian Pulsed Power Conference, Seoul, S. Korea, 2022) outstanding Young Researcher Award with this research.

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