Plasma formation in underwater gas bubbles

The propagation of pulsed negative corona discharges in water as a function of electrical pulse width ranging from 100 ns to 100 μs has been studied experimentally. Using point‐to‐plane electrodes, it is demonstrated that the propagation of streamers exhibits different behavior under excitations with different pulse width. For pulses with width shorter than 1 µs, the average velocity stays relatively constant at about 1000 m s−1. For pulses with width longer than 1 µs, the average velocity decreases dramatically with increasing pulse width. Numerical fitting shows that the relationship between the velocity and pulse width follows u ∝ τ−0.72. Two different mechanisms are proposed to explain the different discharge characteristics observed at different time scales. At the initial stage before the generation of any significant heat, we show that the electrostatic force may play a major role in supplying the driving force. As the pulse width increases, the gas temperature rises, and the pressure caused by evaporation may become the dominant force to push the head of the filament to propagate. The transition time between two modes was estimated to be in the order of microseconds. Our quantitative predictions are in reasonable agreement with experimental results.

Section: Introductionmentioning

confidence: 99%

Effect of pulse width on streamer propagation of underwater corona discharge

Yang

Zhang

Cheng

et al. 2018

“…Under such context, it is imperative to get a deeper insight into the fundamental streamer behavior and plasma development inside the submerged bubbles. In experiments, discharges in single bubble or a series of bubbles were studied . The single bubble was either attached to electrode or suspended in water using acoustic trapping.…”

Section: Introductionmentioning

confidence: 99%

Time‐resolved imaging of electrical discharge development in multiple bubbles immersed in water

Xian

Yang

et al. 2017

The formation and development of plasma in multiple air bubbles submerged in water was investigated using a pin‐pin electrode system. The discharge dynamics with different bubble‐bubble and bubble‐electrode distance was investigated using a 300 000 frame per second high‐speed charge‐coupled device (CCD) camera. It was observed that the proximity of bubbles and electrodes is crucial for the breakdown process. Depending on the position of the bubbles and electrodes, the breakdown could be categorized into three modes: (1) the axial mode, where the streamer propagates along the axis of the bubbles; (2) the surface mode, where the streamer propagates along the inner curved surface of the bubbles; and (3) the hybrid mode, where the streamer propagates both along the axis and the inner surface simultaneously. For larger electrode gap, the discharge only initiates at the tip of the electrode, and does not propagate into the bubble.

“…As electrical breakdown in water requires a stronger electric field than in gas, gas bubbles have been externally introduced between submerged electrodes to reduce the required breakdown threshold. These discharges have been investigated by electrical characterization and emission spectroscopy . However, selectivity for the desired reactive species and efficient production of the required species are still key challenges.…”

Section: Introductionmentioning

confidence: 99%

“…These discharges have been investigated by electrical characterization and emission spectroscopy. [8][9][10][11][12] However, selectivity for the desired reactive species and efficient production of the required species are still key challenges.…”

Section: Introductionmentioning

confidence: 99%

Efficient and Selectable Production of Reactive Species Using a Nanosecond Pulsed Discharge in Gas Bubbles in Liquid

Dai

Corr

Ponraj

et al. 2015

A plasma gas bubble‐in‐liquid method for high production of selectable reactive species using a nanosecond pulse generator has been developed. The gas of choice is fed through a hollow needle in a point‐to‐plate bubble discharge, enabling improved selection of reactive species. The increased interface reactions, between the gas‐plasma and water through bubbles, give higher productivity. H2O2 was the predominant species produced using Ar plasma, while predominantly NnormalO3− and NO2 were generated using air plasma, in good agreement with the observed emission spectra. This method has nearly 100% selectivity for H2O2, with seven times higher production, and 92% selectivity for NnormalO3−, with nearly twice the production, compared with a plasma above the water.