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This paper presents an experimental study of the influence of pulsed electrical discharges of low energy (3 to 10 J) on the extraction of polyphenols from grape seeds. To obtain a better understanding, three basic phenomena involved in the whole discharge process are studied separately: pulsed electric field (PEF), pre-breakdown phase (streamer), and breakdown phase (arc). The polyphenol extraction is much more efficient with arcs, compared to streamers and PEF. Therefore, during the discharge process, the enhancement of polyphenol extraction can be mainly ascribed to the final arc phase. The total energy per unit mass CWp required to extract 5000 mg GAE/100 g DM with the arc (CWp = 16 kJ/kg) is 27 times lower compared to streamers alone, and 47 times lower compared to PEF. An optical study shows that the mechanical effects of arcs (shock waves, expanding cavity, and strong turbulence) are much more pronounced compared to streamers. These mechanical effects are responsible for the fragmentation of grape seeds, and strongly promote the release of polyphenols. Other parameters such as the test cell shape and the inter-electrode distance also show that the polyphenol extraction is further enhanced when grape seeds are in close proximity with the breakdown arc. In optimized conditions, the extraction efficiency with low energy discharges can be significantly higher than previous measurements with high energy discharges. Industrial relevance This paper presents relevant information for the design of generating electrical discharges treatment. The study also addresses a specific case of use of by-products and shows the effectiveness of such technology.

In gas-insulated systems, the presence of solid insulators used to hold conductors at high voltage induces the presence of triple interfaces where the metal, solid insulator and gas are in contact. These regions, usually named “triple junction”, constitute weak points for the insulation, mainly due to the mismatch between permittivities of solid and gas, which induces an enhancement of the electric field. If the design of these regions is not carried out with great care, partial discharges (PDs) may appear and accelerate the ageing of the insulator. This paper deals with an experimental study of PDs in a “triple junction” electrode configuration, carried out with sensitive electrical and optical PD measurements. Experiments are done in two pure gases, nitrogen and SF6. Two discharge regimes can be observed: very small discharges (

This paper presents an experimental study of streamer initiation in liquid cyclohexane. The aim is to compare specific features of streamer initiation in positive and negative polarity. Experiments are carried out in point-plane geometry under impulse voltage. A new differential charge measurement system is presented. It allows to obtain a high detection sensitivity under impulse voltage (below 0.1 pC). The investigations presented consider the influence of applied voltage, impulse rise time, hydrostatic pressure. As previously observed under DC voltage, negative streamer initiation is due to an avalanche in the liquid phase, and is not affected by pressure, up to 10 MPa. In contrast, the mechanisms leading to positive streamer initiation are not clearly established. In this polarity, an increase of streamer initiation voltage is observed when the pressure is raised.

For over a decade, our group has been working on the development of distributed electron cyclotron resonance (DECR) plasma sources. The uniform distributed plasma (UDP) is the latest outgrowth of DECR, which has proved to be a flexible concept, leading to task-adapted plasma sources. Our plasma-based ion implantation (PBII) reactor is a 60 cm diameter, 70 cm high cylinder. The inside of the cylinder wall is covered with an array of 24 tubular magnets, 2.45 GHz microwave power feeds, and wave propagators. This peripheral plasma source of a good square meter produces a uniform distributed plasma (UDP), suitable for the treatment of wafers, pipes or objects of arbitrary form. Initial PBII plans concern the nitridation of silicon wafers. At 1 mTorr pressure and 1.3 kW input power, the N 2 plasma has a density of 2 × 10 10 ions cm −3 and an electron temperature of 1.2 eV. The N + /N 2 + ratio of 7/3 in the N 2 UDP plasma, determined by quadrupole mass spectrometry, is favorable for PBII applications. A 45 kV pulsed power supply is available for initial tests, but should be supplanted by a more powerful source for meaningful experiments.