Non-thermal atmospheric-pressure plasma jet represents an excellent approach for the decontamination of bacteria. In this paper, we want to improve and characterize a non-thermal plasma jet to employ it in processes of sterilization. The electrical characteristics was studied to describe the discharge of the plasma jet and the development of plasma plume has been characterized as a function of helium flow rate. Optical emission spectroscopy was employed to detect the active species inside the plasma plume. The inactivation efficiency of non-thermal plasma jet was evaluated against Staphylococcus aureus bacteria by measuring the diameter of inhibition zone and the number of surviving cells. The results presented that the plasma plume temperature was lower than 34 C at a flow rate of 4 slm, which will not cause damage to living tissues. The diameter of inhibition zone is directly extended with increased exposure time. We confirmed that the inactivation mechanism was unaffected by UV irradiation. In addition, we concluded that the major reasons for the inactivation process of bacteria is because of the action of the reactive oxygen and nitrogen species which formed from ambient air, while the charged particles played a minor role in the inactivation process.

No abstract

In this paper, a numerical analysis was carried out using finite element method to analyse the mechanisms for streamer discharges. The hydrodynamic model was used with three charge carriers equations (positive ion, negative ion and electron) coupled with Poisson equation to simulate the dynamic of streamer discharge formation and propagation. The model was tested within a 2D axisymmetric tip-plate electrodes configuration using the transformer oil as the dielectric liquid. The distance between the electrodes was fixed at 1 mm and the applied voltage was 130 kV at 46 ns rising time. Simulation results showed that the time has a clear effect on the streamer propagation along the symmetry axis. In addition, it was observed that the highest value of the voltage was recorded at 46 ns and the minimum voltage required for insulation breakdown was 112 kV at 200 ns. It was revealed that the streamer velocity recorded the highest value when the streamer reaches the plate electrode and the lowest value when the streamer begins to propagate. Results also showed that the streamer discharge was dominated by positive ions while the negative ions have a low effect.

To reveal the impact of formation and development of the streamer discharge on the dielectric liquid formed between pin-plate electrodes, a numerical model of transformer oil discharge in the electrode system is built which is based on the continuity equations coupled with Poisson’s equation. The influence of applied impulse voltage parameters such as rise time and voltage magnitude on the formation and development of the streamer discharge is evaluated in this model. In addition, the characteristic of the streamer discharge such as streamer velocity, electric field, and radius of streamer head have been investigated. Modeling results reveal that the higher impulse voltage amplitude form streamer discharges with longer paths, thicker columns, higher velocity, and greater radius. In addition, we find that the radius of the streamer head is greatly affected by the percentage of the predetermined electric field tube at the head, and slightly affected when streamer length increased. Modeling results also showed that the rise times had a clear effect on the radius streamer discharge and the distribution of electric fields.