Comparison of discharge characteristics and methylene blue degradation through a direct-current excited plasma jet with air and oxygen used as working gases

Through using a direct-current driven plasma jet operated underwater,degradation of methylene blue(MB)is investigated with air and oxygen used as working gases.With a low power voltage,a plasma plume extends from the needle electrode,which is purple in air.It turns pink after it bridges the two electrodes.During the process,oxygen plasma remains white.Discharge operates in a pulsed mode or a continuous one,which depends on the magnitude of power voltage.For the pulsed mode,oxygen discharge has a shorter plume and a higher pulse frequency than air discharge under the same power voltage.For the same current of the continuous mode,both power and gap voltages of oxygen discharge are higher than those of air discharge.Moreover,MB degradation efficiency increases with increasing power voltage or initial concentration of MB solution.Compared with air discharge,oxygen discharge has a higher degradation efficiency with the same power voltage and treatment time.The pulsed oxygen discharge with power voltage of about 6.5 k V has the highest efficiency in degrading MB dye,reaching approximately 85.8%after 10 min treatment.As a comparison,after 10 min treatment in air discharge,the highest degradation efficiency is 63.7%,which appears in the continuous mode at a power voltage of 10.6 kV.Besides,optical spectra from the discharges are also compared for the two types of working gases.

Assessment on gas-polyethylene terephthalate solid interface partial discharge properties of C4F7N/CO_(2)gas mixture for eco-friendly gas insulating transformer

The eco-friendly insulating gas perfluoroisobutyronitrile(C_(4)F_(7)N)is potentially used in gas-insulated transformers(GIT)to replace sulphur hexafluoride(SF_(6)).However,evaluation of the long-term insulation reliability and gas–solid interface discharge decomposition characteristics of the gas–solid film insulation structure in GIT is indispensable.The authors simulated the gas–solid film insulation structure in GIT and explored the interface partial discharge(PD)characteristics of C4F7N/CO_(2)gas mixture with polyethylene terephthalate(PET).The effect of gas pressure,mixing ratio on gas–solid interface gas decomposition,PET degradation was investigated,and the interaction mechanism was analysed.It is found that the interface PD generated three degradation regions on a PET film.The gas–solid interface reaction in the electrode contact region and the discharge development trace was significantly higher than that of halation region.The content of gas decomposition products decreases with the increase of gas pressure and the PD intensity of SF6-PET is inferior to that of C_(4)F_(7)N/CO_(2)under the same condition.Relevant results provide reference for the development and application of C_(4)F_(7)N/CO_(2)based GIT.

A double‐mode planar argon plume produced by varying the distance from an atmospheric pressure plasma jet

Atmospheric pressure planar plumes are desirable for the applications of low temperature plasmas,such as rapid modification of large‐scale surfaces.Up to now,only single‐mode planar plumes with either a streamer mode or a filamentary mode have been reported in the literature.Distinctive from the single‐mode planar plumes,a double‐mode argon planar plume has been generated in this article,which operates in the streamer mode with a larger distance away from a plasma jet and transits to the filamentary mode with decreasing the distance.Discharge characteristics and plasma parameters are compared for the two modes.Results indicate that the streamer mode and the filamentary mode correspond to pulsed and humped discharges respectively.Fast photography reveals that the streamer‐mode plume is composed of stochastically branching streamers,while the filamentary‐mode plume results from a series of moving filaments similar to those in barrier discharge.In contrast to the streamer mode,the filamentary mode has lower excited electron temperature and vibrational temperature,whereas higher electron density and gas temperature.In addition,better hydrophilicity of polyethylene terephthalate surface is achieved in the filamentary mode.