Decontamination of infected plant seeds utilizing atmospheric gliding arc discharge plasma treatment

In agriculture production,plant health is threatened by pathogens parasitic on seeds;hence,it is necessary to disinfect harvested seeds before germination.In this study,a technique of gliding arc plasma treatment was proposed and investigated.The experiment was conducted to treat Astragalus membranaceus(A.membranaceus)seeds that were artificially infected with Fusarium oxysporum(F.oxysporum).The plasma treatment duration varied from 30 s to 270 s.Direct and indirect treatments were compared to evaluate the inactivation efficiency of the F.oxysporum spores on the surface of seeds.The results indicated that the direct treatment behaved significantly better in disinfection than the indirect way.Meanwhile,experiments of the quantitative assessment of seed germination were also conducted,including the germination rate,the germination potential,and the germination index.The results showed that the inactivation efficiency increased as the plasma treatment time was extended.When the treatment time was90 s,the inactivation efficiency reached more than 98%.The plasma treatment of 270 s had a complete devitalization of F.oxysporum spores on the surface of the seeds.After the treatment of 30 s and 90 s,the seed germination parameters improved significantly.This study verified the inactivation efficacy of gliding arc discharge plasma under atmospheric pressure.The technique of gliding arc treatment shows advantages of energy saving and adaptation and has the potential to be utilized in industry.

OH and O radicals production in atmospheric pressure air/Ar/H_2O gliding arc discharge plasma jet

Atmospheric pressure air/Ar/H_2O gliding arc discharge plasma is produced by a pulsed dc power supply. An optical emission spectroscopic(OES) diagnostic technique is used for the characterization of plasmas and for identifications of OH and O radicals along with other species in the plasmas. The OES diagnostic technique reveals the excitation Tx?≈?5550–9000 K, rotational Tr?≈?1350–2700 K and gas Tg?≈?850–1600 K temperatures, and electron density n?(1.1-1.9) ′101 4 cm^(-3) e under different experimental conditions. The production and destruction of OH and O radicals are investigated as functions of applied voltage and air flow rate. Relative intensities of OH and O radicals indicate that their production rates are increased with increasing Ar content in the gas mixture and applied voltage. nereveals that the higher densities of OH and O radicals are produced in the discharge due to more effective electron impact dissociation of H_2O and O_2 molecules caused by higher kinetic energies as gained by electrons from the enhanced electric field as well as by enhanced n e.The productions of OH and O are decreasing with increasing air flow rate due to removal of Joule heat from the discharge region but enhanced air flow rate significantly modifies discharge maintenance properties. Besides, Tgsignificantly reduces with the enhanced air flow rate. This investigation reveals that Ar plays a significant role in the production of OH and O radicals.

Numerical simulation of carbon arc discharge for graphene synthesis without catalyst

In this study, graphene sheets are prepared under a hydrogen atmosphere without a catalyst, and the growth mechanism of graphene by direct current arc discharge is investigated experimentally and numerically. The size and layer numbers of graphene sheets increase with the arc current.Distributions of temperature, velocity, and mass fraction of carbon are obtained through numerical simulations. A high current corresponds to a high saturation temperature, evaporation rate, and mass density of carbon clusters. When the carbon vapor is saturated, the saturation temperatures are 3274.9, 3313.9, and 3363.6 K, and the mass densities are 6.4×1022,8.42×1022, and 1.23×1023 m-3 under currents of 150, 200, and 250 A, respectively. A hydrogen-induced marginal growth model is used to explain the growth mechanism. Under a high current, the condensation coefficient and van der Waals force increase owing to the higher saturation temperature and mass density of carbon clusters, which is consistent with experimental results.

Direct Numerical Simulation of the Pulsed Arc Discharge in Supersonic Compression Ramp Flow

Direct numerical simulation(DNS)of shock wave/turbulent boundary layer interaction(SWTBLI)with pulsed arc discharge is carried out in this paper.The subject in the study is a Ma=2.9 compression flow over a 24-degree ramp.The numerical approaches were validated by the experimental results in the same flow conditions.The heat source model was added to the Navier-Stokes equation to serve as the energy deposition of the pulsed arc discharge.Four streamwise locations are selected to apply energy deposition.The effect of the pulsed arc discharge on the ramp-induced flow separation has been studied in depth.The DNS results demonstrate the incentive locations play a dominant role in suppressing the separated flow.Results show that pulsed heating is characterized by a thermal blockage,which leads to streamwise deflection.The incentive locations upstream the interaction zone of the base flow have a better control effect.The separation bubble shape shows as"spikes",and the downstream flow of the heated region is accelerated due to the momentum exchange between the upper boundary layer and the bottom boundary layer.The high-speed upper fluid is transferred to the bottom,and thus enhances its ability to resist the flow separation.More stripe vortex structures are also generated at the edge of the flat-plate.Furthermore,the turbulent kinetic disturbance energy is increased in the flow filed.The disturbances that originate from the pulsed heating are capable of increasing the turbulent intensity and then diminishing the trend of flow separation.

Hydrogen-induced marginal growth model for the synthesis of graphene by arc discharge

High-quality graphene is prepared by arc discharge with low cost under hydrogen atmosphere. However, the growth mechanism of graphene synthesis by arc discharge remains unclear. In this paper, the hydrogen-induced marginal growth(HIMG) model is deduced to study the growth mechanism of graphene by combining experiment with numerical simulation results. First, the characteristics of thick edges and thin middle and containing hydrogen are verified by transmission electron microscopy and Raman spectroscopy, respectively. In addition, numerical simulation provides the chemical species and temperature range of graphene growth. Second, the marginal growth pattern of hydrogen transfer and carbon addition is introduced because the C–H and C–C reduce configuration energy and island energy, respectively. Meanwhile, the stacking growth at the margin of the graphene island leads to the longitudinal growth of graphene because of the Van der Waals force and the effect of self-assembly,increasing the number of graphene layers. Finally, graphene sheets with a small amount of hydrogen are deposited on the inner wall after annealing. The investigation of the growth mechanism of graphene under hydrogen atmosphere lays a foundation for the large-scale preparation of graphene by arc discharge.

Simulation of temperature distribution and discharge crater of SiC_(p)/Al composites in a single-pulsed arc discharge

SiC_(p)/Al composites are difficult-to-cut materials.In recent years,electrical arc discharge machining has been developed to improve the machinability of these materials.However,there is a big challenge to build a satisfactory heat transfer model of SiC_(p)/Al composites in the arc machining.This is not only because of the material property difference between the reinforcement and matrix material but also because of the micro-dimension Si C reinforcements.This paper established a new heat conduction simulation model considering the Si C particle-Al matrix interface and the phase change effects in a single-pulsed arc discharge of SiC_(p)/Al composites.A novel Si C particle-Al matrix cell geometric model was designed firstly.Then,the temperature distribution at a different depth from the workpiece surface was analyzed,the influence of sic volume fraction on temperature field was studied,and the contribution of the interface thermal resistance and latent heat were explained.To demonstrate the validity of the new numerical model,comparisons and verifications were employed.Finally,the method of improving the model was proposed and the machining mechanism of arc discharge of SiC_(p)/Al matrix materials was discussed.It was found that high temperature is prone to concentrate on the surface layers of the workpiece especially when the Si C fraction is high,also,the temperature fluctuates respectively at the evaporation point of aluminum and Si C,and the Si C-Al resistance has less influence on temperature distribution compared to latent heat,etc.The model build in this work improves the simulation accuracy observably compared to the previous model,and the simulation work will help to acquire a detailed mechanism of material removal of SiC_(p)/Al composites in the arc discharge machining.

Two-dimensional self-consistent numerical simulation of the whole discharge region in an atmospheric argon arc

A 2D self-consistent numerical model of the whole argon-arc discharge region that includes electrodes is developed in this work to facilitate analysis of the physical processes occurring in atmospheric arc plasma.The 2D arc column model contains the ionization and thermal nonequilibrium,which is coupled with a 1D electrode sheath model.The influence of plasma-species diffusion near the electrode region is investigated based on Maxwell–Stefan equations and the generalized Ohm’s law.The numerical results of argon free-burning arcs at atmospheric pressure are then investigated.The simulation shows that the plasma is obviously in the state of thermal and ionization equilibrium in the arc core region,while it deviates from thermal and ionization equilibrium in the arc fringe region.The actual electron density decreases rapidly in the nearanode and near-cathode regions due to non-equilibrium ionization,resulting in a large electron number gradient in these regions.The results indicate that electron diffusion has an important role in the near-cathode and near-anode regions.When the anode arc root gradually contracts,it is easy to obtain a positive voltage drop of the anode sheath(I=50 A),while it remains difficult to acquire a positive anode sheath voltage drop(I=150 A).The current–voltage characteristics predicted by our model are found to be identical to the experimental values.

Experimental study on the improvement of spray characteristics of aero-engines using gliding arc plasma

A gliding arc plasma fuel atomization actuator suitable for aeroengines was designed,and a gliding arc plasma fuel spray experimental platform was built to address the fuel atomization problem in aeroengine combustion chambers.The spray characteristics for different airflows,fuel flows,and discharge voltages were analyzed using laser particle size analysis.The research shows that the fuel atomization effect is improved from the increased airflow.The decreased fuel flow not only reduces the injection pressure of the fuel but also changes the discharge mode of the gliding arc,which affects reductions in the discharge power and inhibits fuel atomization.Gliding arc discharges accelerate the breaking,atomization,and evaporation of fuel droplets while reducing the particle size,which increases the proportion of small droplets.Compared with the working conditions of plasma-assisted atomization without the gliding arc,the D0.5,D0.9,and average particle size of the fuel droplets are reduced by 4.7%,6.5%,and 4.1%,respectively,when the modulation voltage of the gliding arc power supply is 200 V.

Experimental study on surface arc plasma actuation-based hypersonic boundary layer transition flow control

Effective control of hypersonic transition is essential.In order to avoid affecting the structural proflle of the aircraft,as well as reducing power consumption and electromagnetic interference,a low-frequency surface arc plasma disturbance experiment to promote hypersonic transition was carried out in theΦ0.25 m double-throat Ludwieg tube wind tunnel at Huazhong University of Science and Technology.Contacting printed circuit board sensors and non-contact focused laser differential interferometry testing technology were used in combination.Experimental results showed that the low-frequency surface arc plasma actuation had obvious stimulation effects on the second-mode unstable wave and could promote boundary layer transition by changing the spectral characteristics of the second-mode unstable wave.At the same time,the plasma actuation could promote energy exchange between the second-mode unstable wave and other unstable waves.Finally,the corresponding control mechanism is discussed.

An equivalent model of discharge instability in the discharge chamber of Kaufman ion thruster

The industrial application of the Kaufman ion thruster in its arc stage is limited owing to the instability of the discharge pulse.Presently,a complete prediction model that can predict the discharge pulse in the high-current stage does not exist.In this study,a complete prediction model for the pulse in the ion thruster is established using the zero-dimensional plasma discharge model and equivalent circuit model.The zero-dimensional plasma discharge model is used to obtain the corresponding plasma parameters by calculating the beam current,discharge current,voltage,and gas flow under actual working conditions.The input parameters of the equivalent circuit model are calculated using empirical formulae to acquire the estimated discharge waveforms.The pulse waveforms obtained using the model are found to be consistent with the experimental results.The model is used to evaluate the process of rapid changes in plasma density.Additionally,this model is employed to predict changes in the pulse waveforms when the volume of the discharge chamber and grid plate transmittance are changed.

Semiconducting single-walled carbon nanotubes synthesized by S-doping

An approach was presented for synthesis of semiconducting single-walled carbon nanotubes(SWNTs) by sulfur(S) doping with the method of graphite arc discharge. Raman spectroscopy, UV-vis-NIR absorption spectroscopy and electronic properties measurements indicated the semconducting properties of the SWNTs samples. Simulant calculation indicated that S doping could induce convertion of metallic SWNTs into semiconducting ones. This strategy may pave a way for the direct synthesis of pure semiconducting SWNTs.

Dielectric breakdown properties of Al-air mixtures

In order to investigate the influence of aluminum vapor on the breakdown performance of air,this paper makes a study of the dielectric breakdown characteristics of Al-air mixture in the temperature range of 300-5000 K at atmospheric pressure.A Boltzmann analysis method is used to deal with the electron energy distribution function(EEDF),the reduced ionization coefficients(α/N),the reduced attachment coefficients(η/N)and the critical reduced breakdown strength((E/N)cr)so as to explore the influence of temperature and mixing ratio on the dielectric breakdown properties.In the temperature range of 300-2000 K,the property of the mixture is mainly determined by the mixing proportion of aluminum vapor because the composition of particles remains unchanged.In the temperature range of 2000-2500 K,the decomposition of Al2O_(2)leads to the increase of aluminum oxides and NO,and a rise in the percentage of highenergy electrons as well as the increment ofα/N.Also,the joint action of O_(2)and NO makesη/N increase first and then decrease,and(E/N)crgoes down to a smaller temperature range.An increase in the proportion of aluminum vapor causes(E/N)crto decrease in the low-temperature region and to increase in the high-temperature region,which will reduce the transition between these two temperature regions.

Preparation of double-walled carbon nanotubes using lanthanum as promoter

Double-walled carbon nanotubes (DWNTs) were prepared from graphite by arc discharge technique with La as promoter. The DWNTs products were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray diffraction and Raman spectroscopy. The results demonstrated that La was a suitable promoter reagent for making high purity DWNTs with narrow diameter distribution by arc discharge method. The role of La in the growth of the DWNTs was briefly discussed in terms of the relationship with metal catalysts.

Plasma reforming of toluene as a model tar compound from biomass gasification:effect of CO_(2) and steam

In this study, plasma reforming of toluene as a tar model compound from biomass gasification has been carried out using an AC gliding arc discharge reactor. The influence of steam and CO_(2) addition on the reforming of toluene has been evaluated. The results show that the highest toluene conversion (59.9%) was achieved when adding 3 vol% CO_(2) at a toluene concentra-tion of 16.1 g/Nm3 and a specific energy input of 0.25 kWh/m3. Further increasing CO_(2) concentration to 12 vol% decreased the conversion of toluene. The presence of steam in the plasma CO_(2) reforming of toluene creates oxidative OH radicals which contribute to the enhanced conversion of toluene and energy efficiency of the plasma reforming process through stepwise oxidation of toluene and reaction intermediates. Hydrogen and C_(2)H_(2) were identified as the major gas products in the plasma reforming of toluene without CO_(2) or steam, with a yield of 9.7% and 14.5%, respectively, while syngas was the primary products with a maximum yield of 58.3% (27.5% for H_(2) and 30.8% for CO) in the plasma reforming with the addition of 12 vol% CO_(2). The plausible reaction pathways and mechanism in the plasma reforming of toluene have been proposed through the combination of the analysis of gas and condensed products and spectroscopic diagnostics.