Study on characteristics of acoustic signals generated by different DC discharge modes

Acoustic signals contain rich discharge information.In this study,the acoustic signal characteristics of transient glow,spark,and glow discharges generated through DC pin–pin discharge were investigated.The signals were analyzed in the time,frequency,and time–frequency domains,and the correlation between the electric and the acoustic signal was studied statistically.The results show that glow discharge does not produce measurable sound signals.For the other modes,with a decrease in the discharge gap,the amplitude of the acoustic signal increases sharply with mode transformation,the short-time average energy becomes higher,and the frequency components are more abundant.Meanwhile,the current pulse and sound pressure pulse have a one-to-one relationship in the transient glow and spark regimes,and they are positively correlated in amplitude.A brief theoretical analysis of the mechanism of plasma sound and the trends of signals in different modes is presented.Essentially,the change in the discharge energy is closely related to the sound generation of the plasma.

Optimal Scheduling of PEV Charging/Discharging in Microgrids with Combined Objectives

While renewable power generation and vehicle electrification are promising solutions to reduce greenhouse gas emissions, it faces great challenges to effectively integrate them in a power grid. The weather-dependent power generation of renewable energy sources, such as Photovoltaic (PV) arrays, could introduce significant intermittency to a power grid. Meanwhile, uncontrolled PEV charging may cause load surge in a power grid. This paper studies the optimization of PEV charging/discharging scheduling to reduce customer cost and improve grid performance. Optimization algorithms are developed for three cases: 1) minimize cost, 2) minimize power deviation from a pre-defined power profile, and 3) combine objective functions in 1) and 2). A Microgrid with PV arrays, bi-directional PEV charging stations, and a commercial building is used in this study. The bi-directional power from/to PEVs provides the opportunity of using PEVs to reduce the intermittency of PV power generation and the peak load of the Microgrid. Simulation has been performed for all three cases and the simulation results show that the presented optimization algorithms can meet defined objectives.

Numerical study of the self-pulsing of DC discharge:from corona to parallel-plate configurations

We present here an investigation of the self-pulsing phenomenon of negative corona and parallel-plate discharge in argon within one frame of a one-dimensional fluid model in cylinder–cylinder electrode geometry.The transition from corona to parallel-plate discharge is obtained by changing the inner and outer radii of the electrodes.The model reproduces the self-pulsing waveform well and provides the spatiotemporal behaviors of the charged particles and electric field during the pulse.The self-pulsing shows a common feature that occurs in various configurations and that does not depend on a specific electrode structure.The self-pulsing is the transformation between a weak-current Townsend mode and a large-current normal glow mode.The behavior of the positive ions is the dominant factor in the formation of the pulse.

Simulation analysis on microscopic discharge characteristics of the bipolar corona of a floating conductor

A floating conductor exhibits a bipolar corona phenomenon with microscopic discharge characteristics that are still unclear.In this study,a plasma simulation model of the bipolar corona with 108 chemical reaction equations is established by combining hydrodynamics and plasma chemical reactions.The evolution characteristics of electrons,positive ions,negative ions and neutral particles,as well as the distribution characteristics of space charges are analyzed,and the evolutionary flow of microscopic particles is summarized.The results indicate that the positive end of the bipolar corona initiates discharge before the negative end,but the plasma chemistry at the negative end is more vigorous.The electron generation rate can reach 1240 mol(m^(3) s)^(-1),and the dissipation rate can reach 34 mol(m^(3) s)^(-1).The positive ion swarm is dominated by O_(4)^(+),and the maximum generation rate can reach 440 mol((m^(3) s)^(-1).The negative ion swarm is mainly O_(2) and O_(4).The O_(2) content is approximately 1.5-3 times that of O_(4),and the maximum reaction rate can reach 51 mol(m^(3) s)^(-1).The final destination of neutral particles is an accumulation in the form of O_(3) and NO,and the amount of O3 produced is approximately 4-6 times that of NO.The positive end of the bipolar corona is dominated by positive space charges,which continue to develop and spread outwards in the form of a pulse wave.The negative end exhibits a space charge distribution structure of concentrated positive charges and diffused negative charges.The validity of the microscopic simulation analysis is verified by the macroscopic discharge phenomenon.

Study of the Discharge Mode in Micro-Hollow Cathode

In this study, micro-hollow cathode discharge （MHCD） is investigated by a fluid model with drift-diffusion approximation. The MHC device is a cathode/dielectric/anode sandwich structure with one hole of a diameter D=200 um. The gas is a Ne/Xe mixture at a pressure p=50-500 Torr. The evolutions of the discharge show that there are two different discharge modes. At larger pD the discharge plasma and high density excited species expand along the cathode surface and, a ringed discharge mode is formed. At smaller pD, the discharge plasma and the excited species expand along the axis of the cathode aperture to form a columnar discharge.

Simulation of transition from Townsend mode to glow discharge mode in a helium dielectric barrier discharge at atmospheric pressure

The dielectric barrier discharge characteristics in helium at atmospheric pressure are simulated based on a one- dimensional fluid model. Under some discharge conditions, the results show that one discharge pulse per half voltage cycle usually appears when the amplitude of external voltage is low, while a glow-like discharge occurs at high voltage. For the one discharge pulse per half voltage cycle, the maximum of electron density appears near the anode at the beginning of the discharge, which corresponds to a Townsend discharge mode. The maxima of the electron density and the intensity of electric field appear in the vicinity of the cathode when the discharge current increases to some extent, which indicates the formation of a cathode-fall region. Therefore, the discharge has a transition from the Townsend mode to the glow discharge mode during one discharge pulse, which is consistent with previous experimental results.

Operation Mode on Pulse Modulation in Atmospheric Radio Frequency Glow Discharges

The discharge operation regime of pulse modulated atmospheric radio frequency （RF） glow discharge in helium is investigated on the duty cycle and frequency of modulation pulses. The characteristics of radio frequency discharge burst in terms of breakdown voltage, alpha（s）- gamma（γ） mode transition voltage and current are demonstrated by the discharge current voltage characteristics. The minimum breakdown voltage of RF discharge burst was obtained at the duty cycle of 20% and frequency of 400 kHz, respectively. The α-γ mode transition of RF discharge burst occurs at higher voltage and current by reducing the duty cycle and elevating the modulation frequency before the RF discharge burst evolving into the ignition phase, in which the RF discharge burst can operate stably in the γ mode. It proposes that the intensity and stability of RF discharge burst can be improved by manipulating the duty cycle and modulation frequency in pulse modulated atmospheric RF glow discharge.

Time-frequency analysis of Li solid-phase diffusion in spherical active particles under typical discharge modes

Li transient concentration distribution in spherical active material particles can affect the maximum power density and the safe operating regime of the electric vehicles(EVs). On one hand, the quasiexact/exact solution obtained in the time/frequency domain is time-consuming and just as a reference value for approximate solutions;on the other hand, calculation errors and application range of approximate solutions not only rely on approximate algorithms but also on discharge modes. For the purpose to track the transient dynamics for Li solid-phase diffusion in spherical active particles with a tolerable error range and for a wide applicable range, it is necessary to choose optimal approximate algorithms in terms of discharge modes and the nature of active material particles. In this study, approximation methods,such as diffusion length method, polynomial profile approximation method, Padé approximation method,pseudo steady state method, eigenfunction-based Galerkin collocation method, and separation of variables method for solving Li solid-phase diffusion in spherical active particles are compared from calculation fundamentals to algorithm implementation. Furthermore, these approximate solutions are quantitatively compared to the quasi-exact/exact solution in the time/frequency domain under typical discharge modes, i.e., start-up, slow-down, and speed-up. The results obtained from the viewpoint of time-frequency analysis offer a theoretical foundation on how to track Li transient concentration profile in spherical active particles with a high precision and for a wide application range. In turn, optimal solutions of Li solid diffusion equations for spherical active particles can improve the reliability in predicting safe operating regime and estimating maximum power for automotive batteries.

Mesoporous molecular sieve confined phase change materials with high absorption,enhanced thermal conductivity,and cooling energy charging/discharging capacity

The biggest challenge for organic phase change materials(PCMs)used in cold energy storage is to maintain high heat storage capacity while reducing the leakage risk of PCMs during the phase transition process.This is crucial for expanding their applications in the more demanding cold storage field.In this study,novel formstable low-temperature composite PCMs are prepared with mesoporous materials,namely SBA-15 and CMK-3(which are prepared using the template method),as supporting matrices and dodecane as the PCM.Owing to the combined effects of capillary forces within mesoporous materials and interactions among dodecane molecules,both dodecane/SBA-15 and dodecane/CMK-3 exhibit outstanding shape stability and thermal cycling stability even after 200 heating/cooling cycles.In comparison to those of dodecane/SBA-15,dodecane/CMK-3 exhibits superior cold storage performance and higher thermal conductivity.Specifically,the phase transition temperature of dodecane/CMK-3 is-8.81℃ with a latent heat of 122.4 J·g^(-1).Additionally,it has a thermal conductivity of 1.21 W·m^(-1)·K^(-1),which is 9.45 times that of dodecane alone.All these highlight its significant potential for applications in the area of cold energy storage.

Driving frequency effects on the mode transition in capacitively coupled argon discharges

A one-dimensional fluid model is employed to investigate the discharge sustaining mechanisms in the capacitively coupled argon plasmas, by modulating the driving frequency in the range of 40 kHz-613 MHz. The model incorporates the density and flux balance of electron and ion, electron energy balance, as well as Poisson＇s equation. In our simulation, the discharge experiences mode transition as the driving frequency increases, from the γ regime in which the discharge is maintained by the secondary electrons emitted from the electrodes under ion bombardment, to the a regime in which sheath oscillation is responsible for most of the electron heating in the discharge sustaining. The electron density and electron temperature at the centre of the discharge, as well as the ion flux on the electrode are figured out as a function of the driving frequency, to confirm the two regimes and transition between them. The effects of gas pressure, secondary electron emission coefficient and applied voltage on the discharge are also discussed.

Electrical modeling of dielectric barrier discharge considering surface charge on the plasma modified material

We present the variations of electrical parameters of dielectric barrier discharge(DBD)when the DBD generator is used for the material modification,whereas the relevant physical mechanism is also elaborated.An equivalent circuit model is applied for a DBD generator working in a filament discharging mode,considering the addition of epoxy resin(EP)as the plasma modified material.The electrical parameters are calculated through the circuit model.The surface conductivity,surface potential decay,trap distributions and surface charge distributions on the EP surface before and after plasma treatments were measured and calculated.It is found that the coverage area of micro-discharge channels on the EP surface is increased with the discharging time under the same applied AC voltage.The results indicate that the plasma modified material could influence the ignition of new filaments in return during the modification process.Moreover,the surface conductivity and density of shallow traps with low trap energy of the EP samples increase after the plasma treatment.The surface charge distributions indicate that the improved surface properties accelerate the movement and redistribution of charge carriers on the EP surface.The variable electrical parameters of discharge are attributed to the redistribution of deposited surface charge on the plasma modified EP sample surface.

Investigation on pulsed discharge mode in SF6-C2H6 mixtures

The non-chain chemical HF(DF)laser is one of the most powerful electrically-driven lasers operating in mid-infrared,in which SF6-C2H6 mixtures are often used as lasering media.Due to the electronegativity of SF6,the discharge in SF6-C2H6 presents a complicated discharge mode.To achieve reproducible pulsed laser output,pulsed discharge in SF6-C2H6 mixtures is investigated for discharge mode using plane electrodes assisted by array pre-ionization spark pins in cathode surface.Firstly,two modes can be distinguished.One mode is called the selfsustained volume discharge(SSVD),which is characterized by spatial uniformity in the discharge gap and pulse to pulse repeatability.On the contrary,another mode includes random arc passages in the discharge gap and therefore cannot conduct lasering.By varying discharge conditions(gap voltage,gas pressure,etc)two discharge modes are observed.Secondly,the holding scope of the SSVD mode is analyzed for the optimal mixture ratio of 20:1,and the boundary tend of the holding scope of SSVD indicates there exists maximum gas pressure and maximum charging voltage for SSVD.Finally,the peak current of SSVD relates positively to charging voltage,while negatively to gas pressure,from which it is drawn that synchronous electron avalanches initiated by the sliding array overlap spatially into SSVD and thus SSVD is essentially an α ionization avalanche.

Behaviour of the electrochemical intrgrator on the basis of solid electrolyte in galvanoharmonic charging mode

Behaviour of the Electrochemical integrator on the basis of Solid Electrolyte is studied in the galvanoharmonic charging mode. The possibility of application of simpler and more graphic calculation technigue and separation of impedance of electrochemical systems into active and reactive components is shown. The plotting of the dependences of the active and reactive impedance components on ac freguency was used to find the values of parameters of the studied equivalent electric cuircuits.

Establishment of a Kind of Three-dimensional Thunderstorm Cloud Electrification-Discharge Mode

[Objective] The research aimed to study the establishment of a kind of three-dimensional thunderstorm cloud electrification-discharge mode.[Method] Based on a kind of three-dimensional strong convective cloud mode,several parameterization schemes of electrification-discharge mechanism which were mature and had experimental basis were coupled into the strong convective cloud mode.The three-dimensional strong convective mode could simulate electrification-discharge process,and the three-dimensional thunderstorm cloud electrification-discharge mode was established.[Result] By numerical simulation method,a kind of three-dimensional thunderstorm cloud electrification-discharge mode was established.The mode not only could assess the relative importance of various kinds of electrification mechanisms under different environments,but also described formation of charge center and electrical field within the thunderstorm cloud,occurrence position,propagation process and influence on charge distribution of lightning.The most important thing was that it could quantitatively describe the complicated relative relationships between power,microphysics and electric process in the evolution process of thunderstorm cloud.[Conclusion] The research provided powerful foundation for further studying the lightning characteristics of different thunderstorm clouds,the relationships between lightning characteristics and power,microphysical process,and deeply discussing the early-warning forecasting technology of thunderbolt activity.

Development of Numerical Model for Radio Frequency Atmospheric Pressure Glow Discharges in Argon

A one-dimensional,self-consistent fluid model is developed for a computational investigation on discharge characteristics and dynamics of radio frequency(RF) glow discharges in atmospheric argon,which are demonstrated through the spatial and temporal profiles of plasma species,electric field,and mean electron energy.Furthermore,in the discharge current density range from 7.1 mA/cm2 to 119.5 mA/cm2,different discharge operation modes of α and γ are indicated by changing differential conductivity of voltage-current characteristics and sheath dynamics in terms of sheath voltage and sheath thickness.

Charge Structure of a Summer Thunderstorm in North China:Simulation Using a Regional Atmospheric Model System

Electrification and simple discharge schemes are coupled into a 3D Regional Atmospheric Model System （RAMS） as microphysical parameterizations, in accordance with electrical experiment results. The dynamics, microphysics, and electrifi- cation components are fully integrated into the RAMS model, and the inductive and non-inductive electrification mechanisms are considered in the charging process. The results indicate that the thunderstorm mainly had a normal tripole charge structure. The simulated charge structure and lightning frequency are basically consistent with observations of the lightning radiation source distribution. The non-inductive charging mechanism contributed to the electrification during the whole lifetime of the thunderstorm, while the inductive electrification mechanism played a significant role in the development period and the mature stage when the electric field reached a large value. The charge structure in the convective region and the rearward region are analyzed, showing that the charge density in the convective region was double that in the rearward region.

Experimental study on explosion dispersion process of a multi-layer composite charge under different initiation modes

The influe nce of initiation modes on the explosive dispersion process of the multi-layer co mposite charge(MCC) was studied.Overpressure sensors and high-speed photography system were used to investigate the energy release process of an MCC with a specific structure.The shock wave pressure and explosive dispersion characteristics of the MCC under different initiation modes were compared.The forming and expanding process of the shock wave of the composite charge under different initiation modes was determined.The separation position of the shock wave and fireball interface was determined.The calculation formulas of the shock radius and overpressure of the composite charge are presented.The radius of the shock wave of the composite charge was significantly affected by the initiation mode.Moreover,the development process of the composite explosive fireball under different initiation modes was analyzed,the variation rules of the composite charge dispersion radius and fireball dispersion velocity with time were obtained under the different initiation modes,the explosion energy release rate of composite charge under simultaneous initiation modes was the highest,and the peak overpressure under the simultaneous initiation mode was 1.61 times that of central single-point initiation.

Study on the Microsecond Pulse Homogeneous Dielectric Barrier Discharges in Atmospheric Air and Its Influencing Factors

The homogeneous dielectric barrier discharge （DBD） in atmospheric air between two symmetric-columnar copper electrodes with epoxy plates as the dielectric barriers is generated using a us pulse high voltage power supply. The discharge characteristics are studied by measurement of its electrical discharge parameters and observation of its light emission phenom- ena, and the main discharge parameters of the homogenous DBD, such as discharge current and average discharge power, are calculated. Results show that the discharge generated is a homogeneous one with one larger single current pulse of about 2 #s duration appearing in each voltage pulse, and its light emission is radially homogeneous and covers the entire surface of the two elec- trodes. The influences of applied voltage amplitude, air gap distance and barrier thickness on the transition of discharge modes are studied. With the increase of air gap distance, the discharge will transit from homogeneous mode to filamentary mode. The higher the thickness of dielectric barriers, the larger the air gap distance for generating the homogeneous discharge mode. The average discharge power increases non-linearly with increasing applied voltage amplitude, and decreases non-linearly with the increase of air gap distance and barrier thickness. In order to generate stable and homogeneous DBD with high discharge power, thin barriers distance should be used, and higher applied voltage amplitude should be applied to small air gap.

Simulation Study on the Self-Sustained Oscillations in DC Driven Glow Discharges at Atmospheric Pressure Under Different Gas Gaps

In this paper, a one-dimensional plasma fluid model is employed to study the self- sustained oscillations in DC-driven helium glow discharges at atmospheric pressure under different gas gaps. Our simulation results indicate that a harmonic current oscillation with tiny amplitude always occur at the onset of instability and transits into a relaxation one as the conductivity of the semiconductor is decreased. It is found that the dynamics of the oscillations are dependent on the gas gaps. The discharge can only exhibit a simple oscillation with unique amplitude and frequency at smaller gas gaps （〈2 mm） while it can exhibit a more complex oscillation with several different amplitudes and frequencies at larger gas gaps （〉2 mm）. The discharge modes in these current oscillations have also been analyzed.