Electrode Radius Research Articles

Investigation and modeling of various influencing factors on the dielectric breakdown strength of silicone elastomers

Dielectric elastomers are utilized as soft electroactive polymers for actuators, sensors or generator applications to transduce mechanical to electrical energy and vice versa. They are characterized by the ability to change shape while an electrical field is applied. Indeed, this effect is most significant for electrical fields near the electrical breakdown strength, therefore it is a limiting factor for application. This work investigates different factors influencing the dielectric breakdown strength of soft silicone elastomers such as the sample thickness, the force and the radius of the upper electrode, the filling degree and the size of air voids. It can be shown that the main influence is the compression of the sample, thus a novel master curve can be created and fitted by a semi empirical model function. Therefore a comparison of all different experimental set-ups is possible.

A phase-field study of the effect of local deformation velocity on lithiation-induced stress in wire-like structures

The local deformation velocity due to the volumetric change of electrode during lithiation can have a huge influence on the migration of lithium. In this work, we derive an analytical expression for the local flux induced by the local deformation velocity, and propose a modified Cahn–Hilliard type phase-field model, which takes the local deformation velocity into account, to analyze the lithiation of wire-like electrodes with two-phase reaction under potentiostatic operation. The results show that the local deformation velocity greatly alters the distributions of Li-concentration and stresses, and the interphase position varies with the lithiation time, which is due to that the local deformation velocity hinders the Li migration. The influence of the local deformation velocity is dependent on the initial radius of electrode. The delithiation under potentiostatic operation is also studied; and the results reveal that the local deformation velocity has a slighter effect on the diffusion of lithium compared with that during the lithiation.

Experimental verification of modified Paschen’s law in DC glow discharge argon plasma

Breakdown voltage of a gas is the required voltage to start a discharge or electric arc through the gas. Paschen’s law describes the characteristics of gas breakdown voltage between two electrodes. This law states that the Gas breakdown voltage(VB) depends only on the product of gas pressure (p) and gap length(d) between electrodes (VB=f(pd)). In this paper, the effect of electrode separation length(d) and electrode radius (r) on gas breakdown voltage is studied experimentally. A gas discharge system with a large gap length compared to electrode radius is used for the study. Paschen curves are plotted for different electrode separation lengths and electrode radii. It is observed that gas breakdown voltages deviates from Paschen’s law and depend on the d/r ratio also in addition to the product of gap separation and pressure, i.e. VB=f(pd,d/r). This relation, already reported in the analyses of micro gap discharge and theoretical studies, is known as modified Paschen’s law. In order to experimentally verify the modified Paschen’s law in large discharge gaps, many experiments are conducted by varying both electrode separation and electrode radii but keeping the d/r ratio always same. It is observed that for different discharge system geometries, if d/r ratio is same, the break down voltages are same for same pd value. The Paschen’s curves are also plotted for different experiments and it is observed that the curves overlap if d/r ratio is set same for all experiments. Thus, the work presented in this paper experimentally verify the modified Paschen’s law.

Prediction and stabilization of initial resistance between electrodes for small-scale resistance spot welding

Quality of resistance spot-welded joints depends on Joule’s heat generation and, in turn, a current profile, dynamic resistance change, and its initial value. In the present work, the impact of electrode force and dome radius of hemispherical electrodes on initial resistance between electrodes was investigated. Two combinations of workpieces of zirconium alloy thickness of 0.25 + 0.25 mm and austenitic stainless steel thickness of 0.3 + 0.3 mm were used. The experimental results obtained were compared with calculated values using published equations and data on physical properties of these materials. After that, the possibility of stabilization resistance between electrodes by preheating current pulses was studied. The pulses had different algorithms of current rise: discrete and stepwise, as well as sharp and smooth with longer upslope. The results show impossibility of reliable prediction and absolute stabilization of initial values of resistance between electrodes. No clear relationship between these values and electrode force has been found. An increase in dome radius of hemispherical electrodes reduces mean resistance values for zirconium alloy but has no effect for stainless steel. Also, it does not affect dispersion of values for both materials. The rate of preheating current rise has no appreciable effect on stabilization of resistance between electrodes in all cases. Stepwise current rise significantly reduces dispersion of resistance values for zirconium alloy but has no effect for stainless steel. However, their dispersion significantly decreases after preheating in comparison with initial values.

Numerically studying the effects of discharge conditions on plasma-wall transition region of magnetized methane plasma

By combining the global model for rf plasma discharge and the multi-component fluid model for the plasma-wall transition region, the effects of discharge conditions and reactor characteristics on the sheath and pre-sheaths of magnetized methane plasma are studied numerically. The global model determines the density of all species considered in the model as well as electron temperature for the given discharge conditions and reactor size, while the multi-component fluid model uses the parameters calculated by the global model to specify the distribution of potential and species densities in the transition region for a given magnetic field intensity and orientation. The results show that the transition region characteristics are affected by changing the discharge conditions and reactor size. As the sheath and the magnetized pre-sheath become narrower by increasing the input power and background gas pressure, their thicknesses increase with the increase in the electrode radius. Also, they become narrower by increasing the magnetic field intensity and the angle between the electric and magnetic fields.

Comparison between Theoretical and Experimental Radial Electron Temperature Profiles in a Low Density Weakly Ionized Plasma

Experimental and theoretical studies of the radial distribution function of the electron temperature (RDFT) in a low-density plasma and weakly ionized gas for the abnormal glow region are presented. Experimentally, the electron temperatures and densities are measured by a Langmuir probe moved radially from the center to the edge of the cathode electrode for helium gas at different pressures in the low-pressure glow discharge. The comparison of the final experimental data for the radial distribution of electron temperatures and densities for different low pressures ranging from 0.2 to 1.2 torr, with the final proved equation of RDFT confirms that the electron temperatures decrease with increasing product of radial distance and gas pressures, showing a radial decrement dependence of the electron temperature from the center to the edge of the electrode. This is attributed to the increase of the number of electron-atom collisions at higher gas pressures and consequently of the rate of ionization. For the axial distance (L) from the tip of the probe to cathode electrode and the cathode electrode radius (R), a theoretical and experimental comparison for the two conditions L R, for both cases the produced plasma temperatures decrease and densities increase. It is concluded that the RDFT accurately shows a dramatic decrease for L R similar as for conditions of magnetized and unmagnetized effect for DC plasma. This means that the rate of plasma loss by diffusion decreased for L < R, agrees well with the applied of magnetic field behavior

Research on Corona Discharge Characteristics Based on Hybrid Numerical Algorithm

Bar-plate configuration has a vital function in the intensive study of corona discharge mechanism. To study the discharge characteristics of the steady current stage in this configuration, this paper proposes a hybrid numerical algorithm composed by the finite-element method and the finite-volume method. The former solves Poisson’s equation and calculates the value of onset field intensity. The latter solves the current continuity equation, in which a time-varying charge item is added. This charge item can increase the stability of the hybrid algorithm. This paper also proposes a new selection strategy for the initial charge and inception voltage on the bar electrode surface. Based on this algorithm, corona current under different electrode radii, gap distances, and applied voltages was calculated. In this way, the distribution characteristics of an electric field intensity and space charge density along the whole gap in the model can be obtained through the experiment. To verify the validity of the algorithm, the related experiment is carried out in the laboratory. The simulation results have a good consistency with the experimental results, verifying the validity of the algorithm proposed in this paper.

An Investigation of the Control of Electron Energy in the Atmospheric-Pressure Helium Plasma Jet

In this paper, an investigation of the control of electron energy in the atmospheric-pressure helium plasma jet produced by a needle–plane discharge system has been performed by means of the numerical simulation based on a 2-D self-consistent fluid model. Due to the consideration of practical application of the cold atmospheric-pressure plasma jet (CAPPJ) in the fields of biomedicine, in this paper, the mean electron energy (MEE) nearby the cathode plane is accounted for. The parameter dependences of the MEE have been systematically calculated. The considered parameters include the voltage amplitude and rising time $t_{r}$ of the applied voltage pulse as well as needle electrode radius. The voltage amplitude is changed in the range from 3 to 19 kV, and $t_{r}$ is from 1 to 200 ns. The spatial electric field has also been analyzed in detail because of its dominant role in controlling electron energy. In addition, the effect of electron energy on the production of the reactive species OH, O3, and H2O2 has also been investigated when considering the addition of humid air to the working gas helium. This paper gives the following significant results. For a given $t_{r}$ , the MEE increases almost linearly with increasing voltage amplitude. The effect of voltage amplitude on the MEE becomes much more evident for smaller $t_{r}$ and is obviously weak for the $t_{r}$ with a few hundreds of nanoseconds. Fixing the voltage amplitude, the MEE decreases with the increase in $t_{r}$ . The dependence of the MEE on $t_{r}$ is evident for a high voltage amplitude and the reverse is true for the lower voltage amplitudes. As a whole, the higher voltage amplitude and smaller rising time $t_{r}$ or their synergism should be considered for obtaining high electron energy. Especially, an MEE of about 10 eV can be obtained, which covers the energy thresholds inducing all the processes of dissociative electron attachment to water molecule and thus is of essential importance for the production of the reactive species such as OH, H2O2, and O3 in the interactions of plasmas with the aqueous solution embedded in biofilms or tissues. The needle electrodes with different radii result in a minor variation of the MEE under the fixed voltage amplitude and $t_{r}$ . Therefore, changing the radius of the needle electrode is not an effective solution to the control of electron energy in the CAPPJ. Furthermore, the parameter dependence of the spatial electric field is similar to that of the MEE, which reveals the dominant role played by the spatial electric field in controlling electron energy in CAPPJs. Considering the addition of humid air to the working gas helium, with the increase in electron energy, the averaged densities of OH and O3 increase, but that of H2O2 decreases.

THE Simulation Study of DC Grounding Electrode Based on CDEGS and ANSYS

When the UHVDC project was put into operation, grounding electrode grounding current may affect the transformer in the substation near the pole, it will cause transformer DC bias saturation, which leads to higher transformer temperature rise, too high harmonic and reactive power consumption, which will cause transformer damage or power grid blackout. The earth resistivity model of grounding pole is not accurate enough and the calculation of surface potential distribution is not accurate enough, which will cause the deviation between the evaluation and actual damage degree before and after the project put into operation. In order to simulate the grounding potential distribution directly after grounding, the simulation analysis with different methods can be checked with each other, and the related design units used CDEGS to simulate the earth potential rise. In this paper, the influence of DC transmission grounding electrode on the distribution of ground surface potential is analyzed, and the calculation method of DC grounding electrode current field is deduced. The 6 layers earth soil model was established. CDEGS and ANSYS were applied. The earth potential rise distribution in the 0~100 km radius of the earth electrode was calculated respectively. In this paper, the results of the earth potential distribution in the 0-50 km range of the two schemes were compared and analyzed. The results show that the calculation results of ANSYS were slightly smaller than those calculated by CDEGS, and the difference was about 0.6 V. The calculation results of the two schemes could provide reference for field practical monopole operation and commissioning.

Electrohydrodynamic drying of food: New insights from conjugate modeling

Abstract Electrohydrodynamic (EHD) drying is a non-thermal technology with promising perspectives to dehydrate heat-sensitive materials such as foods. With EHD drying, corona discharge is used to generate airflow, which enhances convective drying of the food product. Further development and upscaling of this technology are hindered by a lack of insight in both the airflow and the dehydration process inside the material during drying. This study is the first to develop a conjugate continuum model which couples EHD-generated airflow directly to the convective heat transfer and moisture removal from the food. For the wire-to-plate configuration with impinging flow, the impact of different geometrical and operational parameters (wire radius, distance to collector electrode, emitter voltage) on the EHD-driven airflow and resulting drying kinetics is quantified. The fruit drying time is found to increase linearly with increasing distance between electrodes or increasing emitter electrode radius, but decreases in a non-linear way with increasing voltage between the electrodes. For other emitter-collector configurations, where airflow passes around the fruit, such as wire-to-mesh, wire-to-plate, wire-to-wires and wire-to-parallel plates, significant differences in drying kinetics were quantified. Such configurations provide better perspectives towards upscaling to dry large amounts of products uniformly. Of all tested configurations, the wire-to-mesh configuration provided the highest drying rate. Placing the fruit on a mesh also showed to be advantageous since the fruit can be dried more uniformly. The developed conjugate approach has the distinct advantage that the impact of EHD process parameters and geometrical configurations on the drying rate can be quantified very swiftly. Such modeling approach is thereby a valuable tool for further optimization of EHD drying technology towards industrial implementation.

Effect of Current and Duty Factor for Different Electrode Shapes on Material Removal Rate in EDM

This paper discusses the performance of Electrical Discharge Machining (EDM) process by changing the bottom shape of the electrode, including two stages: designing the electrodes by turning process then the resulted electrodes were used to machine the workpiece by EDM. The effect of electrode shape on material removal rate (MRR) has been investigated for material of CK 60 carbon steel for workpiece and material of brass for electrode. The shapes of the electrode bottom were flat, conical (with 90º apex angle) and round (with 8 mm radius) of constant diameter electrode of 16 mm. Experiments were repeated for three current values of (10, 20 and 42 A) and three duty factor values of (0.4, 0.8, and 1). The results of experiments showed the main effect of current and duty factor on MRR. From experimental work, it is found that for most of experiments flat electrode gives highest MRR as compared to the two other shapes. A mathematical model was developed by factorial design to predict the values of MRR for different electrode shapes, currents, and duty factors by the Minitab Statistical Software (MSS).

The influence of parameters of disk electrode with guard electrode system and sample on permittivity error caused by equivalent electrode area calculation and its correction method

To improve the accuracy in the permittivity measurement using disk electrode with guard electrode, a 3D model of this type of electrode is built in Comsol software and validated. The influence of parameters of sample and disk electrode with guard electrode system on the permittivity error caused by equivalent electrode area calculation is systematically investigated. The results reveal that the permittivity errors by means of the equivalent electrode area presented by the IEC 60250 standard are nearly always negative. From a global perspective, the area of the guarded electrode is closer to the accurate equivalent electrode area than the area provided by the IEC 60250 standard. The error decreases with increasing sample thickness and increases with increasing sample permittivity, gap width, radius of the electrode corner. If the sample is thick and the permittivity is low, the error increases significantly with increasing guarded electrode potential. The sample radius has nothing to do with the accuracy if it is slightly larger than the inside radius of the guard electrode. In the normal range, the size of shielding box, the electrode location, the deviation between the guarded electrode and the whole electrode center, the deviation between the guard electrode and the unguarded electrode, and the potential of the bolt have little effect on the accuracy. Based on the model, a permittivity correction method based on interpolation is proposed. First, the models with different parameters of electrode system and sample, measured and real values of permittivity are built. Second, the relationship among parameters of electrode system and sample is obtained. Finally, the measured permittivity can be corrected by using the relationship and the interpolation method. The accuracy in the permittivity measurement is greatly improved. Because of taking potential of guarded electrode and radius of the electrode corner into account, the error introduced by the proposed method is less than that of the existing correction methods in some situations.

Proposals for Inclusion of the Electrode Radius in Grounding Systems Analysis Using Interpolating Element-Free Galerkin Method

In this paper, the interpolating element-free Galerkin meshless method is presented as a new, simple, and accurate proposal for the analysis of electrostatic grounding problems. A very important aspect to ensure the precision of this numerical solution is the correct modeling of the electrode radius. So, two techniques are proposed to include the electrode radius effect in the analysis. The problem of a vertical electrode introduced in a homogeneous soil is considered as study case. The results of the electrical potential along the ground surface and grounding resistance calculated using interpolating element-free Galerkin method, for different values of radius, are compared with those generated by the method of moments.

On the Modeling of Thermal Radiation at the Top Surface of a Vacuum Arc Remelting Ingot

Two models have been implemented for calculating the thermal radiation emitted at the ingot top in the VAR process, namely, a crude model that considers only radiative heat transfer between the free surface and electrode tip and a more detailed model that describes all radiative exchanges between the ingot, electrode, and crucible wall using a radiosity method. From the results of the second model, it is found that the radiative heat flux at the ingot top may depend heavily on the arc gap length and the electrode radius, but remains almost unaffected by variations of the electrode height. Both radiation models have been integrated into a CFD numerical code that simulates the growth and solidification of a VAR ingot. The simulation of a Ti-6-4 alloy melt shows that use of the detailed radiation model leads to some significant modification of the simulation results compared with the simple model. This is especially true during the hot-topping phase, where the top radiation plays an increasingly important role compared with the arc energy input. Thus, while the crude model has the advantage of its simplicity, use of the detailed model should be preferred.

Critical radius phenomenon and mechanism for SF6 gaps under very fast transient and lightning impulse voltages

Insulation‐related accidents of gas‐insulated switchgear, induced by very fast transient overvoltage, have become increasingly serious in high‐voltage power systems. A steep‐fronted impulse voltage test equipment is developed for studying the discharge characteristics and mechanisms in the SF6 gap. The influence of the electrode radius on the breakdown characteristic of a fixed‐distance SF6 gap is studied. It is found that discharge behaviors of the SF6 gap show the so‐called critical radius effect. With decreasing electrode radius r, the 50% breakdown voltage of the gap decreases till a critical radius Rcr is reached, and then remains practically constant for further reduction of r. Rcr increases with decreasing gas pressure and wave front time. Calculation results show that Rcr is physically close to the length of the filamentary streamer zone L for negative voltages, whereas for positive voltages, Rcr is close to the length of the homogeneous streamer zone l. The critical radius phenomenon is related to the streamer–precursor–leader discharge process in SF6 gas, which is discovered and explained for the first time in this paper by the proposed critical charge criterion of leader breakdown. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

A theoretical model for effect of electron radial diffusion on breakdown characteristics of DC Townsend discharge in uniform axial magnetic field

The breakdown characteristics of gas discharge between two parallel disks including the electron losses in the discharge process due to radial diffusion have been discussed. A theoretical approach was established to determine the fraction of electrons lost from the discharge cell due to radial diffusion. Then, the dependency of the effective secondary electron emission coefficient on the inter-electrode spacing d, the electrode radius R, and the axial magnetic field B was studied. A particle-in-cell, Monte Carlo collision technique was employed to obtain the values of electron loss coefficient, δ, for d from 1 cm to 10 cm, R between 1 and 10 cm, B up to 300 G, and the gas pressures from 50 mTorr to 250 mTorr. The results show that the loss of the electrons increases exponentially with the distance d, while it decreases by increasing R. Based on the model, the applied magnetic field lowers the Paschen curve that is in agreement with the experimental data.

Bromate electroreduction from acidic solution at spherical microelectrode under steady-state conditions: Theory for the redox-mediator autocatalytic (EC″) mechanism

Process of bromate reduction from aqueous acidic medium at (hemi)spherical microelectrode under steady-state conditions has been analyzed theoretically. Since bromate anion is non-electroactive within the potential range under consideration its transformation is based on the electroreduction of bromine which is present in bulk solution in small (even trace) amounts while the bromine reduction product, bromide anion, reacts irreversibly in acidic conditions with bromate anion, with regeneration of bromine, thus forming a redox mediator cycle. Similar to our previous studies of this process at rotating disk electrode it has been shown that this process possesses autocatalytic features, which may under certain conditions leads to considerable accumulation of the redox-couple components, Br2 and Br−, near the electrode surface. As a result the rate of the bromate transformation by the catalytic cycle becomes so rapid that the rate of the whole process is controlled by the bromate transport from the bulk solution to the kinetic layer near the electrode surface, i.e. the current becomes comparable to a very high BrO3− diffusion limited one. For such an autocatalytic passage of the process the radius of the microelectrode has to exceed a critical value which depends on the solution composition. This peculiarity of the system leads to the anomalous dependence of the maximal current density of the bromate reaction on the electrode size: if the electrode radius is under its critical value the current density is very small since it is determined by the discharge of bromine species from the bulk solution, with no significant transformation of bromate. On the contrary, for larger electrodes the autocatalytic EC″ mechanism becomes efficient and the passing current density can exceed the bromate diffusion limited one, i.e. it is a very strong one. The theory also predicts a complicated dependence of the maximal current on the bulk solution concentrations of bromate and protons.

Epoxy-sealed single Pt nanoelectrodes: Fabrication and electrocatalytic performance for the methanol oxidation reaction

Epoxy-sealed single Pt nanoelectrodes (SPNEs) ranging in size from 3 to 300nm have been fabricated by a laser-assisted pulling method and characterized by optical microscopy, transmission electron microscopy (TEM) and electrochemical methods. The prepared SPNEs were used to investigate the methanol oxidation reaction (MOR), and the results show that the electrocatalytic activity of the SPNEs towards MOR depends on the radius of the electrode. In the range of electrode radii tested (3nm–280nm), the electrocatalytic activity decreases if the radius of the SPNE is either too small or too large, with optimal electrocatalytic efficiency being observed when the radius is about 4.2nm.

Modeling of cross-talk phenomena in thin film ferroelectric nanocapacitor arrays by finite element method combined with Monte Carlo calculations

In the last few years, the interest in developing ferroelectric systems with high recording density close to 1Tb/in.2 has strongly increased. The ferroelectric thin films are subjected to the electric field applied by using nanocapacitors (diameters of ∼70 nm) containing a ferroelectric active material. In order to increase the memory density, the nanocapacitor dimensions and the distance between them have to be strongly decreased. However, if the lateral distance between the nanoelectrodes is reduced too much, a domain wall propagation from the nanocapacitor subjected to the voltage to the neighboring capacitors (so-called “cross talk”) is observed. This phenomenon is undesired because the memory spatial resolution is affected. In the present paper, the role of the geometrical characteristics (electrode radius, lateral distance between the electrodes and the film thickness) is investigated, by using a combined Finite Element Method with the Monte Carlo model to describe the local switching properties. The distributions of the electrical potential and local fields were computed by using the Finite Element Method. After describing the conditions for the appearance of the “cross-talk” phenomenon in ferroelectric nanocapacitor systems, some valuable solutions to avoid it are presented.

A numerical‐analytical methodology for acquiring the electrical force of carbon nanotube–based nanoactuator assuming an out‐of‐plane electrodes arrangement

AbstractIn this paper, we develop a simple expression to evaluate the electric force acting on a carbon nanotube–(CNT) based nanoactuator assuming a nonparallel actuating plates (out‐of‐plane) arrangement. The actuating force is initiated by the asymmetry of the resultant electric fringing fields caused mainly due to the nonparallel electrodes arrangement. The nanoactuator is designed based on a CNT flexible electrode (nonstationary) and 2 symmetrically located actuating stationary rectangular shaped out‐of‐plane plates. The resultant electric force is mathematically approximated from the outcomes of a planar (2‐D) numerical solution of the electric problem via a finite element–based numerical analysis. The influence of the design geometrical parameters on the resultant electric force are examined. Several key design parameters were inspected: the width and thickness of the stationary actuating electrodes, the radius of the flexible electrode (the CNT), and the lateral and vertical separation distances between the movable and grounded electrodes. Through several simulations, we show the effect of the lateral and vertical offsets as well as the electrodes thickness in the optimization of the performance of the nanoactuator assuming such nonparallel plates actuating configuration. We also simulate the effect on the resultant actuating force level with the electrode thickness as well as the electrodes lateral separation distance.