Electric Current Density Distribution Research Articles

Motion of a colloidal sphere with interfacial self-electrochemical reactions induced by a magnetic field

The motion of a spherical colloidal particle with spontaneous electrochemical reactions occurring on its surface in an ionic solution subjected to an applied magnetic field is analyzed for an arbitrary zeta potential distribution. The thickness of the electric double layer adjacent to the particle surface is assumed to be much less than the particle radius. The solutions of the Laplace equations governing the magnetic scalar potential and electric potential, respectively, lead to the magnetic flux and electric current density distributions in the particle and fluid phases of arbitrary magnetic permeabilities and electric conductivities. The Stokes equations modified with the Lorentz force contribution for the fluid motion are dealt by using a generalized reciprocal theorem, and closed-form formulas for the translational and angular velocities of the colloidal sphere induced by the magnetohydrodynamic effect are obtained. The dipole and quadrupole moments of the zeta potential distribution over the particle surface cause the particle translation and rotation, respectively. The induced velocities of the particle are unexpectedly significant, and their dependence on the characteristics of the particle-fluid system is physically different from that for electromagnetophoretic particles or phoretic swimmers.

A Simulation Study on Rod Electrode Wear in Micro-EDM

Electrode wear has a great adverse effect on the accuracy of Micro Electrical Discharge Machining (Micro-EDM) and impedes the improvement of Micro-EDM. In this study the distribution of electric field and current density was analyzed exhaustively in order to explore the generating mechanisms of rod electrode wear by finite element analysis and experiment. Experimental results indicated that corner wear occurred first, followed by side wear resulted from skin effect and debris in Micro-EDM, which was significant in enhancing the accuracy of machining.

Electric field and current density distribution in an anatomical head model during transcranial direct current stimulation for tinnitus treatment

Tinnitus is considered an auditory phantom percept. Recently, transcranial direct current stimulation (tDCS) has been proposed as a new approach for tinnitus treatment including, as potential targets of interest, either the temporal and temporoparietal cortex or prefrontal areas. This study investigates and compares the spatial distribution of the magnitude of the electric field and the current density in the brain tissues during tDCS of different brain targets. A numerical method was applied on a realistic human head model to calculate these field distributions in different brain structures, such as the cortex, white matter, cerebellum, hippocampus, medulla oblongata, pons, midbrain, thalamus, and hypothalamus. Moreover, the same distributions were evaluated along the auditory pathways. Results of this study show that tDCS of the left temporoparietal cortex resulted in a widespread diffuse distribution of the magnitude of the electric fields (and also of the current density) on an area of the cortex larger than the target brain region. On the contrary, tDCS of the dorsolateral prefrontal cortex resulted in a stimulation mainly concentrated on the target itself. Differences in the magnitude distribution were also found on the structures along the auditory pathways. A sensitivity analysis was also performed, varying the electrode position and the human head models. Accurate estimation of the field distribution during tDCS in different regions of the head could be valuable to better determine and predict efficacy of tDCS for tinnitus suppression.

Electric Field and Ion Current Environment of HVdc Transmission Lines: Comparison of Calculations and Measurements

The electric field and ion current environment under HVdc transmission lines is an important design consideration. The flux tracing method (FTM) for calculating the ground-level electric field and ion current density distributions is reviewed and the possible errors caused by the use of Deutsch's assumption in the FTM are estimated. Experimental data obtained under one dc test line and three operating dc transmission lines are compared with calculations made with the FTM. The results show that the most important factor influencing the electric field and ion current distributions is the corona onset gradient of the conductors, or indirectly, the conductor surface roughness factor. The results also show that for practical dc transmission-line configurations, any errors caused by Deutsch's assumption are quite small compared with the observed variations in experimental data.

Electric current focusing efficiency in a graphene electric lens

In the present work, we study theoretically the electron wave’s focusing phenomenon in a single-layered graphene pn junction (PNJ) and obtain the electric current density distribution of graphene PNJ, which is in good agreement with the qualitative result in previous numerical calculations (Cheianov et al 2007 Science, 315, 1252). In addition, we find that, for a symmetric PNJ, 1/4 of total electric current radiated from the source electrode can be collected by the drain electrode. Furthermore, this ratio reduces to 3/16 in a symmetric graphene npn junction. Our results obtained by the present analytical method provide a general design rule for an electric lens based on negative refractory index systems.

Numerical Investigations of the Influence of Metal Vapour in GMA Welding

Current numerical models of gas metal arc welding (GMAW) attempt to combine a magnetohydrodynamic (MHD) model of the arc and a volume-of-fluid (VoF) model of metal transfer. But in these models vaporization of metal is neglected and the arc region is assumed to be composed of pure argon, as it is common practice for models of gas tungsten arc welding (GTAW). These models predict temperatures over 20 000 K and a temperature distribution similar to GTAW arcs. However, recent spectroscopic temperature measurements in GMAW arcs have demonstrated much lower arc temperatures. In contrast to GTAW arcs, they found a central local minimum of the radial temperature distribution. The paper presents a GMAW arc model that considers metal vapour and which is in very good agreement with experimentally observed temperatures. Furthermore, the model is able to predict the local central minimum in the radial temperature and the radial electric current density distributions for the first time. The axially symmetric model of the welding torch, the workpiece, the wire and the arc (fluid domain) implements MHD as well as turbulent mixing and thermal demixing of metal vapour in argon. The mass fraction of iron vapour obtained from the simulation shows an accumulation in the arc core and another accumulation on the fringes of the arc at 2 000 to 5 000 K. The demixing effects lead to very low concentrations of iron between these two regions. Sensitive analyses demonstrate the influence of the transport and radiation properties of metal vapour, the welding current and the evaporation rate.

Current Density Distribution Measurement in HT-PEFC Stacks Operated with Reformate Gas from Middle Distillates

A promising application for high temperature polymer electrolyte fuel cells (HT-PEFC) is the use in auxiliary power units (APU). In combination with a fuel gas processor for middle distillates like kerosene or diesel it can efficiently provide on board electric energy for mobile applications. Current R&D work focuses on robust, long-term stable and efficient operation of HT-PEFC stacks. In order to gain insight into internal electrical and thermal behavior current density and temperature distribution measurements in a five cell short stack have been performed. With this method it is shown, how reactant supply and temperature management impacts on local polarization characteristics and temperature distribution.

Understanding the failure mechanisms of microwave bipolar transistors caused by electrostatic discharge

Electrostatic discharge (ESD) phenomena involve both electrical and thermal effects, and a direct electrostatic discharge to an electronic device is one of the most severe threats to component reliability. Therefore, the electrical and thermal stability of multifinger microwave bipolar transistors (BJTs) under ESD conditions has been investigated theoretically and experimentally. 100 samples have been tested for multiple pulses until a failure occurred. Meanwhile, the distributions of electric field, current density and lattice temperature have also been analyzed by use of the two-dimensional device simulation tool Medici. There is a good agreement between the simulated results and failure analysis. In the case of a thermal couple, the avalanche current distribution in the fingers is in general spatially unstable and results in the formation of current crowding effects and crystal defects. The experimental results indicate that a collector-base junction is more sensitive to ESD than an emitter-base junction based on the special device structure. When the ESD level increased to 1.3 kV, the collector-base junction has been burnt out first. The analysis has also demonstrated that ESD failures occur generally by upsetting the breakdown voltage of the dielectric or overheating of the aluminum-silicon eutectic. In addition, fatigue phenomena are observed during ESD testing, with devices that still function after repeated low-intensity ESDs but whose performances have been severely degraded.

Numerical investigations of arc behaviour in gas metal arc welding using ANSYS CFX

Current numerical models of gas metal arc welding (GMAW) are trying to combine magnetohydrodynamics (MHD) models of the arc and volume of fluid (VoF) models of metal transfer. They neglect vaporization and assume an argon atmosphere for the arc region, as it is common practice for models of gas tungsten arc welding. These models predict temperatures above 20 000 K and a temperature distribution similar to tungsten inert gas (TIG) arcs. However, current spectroscopic temperature measurements in GMAW arcs demonstrate much lower arc temperatures. In contrast to TIG arcs they found a central local minimum of the radial temperature distribution. The paper presents a GMAW arc model that considers metal vapour and which is in a very good agreement with experimentally observed temperatures. Furthermore, the model is able to predict the local central minimum in the radial temperature and the radial electric current density distributions for the first time. The axially symmetric model of the welding torch, the work piece, the wire and the arc (fluid domain) implements MHD as well as turbulent mixing and thermal demixing of metal vapour in argon. The mass fraction of iron vapour obtained from the simulation shows an accumulation in the arc core and another accumulation on the fringes of the arc at 2000 to 5000 K. The demixing effects lead to very low concentrations of iron between these two regions. Sensitive analyses demonstrate the influence of the transport and radiation properties of metal vapour, and the evaporation rate relative to the wire feed. Finally the model predictions are compared with the measuring results of Zielinska et al.

Numerical Simulation of Fluid Flow and Heat Transfer in a DC Non-Transferred Arc Plasma Torch Operating Under Laminar and Turbulent Conditions

In this work, a magnetic fluid dynamics (MHD) model is used to simulate the electromagnetic field, heat transfer and fluid flow in a DC non-transferred arc plasma torch under laminar and turbulent conditions. The electric current density, temperature and velocity distributions in the torch are obtained through the coupled iterative calculation about the electromagnetic equations described in a magnetic vector potential format and the modified fluid dynamics equations. The fluid-solid coupled calculation method is applied to guarantee the continuity of the electric current and heat transfer at the interface between the electrodes and fluid. The predicted location of the anodic arc root attachment and the arc voltage of the torch are consistent with corresponding experimental results. Through a specific analysis of the influence of mass flow rates and electric current on the torch outlet parameters, the total thermal efficiency, thermal loss of each part, and the laws of the variation of outlet parameters with the variation of mass flow rates and electric current was obtained. It is found that operation under a laminar condition with a limited area of the anode could increase the total thermal efficiency of the torch.

Topological analysis of separation phenomena in liquid metal flow in sudden expansions. Part 2. Magnetohydrodynamic flow

A numerical study has been carried out to analyse liquid metal flows in a sudden expansion of electrically conducting rectangular ducts under the influence of an imposed uniform magnetic field. Separation phenomena are investigated by selecting a reference Reynolds number and by increasing progressively the applied magnetic field. The magnetic effects leading to the reduction of the size of separation zones that form behind the cross-section enlargement are studied by considering modifications of flow topology, streamline patterns and electric current density distribution. In the range of parameters investigated, the magnetohydrodynamic flow undergoes substantial transitions from a hydrodynamic-like flow to one dominated by electromagnetic forces, where the influence of inertia and viscous forces is confined to thin internal layers aligned with the magnetic field and to boundary layers that form along the walls. Scaling laws describing the reattachment length and the pressure drop in the sudden expansion are derived for intense magnetic fields.

Characteristics and structure of magnetotail flux rope recovered from Grad-Shafranov method

On 21 February 2009, THEMIS-C satellite observed the classical signal of magnetic flux rope at magnetotail of X=-15.7RE.We take the method of Grad-Shafranov reconstruction to investigate the characteristics and structure of magnetotail flux rope. The results give the characteristic physics parameters such as the invariant axis direction, the cross scale length, the magnetic flux in flux rope, etc. With no constraint from model on shape of the flux rope, we reconstruct the distribution of magnetic field and electric current density in the cross section of magnetic flux rope at magnetotail. Our results show that the magnetic field in the central region of magnetic flux rope can be described as being force-free, while with the increase of radial distance, the fields display no force-free feature in the region where the magnetic fields deviate from the axial symmetric distribution.

Modelling of gas–metal arc welding taking into account metal vapour

The most advanced numerical models of gas–metal arc welding (GMAW) neglect vaporization of metal, and assume an argon atmosphere for the arc region, as is also common practice for models of gas–tungsten arc welding (GTAW). These models predict temperatures above 20 000 K and a temperature distribution similar to GTAW arcs. However, spectroscopic temperature measurements in GMAW arcs demonstrate much lower arc temperatures. In contrast to measurements of GTAW arcs, they have shown the presence of a central local minimum of the radial temperature distribution.This paper presents a GMAW model that takes into account metal vapour and that is able to predict the local central minimum in the radial distributions of temperature and electric current density. The influence of different values for the net radiative emission coefficient of iron vapour, which vary by up to a factor of hundred, is examined. It is shown that these net emission coefficients cause differences in the magnitudes, but not in the overall trends, of the radial distribution of temperature and current density. Further, the influence of the metal vaporization rate is investigated. We present evidence that, for higher vaporization rates, the central flow velocity inside the arc is decreased and can even change direction so that it is directed from the workpiece towards the wire, although the outer plasma flow is still directed towards the workpiece. In support of this thesis, we have attempted to reproduce the measurements of Zielińska et al for spray-transfer mode GMAW numerically, and have obtained reasonable agreement.

Modelling of transient state phenomena of composite superconducting conductors during pulse Ic(B) measurements

Computational modelling of pulsed current characterisation in composite superconducting conductors has been performed as the first step towards understanding the electromagnetic processes occurring during pulse Ic(B) measurements in the Cryo-BI-Pulse System. A simplified 2D model was created using the Finite Element Method (FEM) software ANSYS to investigate the current transfer process in a multifilamentary conductor, resulting in time dependent 2D distributions of electrical potential and current density along the wire axis. Experimental measurements were performed for two dissimilar NbTi wires and MgB2 tape: excellent agreement between pulse and DC results were found for one NbTi wire and the MgB2 tape, but the critical current for the other NbTi wire (Luvata OK3900) was significantly lower in pulsed current than DC characterisation. This behaviour has been interpreted in relation to current transfer phenomena using results from the FEM modelling.

Electric current density distribution in planar solid tumor and its surrounding healthy tissue generated by an electrode elliptic array used in electrotherapy

The knowledge of the electric current density distribution generated by an electrode array is very useful in electrotherapy for tumor treatment. We propose an innovative mathematical approach that takes into account planar solid tumor elliptic geometry, electrical differences between it and its surrounding healthy tissue, and positioning of the electrodes with respect to tumor-surrounding healthy tissue interface. We show the distributions of the electric current density in leading order and first correction terms in a heterogeneous planar medium formed by two regions (tumor and its surrounding healthy tissue) in function of these parameters. The results show that when electrodes are completely inserted in tumor and/or its conductivity is higher than that of its surrounding healthy tissue, the electric current density lines concentrate more in tumor and its tumor-surrounding healthy tissue interface. No significant differences are reported between the electric current density distributions in leading-order and first-order correction for each parameter investigated. However, norm of this physical magnitude reveals that these distributions are different when the ratio between radius of the electrodes and radius of the tumor is less than 0.8. We conclude that the analytical modeling presented in this study is of practical interest because it provides a convenient way to visualize the electric current density distributions generated by an electrode elliptic array in order to efficiently destroy the localized planar tumors with the minimum damage to organism, through an increase of the potential applied to the electrodes, the tumor conductivity with respect to its surrounding healthy tissue and insertion of all electrodes into tumor.

Investigation of low-temperature plasma generator with divergent channel of the output electrode and some applications of this generator

A review is made of experimental and theoretical investigations of processes occurring in low-temperature plasma generators (LTPG) with divergent channel of the output electrode, and the possibilities of utilizing these generators in new plasma technologies are analyzed. Comparison is made of the characteristics of discharge (including the current-voltage characteristic) in a divergent channel and in a cylindrical channel of uniform cross section. The effect of divergent channel of the output electrode and of its expansion ratio on the pattern of physical processes in LTPGs of different designs is studied. Investigations are performed of the distribution of electric current and heat flux density along a channel with a segmented output electrode. The voltaic equivalents of heat fluxes to cathode and anode are determined. The process of “shunting” of discharge is investigated, which causes fluctuations of electric arc-burning voltage. The investigations involving an LTPG with divergent channel reveal that the voltage amplitude in the case of shunting decreases with increasing current strength and, at high currents of argon arc, does not exceed 1–2 V. Results are given of spectral and visual investigations of LTPG. It is demonstrated that, in an LTPG with divergent channel, the plasma temperature in the region of energy input at currents of 300 A and higher exceeds 30 000 K. The significant part is found which is played by vacuum ultraviolet radiation in the process of closing the arc to anode. The mechanisms of erosion of the tungsten cathode tip are investigated, which play an important part in increasing the cathode service life by way of recirculation of tungsten atoms because of their ionization in the discharge gap. Results are given of using an LTPG with divergent channel of the output electrode in plasma technologies of surface hardening, cutting, and hard-facing of metals. The technology of plasma hardening of wheel pairs, adopted by the RZhD (Russian Railroads) Joint-Stock Company, provides for increasing the service life of railroad wheels by a factor of 1.5–2.

Study on Optimization and Scale-up of Pressurized Solid Oxide Fuel Cells

The standard solid oxide fuel cell (SOFC) performance is related to its chemical reaction, electrical resistance, gas diffusion polarization, and operating temperature. We start this paper by discussing the performance simulation from our research. A tubular-type SOFC has an axial direction distribution of the gas concentration, and its electrodes and electrolyte have an electric current density distribution. In addition, these distributions are important to the performance simulation. The analysis results were in good agreement with the experimental data, and this indicates that these are useful for a high performance SOFC design. The last part of this paper is about temperature distribution calculation for the SOFCs sub-module. Since performance change is by temperature, numerical thermal and fluid analysis is really important for SOFC module design. In this study, we discuss numerical analysis in SOFC module, considering the electrochemical /reforming reaction. The analysis results agreed well with the experimental data, thus demonstrating the effectiveness of the prediction model.

Visible Human Utilization to Render Induced Electric Field and Current Density Images Inside the Human

The external and internal exposure to power frequency electromagnetic field, generated by high-voltage power transmission lines, raises serious safety concerns. Since we cannot measure the induced electric fields and current densities inside the human body, we used the Visible Human (VH) to investigate the induced electric fields and currents in human body tissues and organs of a worker standing 2 m away from conductor phase C of a double-circuit 132 kV transmission line. The double circuit 132 kV 60 Hz transmission line has a power rating of 293 MVA and a maximum recorded peak load current of 603 A. Charge simulation method and the Biot-Savart law have been used for computation of external electric and magnetic fields. Finite-difference time-domain technique was used to calculate the organs' internal induced electric field and circulating current densities in more than 40 different tissues of the VH with 3 mm voxel size. The simulation indicates that, at 2 m away from a 132 kV transmission line, the computed external electric field is 6.485 kV/m and the external magnetic field is 66.4 muT, which are below the limits set by the IEEE standards for external exposure for live-line workers. The maximum induced electric fields in the brain and heart are 23 and 14 mV/m, respectively. These values are below the IEEE standard recommended limits of 53 mV/m for the brain and 943 mV/m for the heart. The VH data allowed us to obtain two- and three-dimensional images of the induced electric field and current density distribution in different organs, tissues, and cross-sections of the human body.

A computer simulation of continuous ion exchange membrane electrodialysis for desalination of saline water

A computer simulation program including the principle of ① mass transport, ② current density distribution, ③ energy consumption and ④ limiting current density is developed for predicting desalinating performance of a continuous (one-pass flow) electrodialysis process. In this simulation the following parameters are inputted; ① membrane characteristics such as overall transport number, overall solute permeability, overall electro-osmotic permeability, overall hydraulic permeability, direct current electric resistance etc. ② electrodialyzer specifications such as flow-pass thickness, flow-pass width and flow-pass length of a desalting cell etc. and ③ electrodialytic conditions such as current density, electrolyte concentration in a feeding solution, linear velocity in desalting cells, standard deviation of normal distribution of solution velocity ratio etc. In a practical-scale electrodialyzer, electrolyte concentration in a desalting cell is decreased along a flow-pass and it gives rise to electrolyte concentration distribution. It causes electric resistance distribution and current density distribution. Solution velocities in desalting cells vary between the cells, and give rise to solution velocity distribution. In this simulation, these distributions are taken into account assuming that the frequency distribution of solution velocity ratio is equated by the normal distribution. Further, the influences of electrodialyzer specifications and elctrodialysis conditions described above on the performances of an electrodialyzer (desalting ratio, current efficiency, electrolyte concentration at the outlets of desalting cells, cell voltage, energy consumption, electrolyte concentration distribution, current density distribution, and limiting current density) are predicted. The simulation model is developed on the basis of the experiments and its reasonability is supported by the performance of electrodialyzers operating in salt-manufacturing plants.

Impact of Flowfield Design on Solid Oxide Fuel Cell Performance

In the present work a finite element method (FEM) model was developed to investigate the impact of the flowfield design on the performance of a planar SOFC repeat unit. The 2-D FEM model, which considers the performance data of an ideal contacted cell, the electrical conductivities of the electrode materials and the contact resistance between the electrodes and the metallic interconnectors, provides the electrical potential and current density distribution in the repeat unit. Simulations and experimental studies for different flowfield geometries were performed to evaluate the cell performance decrease due to the in plane ohmic losses in the electrode and the contact resistance. Experimental and modeling data are in good agreement. With respect to anode supported cells, the flowfield design on the cathode side has a significant impact (~ 48 % power loss) on the cell performance, whereas the flowfield design in the anode is of minor importance (< 1% power loss).