Current Distribution Data Research Articles

In-situ methods for the determination of current distributions in PEM fuel cells

This article describes three different techniques for the determination of the current density distribution in operating fuel cells and compares their relative benefits with respect to ease of implementation and information gain. Real-time current density distribution data under steady state as well as transient conditions are presented and it is shown that they can contribute to an improved understanding of water management and reactant distribution over the active fuel cell area. The importance of these factors for the optimisation of fuel cell performance is discussed.

Effect of mass transfer on the current distribution in monopolar and bipolar electrochemical reactors with a gas-evolving electrode

The current distribution in an electrochemical reactor with vertical parallel-plate electrodes was experimentally determined. The research was performed with monopolar and bipolar electrodes. The reactor has a gas-evolving electrode and at the counter electrode an electrochemical reaction with combined diffusion and charge-transfer kinetic control, takes place. Therefore the kinetics at the counter electrode are influenced by the bubble-induced convection and by the forced convection of the electrolyte. These reactors are found in many electrochemical processes, for example, electrowinning of metals and electrosynthesis. The test reactions were hydrogen evolution at the cathode and the anodic oxidation of sulphite to sulphate from basic solutions. The current distribution shows a minimum at a distance of approximately six times the equivalent diameter of the reactor from the inlet region. This minimum is a consequence of the interaction between forced convection and the bubble-induced convection, which shifts the mass transfer coefficient of the anodic reaction along the reactor. The effects of the total current, the volumetric electrolyte flow rate and the metal phase resistance on the current distribution are also analysed. The experimental current distribution data are compared with theoretical expectations and good agreement is found.

Flow characteristics at the rip current neck under low energy conditions

This paper presents the flow signature of the rip current neck as determined by fourteen near-bottom velocity records, with a comparison made to 63 recordings in the surf zone. The field experiments, including wave monitoring and morphological mapping, were conducted under relatively calm, dissipative wave conditions ( T sig = 3–6 s, H sig = 0.3-1.1 m) at Herzliya beach, Israel, on the Mediterranean shore. The current data were analysed for shore-normal and resultant components. The processing of the time series in the form of instantaneous and smoothed velocities, provided spectral energy, orbital and current velocity, specific current discharge and directional distribution data. The unique characteristic of the neck environment was found to be its continuous unidirectional seaward flow. Due to the channeling effect, this steady offshore drift constituted the fastest flow in the surf zone with a typically narrow (35°–94°) directional range. Through spectral analysis of the unidirectional return flow the morphodynamic process signature at the rip neck was defined by the relative contribution from the incident waves (78%), the subharmonic edge waves (14%) and the infragravity oscillations (8%). The pulsatory, jet-like rip model with concentration of energy at low frequencies is not corroborated by this study. The studied environment of the rip and bar pattern represented an inherited beach morphology, at an initial accretional, although not yet reflective, stage.

High‐Speed Selective Electroplating with Single Circular Jets

High‐speed selective electroplating of circular deposits with a jet system was investigated by both experimental and theoretical studies. Direct measurement of current distribution was made with a sectioned electrode made of concentric rings. Three systems were studied, including alkaline ferricyanide reduction, copper deposition from acidified sulfate solution, and copper deposition from an acidified sulfate solution that also contained a ferric/ferrous redox couple. In these systems, current distribution data were obtained upon controlled variation of jet Reynolds number, electrolyte conductivity, reactant concentration, and applied total current. A mathematical model of the process was developed that included mass transfer, ohmic resistance, charge transfer, cell geometry, and multiple electrode reactions. The mathematical model was used to generate dimensionless contour maps indicating generalized conditions under which selective high‐speed electroplating can be accomplished.

The ecology and status of geochelone yniphora: a critically endangered tortoise in northwestern madagascar

Abstract The endemic Madagascar tortoise Geochelone yniphora exhibits a very localised distribution in the vicinity of Baly Bay on the northwest coast of the island. Data on growth, feeding, activity patterns, and habitat preference relate to adaptations in a strongly seasonal (wet-dry), tropical climate. Current distribution and density data indicate that G. yniphora is on the verge of extinction. This endangered status can be attributed to: (1) commercial exploitation in the past; (2) current heavy predation by the African bush pig; and (3) continuing habitat modification by indigenous agriculturists who create and maintain anthropogenic savannas through annual burning.

An Engineering Model for Electro‐Organic Synthesis in Continuous Flow‐Through Porous Electrodes

Under controlled experimental conditions, 9–10 diphenylanthracene (DPA) was oxidized in a sectioned flow‐through porous electrode in order to study the relation between operating conditions and product yield. The DPA solution contained 0.2N tetraethylammonium perchlorate in acetonitrile. The electrode was fabricated from 100‐mesh platinum screens. The reaction rate distribution within the sectioned electrode was measured directly, and the reactor effluent was analyzed to obtain the concentrations of DPA and its cation radical (DPA+). Experimental data were compared with calculations based on flow‐through porous electrode theory with consideration of the multiple reaction sequence (EEC) under study. Literature values, where available, were used without adjustment in making theoretical calculations with use of a mathematical model of the reactor system. The model calculations predicted total currents which were within 4% of experimental data, and gave good agreement with current distribution data at various flow velocities and applied potentials.

Current Distribution in a Tubular Electrode under Laminar Flow: Two Electrode Reactions

A computational method has been developed for calculating the current distribution along a tubular electrode when two electrode reactions occur simultaneously. The model is valid for all operating conditions between the secondary current distribution and the limiting current distribution. The model includes the LévÊque equation of convective diffusion, a one‐dimensional potential distribution, and Butler‐Volmer charge‐transfer kinetics for each electrode reaction. Experiments on copper deposition in the presence of a Fe(III)/ Fe(II) redox couple were carried out with a sectioned tubular electrode. Current distribution data were compared with theoretical expectations and good agreement was found.

Studies on Flow‐By Porous Electrodes Having Perpendicular Directions of Current and Electrolyte Flow

An engineering analysis was carried out on a packed‐bed electrochemical reactor in which the electrolyte flowed in the axial direction and current flowed in the radial direction. Experimental measurements with a sectioned porous electrode were conducted to measure the axial current distribution both at and below the limiting current. The experiments involved deposition of copper onto stacks of copper screens with acidified copper sulfate electrolyte. Although the presence of flow channeling caused the mass transfer coefficient to be less than the value reported in the literature, an empirical correlation was established for estimating the mass transfer coefficient. The reactor system gave polarization curves which indicated that the exchange current density was 0.067 mA/cm2 in . Comparison between axial current distribution data and theory was made with respect to collection efficiency, axial current distribution, electrode polarization, and total current. Agreement was found for a range of reactors having various geometric dimensions, porosities, flow rates, and reactant concentrations. The theory was used to generate criteria for estimating the volumetric reaction rate, as well as for estimating conditions under which the perpendicular configuration reactor gives higher volumetric reaction rates than when the current and electrolyte flow in parallel directions.

Current Distribution in a Tubular Electrode under Laminar Flow: One Electrode Reaction

The reaction rate distribution along a tubular electrode was measured directly with a sectioned electrode during steady laminar flow of electrolyte through the electrode. The Fe(III)/Fe(II) redox reaction was studied at the limiting current, and the Cu(II) deposition reaction was studied at all fractions of the limiting current, The experimental conditions were systematically varied in order to determine the effect of counterelectrode placement, tube radius and length, reactant concentration, flow rate, and current density. Experimental polarization curves, limiting current, and current distribution data were compared with a theoretical model of the electrochemical system, and agreement was obtained over a wide range of parameter space. Theoretical calculations were carried out in order to make additional predictions of tubular electrode behavior at and below the limiting current.

An experimental investigation of dielectric-coated antennas

The characteristics of a monopole antenna embedded in a cylinder of low-loss dielectric have been measured. A cylinder of infinite length was approximated by extending the length of a finite cylinder until the admittance did not change. Admittance and current distribution data are represented as a function of antenna length for various diameters and dielectric constants of the cylinders. The results compare well with a theoretical analysis by Ting. The effect of the cylinder is to increase the electrical length of the antenna and decrease the bandwidth.

On Cooled Anodes in Contact with a Laminar Arc-Heated Flow

This paper is concerned with the physics and operating characteristics of cooled anodes In contact with an arc-heated laminar plasma flow in a constant area duct. Various modes of anode behavior are identified and described. Some Influences of gas type, flow rate, arc current, anode material and geometry are demonstrated. A theory is developed to explain the low-current mode of the anode characteristic. It is shown that the local current density on the anode surface is related approximately to the surface's local bias relative to its electrically floating voltage. Anode current distribution data is presented; the distribution is shown to be unstable above a transition bias volt,. age, with the current concentrating intensely on the edge of the anode toward the cathode. Neighboring points on the duct wall are shown to be electrically independent. This fact greatly simplifies an interpretation of anode phenomena. The information presented makes a fairly complete picture of the physical behavior of finite-length, cooled anodes in contact with fully-developed laminar plasma-arc flows.

Distribution of Current in Porous Electrodes

An experimental test is made of the applicability of Kirchoff's law to porous electrodes. The theory is applied to a dry cell made with three bodies of mix separated from each other by paper walls wet with electrolyte. The three bodies are thus isolated electronically but connected ionically. All three are connected to the external load. Thus, the electronic current flowing into each body of mix is equal to the polarizing current in each body and hence is a measure of the rate of reduction of manganese dioxide in each body. It is shown that established theory explains the distribution of current, using two parameters determined directly from the current distribution data.