Measurement Of Current Distribution Research Articles

DMFC: Galvanic or electrolytic cell?

We report measurements of local current distribution in a direct methanol fuel cell with single straight channels and segmented electrodes. The experiments directly confirm the existence of a bifunctional regime of DMFC operation: at low air flow rate the segments located close to the inlet of the oxygen channel generate current (galvanic domain), while the other segments consume current to produce hydrogen (electrolytic domain). The cell voltage in this regime in not a single-valued function of current in the external load. The electrolytic domain disappears at a critical air flow rate, which does not depend on current in the cell. We show that a model (A.A. Kulikovsky, Electrochem. Commun. 6 (2004) 1259) explains this critical behavior. Finally, we extend the method of measurement of methanol crossover rate suggested by Ye and Zhao (J. Electrochem. Soc. 152 (2005) A2238) to the case of arbitrary current in the load.

In Situ Experimental Technique for Measurement of Temperature and Current Distribution in Proton Exchange Membrane Fuel Cells

Current distribution data is vital for improved fuel cell designs and improved performance. However, none of the common current mapping techniques is simple to perform and often compromise the design and operation of the fuel cell. By comparison, local temperature measurements with thermocouples are easier to set up and can be done in an unobtrusive way with minimal impact on the fuel cell. Our results show that current mapping can be indirectly conducted through local temperature measurements and have the potential to provide in situ high-resolution data capable of following load cycling and use in real applications.

NONUNIFORMITY OF WIND DISTRIBUTION OVER LAKE SUWA AND THEIR EFFECT ON LAKE CURRENT

Wind has an important role in the behavior of lake current. In this study, the field measurement of wind and currentdistribution was performed simultaneouslyin Lake Suwa. The results proved the spatially nonuniformity of winddistribution over the lakeand counterclockwise horizontal water circulation in the lake when the strong north-west wind was observed. It was examined the effect of spatially non-uniform wind on the lake currentusing a quasi 3-D numerical model by comparingwith the calculation result when the spatially uniform wind allover the lake was assumed. In result, the horizontal water circulation obtained by the fieldmeasurement was recognized byconsideringthe measured wind distribution. This showed that spatially nonuniformity of wind distribution had a great influence on the movement of lake current.

A novel technique for measuring current distributions in PEM fuel cells

A novel and simple technique was developed to measure current distribution in PEM fuel cells with serpentine flow fields. In this technique, a specially designed measuring gasket was inserted between the flow field plate and the gas diffusion layer, and the current at each sub-area of the fuel cell was measured by each of the current collecting strips on the measuring gasket. The current distribution measurement gasket was independent of PEM fuel cells, and can be used in any fuel cell without the need of a special fuel cell or modification of any component of an existing fuel cell. More importantly, this technique can be easily used to measure current density distribution in any cell or every cell in a fuel cell stack. In addition, this technique is very inexpensive, with the only additional cost being that of the measuring gasket. In this work, this measurement gasket technique was used to study the influences of humidification temperatures, cell operating temperatures, reactant flow rates, and operating pressures on current distributions in a PEM fuel cell. Local membrane hydration, reactant depletion and possible cathode flooding can be deduced from the measurement results, and some potential improvements in fuel cell designs are suggested.

Analysis of Single PEM Fuel Cell Performances Based on Current Density Distribution Measurement

A new in situ measurement method of mapping the current density distribution in polymer electrolyte fuel cells (PEFC) is used to analyze the performance of a fuel cell under different operating conditions. The present method is useful in investigating the current density distribution in a single cell as well as a stack, which carries the information about the local reactant activity over the electrode area. It was found that the current density close to the gas inlets is strongly influenced by the reactants' relative humidity. The performance close to the gas outlets is greatly influenced by the inlet gas pressures and the stoichiometry factors of the reactant gases, mainly on the cathode side. It was also observed that the performance of the fuel cell drops with the increase in operating temperature if the reactant gases are not sufficiently humidified.

Measurement of ion current distribution on a three-dimensional workpiece in the positive pulse bias PBII

The feasibility of a metal liner for controlling the wall current has been studied for the positive pulse bias (PPB) method, a new proposing method of the PBII process. In the PPB method, the plasma is positively biased with respect to the grounded workpiece. While it has merits over a negative pulse bias (NPB) method, it requires an enclosure or a liner to suppress the electrical current to the chamber wall. We have tested a floating stainless steel liner in place of the Kapton liner previously used to avoid plasma contamination; the plasma floating potential, the ion energy spectrum on a disc target and the ion current distribution on a trench target have been investigated in an argon plasma of 1015m−3 supplied into the liner from the ICP source. The results have proved that the metal liner is quite suitable for the PPB method.

Measurements of humidity and current distribution in a PEFC

Voltage decreases of polymer electrolyte fuel cells (PEFC) are affected by the relative humidity of the reaction gas inside the cells. A study was conducted to establish a method for measuring relative humidity and current distribution inside PEFC cells in order to identify the factors affecting the voltage decay of such fuel cells. The humidity distribution was measured using a humidity sensor for directly monitoring the relative humidity of the reaction gas flowing through the air flow channel of the cathode separator. The current distribution was measured directly by attaching a current sensor to the rib of the cathode separator. Typical results of relative humidity and current distribution are described and interpretations are discussed.

In situ approach for current distribution measurement in fuel cells

In this paper, a new, simple method for measuring the current density distribution in fuel cells with meander flow fields is described. This method has been used to investigate the reactant activity along the meander channel. The corresponding experimental hardware is very simple, cost-effective and easy to integrate into the fuel cells. A thin semi-segmented plate made of expanded graphite serves as a passive resistor network. The set-up is based on the idea that the electronic conductivity of the expanded graphite is relatively low in current direction. For typical current densities in polymer electrolyte fuel cell (PEFC), this leads to voltage drops in the range of several millivolts using usual current densities. On the other hand, the conductivity in-plane is considerable higher which is beneficial for equalizing the potential across the segment area. The new set-up can be used to measure the current density distribution in a single cell as well as in a stack at any desired position. The local potential difference across the graphite plate is caused by the local current flowing through it. By mapping these potential differences at different locations, the current distribution in the fuel cell can be derived. This experimental set-up has been used to investigate the current distribution of a 240 cm 2 PEFC single cell with different operating conditions. The real-time current density distributions measured by the present method are described in this paper.

Indirect Measurement of AC Current Distributions in a Bi-2223 Solenoidal Coil by a Pickup Coil Method

In order to investigate AC current distributions in high Tc superconducting (HTS) coils, we have developed a measurement method to evaluate the current distributions in a HTS solenoidal coil. In this method, the current distributions are indirectly found from the results of the field distributions measured by pickup coils located around the sample coil surface. To confirm the accuracy and sensitivity of this method, current distributions in a test coil made of insulated copper wires are measured. Numerical and measured field distributions are compared, and it is found that our method is accurate enough to measure the current distributions for the HTS coils. Using this method, we measured the current distributions in a Bi-2223 solenoidal coil at room temperature and 77 K. The comparison between the experimental and numerical results shows that the current distributions in the HTS coil are not uniform. On the basis of the obtained results, the characteristics of the AC current distributions in the HTS coils are discussed.

Design and Manufacture of a Full Size Joint Sample (FSJS) for the Qualification of the Poloidal Field (PF) Insert Coil

Within the framework of the European Fusion Programme a FSJS has been designed and manufactured by European Industry using PF coil NbTi superconductor manufactured and supplied by the Russian Federation as part of the R&D for the PF Conductor Insert (PFCI) coil. In addition to the superconductor, this sample contains a number of unique features. In contrast to other samples previously manufactured in Europe, the FSJS has used the Central Solenoid Model Coil (CSMC) joint design with NbTi conductor and a thick square jacket. One leg of the FSJS has had the conductor and sub-petal steel wraps removed before jacketing to assess the difference in the conductor performances between the two configurations. This paper will report on the development and manufacture of the FSJS, in particular the use of the Central Solenoid jacketing and swaging tools for compaction of the conductor and swaging of the joints, the preparation and qualification of the manufacturing route for the joint, the jacketing of a special length without conductor wraps and the high level of instrumentation required for the testing of the joint. The sample has been instrumented with more sensors than any other previous European sample, including temperature sensors, a large number of voltage taps for quench detection and Tcs measurements, quadrupoles to detect uneven voltage distribution, hall arrays for current distribution measurements and saddle coils.

Simultaneous Measurements of Species and Current Distributions in a PEFC under Low-Humidity Operation

An experimental technique has been developed to conduct simultaneous measurements of species concentration and current density distributions using a segmented cell of . Twelve segmented subcells in conjunction with a multichannel potentiostat were employed to measure the current distribution, and two sets of multiposition microactuators and micro gas chromatographs were used to measure gas concentration distributions on the anode and cathode sides simultaneously. Distribution data are shown systematically for a polymer electrolyte fuel cell (PEFC) operated under low-humidity cathode conditions and at and . The concentration profile for the PEFC is generally linear and can be well predicted by a simple mass balance analysis, the anode water concentration profile is closely tied to the net water transport rate through the membrane, and the net water transport coefficient ranges between 0.05 and 0.30 even under very dry cathode conditions, suggesting the presence of strong back-diffusion of water from the cathode to the anode despite rather dry cathode gas.

Magnetotomography—a new method for analysing fuel cell performance and quality

Magnetotomography is a new method for the measurement and analysis of the current density distribution of fuel cells. The method is based on the measurement of the magnetic flux surrounding the fuel cell stack caused by the current inside the stack. As it is non-invasive, magnetotomography overcomes the shortcomings of traditional methods for the determination of current density in fuel cells [J. Stumper, S.A. Campell, D.P. Wilkinson, M.C. Johnson, M. Davis, In situ methods for the determination of current distributions in PEM fuel cells, Electrochem. Acta 43 (1998) 3773; S.J.C. Cleghorn, C.R. Derouin, M.S. Wilson, S. Gottesfeld, A printed circuit board approach to measuring current distribution in a fuel cell, J. Appl. Electrochem. 28 (1998) 663; Ch. Wieser, A. Helmbold, E. Gülzow, A new technique for two-dimensional current distribution measurements in electro-chemical cells, J. Appl. Electrochem. 30 (2000) 803; Grinzinger, Methoden zur Ortsaufgelösten Strommessung in Polymer Elektrolyt Brennstoffzellen, Diploma thesis, TU-München, 2003; Y.-G. Yoon, W.-Y. Lee, T.-H. Yang, G.-G. Park, C.-S. Kim, Current distribution in a single cell of PEMFC, J. Power Sources 118 (2003) 193–199; M.M. Mench, C.Y. Wang, An in situ method for determination of current distribution in PEM fuel cells applied to a direct methanol fuel cell, J. Electrochem. Soc. 150 (2003) A79–A85; S. Schönbauer, T. Kaz, H. Sander, E. Gülzow, Segmented bipolar plate for the determination of current distribution in polymer electrolyte fuel cells, in: Proceedings of the Second European PEMFC Forum, vol. 1, Lucerne/Switzerland, 2003, pp. 231–237; G. Bender, S.W. Mahlon, T.A. Zawodzinski, Further refinements in the segmented cell approach to diagnosing performance in polymer electrolyte fuel cells, J. Power Sources 123 (2003) 163–171]. After several years of research a complete prototype system is now available for research on single cells and stacks. This paper describes the basic system (fundamentals, hardware and software) as well as the state of development until December 2003. Initial findings on a full-size single cell will be presented together with an outlook on the planned next steps.

DETECTING ABNORMAL FEED RATE IN ALUMINIUM ELECTROLYSIS USING EXTENDED KALMAN FILTER

One factor influencing the current efficiency in an aluminium electrolysis cell is the concentration of dissolved alumina in the electrolyte. Unfortunately, no direct measurement of alumina concentration is usually available and present control strategies for alumina feed control rely heavily on the change in cell pseudo-resistance. This paper describes work done to investigate the possibility of using additional measurements of anode current distribution in an extended Kalman filter for the purpose of detecting malfunctioning alumina feeders.

3618 固体高分子形燃料電池内現象の可視化と電流密度分布の同時計測(G08-1 燃料電池,G08 動力エネルギーシステム)

A fuel cell was made to allow direct observation of the phenomena in the cell, 2-D temperature measurement in cathode channels, and local current density measurements in anode side. The experimental results showed good correlation among direct view in the cell, temperature distribution and local current density. The experiment indicates transition phenomena of dry out and flooding depending on the flow and current conditions. The results suggests the possibility of different current density distribution for the same experimental conditions depending on the previous MEA condition history.

Signal formation analysis of the electron beam current distribution measurements

The Fourier spectra of signals and the modulation transfer functions are chosen as main characteristics of the electron beam (EB) analyzers. This approach can be used for EB analyzer design and optimization. It is concluded that the space–frequency characteristics of the scanning (modulation) system are the limiting factors for the signal distortion. A matrix of more than 32×32 sufficiently short impulses and at a transfer rate twice higher than the maximum spectrum frequency can create an adequate image of the beam current radial or angular distribution. At the data processing of the rotating probe or of the moving slit measurements an inverse transformation is needed and a false minimum can appear in the calculated current distributions.

Characterising PEM Fuel Cell Performance Using a Current Distribution Measurement in Comparison with a CFD Model

AbstractThe characterisation of a proton exchange membrane (PEM) fuel cell with a straight channel flow field design is performed. Spatially resolved current distribution measurements, at different air flow rates, are compared to numerical simulation results. The numerical model is validated by agreement of the measured and simulated current distribution.The test cell is segmented. It is operated at steady state conditions and the gas flow rates and cell temperature are controlled. The numerical simulation is realised with a PEM fuel cell model based on FLUENT™ computational fluid dynamics (CFD) software. It accounts for mass transport in the gaseous phase, heat transfer, electrical potential field and the electrochemical reaction. It provides three‐dimensional distributions of, e.g., current densities, reactant concentrations and temperature.

Effect of electrode configuration and electronic conductivity on current density distribution measurements in PEM fuel cells

Abstract Current density and potential distribution measurements were conducted using a segmented current collector and flow field setup on membrane electrode assemblies prepared with segmented and unsegmented electrodes made from two different types of commercially available gas diffusion layers. Both galvanostatic and potentiostatic discharge modes were employed. Irrespective of the type of gas diffusion layer, when a common electrode was employed, significant performance variations were encountered between current collector segments in the constant voltage mode, while the segment to segment variations were minimal in the constant current mode. Both types of discharge modes showed negligible variations between segments in the case of segmented electrode. A simple mathematical model was developed to assist in the interpretation of the experimental results. The differences in contact resistances between the current collectors and the gas diffusion layer, especially on the cathode side have been identified as the primary reason for the experimentally observed behavior. Based on the results presented here, segmenting the electrode along with the current collector is recommended for current distribution studies. When using a common electrode, only the galvanostatic mode is preferred to minimize contact artifacts.

AC Loss and Current Distribution Measurement for Superconducting Tapes

We made a co-axial copper tube measurement device in order to measure AC losses of HTS tapes. This device can minimize the external disturbance for high accuracy measurement. Also it is easy to fix the tape inside the copper tube. We used a linear amplifier in order to measure the voltage in high accuracy because the transport current was large. The voltage taps are located at the center and the edge of the tapes to measure the voltage drop on the samples. Our experimental data show that the inductive voltages are proportional to the frequency, and therefore this means that the main loss depends on hysteresis loss. In this study, the AC loss characteristics of twisted Bi-2223 tapes and untwisted tapes carrying AC transport current in self field is investigated. The magnetic flux generated by the transport current flowing in the HTS tape can be measured by using the same experimental setup. If the superconducting filament is twisted to reduce the AC losses, a relatively higher magnetic flux is induced at low frequencies, this is measured by winding the measuring wire around the tape - winding pick up method.

Measurements of current distributions in a multi-laminated HTS tape conductor for solenoid coils

A multi-laminated HTS tape conductor has recently been developed for large coils. If the HTS tapes are simply laminated to form the conductor, the current distribution in the laminated tape conductor of the coil is unbalanced because of the differences among all tape inductances. Transposition of the tape in the conductor is effective for homogeneous current distribution, but the tape may be damaged due to the lateral bending. In our previous paper, we proposed a new theory to analyze and control current distributions in the multi-laminated tape conductor for a solenoid coil with arbitrary layers. We applied the Maxwell integral equation to the region contoured by adjacent laminated tapes to analyze the current distributions of the tapes in the infinite solenoid coil, demonstrated that the flux across the region is conserved as long as the tapes are not saturated, and finally induced fundamental equations as functions of coil construction parameters, such as layer radius, laminated tape space, and winding pitch. In order to verify the theory, we designed two kinds of coils with homogeneous and inhomogeneous current distributions in the two-laminated tape conductor by adjusting the space between the tapes in the second layer, and fabricated them. In the case when the space between the tapes in the second layer is the same as that of the first layer, 0.31 mm in thickness, we measured the tape currents of 7:3 for the inner and outer tape of the first layer, respectively. We adjusted the space between the tapes of the second layer, 1.78 mm in thickness, while the space of the first layer remained unchanged, 0.31 mm in thickness. We obtained the homogeneous current distribution in the tape conductor. The experimental data were in good agreement with the theory.

A PEM fuel cell for combined measurement of current and temperature distribution, and flow field flooding

A fuel cell has been designed that combines three methods of spatially resolved measurements. The experimental setup allows to perform a simultaneous evaluation of current, temperature and water distribution in a polymer electrolyte fuel cell (PEFC) under operation. The test cell has a segmented anode flow field for current distribution measurement. The back plate of the cathode flow field is made of an optical window, which is transparent for infrared (IR) as well as for visible wavelengths. This allows infrared thermography and optical surveillance of water droplets and flow field flooding.