The Experts below are selected from a list of 8310 Experts worldwide ranked by ideXlab platform
Tatsuhiro Okada - One of the best experts on this subject based on the ideXlab platform.
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numerical simulation of enhancement of mass transfer in the Cathode electrode of a pem fuel cell by magnet particles deposited in the Cathode Side catalyst layer
Chemical Engineering Science, 2005Co-Authors: L B Wang, Nobuko I Wakayama, Tatsuhiro OkadaAbstract:Abstract Recent experimental results show that performance of a proton exchange membrane (PEM) fuel cell is improved when small particles of permanent magnet are deposited in the catalyst layer on the Cathode Side. In this study, the mechanism of this phenomenon was clarified by using numerical simulation. Permanent magnet particles induce a Kelvin (magnetic) repulsive force against liquid water and an attractive force towards oxygen gas. To precisely study the behavior of oxygen and liquid water flows near the interface between the catalyst layer and gas diffuser, the simulation domain included the catalyst layer and gas diffuser. The simulation results revealed the following. The Kelvin repulsive force against liquid water mainly “manages” the liquid water flow and improves the performance of the fuel cell, especially in the current-limited region. In the presence of Kelvin forces, the liquid water saturation near the interface between the catalyst layer and gas diffuser decreases, thus making more pore space available for transport of oxygen gas. Furthermore, the water velocity moving from the interface increases in the upstream region. The gas velocity near the interface also increases, and thus more oxygen is supplied to the reaction sites. In summary, the Kelvin force promotes removal of liquid water from the catalyst layer, thus providing more oxygen to the catalyst and improving the performance of the fuel cell.
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management of water transport in the Cathode of proton exchange membrane fuel cells using permanent magnet particles deposited in the Cathode Side catalyst layer
Isij International, 2005Co-Authors: L B Wang, Nobuko I Wakayama, Tatsuhiro OkadaAbstract:Recently, it was found that the performance of proton-exchange membrane (PEM) fuel cells was improved by the deposition of small magnet particles in the Cathode-Side catalyst layer. We developed a numerical simulation to clarify this effect, for a PEM fuel cell equipped with an interdigitated gas distributor. A two-dimensional, two-phase model was used. Cathode electrode consisted of gas diffusion layer and catalyst layer, and the latter was treated as a line. Darcy's law was used to describe the transport of the gas phase. The forces from the shear of the gas flow and of the capillary action move the liquid water through the porous Cathode electrode. The magnetic field was modeled by using an equivalent magnetic field. Our numerical results show that the repulsive Kelvin forces acting on liquid water can control the liquid water flow through a porous gas diffusion layer. With increasing residual flux density of magnet particles, the velocity of liquid water near the interface of the catalyst/diffusion layers increases, the saturation of liquid water near the interface decreases, and increasing more pore space is freed for O2 transport and reactions. Therefore, the mechanism of the improvement of the cell performance by magnet particles is clarified using such a numerical model. The use of permanent magnets will be especially useful for portable fuel cell in which there is no power to supply air.
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theory for water management in membranes for polymer electrolyte fuel cells part 1 the effect of impurity ions at the anode Side on the membrane performances
Journal of Electroanalytical Chemistry, 1999Co-Authors: Tatsuhiro OkadaAbstract:Abstract Performance degradation in membranes for polymer electrolyte fuel cells was discussed theoretically for the case where the membrane is contaminated with foreign impurity cations at the Cathode Side. Water transport in a two-cation system membrane was conSidered by assuming an ‘infected zone’ of finite thickness. Four kinds of boundary value problems were solved, and analytical formulae derived for the water concentration profile across the membrane. The water content in the membrane, the net water flux and the membrane resistance overvoltage were calculated systematically as functions of several relevant parameters in fuel cell operations. Localized contamination at the Cathode ∣ membrane interface turned out to be even more serious than the uniform contamination of the membrane or localized contamination at the anode Side. It is noted that special caution should be directed in order to avoid the membrane contamination, especially at the Cathode Side, because contaminant will easily enter from the air stream through the Cathode compartment of a fuel cell.
Ken Okazaki - One of the best experts on this subject based on the ideXlab platform.
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phase change in the Cathode Side of a proton exchange membrane fuel cell
Journal of Power Sources, 2010Co-Authors: N Khajehhosseinidalasm, Kazuyoshi Fushinobu, Ken OkazakiAbstract:Abstract A three-dimensional steady state two-phase non-isothermal model which highly couples the water and thermal management has been developed to numerically investigate the spatial distribution of the interfacial mass transfer phase-change rate in the Cathode Side of a proton exchange membrane fuel cell (PEMFC). A non-equilibrium evaporation–condensation phase change rate was incorporated in the model which allowed supersaturation and undersaturation take place. The most significant effects of phase-change rate on liquid saturation and temperature distributions are highlighted. A parametric study was also carried out to investigate the effects of operating conditions; namely as the channel inlet humidity, cell operating temperature, and inlet mass flow rate on the phase-change rate. It was also found that liquid phase assumption for produced water in the Cathode catalyst layer (CL) changed the local distribution of phase-change rate. The maximum evaporation rate zone (above the channel near the CL) coincided with the maximum temperature zone and resulted in lowering the liquid saturation level. Furthermore, reduction of the channel inlet humidity and an increase of the operation temperature and inlet mass flow rate increased the evaporation rate and allowed for dehydration process of the gas diffusion layer (GDL) to take place faster.
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transient phase change in the Cathode Side of a pem fuel cell
Journal of The Electrochemical Society, 2010Co-Authors: N Khajehhosseinidalasm, Kazuyoshi Fushinobu, Ken OkazakiAbstract:We numerically investigated the temporal variation and spatial distribution of interfacial mass-transfer phase-change rate in the Cathode Side gas diffusion layer of a proton exchange membrane (PEM) fuel cell during startup. For this purpose, a three-dimensional transient two-phase nonisothermal model was used. A nonequilibrium evaporation-condensation interfacial mass-transfer rate is incorporated in the model, which enables us to take supersaturation and subsaturation into conSideration. This helps us to investigate the most significant contribution of the phase-change rate to the transient response and thermal behavior of the cell. The effects of the operating temperature and channel inlet humidity on the phase-change rate are also investigated. It is observed that when condensation is dominant, the transient time decreases. It is also observed that the maximum temperature decreases with time due to vapor-phase diffusion and phase change.
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three dimensional transient two phase study of the Cathode Side of a pem fuel cell
International Journal of Hydrogen Energy, 2010Co-Authors: N Khajehhosseinidalasm, Kazuyoshi Fushinobu, Ken OkazakiAbstract:A three-dimensional transient two-phase isothermal model has been developed for the Cathode Side of a proton exchange membrane fuel cell (PEMFC). This has been done in order to fully investigate the effects and the time variation of liquid water formation as well as the gas phase transport under the start up condition. It is conSidered that the generated water in the Cathode catalyst layer (CL) is liquid water and that the gas diffusion layer (GDL) is hydrophobic. A non-equilibrium water condensation-evaporation is also assumed. The time variations of liquid water distribution in along-channel and through-plane directions are investigated. This is to determine the liquid water accumulation at the start up time (above the channel under the CL), then the movement of the liquid water in the domain and the final accumulation at the steady state condition (above the rib and near the CL). It has also been found that it takes less time for a high average current density to attain the steady state condition which is due to the capillary pressure gradient inSide the porous media. Validation of the numerical results has been implemented via a polarization curve comparison with the experimental data. Both sets show good agreement.
Roman Baburske - One of the best experts on this subject based on the ideXlab platform.
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switching ruggedness and surge current capability of diodes using the self adjusting p emitter efficiency diode concept
Iet Circuits Devices & Systems, 2014Co-Authors: Thomas Basler, Roman Baburske, Hans Joachim Schulze, Franz Josef Niedernostheide, Hanspeter Felsl, Manfred Pfaffenlehner, Frank Pfirsch, Josef LutzAbstract:The surge-current ruggedness of free-wheeling diodes can be improved by implementing the self-adjusting p emitter efficiency diode concept (SPEED). Simulations indicate that the switching ruggedness is reduced because of the occurrence of Cathode-Side filaments during reverse-recovery. Experiments confirm the weak switching performance of such a diode in comparison to a conventional diode. By implementing the controlled injection of backSide holes concept Cathode-Side filaments can be suppressed. However, this measure is not sufficient to regain the switching ruggedness of a conventional diode. It is also necessary to fully embed the p + -areas of the SPEED anode in the low-doped p-type area to avoid high electrical field strengths at the p + p-junction and pinning of anode-Side filaments. However, anode-Side adjustments for improving the switching ruggedness can reduce the benefit of the SPEED concept regarding the surge-current capability.
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Cathode-Side Current Filaments in High-Voltage Power Diodes Beyond the SOA Limit
IEEE Transactions on Electron Devices, 2013Co-Authors: Roman Baburske, Elmar Falck, Hans Joachim Schulze, Franz Josef Niedernostheide, Josef Lutz, Josef Georg BauerAbstract:An analysis of the plasma front velocities during turnoff of a power diode is used to explain the differences between the formation and the behavior of Cathode-Side and anode-Side filaments. Device simulations show, how Cathode-Side filaments may trigger a thermal runaway at the end of a reverse-recovery period of diodes turned off with extremely high current rates operating the diode in a regime far away from the safe operating area. From the transient voltage curve, the analysis of the reverse-recovery charge as a function of the dc-link voltage and an analysis of the turnoff transients in the current-voltage phase space, it is, however, deduced that the appearance of a Cathode-Side filament by itself does not necessarily lead to diode destruction. The transformation of the initially avalanche-generated filaments into filaments that are essentially driven by thermal mechanism seems to be a further important condition for device destruction.
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filament induced thermomigration of an aluminum drop at the Cathode Side of high voltage power diodes
International Symposium on Power Semiconductor Devices and IC's, 2011Co-Authors: H J Schulze, Franz Josef Niedernostheide, Josef Lutz, Josef Bauer, Hanspeter Felsl, J Biermann, Roman BaburskeAbstract:This paper shows how a buried aluminum eutectic drop at the Cathode-Side of a high-voltage power diode can affect the device behavior. The aluminum drop driven by thermo-migration, moves from the contact metallization some micrometers into the chip and forms a buried eutectic. Thermomigration [1] becomes stronger as the temperature gradient increases. High temperature gradients can be achieved at the Cathode Side if a single filament is triggered. Simulation results show that an early surface-punch-through at a spike may reduce the reverse-recovery ruggedness of the power diode. Such a detrimental filamentation can be avoided by a well-defined fabrication process of the device.
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on the formation of stationary destructive Cathode Side filaments in p n n diodes
International Symposium on Power Semiconductor Devices and IC's, 2009Co-Authors: Roman Baburske, Franz Josef Niedernostheide, Josef Lutz, B Heinze, Dieter SilberAbstract:Analyzing the dynamics of current filaments is essential for a correct understanding of SOA limitations. Current filaments can occur during the reverse-recovery period of p+-n−-n+ diodes. In this work, we apply the results from an analysis of the plasma-front dynamics for the one-dimensional case to conditions under which current filaments appear in the depletion layers due to dynamic avalanche. We show that the anode-Side plasma front velocity is higher in the vicinity of the filament than far away from the filament center, favoring the evolution of a lateral traveling anode-Side filament. Furthermore, we find that the Cathode-Side plasma front changes its vertical propagation direction when a dynamic avalanche in the Cathode-Side depletion layer causes current crowding. As a result, the Cathode-Side depletion layer in the vicinity of the filament decreases, favoring the formation of a standing Cathode-Side filament that may cause final destruction of the device. The analytical results are in good agreement with numerical simulations and results of previously published work.
Kat Suaki Suganuma - One of the best experts on this subject based on the ideXlab platform.
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electromigration behavior in cu ni p sn cu based joint system with low current density
Microelectronics Reliability, 2015Co-Authors: Kimihiro Yamanaka, Takuya Kadoguchi, Keisuke Gotou, Shijo Nagao, Kat Suaki SuganumaAbstract:Abstract Although electromigration in solder joints has great influence on reliability, few study has been reported on the Cu/Ni–P/Sn–Cu based joint system electromigration with realistic current density range lower than 10 kA/cm 2 . We investigated a Cu/Ni–P/Sn–0.7Cu/Ni–P/Cu joint with current densities of 5.0 and 7.5 kA/cm 2 at 423 K. Solder joint breakdown at the Cathode Side was detected for both stress conditions. Ni–P plating disappeared completely at the Cathode Side and a Cu–Sn intermetallic compound (IMC) formed at the interface. Cu–P IMC formed on the solder breakdown interface. Ni diffusion in Ni–P plating at the Cathode was accelerated and the P-rich layer grew thicker than at the anode Side before breaking down under electromigration stress. The P-rich layer reached the Cu electrode resulting in cracking along the interface between solder layer and Cu. Sn was diffused from the Ni 3 SnP IMC to the P-rich layer cracks and formed Cu 3 Sn IMC with the Cu electrode. Thus, the electromigration mechanism in an electroless Ni–P plating/Sn–Cu based joint system with low current density was clarified.
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Electromigration effect on solder bump in Cu/Sn–3Ag–0.5Cu/Cu system
Scripta Materialia, 2006Co-Authors: Kimihiro Yamanaka, Yutaka Tsukada, Kat Suaki SuganumaAbstract:The electromigration effect on solder bump and interfacial reactions in the Cu/Sn–3Ag–0.5Cu/Cu flip chip joint was investigated at 453 K with 10 kA/cm2. Cu was transported towards the anode and avoid nucleated at the highest current density point near the Cathode. The void nucleated at the Sn/Cu6Sn5 interface and grew along the Cathode Side. It was observed that the unique solder bump deformation towards the Cathode started in the early stage of the electromigration test.
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electromigration effect on solder bump in cu sn 3ag 0 5cu cu system
Scripta Materialia, 2006Co-Authors: Kimihiro Yamanaka, Yutaka Tsukada, Kat Suaki SuganumaAbstract:The electromigration effect on solder bump and interfacial reactions in the Cu/Sn–3Ag–0.5Cu/Cu flip chip joint was investigated at 453 K with 10 kA/cm2. Cu was transported towards the anode and avoid nucleated at the highest current density point near the Cathode. The void nucleated at the Sn/Cu6Sn5 interface and grew along the Cathode Side. It was observed that the unique solder bump deformation towards the Cathode started in the early stage of the electromigration test.
Seunghun Jung - One of the best experts on this subject based on the ideXlab platform.
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non isothermal multi dimensional direct methanol fuel cell model with micro porous layers mitigating water methanol crossover
Journal of Power Sources, 2013Co-Authors: Seunghun JungAbstract:Abstract A two-phase three-dimensional direct methanol fuel cell (DMFC) model with the capability of saturation jump is developed in order to investigate the effect of micro-porous layers (MPL) on the water/methanol crossover in a DMFC. It is found that hydrophobic MPL on the Cathode Side helps Cathode catalyst layer reserve water whereas hydrophobic MPL on the anode Side blocks liquid flow to the Cathode Side, which effectively reduces water/methanol crossover. As the water transport in a DMFC occurs in two-phase, energy equation conSidering the heat-pipe effect with latent heat is solved together. Calculation result revealed thermal conductivity of gas diffusion layer has a strong influence on both temperature and water transport. Finally, a large-scale simulation of 28 cm 2 cell is conducted to examine current density and fuel concentration distribution.
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Non-isothermal multi-dimensional direct methanol fuel cell model with micro-porous layers mitigating water/methanol crossover
Journal of Power Sources, 2013Co-Authors: Seunghun JungAbstract:Abstract A two-phase three-dimensional direct methanol fuel cell (DMFC) model with the capability of saturation jump is developed in order to investigate the effect of micro-porous layers (MPL) on the water/methanol crossover in a DMFC. It is found that hydrophobic MPL on the Cathode Side helps Cathode catalyst layer reserve water whereas hydrophobic MPL on the anode Side blocks liquid flow to the Cathode Side, which effectively reduces water/methanol crossover. As the water transport in a DMFC occurs in two-phase, energy equation conSidering the heat-pipe effect with latent heat is solved together. Calculation result revealed thermal conductivity of gas diffusion layer has a strong influence on both temperature and water transport. Finally, a large-scale simulation of 28 cm 2 cell is conducted to examine current density and fuel concentration distribution.