• Journal of the Korean Society of Visualization
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• v.21 no.3
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• pp.49-56
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• 2023

The Polymer electrolyte membrane fuel cell (PEMFC) operates at ambient temperature as a low-temperature fuel cell. During its operation, voltage losses arise due to factors such as operating conditions and material properties, effecting its performance. Computational simulations of fuel cells can be categorized into 1D simulation and CFD, chosen based on their specific application purposes. In this study, we carried out an analysis validation using 1D geometry and compared its performance with the results from 2D geometry analysis. CFD allows for the representation of pressure, velocity distribution, and fuel mass fraction according to the geometry, enabling the analysis of current density. However, the 1D simulation, simplifying governing equations to reduce time cost, failed to accurately account for fuel distribution and changes in fuel concentration due to fuel cell operations. As a result, it showed unrealistic results in the cell voltage region dominated by concentration loss compared to CFD.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.9
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• pp.683-694
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• 2008

The performance and durability of Polymer Electrolyte Fuel Cells (PEFCs) are strongly influenced by the uniformity of current density, temperature, species distributions inside a cell In order to obtain uniform distributions in them, the optimal design of flowfield must be a key factor. In this paper, the numerical study of land/channel flowfield optimizations is performed, using a multi-dimensional, multi-phase, non-isothermal PEFC model. Numerical simulations reveal more uniform current density and HFR(High Frequency Resistance) distributions and thus better PEFC performance with narrower land/channel width where the less severe oxygen depletion effect near the land region and more uniform contact resistance variation along the in-plane direction are achieved. The present study elucidates detailed effects of land/channel width and assist in identifying optimal flow-field design strategies for the operation of PEFCs.

• Proceedings of the KIEE Conference
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• 2003.07a
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• pp.555-557
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• 2003

As electric power transmission systems grow to supply the increasing electric power demand, transmission capacity is larger. but that's really difficult to secure the location for power transmission and distribution to user. The high temperature superconducting(HTS) cable is a method to solve this problem. But for applying to real systems, it needs to investigate the effect of HTS cable. The most important things is the investigation of fault condition. the fault on HTS cable include the quench state. When a fault occur in a circuit, three critical parameters(temperature, current density, magnetic field) exist. when one of these parameters exceeds the critical value, the superconducting becomes normal-conducting. f the cooling power is insufficient to recover the superconducting state, the normal-conducting zone expands. In order to solve these problem, this paper present simulate the quench state considering the over-current and over-voltage in the informal circuit and analyze the quench state.

• Proceedings of the KIEE Conference
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• 1995.11a
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• pp.435-437
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• 1995

It is important to understand tile behaviours of tile high pressure DC glow discharge with a micro gap inside a pixel of the plasmas display panel. We prepared a narrow gap discharge system and have measured electron temperature and density by means of double probe methods in high pressure which was between 100torr and 200torr. And the electrode gap was 7mm. When the pressure varied from 100torr to 200torr, the negative glow was created at a distance less than 1mm from the cathode. And the length of the faraday dark space decreased from 8mm to 5mm. Hence probe measurements was mainly, performed in the region of the Faraday dark space. The dependence of electron temperature and density on the pressure and current density was same with that of the general flow discharge, i.e. as the pressure increased the electron temperature decreased and the density increased. But the spatial electron density distribution in the Faraday dark space was highly distorted because of the effect of high pressure.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.1
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• pp.24-31
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• 2011

In order to measure corrosion level of reinforcement rebar in RC structures, non-destructive test methods which are concrete surface current density method and infrared thermographic technique were employed to measure corrosion levels. Experimental test parameters were various levels of corrosion states(0, 1, 3, 5, 7% of weight loss) and concrete cover depth(30 mm, 40 mm) and two different reinforcing rebar arrangements. The larger amount of concrete surface current density, the higher corrosion level in reinforcement rebar. The laboratory conditions which are ambient temperature and humidity have negligible effect on the infrared thermographical data. After analysis of current density and temperature distribution from concrete surface, corrosion level of reinforcement rebar embedded in concrete can be measured qualitatively based on the amount of electric current and heat flux.

• Journal of the Korean Institute of Navigation
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• v.21 no.4
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• pp.39-47
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• 1997

We researched the mechanism on th flucturain of Bottom Cold Water in the western channel of Korea Strait, using 13 years(1981~1933) oceanographic data of FRDA. The bottom cold water in the western channel appears more often in summer and fall than in winter and spring, and its year-to-year variation of temperature is very large. Such variation seems to be closely related with the variations of cold waters in the subsurface layer of the southwestern East Sea. According to the longitudinal temperature distribution along the korean southeastern coast, a density difference occurs all the time at the still deepth between the western channel and the southwestern East Sea. Thus, it is inferred that the cold waters would intrude into the western channle form the subsurface layer in the southwestern East Sea as a density-driven current, and it intensity depends upon the density difference.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.49 no.11
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• pp.729-736
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• 2000

This paper deals with the characteristic analysis of magnetizer for convergence purity magnet by the finite element method. The analysis utilizes combined method of the time-stepped finite element analysis and the Preisach model with hysteresis phenomena. In the finite element analysis, the non-linearity and the eddy current of the magnetizing fixure and permanent-magnet are taken account. The magnetization distribution in the permanent magnet is determined by using Preisach model which are composed of Everett function table and the first order transition curves is obtained by the Vibrating Sample Magnetometer. The calculated flux density values on the surface of the permanent magnet are led to the approximated gauss density values measured by the gauss meter. As a result, winding current, copper loss, eddy current loss of the magnetizing yoke, flux plot, surface gauss plot, temperature rise of the coil and resistor variation, vector diagram of magnetization distribution are shown.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.7
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• pp.963-972
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• 2003

Performance characteristics of the planar-type solid oxide fuel cell (SOFC) are investigated by the analysis of flow fields coupled with heat and mass transfer phenomena in anode and cathode channels. For these purposes, performance analysis of the SOFC is conducted based on electrochemical reaction phenomena in electrodes and electrolyte coupled with flow fields in anode and cathode channels. In the present study, the isothermal model adopted in the previous paper prepared by the same authors is extended to the non-isothermal model by solving energy equation additionally with momentum and mass transfer equations using CFD technique. It is found that the difference between isothermal and non-isothermal models come from non-uniform temperature distribution along anode and cathode electrodes by solving energy equation in non-isothermal model. Non-uniform temperature distribution in non-isothermal model contributes to the increase of average temperature of the fuel cell and influences its performance characteristics.

• Transactions of the Korean hydrogen and new energy society
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• v.20 no.3
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• pp.208-215
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• 2009

PEMFC stack power output is needed to be around 100 kW to meet the requirements of automotive application and scaling-up the active area of the stack cells will allow a higher power. In the case of scaling-up the active area of cells, it is difficult to obtain uniform in-plane internal conditions such as temperature, relative humidity and stoichiometry of the feed gas. These ununiformity with the location in the cell would affect both the performance and durability of the stack, so it is important to understand phenomena in the cell for improving them. In this study, the current density, electrochemical resistance and performance distribution measurement was performed to understand the ununiformity in a single cell using in-situ method; (1) Current Density Distribution (CDD) Device and (2) Segmented Cell Fixture. The influence of location of feed gas on the performance of a single cell was experimentally measured and discussed by using a segmented single cell which was composed of 8 compartments. The correlation between the location and performance in a single cell was discussed by these two tools and it was extended between the local characterization and the durability in a MEA by comparing the used cell with a fresh one. It was also studied in terms of electrochemistry by Electrochemical Impedance Spectroscopy.

• Applied Chemistry for Engineering
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• v.19 no.2
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• pp.228-235
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• 2008

Nickel plating thickness increased with the electric current density, and the augmentation was more thick in $6{\sim}10A/dm^2$ than low current. Hull-cell analysis was tested to evaluate the current density. Optimum thickness was obtained at a temperature of $60^{\circ}C$, and the pH fluctuation of 3.5~4.0. Over the Nickel ion concentration of 300 g/L, plating thickness increased with the current density. The rate of decrease in nickel ion concentration was increased with the current density. The quantity of plating electro-deposition was increased at the anode surface, which was correlated with the increase of plating thickness. The plating thickness was increased because of the quick plating speed. However, the condition of the plating surface becomes irregular and the minuteness of nickel plating layer was reduced with the plating rate. After the corrosion test of 25 h, it was resulted in that maintaining low electric current density is desirable for the excellent corrosion resistance in lustered nickel plating. According to the program simulation, the thickness of diffusion layer was increased and the concentration of anode surface was lowered for the higher current densities. The concentration profile showed the regular distribution at low electric current density. The field plating process was controlled by the electric current density and the plating thickness instead of plating time for the productivity. The surface physical property of plating structure or corrosion resistance was excellent in the case of low electric current density.