Papers by Author: Hong Gun Kim

Abstract: The temperature uniformity of most carbon fiber is degraded on the entire area. Therefore, understanding the thermal characteristics based on surface density and electrode shape becomes necessary. In this paper, the samples were fabricated according to the area density of carbon fiber and polyethylene terephthalate (8.8 g/m2, 20.2 g/m2, 42.1 g/m2). Different voltages (2V, 4V, 6V) were applied on them and the image was taken using thermal camera. Initially, the samples were investigated for morphology and element characterization by SEM-EDAX of surface heating elements and found that increased area density resulted in increase in the number of carbon atoms and decrease in number of oxygen atoms. It was also found from sheet resistance test that area density has inverse proportional relation with sheet resistance. In addition to that, regardless of the shape of the electrode, the increase in area density leads to a rise in temperature. It also increased the range of the temperature variation. Therefore, the uniformity and temperature stability can be satisfied by securing the electrode part as wide as possible through uniform electrode shape. In case of homogeneous electrode type, the saturation time of maximum temperature was 270 seconds, and the loading time was longer than 70 seconds of the concentrated electrode type. Therefore, in order to satisfy the reference temperature (30°C~ 50°C), the required surface heating product should be manufactured with the area density of 20.2 g/m2 at a voltage applied around 6V or less.

Abstract: The electrochemical hydrogen compressor (EHC) is used as a moisture elimination tool for the wet hydrogen gas. As the pressure of cathode compartment increases, the moisture contents of hydrogen decrease, however, the electrochemical performance of the compression cell is deteriorated. In the high enough pressure difference conditions between anode and cathode the electrochemical performance loss results mainly from the dehydration of the proton exchange membrane. In this article the MEA (membrane electrodes assembly) is modified to keep the water molecules not only in the membrane but also in the cathode catalytic layer. Then the electrochemical performance of the hydrogen compression cell is measured with the moisture elimination ability. The variously modified MEAs are tested and the surfaces of modified electrodes are pictured by scanning electron microscope.

Abstract: The production of hydrogen and oxygen using the water electrolysis technology is mostly influenced by the performance and efficiency of the components that are used in the production systems. In this study, the flow field’s channels of the bipolar plates of polymer electrolyte membrane electrolyzer were replaced by 3-D titanium mesh, and the polymer electrolyte membrane (PEM) electrolyzer cell that uses 3-D titanium mesh was designed. A numerical analysis was conducted to study the performance of the designed model. By comparing the results with the electrochemical performance of PEM electrolyzer cell with flow field channels on the plates, it was found that the cell with 3-D titanium mesh has greater performance and higher total power dissipation density. Therefore, the use of 3-D mesh can be used instead of machining the flow field channels on the bipolar plates.

Abstract: The fiber is considered the most important element in fiber reinforced composite materials, as it generally occupies the largest volume in a composite material; further, delivers the heaviest loads. therefore, it is important to select types, quantity and proper stacking angles of the fiber. In this study, the fiber directions were arranged in different orientation angles, i.e. in symmetric (0°/0°,15°/15°,30°/30°,45°/45°,90°/90°) and asymmetric (0°/15°,0°/30°,0°/45°,0°/90°), to analyze the tensile strengths depending on the fiber orientation angles through the tensile test. In addition, a thermal imaging camera was used to investigate the thermal characteristics of the test specimens generated during the tensile test. the tensile strength showed a tendency of decreasing while the orientation angle increased. the maximum temperature generated when the fracture occurred increased at the fiber orientation angle of 30°, and showed a tendency of decreasing as the orientation angle increased.

Abstract: The prepreg process among the CFRP (Carbon Fiber Reinforced Plastic) forming methods is the short term of ‘Pre-impregnation’, which is widely used for aerospace composites that require a high quality property such as a fiber-reinforced woven fabric, in which an epoxy hardening resin is impregnated. the reality is, however, that this process requires continuous researches and developments for its commercialization because the delamination characteristically develops between the layers when a great weight is loaded from outside. to supplement such demerit, three lamination methods among the prepreg lamination methods of CFRP were designed to minimize the delamination between the layers due to external impacts. Further, the newly designed methods and the existing lamination methods were analyzed through a mechanical characteristic test, tensile test and infrared thermal device during the tensile tests, to obtain a better property than the existing lamination methods. the tensile test result showed that the newly designed three lamination methods, i.e. Roll, Half and Zigzag lamination methods, appeared superior to the Play lamination method in the aspects of the strength and strain. The strength of the Zigzag lamination method, which was the highest, was confirmed as being improved by about 20% than that of the Ply method.

Abstract: As society became more complex, the logistics also increased, demanding for logistics transport vehicles and feeder has increased. Because the self-weight of skate for cargo transport used in this study is heavy, it needs to be weight lightening. However there is a lack of capital and technology not to improve lasting. We conducted FEM studies about weight lightening applying composites on cargo transport skate and the stiffness can be obtained at the same time. However, due to the presence of discontinuities such as holes in the parts. If you are applying composite, Because this causes the degradation of the strength of the material under static and fatigue load induced stress concentration in parts. In order to examine the safety of the cargo transport skate, you must consider the impact of the static strength damage on the stress concentration because of the discontinuous parts. In this study, therefore, the cargo skate was performed to evaluate the structural analysis through the FEM analysis. As a result, it was found that CFRP compared to existing SM45C is superior 25% when considering the characteristics. It indicated the best results in about 30% of the weight lightening.

Abstract: Load bearing skate for the current weight is heavy and requires its own weight, but persist without improvement in the lack of capital and technology, but it is a reality. In this study, carried out phase optimal design to remove unwanted elements that do not have a stress to reduce the weight of skating that is being used for cargo transportation for, it reduces the weight of the objective function, we examined the safety associated with it.Using the FEM analysis Let's examine the effect on the failure strength by extreme temperatures that are used in the field of stress concentration due to discontinuity in the analysis at the time, structure - was carried out thermal analysis.Further, while ensuring safety through safety factor 2.1 and 20% weight reduction by the phase volume of for weight reduction.

Abstract: Topology optimization and shape optimization of structural optimization techniques are applied to transport skate the lightweight. Skate properties by varying the design variables and minimize the maximum stress and strain in the normal operation, while reducing the volume of the objective function of optimal design and Skate the static strength of the constraints that should not degrade compared to the performance of the initial model. The skates were used in this study consists of the main frame, sub frame, roll, pin main frame only structural analysis and optimal design was performed using the finite element method. Simplified initial model set design area and it compared to SM45C, AA7075, CFRP, GFRP was using the topology optimization. Strength does not degrade compared to the initial model, decreased volume while minimizing the stress and strain results, the optimum design was achieved efficient lightweight.

Abstract: Of the advanced composite materials for aerospace structures such as aircrafts and space devices, the carbon fiber reinforced plastics (CFRP) is applied to many sectors that require lightweight materials for its high strength and stiffness. One of the disadvantages of the CFRP, however, is that it is weak against impact. In this study, impact test specimens were manufactured with five fiber stacking angles (0°/0°, 0°/15°, 0°/30°, 0°/45°, 0°/90°) according to ASTM D7136[15], and a falling weight test was performed to analyze the correlation between their mechanical and thermal characteristics. As a result, the impact energy applied to the five test specimens with different fiber stacking angles was almost constant at 30.63 J - 30.78 J. The absorbed energy increased with the increase in the fiber stacking angle, and decreased after 0°/45°. The average temperature on the fractured surface increased with the increase in the fiber stacking angle in all specimens other than the 0°/0° specimen.

Abstract: Recently, polymer electrolyte membrane (PEM) electrolyzers consist of the layered structure of membrane and electrode assembly (MEA), titanium flow field plate, gasket, end plate, and others. Among these components, MEA and titanium flow field plate take account for most of the device cost. The cost and time for manufacturing device can be reduced with the gasket-integrated 3-D mesh-applied PEM electrolyzer (Fig. 3), while maintaining the same performance as that of the existing titanium flow field plate devices. The 3-D mesh is found to perform the roles of the existing flow plate which ensures the smooth fluid flow and uniform power supply. The voltage shows 19.3V at current density (0.5 A/cm²), a little lower than 19.6V that is 10 times of 1.96V which is the average cell voltage at the same current density. In addition, hydrogen production and stability for performance are equal to or higher than that of the device for titanium flow field plate.