• Membrane Journal
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• v.33 no.3
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• pp.127-136
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• 2023

In this study, the electrochemical performance of a 5-layer fuel cell stack using silica composite membranes as polymer electrolyte membranes was evaluated. It was observed that the flow rate of the fuel gases plays a crucial role in stack performance, particularly being mainly dependent on the flow rate of hydrogen. Increasing the flow rate of oxygen resulted in negligible changes in performance, whereas an increase in the flow rate of hydrogen demonstrated performance improvements. However, this led to an imbalance in the ratio of hydrogen to oxygen flow rates, causing significant degradation in stack performance and durability. A decline in stack performance was also observed over time due to the degradation of stack components. This phenomenon was consistently observed in individual unit cells. Based on these findings, it was emphasized that, in addition to optimizing the performance of each component during stack operation, it is important to optimize design and operating conditions for uniform flow rate control. Lastly, the developed silica composite membrane was assessed to have sufficient performance for application in actual fuel cell systems, exhibiting a performance of over 25 W based on maximum power.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1752-1756
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• 2008

A simple, accurate and efficient mesh generation technique, the cut-cell method, is able to represent an arbitrarily complex geometry. Both structured and unstructured grid meshes are used in this method. First, the numerical domain is constructed with regular Cartesian grids as a background grid and then the solid boundaries or bodies are cut out of the background Cartesian grids. As a result, some boundary cells can be contained two numerical conditions such as the flow and solid conditions, where the special treatment is needed to simulate such physical characteristics. The HLLC approximate Riemann solver, a Godunov-type finite volume method, is employed to discretize the advection terms in the governing equations. Also, the TVD-WAF method is applied on the Cartesian cut-cell grids to stabilize numerical results. Present method is validated for the rectangular dam break problems. Initially, a conventional grid is constructed with the Cartesian regular mesh only and then applied to the dam-break flow simulation. As a comparative simulation, a cut-cell grids are applied to represent the flow domain rotated with arbitrary angles. Numerical results from this study are compared with the results from the case of the Cartesian regular mesh only. A good agreement is achieved with other numerical results presented in the literature.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.12
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• pp.1596-1607
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• 2000

The optimal design of auto-catalyst needs a good compromise between the pressure drop and flow uniformity in the substrate. One of the effective methods to achieve this goal is to use the concept of radially variable cell density. But this method has not been examined its usefulness in terms of chemical behavior and conversion performance. In this work, two-dimensional performance prediction of catalyst coupled with turbulent reacting flow simulation has been used to evaluated the benefits of this method n the flow uniformity and conversion efficiency. The results showed that two cell combination of 93cpsc and 62 cpsc was the most effective for improved pressure drop and conversion efficiency due to balanced space velocity and efficient usage of geometric surface area of channels. It was also found that large temperature difference between the bricks in case that the edge of the frontal face of brick has too much lower cell density(less than 67% of cell density of the center of the brick). This study has also demonstrated that the present computational results show the better prediction accuracy in terms of CO, HC and NO conversion efficiencies compared to those of conventional 1-D adiabatic model by comparison with experimental results.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.4
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• pp.283-290
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• 2008

In this paper, experiments with an air-breathing proton exchange membrane fuel cell (PEMFC) for mobile devices were carried out according to cathode conditions. These conditions are defined by the cathode flow field plate type (the channel type, the open type) and the cathode surface direction. Single-cell and 6-cell stack were used in the experiments. The experimental results showed that the open-type cathode flow field plate gave a better performance than the small channel type. In the experiments related to the direction of the slits on the cathode flow field plate, the horizontal slit cell was better than the vertical one. With respect to the cathode surface direction, when the cathode surface is placed in the direction normal to the ground, the PEMFC generated more stable power in the mass transport loss region. Since stable power in the mass transport region is closely related to the air supply, computational fluid dynamics (CFD) analysis for air-breathing PEMFC of different cathode surface directions was performed.

• KSBB Journal
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• v.15 no.4
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• pp.388-392
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• 2000

An on-line glucose flow injection analysis system was developed and used for the automatic analysis and addition of glucose in the cultivationof a Saccharomyces cerevisiae in a korean paper digestion wastewater in order to increase the cell concentration. The system was composed of a ceramic sampler a sampling valve an injection valve an immobilized glucose oxidase column a debbble a flow cell with platinum electrodes a potentiostat a computer and interface system and tubing pumps. The glucose concentration of the wastewater medium was mainitained at the low concentration of $176{\pm}31 mg/L$ with the on-line FIA system and by adding glucose and $>(NH_4)_2S0_4$ the cell concentration as total cell count can be increased by 3.1times.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.12
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• pp.3970-3979
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• 1996

A fluid flow inside a circular cylinder subject to horizontal, circular oscillation is analyzed numerically and experimentally. The steady streaming velocities at the edges of the boundary layers on the bottom and side surfaces of the cylinder obtained in the previous paper are used as the boundary conditions in the governing equations for the steady flow motion in the interior region. The Stokes' drift velocity obtained in the previous paper also constitutes the Lagrangian velocity which is used in the momentum equations. It turns out that the interior steady flow is composed of one cell, ascending at the center and descending near the side surface, at the streaming Reynolds number 2500. However, at the streaming Reynolds number 25, the flow field is divided into two cells resulting in a descending flow at the center. The experimentally visualized flow patterns at the bottom surface agree well with the analytical solutions. The visualization experiment also confirms the flow direction as well as the center position of the cell obtained by the numerical solutions.

• Journal of the Korea Furniture Society
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• v.26 no.2
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• pp.179-185
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• 2015

A study was carried out to observe the 1% aqueous safranine solution flow speed in longitudinal and radial directions of softwood G. biloba, ring-porous wood A. altissima, and diffuse- porouswood D. kaki. In radial direction, ray cells and in longitudinal direction tracheids, vessel and wood fiber were considered for the measurement of liquid penetration speed at less than 12% moisture contents (MC). The length, lumen diameter, pit diameter, end wall pit diameter and the numbers of end wall pits determined for the flow rate. The liquid flow in the those cells was captured via video and the capillary flow rate in the ones were measured. Vessel in hardwood species and tracheids in softwood was found to facilitate prime role in longitudinal penetration. Radial flow speed was found highest in ray parenchyma of G. biloba. Anatomical features like the length and diameter, end-wall pit numbers of ray parenchyma were found also responsible fluid flow differences. On the other hand, vessel and fiber structure affected the longitudinal flow of liquids. Therefore, the average liquid penetration depth in longitudinal tracheids of G. biloba was found the highest among all cells considered in D. kaki and A. altissima.

• Journal of Chest Surgery
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• v.25 no.5
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• pp.451-457
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• 1992

The hollow fiber oxygenator is the most advanced one for the cardiopulmoanry bypass. They have two different types of the hollow fiber systems according to the way how the blood go through the fibers. One is inside blood flow type and the other outside type. In order to find out which is better to prevent blood cell destruction, we selected 40 valve replacing patients and divided them into 2 groups prospectively. In group I [n=20], inside blood flow type[BCM-7a], CO2 excretion is more effective than group II, that is partly because of the relative large surface area of the BCM-7. In group II [n=20], outside blood flow type [MAXIMAa], they have better quality to preserve platelet count. We also studied about several other items such as SaO2, Hemoglobin and RBC, WBC, fibrinogen, LDH, plasma hemoglobin, haptoglobulin and so on. But we cannot find any differences between two groups with any statistical meanings [p<0.05]. We conclude that both of two oxygenators are excellent in the aspects of gas exchange and blood cell preservation.

• Journal of Korea Foundry Society
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• v.43 no.6
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• pp.302-309
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• 2023

In general, castings often have complex shapes and significant variations in thickness within a single product, making grid generation for simulations challenging. Casting flows involve multiphase flows, requiring the tracking of the boundary between air and molten metal. Additionally, considerable time is spent calculating pressure fields due to density differences in a numerical analysis. For these reasons, the Cartesian grid system has traditionally been used in mold filling simulations. However, orthogonal grids fail to represent shapes accurately, leading to a momentum loss caused by the stair-like grid patterns on curved and sloped surfaces. This can alter the flow of molten metals and result in incorrect casting process designs. To address this issue, simulations in the Cartesian grid system involve creating a large number of grids to represent shapes more accurately. Alternatively, the Cut Cell method can be applied to address the problems arising from the Cartesian grid system. In this study, analysis results based on the number of grid in the Cartesian grid system for a casting flow analysis were compared with results obtained using the Cut Cell method. Casting flow simulations of actual products during various casting processes were also conducted, and these results were analyzed with and without applying the Cut Cell method.

• 한국전산유체공학회:학술대회논문집
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• 2008.08a
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• pp.46.4-46.4
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• 2008