• Journal of Power System Engineering
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• v.7 no.4
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• pp.61-66
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• 2003

In this paper, the relation between displacement of piezoelectric material and electric field was proposed. FEA was introduced to predict the displacement and reaction force of plate spring attached in the piezoelectric material. The relation between displacement of piezoelectric material forced by plate spring and applied electric field were further verified by experimental investigation. Also, the flow rate of gas in piezoelectric valve was examined by experiment. Finally, the relation between electric field and gas flow was derived. Based on these results, these relations can be used in the design of mass flow controller.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.141-142
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• 2003

When the under-expanded supersonic jet impinges on the perpendicular plate, it is well known that the self-induced flow oscillation occurs at the specific conditions. This phenomenon is related with the noise problems of aeronautical and other industrial engineering. But, the very complicated flow field is formed and it is difficult to clear the flow structure and the mechanism of oscillation. This paper aims to clear the characteristics of flow field and the wave pattern during the under-expanded supersonic jet impinges on the plate. The numerical calculation was carried out using the TVD numerical method. In this paper, the flow visualization, the pressure fluctuation on the surface of plate and the mechanism of oscillation are discussed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.9
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• pp.1201-1208
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• 2002

A numerical flow-field analysis is performed to investigate flow configurations in the anode, cathode and cooling channels on the bipolar plates of a proton exchange membrane fuel cell (PEMFC). Continuous open-faced flow channels are formed on the bipolar plate surface to supply hydrogen, air and water. In this analysis, two types of channel pattern are considered: serpentine and spiral. The averaged pressure distribution and velocity profiles of the hydrogen, air and water channels are calculated by two-dimensional flow-field analysis. The equations for the conservation of mass and momentum in the two-dimensional fluid flow analysis are slightly modified to include the characteristics of the PEMFC. The analysis results indicate that the serpentine flow-fields are locally unstable (because two channels are cross at right angles). The spiral flow-fields has more stable than the serpentine, due to rotational fluid-flow inertia forces. From this study, the spiral channel pattern is suggested for a channel pattern of the bipolar plate of the PEMFC to obtain better performance.

• Korean Membrane Journal
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• v.3 no.1
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• pp.59-68
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• 2001

Unlike existent field flow fractionation, new method, osmotic sink field flow fractionation is introduced and used ultrafiltration hollow fiber membranes as separation channel. This hollow fiber osmotic sink field flow fractionation is called HF-OSFFF. A theory that describes the retention, relaxation, resolution, plate number for the system, has been developed and experimentally verified by separation model of po1ystyrene latex beads. At external field, it is measured that radial flow rates change according to various concentrations of PEG solutions. Concentration of PEG solution vs. radial flow rate is a linear relation. For diameter distribution of unknown polymer sample, HF-OSFFF compared with the commercial capillary hydrodynamic flow fractionation (CHDF).

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.550-553
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• 2008

In this paper, experiments of air-breathing proton exchange membrane fuel cell (PEMFC) for mobile devices were carried out according to the 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 this experiments. The experimental results showed that the open type cathode flow field plate gave better performance for small size PEMFCs because the open type cathode plate allowed better air convection than the channel type cathode plate. 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 slit cell. With respect to the cathode surface direction, when the cathode surface is placed in the direction normal to the ground, PEMFC generated more stable power in the mass transport loss region.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.1919-1932
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• 1991

Experimental studies are conducted to investigate the Flow-Induced Vibration mechanism for cantilever plate model with the angle of attack (.alpha.=10.deg., 20.deg., 30.deg.). Research is divided into two parts. First, the flow fields around two dimensional flat plate model are investigated using LDV system. Second, the vortex shedding frequency and response spectra of cantilever plate are obtained experimentally using gap sensor and hot wire anemometer. Finite element method program was used in order to predict the flow field and pressure field around thin flat plate. And some predicted results were compared with the experimental data. The aspect ration of test model is d/t=25 (d; width, t; thickness). From the measurement of the flow field it was found that in the case of small inclined (.alpha.=10.deg., 20.deg.) relatively, the separated boundary layer at sharp leading edge developed smoothly downstream. With increasing the angle of attack of the plate, stagnation region was appeared on the back side of the plate and separated boundary layer was extended downstream. These trends are a good agreement with the computational results. It was found by analysis of response spectra of cantilever plate that the influences of vortex shedding frequency were important at the large of attack (.alpha.=30.deg.), and two peak values appear in entire test model at 24Hz, 150Hz.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.375-376
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• 2006

Turbulent structure of a boundary-layer over a flat plate coated with micro riblet film(MRF) has been investigated experimentally. The turbulent structure was visualized using a dynamic particle image velocimetry (Dynamic PIV) system. We identified the vortex structures from 2-D velocity field data by applying the complex eigenvalue definition. The velocity field images acquired by using the complex eigenvalue definition showed the whole 2-D vortex structures clearly. In addition, the spatial distributions of small-scale vortices as well as large-scale vortices were obtained with high accuracy. The difference of vortex structures between the MRF coated flat plate and the smooth flat plate was analysed in detail. With varying upstream flow speed, the characteristics of vortex structure over the MRF coated flate plate was compared with those over the smooth flat plate.

• Transactions of the Korean hydrogen and new energy society
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• v.20 no.4
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• pp.265-273
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• 2009

Proton Exchange Membrane Fuel Cell (PEMFC) has low operating temperature and high efficiency. And PEMFC consists of many components as bipolar plate, gas diffusion layer, membrane etc.. Flow-field in bipolar plate roles path for transporting reactants to membrane. Therefore a design of flow-field has an effect on PEMFC's performance. In this study, Computational Fluid Dynamics (CFD) simulations were performed for comparing mixed multiple serpentine (MMS) flow-field and multiple serpentine (MS) flow-field. And we studied an effect according to change mixing region design in MMS flow-field. Finally the applicability of results is verified by performing CFD simulation about fixed MMS flow-field which is combined good designs.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.2
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• pp.217-224
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• 1995

The effects of duct inlet conditions on fan characteristics and upper wind velocity fields were investigated for two kinds of impellers. As the duct inlet condition, the relative positions between duct inlet and fan impeller and the size of baffle plate mounted on a duct inlet were selected. The 3-dimensional velocity components in flow fields were measured by a 5-holes pitot tube. From the results of measurements, it was found that the size of baffle plate scarecely effect on upper wind flow fields and characteristics of fan. It was also confirmed that the upper wind velocity distributions can be estimated by the potential flow field with large baffle plate at duct inlet.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.4
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• pp.104-109
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• 2005

The catalyst layer design is one of the most important factors to enhance the performance of PEMFC(Proton Exchange Membrane Fuel Cell) system. The hydrophobic and ion conductive type is studied for the MEA(Membrane Electrolyte Assembly). It is found that those have some limitations for performance enhancement when they are used separately. Thus, the dual catalyst type, a mixed model, is developed for the better MEA performance. In the meantime, the design of flow field plate is subsequently carried out in order to give more enhanced output during its operation. The conductivity of flow field plate showed better performance in the case of manufactured by the more compressed process(20MPa) than by the less compressed process(10MPa). The micro-structure of the flow field plate is examined in details using SEM(Scanning Electron Microscope) to analyse the effects on the different compression processes.