• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.5
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• pp.27-35
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• 2019

Stealth technology is a technique to avoid detection from detectors such as radar and infrared seekers. In particular, detection by infrared signature is more threatening because infrared missiles detect heat from the aircraft itself. Therefore, infrared stealth technology is essential for ensuring the survival of aircraft and unmanned combat aerial vehicles (UCAV). In this study, we analyzed aerodynamic and infrared stealth performance in relation to UCAV nozzle design. Based on simulation results, a double serpentine nozzle was effective in reducing the infrared signature because it could shield high-temperature components in the engine. In addition, we observed that the infrared signature was reduced at the turning position of the duct located at the rear part of the double serpentine nozzle.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.4
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• pp.297-305
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• 1991

Recently, automotive air conditioning system manufacturers have been made a great efforts on the system compactness and high efficiency. This growing interest comes improvements in evaporator thermal performance, one of the most important factors affecting the performance of air conditioning system. In order to improve design of compact type evaporator, this study executes performs to develop a computer program for evaporator thermal performance prediction of automotive air conditioning system. The brief summaries of this study are as follows: 1) To predict the overall thermal performance of serpentine type evaporator, the new simulating method is developed. 2) The calculations are performed as functions of oil mass concentration and refrigerant two-phase distribution at inlet manifold of evaporator. 3) The validity of this simulating program is confirmed by comparing the predicted thermal performance results to experimental results of practical available evaporator. 4) Based on these results, suggestions are made to improve the thermal performance of evaporator.

• Journal of the Korean Institute of Gas
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• v.8 no.2 s.23
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• pp.15-27
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• 2004

The purpose of this paper is to improve the performance of Polymer electrolyte fuel cell(PEMFC) by studying the channel dimension of bipolar plates using commercial CFD program 'Fluent'. Simulations are done ranging from 0.5 to 3.0mm for different size in order to find the channel size which shoves the highst hydrogen consumption. The results showed that the smaller channel width, land width, channel depth, the higher hydrogen consumption in anode. When channel width is increased, the pressure drop in channel is decreased because total channel length Is decreased, and when land width is increased, the net hydrogen consumption is decreased because hydrogen is diffused under the land width. It is also found that the influence of hydrogen consumption is larger at different channel width than it at different land width. The change of hydrogen consumption with different channel depth isn't as large as it with different channel width, but channel depth has to be small as can as it does because it has influence on the volume of bipolar plates. however the hydrogen utilization among the channel sizes more than 1.0mm which can be machined in reality is the most at channel width 1.0, land width 1.0, channel depth 0.5mm and considered as optimum channel size. The fuel cell combined with 2cm${\times}$2cm diagonal or serpentine type flow field and MEA(Membrane Electrode Assembly) is tested using 100W PEMFC test station to confirm that the channel size studied in simulation. The results showed that diagonal and serpentine flow field have similarly high OCV and current density of diagonal (low field is higher($2-40mA/m^2$) than that of serpentine flow field under 0.6 voltage, but the current density of serpentine type has higher performance($5-10mA/m^2$) than that of diagonal flow field under 0.7-0.8 voltage.

• Journal of Hydrogen and New Energy
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• v.20 no.6
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• pp.492-498
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• 2009

Six sigma methode was applied for optimization of flow field design of a proton exchange membrane fuel cell (PEMFC). The optimization between number of channel and channel/rib width was suggested in this paper with six sigma method. With the help of six sigma design of experiment (DOE) the number of experiments may be reduced dramatically. The fuel cell channel design optimization with results of these experiments with a 100 $cm^2$ serpentine flow field indicates a optimization data for a given constant operating conditions.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.197-202
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• 2007

In this study, the cooling characteristics of a liquid cooler using thermoelectric module was experimentally investigated. The experiment was conducted for various inner structures of liquid cooler (4 cases), hot fluid flow rates (0.15-0.25 L/min), number of T.E module (2, 4, 6 set), and the cooling water flow rates (200-600 cc/min) for both parallel and counter flow types. Among the results, better cooling performance geometry was selected. And experiment was also carried out to examine further enhancement of cooling performance by inserting coils (pitches: 0.2, 3, 6 mm) into the hot-fluid channel. Present results showed that the short serpentine type(case2) indicated the best cooling performance. In the case of coil pitch of 3 mm, the best cooling performance was shown, more than 10% increase of the inlet and outlet temperature difference, compared with the case of the cooler without coil. Consequently, the inserted coil pitch should be properly selected to improve cooling performance.

• Journal of Mechanical Science and Technology
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• v.17 no.9
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• pp.1358-1370
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• 2003

The effects of anode, cathode, and cooling channels for a Proton Exchange Membrane Fuel Cell (PEMFC) on flow fields have been investigated numerically. Continuous open-faced fluid flow channels formed in the surface of the bipolar plates traverse the central area of the plate surface in a plurality of passes such as a serpentine manner. The pressure distributions and velocity profiles of the hydrogen, air and water channels on bipolar plates of the PEMFC are analyzed using a two-dimensional simulation. The conservation equations of mass, momentum, and energy in the three-dimensional flow solver are modified to include electro-chemical characteristics of the fuel cell. In our three-dimensional numerical simulations, the operation of electro-chemical in Membrane Electrolyte Assembly (MEA) is assumed to be steady-state, involving multi-species. Supplied gases are consumed by chemical reaction. The distributions of oxygen and hydrogen concentration with constant humidity are calculated. The concentration of hydrogen is the highest at the center region of the active area, while the concentration of oxygen is the highest at the inlet region. The flow and thermal profiles are evaluated to determine the flow patterns of gas supplied and cooling plates for an optimal fuel cell stack design.

• Journal of the Korean Electrochemical Society
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• v.11 no.4
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• pp.273-283
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• 2008

GDL(Gas Diffusion Layer) is one of the main components of PEM fuel cell. It transports reactants from the channel to the catalyst and removes reaction products from the catalyst to the channels in the flow filed plate. It is known that higher permeability of GDL can make it possible to enhance the gas transport through GDL, leading to better performance. And MEA's temperature is determined by gas and heat transport. In this paper, three dimensional numerical simulation of PEM fuel cell of parallel channel and serpentine channel by the permeability of GDL is presented to analysis heat and mass transfer characteristics using a FLUENT modified to include the electrochemical behavior. Results show that in the case of parallel channel, performance variation with change of permeability of GDL was not so much. This is thought because mass transfer is carried out by diffusion mechanism in parallel channel. Also, in the case of serpentine channel, higher GDL permeability resulted in better performance of PEM fuel cell because of convection flow though GDL. And mass transfer process is changed from convection to diffusion when the permeability becomes low.

• 한국가시화정보학회:학술대회논문집
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• 2007.11a
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• pp.63-65
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• 2007

The paper reports on a new type of combinatorial chaotic and serpentine micromixer. Such a new and novel micromixer is simple to fabricate and easy to use. The micromixer is characterized and visualized with the help of the Micro-LIF technique. The new micromixer will e further applied to lab-on-chip device. The mixing capabilities of this mixer is about 30-33%.

• Journal of Hydrogen and New Energy
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• v.15 no.4
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• pp.291-300
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• 2004

Performance of PEMFC is affected by many factors such as that of MEA, configuration of flow field, operating conditions, humidification, cooling and so on. In this study, in order to improve the performance of fuel cell, a small area fuel cell stack was made and its performance was tested under various operating conditions. Stack consists of 3 single PEM fuel cells. Channel is serpentine type and the active area of the electrode is $50cm^2$. The test results show that the peak power is 60W at $70^\circ{C}$ of stack temperature with humidification condition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.2
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• pp.85-92
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• 2009

Polymer electrolyte membrane (PEM) fuel cells are a promising technology for short-term power generation required in residential and automobile applications. Proper management of water has been found to be essential for improving the performance and durability of PEM fuel cells. This study investigated the liquid water exhaust capabilities of various flow channels having different geometries and surface properties. Three-pass serpentine flow fields were prepared by patterning channels of 1 mm or 2 mm width onto hydrophilic Acrylic plates or hydrophobic Teflon plates, and the behaviors of liquid water in those flow channels were experimentally visualized. Computational fluid dynamics (CFD) simulations were also conducted to quantitatively assess the liquid water exhaust capabilities of flow channels for PEM fuel cells. Numerical results showed that hydrophobic flow channels have better liquid water exhaust capabilities than hydrophilic flow channels. Flow channels with curved corners showed less droplet stagnation than the channels with sharp corners. It was also found that a smaller width is desirable for hydrophobic flow channels while a larger width is desirable for hydrophilic ones. The above results were explained as being due to the different droplet morphologies in hydrophobic and hydrophilic channels.