• 대한기계학회논문집B
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• 제29권6호
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• pp.722-729
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• 2005

Design analysis of the solid oxide fuel cell and gas turbine combined power system is performed considering different methods for preheating cell inlet air. The purpose of air preheating is to keep the temperature difference between cell inlet and outlet within a practical design range thus to reduce thermal stress inside the cell. Three different methods considered are (1) adopting a burner in front of the cell, (2) adopting a preheater (heat transfer from the main combustor) in front of the cell and (3) using recirculation of the cathode exit gas. For each configuration, analyses are carried out for two values of allowable maximum cell temperature difference. Performance characteristics of all cases are compared and design limitations are discussed. Relaxation of the cell temperature difference (larger difference) is proved to ensure higher efficiency. Recirculation of the cathode exit gas exhibits better performance than other methods and this advantage becomes more prominent as the constraint of the cell temperature difference becomes more severe (smaller temperature difference).

• 한국수소및신에너지학회논문집
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• 제18권1호
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• pp.60-66
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• 2007

In terms of the vehicle efficiency, a fuel cell hybrid system has advantages compared to a conventional internal combustion engine and a fuel cell alone-powered system. The efficiency of the fuel cell hybrid vehicle mainly depends on the maximum power of the fuel cell and therefore it is important to decide the design value of the fuel cell maximum power. In this paper, to estimate the performance of the fuel cell hybrid mini-bus in the design phase the simulator based on the models for the fuel cell stack, the electric battery, the fuel cell balance of plant, the controller, and the vehicle itself is proposed. Additionally, the hybrid mini-bus efficiencies with several different fuel cell powers are simulated for a city driving schedule and are compared on another. Consequently, the proposed simulation scheme is useful to determine the best design value of the fuel cell hybrid vehicles.

• 한국재료학회지
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• 제14권5호
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• pp.368-373
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• 2004

To improve the conventional cathode-supported tubular solid oxide fuel cell (SOFC) from the viewpoint of low cell power density, expensive fabrication process and high operation temperature, the anode-supported tubular solid oxide fuel cell was investigated. The anode tube of Ni-8mol% $Y_2$O$_3$-stabilized $ZrO_2$ (8YSZ) was manufactured by extrusion process, and, the electrolyte of 8YSZ and the multi-layered cathode of $LaSrMnO_3$(LSM)ILSM-YSZ composite/$LaSrCoFeO_3$ were coated on the surface of the anode tube by slurry dip coating process, subsequently. Their cell performances were examined under gases of humidified hydrogen with 3% water and air. In the thermal cycle condition of heating and cooling rates with $3.33^{\circ}C$/min, the anode-supported tubular cell showed an excellent resistance as compared with the electrolyte-supported planar cell. The optimum hydrogen flow rate was evaluated and the air preheating increased the cell performance due to the increased gas temperature inside the cell. In long-term stability test, the single cell indicated a stable performance of 300 mA/$\textrm{cm}^2$ at 0.85 V for 255 hr.

• 대한산업공학회지
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• 제29권2호
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• pp.135-144
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• 2003

Traffic performance in a microcellular system is much more affected by cell dwell time and channel holding time in each cell. Cell dwell time of a call is characterized by its mobility pattern, i.e., stochastic changes of moving speed and direction. Cell dwell time provides important information for other analyses on traffic performance such as channel holding time, handover rate, and the average number of handovers per call. In the next generation mobile communication system, the cell size is expected to be much smaller than that of current one to accommodate the increase of user demand and to achieve high bandwidth utilization. As the cell size gets small, traffic performance is much more affected by variable mobility of users, especially by that of pedestrians. In previous work, analytical models are based on simple probability models. They provide sufficient accuracy in a simple second-generation cellular system. However, the role of them is becoming invalid in a picocellular environment where there are rapid change of network traffic conditions and highly random mobility of pedestrians. Unlike in previous work, we propose an improved probability model evolved from so-called Random walk model in order to mathematically formulate variable mobility of pedestrians and analyze the traffic performance. With our model, we can figure out variable characteristics of pedestrian mobility with stochastic correlation. The above-mentioned traffic performance measures are analyzed using our model.

• 대한기계학회논문집B
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• 제33권12호
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• pp.1022-1030
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• 2009

Numerical analysis was carried out to investigate the effect of GDL (Gas diffusion layer) porosity on the performance of PEMFC (proton exchange membrane fuel cell). A complete three-dimensional model was chosen for single straight channel geometry including cooling channel. Main emphasis is placed on the heat and mass transfer through the GDL with different porosity. The present numerical results show that at high current densities, the cell voltage is influenced by the GDL porosity while the cell performance is nearly the same at low current densities. At high current densities, low value of GDL porosity results in decrease of the fuel cell performance since the diffusion of reactant gas through GDL becomes slow with decreasing porosity. On the other hand, for high GDL porosity, the effective thermal conductivity becomes low and the heat generated in the cell is not removed rapidly. This causes the temperature of fuel cell to increase and gives rise to dehydration of the membrane, and ultimately increase of the ohmic loss.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권5호
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• pp.2124-2143
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• 2016

In Long Term Evolution-Advanced (LTE-A) systems, Inter-cell Interference (ICI) is a prominent limiting factor that affects the performance of the systems, especially at the cell edges. Based on the literature, Fractional Frequency Reuse (FFR) methods are known as efficient interference management techniques. In this report, the proposed Dynamic Fractional Frequency Reuse (DFFR) technique improved the capacity and cell edge coverage performance by 70% compared to the Fractional Frequency Reuse (FFR) technique. In this study, an improved power allocation method was adopted into the DFFR technique to reach the goal of not only reducing the ICI mitigation at the cell edges, but also improving the overall capacity of the LTE-A systems. Hence, an improved water-filling algorithm was proposed, and its performance was compared with that of other methods that were considered. Through the simulation results and comparisons with other frequency reuse techniques, it was shown that the proposed method significantly improved the performance of the cell edge throughput by 42%, the capacity by 75%, and the coverage by 80%. Based on the analysis and numerical expressions, it was concluded that the proposed DFFR method provides significant performance improvements, especially for cell edge users.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2009년도 추계학술발표대회 논문집
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• pp.199-204
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• 2009

This study analyzed the central heating system and the cogeneration system among the methods of supplying energy which have application to the Hydrogen Fuel Cell system and apartment complexes for performance evaluations. Therefore, a feasibility study on the first application of this system in an apartment complexes was considered to evaluate the energy performance by the amount of fuel consumed by the system using Hydrogen Fuel Cell energy and environmental performance by the amount of greenhouse gas emissions. As a result, the Hydrogen Fuel Cell system consumes 83% of fuel while the cogeneration system consumes 81% of fuel comparison to conventional central heating system. The Hydrogen Fuel Cell and the cogeneration system produce 73%t and 70% of greenhouse gas emissions in comparison to conventional central heating system.

• 산업공학
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• 제17권spc호
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• pp.152-159
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• 2004

The Purpose of this paper is to propose performance evaluation schemes of flexible manufacturing cell using a generalized stochastic Petri net. In the competitive and global manufacturing environment, to evaluate the feasibility and manufacturability of a product in the product design stage is highly required. Through this process, all the possible problems which may occur in the manufacturing stage can be fixed in early stage. The scheme of generalized stochastic Petri net utilizing both immediate and exponential distributed transitions are applied to model a manufacturing cell with flexible machines, material handler, transporter and buffers. Performance analyses are performed based on behavioral, structural and quantitative properties. A flexible manufacturing cell is evaluated using a Petri net simulator.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 C
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• pp.1409-1411
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• 1996

Direct Methanol Fuel Cell(DMFC) using Pt-Ru electrocatlayst and Nafion menbrane can provide high performance if operating conditions are well designed. In this study, operating temperature, pressure, and fuel flow rate were changed to obtain optimum operating conditions of DHFC single cell. Performance of DMFC were increased by the increase of operating temperature. The concentration of fuel methanol was 2.0M $CH_{3}OH$ and pressure difference of cathode and anode was 2 atm were showed maximum performance of DMFC single cell with showing the current density of 160 $mA/cm^2$ at 0.2V cell voltage.

• 전기화학회지
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• 제13권4호
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• pp.283-289
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• 2010

2차원 전산 해석 모델을 사용하여 고온 고분자 전해질 연료전지의 전산해석을 수행하였다. 해석 모델은 기존의 실험데이터와의 비교를 통해 검증하였으며, 다양한 작동 조건이 연료전지의 성능에 미치는 영향을 파악하기 위해 일련의 전산해석을 수행하였다. 본 전산해석의 결과를 통해 교환전류밀도, 이온전도도, 공급유량 및 작동압력이 증가할수록 연료전지의 성능이 향상됨을 확인하였다. 또한, 기체 확산층의 기공율이 높을수록 기체의 확산이 향상되어 연료전지의 성능이 향상되었으며, 양극 기체 확산층의 기공율에 의한 효과가 음극에 비해 더 두드러지게 나타났다.