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Soft Magnetic Properties of Conetic Co-Sputtered with Aluminum
Jongkoo Lim,손장엽,홍종일 대한금속·재료학회 2014 METALS AND MATERIALS International Vol.20 No.3
Conetic (Ni77Fe14Cu5Mo4) and conetic co-sputtered with aluminum thin films are prepared and their softmagnetic properties are examined in order to investigate their eligibility for application in the free layer ofspin valve-based magnetic sensors. As the aluminum concentration increases, the coercivity and anisotropyfield of the film is reduced by more than 60%, which indicates that the soft magnetism is significantlyimproved. The thermal treatment further enhances the soft magnetic properties. This improvement can be attributedto the enhanced random anisotropy that results from the reduction in the grain size, which is caused by theincorporation of the aluminum into the conetic. These encouraging results imply that the conetic co-sputteredwith Al is sufficiently magnetically soft to be applied in spin valve-based sensors.
Optimization of Vent Logic for Cascade Type Fuel Cell Module
임종구(Lim, Jongkoo),박종철(Park, Jongcheol),권기욱(Kwon, Kiwook),신현길(Shin, Hyun Khil) 한국신재생에너지학회 2011 한국신재생에너지학회 학술대회논문집 Vol.2011 No.11
Many type of fuel cell stacks have been developed to improve the efficiency of reactants usage. The cascade type fuel cell stack using dead end operation is able to attain above 99% usage of hydrogen and oxygen. It is sectionalized to several parts and the residual reactants which are used previous parts would be supplied again to next parts which have less number of cells in dead end operation stack. The oversupply of reactants which is usually 120%~150% of the theoretical amount to generate current for preventing the flooding effect could be provided to each part except the last one. The final section which is called monitoring cells is supposed to be supplied insufficient the fuel or oxidant that would have some accumulated inert gas from former parts. It makes some voltage drop in the part and the fresh reactants must be supplied to the part for recovering it by venting the residual gas. So the usage of fuel and oxidant is depend on the time and frequency of opening valves for venting of residual gas and it is important to optimize the vent logic for achieving higher usage of hydrogen and oxygen. In this research, many experiments are performed to find optimal condition by evaluating the effect of time and frequency under several power conditions using over 100kW class fuel cell module. And the characteristics of the monitoring cells are studied to know the proper cell voltage which decide the condition of opening the vent valve for stable performance of the cascade type fuel cell module.
임종구(Lim, Jongkoo),박종철(Park, Jongcheol),고백균(Kho, Back Kyun),권기욱(Kwon, Ki Wook),신현길(Shin, Hyunkhil),허태욱(Hur, Taeuk),조성백(Cho, Sungbaek) 한국신재생에너지학회 2010 한국신재생에너지학회 학술대회논문집 Vol.2010 No.11
캐스케이드형 연료전지 시스템에 있어서 각 스택의 단에서 전기화학반응에 의해 생성된 물을 분리하여 적절하게 배출시켜주는 것은 스택의 성능 및 내구성 향상을 위해 매우 중요하다. 이를 위해 연료전지 스택 각 단의 상이한 조건에 맞는 기액분리기의 설계가 필요하다. 유량에 따른 기액분리기의 부피와 원활한 연료 가스와 생성수의 분리를 위한 내부구조 및 입구 속도 등의 변수들에 따라 기액분리기의 성능 뿐만 아니라 연료전지 시스템 전체의 성능에 영향을 준다. 그러나 기액분리기의 폐쇄적 구조 때문에 실험을 통해 내부의 거동 및 현상을 파악할 수 없어 앞서 언급한 변수들의 효과를 확인할 수 없는 문제점이 있다. 이에 CFD(Computational Fluid Dynamics, 전산유체역학)를 활용하여 각 조건에 따른 기액분리기 내부의 현상을 파악하고 이를 통해 기액분리기 설계를 최적화하였다.
Hα filter based accuracy improvement of heterodyne laser interferometer
Lee, Kyunghyun,Lim, Minwoo,Park, Jongkoo,You, Kwan-Ho IET 2014 Electronics letters Vol.50 No.4
<P>The advantage of a laser interferometer is in the high resolution it provides, especially in extremely sensitive nanometrology. The laser interferometer plays a crucial role in ultra-precision measurement areas. However, the measurement accuracy is limited by a nonlinearity error. The nonlinearity error of the heterodyne laser interferometer needs to be compensated for. An <I>H</I><SUB>∞</SUB> filter is applied to compensate for the nonlinearity error caused by the elliptic polarisation, two non-orthogonal beams and an imperfect optical alignment. The proposed compensation method using an <I>H</I><SUB>∞</SUB> filter can reduce the nonlinearity error. The experimental results show an improved accuracy and reliability.</P>
CFD-based Flow Simulation Study of Fuel Cell Protective Gas
권기욱(Kwon, Kiwook),임종구(Lim, Jongkoo),박종철(Park, Jongcheol),신현길(Shin, Hyun Khil) 한국신재생에너지학회 2011 한국신재생에너지학회 학술대회논문집 Vol.2011 No.11
To improve the safety, the fuel cell operate inside a pressurized enclosure which contains inert gas so called protective gas. The protective gas not only prevents the mixture of hydrogen and oxygen, but also removes the water in the vessel with the condenser. This study presents the details of the flow optimization in order to reduce the humidity in the fuel cell housing. The protective gas flow in the fuel cell container is studied by Computational Fluid Dynamics(CFD) simulations. This study focuses on optimizing the geometry of an protective gas circulation system in fuel cell module to reduce the humidity in the vessel. CFD analysis was carried out for an existing model to understand the flow behavior through the fuel cell system. Based on existing model CFD results, geometrical changes like inlet placement, optimization of outlet size, modification of fuel cell module system are carried out, to improve the flow characteristics. The CFD analysis of the optimized model is again carried out and the results show good improvement in protective gas flow behavior.
Gas diffusion layer/flow-field unified membrane-electrode assembly in fuel cell using graphene foam
Park, Ji Eun,Lim, Jongkoo,Lim, Myung Su,Kim, Sungjun,Kim, Ok-Hee,Lee, Dong Woog,Lee, Ji Hyun,Cho, Yong-Hun,Sung, Yung-Eun Pergamon Press 2019 Electrochimica Acta Vol. No.
<P><B>Abstract</B></P> <P>The integration of a gas diffusion layer with a flow-field is essential for enhancing the polymer electrolyte membrane fuel cell performance. This is achieved by exploiting the ability of a gas diffusion layer-flow-field combination to decrease the size of the reactant pathway and the thickness of the membrane-electrode assembly, thereby reducing electrical and mass transport resistance. This study proposes a unified membrane-electrode assembly that incorporates graphene foam that functions as both a flow-field and a gas diffusion layer. The unified membrane-electrode assembly exhibits higher performance than conventional membrane-electrode assembly on overall current densities region, which is attributed to the increased the pressure drop. Furthermore, its estimated volume power density can be increased because of the 82% decrease in its thickness. Also, the simulation results show that this design enhances the exchange current density due to pressure drop in the graphene foam.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Unified MEA using graphene-foam that functions as flow-field and GDL is prepared. </LI> <LI> Unified MEA enhances cell performance and volume power density by 8.2 times. </LI> <LI> Simulation results exhibits that unified MEA improved exchange current density. </LI> <LI> This enhancement is attributed to the increased internal pressure. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
문일,Valeri A. Danilov,Jongkoo Lim,Kyoung Hwan Choi 한국화학공학회 2006 Korean Journal of Chemical Engineering Vol.23 No.5
study presents a 3D CFD model for modeling gas evolution in anode channels of a DMFC underhigh stoichiometric feed. The improved two-phase model includes a new submodel for mass source and interphasetransfer in anode channels. Case studies of typical flow field designs such as parallel and serpentine flow fields illustrateapplications of the CFD model. Simulation results reveal that gas management of typical flow fields is ineffective undercertain operating conditions. The CFD-based simulations are used to visualize and to analyze the gas evolution andment in DMFC.