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비압축성 나비어-스톡스 방정식의 완전 내재적 분리 방법
김경연,백승진,성형진,Kim, Kyoung-Youn,Baek, Seung-Jin,Sung, Hyung-Jin 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.10
A new efficient numerical method for computing three-dimensional, unsteady, incompressible flows is presented. To eliminate the restriction of CFL condition, a fully-implicit time advancement in which the Crank-Nicolson method is used for both the diffusion and convection terms, is adopted. Based on an approximate block LU decomposition method, the velocity -pressure decoupling is achieved. The additional decoupling of the intermediate velocity components in the convection term is made for the fully -implicit time advancement scheme. Since the iterative procedures for the momentum equations are not required, the velocity components decouplings bring forth the reduction of computational cost. The second-order accuracy in time of the present numerical algorithm is ascertained by computing decaying vortices. The present decoupling method is applied to minimal channel flow unit with DNS (Direct Numerical Simulation).
작동 조건에 따른 고온 고분자 전해질 연료전지의 성능 변화에 대한 전산해석 연구
김경연,손영준,김민진,양태현,Kim, Kyoung-Youn,Sohn, Young-Jun,Kim, Min-Jin,Yang, Tae-Hyun 한국전기화학회 2010 한국전기화학회지 Vol.13 No.4
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. A two-dimensional isothermal model has been employed for numerical simulations of a high temperature hydrogen fuel cell with proton exchange membrane. The model is validated with existing experimental data and used for examination on the effects of various operating conditions on the fuel cell performance. The present numerical results show that the cell performance increases with increasing exchange current density, ion conductivity of the membrane, inlet gas flow rate as well as operating pressure. Also, higher porosity of gas diffusion layer (GDL) results in higher cell performance due to enhancement of the diffusion through the GDL, where the cathode GDL porosity more influences on the performance as compared with the anode one.
김중년,김경연,성형진,Kim, Joong-Nyon,Kim, Kyoung-Youn,Sung, Hyung-Jin 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.9
A direct numerical simulation of a spatially-developing turbulent boundary layer is performed to examine the characteristics of wall pressure fluctuations after the sudden application of wall blowing or suction. The uniform blowing or suction is given by the wall-normal velocity through a spanwise slot at the wall. The response of wall pressure fluctuations to uniform blowing or suction is analyzed by computing the turbulence statistics and frequency spectra. It is found that wall pressure fluctuations are more affected by blowing than by suction. The large elongated structure of wall pressure fluctuations is observed near the maximum location of $(p_w)_{rms}$ for blowing. The convection velocities for blowing increase with increasing the streamwise location after the slot. For both blowing and suction, the small scale of wall pressure fluctuations reacts in a short downstream distance to the spanwise slot, whereas the large scale recovers slowly in a farther downstream.
Thermal managing effects by cooling channels on performance of a PEMFC
손영준(Sohn, Young-Jun),김민진(Kim, Min-Jin),박구곤(Park, Gu-Gon),김경연(Kim, Kyoung-Youn),이원용(Lee, Won-Yong) 한국신재생에너지학회 2009 한국신재생에너지학회 학술대회논문집 Vol.2009 No.06
Relative humidity, membrane conductivity and water activity are critical parameters of polymer electrolyte membrane fuel cells (PEMFC) for high performance and reliability. These parameters are closely related with temperature. Moreover, the ideal values of these parameters are not always identical along the channels. Therefore, the cooling channel design and its operating condition should be well optimized along the all location of the channels. In the present study, we have performed a numerical investigation on the effects of cooling channels on performance of a PEMFC. Three-dimensional Navier-Stokes equations are solved with the energy equation including heat generated by the electrochemical reactions in the fuel cell. The present numerical model includes the gas diffusion layers (GDL) and serpentine channels for both anode and cathode gas flows, as well as cooling channels. To accurately predict the water transport across the membrane, the distribution of water content in the membrane is calculated by solving a nonlinear differential equation with a nonlinear coefficient, i.e., the water diffusivity which is a function of water content as well as temperature. Main emphasis is placed on the heat transfer between the solid bipolar plate and coolant flow. The present results show that local current density is affected by cooling channels due to the change of the oxygen concentration and the membrane conductivity as well as the water content. It is also found that the relative humidity is influenced by the generated water and the gas temperature and thus it affects the distribution of fuel concentration and the conductivity of the membrane, ultimately fuel cell performance. Unit-cell experiments are also carried out to validate the numerical models. The performance curves between the models and experiments show reasonable results.
손영준(Sohn, Young-Jun),임성대(Yim, Sung-Dae),박구곤(Park, Gu-Gon),김경연(Kim, Kyoung-Youn),김민진(Kim, Min-Jin),이원용(Lee, Won-Yong) 한국신재생에너지학회 2008 한국신재생에너지학회 학술대회논문집 Vol.2008 No.10
Air-breathing polymer electrolyte membrane fuel cells (PEMFC) are highly promising particularly for small-power applications up to tens watts class. A distinctive feature of the air-breathing PEMFC is its simple system configuration in which axial fans operate for dual purposes, supplying both oxidant and coolant in a single manner. In the present study, a nominal 80W air-breathing PEMFC system is developed and investigated to determine the optimal operating strategy through parametric studies (i.e., reactant humidity, and fanblowing flow rate). The cell voltage distributions are examined as a function of time to evaluate the system performance under various operating conditions.
수확시기 및 저장온도에 따른 돼지감자 괴경의 가용성당 조성변화
강수일(Su Il Kang),한종인(Jong In Han),김경연(Kyoung Youn Kim),오선진(Sun Jin Oh),김수일(Su Il Kim) 한국응용생명화학회 1993 Applied Biological Chemistry (Appl Biol Chem) Vol.36 No.4
The composition of soluble neutral carbohydrates in Jerusalem artichoke tubers was measured and compared according to harvest dates and storage temperatures using HPLC. The breakdown of inulin (≥GF8) into sucrose and fructo-oligosaccharides (GF2-GF7) was highest on November just after cold-shock. The composition of sucrose and fructo-oligosaccharides on March was much higher than that on September of previous year. Inulin (≥GFB) proportion decreased from 66.4% to 33.1% but the proportion of fructo-oligosaccharides (GF2-GF7) and sucrose increased from 25% to 61% and from 3.4% to 13.6%. respectively. The storage at a low temperature (4℃) for 34 days increased the composition as well. However, the amount of fructo-oligosaccharides was decreased when the tubers harvested in March were stored at high temperature (25∼40℃). For the maximum yield of fructo-oligosaccharides in jerusalem artichoke, it is concluded that the tubers be harvested in March and/or stored at the low temperature.
High performance liquid chromatography 에 의한 fructo 및 inulo 올리고당의 정량
강수일(Su Il Kang),한종인(Jong In Han),김경연(Kyoung Youn Kim),오선진(Sun Jin Oh),김수일(Su Il Kim) 한국응용생명화학회 1993 Applied Biological Chemistry (Appl Biol Chem) Vol.36 No.4
High performance liquid chromatographic method using a TSK-gel amide 80 column and isocratic elution with acetonitrile-water (63 : 35 ;v/v) mixture was used for the separation and the quantitation of fructo (GF2-GF7)- and inulo-oligosaccharides (F2-F4). Retention time of each standard carbohydrate was highly reproducible. Standardization curves obtained by plotting the peak areas against the amounts of each carbohydrate showed very high coefficient of determination(≥0.9884) and similar slopes, and a wide range of y-intercepts. Our results suggest the use of each pure oligosaccharide for its own standardization curve instead of using a certain carbohydrate as an internal standard.