기체확산층의 기공률이 고분자 전해질 연료전지 성능에 미치는 영향에 관한 전산해석 연구

김경연(Kyoungyoun Kim),손영준(Young-Jun Sohn),김민진(Minjin Kim),이원용(Won-Yong Lee) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.12

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.

도자기 보존을 위한 복원제의 특성 연구 : - 색도·기공률·침전률·황변도를 중심으로 -

이해순 국립중앙박물관 2005 박물관보존과학 Vol.6 No.-

도자기 복원재로서 사용되는 에폭시수지 3종(Epo-Tek 301, Araldite 103, Araldite 106 )과 안료 3종(분채, 파스텔, 콘테)을 실험재료로 선택하고, 이 재료들을 다양한 비율로 혼합한 시편들에서 색도변화율과 기공률, 그리고 침전률을 관찰하였다. 또한 저점도의 맑고 투명한 특징을 가진 Epo-tek 301에 4종의 백색안료와 6종의 충진제를 혼합한 시편들을 만들고 200시간동안 자외선을 조사하여 에폭시 수지의 산화를 관찰하였다. 그 결과, 파스텔은 Epo-tek 301과 혼합하면 화학적 변화가 심하였다. 분채와 콘테는 안료 발색력이 높았지만 다른 첨가물이 혼합되면 콘테의 발색력이 낮아졌다. Epo-tek 301은 소량의 첨가물에서는 몰림 현상이 나타났고 다량의 첨가물에는 포화상태가 되면서 끓어 넘쳤으며, AW 106은 점도가 높기 때문에 소량안료에는 발색이 잘 안되었지만 첨가물이 많을 때 오히려 발색이 잘되었다. AY 103은 첨가물의 양에 상관없이 규칙적이면서도 급격하지 않은 색도 변화를 나타내었다. 기공률은 [파스텔> 분채≒ 콘테], [Epo tek 301< AY 103< AW 106]순서로, 침전률은 [분채>콘테>파스텔], [Epo-tek 301>AY 103>AW 106]순서로 나타났다. 황변도 측정에서 티타늄, 파스텔, 실리콘디옥사이드와 카올린은 황변이 잘되었고 분채, 콘테, 규조토와 수산화칼슘은 황변에 강했다. Three types of epoxy resins (Epo-Tek 301, Araldite 103, and Araldite 106) and three types of pigments(bunche, pastel, and conté), which are materials for porcelain restoration, were selected as examination materials. The tone change, porosity, and sedimental resulting from the mixtures of varying ratios of these three materials were observed. Samples were also made from the mixture of Epo-teck 301, four kinds of white pigments, and six types of fillers and subjected to ultraviolet ray penetration for 200 hours to observe the oxidation of the epoxy resins. The result showed that the chemical composition of pastel drastically changed when mixed with Epo-tek 301. Although bunche and conté displayed clear colors, those of conté were less clear when it was mixed with other substances. Adding a small amount of Epo-tek 301 tended to be driven into the corner, whereas mixing a large amount caused saturation and boiling. On the other hand, AW 106 did not display clear colors owing to its high viscosity; when mixed in large amounts, however, the clarity of colors improved. For AY 103, a similar standard of color clarity was maintained regardless of the mixture ratio. The following was ranked according to the level of porosity: [Pastel>bunche≒conté]. In terms of sedimentary, however, [bunche>conté>Pastel], [Epo-tek 301>AY 103>AW 106]. The result of measuring the degree of yellowing revealed that titanium, pastel, silicon dioxide, and kaolin tended to turn yellow, whereas bunche, conté, diatomaceous earth, and calcium hydroxide tended to resist yellowing.

다이캐스팅 보의 등가 기공결함을 고려한 강도평가

박문식(Moon Shik Park) 대한기계학회 2017 大韓機械學會論文集A Vol.41 No.5

각종 기공과 같은 결함을 허용하는 다이캐스팅 부품의 강도를 현장 수준에서 평가할 수 있는 이론적 방법을 제안한다. 결함을 갖는 부재의 탄성시험을 통해 강성도를 구하고 이를 결함이 없는 이론적 강성도와 비교함으로써 등가 기공률을 산출한다. 등가 기공률 식은 Eshelby의 함유이론으로부터 유도하였다. 산출된 등가 기공률은 Mori-Tanaka 법을 이용하여 기공결함을 포함하는 재료의 응력-변형률 선도를 그리기 위하여 사용된다. 본 연구에서는 Hollomon 변형경화 모델을 사용하였다. 이 응력-변형률 선도를 이용하면 균일분포의 기공결함을 갖는 다이캐스팅 부재의 강도를 평가할 수 있게 된다. 등가 기공률을 고려한 하나의 이론해로서 직사각형 단면의 다이캐스팅 보에 대한 삼점 굽힘의 탄소성 강도를 소성힌지의 방법으로 유도하였다. As a shop practice, a strength estimation method for die cast parts is suggested, in which various defects such as pores can be allowed. The equivalent porosity is evaluated by combining the stiffness data from a simple elastic test at the part level during the shop practice and the theoretical stiffness data, which are defect free. A porosity equation is derived from Eshelby’s inclusion theory. Then, using the Mori? Tanaka method, the porosity value is used to draw a stress?strain curve for the porous material. In this paper, the Hollomon equation is used to capture the strain hardening effect. This stress?strain curve can be used to estimate the strength of a die cast part with porous defects. An elastoplastic theoretical solution is derived for the three-point bending of a die cast beam by using the plastic hinge method as a reference solution for a part with porous defects.

기공률 경사 구조를 갖는 세포지지체 제작을 위한 와이어 네트워크 몰딩 기법

허창민(Chang Min Heo),송영국(Young Koog Song),이세환(Se Hwan Lee),김태영(Tae Young Kim),이승재(Seung-Jae Lee),조영삼(Young-Sam Cho) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11

We modified “wire-network molding” technique to fabricate a scaffold with porosity-gradient structure for potential application in bone tissue engineering. Wire-network molding technique uses a mold coupled with several wires having network. Grinded PCL (polycaprolactone) could be filled in the mold and heated to melt down for reconfiguration. After that, we should separate wires from the mold and remove the mold from PCL. Afterward, the remained PCL has an interconnected porosity with a configuration of wire-network, that is, the required design for cell-culturing scaffold. In this study, we modified the position of wire coupled with the mold to get the scaffold with porosity-gradient structure.

기공률, 상대습도, 전기전도도 변화에 따른 고분자 전해질 연료전지 성능해석

조재혁,김우태 한국기계기술학회 2013 한국기계기술학회지 Vol.15 No.1

GDL 기공률과 Cathode 입구가습조건 변화에 따른 고분자 전해질 연료전지 성능분석

소재현,이찬규,김우태 한국기계기술학회 2012 한국기계기술학회지 Vol.14 No.6

2LCD 이송 로봇재(AC4C-T6)의 피로강도에 미치는 주조 결함의 영향

이용석(Yong-Sok Lee),심희진(Hee-Jin Shim),김정규(Jung-Kyu Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

The porosity is well known to be a potent initiator of fatigue cracks in cast aluminum alloys. This article addresses the observed fatigue life of a cast AC4C-T6 aluminum alloy due to the presence of porosity. Two types of specimens containing a controlled amount of porosity were produced by the difference of melting temperature, and the amount of pore is inspected by CT-scanning. Moreover, Fatigue tests were conducted under 4 level-stress amplitude conditions, and the results of tests were stochastically assessed by 2-parameters Weibull distributions. And all of the fatigue-test specimens were observed of SEM in order to find that pore was main domain of fatigue crack in all of test specimens. Based on these results, the variation of the fatigue stregnth was evaluated by a durability analysis for LCD transfer robot. The reuslts for the fatigue life were compared with respect to the fatigue life.

주조용 17-4PH 스테인레스강의 내부 기공률과 기계적 물성과의 상관관계 분석

김종엽(Jong-Yup Kim),이준현(Joon-Hyun Lee),남승훈(Seung-Hoon Nahm) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11

Complex shaped components could be fabricated by casting process in order to improve the performance and economic efficiency for aircraft gas turbine engine. Casting can reduce the manufacturing cost, however service life could be reduced, or unpredictable failure would be occurred because of internal casting defects that may be occurred during the process. Therefore, the defect and integrity evaluation on casting products are very important techniques in order to ensure the reliability of gas turbine engines. In this study, the specimens with internal casting defects made of 17-4PH stainless steel were prepared and evaluated for characterization based on volume fraction of casting porosity. The relation between mechanical properties and defect volume fraction has been investigated. As a result of analysis, the mechanical properties of 17-4PH decreased as the defect volume fraction increased with very good linearity.

탄소소재 산업부산물을 사용한 시멘트 모르타르의 전기 ‧ 물리적 특성 연구

조정훈,김남일,이영준,서성관,추용식 한국자원리싸이클링학회 2021 資源 리싸이클링 Vol.30 No.6

본 연구에서는 탄소소재 산업부산물을 사용한 전기전도성 발열 모르타르를 제조 및 분석하였다. 이때 탄소소재 및 혼합수 함량을 제어하였으며, 전압 인가 시 전극간 거리는 0.42 m 및 0.88 m로 고정하였다. 본 연구에서 사용한 탄소소재 산업부산물은 판상형 구조의 흑연이었다. 탄소소재는 입도에 따라 미분말 및 골재 대체용으로 사용하였으며, 각각의 평균 입도는 18 μm 및 546 μm, 전기전도도는 62.3 S/m 및 32.5 S/m로 측정되었다. 동일한 모르타르 플로우 값 유지를 위해 탄소소재 혼합량 증가에 따라 혼합수 함량을 증가시켰으며, 이에따라 기공률은 상승하였다. 모르타르(6주차)의 전극거리 0.42 m에서 전압-전류값은 342 V-1.48 A(S20) 및 349 V-1.44 A(S30)이었으며, 0.88 m에서는 513 V-0.98 A(S20) 및 500 V-1.01 A(S30)으로 확인되었다. 또한 발열 특성은 산업부산물인 탄소소재 함량이 증가하고, 전극간 거리가 감소할수록 우수하였다. Electrically conductive mortar used in industrial carbon material byproducts was manufactured and analyzed in this study. The contents of the carbon material and mixed water were controlled, and the distance between electrodes was set to 0.42 m and 0.88 m. The carbon material was graphite with a layered structure. The carbon material was used as fine powder and aggregate substitutes according to particle size. The average particle sizes of each materials were 18.4μm and 546.1 μm and the electrical conductivities were 62.3 S/m and 32.5 S/m, respectively. To maintain similar mortar flow in each sample, the water content was increased with increasing carbon material, and accordingly, the porosity showed an increasing trend. When electrode distance of the mortar (week 6) was 0.42 m, the voltage-current values were 342 V-1.48 A (S20) and 349 V-1.44 A (S30). For electrode distance of 0.88 m, these values were 513 V-0.98 A (S20) and 500 V-1.01 A (S30). The exothermic properties improved with increasing carbon material content and decreasing electrode distance.

고분자 전해질 연료전지의 가스채널, 기체확산층, 촉매층 조건변화에 따른 온도특성 분석

조재혁,김우태 한국기계기술학회 2013 한국기계기술학회 학술대회논문집 Vol.2013 No.02

In this paper, a three dimensional numerical analysis tool was applied to study the PEMFC performance characteristics. The porosity and electrical conductivity of GDL and CL as well as the relative humidity of anode and cathode channel gas were selected as simulation parameters. As the porosity of GDL and CL increases, current density and temperature increase because reactant gases diffuse well. As the electrical conductivity of GDL and CL increases, current density and temperature increase due to increased electron transfer rate. As anode relative humidity increases, current density and temperature increase. Unlike anode, current density and temperature increase when cathode relative humidity increases from 0 percent to 60 percent. Then current density and temperature decrease when cathode relative humidity increases from 60 percent to 100 percent.