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Effect of flexural wave on flooding in PEM fuel cell channel
변재기 고려대학교 2010 虎院論集 Vol.18 No.-
Energy is an essential driving force for modern society. In particular, electricity has become the standard source of power for almost every aspect of life. Electric power runs lights, televisions, cell phones, laptops, etc. However, it has become apparent that the current methods of producing this most valuable commodity, combustion of fossil fuels, are of limited supply and has become detrimental for the earth’s environment. It is also self evident, given the fact that these resources are non-renewable, that these sources of energy will eventually run out. One of the most promising alternatives to the burning of fossil fuel in the production of electric power is the proton exchange membrane (PEM) fuel cell. The PEM fuel cell is environmentally friendly and achieve much higher efficiencies than a combustion engine. Water management is an important issue of PEM fuel cell operation. Water is the product of the electrochemical reactions inside fuel cell. If liquid water accumulation becomes excessive in a fuel cell, water columns will clog the gas flow channel. This condition is referred to as flooding. A number of researchers have examined the water removal methods in order to improve the performance. In this paper, a new water removal method that investigates the use of vibro-acoutic methods is presented. Piezo-actuators are devices to generate the flexural wave is attached at end of a cathode bipolar plate. Flexural wave is used to impart energy to resting droplets and thus cause movement of the droplets in the direction of the traveling wave. In order to prove how much flexural wave affects cell performance of PEM fuel cell, performance experiments are carried out at various reactant RH, stoichiometric flow rates and inlet temperature of reactant.
지역난방 공동주택의 열부하 예측에 의한 열공급제어 알고리즘에 관한 해석적 연구
변재기 고려대학교 2012 虎院論集 Vol.20 No.-
In this study, we developed a heat supply control algorithm that minimizes the heat loss in heat distribution pipelines used for supplying heat energy to shared households. Controlling the temperature and flow rate of the hot water supplied to a boiler room heat exchanger for shared households enables us to develop a heat supply control technique that meets the heating load required by each household in a shared community building in accordance with changes in the outdoor air temperature and that minimizes the heat loss occurring in the heat distribution pipeline. A one-year study in 2008 on a 1,473 households D-community building in Hawseong, Gyeonggi, South Korea, compared the heat capacity used by each household as well as the heat capacity supplied to the boiler room of the community building to calculate the amount of heat loss in the heat distribution pipeline. The results confirmed that 27.6% of the heat supplied was lost in the piping. In the present study, controlling the variable hot water temperature and flow rate of the heat supply lowered the heat loss rate in the piping to 8.59%
변재기 해군대학 1983 海洋戰略 Vol.- No.26
우리군이 장차전에 있어서 국토 통일의 목표를 달성하기 위하여 필연적으로 수행해야 할 반격전은 우리군의 지상과제이다. 따라서, 장차 반격전에 대비하여 한반도의 지세적 여건과 북괴의 철벽전선 요새지대 편성을 고려한 기동축선을 선정함에 있어서 "리델하트"의 "간접 접근 전략"을 대입, 한국적 최소 예상선, 최소 저항선, 최소 저항선을 도출하여, 효과적인 반격전 수행방안을 제시하는데 연구 목적을 두었다. 본 목적을 달성하기 위해서 연구한 주요 내용은 다음과 같다. 1. 북괴의 전지역 요새화 실태파악 및 분석 2. 요새지 공격에 따른 전례분석 및 공자의 성공요인 3. "리델하트"의 "간접 접근 전략"의 요체 4. 간접 접근의 전례소개 및 분석 5. 한국적 간접 접근 작전선 도출 6. 반격전을 위한 발전방향 제시이상과 같은 주요 내용을 연주한 결과와 기대되는 효과는 첫째 :반격전 수행시 직접적 돌파식 기동보다는 한국적 최소 예상선, 최소 저항선인 서해도서 (백령도)를 이용한 간접 접근의 선행(先行)만이 주전선 돌파의 효과를 증대시킬 수 있을 뿐만 아니라 둘째 :서해도서 (백령도)를 이용한 간접 접근 자전선으로 반격전을 수행함에 있어서 백령도로 하여금 북괴의 중추 지역을 위협하며, "세계 최대의 떠있는 전함"역할을 할 수 있는 전진기지 내지는 공세적 발전 기지로서의 군사력 건설과 이에 대한 계칙의 연구발전에 박차를 가해야 하겠다. 결론적으로 "한국판 알덴느 고원"발견을 위해 논자 나름대로 연구한 본 주제가 "공세적 방어 전략"수립과 반격의 문을 여는데 한줌의 밑거름이 되어 다소나마 기여하길 바라며, 우리군은 정적인 고정관념에서 탈피하여 동적인 사고 의식을 가지고 거시적이며, 과감한 반격 계획을 계속적으로 연구 발전시켜야 말 것이다.
상변화 물질을 적용한 급속 축냉기술에 관한 수치해석 연구
변재기,권영철,박상배,손석권,곽동걸,신종근 한국기계기술학회 2017 한국기계기술학회지 Vol.19 No.6
Recently, uncertainty of demand and supply for energy has expanded as energy market change rapidly. Rapid accumulation storing of cold heat is a method for decreasing the gap between demand and supply of time, quantity and quality of heat energy. It is stored rapidly when electric power is on. And cold heat energy in heat is phase change material (PCM) heat storage is used when electric power is off. Porous media for cold heat is PCM. The present study has been conducted for improving performance of cold heat storage in refrigerator using characteristics on laten heat and phase change of PCM. This study provide basic data to improve performance of cold heat using characteristic of PCM. Also, this study predicts and measures specific points in PCM heat storage during process of phase change.