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수직원통형 빙축열조내 외향용융과정시 열전달특성에 관한 연구 -작동유체의 유동방향 및 축열조 형상비에 따른 열성능 비교-
김동환,김동춘,김일경,김영기,임장순,Kim, D.H.,Kim, D.C.,Kim, I.G.,Kim, Y.K.,Yim, C.S. 대한설비공학회 1997 설비공학 논문집 Vol.9 No.2
During the day time in summer, peak of air conditing load, and electric power management system lies under overloaded condition. The reason is the enlarged peak load value of electric power caused by increased air-cooling load in summer. To prevent load concentration during day time and overloaded condition of power management system, some energy storage methods are suggested. One of these methods is ice storage system. Water has some good properties as P.C.M.(Phase Chang Material) : Its melting point is the range of required operation temperature. It has large specific latent heat and is chemically stable compared to other organic or inorganic substances. It is cheap and easy to treat. This study represents experimental results of heat transfer characteristics of P.C.M. under the outward melting process in a vertical cylinder. We experimented with twelve combinations of conditions, i.e., three different inlet temperatures($7^{\circ}C,\;4^{\circ}C\;and\;1^{\circ}C$), two working fluid directions(upward and downward), and two aspect ratios, H/R(4 and 2). At the inlet temperature of $7^{\circ}C$ and $4^{\circ}C$, there was temperature stagnation region where the temperature of P.C.M. remains constant at $4^{\circ}C$ regardless of aspect ratio and direction of working fluid. This temperature stagnation occurs as the water, at its maximum density, flows down to the lower region. The phase change interface formed bell-shaped curve as the melting process continued. With a new set of conditions(4H/R, inlet temperature $4^{\circ}C$ and $1^{\circ}C$, downward/upwerd inlet direction), the movement of phase change interface was faster when the working flued inlet direction was downward. With the same set of conditions, melting rate and total melting energy were larger when the working fluid inlet direction was downward. The results were reversed when the other sets of conditions were applied.
ThMn₁₂ 형 Sm - Fe - Ti 급냉응고리본의 미세구조 및 자기특성
김윤배(Y.B.Kim),유권상(K.S.Ryu),김동환(D.H.Kim),김창석(C.S.Kim) 한국자기학회 1991 韓國磁氣學會誌 Vol.1 No.1
It has been found that the as-quenched ribbons of Sm_xFe_(100-x-y)Ti_y(3.8 ≤ x ≤ 11.5, 3.8 ≤ y ≤ 19.2) are composed of metastable TboCu_7-type structure, α-(Fe, Ti), Fe₂Ti and an unknown phase accompanying strong diffraction line at d=2.l4 Å. The metastable TbCu_7-type phase, which was formed by rapid quenching, did not transform fully to the stable phases after annealing at 850℃ for 45 minutes except the one existed in SmFe₁₁Ti melt-spun ribbon. The SmFe₁₁Ti melt-spun ribbon, annealed at 850℃ for 45 minutes in vacuum, was found to be composed of ThMn₁₂, α-(Fe, Ti) and Fe₂Ti phases. The formation of α-(Fe, Ti) and Fe₂Ti phases in this melt-spun ribbon was due to the evaporation of Sm atoms during the high temperature annealing. The atomic ratios for the surface and the inside of SmFe₁₁Ti melt-spun ribbon annealed in vacuum were SmFe_(25.8)Ti_(2.6) and SmFe_(11.7)Ti_(1.0) respectively. It is thought to be that much of α-(Fe, Ti) and Fe₂Ti phases exist on the surface of ribbon.
60 kgf/㎟급 자동차용 변태유기소성강화강 Zn-Ni 전기도급 특성 연구
김동환(D. H. Kim),김병일(B. I. Kim),전유택(Y. T. Jeon),정연수(Y. S. Jeong) 한국표면공학회 2004 한국표면공학회지 Vol.37 No.5
High strength steels such as transformation induced plastic steel, dual phase and solid solution Hardening have been developed and continuously improved due to the intensified needs in the automotive industry. But silicon and manganese in transformation induced plastic steels were known to exhibit harmful effects on galvannealing reaction by oxide film formed during heat treatment. Therefore, in this work, the applicability of Zn-Ni electrodeposition instead of hot dip galvannealed coating to transformation induced plastic steels was evaluated and optimum electroplating condition was investigated. Based on these investigations optimized electroplating conditions were proposed and Zn-Ni electrogalvanized steel sheet was produced by EGL (electrogalvanized line). Its performance properties for automotive steel was evaluated.