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자연대류형 태양열 온수기용 맨틀 축열조의 열전달 현상에 관한 연구
조현정(H.J.Cho),서태범(T.B.Seo),강용혁(Y.H.Kang) 한국태양에너지학회 2001 한국태양에너지학회 논문집 Vol.21 No.3
A horizontal mantle heat exchanger for a thermosyphon-driven SDHW (solar domestic hot water) was numerically simulated and fluid flow and heat transfer in the annulus of the mantle heat exchanger were quantitatively investigated. The Reynolds number, the location of the inlet, and the gap of the annulus were selected as the important design variables. The effects of the design variables on the heat transfer characteristics were thoroughly studied. Based on the numerical results, a correlation for predicting the heat transfer coefficient was suggested as the conclusion of this study.
Fe계 나노결정 분말코아의 연자성특성에 미치는 입도제어 및 바인더 첨가의 영향
조은경,조현정,권훈태,조은민,류혁현,손근용,박원욱,Cho E.K.,Cho H.J.,Kwon H.T.,Cho E.M.,Ryu H.H.,Sohn K.Y.,Park W.W. 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.4
The amorphous $Fe_{73}Si_{16}B_7Nb_3Cu_1$ alloy strip was pulverized to get a flake-shaped powder after annealing at $425^{\circ}C$ for 90 min and subsequently ground to obtain finer flake-shaped powder by using a ball mill. The powder was mixed with polyimide-based binder of $0.5{\sim}3wt%$, and then the mixture was cold compacted to make a toroidal powder core. After crystallization treatment for 1 hour at $380{\sim}600^{\circ}C$, the powder was transformed from amorphous to nanocrystalline with the grain size of $10{\sim}15nm$. Soft magnetic characteristics of the powder core was optimized at $550{\sim}600^{\circ}C$ with the insulating binder of 3wt%. As a result, the powder core showed the outstanding magnetic properties in terms of core loss and permeability, which were originated from the optimization of the grain size and distribution of the insulating binder.
Al<sub>2</sub>O<sub>3</sub> 첨가에 따른 Fe계 나노결정립 P/M시트의 전자파 흡수특성
우수정,조은경,조현정,이재준,손근용,박원욱,Woo, S.J.,Cho, E.K.,Cho, H.J.,Lee, J.J.,Sohn, K.Y.,Park, W.W. 한국분말야금학회 2007 한국분말재료학회지 (KPMI) Vol.14 No.4
Electromagnetic wave absorbing materials have been developed to reduce electromagnetic interference (EMI) for electronic devices in recent years. In this study, Fe-Si-B-Nb-Cu base amorphous strip was pulverized using a jet mill and an attritor and heat-treated to get flake-shaped nanocrystalline powders, and then the powders were mixed, cast and dried with dielectric $Al_{2}O_{3}$ powders and binders. As a result, the addition of $Al_{2}O_{3}$ powders improved the absorbing properties of the sheets noticeably compared with those of the sheets without dielectric materials. The sheet mixed with 2 wt% $Al_{2}O_{3}$ powder showed the best electromagnetic wave absorption, which was caused by the increase of the permittivity and the electric resistance due to the dielectric materials finely dispersed on the Fe-based powder.