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이성국(Chengguo Li),김두현(Doohyun Kim),권영환(Yunghwan Kwon),조용현(Yonghyeon Cho),이재근(Jaekeun Lee) 대한설비공학회 2010 대한설비공학회 학술발표대회논문집 Vol.2010 No.6
In recent years many experimentalists have reported an anomalously enhanced thermal conductivity in liquid suspensions of nanoparticles, comprehansive experimental dataset is obtained for thermal conductivity of Al₂O₃, SiO₂, ZnO nanofluids with various volume fraction ranging from 1.0 to 5.0%. Transient hot wire (THW) equipment are developed for the measurements show that, we found that the thermal conductivity increasing with increase viscosity of nanofluids. Therefore, theoretical models are developed to predict thermal conductivity with well established Aggregation models. The result show that aggregation mechanism on the remarkable enhancement of the thermal conductivity of nanofluids.
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다공성 니켈 연료 전극 내부에서 탄화수소의 열분해를 통한 직접 탄소 연료 전지의 연료공급
이학규(Hakgyu Yi),이성국(Chengguo Li),타헤레 잘랄라바디(Tahereh Jalalabadi),이동근(Donggeun Lee) 대한기계학회 2015 大韓機械學會論文集B Vol.39 No.6
본 연구에서는 직접 탄소 연료전지(DCFC)에서 세 종류의 탄화수소(메탄, 에탄, 프로판) 열분해를 이용하여 다공성 니켈 연료극에 탄소를 직접 생성시켜 연료극과 연료간의 물리적 접촉을 향상시켰다. 전자현미경으로 각각의 탄화수소로부터 생성된 탄소 입자들이 탄소 수가 증가함에 따라 각각 탄소구형체(CS), 탄소나노튜브(CNT), 탄소나노섬유(CNF)임을 확인하였다. 그리고 탄소 샘플들의 결정성을 알아보기 위해 라만 산란 분석을 수행하였고, 탄화수소의 탄소 수가 증가할수록 생성된 탄소의 결정성이 떨어지고 더 유연하였다. 동일한 질량의 탄소로 채워진 연료극의 DCFC 성능을 700 ℃ 에서 측정하였고, CNT와 CNF 가 CS 보다 반응성이 좋아 각각 148%, 210% 높은 전력밀도를 보였다. 이는 결정성이 떨어지는 CNT 와 CNF 의 낮은 전하전달저항에 의한 것으로 사료된다. This study offers a novel method for improving the physical contact between the anode and fuel in a direct carbon fuel cell (DCFC): a direct generation of carbon in a porous Ni anode through the thermal decomposition of gaseous hydrocarbons. Three kinds of alkane hydrocarbons with different carbon numbers (CH4, C2H6, and C3H8) are tested. From electron microscope observations of the carbon particles generated from each hydrocarbon, we confirm that more carbon spheres (CS), carbon nanotubes (CNT), and carbon nanofibers (CNF) were identified with increasing carbon number. Raman scattering results revealed that the carbon samples became less crystalline and more flexible with increasing carbon number. DCFC performance was measured at 700 °C with the anode fueled by the same mass of each carbon sample. One-dimensional carbon fuels of CNT and CNF more actively produced and had power densities 148 and 210 times higher than that of the CS, respectively. This difference is partly attributed to the findings that the less-crystalline CNT and CNF have much lower charge transfer resistances than the CS.
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나노유체 적용에 따른 판형 열교환기의 대류열전달 및 압력강하 특성에 관한 연구
조용현(Yonghyeon Cho),권영환(Younghwan Kwon),이성국(Chengguo Li),이재근(Jaekeun Lee),김두현(Doohyun Kim) 대한설비공학회 2010 대한설비공학회 학술발표대회논문집 Vol.2010 No.6
The purpose of this study is to investigate heat transfer characteristics and pressure drop in applying Al₂O₃ nanofluids to plate heat exchanger. Experiments were performed under Reynolds number from 100 to 500 and respective volumetric flow rate. The working temperature of heat exchanger was in the range of 20℃ to 40℃. The measured thermophysical properties, such as thermal conductivity and kinematic viscosity, were applied to calculating convective heat transfer coefficient of plate heat exchanger according to Al₂O₃ nanofluids made by two-step method. As the Reynolds number increases, the overall heat transfer coefficient under 6 vol% of Al₂O₃ went up to almost 30% respectively. But it was observed that for a given volumetric flow rate the performance is not increased. Also pumping power enhancement due to viscosity.
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