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1%미만의 부피비를 가지는 알루미나 나노유체의 유효 열전도도
황교식 ( Kyo Sik Hwang ),이병호 ( Byeong Ho Lee ),김준호 ( Jun Ho Kim ),장석필 ( Seok Pil Jang ) 한국항공운항학회 2007 한국항공운항학회지 Vol.15 No.3
In this paper, effective thermal conductivities of water-based Al2O3-nanofluids with low concentration from 0.01 vol. % to 0.3 vol. % are experimentally obtained by transient hot wire method (THWM). The water-based Al2O3-nanofluids are manufactured by two-step method which is widely used. To examine suspension and dispersion characteristics of the water-based Al2O3-nanofluids, Zeta potential as well as transmission electron micrograph (TEM) is observed. We confirm the manufactured Al2O3-nanofluids have good suspension and dispersion. The effective thermal conductivities of the water-based Al2O3-nanofluids with low concentration are enhanced up to 1.64% compared with that of DI water at 21℃. In addition, experimental results are compared with theoretical results from Jang and Choi model.
나노입자 형상 변화에 따른 알루미나 나노유체의 유동 특성
황교식(Kyo Sik Hwang),하효준(Hyo Jun Ha),장석필(Seok Pil Jang) 대한기계학회 2011 大韓機械學會論文集B Vol.35 No.3
본 연구에서는 다양한 형상의 나노입자를 분산시킨 알루미나 나노유체의 유동 특성을 실험적으로 조사하기 위하여 나노입자의 형상 변화에 따른 알루미나 나노유체의 압력강하를 층류영역에서 측정하였다. 이를 위해 Sphere, Rod, Platelet, 그리고 Brick 의 형태를 갖는 알루미나 나노입자를 물에 분산시켜 부피비 0.3%를 갖도록 Two-step 방법으로 제작하였다. 제작된 나노유체의 분산성을 파악하기 위하여 제타포텐셜을 조사하였으며, 나노입자의 형상을 파악하기 위하여 TEM 사진을 측정하였다. 다양한 형상의 나노입자를 분산시켜 0.3%의 부피비를 갖는 나노유체의 압력강하를 측정하였을 때, 입자형상이 나노유체의 유동특성에 영향을 미치는 것을 확인하였다. 실험 결과를 바탕으로 나노입자의 단위질량당 표면적과 분산된 나노입자의 크기를 이용하여 나노유체의 압력강하 특성을 설명하였다. To study the flow characteristics of water-based Al₂O₃ nanofluids according to the shape of the nanoparticles, we measure the pressure drop in a fully developed laminar flow regime. Water-based Al₂O₃ nanofluids of 0.3 Vol.% with sphere-, rod-, platelet-, and brick-shaped nanoparticles are manufactured by the two-step method. Zeta potential is measured to examine the suspension and dispersion characteristics, and TEM image is considered to confirm the shape characteristics of the nanoparticles. The experimental results show that the pressure drop of Al₂O₃ nanofluids depends on the shape of the nanoparticles although the nanofluids has same volume fraction of nanoparticles. This is explained by the surface area per unit mass of the nanoparticles and the size of the nanoparticles suspended in the base fluids.
층류 유동에서 알루미나 나노유체의 유동 및 대류 열전달 특성
황교식(Kyo Sik Hwang),이지환(Ji-Hwan Lee),장석필(Seok Pil Jang) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
In this paper, convective heat transfer and flow characteristics of Al₂O₃ nanoparticles suspended in water flowing through uniformly heated tubes are experimentally investigated under the laminar flow regime. The heat transfer coefficient and the pressure drop of nanoparticles suspended in water are experimentally presented according to the pumping power. In addition, the heat transfer coefficient and the pressure drop of Al₂O₃ nanoparticles suspended in water are compared with those of pure water under the fixed pumping power. It is shown that the heat transfer coefficient of Al₂O₃ nanofluids with 1 % volume fraction is enhanced by about 12% although the increment of the pressure drop of those is 3% compared with those of pure water.
황교식(Kyo Sik Hwang),장석필(Seok Pil Jang) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
In this paper, effect of the volume fraction on the convective heat transfer characteristics of water-based Al₂O₃ nanofluids flowing through a circular tube with the constant heat flux under fully developed laminar flow regime is experimentally investigated. For the purpose, water-based Al₂O₃ nanofluids with various volume fractions ranging from 0.01% to 0.3% are manufactured by the two-step method. Based on the experimental results, it is shown that the heat transfer coefficient of water-based Al₂O₃ nanofluids is enhanced by 8% for a 0.3 Vol. % compared with that of pure water and is increased with the volume fraction of Al₂O₃ nanoparticles, but can not be predicted by well known Shah Equation. In addition, the slip mechanisms in nanofluids such as Brownian diffusion and thermophoresis are discussed to understand the convective heat transfer characteristics of water-based Al₂O₃ nanofluids flowing through a circular tube.