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개질된 표면을 이용한 풀비등 임계열유속 증진에 관련한 실험적 연구
강순호(Soonho Kang),안호선(Hoseon Ahn),조항진(Hangjin Jo),김무환(MooHwan Kim),김형모(Hyungmo Kim),김준원(Joonwon Kim) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.11
In the boiling heat transfer mechanism, CHF(critical heat flux) is the significantly important parameter of the system. So, many researchers have been struggling to enhance the CHF of the system in enormous methods. Recently, there were lots of researches about enormous CHF enhancement with the nanofluids. In that, the pool boiling CHF in nanofluids has the significantly increased value compared to that in pure water because of the deposition of the nanoparticle on the heater surface in the nanofluids. The aim of this study is the comparison of the effect of the nanoparticle deposited surface and the modified surface which has the similar morphology and made by MEMS fabrication. The nanoparticle deposited surface has the complex structures in nano-micro scale. Therefore, we fabricated the surfaces which has the similar wettability and coated with the micro size post and nano structure. The experiment is performed in 3 cases : the bare surface with 0.002% water-ZnO nanofluids, the nanoparticle deposited surface with pure water and the new fabricated surface with pure water. The contact angle, a representative parameter of the wettability, of the all 3 cases has the similar value about 0 and the SEM(scanning electron microscope) images of the surfaces show the complex nano-micro structure. From the pool boiling experiment of the each case, the nanoparticle deposited surface with pure water and the fabricated surface with pure water has the almost same CHF value. In other words, the CHF enhancement of the nanoparticle deposited surface is the surface effect. It also shows that the new fabricated surface follows the nanoparticle deposited surface well.
평판형 히터를 이용한 알루미늄과 타이타늄 산화물 나노유체의 풀비등 임계열유속에 관한 실험적 연구
안호선(HoSeon Ahn),김형대(Hyung Dae Kim),조항진(Hangjin Jo),강순호(Soonho Kang),김무환(Moo Hwan Kim) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.10
Pool boiling heat transfer and critical heat flux (CHF) of water-based nanofluids with alumina and titania nanoparticles of 0.01% by volume were investigated on a disk heater at saturated and atmospheric conditions. The experimental results showed that the boiling in nanofluids caused the considerable increase in CHF on the flat surface heater. It was revealed by visualization of the heater surface subsequent to the boiling experiments that a major amount of nanoparticles deposited on the surface during the boiling process. Pool boiling of pure water on the surface modified by such nanoparticle deposition resulted in the same CHF increases as what boiling nanofluids, thus suggesting the CHF enhancement in nanofluids was an effect of the surface modification through the nanoparticle deposition during nanofluid boiling. Possible reasons for CHF enhancement in pool boiling of nanofluids are discussed with surface property changes caused by the nanoparticle deposition.
실리콘 표면 위에 소수성 점을 이용한 비등 열전달 증진에 관한 실험적 연구
조항진(Hang Jin Jo),김형모(Hyungmo Kim),안호선(Ho Seon Ahn),강순호(Soonho Kang),김준원(Joonwon Kim),신정섭(Jeong-Seob Shin),김무환(Moo Hwan Kim) 대한기계학회 2010 大韓機械學會論文集B Vol.34 No.6
표면 젖음성은 비등 상황에서 주요 인자인 임계열유속과 비등열전달 모두에 영향을 미치는 중요한 표면인자이다. 지금까지 표면 젖음성을 이용한 비등 조건 개선에 대한 연구는 한가지 물질의 표면 구조를 개질하는데 국한되었다. 본 논문에서는 최적화된 비등 조건을 이룰 수 있는 표면 젖음성을 찾기 위한 연구의 일환으로 소수성 물질과 친수성 물질의 혼합을 시도하였다. 가열 표면은 표면 접촉각이 60° 인 친수성 표면위에 표면 접촉각 120° 의 소수성 물질 점이 생기도록 개질되었다. 개질된 소수성 점은 마이크로 단위와 밀리 단위로 그 크기를 변화시켜 가며 풀 비등 성능을 평가하였다. Wettability is important to enhance not only CHF but also nucleate boiling heat transfer, as shown by the results of different kinds of boiling experiments. In this regard, an excellent boiling performance (a high CHF and heat transfer performance) could be achieved in the case of pool boiling by some favorable surface modifications that can satisfy the optimized wettability condition. To determine the optimized boiling condition, we design special heaters to examine how two materials, which have different wettabilities (e.g., hydrophilic and hydrophobic materials), affect the boiling phenomena. The special heaters have hydrophobic dots on a hydrophilic surface. The contact angle of the hydrophobic surface is 120° to water at the room temperature. The contact angle of the hydrophilic surface is 60° at same conditions. Experiments involving micro hydrophobic dots and two types of milli hydrophobic dots are performed, and the results are compared with a reference surface.