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적응축현상에서 증기 유속이 액적이탈반경과 열전달에 미치는 영향
강주원(Joo Won Kang),황경원(Kyoung Won Hwang),박현선(Hyun Sun Park),모리야마 키요후미(Kiyofumi Moriyama),김무환(Moo Hwan Kim) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
Steam velocity is one of the most significant parameter in dropwise condensation heat transfer. However, analysis on the effect of steam velocity on dropwise condensation was very restricted because of the difficulty in analyzing the drag force effect. In this paper, droplet departure diameter will be proposed as a function of the steam velocity with other conventional parameters. Also, dropwise condensation heat transfer will be computed by the dropwise condensation modeling, suggested by Rose and Le Fevre [1], firstly. In dropwise condensation heat transfer calculation, the droplet departure diameter according to the steam velocity will be considered. As steam velocity was increased, the droplet departure diameter was decreased, and the condensation heat transfer was increased.
급속 냉각을 통한 완전 젖음성 표면에서의 과냉 조건 막비등 열전달에 대한 실험적 연구
강준영(Jun-young Kang),이기철(Gi Cheol Lee),김설하(SeolHa Kim),박현선(Hyun Sun Park),모리야마 키요후미(Kiyofumi Moriyama),김무환(Moo Hwan Kim) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
We experimentally studied on an liquid-spreading effect on a completely wettable surface (CWS) under subcooled (Tcoolant~85℃) film boiling condition in the quenching experiments. The surface was fabricated by anodic oxidation on zirconium-702 vertical rod, and, had liquid-spreading effect. This was originated from capillary-wicking into micro-/nano- structures. At CWS, quenching performance was significantly improved showing the shorter overall cooling time on CWS by 46 percent in comparison to one on BZS (Bare Zirconium Surface). The visualized images taken in the CWS tests shows numerous micro-scale bubbles emitted in the initial quenching; Micro-bubble Emission Boiling (MEB). This was explained by vigorous evaporation due to intermittent wetting on CWS under film boiling regime.
노현우(Hyunwoo Noh),조항진(HangJin Jo),유동인(Dong In Yu),박현선(Hyun Sun Park),모리야마 키요후미(Kiyofumi Moriyama),김무환(Moo Hwan Kim) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
Pool boiling experiments were conducted on flat and structured SiO₂ surfaces to investigate the effects of surface structures on boiling performances. A micro-structured surface was prepared with the MEMS fabrication methodology, and has regularly distributed micro-scale pillar array. Critical heat flux was enhanced on micro-structured surface up to ~1.7 ㎿/㎡, compared to flat surface with ~0.8 ㎿/㎡. Heat transfer coefficient of the micro-structured surface was higher than that of flat one at high heat flux region, and the difference became larger as applied heat flux increased. Droplet and bubble dynamics were studied and the results presented pinning behavior of liquid film and smaller bubble departure diameters on the micro-structured surface. At high heat flux region, liquid path was observed only on micro-structured surface, which guarantees consistent liquid supply rate to the heating surface.
마이크로-나노 구조가 있는 표면에서의 액적 계면 거동 현상에 대한 연구
곽호재(Ho Jae Kwak),유동인(Dong In Yu),김무환(Moo Hwan Kim),박현선(Hyun Sun Park),키요후미 모리야마(Kiyofumi Moriyama),안호선(Ho Sun Ahn),김동억(Dong Eok Kim) 대한기계학회 2015 大韓機械學會論文集B Vol.39 No.5
최근 표면개질을 통한 젖음성 향상을 위하여, 마이크로와 나노 구조가 계층적(hierarchical)으로 존재하는 표면에 대한 연구가 공학 및 다양한 연구 분야에서 활발하게 진행되고 있다. 계층적구조가 존재하는 표면에서 초친수성(super-hydrophillic)은 대개 물방울(water droplet)의 계면 거동에 의해 그 특성이 확인된다. 따라서, 본 연구에서는 초친수성 표면위에서의 물방울 계면 거동에 대한 실험적 연구를 수행하였다. 포토리소그래피(photo lithography)공정과 건식 식각공정을 이용하여, 정량적으로 표면을 제작하였으며, 실험 표면에서의 계면 거동은 초고속카메라로 가시화하였다. 가시화 자료를 바탕으로, 물방울 계면거동은 표면에 존재하는 마이크로 및 나노구조의 지형학적 특성에 의해 영향을 받음을 확인하였다. Recently, surfaces with micro and nano structures are the focus of various research and engineering fields to enhance wetting characteristics of the surfaces. Hydrophilic surfaces with hierarchical structures are generally characterized by the interfacial behavior of water droplets. In this study, the interfacial behavior of water droplets is experimentally investigated considering the scale of structures. Using the dry etching and conventional lithography method, quantitative hierarchical structured surfaces are developed. The behavior of the liquid?vapor interface on the test sections is visualized using an automatic goniometer and a high-speed camera. On the basis of the visualized data, the interfacial behavior of water droplets is intensively investigated according to surface geometrical characteristics.