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고분자 전해질 연료전지의 동결이 성능 및 내부 물 분포 변화에 끼치는 영향
고동건(Donggun Ko),도승우(Seungwoo Doh),박현선(Hyun Sun Park),김무환(Moo Hwan Kim) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
In this research, the effect of freezing on the performance and water distribution of PEMFC (Polymer Electrolyte Membrane Fuel cell), was analyzed. Total 40 freezing – thawing cycles were conducted and the performance was measured at some points of fixed current density. The performance of PEMFC was degraded after freezing about 35% at the high current density region. To analyze the reason of degradation, visualization and quantification of water in PEMFC was conducted using the X – ray radiography method. In situ visualization was conducted and the water thickness in PEMFC was measured based on the Beer-Lambert law. The result showed reduced water contents in MEA(Membrane Electrolyte Assembly). It was suggested that the reason of degradation. To analyze the reason of water distribution change, the structural change of GDL(Gas Diffusion Layer) was investigated by comparison of SEM(Scanning Electron Microscope) image. The image showed the crack on MPL(Micro Porous Layer) and detachment of MPL from GDL. It destroyed the effective water management in PEMFC and reduced the performance.
중성자 영상법을 이용한 Heat Pipe 내의 이상유동 가시화
김태주(TaeJoo Kim),박수지(SuJi Park),김종열(JongYul Kim),도승우(SeungWoo Doh) 한국가시화정보학회 2016 한국가시화정보학회지 Vol.14 No.3
The circular and flat heat pipe were experimentally investigated by using neutron imaging technique. This experimental study was performed at the DINGO of OPAL research reactor, Australia. The diameter of the circular heat pipe is 10 mm and the dimension of flat is 10(width) × 3(thickness) mm2, respectively. We used the distilled water as a coolant. The coolant distributions and 2-phase flow patterns were measured under heating conditions. Experimental results show that neutron imaging technique is a good tool to visualize the 2-phase flow and phenomena in the heat pipe. The coolant distributions and 2-phase flow patterns depend on installation posture of the heat pipe and volume ratio of the coolant. Finally, it was discussed to calculate the void fraction by neutron imaging technique.
방사광 X-선 영상법을 활용한 마이크로/나노 구조 표면에서의 액체 퍼짐 가시화 연구
곽호재(Ho Jae Kwak),유동인(Dong In Yu),도승우(Seungwoo Doh),박현선(Hyun Sun Park),김무환(Moo Hwan Kim) 대한기계학회 2017 大韓機械學會論文集B Vol.41 No.8
최근들어 고체 표면의 젖음성을 향상시키기 위해 표면에 나노/마이크로 기술을 적용하는 연구가 진행되고 있다. 이러한 연구를 통하여 나노 구조가 표면 젖음성을 향상 시킬 수 있고, 액체 퍼짐은 실 모세관(Capillary wicking)에 의해 형성된다는 것을 확인하였다. 그러나 대부분의 연구는 나노 구조의 작은 스케일 때문에 분석하는데 어려움이 있어서 퍼짐현상을 정성적으로 분석하고 있다. 본 연구에서는 마이크로/나노/마이크로-나노 구조를 갖는 실리콘 표면에서의 액적 계면 거동을 정량적으로 분석하였으며, 계면의 거동은 방사광 X선 영상법으로 직접 측면가시화를 진행하였다. 그 결과 모든 구조 표면에서 퍼짐 현상이 발생하였고, 액체 계면의 거동이 서로 다르게 나타났다. 마이크로구조의 경우 일정한 액막 두께를 유지하며 퍼졌고, 나노구조는 완만한 경사를 갖는 것으로 나타났다. 마이크로-나노 구조의 경우 두 가지가 결합된 형태의 퍼짐현상을 보였다. 또한, 액체의 퍼짐은 마이크로-나노 구조에서 가장 증진됨을 확인하였다. Nano/micro technology is currently applied to improve solid surface wettability, with recent research studies indicating that nanostructures can improve surface wettability in the hydrophilic direction, and liquid spreading (propagation) is generated by capillary wicking. The majority of the existing research involves qualitative analysis of the spreading phenomena, owing to the difficulty in conducting small-scale analysis (nanostructures). In this study, the droplet interfacial behavior on silicon surfaces with micro/nano/micro-nano structures is experimentally investigated. The interfacial behavior is directly visualized using synchrotron X-ray imaging (side view). The spreading phenomena occur on structured surfaces, and the liquid interface behaviors on the surfaces differ. The liquid film thickness is uniform during spreading on the microstructured surface, but not on the nano case which shows a gentle slope. These combined spreading shapes were observed on a micro-nano structured surface, and liquid propagation was enhanced when the micro- and nano-structures are combined.