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Ryu, Hojun,Kim, Jisoo,Kim, Jongkuk,Kim, Do Hyun,Kang, Yong-Jin,Jang, Young-Jun,Jeong, Ji Hwan Elsevier 2020 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.148 No.-
<P><B>Abstract</B></P> <P>Dropwise condensation (DWC) is one of the most important phenomena to improve the heat transfer performance of steam condensation system. To promote DWC on hydrophilic metals, non-metallic hydrophobic promoters are coated on the surface. Non-metallic coatings are relatively easy to be degraded due to lack of mechanical and chemical properties. In this study, fluorine-doped diamond-like carbon (F-DLC) was used to obtain DWC on Al6061. Prior to F-DLC coating, microtextures were fabricated on Al6061 for the structural wettability control. DWC was successfully obtained with a small size of condensates after the microblasting and nanostructured F-DLC coating on Al6061. The synergic effects of microtextures with Cassie-state contact angle and hydrophobicity of nanostructured F-DLC led the superhydrophobic transformation of the surface. The contact angle increased about 115% from 66° to 142° after the microblasting and nanostructured F-DLC coating. The resulting DWC improved heat transfer performance of Al6061 significantly, 205%, as the dropwise condensates were rapidly eliminated from the surface. The variations on contact angle hysteresis before and after the steam condensation analysis revealed that the superhydrophobicity and DWC mode can be stably maintained under the steam condensing conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fabrication of the superhydophobic surface to improve the heat transfer resistance was proposed using the microblasting and nanostructured F-DLC coating. </LI> <LI> Microtextures fabricated by the microblasting induced Cassie-state contact angle on Al6061 surface. </LI> <LI> Nanostructured F-DLC coating led the transformation of condensation mode from FWC to DWC. </LI> <LI> The heat transfer efficiency in the steam condensation system was improved 205% on average following the transformation to DWC mode. </LI> <LI> The stable contact angle hysteresis before and after the steam condensation analysis specified the durability of nanostructured F-DLC coating under steam condensing environment. </LI> </UL> </P>
Microscopic behavior of Sb in chalcogenide materials for crystallization process
Ryu, Hojun,Yoo, Yonggoo,Paek, Mun Cheol,Kang, Kwangyong Elsevier Sequoia 2007 Materials science & engineering Structural materia Vol.449 No.-
<P><B>Abstract</B></P><P>The microscopic behavior of the chalcogenides materials alloys has been investigated for the understanding of the crystallization process. To analyze the crystallization–amorphization temperature by endo–exothermic process differential scanning calorimetry is carried out. Knowing the crystallization activation energy, we have performed in situ transmission electron microscopy with heating-rate change. With increasing temperature, as-deposited amorphous films transform to the crystalline phase, and Sb depletion takes place near 573K. For the calculation of activation energy, the measured data obtained from heating-rate changes is plotted according to the Kissinger equation. The crystallization activation energy of the chalcogenide material is 2.03±0.2eV.</P>
Evaluation of 1/f Noise Characteristics for Si-Based Infrared Detection Materials
Hojun Ryu,Sanghoon Cheon,Seong Mok Cho,Woo Seok Yang,Chang Auck Choi,Sein Kwon 한국전자통신연구원 2009 ETRI Journal Vol.31 No.6
Silicon antimony films are studied as resistors for uncooled microbolometers. We present the fabrication of silicon films and their alloy films using sputtering and plasma-enhanced chemical vapor deposition. The sputtered silicon antimony films show a low 1/f noise level compared to plasma-enhanced chemical vapor deposition (PECVD)-deposited amorphous silicon due to their very fine nanostructure. Material parameter K is controlled using the sputtering conditions to obtain a low 1/f noise. The calculation for specific detectivity assuming similar properties of silicon antimony and PECVD amorphous silicon shows that silicon antimony film demonstrates an outstanding value compared with PECVD Si film.
교원양성기관 역량 강화 기제로서의 수업품질개선보고서(CQI) 활용 가능성 탐색
유호준(Hojun Ryu),박소영(Soyoung Park),안은비(Eunbi An) 한국문화융합학회 2023 문화와 융합 Vol.45 No.10
본 연구의 목적은 교원양성기관 역량진단 대비 사범대학 수업의 질 향상과 소속 교원의 자발적인 역량개발 지원에 대한 실질적 도움을 제공하는 것이다. 이를 위해 연구의 대상은 2022학년도 1학기 사범대학 개설 교원양성 교육과정 304개 CQI로, 연구문제는 사범대학 개설 교과목을 수강하는 학생들의 교과목 강의평가 핵심 내용, 사범대학 교원이 인식하는 교원양성과정 교과목에 대한 만족요인과 불만족요인이었고, 텍스트마이닝을 통한 키워드 출현 빈도, 네트워크분석 등을 통해 결과를 도출하였다. 분석결과첫째, 학생 평가내용에서 출현한 주요 단어를 토대로 수업방식, 수업에 대한 태도 등 수업의 질이 향상되고 있는 것을 확인하였고, 둘째 사범대학 학생들의 다양한 수업방식에 대한 요구, 예컨대 실습 중심, 원격 중심 등을 확인하였고, 셋째 수업에 대한 교수자 대표적 만족요인은 학생들이 수업에 대하는 적극적인 자세, 열정 등으로부터 얻는 심리적 요인이 컸고 대표적인 불만족요인은 여전히 노후화된 강의실및 기자재 등 열악한 교육환경인 것을 확인하였다. 따라서 교원양성기관 역량 강화에 초점을 둔 CQI 문항 개발이 필요하고, 교수자의 수업 질 제고를 위한 유관부서의 협업 및 지원이 필요하다. The purpose of this study is to provide practical help for the improvement of the quality of teachers' education in preparation for the competency diagnosis of teacher education institutions and to support the voluntary development of teachers' competencies at A University. The subjects of the study were 304 CQI of curricula(2022-1) and the research questions were the core contents of lecture evaluations of students, satisfaction and dissatisfaction factors of teacher education curricula perceived by teachers. As a result of the analysis, it was confirmed that the quality of classes is improving based on key words, it was confirmed that students' demands for various teaching methods are increasing; third, the teacher satisfaction factors were psychological factors and the dissatisfaction factors were still poor educational environments. Therefore, it is necessary to develop a CQI questionnaire that focuses on strengthening the capacity of teacher training and to collaborate with and support relevant departments to improve the quality of teaching.
Singil Kang,Hojun Cha,Seungcheol Ryu,Kiwhan Kim,Seungmin Jeon,Jaesun Lee,Seokho Kim 한국초전도저온학회 2022 한국초전도저온공학회논문지 Vol.24 No.1
Recently, research on applying composite materials to various industrial fields is being actively conducted. In particular, composite materials fabricated by Fused Deposition Modeling 3D printers have more advantages than existing materials as they have fewer restrictions on manufacturing shape, reduce the time required, weight. With these advantages, it is possible to consider utilizing composite materials in cryogenic environments such as the application of liquid oxygen and liquid hydrogen, which are mainly used in an aerospace and mobility. However, FDM composite materials are not verified in cryogenic environments less than 150K. This study evaluates the characteristics of composite materials such as tensile strength and strain using a UTM (Universal Testing Machine). The specimen is immersed in liquid nitrogen (77 K) to cool down during the test. The specimen is fabricated using 3D print, and can be manufactured by stacking reinforced fibers such as carbon fiber, fiber glass, and aramid fiber (Kevlar) with base material (Onyx). For the experimental method and specimen shape, international standards ASTM D638 and ASTM D3039 for tensile testing of composite materials were referenced.