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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.
증발-결정화 방법을 이용한 응축 성능 증진: 자기 배열된 친수성 결정의 효과
한태양(Taeyang Han),최영현(Younghyun Choi),김무환(Moo Hwan Kim),조항진(Hang Jin Jo) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.12
Biphilic surfaces having heterogeneous wettability have proved their outstanding condensation efficiency compared to surfaces having homogeneous wettability. However the application of the biphilic surfaces in practical industries is limited due to the difficulty of the fabrication of the surfaces. In this study, we developed a simple and low-cost method to make a biphilic surface using evaporation-crystallization method. The developed surface enhanced the efficiency of condensation by up to 63% compared to a conventional superhydrophobic surface. Furthermore, the evaporation crystallization method induced ‘self-arrangement of hydrophilic crystals’ on a zigzag structured surface. The efficiency of condensation on the zigzag structured surface was increased by 2.4 times using the evaporation-crystallization method. The developed method not only enhanced the condensation efficiency of flat surfaces but also can be applied to complex shapes, increasing the applicability of biphilic surfaces in various industries.
경제성 평가를 통한 초임계 CO₂ 브레이튼 사이클 적용을 위한 에어포일형 PCHE 설계
이수원(Su-Won Lee),정성균(Sung-Kun Chung),조항진(Hang-Jin Jo) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.12
The Supercritical CO₂ Brayton cycle has the advantage of high thermal efficiency utilizing the characteristics of high density of working fluid in supercritical region. This cycle consist of a number of components such as compressor, turbine, and heat exchanger. Among them, the component of largest volume is the heat exchanger. Thus, the design of the heat exchanger is important because it will be changed the economics. PCHE is recommended in the cycle because it is stable under high temperature and pressure conditions, has the advantages of high heat transfer performance and small volume. In this paper, the airfoil type PCHE known to have low pressure drop and high heat transfer performance was analyzed according to the shape variable (vertical number and horizontal number) and the number of tubes. The economical shape variable was the vertical number 2.0, the horizontal number 2.0, and the number of tubes 1,600,000.
마이크로크기 액적의 거동 제어를 통한 액적-점핑 응축 성능 증진
한태양(Taeyang Han),최영현(Younghyun Choi),권정태(Jeong-Tae Kwon),조항진(Hang Jin Jo),김무환(Moo Hwan Kim) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11
To increase the efficiency of jumping-droplet condensation, this study proposes a novel surface that promotes coalescence-induced jumping. Inspired the phenomenon in which a growing droplet moves spontaneously within a superhydrophobic V structure, we fabricated nanograssed zigzag structures on the surface to induce spontaneous motion of condensed droplets. The direction of the motion is parallel to the surface, so the condensed droplets easily coalesce on it. Compared to a conventional nanostructured superhydrophobic surface, the proposed surface increased the frequency of coalescence-induced jumping by ≥ 17 times and increased the cumulative volume of jumping droplets by ~ 1.8 times. The proposed surface has great potential to increase the efficiency of various applications that exploit condensation. Furthermore, we expect that the enhanced heat transfer coefficient of jumping-droplet condensation will solve thermal problem of high power electronics, which will be faced with commercialization of 5G.
단면 열속부하된 Hypervapotron 냉각채널의 과냉비등상황 임계열유속 실험적 연구
임지환(Ji Hwan Lim),박민규(Min Gyu Park),오훈교(Hun Gyo Oh),황돈관(Don Koan Hwang),김무환(Moo Hwan Kim),조항진(Hang Jin Jo) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11
In Korea, KSTAR’s tokamak long-time operation technique has reached 70 seconds in 2016, and steady-state plasma control technique is estimated to reach world-class level. However, the lack of cooling capacity to maintain the thermal steady state of the tokamak is becoming a severe engineering problem in preparation for K-DEMO. To simulate the fusion thermal condition, a test loop was constructed to withstand high temperature (150℃) and high pressure (20 bar). Through this loop, CHF experiments were carried out for the Hypervapotron channel and the results were compared with Baxi Hypervapotron CHF correlation. But, a high error average of 173.46% was found, and the Ja number index was changed to 0.45 in consideration of the 10 bar pressure to enable a reasonable prediction of 6.85% lower error. If CHF modeling and verification test is performed later, it will be possible to predict CHF over a wider range.
2% Dorzolamide 점안액을 사용한 녹내장환자에서의 안압 변화 : A Clinical Study
김창식,조항진,이강일 충남대학교 의과대학 지역사회의학연구소 1997 충남의대잡지 Vol.24 No.2
2% dorzolamide solution (Trusopt ^TM) is commercially available recently, and we applied this new agent to glaucoma patients to assess the effect on the korean glaucoma patients. We prescribed 2% dorzolamide solution three times a day for the patient who had not shown a significant fluctuation of intraocular pressure (IOP) under the same regimen at least 4 weeks interval. We assessed the IOP of the 30 eyes of 18 patients before and 4 weeks and 8 weeks after initiation of this agent retrospectively. The patients were divided into 3 groups ; group 1 composed of 3 eyes of 2 patients who had not used any ocular hypotensive drugs before this study. Group 2 was composed of the patients who had used more than 1 ocular hypotensive solutions, and 2% dorzolamide was added to their regimen. Patients who had used more than 1 ocular hypotensive agents including oral acetazolamide was classified as group 3, and one of their regimen was substituted to 2% dorsolamide solution. The mean IOP of group 1 was decreased by 27.3% at 4 weeks and 21.6% at 8 weeks after initiation of new drug. In group 2, there was an additional decrement of mean IOP by 19.0% at 4 week and 23.6% at 8 weeks. And in group 3, there was a decrement of mean IOP by 19.4% at 4 weeks and 20.9% at 8 weeks for the 3 eyes for which we substituted pilocarpine solution with dorzloamide. In the 4 eyes to which we exchanged beta-blockers with dorzolamide, the IOP decreased slightly by 9.9 and 6.3% respectively. In the 11 eyes for which we discontinued acetazolamide and used dorzolamide, the IOP was decreased by 7.1% at 4 weeks, but the IOP was increased by 13.0% at 8 weeks after substitution. Although we need more long term study with more large numbers of subjects, from the above result we can expect hypotensive effect when we use this drug as a single regimen, and additional hypotensive effect when we add this solution to other regimen. And this drug may substitute pilocarpine or beta-blocker effectively, but we should be careful when we are trying to replace the acetazolamide with dorzolamide.