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표면 개질된 유리중공구체가 고무 복합체에 미치는 영향에 대한 연구
남영석,유재근,박건욱,김효준,김동건,김민근,현규 한국고분자학회 2019 폴리머 Vol.43 No.4
유리중공구체(hollow glass microsphere, HGM)는 중공을 가지는 무기 충전제로 고무 복합체에 적용될 경우경량화라는 장점이 있지만 기계적 특성을 저하시킨다는 단점이 있다. 따라서 고무와의 결합을 향상시키기 위해 유리중공구체의 계면 특성을 향상시키기 위한 다양한 연구가 진행되고 있다. 이러한 연구 중 본 연구에서는 다양한종류의 실란 커플링제로 유리중공구체의 표면을 개질시키는 방법에 대해서 살펴보았다. 실란 커플링제(silane coupling agent)는 2개 이상의 다른 반응기를 가져 유기질 재료와 무기질 충전제간 화학적 결합을 형성하는 재료이며, 분자내 기능성기에 따라 다양한 종류가 존재한다. 표면 개질 특성을 FTIR 및 SEM을 통해 살펴보았다. 그리고 개질된유리중공구체를 이용하여 고무복합체를 제조하여 유변학적, 기계적 및 형태학적 특성을 평가하였다. 그 결과, 표면개질된 유리중공구체가 들어간 고무 복합체의 기계적 물성 및 고무와의 상용성이 우수하게 나타났으며, 이는 계면특성이 증대되어 고무와의 상용성 및 분산성을 향상시킨 것으로 판단된다.
PIV 계측 및 수치해석 기법을 이용한 고효율 냉장고 설계
남영석(Young-Sok Nam),조성호(Sung-Ho Cho),최제호(Jayho Choi),이인섭(In-Seop Lee) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.5
A PIV measurement and numerical analysis of the flow inside the refrigeration compartment was conducted to increase the refrigerator performance. This study was especially focused on temperature uniformity and cooling speed performance. 2D PlY and stereoscopic PlY were used for the experiments on an actual-size operating refrigerator. The flow patterns inside the shelves and door baskets were measured by 2D PIV and the flow-rates at cooling duct outlets were measured by stereoscopic PlY. For numerical analysis, commercial software was used. 320,000 structured grid systems made with body fitted coordinate and the standard k-ε turbulence model were used for numerical analysis. Numerical analysis was used to calculate velocity vectors and temperature distributions inside cooling ducts and the refrigeration compartment as a whole. The new cooling system developed with the results of this analysis, cooled the door baskets effectively and according to chamber tests, temperature uniformity and cooling speed performance were increased 25%, and 11 %, respectively.
Youngsuk Nam(남영석),Hyunsik Kim(김현식),Seungwon Shin(신승원) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
We report our energy and hydrodynamic analyses of coalescence-induced jumping on superhydrophobic surfaces. A full three-dimensional numerical model is developed using the level contour reconstruction method to investigate complex dynamics of contact lines and interfacial areas during the droplet coalescence on superhydrophobic surface (d ? 30μm and contact angle ? 160˚). The experimental characterization of coalescence-induced jumping is conducted with silanated CuO nanostructured surfaces to support the numerical study. The energy analysis shows that approximately half (40%-60%) of the excess amount of surface energy released during the coalescence is converted to kinetic energy on the superhydrophobic surface before the droplet detachment starts. The hydrodynamic analysis shows that the rapid increase in the kinetic energy at the beginning of the coalescence is initiated from low pressure associated with the high negative curvature of the liquid bridge. It also confirms that the asymmetric nature of the droplet evolution with the superhydrophobic wall generates high pressure at the bottom contact area that provides enough driving force to make the merged droplet jump from the wall. This work clarifies the dynamic mechanisms of selfpropelled jumping droplets and provides the necessary framework to develop the superhydrophobic condenser surfaces for various applications.
Evaluation of Heat Transfer Fluids for Solar Thermal Applications
Youngsuk Nam(남영석),Andrej Lenert,Evelyn Wang 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
The choice of heat transfer fluids has significant effects on the performance, cost and reliability of solar thermal collector. We evaluate existing heat transfer fluids such as oils and molten salts based on new figure of merit capturing the combined effects of thermal storage capacity, convective heat transfer characteristics and hydraulic performance of the fluids. Other issues including thermal stability, freezing point and safety are also discussed. This work will help evaluate and engineer heat transfer fluids for solar thermal applications such as solar thermal power plants.