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오일 도포 표면의 온도에 독립적인 오일 파울링 저감 성능
오승태(Seungtae Oh),이주영(Jooyoung Lee),서동현(Donghyun Seo),이충엽(Choongyeop Lee),남영석(Youngsuk Nam) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
Oil-fouling on surfaces which happens during oil production and transportation has been a detrimental problem in industries. Here, we fabricated lubricant-impregnated surfaces (LIS) and investigated their anti-oil fouling performance at a wide range of operating temperature (20~90℃). Two types of lubricant oils which have different chemical components were impregnated into SAM-coated CuO nanostructures. The oil-fouling tests were conducted in a temperature-controlled oil-fouling experimental setup, and the performance was characterized by measuring mass of adhered fouling on the surfaces. LIS showed the best anti-oil-fouling performance. The operating temperature significantly changed the size of the emulsion and it resulted in various oil-fouling results of the other surfaces. However, the lubricant oil layer on LIS effectively prevented any crystallization of the emulsions and provided almost steady good anti-oil fouling ability at a wide range of operating temperature. The adhesion strength between the emulsion and the surfaces was analyzed to understand the different anti-oil fouling performance, and the effect of the types of the impregnated oils on LIS was investigated by using thermodynamical energy criteria. We believe that our works help to understand the role of the surface wettabilities during oil fouling process and offer a guideline to fabricate stable LIS for oil-fouling applications.
서동현(Donghyun Seo),오승태(Seungtae Oh),이충엽(Choongyeop Lee),남영석(Youngsuk Nam) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
Frost formation and accumulation have widely caused serious performance degradation and economic/safety problems in a variety of industrial and residential applications including aircraft, ships, wind turbines, dams, power transmission liens, heat pumps, refrigerators and air conditioners. Recent studies have reported that oil-infused superhydrophobic (Oil-SHPo) surfaces have excellent anti-icing ability due to its high droplet mobility, but few studies have clearly demonstrated detailed mechanisms of freezing delay on the surfaces. Here, we apply the Oil-SHPo wettability on commercially available Al surfaces and investigate how such wetting property effectively suppresses ice spreading under condensation frosting condition. Observed in a microscope test setup, microscale icing behaviors on the surfaces exhibit that its high droplet mobility makes droplet distribution with small mass diffusion rate between frozen drops and liquid drops, it leads to low ice propagation velocity. In particular, it is shown that infused oil viscosity plays a critical role in condensation growth rate and small viscosity is more desirable for icephobic surfaces. Heat exchangers with the Oil-SHPo wettability exhibit high droplet removal rate thanks to the influence of its extremely low contact angle hysteresis and it leads to the best anti-icing ability when compare to other test surfaces.
심재환(Jaehwan Shim),오승태(Seungtae Oh),남영석(Youngsuk Nam) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
Condensation frosting phenomena causes serious economic/safety problems in many industrial applications. Recently, superhydrophobic surface have been attracted attention as a promising way to improve anti-frosting performance, but high cost, difficult methods to scale and poor durability limited its applicability in practical applications. In this work, we introduce superhydrophobic cerium oxide coatings formed by a dipping-based scalable fabrication process. The excellent superhydrophobicity was successfully obtained on two types of the developed cerium oxide samples, which provided the freezing delay of ~66% and ~98% lower ice adhesion strength compared to Bare aluminum. The cerium oxide samples also showed the enhanced stability against the harsh environmental conditions including the repetition of frosting/de-frosting and acidity/salinity solution exposure compared to a conventional hydrophobic coating. The coating was successfully applied to a plain fin-tube heat exchanger with a large area and complex geometry, and the anti-frosting performance was investigated. The results demonstrated that the suggested cerium oxide surfaces can provide ~60% lower pressure drop and ~23% higher heat transfer rate.
초소수성 PMN-PT 표면에서의 액적 충돌을 통한 파이로 전력 생산
한정훈(Jeonghoon Han),오승태(Seungtae Oh),황희재(Hee Jae Hwang),최덕현(Dukhyun Choi),이충엽(Choongyeop Lee),남영석(Youngsuk Nam) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
Single crystalline pyroelectric materials offers new opportunities for efficient thermal energy harvesting utilizing temperature fluctuation. Recent works have demonstrated the pyroelectric generators utilizing various thermal energy such as body heat and latent heat of fluids. However, the sustainable and high performance pyroelectric thermal harvesting has not been realized yet. In this work, we introduce the pyroelectric generator utilizing the rapid temperature fluctuation during a droplet impact. The thin single-crystalline PMN-PT of 100 μm thickness was incorporated to the generator in order to improve the pyroelectric coefficient with reducing the thermal mass. Based on the measured pyroelectric current and voltage values, the pyroelectric current prediction model was developed utilizing the correlation of the maximum spreading diameter during drop impact. We believe this work will help to develop efficient pyroelectric thermal energy harvesters.