• 한국표면공학회지
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• 제56권1호
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• pp.1-11
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• 2023

Lubricant-impregnated nanoporous surfaces (LIS), which is created by impregnating water-immiscible oil into nanoporous surface structure, have been explored considering wide range of application fields. Due to the lubricant impregnated in nanoporous structure, the surface shows extreme de-wetting with a high mobility of water droplets, so that various functionalities can be realized. The lubricant layer inhibits the contact of corrosive media to porous structure as well as metal substrate, thus the surface improves the corrosion resistance. The water on the surface freeze without any contact to solid porous structure, showing a low ice adhesion for de-icing an anti-icing. The extremely high mobility of water droplets on lubricant-impregnated porous surfaces also contributes the enhancement of condensation heat transfer as well as water harvesting from fog and moisture. Moreover, the bacteria adhesion on metal surface forming biofilms causing serious hygiene issues can be inhibited on the lubricantimpregnated surfaces. Despite of such superior functionalities, the lubricant-impregnated porous surface has a limitation of lubricant depletion by external flow of fluids. Therefore, extensive efforts to improve the durability of lubricant-impregnated surface are required for practical applications.

• Bulletin of the Korean Chemical Society
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• 제33권10호
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• pp.3258-3264
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• 2012

Aluminum oxide ($Al_2O_3$) nanofibers were treated thermally under an ammonia ($NH_3$) gas stream balanced by nitrogen to form a thin aluminum nitride (AlN) layer on the nanofibers, resulting in the enhancement of thermal conductivity of $Al_2O_3$/epoxy nanocomposites. The micro-structural and morphological properties of the $NH_3$-assisted thermally-treated $Al_2O_3$ nanofibers were characterized by X-ray diffraction (XRD) and atomic force microscopy (AEM), respectively. The surface characteristics and pore structures were observed by X-ray photoelectron spectroscopy (XPS), Zeta-potential and $N_2$/77 K isothermal adsorptions. From the results, the formation of AlN on $Al_2O_3$ nanofibers was confirmed by XRD and XPS. The thermal conductivity (TC) of the modified $Al_2O_3$ nanofibers/epoxy composites increased with increasing treated temperatures. On the other hand, the severely treated $Al_2O_3$/epoxy composites showed a decrease in TC, resulting from a decrease in the probability of heat-transfer networks between the filler and matrix in this system due to the aggregation of nanofiber fillers.

• 대한기계학회논문집B
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• 제37권7호
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• pp.647-653
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• 2013

본 연구에서는 산화구리(CuO) 나노분말과 순수 물을 혼합하여 제조한 나노유체를 이용하여 가열된 고체표면에 있어서 나노유체 액적의 증발특성에 대한 실험적 연구를 수행하였다. 실험결과로부터 가열된 표면에서 나노유체 액적의 증발속도는 순수 물 액적보다 증발속도가 약간 증가하는 경향이 있음을 알 수 있었으며, 이는 나노유체에 포함된 나노입자가 유체의 열전도도를 향상시켜 고체 표면에서 액적으로의 열전달이 촉진되었기 때문인 것으로 판단된다. 또한 고체의 표면조도가 커질수록 액적의 증발속도가 약간 증가하였으며, 이는 고체의 표면조도가 커질수록 고체-액체의 접촉 면적이 증가하여 열전달이 촉진되었기 때문인 것으로 추정된다.

• 한국지하수토양환경학회지:지하수토양환경
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• 제17권2호
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• pp.7-14
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• 2012

Batch tests were carried out to evaluate the thermal treatment of low volatile organic compounds in low-permeability soil. The chemical oxidation by sodium persulfate catalyzed by heat and Fe (II) was evaluated. Enhanced persulfate oxidation of n-decane (C-10), n-dodecane (C-12), n-tetradecane (C-14), n-hexadecane (C-16), and phenanthrene was observed with thermal catalyst, indicating increased sulfate radical production. Slight enhancement of the pollutants oxidation was observed when initial sodium persulfate concentration increased from 5 to 50 g/L. However, the removal efficiency greatly decreased as soil/water ratio increased. It indicates that mass transfer of the pollutants as well as the contact between the pollutants and sulfate radical were inhibited in the presence of solids. In addition, more pollutants can be adsorbed on soil particles and soil oxidant demand increased when soil/water ratio becomes higher. The oxidation of the pollutants was significantly improved when catalyzed by Fe(II). The sodium persulfate consumption increased at the same time because the residual Fe(II) acts as the sulfate radical scavenger.

• International Journal of Air-Conditioning and Refrigeration
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• 제14권2호
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• pp.41-48
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• 2006

Absorption performance at the vertical interface between refrigerant vapor and liquid solution of $LiBr-H_{2}O$ solution was enhanced by the waves formed due to the interfacial shear stress. The present study investigated experimentally and analytically the improvements of absorption performance in a falling film by wavy film flow. The dynamic parameter was the film Reynolds numbers ranged from 50 to 150. The energy and diffusion equations were solved simultaneously to find the temperature and concentration profiles at the interface of liquid solution and refrigerant vapor. Absorption characteristics due to heat and mass transfer were analyzed for the falling film of the LiBr aqueous solution contacted by refrigerant vapor in the absorber. Absorption performance showed a peak value at the solution flow rate of $Re_{f}>100$. Absorption performance for the wavy film flow was found to be greater by approximately 10% than that for uniform film flow. Based on numerical and experimental results, the maximum absorption rate was obtained for the wavy flow caused by spring insert. The difference between the measured and the predicted results were ranged from 5.8 to 12%.

• 한국자동차공학회논문집
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• 제12권4호
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• pp.1-11
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• 2004

Combustion and fuel distribution characteristics of heavy duty engine with the liquid phase LPG injection(LPLI) were studied in a single cylinder engine, Swirl ratio were varied between 1.2, 2.3, and 3.4 following Ricardo swirl number(Rs) definition, Rs=2.3 showed the best results with lower cycle-by-cycle variation and shorter burning duration in the lean region while strong swirl(Rs=3.4) made these worse for combustion enhancement. Excessive swirl resulted in reverse effects due to high heat transfer and initial flame kernel quenching. Fuel injection timings were categorized with open valve injection(OVI) and closed valve injection(CVI). Open valve injection showed shorter combustion duration and extended lean limit. The formation of rich mixture in the spark plug vicinity was achieved by open valve injection. With higher swirl strength(Rs=3.4) and open valve injection, the cloud of fuel followed the flow direction and the radial air/fuel mixing was limited by strong swirl flow. It was expected that axial stratification was maintained with open-valve injection if the radial component of the swirling motion was stronger than the axial components. The axial fuel stratification and concentration were sensitive to fuel injection timing in case of Rs=3.4 while those were relatively independent of the injection timing in case of Rs=2.3.

• 한국수소및신에너지학회논문집
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• 제25권4호
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• pp.425-435
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• 2014

Simulation studies on catalytic methanation reaction in externally cooled tubular reactor filled with monolithic catalysts were carried out using a general purpose modelling tool $gPROMS^{(R)}$. We investigated the effects of operating parameters such as gas space velocity, temperature and pressure of feeding gas on temperature distribution inside the reactor, overall CO conversion, and chemical composition of product gas. In general, performance of methanation reaction is favored under low temperature and high pressure for a wide range of their values. However, methane production becomes negligible at temperatures below 573K when the reactor temperature is not high enough to ignite methanation reaction. Capacity enhancement of the reactor by increasing gas space velocity and/or gas inlet pressure resulted no significant reduction in reactor performance and heat transfer property of catalyst.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.46-46
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• 2008

스텔스 기능을 가진 군사용 항공기는 레이다 망의 추적을 피하기 위해 일반 냉각수 대신에 절연유를 냉각매체로 사용한다. 그러나 절연유는 물에 비하여 열전달특성이 매우 낮기 때문에 항공기 전기전자 기기/부품 발열부를 효과적으로 냉각시키지 못하는 한계성을 가지고 있다. 따라서 본 연구에서는 나노유체(Nanofluid) 개념을 이용하여 절연유에 알루미나 및 질화알루미늄 나노분말을 미랑 분산시킨 나노절연유를 제조하고 이것의 열전달특성을 순수 절연유의 그것과 비교 평가함으로써, 냉각특성이 크게 개선된 새로운 냉매로서의 적용 가능성을 확인하고자 하였다. 다만 나노절연유를 제조함에 있어서 가장 큰 장애물은 오일에 대한 분산성 확보에 있기 때문에, 비드밀 및 초음파를 이용한 나노분말 응집체의 습식분산 및 분산제를 이용한 친유성 표면개질을 동시에 수행함으로써 장시간 안정된 분산성을 확보하도록 노력하였다. 나노유체의 열전도도 및 대류열전달계수는 비정상열선법을 이용하여 측정하였으며, 유체 속의 분말 분산 상태는 원심력을 이용한 분산안정성 평가장치 및 cryo FE-SEM을 이용하여 확인하였다. 또한 분말 형상이 대류열전달에 미치는 영향을 조사하기 위하여 알루미나 나노분말은 구상과 침상의 분말을 모두 사용하였고, 질화알루미늄 외에 다이아몬드 나노절연유도 함께 제조, 평가함으로써 냉각 및 절연특성, 그리고 물리화학적 안정성이 우수하고 실적용 가능성이 가장 높은 재료를 도출하고자 하였다.

• 한국산학기술학회논문지
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• 제14권2호
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• pp.592-597
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• 2013

인버터 일체형 전동식 압축기 내부의 모터 및 인버터에서 발생된 열은 차가운 냉매에 의해 냉각되기 때문에 열적인 문제가 거의 발생하지 않는다. 하지만, 압축기 모터 및 인버터의 열전달 성능은 압축부와의 상호 열전달에 의하여 압축기 성능에 영향을 미친다. 또한 외기 환경 및 시스템 운전조건에 따라, 모터 및 인버터의 온도 증가는 이러한 모터 시스템의 출력 밀도에 영향을 미치고, 특히 인버터는 온도 상한치 관리에 의해 작동이 멈추어질 수 있다. 본 연구에서는 전동식 압축기 모터 시스템의 열유동 해석을 수행하였고, 모터 및 인버터의 방열성능 향상에 대해 분석하였다. 현 모델의 해석 결과는 압축기 운전영역에서 모터가 전반적으로 낮은 온도 경향을 나타내었으며, 인버터의 경우는 고속조건에서 관리 온도인 $85^{\circ}C$ 이내 범위를 만족하지만, 저속 가혹조건에서 제한 온도를 $10^{\circ}C$ 정도 초과하였다. 따라서 가혹 운전조건에서의 방열 문제를 해결하기 위해, 압축기 유로개선 뿐만 아니라 모터 및 인버터의 발열 저감기술의 개발이 요구된다.

• 대한기계학회논문집B
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• 제36권9호
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• pp.895-900
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• 2012

본 논문에서는 암모니아/물 흡수식 시스템의 흡수성능 촉진에 대한 나노액적의 영향을 파악하고 흡수성능과 분산안정성의 상관관계를 규명함으로써 흡수식 시스템에 대한 이성분 나노에멀전유체의 적용가능성을 제시하고자 한다. 이성분 나노에멀전 유체는 암모니아/물 용액을 모유체로 하며, N-decane 오일을 모유체에 분산시키기 위하여 $C_{12}E_4$와 Tween20을 첨가제로 사용하였다. 이성분 나노에멀전유체의 안정적인 분산을 위하여 교반과정과 초음파 처리과정을 거쳤으며, 이렇게 분산된 유체는 입도측정과 틴들현상 분석을 통해 분산안정성 평가를 수행하였다. 그 결과, 이성분 나노에멀전 유체의 흡수성능 및 열전달 성능에 대한 분산안정성의 영향 및 흡수식 시스템으로의 적용가능성을 확인하였다.