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Oh, Seungtae,Ko, Won-Ha IOP Pub 2011 Measurement Science and Technology Vol.22 No.4
<P>The collective optical design is described for the charge exchange spectroscopy (CES) of the Korea superconducting tokamak advanced research (KSTAR) device. The CES diagnostic measures the ion temperature of carbon and other impurities, in conjunction with the neutral heating beam in KSTAR. The visible light from the plasma is concentrated via collection optics and imaged onto quartz fibers. The collection optics in the system is the key component for the CES system. The final design is derived through four steps and its performance is examined in a simulation step. In this paper, the design details of the collective optical system for the KSTAR CES are discussed.</P>
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.
김승태(Seungtae Kim),박서현(Seohyeon Park),손세호(Seho Son),오종석(Jongseok Oh) 한국경제통상학회 2021 경제연구 Vol.39 No.4
본 연구는 사업체패널 1~7차 데이터를 활용하여 임금피크제 도입에 따른 고용효과를 실증적으로 분석하였다. 이 때, 관찰되지 않은 개별 기업들의 특성을 통제하지 못하면 내생성 문제가 발생하여 올바른 추정량을 얻지 못하게 된다. 이에 본 연구는 고정효과모형(Fixed Effect: FE)을 활용하여 시간에 대해 변하지 않는 기업의 특성들을 통제하여 내생성 문제를 완화하였고, 단기간에 그친 임금피크제 효과 분석을 다기간으로 확장하였다. 분석 결과, 임금피크제의 도입은 단기간, 장기간에 걸쳐 고용에 영향을 미치지 않는 것으로 나타났다. 다만 임금피크제 도입 이후 시간이 지날수록 정규직 비율이 낮아지고 비정규직 비율이 높아지는 것으로 나타났다. 이는 임금피크제 도입에 따른 고용효과를 개선하기 위해 인력 운용과 관련한 실질 적인 논의가 필요하다는 것을 시사한다. Using the Workplace Panel Survey(WPS) data, This paper examined the employment effect of introducing the wage peak system. Conducting an analysis without consideration regarding unobserved characteristics of a company may lead to problem with endogeneity. Based on the Fixed Effect(FE) Model, this paper alleviated this problem and analysed the effect for a long period. The results do not show any evidence that introducing the wage peak system has both long-term and short-term impacts on employment. As time goes by since the introduction of wage peak system, the rate of regular workers decreased while the rate of regular workers irregular increased. With considerations the current trend that the wage peak system has been implemented, this paper suggests that there should be deeper discussion pertaining to human resource management to have a positive effect on the pending employment rate issue.
Seo, Donghyun,Oh, Seungtae,Shin, Seungwon,Nam, Youngsuk Pergamon Press 2017 International journal of heat and mass transfer Vol. No.
<P><B>Abstract</B></P> <P>We present the dynamic heat transfer analysis of condensed droplets growing and coalescing on hydrophobic (HPo) and superhydrophobic (SHPo) surfaces using a full 3D numerical simulation. In the model, two water droplets surrounded by fully-saturated water vapor grow on a horizontal surface through condensation until they coalesce together. The dynamic changes in the interfacial areas, temperature distributions and heat flux through each interface were analyzed. The effects of vapor phase temperature distribution, parasitic thermal resistance and surface flooding on the heat transfer rate are also quantified. The results show that a relatively high heat transfer rate through solid–vapor interface on SHPo partially compensates the low heat transfer rate through solid–liquid interface. The parasitic thermal resistance of the suggested SHPo may reduce the heat transfer performance over 30%. When the flooding occurs on HPo, the heat transfer rate rapidly decreases below a half of the value obtained at the beginning of coalescence. This work shows the importance of the heat transfer analysis considering dynamic changes in the interfacial area and resulting 3D temperature distributions, and will help develop the optimal condensation heat transfer surfaces.</P> <P><B>Highlights</B></P> <P> <UL> <LI> 3D dynamic thermal analysis of growing and merging condensates was performed. </LI> <LI> Dynamic changes in interfacial areas, temperature distribution were analyzed. </LI> <LI> The importance of vapor phase temperature on heat transfer rate was reported. </LI> <LI> The effects of parasitic thermal resistances and flooding on heat transfer were quantified. </LI> <LI> The framework for accurately predicting the condensation heat transfer was suggested. </LI> </UL> </P>
Seo, Donghyun,Oh, Seungtae,Moon, Byungyun,Kim, Hyunsik,Kim, Juhyok,Lee, Choongyeop,Nam, Youngsuk Elsevier 2019 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.128 No.-
<P><B>Abstract</B></P> <P>Condensation frosting causes serious economic and safety problems in many industrial applications. Recently, lubricant-impregnated surfaces (LIS) have been attracting much interest with their excellent anti-frosting ability. The facilitated removal of drops due to the low contact angle hysteresis of LIS has been suggested as the frosting suppression mechanism. Here, we demonstrate a hitherto-unexplored microscale frosting suppression mechanism on LIS by investigating microscopic condensation and freezing dynamics on LIS by varying the viscosities of the lubricants. Based on the ice propagation model, we show that the frosting propagation is suppressed on LIS with a low viscosity oil where the coalescence of droplets is promoted by the presence of oil. On the contrary, the coalescence between droplets is interrupted on LIS with a high viscosity oil, which facilitates the frost propagation. The criteria for the delay of condensation frosting were explained based on the competition between the lubricant drainage time and the drop growth time scale. Finally, we verify that microscopic frosting suppression mechanism of LIS persists up to macroscopic level by demonstrating that LIS is effective in suppressing condensation frosting on heat exchangers.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Frosting delay on lubricant impregnated surfaces was investigated. </LI> <LI> Overlapped oil meniscus induced an active drop coalescence and frosting delay. </LI> <LI> Frost was quickly propagated on high viscosity lubricant due to drop packing phenomena. </LI> <LI> The packing phenomena was analyzed by considering oil drainage time and drop growth time. </LI> <LI> Suggested frosting delay mechanism was applied to macroscopic heat exchangers. </LI> </UL> </P>
산업용 버너에서의 LNG, LPG/Air 연소특성 비교연구
오창용(Changyong OH),성연모(Yonmo SUNG),김승태(Seungtae KIM),유승우 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
The influence of gaseous fuel type and load on flame characteristics was experimentally investigated in a 1.3 MWth reheating furnace burner. In this study, LNG, LPG, and LPG/Air were selected as fuel, and fuel loads were set to 15%, 30%, and 60% in order to study gas interchangeability. The experimental results showed that the fuel change shows minor effect on the flame appearance for different fuel load conditions. The flame straightness performance was degraded under 30% fuel load conditions. The flame straightness performance was improved by injection of the burner center air. Minimum 10% air was required to improve the flame straightness performance compared to without burner center air conditions.