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전기방사법으로 제조된 Cu<sub>2</sub>O-PVP 나노사의 전기적 특성
곽기열,조경아,윤정권,김상식,Kwak, Ki-Yeol,Cho, Kyoung-Ah,Yun, Jungg-Won,Kim, Sang-Sig 한국전기전자재료학회 2009 전기전자재료학회논문지 Vol.22 No.8
Hybrid nanofibers made of $Cu_2O$ and polyvinyl pyrrolidone were fabricated by electrospinning on glass substrates. The current magnitude of the $Cu_2O$-PVP hybrid nanofibers is 10 times larger than that of pure PVP nanofibers. In addition, $Cu_2O$-PVP nanofibers possess high sensitivity to air at room temperature than pure PVP nanifibers.
Forming-Die-Free Integrated Stub-End Manufacturing Process using Spinning
곽기열,조종래,최진영,김재수 한국정밀공학회 2016 International Journal of Precision Engineering and Vol.17 No.5
Stub ends are used to connect pipes in piping arrangements and are generally manufactured by welding two sub-components. This welding process is time consuming and causes pollution. Stub ends can also be produced without welding via a general spinning process using thicker pipe; however, the production cost is high, because different forming dies must be prepared in order to obtain various stub end sizes. Material loss also occurs. A flexible manufacturing process that does not use forming dies is proposed in this paper. The stub-end shape is formed by rolling dies instead of an outer mold. During this process, the lap roller motion is dependent on the required degree of forming. To determine the effects of the process parameters and to identify the optimal process, a commercial finite-element-method (FEM) code, DEFORM Ver. 11.0, is employed here. The lap-guide and lap-roller movement speeds are the main process parameters. Based on the simulation results, a 3-inch stub end meeting the ASME B16.9-2007 code requirements is fabricated. After production, the forming load is examined and the measured pressure on the ring roller is found to agree with the calculated value. The dimensions of each part of the stub end also satisfy requirements.
Development of Integrated Stub End by Spinning Process
곽기열,전종원,조종래,최진영,김재수 한국정밀공학회 2015 International Journal of Precision Engineering and Vol. No.
The stub end is used to connect pipes in piping arrangement. Generally the components are manufactured by welding two subcomponents. But this method requires a large amount of time and money and also has a problem due to welding process like thermal deformation or embrittlement at heat affected zone. The spinning process, eco-friendly incremental process, was adopted to develop stub end without weld. It allows the component to be produced by non-welding with low cost and short process time. The major goal of this study is to develop optimum spinning process for manufacturing integrated stub end in keeping with the dimensions presented in the code. The suitable multi-step spinning process and rollers which can set required shapes and dimensions at each location of the component were designed by simulation. Base on the result of analysis and test, the 4 inch’s stub end specified in the code was developed. The spinning machine was also developed to manufacture specimens. Hardness was measured to predict the strength of flange part. Along with the shapes, all dimensions at each part were satisfied the required values.
Optoelectronic Characteristics of Transparent Cu₂O Films Spin-coated on Glass Substrates
곽기열(Kiyeol Kwak),조경아(Kyoungah Cho),김상식(Sangsig Kim) 대한전기학회 2010 전기학회논문지 Vol.59 No.1
Cu₂O nanoparticles-based films are fabricated by spin-coating on glass substrates and their optoelectronic characteristics are investigated in this study. The Cu₂O films are nearly all-transparent as high as 98% in a wavelength range from 400 ㎚ to 900 ㎚ and three exciton peaks associated with the sublevels in the conduction band are observed at the wavelengths shorter than 400 ㎚ in the absorption spectrum. Under the illumination of the 325 ㎚ wavelength light, the photocurrent efficiency of the Cu₂O film is 1.8×10? ㎂/W at a voltage of 2.5 V in air.
Viscosity and thermal conductivity of copper oxide nanofluid dispersed in ethylene glycol
김종엽,곽기열 한국유변학회 2005 Korea-Australia rheology journal Vol.17 No.2
Nanofluid is a novel heat transfer fluid prepared by dispersing nanometer-sized solid particles in traditional heat transfer fluids to increase thermal conductivity and heat transfer performance. In this research we have considered the rheological properties of nanofluids made of CuO particles of 10-30 nm in length and ethylene glycol in conjunction with the thermal conductivity enhancement. When examined using TEM, individual CuO particles have the shape of prolate spheroid of the aspect ratio of 3 and most of the particles are under aggregated states even after sonication for a prolonged period. From the rheological property it has been found that the volume fraction at the dilute limit is 0.002, which is much smaller than the value based on the shape and size of individual particles due to aggregation of particles. At the semi-dilute regime, the zero shear viscosity follows the Doi-Edwards theory on rodlike particles. The thermal conductivity measurement shows that substantial enhancement in thermal conductivity with respect to particle concentration is attainable only when particle concentration is below the dilute limit.
신 장애물제한표면에 관한 이론적 고찰과 실증분석 - 인천국제공항을 중심으로 -
최상일,유수정,곽기열,김현미,김휘양,Choi, Sangil,Yu, Soojeong,Kwak, Kiyeol,Kim, Hyeonmi,Kim, Huiyang 한국항공운항학회 2022 한국항공운항학회지 Vol.30 No.3
Obstacle Limitation Surface (OLS) is conceptual surface establishing the airspace around aerodromes to be maintained from obstacles to ensure safe aircraft operations. Despite advances in the technologies for aircraft, navigation systems and the development of new flight procedures, the criteria defining OLS have not been amended since its initial establishment, resulting in the overestimation of areas for height restriction. As there were requests to examine OLS at the 12th Air Navigation Conference and the 38th ICAO Assembly, the research on the OLS revision began in earnest and ICAO has proposed Obstacle Free Surface (OFS) and Obstacle Evaluation Surface (OES) as an alternative of the existing OLS. OFS is surfaces where obstacles shall not be permitted, and OES is ones where obstacles be evaluated with an aeronautical study and could be permitted under some conditions. The purpose of this study is to preemptively assess the efficiency and safety of OFS and OES by applying them to the second runway (15L/33R) of Incheon International Airport. The results show that OFS and OES are capable of serving the instrument flight procedure safely with a smaller obstacle clearance area compared to the existing OLS.