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안내덕트 내부 난류유동구조에 따른 열전달 특성변화 수치해석
유근종(Geun Jong Yoo),최훈기(Hoon Ki Choi),최기림(Kee Lim Choi) 대한기계학회 2011 大韓機械學會論文集B Vol.35 No.9
본 연구에서는 복합화력발전소 가스터빈 출구가스 안내덕트 내부의 가스유동장이 배열회수보일러 전열기구에 미치는 영향을 CFD기법을 이용하여 분석하였다. 안내덕트 내부 난류흐름의 경우, 유속의 편차가 크고 선회 효과 및 상승류 현상이 심한 특징을 가지고 있음으로 이와 같은 유동의 수치해석을 위해 2개 방정식 난류점성 모델 중 RNG k-? 모델을 사용하였으며 유동장의 영향을 가장 많이 받는 배열 회수보일러 최종과열기관의 열전달특성변화를 파악하기위하여 NTU 방식을 이용한 수치해석결과와, 산업계에서 적용하는 설계기법에 의한 결과를 비교하였다. Because of the instability of a flow pattern in the inlet transition square duct (hereinafter referred to as “transition duct”) of a heat recovery steam generator (hereinafter referred to as “HRSG”) in a combined cycle power plant, the Reynolds number in the first row of a tube bank is differs sharply from that in the sectional area of the transition duct. This causes differences in the heat flux in each tube in the tube bank. The computational fluid dynamics (CFD) predictions provide three-dimensional results for velocity, temperature, and other flow parameters over the entire domain of the duct and HRSG. A renormalization group theory (RNG) based k-? turbulent model is used for obtaining the results cited in this study. A porous media option is used for modeling the tube banks and the number of transfer units method is used for determining the heat transfer characteristics. This study describes a comparison between the numerical simulation results and actual design output.
지원 및 상황중심적 숲활동 과정에서 나타난 유아와 교사의 적응적 변화
유근종(Yoo, Keun-Jong),이대균(Lee, Dae-Kyun) 한국열린유아교육학회 2018 열린유아교육연구 Vol.23 No.2
본 연구는 수도권 도시지역의 유치원에서 지원 및 상황중심적 숲활동을 실행하는 과정에서 보이는 유아 및 교사의 반응과 변화의 내용이 어떠한지를 살펴보는 연구이다. 연구현장은 연구자가 숲활동 프로그램을 실시하고 있는 두 곳의 유치원으로 주 1회 숲활동을 실시하고 있다. 연구를 위한 자료는 2015년 4월부터 12월까지 수집된 교사의 자기보고서, 집중질문지, 면담 등이었고, 근거이론에 따라 이를 분석하였다. 연구결과 숲을 만나는 유아들은 초기 반응을 거쳐 숲에 적응하였고 신체적·인지적·정서적으로 성장하고 있었다. 계절의 변화 속에서 숲길을 오고가거나 놀이하는 과정을 통해 신체적으로 변화하였고, 숲에서 자신의 생각을 변형시키고 창의적 문제해결과 공간구성 하기 등을 통해 인지적으로, 그리고 자연과 만나는 경험이 증가하면서 즐거움, 친밀감, 생명의 소중함을 알게 되는 등 정서적으로 변화하였다. 또한, 교사는 숲에서 보이는 초기반응을 거치면서 숲활동에 대한 긍정적 인식을 갖게 되었고, 계절의 변화와 함께 숲에서 겪는 다양한 경험과 교수 활동을 통해 궁극적으로 숲활동 교수능력의 향상을 보이고 있었다. The purpose of this study is to investigate reaction and changes in young children and teachers through forest activities in metropolitan kindergartens. The research field for this study is two kindergartens in which the researchers have been implementing forest activities program once a week. The data used for this research included self-reports, intensive questionnaire, and interviews collected from April to December, 2016, and they were analyzed based on grounded theory. As a result, infants were gradually growing physically, cognitively, and emotionally as they went through initial reaction while visiting forests. Along with seasonal changes, infants experienced physical changes through visiting and playing in the forests, cognitive changes through creative problem solving and space composition, not to mention changes in thought process in the forests, and emotional changes, such as awareness of joy, intimacy, and importance of life as infants’ experience with nature increased. In addition, teachers gradually learned to possess positive awareness about forest and forest activities as they went through initial reaction, and the teachers demonstrated ultimate improvement in their ability with forest activities through various experiences and teaching activities in the forests along with seasonal changes.
유근종(Geun Jong Yoo),최훈기(Hoon Ki Choi),최기림(Kee Lim Choi),신병주(Byeong Ju Shin) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.7
Configuration of the inlet transition square duct (hereinafter referred to as "transition duct") for heat recovery steam generator (hereinafter referred to as "HRSG") in combined cycle power plant is limited by the construction type of HRSG and plant site condition. The main purpose of the present study is to analyze the effect of a variation in turbulent flow pattern by roof slop angle change of transition duct for horizontal HRSG, which is influencing heat flux in heat transfer structure to the finned tube bank. In this study, a computational fluid dynamics(CFD) is applied to predict turbulent flow pattern and comparisons are made to 1/12th scale cold model test data for verification. Re-normalization group theory (RNG) based k-ε turbulent model, which improves the accuracy for rapidly strained flow and swirling flow in comparison with standard k-ε model, is used for the results cited in this study. To reduce the amount of computer resources required for modeling the finned tube bank, a porous media model is used.
소산율 방정식의 개선을 통한 저레이놀즈수 k-.epsilon. 모형의 개발
송경,유근종,조강래,Song, K.,Yoo, G.J.,Cho, K.R. 대한기계학회 1998 大韓機械學會論文集B Vol.22 No.5
Series of recent k-.epsilon. model modification have been carried out with the aid of DNS data to include the effect of near wall. Though these methods opened new way of turbulence modelings, newly developed turbulence models of its kind had yet shortcomings in prediction for the turbulent flows with various Reynolds numbers and various geometric conditions. As a remedy for these shortcomings, a new k-.epsilon. model proposed here by improving the dissipation rate equation and the damping function for eddy viscosity model. The new dissipation rate equation was modeled based on the energy spectrum and magnitude analysis. The damping function for eddy viscosity was also formulated on the ground of distribution of dissipation rate length scales near a wall and the DNS data. The new k-.epsilon. model was applied to the fully developed turbulent flows in a channel and a pipe with a wide range of Reynolds numbers. Prediction results showed that the present model represents properly the turbulence properties in all turbulent regions over a wide range of Reynolds numbers.
보텍스튜브 유동의 에너지분리 및 열역학특성에 관한 수치적 연구
최훈기(H.K. Choi),유근종(G.J. Yoo),임윤승(Y.S. Lim) 한국전산유체공학회 2018 한국전산유체공학회지 Vol.23 No.2
A vortex tube is a simple energy separating device which splits a compressed air stream into a cold and hot stream without any external energy supply or chemical reactions. In this article computational fluid dynamics analysis of a 3-D steady state and turbulent flow has been carried out through a vortex tube. The present research has focused on the energy separation and thermodynamic behavior of a vortex tube have been investigated. The temperature separation occurs because of the heat transfer from the central flow to the peripheral flow. Through the interpretation of the second law of thermodynamics, the generation of entropy shows that irreversible processes occur in the vortex tube.
루프 환기구에 따른 보일러빌딩 내부 환기성능에 관한 수치적 연구
최훈기 ( Hoon Ki Choi ),유근종 ( Geun Jong Yoo ),이상헌 ( Sang Heon Lee ) 한국산업보건학회 (구 한국산업위생학회) 2016 한국산업보건학회지 Vol.26 No.3
Objectives: The objective of this paper is to find flow and heat transfer characteristics numerically in boiler buildings for three different ventilation window configurations. Methods: Turbulent natural convection flow in boiler buildings with a constant heating wall temperature was analyzed numerically . Governing equations were solved with standard finite-volume method using the SIMPLE algorithm. Conclusions: Flow and heat transfer characteristics are found for three different ventilation types. In the lower area under furnace, velocity and temperature distributions show similar patterns among the three different ventilation types. In the upper area over furnace, however, air flow is well mixed with lower peak temperatures for types B and C, which have roof ventilation windows, compared to type A which has side wall louvers only. Also, type B, with a single large roof window, shows better ventilation effect than does type C with its distribution roof windows.