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미소 농도구배 조건에서 열손실 및 가연한계가 삼지화염의 확산화염에 미치는 영향에 대한 기초 연구
조상문(Sang Moon Cho),이민정(Min Jung Lee),김남일(Nam Il Kim) 대한기계학회 2010 大韓機械學會論文集B Vol.34 No.5
삼지화염 구조는 화염 선단의 구조로서 다루어져 왔으며, 많은 연구자들에 의해 해석적인 방법과 실험적인 방법으로 연구가 되어왔다. 그러나 연료의 종류에 따른 가연한계의 차이가 삼지화염의 구조에 미치는 영향에 대한 연구는 깊이 있게 다루어지지 않았다. 본 연구에서는 화염 구조에 대한 비대칭 가연한계의 영향을 예혼합화염과 확산화염에 관한 몇 가지 층류화염 이론에 근거한 간단한 수치 기법을 통해 연구하였다. 고정된 유동장이 사용되었으며, 예혼합 화염 가지에서의 경계조건이 연계되었다. 예혼합 화염 후류의 확산화염의 형성과 소멸을 성공적으로 모사할 수 있었다. 비대칭 가연한계 조건과 열손실에 따른 확산화염의 변화가 연구되었다. 본 연구는 화염의 기초 구조에 대한 이해를 도울 수 있으며, 이후의 연구를 위한 기초로 활용될 수 있을 것이다. The tribrachial flame has attracted interest as a basic structure of the flame edge. This flame structure helps understand stabilization of laminar flames and re-ignition of turbulent flames. A number of analytical and experimental studies have been carried out on the tribrachial flame. However, the effect of the variation of the flammability limits on the structure of the tribrachial flame has not been studied in detail. In this study, the effect of non-symmetric flammability limits on the flame structure was investigated by adopting a simple numerical scheme based on several laminar flame theories. A fixed velocity field was considered and boundary matching algorithm was used on the premixed branch. The variation of the diffusion branches under the non-symmetric flammability limits and heat loss was investigated. The formation and extinction of the diffusion branch behind the premixed branch were successfully described. This basic study can help understand the fundamental structure of the flame and can form the basis of subsequent detailed studies.
변압기용 방열기 효율 계산을 위한 고전적 접근과 CFD 해석
조상문(Sang Moon Cho),김철숙(Chul Sook Kim) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
Recently, thermal problems in power transformer have been issued due to their lifetime and reliability. With a tendency to minimize a product, accurate prediction about efficiency of radiator becomes more important. In this background, this paper presents the method of calculation to estimate the efficiency of radiator used in power transformer cooling system. Two classical model was adopted to solve heat transfer induced by natural convection between radiator and air boundary. Temperature disribution and heat transfer coefficient were analytically investigated. To compare the result with those real case, CFD analysis and experimental investigation were companied. The overall efficiencies in each case of radiators were lower than we expected because of surrounding conditions which are different to real case. This result can help understand heat transfer phenomena in radiator and utilize to design optimum cooling system of power transformer.
대향류 채널 열재생 연소기의 스케일 변화 효과에 관한 실험적 연구
이민정(Min Jung Lee),조상문(Sang Moon Cho),김남일(Nam Il Kim) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
Small combustors that consist of two channels and a combustion space for heat regeneration were fabricated. To investigate the scale down effect on the flame stabilization, flame stabilization conditions of 50 % scale down stainless combustor was examined and compared with those of a base combustor of stainless. And the effect of material variation was investigated by comparing the flame characteristics of 50% scaled stainless combustor and the 50% scaled quartz combustor. As results, in spite of the significant reduction in the scale of combustor by 50%, flame stabilization conditions was just slightly affected for the same material. However, change in the material of the combustor significantly varied the flame stabilization conditions and the characteristics of flames. One outstanding result is that a well stirred reaction (WSR) mode in which a flame front is strongly disturbed to make a broad reaction zone was easily observed in quartz combustors and the experimental conditions corresponding to the WSR mode were wide. These results show that the development of a smaller heat regenerative combustor is still possible and the application of the smaller combustor as a kind of fuel reformer is also possible.
좁은 채널 내의 대향분류 메탄-공기 비예혼합 화염의 거동 특성
윤영민(Young Min Yun),이민정(Min Jung Lee),조상문(Sang Moon Cho),김남일(Nam Il Kim) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.4
Characteristics of a counter flowing diffusion flame, which is formulated by an oppositely-injected methane-jet flow in a narrow channel of a uniform air flow. The location of the flame fronts and the flame lengths were compared by changing the flow rates of fuel. To distinguish the effects of the narrow channel on the diffusion flame, a numerical simulation for an ideal two-dimensional flame was conducted. Overall trends of the flame behavior were similar in both numerical and experimental results. With the increase of the ratio of jet velocity to air velocity flame front moved farther upstream. It is thought that the flow re-direction in the channel suppresses fuel momentum more significantly due to the higher temperature and increased viscosity of burned gas. Actual flames in a narrow channel suffer heat loss to the ambient and it has finite length of diffusion flame in contrast to the numerical results of infinite flame length. Thus a convective heat loss was additionally employed in numerical simulation and closer results were obtained. These results can be used as basic data in development of a small combustor of a nonpremixed flame.
김철숙(Chul-Sook Kim),차창환(Chang-Hwan Cha),조상문(Sang-Moon Cho),이승호(Seung-Ho Lee) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
Vegetable oil is the clean insulation oil which has less problem when there is the oil leakage from the transformers due to accidents or explosion of them because the biodegradability of vegetable oil is over 90%. Also it has advantage as noninflammable oil due to over 300℃ flashing point. Even though vegetable oil has many advantages, it has limitations as low cooling performance due to three times higher viscosity than existing mineral oil and poor insulation characteristic caused by high moisture content and water affinity. In this paper, we estimated the cooling performance between the mineral and vegetable oil. In the case of vegetable oil, this could predict that the temperature rise of top oil will increase about 4℃ than that of mineral oil. Also, on the basis of these results we can suggest cooling design to substitute vegetable oil for mineral oil.