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Hot Wall Epitaxy(HWE)법에 의한 CdGa<sub>2</sub>Se<sub>4</sub> 단결정 박막 성장과 열처리 효과
홍명석,홍광준,Hong, Myung-Seok,Hong, Kwang-Joon 한국전기전자재료학회 2007 전기전자재료학회논문지 Vol.20 No.10
The stochiometric mix of evaporating materials for the $CdGa_2Se_4$ single crystal thin films was prepared from horizontal furnace. To obtain the single crystal thin films, $CdGa_2Se_4$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperature were $630^{\circ}C$ and $420^{\circ}C$, respectively. The crystalline structure of single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD).The carrier density and mobility of $CdGa_2Se_4$ single crystal thin films measured from Hall effect by van der Pauw method are $8.27{\times}10^{17}\;cm^{-3},\;345\;cm^2/V{\cdot}s$ at 293 K. respectively. The temperature dependence of the energy band gap of the $CdGa_2Se_4$ obtained from the absorption spectra was well described by the Varshni's relation, $Eg(T)\;=\;2.6400\;eV\;-\;(7.721{\times}10^{-4}\;eV/K)T^2/(T+399\;K)$. After the as-grown single crystal $CdGa_2Se_4$ thin films were annealed in Cd-, Se-, and Ga -atmospheres, the origin of point defects of single crystal $CdGa_2Se_4$ thin films has been investigated by PL at 10 K. The native defects of $V_{Cd}$, $V_{Se}$, $Cd_{int}$, and $Se_{int}$ obtained by PL measurements were classified as donors or accepters. We concluded that the heat-treatment in the Cd-atmosphere converted single crystal $CdGa_2Se_4$ thin films to an optical p-type. Also, we confirmed that Ga in $CdGa_2Se_4/GaAs$ did not form the native defects because Ga in single crystal $CdGa_2Se_4$ thin films existed in the form of stable bonds.
서동표(Dong-Pyo Seo),홍명석(Myung-Seok Hong),오율권(Yool-Kwon Oh) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
The characteristics of upward bubble flow were experimentally investigated in a liquid bath, In the present study, a thermal-infrared camera and high speed CCD camera were used to measure their temperature and local rising velocity, respectively. Heat transfer from bubble surface to tater is largely completed within z=10mm from the zozzle, and then the temperature of bubble surface reaches that of water rapidly. The rising velocity of bubble was calculated for two different experimental conditions: 1) bubble flow without kinetic energy 2) with kinetic energy. Bubble flow without kinetic energy starts to undergo the effect of inertia force 10cm away from the nozzle. Whereas, kinetic energy is dominant before 30 cm away from the nozzle in bubble flow, but after this point, kinetic energy and inertial force are applied on bubble flow at the same time.
SI 엔진에서 Fractal Geometry를 이용한 난류 연소 모델
홍명석,손정배 조선대학교 에너지.자원신기술연구소 1998 에너지·자원신기술연구소 논문지 Vol.20 No.2
Use of fractal geometry to model the effects of turbulence on flame propagation in an engine is explored using a quasidimensional, 4-stroke, homogeneous charge, SI engine code. Various assumptions are made in the model formulation to allow this technique to be investigated as expeditiously as possible. Model predictions are compared to experimental data from an engine with an axisymmetric pancake-shaped combustion chamber. The sensitivity of the model predictions to the fractal dimension, to the effects of flame stretch, and to the ratio of maximum-to-minimum flame wrinkling scales is invested. It is shown that the predicted initial rate of pressure rise is a strong function of fractal dimension but is relatively insensitive to the flame wrinkling scales or the effects of stretch over the ranges of these parameters expected for the engine application. This model and a modification of this model appear to be reasonable and yield values for the fractal dimension which agree with the limited experimental engine data avaliable. It is shown that flame stretch is dominated by flame strain and decrease throughout the combustion process. By allowing the maximun flame wrinkling scale to be equal to the instantaneous flame radius, the correct trend of the turbulent flame speed is predicted. The model results that the use of fractals to model turbulent combustion is an important new tool for engineering design.
직접분사 성층 연소방식에서 수소의 첨가에 의한 연소성능의 개선
홍명석,하옥남 조선대학교 생산기술연구소 1995 生産技術硏究 Vol.17 No.1
The direct injection stratified charge (DISC) engine is considered to be an alternative to the conventional spark ignition engines. Its actual utilization is, however, prevented by high emission levels of unburned hydrocarbons during light load operation. Over-lean mixtures due to the long combustion duration and wall quenching due to these lean mixtures will be the main causes of unburned hydrocarbons in the DISC system. In order to solve this problem, small amount of hydrogen was added to the charging air or injected fuel. When hydrogen was added to the charge of air, the combustion pressure was increased and the unburned hydrocarbons was reduced with increasing the amount of hydrogen addition. In the case hydrogen was added to the fuel, the combustion pressure was more increased than the case that the same amount of hydrogen was added to the charge.
엔진 연소실 내에서 노크와 화염 소화가 발생할 때의 열전달 모델링
홍명석,안철봉 조선대학교 생산기술연구소 1996 生産技術硏究 Vol.18 No.2
Heat transfer rates present in an engine cylinder undergoing knock are known to be larger than the rates associated with normal engine operation. Further, at the time of knock the largest heat fluxes are associated with locations on the cylinder wall where the flame is locally quenching. In this study, heat transfer processes at the flame wall interface during a knock event are analytically and computationally investigated. Computationally, the governing equations for a one dimensional flame quenching event are solved using a reduced chemical reaction mechanism. Analytically, scaling relations for the flame heat release rates are used in the governing equations to determine the heat transfer rates. It is found that while pressure transients modify the wall heat flux. the absolute value of the pressure is the most significant parameter in predicting the maximum heat flux. The magnitudes of the peak wall heat flux are accurately predicted with respect to the peak pressure for both the analytical and computational models. In the range of pressure examined, a linear relationship was found between the peak flux and pressure both for the computational and analytical models. The linear relationxhip between the pressure and the peak flux was found to be invalid when the flame quenching process was disrupted by the pressure fluctuations for pressure oscillations with characteristic time on the order of the quenching process.
반응섬을 갖는 예혼합 난류 화염 구조와 연소속도의 모델
홍명석 朝鮮大學校 機械技術硏究所 1999 機械技術硏究 Vol.2 No.1
예혼합 난류화염구조에 대한 모델을 개발하였다. 여기서 난류화염의 화염대는 주름상화염면과 그 뒷면을 이은 섬형화염면의 두 부분으로 구성되어 있다. 그 두 부분의 구성비율은 난류강도 u´와 층류화염속도인 S??의 함수인 u´/S 에 의해 연속적으로 변한다고 가정되었다 모든 화염면은 프랙탈(fractal)형상으로 가정되었다. 난류화염의 모델에 층류화염의 화염두께와 특성시간의 개념이 이용되었다. 본 모델에 의한 화염구조의 여러 인자뿐만 아니라 난류화염의 연소 속도를 예상할 수 있다. A model for the premixed turbulent flame structure has been developed in which the flame zone of a turbulent flame is composed of two parts : a wrinkled flame front and some island flamelets behind it. Their fractions are supposed to vary continuously according to a proposed function of u´/S , where u´ is the turbulence intensity and S is the laminar burning velocity. All flamelets were assumed to be fractal ones. The concepts of "flame thickness" and "transition time" for laminar flames were introduced into the model for turbulent flames. The model provides not only the structural parameter but also the burning velocities of turbulent flames.