• International Journal of Fuzzy Logic and Intelligent Systems
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• v.1 no.1
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• pp.87-94
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• 2001

Silicon nitride films grown by plasma-enhanced chemical vapor deposition (PECVD) are useful for a variety of applications, including anti-reflecting coatings in solar cells, passivation layers, dielectric layers in metal/insulator structures, and diffusion masks. PECVD systems are controlled by many operating variables, including RF power, pressure, gas flow rate, reactant composition, and substrate temperature. The wide variety of processing conditions, as well as the complex nature of particle dynamics within a plasma, makes tailoring SiN film properties very challenging, since it is difficult to determine the exact relationship between desired film properties and controllable deposition conditions. In this study, SiN PECVD modeling using optimized neural networks has been investigated. The deposition of SiN was characterized via a central composite experimental design, and data from this experiment was used to train and optimize feed-forward neural networks using the back-propagation algorithm. From these neural process models, the effect of deposition conditions on film properties has been studied. A recipe synthesis (optimization) procedure was then performed using the optimized neural network models to generate the necessary deposition conditions to obtain several novel film qualities including high charge density and long lifetime. This optimization procedure utilized genetic algorithms, hybrid combinations of genetic algorithm and Powells algorithm, and hybrid combinations of genetic algorithm and simplex algorithm. Recipes predicted by these techniques were verified by experiment, and the performance of each optimization method are compared. It was found that the hybrid combinations of genetic algorithm and simplex algorithm generated recipes produced films of superior quality.

• Journal of the Korean Society of Combustion
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• v.19 no.3
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• pp.18-25
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• 2014

Bottom ash from a coal-fired power plant is usually landfilled to a nearby site, which causes a growing environmental concern and increased operating costs. One way of recycling the bottom ash is to produce light-weight aggregate (LWA) using a rotary kiln. This study investigated the temperature profiles of raw LWA particles in a rotary kiln to identify the range of operating conditions appropriate for ideal bloating. For this purpose, a new simulation method was developed to integrate a 1-dimensional model for the bed of LWA particles and the computational fluid dynamics (CFD) for the fuel combustion and gas flow. The temperature of LWA particles was found very sensitive to the changes in the air preheating temperature and excess air ratio. Therefore, an accurate control of the operation parameters was essential to achieve the bloating of LWA particles without excessive sintering or melting.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.117-117
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• 2010

나노입자 제조 기술이 점차 발전하면서 금속산화물, 반도체용 및 태양전지용, 신소재 등 다양한 응용분야에 사용하고 있다. 따라서 이와 같은 나노입자 제조방법으로는 펄스 레이저 용사법(pulsed laser ablation), 플라즈마 아크 합성법(plasma arc synthesis), 열분해법(pyrolysis), plasma-enhanced chemical vapor deposition (PECVD)법 등과 같은 기상공정이 많이 사용되고 있다. 기상공정은 기존의 공정에 비해 고순도 입자의 대량 생산, 다성분 입자의 화학적 균질성 유지, 비교적 간단하고 깨끗한 공정 등의 장점을 가지고 있다. 기상공정에서 일반적인 입자 형성 메커니즘은 기체 상태의 화학 물질이 물리적 공정 혹은 화학 반응에 의해 과포화상태에 도달하게 되며, 이 때 동질 핵생성(homogeneous nucleation)이 일어나고 생성된 핵(nuclei)에 기체가 응축되고 충돌, 응집하면서 입자는 성장하게 된다. 열분해법은 실리콘 나노입자를 생산하는 기상공정 중 하나이다. 일반적으로 열분해 공정은 지속적으로 열이 가해지는 반응기 내에 반응기체인 $SiH_4$을 주입하고, 운반기체는 He, $H_2$, Ar, $N_2$ 등을 사용하였을 때, 높은 열로 인해 $SiH_4$가 분해되며, 이 때 가스-입자 전환 현상(gas to particle conversion)이 일어나 실리콘 입자가 형성된다. 그러나 입자 형성과정은 $SiH_4$ 농도, 유량, 작동 압력, 온도 등 매우 다양한 요소에 영향을 받는다. 고, 복잡한 화학반응 메커니즘에 의해 명확히 규명되지는 못하고 있다. 이에 본 연구에서는 복잡한 화학반응을 해석하는 상용코드 CHEMKIN 4.1.1을 이용하여 열분해 반응기 내에서의 실리콘 입자 형성, 성장, 응집, 전송 모델을 만들고 이를 수치해석하였다. 표면 반응, 응집, 전송에 의한 입자 성장 메커니즘을 포함하고 있는 aerosol dynamics model을 method of moment법으로 해를 구하였으며, 이를 실험 결과와 비교하여 모델링을 검증하였다. 또한 반응기의 온도, 압력, 가스 농도, 유량 등의 요소를 고려하여 실리콘 나노입자를 형성하는 최적의 조건을 연구하였다.

• 한국가시화정보학회:학술대회논문집
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• 2002.11a
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• pp.1-6
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• 2002

How is the flow in a rotating impeller. About 35 years have passed since one experimentalist rotating with the impeller. of a huge centrifugal blower made the flow measurements using a hot-wire anemometer (Fowler 1968). Optical measurement methods have great advantages over the intrusive methods especially for the flow measurement in a rotating impeller. One is the optical flow visualization (FV) technique (Senoo, et al., 1968) and the other is the application of laser velocimetry (LV) (Hah and Krain, 1990). Particle image velocimetries (PIVs) combine major features of both FV and LV, and are very attractive due to the feasibility of simultaneous and multi-points measurements (Hayami and Aramaki, 1999). A high-pressure-ratio transonic centrifugal compressor with a low-solidity cascade diffuser was tested in a closed loop with HFC134a gas at 18,000rpm (Hayami, 2000). Two kinds of measurement techniques by image processing were applied to visualize a flow in the compressor. One is a velocity field measurement at the inducer of the impeller using a PIV and the other is a pressure field measurement on the side wall of the cascade diffuser using a pressure sensitive paint (PSP) measurement technique. The PIV was successfully applied for visualization of an unsteady behavior of a shock wave based on the instantaneous velocity field measurement (Hayami, et al., 2002b) as well as a phase-averaged velocity vector field with a shock wave over one blade pitch (Hayami, et al., 2002a. b). A violent change in pressure was successfully visualized using a PSP measurement during a surge condition even though there are still some problems to be overcome (Hayami, et al., 2002c). Both PIV and PSP results are discussed in comparison with those of laser-2-focus (L2F) velocimetry and those of semiconductor pressure sensors. Experimental fluid dynamics (EFDs) are still growing up more and more both in hardware and in software. On the other hand, computational fluid dynamics (CFDs) are very attractive to understand the details of flow. A secondary flow on the side wall of the cascade diffuser was visualized based either steady or unsteady CFD calculations (Bonaiuti, et al.,2002). EFD and CFD methods will be combined to a hybrid method being complementary to each other. Measurement techniques by image processing as well as CFD calculations give a huge amount of data. Then, data mining technique will become more important to understand the flow mechanism both for EFD and CFD.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.2
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• pp.165-174
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• 2010

The numerical modeling of a coal gasification reaction occurring in an entrained flow coal gasifier is presented in this study. The purposes of this study are to develop a reliable evaluation method of coal gasifier not only for the basic design but also further system operation optimization using a CFD(Computational Fluid Dynamics) method. The coal gasification reaction consists of a series of reaction processes such as water evaporation, coal devolatilization, heterogeneous char reactions, and coal-off gaseous reaction in two-phase, turbulent and radiation participating media. Both numerical and experimental studies are made for the 1.0 ton/day entrained flow coal gasifier installed in the Korea Institute of Energy Research (KIER). The comprehensive computer program in this study is made basically using commercial CFD program by implementing several subroutines necessary for gasification process, which include Eddy-Breakup model together with the harmonic mean approach for turbulent reaction. Further Lagrangian approach in particle trajectory is adopted with the consideration of turbulent effect caused by the non-linearity of drag force, etc. The program developed is successfully evaluated against experimental data such as profiles of temperature and gaseous species concentration together with the cold gas efficiency. Further intensive investigation has been made in terms of the size distribution of pulverized coal particle, the slurry concentration, and the design parameters of gasifier. These parameters considered in this study are compared and evaluated each other through the calculated syngas production rate and cold gas efficiency, appearing to directly affect gasification performance. Considering the complexity of entrained coal gasification, even if the results of this study looks physically reasonable and consistent in parametric study, more efforts of elaborating modeling together with the systematic evaluation against experimental data are necessary for the development of an reliable design tool using CFD method.

• Korean Chemical Engineering Research
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• v.59 no.3
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• pp.417-428
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• 2021

The combustion characteristics of anthracite, which follow a complex process with low reactivity, must be considered through the dynamic behavior of circulating fluidized bed (CFB) boilers. In this study, computational fluid dynamics (CFD) simulation was performed to analyze the combustion characteristics of anthracite in a pilot scale 0.1 MW_th Oxy-fuel circulating fluidized bed (Oxy-CFB) boiler. The 0.1MW_th Oxy-CFB boiler is composed of combustor (0.15 m l.D., 10 m High), cyclone, return leg, and so on. To perform CFD analysis, a 3D simulation model reactor was designed and used. The anthracite used in the experiment has an average particle size of 1,070 ㎛ and a density of 2,326 kg/m³. The flow pattern of gas-solids inside the reactor according to the change of combustion environment from air combustion to oxygen combustion was investigated. At this time, it was found that the temperature distribution in air combustion and oxygen combustion showed a similar pattern, but the pressure distribution was lower in oxygen combustion. addition, since it has a higher CO₂ concentration in oxygen combustion than in air combustion, it can be expected that carbon dioxide capture will take place actively. As a result, it was confirmed that this study can contribute to the optimized design and operation of a circulating fluidized bed reactor using anthracite.