• 대한토목학회논문집
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• 제26권5B호
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• pp.459-467
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• 2006

본 연구에서는 화력발전소 순환수취수로의 유량증가가 취수펌프장 흐름에 미치는 영향을 해석하고 개선하기 위하여 수리 및 수치모형실험을 수행하였다. 수치모형실험결과에 의하면 화력발전소 순환수취수로의 유량이 증가하면 취수로내의 유속과 순환수취수 펌프장의 연직방향와도가 증가하여 순환수취수 펌프장내의 와류발생가능성이 크게 증가하는 것을 알 수 있었다. 수리모형실험을 수행하여 순환수취수펌프장 유입부의 수면 근처 흐름은 거의 균등한 유량 배분이 이루어지고 반면에, 바닥 근처의 흐름은 유량 배분이 균등하게 이루어지지 못하여 취수펌프장내에서 역류현상이 발생하는 것을 밝혀냈다. 삼각형 도류벽을 취수펌프장 유입부에 설치하여 유속분포의 불균일성을 제거할 수 있었고 역류발생문제를 제거하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.150.1-150.1
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• 2014

Showerhead is used as a main part in the semiconductor equipment. The face plate flatness should remain constant and the cleaning performance must be gained to keep the uniformity level of etching or deposition in chemical vapor deposition process. High operating temperature or long period of thermal loading could lead the showerhead to be deformed thermally. In some case, the thermal deformation appears very sensitive to showerhead performance. This paper describes the methods for robust design using computational fluid dynamics. To reveal the influence of the post distribution on flow pattern in the showerhead cavity, numerical simulation was performed for several post distributions. The flow structure appears similar to an impinging flow near a centered baffle in showerhead cavity. We took the structure as an index to estimate diffusion path. A robust design to reduce the thermal deformation of showerhead can be achieved using post number increase without ill effect on flow. To prevent the showerhead deformation by heat loading, its face plate thickness was determined additionally using numerical simulation. The face plate has thousands of impinging holes. The design key is to keep pressure drop distribution on the showerhead face plate with the holes. This study reads the methodology to apply to a showerhead hole design. A Hagen-Poiseuille equation gives the pressure drop in a fluid flowing through such hole. The assumptions of the equation are the fluid is viscous-incompressible and the flow is laminar fully developed in a through hole. An equation can be expressed with radius R and length L related to the volume flow rate Q from the Hagen-Poiseuille equation, $Q={\pi}R4{\Delta}p/8{\mu}L$, where ${\mu}$ is the viscosity and ${\Delta}p$ is the pressure drop. In present case, each hole has steps at both the inlet and the outlet, and the fluid appears compressible. So we simplify the equation as $Q=C(R,L){\Delta}p$. A series of performance curves for a through hole with geometric parameters were obtained using two-dimensional numerical simulation. We obtained a relation between the hole diameter and hole length from the test cases to determine hole diameter at fixed hole length. A numerical simulation has been performed as a tool for enhancing showerhead robust design from flow structure. Geometric parameters for the design were post distribution and face plate thickness. The reinforced showerhead has been installed and its effective deposition profile is being shown in factory.

• 항공우주기술
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• 제13권2호
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• pp.150-159
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• 2014

본 연구에서는 액체산소/케로신 추진 로켓 엔진 연소장치의 국내 개발에 있어서의 전산유체역학 응용 사례를 간략히 소개하였다. 추진제 공급부에 대한 다차원 유동 해석을 통해 유동 균일성을 확인하고 및 압력 손실을 예측할 수 있으며, 개념 설계 단계에서 추진제 매니폴드 형상 설계안을 비교/선택할 수 있다. 다분야 연소/냉각 성능 통합 해석을 통해 로켓 엔진 연소기의 연료 막냉각 및 열차폐 코팅 조건 등 연소/냉각 성능 관련 설계 문제 해결에 필요한 주요 정보를 도출할 수 있다. 향후 분사면 근처에서의 추진제 혼합 및 연소특성을 파악할 수 있는 해석 모델/기법을 개발할 필요가 있다.

• 한국결정성장학회지
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• 제20권3호
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• pp.125-132
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• 2010

For typical governing dimensionless parameters of Ar = 5, Pr = 1.16, Le = 0.14, Pe = 3.57, Cv = 1.02, $Gr_s=2.65{\times}10^6$, the effects of thermo physical properties such as a molecular weight, a binary diffusivity coefficient, a partial pressure of component B on solutally buoyancy-driven convection (solutal Grashof number $Gr_s=2.65{\times}10^6$) are theoretically investigated for further understanding and insight into an essence of solutal convection occurring in the vapor phase during the physical vapor transport of a $Hg_2Cl_2-N_2$ system. The solutally buoyancy-driven convection is significantly affected by any significant disparity in the molecular weight of the crystal components and the impurity gas of nitrogen. The solutal convection in a vertical orientation is found to be more suppressed than a tenth reduction of gravitational accelerations in a horizontal orientation. For crystal growth parameters under consideration, the greater uniformity in the growth rate is obtained for either solutal convection mode in a vertical orientation or thermal convection mode in horizontal geometry. The growth rate is also found to be first order exponentially decayed for $10{\leq}P_B{\leq}200$ Torr.

• Applied Microscopy
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• 제47권3호
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• pp.208-213
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• 2017

The microstructural changes in Co nanoparticles and an Au-10at.%Pd thin film have been investigated using an in situ heating holder with a micro-electro-mechanical system (MEMS). In Co nanoparticles, two phases (face-centered cubic and hexagonal close-packed crystal structures) were found to coexist at room temperature and microstructures at temperatures, higher than $1,000^{\circ}C$, were observed with a quick response time and significant stability. The actual temperature of each specimen was directly estimated from the changes in the lattice spacing (Bragg-peak separation). For the Au-10at.%Pd thin film, at a set temperature of $680^{\circ}C$, the actual temperature of the sample was estimated to be $1,020^{\circ}C{\pm}123^{\circ}C$. Note that the specimen temperature should be carefully evaluated because of the undesired effects, i.e., the temperature non-uniformity due to the sample design of the MEMS chip, and distortion due to thermal expansion.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.301.1-301.1
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• 2016

We report an ultraclean, cost-effective, and easily scalable method of transferring and patterning large-area graphene using pressure sensitive adhesive films (PSAFs) at room temperature. This simple transfer is enabled by the difference in wettability and adhesion energy of graphene with respect to PSAF and a target substrate. The PSAF transferred graphene is found to be free from residues, and shows excellent charge carrier mobility as high as ${\sim}17,700cm^2/V{\cdot}s$ with less doping compared to the graphene transferred by thermal release tape (TRT) or poly(methyl methacrylate) (PMMA) as well as good uniformity over large areas. In addition, the sheet resistance of graphene transferred by recycled PSAF does not change considerably up to 4 times, which would be advantageous for more cost-effective and environmentally friendly production of large-area graphene films for practical applications.

• 한국기계가공학회지
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• 제19권6호
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• pp.36-42
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• 2020

Nowadays, the touch screen panel (TSP) cover glass for mobile smart devices is being developed with a curved glass shape due to different design requirements. Because the sizes of mobile smart devices continue to increase, there has also been a great increase in the demand for large-area curved glass greater than 20 inches. In this study, heat and fluid flow analysis using CFD was performed to optimize the heating surface temperature distribution of the large curved glass formation system. Five cooling water flow paths in the cooling block were designed and analyzed for each case. A function that can quantitatively calculate the temperature uniformity of the heating surface was proposed and these values were obtained for the five models. The temperature distributions of the heating surface and the energy consumption of the heating system were also compared and comprehensively analyzed. Based on the analysis results of the five different cooling channel path models, the optimal path design could be presented.

• 한국결정성장학회지
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• 제8권4호
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• pp.555-562
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• 1998

비균일 자장이 도가니에 인가되어 있는 상황에서 정상상태의 Czochralski 유동장과 비정상상태의 산소농도장에 대한 연구가 수치해석적인 방법으로 연구되었다. 여기에서 기준 자장의 세기가 B=0.1T, 0.2T, 0.3T의 경우에 대한 연구가 수행되었다. 가열에 의한 부력의 효과와 자유표면의 표면장력에 의한 열모세관 효과에 의하여 유발되는 자오면 유동은 비균일 자장에 의하여 차등적으로 억제되고 있다. 자자의 세기가 증가하면 자오면 유동에서 발생하는 순환류의 중심은 결정으로 접근하며, 순환류의 크기도 작아진다. 결정으로 흡수되는 산소의 세기가 클수록 낮아지며 농도분포는 균일해지는 경향을 갖는다.

• 한국결정성장학회지
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• 제12권6호
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• pp.272-282
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• 2002

Mercurous bromide ($Hg_{2}0Br_{2}$) crystals hold promise for many acousto-optic and opto-electronic applications. This material is prepared in closed ampoules by the physical vapor transport (PVT) growth method. Due to the temperature gradient between the source and the growing crystal region, the buoyancy-driven convection may occur. The effects of thermal convection on the crystal growth rate was investigated in this study in a horizontal configuration for conditions ranging from typical laboratory conditions to conditions achievable only in a low gravity environment. The results showed that the growth rate increases linearly with Grashof number, and for 0.2 $\leq$ Ar (transport length-to-height, L/H)$\leq$1.0 sharply for Ar=5 and $\Delta$T=30 K. We have also shown that the magnitude of convection decreases with the Ar. For gravity levels of less than $10^{-2}$g the non-uniformity of interfacial distribution is negligible.

• 한국수소및신에너지학회논문집
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• 제17권4호
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• pp.403-408
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• 2006

The plate reformer consisting of combustion chamber and reforming chamber for 25 kW MCFC stack has been operated and computational fluid dynamics was applied to estimate reactions and thermal fluid behavior in the reformer. The methane air 2-stage reaction was assumed in the combustion chamber, and three step steam reforming reactions were included in the calculation. Flow uniformity, reaction rate and species distribution, and temperature distribution were analyzed. In particular, temperature distribution was compared with the measurements to show good agreement in the combustion chamber, however, inappropriate agreement in the reformer chamber.