• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.463-463
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• 2010

고휘도 고효율 백색 LED (lighting emitting diode)가 차세대 조명광원으로 급부상하고 있다. 백색 LED를 생산하기 위한 공정에서 MOCVD (유기금속화학증착)장비를 이용한 Epi wafer공정은 에피층과 기판의 격자상수 차이와 열팽창계수차이로 인하여 생성되는 에피결함의 제거를 위하여 기판과 GaN 박막층 사이에 완충작용을 해줄 수 있는 버퍼층 (Buffer layer)을 만들고 그 위에 InGaN/GaN MQW (Multi Quantum Well)공정을 하여 고휘도 고효율 백색 LED를 구현할 수 있다. 이 공정에서 기판의 온도가 불균일해지면 wafer 파장 균일도가 나빠지므로 백색 LED의 yield가 떨어진다. 균일한 기판 온도를 갖기 위한 조건으로 기판과 induction heater의 간격, 가스의 흐름, 기판의 회전, 유도가열코일의 디자인 등이 장비의 설계 요소이다. 코일에 교류전류를 흘려주면 이 코일 안 또는 근처에 있는 도전체에 와전류가 유도되어 가열되는 유도가열 방식은 가열 효율이 높아 경제적이고, 온도에 대한 신속한 응답성으로 인하여 열 손실을 줄일 수 있으며, 출력 온도 제어의 용이성 및 배출 가스 등의 오염 없다는 장점이 있다. 본 연구에서는 유도가열방식의 induction heater를 이용하여 회전에 의한 기판의 온도 균일도 측정을 하였다. 기초 실험으로 저항 가열 히터를 통하여 대류에 의한 온도 균일도를 평가하였다. 그 결과 gap이 3 mm일 때, 평균 온도 $166.5^{\circ}C$ 에서 불균일도 6.5 %를 얻었으며 이를 바탕으로 induction heater와 graphite susceptor의 간격이 3 mm일 때, 회전에 의한 온도 균일도를 측정을 하였다. 가열원은 induction heater (viewtong, VT-180C2)를 사용하였고, 가열된 graphite 표면의 온도를 2차원적으로 평가하기 위하여 적외선 열화상 카메라(Fluke, Ti-10)을 이용하여 온도를 측정하였다. 기판을 회전하면서 표면 온도의 평균과 표준 편차를 측정한 결과 2.5 RPM일 때 평균온도 $163^{\circ}C$ 에서 가장 좋은 5.5 %의 불균일도를 확인할 수 있었고, 이를 상용화 전산 유체 역학 코드인 CFD-ACE+의 모델링 결과와 비교 분석 하였다.

• Applied Chemistry for Engineering
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• v.33 no.1
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• pp.96-102
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• 2022

Reactants of PEMFC are hydrogen and oxygen in gas phases and fuel cell overpotential could be reduced when reactants are smoothly transported. Numerous studies to modify cathode flow field design have been conducted because oxygen mass transfer in high current density region is dominant voltage loss factor. Among those cathode flow field designs, a block in flow field is used to forced supply reactant gas to porous gas diffusion layer. In this study, the block was installed on a simple fuel cell model. Using computational fluid dynamics (CFD), effects of forced convection due to blocks on a polarization curve and local current density contour were studied when different air flow rates were supplied. The high current density could be achieved even with low air supply rate due to forced convection to a gas diffusion layer and also with multiple blocks in series compared to a single block due to an increase of forced convection effect.

• Applied Chemistry for Engineering
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• v.32 no.6
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• pp.613-620
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• 2021

A flow channel shape of PEMFC has an influence on the internal flow uniformity. If the reactant distribution in a flow path is not uniform during operation, both catalyst deactivation and mechanical damage of membrane could occur resulting in decreasing the membrane electrode assembly (MEA) durability. Numerous studies concerning flow design have been conducted to make smooth supply and uniform distribution of reactants in fuel cells. The baffle of flow path could improve fuel cell performance through the forced convection effect. A sub-channel, as an additional air flow path, could increase the reactant concentration and reduce the mass transfer loss via a smooth water discharge. In this study, computational fluid dynamics (CFD) was used to analyze the effect of blocks and sub-channels on the current density and oxygen concentration of the fuel cell. As a result, the limit current density and oxygen concentration at a rear block increased when using blocks and sub-channels in a flow channel. In particular, the current density increased significantly when the sub-channel was placed between two blocks. Also, the sub-channel position was optimized by analyzing the oxygen concentration, and the oxygen concentration was recovered at a rear block in the fuel cell.

• Applied Chemistry for Engineering
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• v.31 no.6
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• pp.596-602
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• 2020

Blending process of adhesive production has a cooling process to cool down the temperature of the solution which was heated up to 76 ℃ with a mineral insulated (MI) cable by 30 ℃ at room temperature. Using a MI cable in the adhesive production process makes the production inefficient because it takes about 10 h for the cooling process. If a jacketed vessel is used instead of the MI cable, it would shorten the cooling downtime without any additional cooling system by using cold water. However, there are various types of jacketed vessels, and thus the most suitable type should be found before set up. In this study, we designed the optimized jacketed vessel for the adhesive production process by calculating the cooling downtime, which impacts production efficiency, as a function of the jacket types using computational fluid dynamics. As a result, the cooling performance of the plain jacket was 32.7% superior to that of the half-pipe coil jacket with the same height. In addition, the plain jacket with 60% spiral baffle reduced the cooling downtime and operating time by 80.4% and 25.1%, respectively.