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Experimental study on CIS thin film deposition via electrostatic spray technique
윤현(Yoon, Hyun),윤석구(Yoon, Sukgoo),김호영(Kim, Hoyoung) 한국신재생에너지학회 2010 한국신재생에너지학회 학술대회논문집 Vol.2010 No.11
Electrostatic spray deposition is an innovative coating technique that produces fine, uniform, self-dispersive (due to the Coulombic repulsion), and highly wettable, atomized drops. Copper-indium salts are dissolved in an alcohol-based solvent, which is then electrostatically sprayed onto a moderately heated, molybdenum-coated substrate. Solvent flowrates range from 0.02 to 5 ml/hr under applied voltages of 1 to 20 kV yielding drop sizes around a few hundred nanometers. By comparing the scanning electron miscrscope images of coated samples, the substrate temperature, applied voltage, solvent flowrate, and nozzle-substrate distance are demonstrated to be the primary parameters controlling coating quality. Also, the most stable electrostatic spray mode that reliably produces uniform and fine drops is the cone-jet mode with a Taylor cone issuing from the nozzle.
액체 점성 변화에 따른 균일액적 충돌 특성에 대한 실험적 연구
황인혁(InHyuk Hwang),윤석구(SukGoo Yoon),김호영(HoYoung Kim),이동조(DongJo Lee) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Spray impingement applies to a variety of practical applications for spray-drying, pharmaceutical coating, painting, fire suppression, and surface coating materials. In this work, the complex splashing characteristics of monodisperse spray was investigated. Liquid drops of fairly uniform size are continuously injected onto a flat, 2-㎜-diameter, aluminum cylindrical rod at a pressure of 2 bars. Droplets are impacted and splashed onto the top of the rod, resulting in formation of numerous satellite drops of smaller size. The working fluid is a mixture of water and glycerine which facilitates viscosity changes. The impinging behavior was visualized and recorded using a CCD camera and Sauter Mean Diameter, splashed droplet size distribution, and splash volume fraction was measured using a Malvern particle sizer. Splashed droplets of water tends to be breakup more easily than water-glycerine mixture.
CIGS 나노입자를 포함한 전구체의 전기수력학적 분무에 관한 실험적 연구
우지훈(Woo, Jihoon),윤석구(Yoon, Sukgoo),김호영(Kim, Hoyoumg) 한국신재생에너지학회 2010 한국신재생에너지학회 학술대회논문집 Vol.2010 No.11
전기수력학적 분무를 이용한 액적 미립화 기술은 나노사이즈의 액적 형성, 쿨롱 반발력에 의한 균일한 액적 형성, 그리고 향상된 액적 타겟팅을 가능하게 한다. 따라서 이를 이용하여 매우 균일한 박막 코팅이 가능하다. 이러한 점에 힘입어 현재 진공 공정으로 제작되고 있는 CIGS태양전지의 광흡수층을 비진공 공정중 하나인 전기수력학적 미립화를 이용하여 실험하였다. Ethanol-based 의 CIGS나노 입자를 포함하는 콜로이드 상태의 전구체를 이용하여 적절히 가열된 몰리브덴 배면 전극위에 적용하였다. 미립화한 액적은 접지된 몰리브덴 층에 부착되는 즉시 증발하여 CIGS입자를 남긴다. 여기서 가장 중요하게 다루어야 할 조건은 기판의 온도, 인가 전압, 전구체의 유량이다. 분사 모드는 Cone-jet을 적용하였으며 5~15kV의 인가 전압에서 1ml/hr내외의 유량을 공급하여 3분 이내에 적절한 광흡수층 두께인 1마이크론 내외에 도달할 수 있다. 이와같은 조건으로 형성된 박막층에 관한 SEM image를 통해 다른 비진공 코팅 방식과 비교하였다.
초음속 유동 내 입자의 크기에 따른 속도 발달 및 유동과의 상호작용에 관한 수치해석적 연구
이민욱(MinWook Lee),윤석구(SukGoo Yoon),김호영(HoYoung Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
The method in which solid particles are accelerated through a supersonic gas flow via a de Laval convergent-divergent nozzle is known as cold-spray coating. In the current unsteady computation, particles of various sizes are stagnated inside the supersonic nitrogen gas to examine the effect of particle size on the shock interaction around the particle. A particle is hypothetically situated inside the supersonic flow in which distinctive discontinuity of shock characteristics is simulated and analyzed. Under given Nozzle Pressure Ratio of NPR=P<SUB>o</SUB>/P<SUB>e</SUB>=9.5, the exit Mach number is set to 2.2. The diameter of the titanium particle, circular in shape, is varied from 1, to 10, 50, and 100 ㎛. The results indicate that the smaller the particle, the easier it is to accelerate the particles because of their faster response or relaxation time. This trend is also consistent and verified with a steady computation. The flow downstream tends to pulsate due to fluctuations caused by the shockwave which leads to moderate turbulence in flow behind the shockwave.
직접분사식 가솔린 엔진의 분사 조건 변화에 따른 유동 및 연소 특성에 관한 수치적 연구
이진휘(Jinhwi Lee),김호영(Ho Young Kim),윤석구(Sam Sukgoo Yoon) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11
The development of future engine generations for GDI(Gasoline Direct Injection) engine requires sophisticated combustion systems to reach reduced fuel consumption and future emission standards. The design process of these combustion systems has to be based on a fundamental knowledge of the interacting mixture preparation mechanism. Therefore, In this study, 3D full cycle simulation were carried out to investigate the effects of fuel injection timing and inclined injector angle on air-fuel mixing and to obtain subsequent combustion and emission characteristics of the GDI engine. Computational results showed that turbulence of the in-cylinder charge is enhanced by retarding fuel injection timing although the uniformity is decreased as the time for fuel-air mixing is insufficient. Also, increasing inclination angle of injector improve evaporation rate and turbulence intensity.
엇갈린 배열에서 미분탄 입자의 간극과 산소 농도가 연소 특성에 미치는 영향
서주형(Ju-Hyeong Seo),김호영(Ho-Young Kim),윤석구(Sukgoo Yoon),조상필(Sang-Pil Jo),김기덕(Ki-Duck Kim) 한국연소학회 2008 KOSCOSYMPOSIUM논문집 Vol.- No.-
The combustion characteristics of interacting pulverized coal particles in a convective flow are numerically investigated at various oxygen concentrations and particle spacing considering 2-dimensional particle staggered arrangement. The numerical simulation includes detailed interaction among the inter-spaced particles, undergoing devolatilization and subsequent char burning. Several parametric studies, which include the effect of oxygen concentration and variation in geometrical particle spacing on the volatile release rate along the char combustion rate, have been carried out. The particle spacing and the oxygen concentration level were varied from 4R? to 15R? and from 15% to 90%, respectively. The initial conditions of particle size and temperature were assumed to be 100㎛ and 600K. The predicted results show that the third particle is very highly influenced by the particle spacing and has the smallest particle life time at whole particle spacing. When O₂ concentration levels are 50% and 90%, volatile combustion and subsequent devolatilization burning rate are increased by 15% and 29% compared to 21% O₂ concentration level, respectively.
가솔린 직접분사식 엔진에서 연료온도와 피스톤 상면온도 변화가 연료 액막 형성에 미치는 영향
배진우(Jin Woo Bae),서주형(Ju Hyeong Seo),김호영(Ho Young Kim),윤석구(Sam Sukgoo Yoon),명차리(Cha Lee Myung) 한국자동차공학회 2010 한국자동차공학회 학술대회 및 전시회 Vol.2010 No.11
The subsequent behavior of the liquid fuel film has a strong influence on mixture preparation, combustion and emission. To achieve subsequent engine performance, liquid fuel film must be avoided after spray impingement. So evaporated fuel mass must be increase to reduce liquid fuel film. This study presents the CFD modeling using S/W STAR-CD to study the effect of the cylinder wall and piston crown temperature on the liquid fuel film quantity. Bai and Gosman’s model has been used for the liquid fuel film model. Results including liquid fuel film mass and thickness were obtained under transient condition and WOT (Wide Open Throttle). The result shows that Total liquid fuel film mass and average liquid fuel thickness tended to reduce when variables temperature increased more than certain range. But liquid fuel thickness on the piston wall tended to increased.
차유홍(You-Hong Cha),방부형(Boo Hyoung Bang),박정재(Jung-Jae Park),윤석구(Sam Sukgoo Yoon) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
The greatest risk to safety in petrochemical refinery plants is an unexpected explosion. Although thermal damage to equipment may be significant, perhaps the more critical immediate risk is the pressure rise from the blast wave that could damage or destroy essential infrastructure and lead to loss of life. For this reason, numerical prediction of blast wave characteristics and their effects on the nearby structures, such as pipes and tanks, is crucial to assessing the risks of potential accidents. To this end, numerical simulations of pipe damage due to blast waves from a methane explosion are presented. Predicting the features and characteristics of the blast waves, which may result in pipe deformation, will help refinery engineers improve plant safety.
가솔린 직접분사식 엔진의 분무각에 따른 실린더 내 유동 및 연소 특성 해석
서주형(Ju Hyeong Seo),김호영(Ho Young Kim),윤석구(Sukgoo Yoon),이진휘(Jinhwi Lee) 한국자동차공학회 2010 한국자동차공학회 부문종합 학술대회 Vol.2010 No.5
GDI(Gasoline Direct Injection) engine which is one among DISI(Direct Injection Spark Ignition) engine is one major approach in reducing Nox emission and increase the fuel efficiency. Numerical simulations for the GDI engine characteristics have been investigated from the effects of the spray cone angle on the process. In this study, a 3D unsteady Eularian-Langrangian two-phase model was used to account an optimal operating condition for a GDI engine using S/W STAR-CD (CD-adapco). Our simulation results indicate both flow field and mixture characteristics to obtain subsequent combustion and emission characteristics inside the cylinder. To improve mixing quality and evaporation rate, spray cone angle is commonly increased. As the spray cone angle increased, the uniformity index of the fuel has increased. With the variation of spray cone angle, Case BMwith spray cone angle 30 degree has the minimum NOx emission in the cylinder.