Silicon nanoparticle is a promising material for electronic devices, photovoltaics, and biological applications. Here, we synthesize silicon nanoparticles via CO2 laser pyrolysis and study the hydrogen flow effects on the characteristics of silicon nanoparticles using high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and UV-Vis-NIR spectrophotometry. In CO2 laser pyrolysis, used to synthesize the silicon nanoparticles, the wavelength of the CO2 laser matches the absorption cross section of silane. Silane absorbs the CO2 laser energy at a wavelength of 10.6μm. Therefore, the laser excites silane, dissociating it to Si radical. Finally, nucleation and growth of the Si radicals generates various silicon nanoparticle. In addition, researchers can introduce hydrogen gas into silane to control the characteristics of silicon nanoparticles. Changing the hydrogen flow rate affects the nanoparticle size and crystallinity of silicon nanoparticles. Specifically, a high hydrogen flow rate produces small silicon nanoparticles and induces low crystallinity. We attribute these characteristics to the low density of the Si precursor, high hydrogen passivation probability on the surface of the silicon nanoparticles, and low reaction temperature during the synthesis.

Numerical analysis has been carried out to investigate thermal characteristics for hydraulic system. Overall performance of hydraulic system is largely influenced by oil flow field with heat transfer. Especially thermal characteristics for operating conditions with high oil temperature caused by heavy load and continuous operation are dominant. Oil temperature variation with time in the system is predicted for various flow conditions. Local fluid flow fields at the pipelines, valves, and oil pump in the hydraulic system are considered with thermodynamic and transport properties such as density and viscosity. These results in the study can be applied to the optimal design of hydraulic system.

This study is about comparison of thermal and flow characteristics on the wind & radiant heat shield with STS mesh type screen for offshore plant. Numerical analysis was conducted to find transmission coefficient in the mesh and then analyse the flow characteristics about wind & radiant heat shield. The experiment method of solar radiation has been used as thermal radiation source to get the performance of radiant heat shield measurement. The sensor radiation device has been used to measure the reduction of solar radiation with various size of cells and at a distance of 0.5m and 1m from the cold face of the wind & radiant heat shield. The present study show reduction in radiation heat flux as various distance from the cold face of the radiant heat shield. Experimental results are presented for different type of mesh and distance of measurement.

Flow control of flow field is essential to design efficient elements relating to fluid machineries. In this study, the flow characteristics of rectangular prism with throughflow at different aspect ratio was investigated to flow control. A particle image velocimetry technique was employed to obtain detailed measurements at throughflow-velocity-based Reynolds numbers. As a results, the throughflow disturbs the development of vertical velocity component and decreased the vortex size.

본 연구에서는 자유낙하 하는 쐐기형 구조물의 슬래밍 충격압력 및 유동특성을 알아보고자 실험을 수행하였다. 유동장의 계측은 2-프레임 그레이레벨 상호상관 PIV 기법을 이용하였으며, 자유낙하 하는 구조물의 충격압력은 압력 계측장비인 Dewetron System을 이용하였다. 모델과 자유수면간 이루는 각도는 15˚, 25˚, 35˚ 및 45˚를 적용하였으며 중량과 자유낙하의 높이에 대해서 다양성을 주어 실험하였다. 속도장은 접수보다 이수에서 빠른 유동특성을 나타냈으며, 접수에서 보다 이수에서 시간이 더 소요됨을 보였으며, 모델 하부에서의 충격압력은 모델의 45도에서 보다, 입수각이 작은 15도와 P1 지점에서 높게 나타났다.

Recently, the quiet fan development is one of important issues for comfort of railroad car. The purpose of this study is to find the vibration and noise source of the line flow fan for reduction the noise level. For a vibration and noise source identification, experiments with microphone and acceleration were carefully carried out. The noise of line flow fan is caused by various factors, such as turbulent flow noise, blade passing frequence and unbalance. In order to reduce the fan noise, the blade shape, distance and angle of housing guide should be modified.

세계는 지금 본격적인 에너지 기후시대로 도래했으며 녹색성장을 이끌 강력한 에너지 정책이 선진국가 진입의 초석으로 신재생에너지를 활용하여 미래의 에너지 자원으로 동력화하는 것이 21세기 에너지 수요를 충족시키는 개발 목표가 되고 있다. 최근 신재생에너지 개발의 필요성에 따라 해양에너지가 주목을 받고 있다. 해양에너지는 아직 개발되지 않은 가장 유망한 재생 및 청정에너지 자원 중 하나이다. 이에 따라 각 해역에 적합한 조류에너지 변환장치의 개발이 매우 필요하다. 본 연구에서는 조류발전용 터빈에 작용하는 유입각, 해저면 효과 및 공동현상 발생에 따른 효율의 변화를 후류유동특성을 통해 파악하였다. 계산 조건하에서 해저면 효과에 의한 효율저하는 크게 나타나지 않았고, 유입각은 10도 이상부터 효율 저하가 나타났고 45도에서는 출력계수가 7 % 낮게 계산되었다. 유입속도가 증가할수록 토크와 출력계수가 증가하였으나, 공동현상이 발생하는 3 m/s이상부터 오히려 출력저하가 나타났다. 또한 유동특성의 고찰을 통해 유입각이 크고 공동현상이 나타날수록 출력감소의 원인이 됨을 확인하였다.

이 연구에서는 정사각 단면을 갖는 덕트 내부에 원심력의 영향을 받는 유동의 천이특성을 실험 및 수치적으로 규명하였다. 실험적 연구로서 레이저도플러 속도계를 이용하여 축방향속도를 측정하였고, 상용소프트웨어인 플루언트를 이용한 전산유체 시뮬레이션으로 천이특성을 고찰하였다. 유동의 발달은 딘수와 굽힘각에 의존한다는 사실을 알 수 있었으며 덕트의 중앙에서의 속도분포는 원심력 때문에 내외벽보다 낮은 값을 나타내었다.

본 연구에서는 자유낙하하는 직사각형 해양구조물(800×250×50mm3)의 슬래밍 충격압력 및 유동특성을 알아보고자 실험을 수행하였다. 유동장의 계측은 2-프레임 그레이레벨 상호상관 PIV기법을 이용하였으며, 자유낙하하는 모델의 충격압력은 압력계측장비(Dewatron)를 이용하였다. 모델과 자유수면간 이루는 각은 10˚와 20˚를 적용하였다. 속도장은 접수보다 이수에서 빠른 유동특성을 나타냈다. 모델 하부에서 충격압력이 가장 높은 지점인 P2 지점에서 10˚보다 경사각이 큰 20˚에서 약 6 % 상승하였다.

본 연구에서는 트랜섬 선미 후류 난류유동 특성을 알아보기 위하여 Re = 3.5×103 및 Re = 7.0×103에서 2-프레임 그레이레벨 상호상관 PIV기법을 적용하여 실험을 수행하였다. 트랜섬 선미의 형상은 선저와 트랜섬이 이루는 각을 기준으로 45˚(모델 A), 90˚(모델 B) 및 135˚(모델 C)로 구분하여 적용하였다. 모델의 침수깊이는 40 mm로 자유수면과 접하도록 설치하였다. 난류유동을 평균하여 난류강도, 레이놀즈 응력, 난류운동에너지에 대한 통계적 유동정보를 제공하였다. 난류강도는 자유수면과 모델의 하부 박리유동과의 상호작용으로 강하게 작용하며, 레이놀즈 응력과 난류운동에너지는 모델 C형(Raked transom)에서 낮은 분포가 나타났다.

This experimental study was performed to investigate wake flow and unsteady flow characteristics using a model for actual shape of a wind breaker and visualization of flow through the particle image velocimetry. Three control angle of flap were selected and instantaneous velocity distributions and flow characteristics were experimently investigated. It is found that as the control angle increases, the flows are characterized by the appearance of the growth of recirculation region.

Numerical simulation has been carried out to analyze seawater flow characteristics for shroud geometry variations with tidal current generation turbine. Seawater flow field characteristics in the turbine system are largely influenced by the shroud geometry. The vortex flow area in the diffuser part of the shroud gradually grows with the increase of shroud angle, but its recirculation velocity gets smaller. The centerline velocity of shroud increases with the length of cylinder part when diffuser part length and angle are constant(2.5m, 0.733rad) for the cylinder-diffuser type shroud system. Seawater velocity on the tip of turbine blade is pretty high, and as radial distance increases from the turbine axis, there is more gap between the fluid velocity isolines. These results in this study will be applicable for optimal design of tidal current generation system.

광양만의 해수유동의 계절별 특성을 현장관측과 3차원 수치모델(EFDC)을 이용하여 파악하였다. 광양만 해수유동 특성은 전반적으로 섬진강 유출량의 계절적 변동, 해수유동구조 및 온배수 등에 의해 복잡한 형태를 보이는 것을 파악할 수 있었고, 이들 자료는 광양만 선박 안전 및 섬진강 하구역 관리의 기초자료로 사용될 수 있을 것으로 판단된다.

The purpose of this study is to investigate the actual field application of the super-charger for heavy equipment. In this paper, the numerical analysis and performance evaluating experiments were performed. ANSYS CFX program has been used to obtain the solutions for the problems of three-dimensional turbulent air flow in the super-charger. To evaluate the flow performance of the super-charger, the performance test facility and data acquisition system were manufactured. We obtained satisfactory results from CFD analysis and flow experiment.

The paper concerns numerical study of fully developed laminar flow of a Newtonian water and non-Newtonian fluids, 0.2% aqueous of sodium carboxymethyl cellulose(CMC) solution in eccentric annuli with combined bulk axial flow and inner cylinder rotation. Pressure losses and skin friction coefficients have been measured when the inner cylinder rotates at the speed of 0～200 rpm. A numerical analysis considered mainly the effects of annular eccentricity and inner cylinder rotation. The present analysis has demonstrated the importance of the drill pipe rotation and eccentricity. In eccentricity of 0.7 of a Newtonian water, the flow field is recirculation dominated and unexpected behavior is observed. it generates a strong rotation directed layer, that two opposing effects act to create two local peaks of the axial velocity. The influences of rotation, radius ratio and working fluid on the annular flow field are investigated.

Flow control of flow field is essential to design efficient elements relating to fluid machineries. In this study, flow characteristics of rectangular prism with center gap through-flow at different aspect ratio was investigated to flow control. It was used a FLUENT 6.3 version to study flow field. It was found that the through-flow disturbs the development of vertical velocity component and decreased the vortex size and critical value of a rapid change in pressure coefficient distribution.