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박한준(Han June Park),이성광(Sung-Gwang Lee),오정석(Jeong Suk Oh),Steven Barrett,황원태(Wontae Hwang) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
After the World Health Organization (WHO) proclamation of the Severe Acute Respiratory Syndrome-2 (SARS-Cov-2) as a pandemic in 2020, there have been various efforts on establishing the correlation between temperature and humidity on the spread of COVID-19. However, worldwide consensus has not yet been established. The cause of this is that the indoor environment in which virus transmission occurs is not considered, and there is also a lack of physical understanding of droplet evaporation with temperature and humidity. Therefore, in this study, we examine actual droplet dynamics by first measuring droplet evaporation within a constant temperature and humidity environmental chamber. Based on this experiment, simulations were conducted to estimate the effects of temperature and humidity on droplet dispersion. Our results showed that there was no significant correlation between temperature, but that high humidity greatly helps in suppressing virus transmission via respiratory droplets.
이성광(Sung-Gwang Lee),박한준(Han June Park),이인재(Injae Lee),남예빈(Yebin Nam),황원태(Wontae Hwang) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
As the critical dimension of semiconductors is miniaturized, the semiconductor fabrication process requires extreme purity and cleanliness, and many semiconductor facilities perform the process after creating a vacuum environment. Precursor gases used during the process make patterns by repeating deposition and etching through wafer surface reaction. In order to increase the production yield of circular wafers, it is essential to predict the behavior of process gases in a vacuum environment. Although computational fluid dynamics (CFD) is being performed to predict the airflow, there are very few studies that visualize and analyze the airflow through an experiment in a vacuum environment due to the difficulty of measuring the airflow. Therefore, there is a limit to verifying the CFD results. This study visualizes a supersonic round jet airflow in a vacuum environment in a 2D plane where the absolute pressure is lowered to 1 Torr. Using PIV, the structure of the jet, turbulent kinetic energy (TKE), and vorticity are analyzed by measuring the flow velocity of the jet. In addition, the location, size, and structure of the shockwave were analyzed using shadowgraphy. Through this study, we intend to provide an experimental basis for visualization of airflow in a vacuum environment.
선택적 촉매환원 장치 내부 유동 모사를 위한 다공성 매질 모델 개발
정원준(Wonjun Jung),한종호(Joungho Han),박한준(Han June Park),황원태(Wontae Hwang) 대한기계학회 2023 대한기계학회 춘추학술대회 Vol.2023 No.11
The complex flow inside SCR facilities can be examined using computational fluid dynamics (CFD) simulations where the screen plate is modeled as porous media owing to its complex shape. This porous media model nominally utilizes the pressure loss across the screen plate. However, a-priori determination of the model is difficult if on-site pressure data are unavailable or additional laboratory experiments cannot be performed. We hereby describe the development of a method for the porous media approach based on mathematical modeling of the force balance on the screen. This allows us to utilize the porous media approach without having any pressure drop information. We conducted particle image velocimetry (PIV) experiments to first validate CFD simulations that fully resolved the screen plate. Subsequently, CFD results using the porous media approach with the newly developed mathematical model were compared to that of the fully resolved simulations, and the overall flow structure including the main recirculation zone was shown to be similar. Thus, using the newly developed mathematical model, the internal flow field in complex engineering systems such as an SCR facility can be rapidly obtained with less computational cost and reasonable accuracy.
이훈상(HoonSang Lee),한규호(KyuHo Han),박한준(Han June Park),정현균(HyunKyun Jung),황원태(Wontae Hwang) 한국가시화정보학회 2018 한국가시화정보학회지 Vol.16 No.1
Homogeneous and isotropic turbulence (HIT) with no mean flow is a very useful type of flow for basic turbulence research. However, it is difficult to generate HIT in the lab. In this study, we implemented HIT in a confined box through synthetic jet actuators using sub-woofer speakers. Characteristics of HIT are varied depending on the strength of the jets. We used 2D PIV to measure the velocity field. Turbulence statistics such as homogeneity, isotropy ratio, turbulence kinetic energy, dissipation rate, Taylor microscale, Kolmogorov scale, and velocity correlation coefficient were calculated. Most of the turbulence statistics increased exponentially according to the strength of the jets, and the Taylor Reynolds number reached up to 185.
오정석(Jeong Suk Oh),윤성근(Sung Gun Yoon),박한준(Han June Park),황원태(Wontae Hwang) 한국가시화정보학회 2019 한국가시화정보학회지 Vol.17 No.3
The dynamic stability of swarms is crucial in preventing collisions in clustered flights and safely moving along a defined path. Although there have been many simulation studies on dynamic stability, there have not been many experimental studies using real clusters due to the difficulty in implementation. In this study, we constructed a particle-lattice structure simulating bird flocks or drone swarms, and conducted experiments within turbulent flow. We identified a criterion that describes dynamically stable particle-lattice structures. The stability increased as this newly defined spatial index increased.