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박근환(Keunhwan Park),손태호(Taeho Son),김원정(Wonjung Kim),김호영(Ho-Young Kim) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
Lungs are natural microfluidic devices that evolution has optimized to extract oxygen from air. In the bronchial tree, airways branch by dichotomy with a systematic reduction of their length and diameter. It is interesting that when we anatomically observe the human lungs, acinar airways diameter is reduced less steeply with progressive generations than the conducting airways. In conducting airways near the mouth, the reduction ratio is deduced by minimizing the total viscous dissipation, known as the Hess-Murray law. Noting that the acinar airways air drift velocity is smaller than the mean diffusion velocity, we construct a diffusion mass transfer model over a series of acinar airways, which allows us to predict the optimal airway reduction ratio that maximizes the oxygen transfer in a finite acinar airway volume. Our theoretical prediction is consistent with our experimental data obtained by using an artificial lung on a chip as well as the reported clinical data.
김태홍(Tae-Hong Kim),박근환(Keunhwan Park),김호영(Ho-Young Kim) 한국가시화정보학회 2011 한국가시화정보학회지 Vol.9 No.1
The bubble oscillations play an important role in ultrasonic cleaning processes. In the ultrasonic cleaning of semiconductor wafers, the cleaning process often damages micro/nano scale patterns while removing contaminant particles. However, the understanding of how patterns in semiconductor wafers are damaged during ultrasonic cleaning is far from complete yet. Here, we report the observations of the motion of bubbles that induce solid wall damage under 26 kHz continuous ultrasonic waves. We classified the motions into the four types, i.e. volume motion, shape motion, splitting or jetting motion and chaotic motion. Our experimental results show that bubble oscillations get unstable and nonlinear as the ultrasonic amplitude increases, which may exert a large stress on a solid surface raising the possibility of damaging microstructures.
이성섭(Seongseob Lee),박근환(Keunhwan Park) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
A rockwool is a porous medium composed of microscale pores and macroscale pores. We quantify the capillary rise height and the capillary rise weight in a rockwool. In wicking experiment in rockwool, we show that the early stages and the late stages. In early stage, weight and height scale follow t1/2. In late stage, weight and height scale follow t1/4. The reason why this occurs is that the effect of gravity depends on the height. this study is expected to be used as an important fundamental study for improving the performance by analyzing the hydrodynamic properties of the rockwool.
이종진(Jongjin Lee),박근환(Keunhwan Park) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.11
This paper describes an experimental study on the cleaning of edge grinding tools using a dual-fluid nozzle. For cleaning with the dual-fluid nozzle, the dropletized ultra-pure water must be smaller than the particles. The dropletization is achieved through the pressure of nitrogen and ultrapure water. We have manufactured a dual-fluid nozzle. To demonstrate the droplet effect, the pressure of nitrogen and ultrapure water was set to 5 bar-5 bar. In this paper, cleaning forces by distance and the cleaning method is explained. The distance was set to 5mm and 10mm. We prove particle removal efficiency through a high-speed camera. The dual-fluid nozzle used 5.208 liters per minute of water. water. Existing nozzles used 7.11 liters per minute of water. This saves 26.75 percent of water. This means that cleaning with the dual-fluid nozzle is more useful.