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알루미늄 평판 및 50 ㎛ 간격 격자 표면에 대한 에탄올 액적 충돌 거동 가시화
강동국,권대희,천두만,염은섭,Kang, Dongkuk,Kwon, Daehee,Chun, Doo-Man,Yeom, Eunseop 한국가시화정보학회 2020 한국가시화정보학회지 Vol.18 No.1
The droplet impact behavior is dominated by some parameters such as surface temperature, We number, surface and fluid property. Especially, Leidenfrost effect which prevents the contact between surface and droplet is very powerful phenomenon for determining droplet impact behavior. Due to this effect, the impact regime is divided into contact boiling regime and film boiling regime whether the droplet contact with the surface. Many studies have found that surface micro-structures which processed by surface processing are effective to overcome the Leidenfrost effect. In this study, droplet impact behaviors were compared using ethanol both on flat and laser-ablated Al surface. On the flat surface, impact regime was mainly divided by surface temperature. And there is key dominant parameter for each regime. On the laser-ablated surface, we could see changed impact regime and different impact behavior such as jetting and ejection of tiny droplets despite of same impact conditions.
초음파 영상 분석을 위한 3D 프린팅 기반 미세유체소자
강동국(Dongkuk Kang),홍현지(Hyeonji Hong),염은섭(Eunseop Yeom) 한국가시화정보학회 2018 한국가시화정보학회지 Vol.16 No.1
For the measurement of biophysical properties related with cardiovascular diseases (CVD), various microfluidic devices were proposed. However, many devices were monitored by optical equipment. Ultrasound measurement to quantify the biophysical properties can provide new insights to understand the cardiovascular diseases. This study aims to check feasibility of microfluidic device for ultrasound image analysis based on 3D printer. To facilitate acoustic transmission, agarose solution is poured around 3D mold connected with holes of the acrylic box. By applying speckle image velocimetry(SIV) technique, flow information in the bifurcated channel was estimated. Considering that ultrasound signal amplitude is determined by red blood cell (RBC) aggregation, RBC aggregation in the bifurcated channel can be estimated through the analysis of ultrasound signal. As examples of microfluidic device which mimic the CVD model, velocity fields in microfluidic devices with stenosis and aneurysm were introduced.
강동국(Dongkuk Kang),권대희(Daehee Kwon),염은섭(Eunseop Yeom) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
Phenomenon of drop impingement is found in numerous industrial applications, and nature. Most applications of the drop impingement involve high temperatures including fuel drop impingement in internal-combustion engines, water droplet impingement on steam turbine blades and in quenching metal castings and extrusions. The droplet impingement on heated wall can induce different behavior compared to that under room temperature. To see these different behavior, the droplet impingement on aluminum plate with and without heating was captured by using high-speed camera at 5,000 fps. To obtain quantitative information, image processing was applied to raw images. The velocity and size of droplet before the impact were varied due to the hot air flow around the droplet. The maximum spreading diameter after the impact was analyzed. In case of the drop impingement on the hot plate, Leidenfrost phenomenon prevented droplet from reaching the plate. The obtained data were well matched with previous literatures. This image processing progress based on matlab program could be utilized as a tool with advantages in term of easy-to-apply, easy-to-access, and transformations. It will be a great help in visualization and quantitative information analysis of two phase flows.
알루미늄 평판 및 50 μm 간격 격자 표면에 대한 에탄올 액적 충돌 거동 가시화
강동국(Dongkuk Kang),권대희(Daehee Kwon),천두만(Doo-Man Chun),염은섭(Eunseop Yeom) 한국가시화정보학회 2020 한국가시화정보학회지 Vol.18 No.1
The droplet impact behavior is dominated by some parameters such as surface temperature, We number, surface and fluid property. Especially, Leidenfrost effect which prevents the contact between surface and droplet is very powerful phenomenon for determining droplet impact behavior. Due to this effect, the impact regime is divided into contact boiling regime and film boiling regime whether the droplet contact with the surface. Many studies have found that surface micro-structures which processed by surface processing are effective to overcome the Leidenfrost effect. In this study, droplet impact behaviors were compared using ethanol both on flat and laser-ablated Al surface. On the flat surface, impact regime was mainly divided by surface temperature. And there is key dominant parameter for each regime. On the laser-ablated surface, we could see changed impact regime and different impact behavior such as jetting and ejection of tiny droplets despite of same impact conditions.
김동우(Dongwoo Kim),강동국(Dongkuk Kang),이수환(Suhwan Lee),강성희(Sunghee Kang),염은섭(Eunseop Yeom) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.12
During operation of the freezer, outdoor air can flow into the freezer through the drain tube. The moisture contained in the incoming air causes freezing around the evaporator. Since the freezing can reduce the performance of the evaporator, thus ice around the evaporator should be removed during the defrost process. Water from melting ice is discharged through the drain tube. In hot and humid conditions, freezing caused by the incoming air occurs at the drain hole (inlet of the drain tube). The flow path of the drain can be blocked due to growth of freezing. This problem should be solved to enhance the reliability of the product, because blocked flow path can affect the opening of the freezer door. In this study, the drain tube connected to the freezer was designed to prevent freezing of the freezer drain. The newly designed tube with shutter, which increases hydraulic resistance, was investigated in terms of actual fabrication possibilities through CFD simulation. By using 3D-printed tubes, the performance of models with different shutters was tested in test section mimicking the operating environment of the freezer. From the results, the drain tubes with the shutter can reduce incoming air and the suction pressure inside the freezer, caused by the door opening and closing, can be released increase of incoming air through the opening of the shutter.