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사각 마이크로채널 내의 2 상 유동 압력강하 상관식의 검증 및 개발
최치웅(Chi-woong Choi),유동인(Dong In Yu),김무환(Moo Hwan Kim) 대한기계학회 2010 大韓機械學會論文集B Vol.34 No.1
2 상 유동 압력강하에 대한 모델은 균질유동모델과 분리유동모델 두 가지가 있다. 많은 선행 연구자들은 마이크로채널에서의 2 상 유동 압력강하에 대한 상관식을 제시하였고, 대부분은 분리유동모델에 해당하는 Lockhart-Martinelli<SUP>(27)</SUP>의 수정된 상관식에 기초하고 있다. 본 연구에서는 사각 마이크로채널에서의 압력강하에 대한 연구를 위해서 액상의 물과 기상의 질소를 사용하여 사각 마이크로채널에서의 실험을 수행하였다. 2 상 마찰 압력강하는 2 상 유동양식에 큰 연관성을 가지고 있는 결과를 확인할 수 있었다. 6 가지의 2 상 점성 모델을 포함한 균질유동 모델 (Owen<SUP>(21)</SUP>’s, MacAdams<SUP>(22)</SUP>’s, Cicchitti et al.<SUP>(23)</SUP>’s, Dukler et al.,<SUP>(24)</SUP> Beattie and Whalley,<SUP>(25)</SUP> Lin et al.<SUP>(26)</SUP>)과 6 가지의 분리유동 모델 (Lockhart and Martinelli,<SUP>(27)</SUP> Chisholm,<SUP>(31)</SUP> Zhang et al.,<SUP>(15)</SUP> Lee and Lee,<SUP>(5)</SUP> Moriyama and Inue,<SUP>(4)</SUP> Qu and Mudawar<SUP>(8)</SUP>)에 대한 평가를 실험결과와 비교를 통해 수행하였다. 가장 우수한 2 상 점성 모델은 Beattie and Whalley 의 모델이었고, 가장 우수한 분리유동 모델은 Qu and Mudawar 의 상관식이였다. 균질유동모델과 분리유동모델 모두에 대해서 2 상 유동양식에 종속성을 나타내었다. 그러므로, 본 연구에서는 2 상 유동 양식에 기초한 새로운 상관식을 균질유동모델과 분리유동모델에 대해 각각을 제시하였다. There are two kinds of models in two-phase pressured drop; homogeneous flow model and separated flow model. Many previous researchers have developed correlations for two-phase pressure drop in a microchannel. Most correlations were modified Lockhart and Martinelli’s correlation, which was based on the separated flow model. In this study, experiments for adiabatic liquid water and nitrogen gas flow in rectangular microchannels were conducted to investigate two-phase pressure drop in the rectangular microchannels. Two-phase frictional pressure drop in the rectangular microchannels is highly related with flow regime. Homogeneous model with six two-phase viscosity models: Owen<SUP>(21)</SUP>’s, MacAdams<SUP>(22)</SUP>’s, Cicchitti et al.<SUP>(23)</SUP>’s, Dukler et al.<SUP>(24)</SUP>’s, Beattie and Whalley<SUP>(25)</SUP>’s, Lin et al.<SUP>(26)</SUP>’s models and six separated flow models: Lockhart and Martinelli<SUP>(27)</SUP>’s, Chisholm<SUP>(31)</SUP>’s, Zhang et al.<SUP>(15)</SUP>’s, Lee and Lee<SUP>(5)</SUP>’s, Moriyama and Inue<SUP>(4)</SUP>’s, Qu and Mudawar<SUP>(8)</SUP>’s models were assessed with our experimental data. The best two-phase viscosity model is Beattie and Whalley’s model. The best separated flow model is Qu and Mudawar’s correlation. Flow regime dependency in both homogeneous and separated flow models was observed. Therefore, new flow pattern based correlations for both homogeneous and separated flow models were individually proposed.
사각 마이크로채널 내의 2 상유동 압력강하와 유동양식에 대한 젖음성의 영향에 대한 연구
최치웅(Chi-woong CHOI),유동인(Dong In Yu),김무환(Moo Hwan Kim) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.12
Wettability is a critical parameter in micro-scale two-phase system. Several previous results indicate that wettability has influential affect on two-phase flow pattern in a microchannel. However, previous studies conducted using circular microtube, which was made by conventional fabrication techniques. Although most applications for micro thermal hydraulic system has used a rectangular microchannel, data for the rectangular microchannel is totally lack. In this study, a hydrophilic rectangular microchannel was fabricated using a photosensitive glass. And a hydrophobic rectangular microchannel was prepared using silanization of glass surfaces with OTS (octa-dethyl-trichloro-siliane). Experiments of two-phase flow in the hydrophilic and the hydrophobic rectangular microchannels were conducted using water and nitrogen gas. Visualization of twophase flow pattern was carried out using a high-speed camera and a long distance microscope. Visualization results show that the wettability was important for two-phase flow pattern in rectangular microchannel. In addition, two-phase frictional pressure drop was highly related with flow patterns. Finally, Two-phase frictional pressure drop was analyzed with flow patterns.
다른 세장비의 사각 마이크로채널 내의 기포 거동에 관한 연구
최치웅(Chi-woong CHOI),유동인(Dong In Yu),김무환(Moo Hwan Kim) 대한기계학회 2010 大韓機械學會論文集B Vol.34 No.5
다른 세장비에 따른 단일 사각 마이크로 채널 내의 이상유동연구를 수행하였다. 본 연구에서는 대략 넓이가 500 ㎛ 이며 수력직경이 각각 490, 322, 143 ㎛ 인 사각 마이크로채널 내에서의 물-질소 유동에 대한 실험이 수행되었다. 또한, 고속카메라와 장거리 현미경을 통해 이상유동양식을 가시화하였다. 본 연구는 이상유동 중 기포류에 중점을 두었으며 가시화 결과를 통해 기포의 속도, 기포의 길이, 관 내 기포의 개수, 기공률을 산출하였고 단위 셀 모델을 기반으로 늘어진 단일 기포의 압력강하를 해석하였다. 실험을 통해 기포의 속도, 기공률, 단일 기포의 압력강하가 각각 겉보기 속도와 체적건도, 세장비와 연관이 있음을 확인하였으며, 사각 마이크로 채널 내 늘어진 단일 기포의 압력강하에 대한 상관식을 개발하였다. The adiabatic two-phase flow in single rectangular microchannels was studied for different aspect ratios. The working fluids were liquid water and nitrogen gas. The hydraulic diameters of the rectangular microchannels were 490, 322, and 143 ㎛, and the widths of the microchannels were around 500 ㎛. The two-phase flow pattern was visualized using a high-speed camera and a long-distance microscope. This study was focused on bubble flow regimes. From the visualized images, the bubble velocity, bubble length, number of bubbles, and void fraction were evaluated. Further, the pressure drop in a single bubble was evaluated by using a unit cell model. The bubble velocity is proportional to the superficial velocity. Further, the relationship between the void fraction and the volumetric quality is linear. The pressure drop in a single elongated bubble is strongly related to the aspect ratio. Finally, the new correlation about the pressure drop of a single elongated bubble in the rectangular microchannel was proposed.
마이크로 구조가 있는 소수성 표면에서 액적의 젖음성 상태에 대한 열역학적 모델 개발
유동인(Dong In Yu),도승우(Seoung Woo Doh),곽호재(Ho Jae Kwak),박현선(Hyun Sun Park),김무환(Moo Hwan Kim) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
In this study, the wetting state on the hydrophobic micro-textured surfaces is experimentally and theoretically investigated. For the quantifiable analysis, the hydrophobic micro-textured surfaces are fabricated by MEMS (Micro Electro Mechanical Systems) technique. To clarify the wetting state depending on the geometrical morphology, the wetting state of a droplet on the surface is visualized by synchrotron X-ray radiography with a high spatial resolution (In this study, the size of a pixel was 1.74μm). On the basis of the visualized wetting state data, the thermodynamic model is theoretically developed to estimate the wetting state on the hydrophobic micro-textured surfaces.
Common Sub-expression Sharing과 Radix-4<SUP>2</SUP> 알고리즘을 이용한 저면적 256-point FFT 구조
이동훈(Dong-Hoon Lee),유동인(Dong-In Yu),김한진(Han-Jin Kim),장영범(Young-Beom Jang) 대한전자공학회 2010 대한전자공학회 학술대회 Vol.2010 No.6
In this paper, an efficient butterfly structure DIF FFT Radix-4<SUP>2</SUP> structure using sub-expression sharing is proposed. Proposed butterflies in all stages utilize CSS techniques, and can reduce the number of adders through sharing common patterns of CSD type coefficients. Simulation of the proposed structure shows 27.2% reduction in the complex multiplication part and 43.8% reduction in overall 256-point FFT structure comparison with those of the conventional structures. Consequently, the proposed FFT structure can be efficiently used in various OFDM systems.
소수성 미니채널 내 움직이는 접촉선을 가진 액체슬러그의 압력 강하에 대한 수치해석
전준호(Jun Ho Jeon),박수청(Su Chung Park),유동인(Dong In Yu),김태훈(Tae Hun Kim),이연원(Yeon Won Lee) 한국가시화정보학회 2020 한국가시화정보학회지 Vol.18 No.3
In this study, a single-phase analysis of droplet slug with different contact angles was performed based on the visualization of experimental results. Droplet slug – flowing between gases in a hydrophobic mini channel – moves with a triple contact line without a gas liquid film on the wall. The results show that the rotational flow inside the droplet occurred; this was compared and verified with the results of two-phase analysis. The pressure field shows pressure rise at the front and rear ends. The effective length – the section that satisfies the laminar flow condition – became shorter as the droplet velocity increased. The Choi’s correlation for the effective length agrees with this analysis results with a slight difference. This difference is judged as the difference in the contact angle of the slug model.