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소수성 표면의 미니채널 내에서의 삼중선에 의한 압력강하의 실험적 연구
유동인(Dongin Yu),최치웅(Choi chiwoong),김무환(Moohwan Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Slug flow regime is more broaden than the others in minichannels, comparing with the flow of the conventional channel. Moreover, the flow pattern is different according to wettability of surface in minichannels. Generally, bubbles at the slug flow regime are lubricated by liquid film in a hydrophilic surface of mini and micro-channel. However, bubbles are not lubricated by liquid film in a hydrophobic surface of mini and micro-channel. Instead, bubbles with triple-lines are developed. And Non-lubricated bubbles made higher pressure drop than lubricated bubbles due to the triple-line moving. To understand the pressure drop of motion of triple-lines of non-lubricated bubble, we studied the dynamic contact angle model and experimented of the pressure drop of triple lines of single droplet. In the experiment, we measured the pressure drop difference between single droplet(Nitrogen)-liquid(DI water) flow and only single Gas flow in the various diameter Teflon tube(1.6, 1.0㎜). Consequently, we could measure the pressure drop of triple lines of single droplet and analyzed the pressure drop relation with channel diameter, droplet length and velocity.
〈학술논문〉 다양한 유체 및 관 직경에 따른 미니 마이크로 채널 내에서의 삼중선에 의한 압력강하의 실험적 연구
유동인(Dongin Yu),최치웅(Chiwoong Choi),김무환(Moohwan Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
Slug flow regime is more broaden than the others in mini-microchannels comparing with the flow of the conventional channel. According to wettability of surface in mini-microchannels, the flow pattern is different. Bubbles at the slug flow regime are lubricated by liquid film in a hydrophilic surface of mini-microchannel. However, bubbles are not lubricated by liquid film in a hydrophobic surface of mini-microchannel. Thus, bubbles with triple-lines are developed. And the non-lubricated bubbles caused higher pressure drop than the lubricated bubbles due to the triple-lines moving. In this research, the experiments were conducted to understand the pressure drop of the motion of the triple-lines in the hydrophobic mini-microchannels. The pressure drop of N₂ gas and water liquid slug flow is measured in the various diameter Teflon tubes (1.5, 1.0, 0.5㎜) and superficial velocity region (0.02m/s~0.4m/s). Additionally, to understand effect of the property (surface tension, viscosity) at the pressure drop of triple-lines, various DI water-ethanol mixture (pure, 1, 5, 10%) liquid slug experiment were conducted.
멀티마이크로채널에서의 표면 젖음성에 따른 유동비등 현상에 대한 실험적연구
박상훈(Sang Hun Park),유동인(Dongin Yu),김무환(Moo Hwan Kim) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
Surface wettability is an important parameter in small scale phenomena, because the surface force becomes dominant as size decreases. Especially, in two-phase flow, it changed flow regime that makes heat transfer characteristic, pressure drop, etc different. In this study, we investigated how surface wettability affects the flow boiling heat transfer in multi-microchannel. The experiments were conducted with distilled water in an aluminum alloy multi-micro-channel heat sink. The heat sink consisted of 10 parallel microchannels each having a 500um rectangular cross-section and a 10mm length. The base heat flux was varied 33 and 70W/cm2, the mass flux was 270 and 400kg/m2s. The modified hydrophilic and bare aluminum surfaces were experimented. The hydrophilic surface was fabricated by simple AAO(Anodic Aluminum Oxidation) process with hydrofluoric acid. Through this study, it is expected to find appropriate surface for the application of two phase flow.
사각 유리 마이크로채널에서의 기포에 의한 압력 강하에 관한 연구
최치웅(Chi Woong Choi),유동인(DongIn Yu),김무환(MooHwan Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Major two-phase flow regime in a microchannel is an elongated bubble. This flow pattern is similar to long slug flow in a macroscale tube. In this study, therefore, mechanical analysis was conducted based on flow pattern. Experiments with water and nitrogen gas two-phase flow in glass rectangular microchannels were conducted. Two microchannels with different aspect ratio were used and their hydraulic diameters were approximately 503 and 332 ㎛. Ranges of superficial velocities of water and nitrogen gas are 0.06 - 0.6 ㎧ and 0.06 - 1 ㎧, respectively. In addition, visualization of two-phase flow was conducted using high-speed camera and long distance microscope. And pressure drop by a single bubble motion was evaluated using a unit cell model. The pressure drop in single bubble was proportional to Capillary number and inverse proportional to hydraulic diameter. Finally, empirical correlation for single elongated bubble was proposed.
방사광 X-선 영상법을 이용한 마이크로/미니채널 내 물-에탄올 액적 슬러그 계면 깨짐 현상에 대한 가시화 연구
김도연(DoYeon Kim),백진기(JinGy Baek),한도희(DoHui Han),김보경(BoGyeong Kim),유동인(DongIn Yu) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
In various multiphase system, development of recent technologies are often limited by interfacial breakup phenomena. Interfacial phenomena with dynamic conditions has investigated intensively by numerous researchers. However, previous researchs have typically been conducted on dynamic contact angle. In our previous research, it was investigated the interfacial break-up phenomena of a water-ethanol mixture slug flow in a hydrophobic minichannel. However, due to the limitation of the visualization techniques based on light ray, it was difficult to visualize clearly interfacial behavior and shapes. Therefore, in this study, we introduce the synchrotron X-ray imaging with high spatial and temporal resolutions. We confirm the previous flow patterns (steady, loss, separation) in previous research via synchrotron X-ray imaging. On the basis of visualization data, we observe the gas creates/destroys the liquid-gas interface continuously due to the speed differences with the high-speed flow conditions.