• 한국전산유체공학회지
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• 제9권2호
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• pp.36-42
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• 2004

Low-speed gas flows in micro-channels are investigated using a kinetic theory analysis. The Boltzmann equation simplified by a collision model is solved by means of a finite difference approximation with the discrete ordinate method. Calculations are made for flows in simple micro-channels and a micro-fluidic system consisting of two micro-channels in series. The results are compared well with those from the DSMC method and an analytical solutions to the Wavier-Stokes equations. It is shown that the present method is a useful tool for the modeling of low-speed flows in micro-channels.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 춘계 학술대회논문집
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• pp.99-105
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• 2004

A kinetic theory analysis is made of low-speed gas flows in microchannels. The Boltzmann equation simplified by a collision model is solved by means of a finite difference approximation with the discrete ordinate method. The method does not suffer from statistical noise which is common in particle based methods and requires much less amount of computational effort. Calculations are made for flows in simple microchannels and a microfluidic system consisting of two microchannels in series. The method is assessed by comparing the results with those from several different methods and available experimental data.

• 대한기계학회논문집B
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• 제30권11호
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• pp.1035-1042
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• 2006

An experimental investigation was performed to study two-phase pressure drop of deionized water in a microchannel. Measurement and evaluation of two-phase frictional pressure gradient were carried out using a single horizontal rectangular microchanne1 having a hydraulic diameter of $100{\mu}m$. Tests were performed for mass fluxes of 90, 169, and 267 $kg/m^2$s and heat fluxes of 200-700 $kW/m^2$. Test results showed that the measured two-phase frictional pressure gradient increased with the mass flux and vapor quality. Most macro-channel correlations of two-phase frictional pressure gradient did not provide reliable predictions except under certain limited conditions.

• 대한기계학회논문집B
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• 제30권11호
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• pp.1043-1050
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• 2006

An experimental investigation was performed to study flow boiling heat transfer of deionized water in a microchannel. Measurement and evaluation of boiling heat transfer coefficients were carried out using a single horizontal rectangular microchannel having a hydraulic diameter of $100{\mu}m$. Tests were performed for mass fluxes of 90, 169 and 267 $kg/m^2$s and heat fluxes of 200-700 $kW/m^2$. Test results showed that the measured boiling heat transfer coefficients had no dependence on mass flux and vapor quality. Most macro-channel correlations of boiling heat transfer coefficient did not provide reliable predictions.

• 한국전산유체공학회지
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• 제14권4호
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• pp.86-92
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• 2009

Nowadays, the development of microfluidic chip [i.e. biochip, micro-total analysis system ($\mu$-TAS) and LOC (lab-on-a-chip)] becomes more active, and the microchannels to deliver fluid by pressure or electroosmotic forces tend to be more complex like electronic circuits or networks. For a simple network of channels, we may calculate the pressure and the flow rate easily by using suitable formula. However, for complex network it is not handy to obtain such information with that simple way. For this reason, Graphic User Interface (GUI) program which can rapidly give required information should be necessary for microchip designers. In this paper, we present a GUI program developed in our laboratory and the simple theoretical formula used in the program. We applied our program to simple case and could get results compared well with other numerical results. Further, we applied our program to several complex cases and obtained reasonable results.

• 대한설비공학회지:설비저널
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• 제37권7호
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• pp.9-13
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• 2008

첨단 건물 및 도시 등에 설치된 유비쿼터스 센서 네트워크의 안정적인 운용을 위하여, 이 시스템에 지속적으로 전력을 공급할 수 있는 Micro Power Generation기술을 소개하고자 한다.

• Korean Chemical Engineering Research
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• 제53권5호
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• pp.597-602
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• 2015

직경이 0.03 m이고 높이가 1.5 m인 마이크로 액적/기포 유동반응기에서 ZnO 입자의 연속제조 특성을 검토하였다. 마이크로 액적을 운반하는 기체의 속도는 6.0 L/min, 전구체 중 Zn이온의 농도는 0.4 mol/L로 유지하였다. ZnO 입자의 합성을 위한 반응의 온도(973 K~1,273 K)와 마이크로 기포의 유속 (0~0.4 L/min)이 합성된 ZnO 입자의 기공 특성에 미치는 영향을 고찰하였다. 본 연구의 실험범위에서 ZnO 입자의 합성온도는 1,073 K가 합성된 ZnO 입자의 기공을 극대화하는데 최적이었다. 또한, 반응기에서 연속 제조되는 ZnO 입자의 평균크기는 반응온도가 증가함에 따라 감소하였으며 입자의 표면은 점점 매끄럽게 단순화되었다. 반응기 내부에 마이크로 기포를 유입함으로써 유입하지 않는 경우와 비교하여 합성된 ZnO 입자 내부에 기공을 효과적으로 형성시킬 수 있었으며, 평균 BET면적을 58%까지 증가시킬 수 있었다. 마이크로 액적/기포 유동반응기를 사용하여 연속 합성한 ZnO 입자의 평균입도는 반응온도에 따라 $1.25{\sim}1.75{\mu}m$이었다.

• 한국항공우주학회지
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• 제36권5호
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• pp.483-490
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• 2008

마이크로 추진장치에서 노즐의 소형화는 많은 유동손실을 유발한다. 이러한 유동손실을 극복하기 위해 본 연구에서는 열적발산원리를 이용한 마이크로 추진장치에 대한 기초연구를 진행하였다. 움직이는 부품 없이 오직 온도구배만으로 추진제를 낮은 온도에서 높은 온도로 자체 펌핑이 가능한 열적발산장치를 설계, 제작 하였으며, 진공환경에서 누센수에 따른 맴브레인 압력구배효율을 분석하였다. 실험결과 천이영역에서는 두꺼운 맴브레인의 효율이 다소 높았으며, 자유분자영역에서는 두께에 관계없이 최대 압력구배 효율이 82%까지 증가하는 것을 확인할 수 있었다.

• 대한기계학회논문집B
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• 제28권9호
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• pp.1015-1021
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• 2004

Micro-resolution Particle Image Velocimetry(Micro-PIV) was used to measure the flow in a micro-branch(Micro-Bypass). In this paper, effects of particle lump at the tip of a Micro-branch and difficulties of Micro-PIV measurements for microfluidics with branch passage were described. Micro-bypass was composed of a straight channel(200(100)${\mu}$m width ${\times}$ 80${\mu}$m height) and two branches which has 100(50)${\mu}$m width ${\times}$ 80${\mu}$m height. One of branches was straight and the other was curved. Experiments were performed at three regions along streamwise direction(entrance, middle and exit of branch) and five planes along vertical direction (0, ${\pm}$10, ${\pm}$20 ${\mu}$m) for the range of Re=0.24, 1.2, 2.4. Numerical simulation was done to compare with the measurements and understand the effects of particle lump at the tip of branch. And another fluid(3% poly vinyl Alcohol aqueous solution) were adapted for this study, so there were no particle sticking. In this case, we could get velocity difference between straight and curved branches.

• 대한기계학회논문집B
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• 제33권12호
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• pp.939-946
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• 2009

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.