• 대한기계학회논문집B
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• 제30권3호
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• pp.255-261
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• 2006

Flow characteristics of DI water in a microchannel with a stenosis were investigated using .a micro PIV system with varying flow rate. The width and depth of the PDMS micro-channel were $100{\mu}m\;and\;50{\mu}m$, respectively. To Investigate flow characteristics in the micro-stenosis, the same experiment was carried out in a straight microchannel under the same flow rate. The measured mean velocity fields were almost symmetric with respect to the channel centerline. The experimental results are well agreed with the theoretical Hagen-Poiseuille profile. In the contraction part of the micro-stenosis, the oncoming flow is accelerated rapidly and the maximum velocity occurs at the throat, almost 4.99 time faster than that without the stenosis.

• 설비공학논문집
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• 제16권9호
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• pp.828-837
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• 2004

The present study investigated two-phase flow distribution, phase separation and pressure drop in multi-microchannel tubes under adiabatic condition. The test section consisted of inlet and outlet headers with the inner diameter of 19.4㎜ and 15 parallel microchannel tubes. Each microchannel tube brazed to the inlet and outlet headers and had 8 rectangular ports with the hydraulic diameter of 1.32㎜. The key experimental parameters were orientation of header (horizontal and vertical), flow direction of refrigerant into the inlet header (in-line, parallel and cross flow) and inlet quality (0.1, 0.2 and 0.3). It was found that the orientation of the header had relatively large effect on the flow distribution and phase separation, while the inlet quality didn't affect much on them. The horizontal header showed the better flow distribution and phase separation characteristics than the vertical one. The parallel flow condition with the horizontal header showed the best performance for the flow distribution and phase separation characteristics under the test conditions. Two-phase pressure drops through the microchannel tubes with the horizontal header were higher than those of the microchennel tubes with the vertical header due to gravitational effect.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.22.2-22.2
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• 2005

• 대한기계학회논문집A
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• 제28권8호
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• pp.1190-1195
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• 2004

A novel manipulation of microfluid width in a microchannel was presented by controlling inflation of a gas boundary. The gas boundary was formed by heating water with a microheater in a semicircular shape from a chamber which was connected symmetrically to the microchannel. The formed gas boundary inflated perpendicularly to the flow direction and, consequently, the microfluid width was narrowed. The inflation and contraction were flexibly like a virtual wall and dependent on two factors: one is the flow velocity of the microfluid and the other is the pressure inside the gas boundary. Dimensions of the chamber and the microchannel width were determined empirically as same of $300\;{\mu}m$ for stable operation. The width of microfluid was manipulated manually with the microheater and could be maintained as up to $22\;{\mu}m$. The stable focusing began to be distorted when the flow velocity exceeded 17.8 mm/s.

• Bulletin of the Korean Chemical Society
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• 제28권12호
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• pp.2426-2430
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• 2007

Dissipative particle dynamics simulations of bead-spring dumbbell models under microchannel flow were performed and the effects of the deformation on their migration behavior were discussed. Dumbbells were found to migrate toward the walls or the channel center depending on the stiffness. Stiff dumbbells migrated toward the walls. In any cases, the dumbbells were found to have a stronger tendency to move toward the channel center in more deformable 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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1783-1788
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• 2004

In the present paper, a micro flow sensor, which can be used at bio-delivery systems and micro heat pumps, is developed. For this, the micro flow sensor is integrated on a quartz wafer ($SiO_2$) and is manufactured by simple and convenient microfabrication processes. The micro flow sensor aims for measuring mass flow rates in the low range of about $0{\sim}20$ SCCM. The micro flow sensor is composed of temperature sensors, a heater, and a flow microchannel. The temperature sensors and the heater are manufactured by the sputtering processes in this study. In the microfabrication processes, stainless steel masks with different patterns are used to deposit alumel and chromel for temperature sensors and nichrome for the heater on the quartz wafer. The microchannel is made of Polydimethylsiloxane(PDMS) easily. A deposited quartz wafer is bonded to the PDMS microchannel by using the air plasma. Finally, we confirmed the good operation of the present micro flow sensor by measuring flow rate.

• 대한기계학회논문집B
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• 제41권1호
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• pp.69-74
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• 2017

마이크로채널은 단위체적당 표면적비가 높기 때문에 컴퓨터 마이크로 프로세서 냉각, 정밀 화학분석 및 바이오 분야로의 응용이 다양하게 적용 될 수 있어 많은 연구가 진행 중이다. 본 연구에서는 3D 프린터를 이용하여 사각 마이크로채널을 제작하였고, 실험에서 마이크로채널을 통과하는 액상 물은 탈이 온수를 사용하여 유량변화에 대한 압력강하를 측정하였다. 마이크로채널의 크기는 $161{\mu}m$에서 $664{\mu}m$로 변화시켜 제작하였으며, 유동의 레이놀즈 수는 16

• 대한기계학회논문집B
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• 제32권12호
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• pp.915-923
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• 2008

The performance experiments for a microchannel printed circuit heat exchanger (PCHE) of high-performance and high-efficiency on the two technologies of micro photo-etching and diffusion bonding were performed in this study. The microchannel PCHE were experimentally investigated for Reynolds number in ranges of 100 $\sim$ 700 under various flow conditions in the hot side and the cold side. The inlet temperatures of the hot side were conducted in range of $40^{\circ}C\;{\sim}\;50^{\circ}C$ while that of the cold-side were fixed at $20^{\circ}C$. In the flow pattern, the counter flow was provided 6.8% and 10 $\sim$ 15% higher average heat transfer rate and heat transfer performance than the parallel flow, respectively. The average heat transfer rate, heat transfer performance and pressure drop increases with increasing Reynolds number in all the experiment. The increasing of inlet temperature in the experiment range has not an effect on the heat transfer performance while the pressure drop decrease slightly with that of inlet temperature. The experimental correlations to the heat transfer coefficient and pressure drop factor as a function of the Reynolds number have been suggested for the microchannel PCHE.

• 한국가시화정보학회지
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• 제3권2호
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• pp.45-50
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• 2005

Electro-osmotic flow (EOF) instability in a microchannel has been experimentally investigated using a micro-PIV system. The micro-PIV system consisting of a two-head Nd:Yag laser and cooled CCD camera was used to measure instantaneous velocity fields and vorticity contours of the EOF instability in a T-shape glass microchannel. The electrokinetic flow instability occurs in the presence of electric conductivity gradients. Charge accumulation at the interface of conductivity gradients leads to electric body forces, driving the coupled flow and electric field into an unstable dynamics. The threshold electric field above which the flow becomes unstable and rapid mixing occurs is about 1000V/cm. As the electric field increases, the flow pattern becomes unstable and vortical motion is enhanced. This kind of instability is a key factor limiting the robust performance of complex electrokinetic bio-analytical devices, but can also be used for rapid mixing and effective flow control fer micro-scale bio-chips.