• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.12
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.12
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• pp.986-993
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• 2007

The microchannel heat sink is promising heat dissipation method far high density electronic devices. The cross-sectional shape of MEMS based microchannel heat sink is limited to triangular, trapezoidal, and rectangular due to their fabrication method. And heat is added to one side surface of heat source. Therefore, those specific conditions make some complexity of heat transfer in microchannel heat sink. Though many previous research of conjugate heat transfer in microchannel was conducted, most of them did not consider heat loss. In this study, numerical investigation of conjugate heat transfer in rectangular microchannel was conducted. The method of heat loss evaluation was verified numerically. Heat distribution was different for each wall of rectangular microchannel due to thermal conductivity and distance from heat source. However, the ratio of heat from each channel wall was correlated. Therefore, the effective area correction factor could be proposed to evaluate accurate heat flux in one side heating condition.

• Journal of the Korean Society of Visualization
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• v.9 no.2
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• pp.21-26
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• 2011

Hydrodynamic focusing technique to generate focused flow has been used for flow cytometry in microfluidic devices. However, devices with circular capillary tubes made of glass are not suitable for flow visualization or optical signal detection because the rays of light are distorted at the curved interface. We devised a new acrylic chamber assembled with a pulled micropipette and a rectangular microchannel made of glass. This new channel geometry enabled us to visualize the three-dimensional (3D) flow characteristics with confocal imaging technique. We analyzed the 3D hydrodynamic focusing in a circular capillary tube and a rectangular microchannel over a practical range of flow rates, viscosities and pressure drops.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1870-1875
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• 2007

The microchannel heat sink is promising heat dissipation method for high heat flux source. Contrary to conventional circular channel, MEMS based microchannel had rectangular or trapezoidal cross-sectional shape. In our study, we conducted three dimensional conjugate heat transfer calculation for rectangular shape microchannel. First, we simulated that channel was completely drained with known heating power. As a result we obtained calibration line, which indicates heat loss was function of temperature. Second, we simulated single phase heat transfer with various mass flux, 100-400 $kg/m^2s$. In conclusion, the single phase test verified that the present heat loss evaluation method is applicable to micro scale heat transfer devices. Heat fluxes from each side wall shows difference due to non-uniform heating. However those ratios were correlated with supplied total heat. Finally, we proposed effective area correction factor to evaluate appropriate heat flux.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.11 s.254
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.5
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• pp.644-654
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• 2003

An analytical solution for a vertically stratified viscous flow in a microchannel with a rectangular cross-section is constructed, assuming fully developed laminar flow where the interfaces between the fluid layers are flat. Although the solution is for n-layer flow, restricted results to symmetrical three-layer flow are presented to investigate the effects of the viscosity and thickness ratios of the fluid layers and the aspect ratio of the microchannel on the flow field. Relations between the flow rate and thickness ratios of the fluid layers with varying viscosity distributions are found, considering the cross -sectional velocity profiles which vary noticeably with the three parameters and differ significantly from the velocity profiles of the flow between infinite parallel plates. Interfacial instability induced by the viscosity stratification in the microchannel is discussed referring to previous studies on the instability analysis for plane multilayer flow. Exact solution derived in the present study can be used for examining a diffusion process and three -dimensional stability analysis. More works are needed to formulate the equations including the effects of interfacial' tension between immiscible liquids and surface wettability which are important in microscale transport phenomena.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.11 s.254
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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.

• Clean Technology
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• v.13 no.3
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• pp.195-200
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• 2007

This study investigated the flow rate changes of the heterogeneous rectangular microchannels which have different hydrophilic property on the bottom surface. The heterogeneous rectangular microchannel has three native PDMS (poly-dimethyl siloxane) surfaces which were patterned by the soft lithography. PDMS bottom surface was treated by the argon plasma and coated by the allyl alcohol (99%). The channel length was 10, 20 and 30 mm and the channel width was 100, 200 and $300\;{\mu}m$, respectively. Several external voltages were applied to make the fluid flow by the electroosmosis in the microchannel. For the same electric field strength and hydrophilicity of the bottom surface, the flow rate is almost same. This result is matched to the theoretical expectation and confirms that the experimental system is reliable. With increasing the channel width, the flow rate increased for the same hydrophilicity of the bottom surface. The flow rate of the microchannel of higher hydrophilicity was larger than that of the microchannel of lower hydrophilicity. This result implies that the hydrophilicity change of the bottom surface could be applied to control the flow rate in the microchannel.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.1
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• pp.69-74
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• 2017

The validity of friction factor theory, based upon conventional-sized passages for microchannel flows, is an active area of research. The high surface to volume ratio of a microchannel offers many advantages over macroscale devices and processes. This study focused on the laminar flow (16$161{\mu}m$ to $664{\mu}m$ for single-phase liquid flow. A controllable syringe pump was used to provide flow while a differential pressure transducer was used to record the pressure drop. These results demonstrated that a 3D printer can drastically simplify custom microchannel fabrication and still support complex features, which are typically only accessible with advanced fabrication techniques.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.1
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• pp.77-82
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• 2010

Our study aims to understand the flow of liquid in an open-top rectangular microchannel that can be used in micro total analysis systems ($\mu$-TAS) because it has advantages in terms of light transmission and energy efficiency. We measured the liquid velocity using particle tracking technique and conducted a simulation with computational fluid dynamics by altering the area of channel cross section and channel length for the capillary-driven flow in the open-top rectangular microchannel. When liquid water drops to an entrance of the fabricated microchannel with a height of 20 μm and a width of 20 ${\mu}m$, it flows along the microchannel by only capillary force. In the wetting behavior of the liquid, important parameters of this flow are channel size, contact angle and liquid properties such as surface tension and viscosity, which are used to control the flow of liquid in the microchannel.