• Journal of the Korean Society of Visualization
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• v.3 no.2
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.3
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• pp.164-169
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• 2009

The slip velocity and the temperature jumps for low-speed flow in microchannels are investigated using Langmuir slip boundary condition. This slip boundary condition is suggested to simulate micro flow. The current study analyzes Langmuir slip boundary condition theoretically and it analyzed numerically micro-Couette flow, micro-Poiseuille flow and grooved microchannel flow. First, to prove validity for Langmuir slip condition, an analytical solution for micro-Couette flow is derived from Navier-Stokes equations with Langmuir slip conditions and is compared with DSMC and an analytical solution with Maxwell slip boundary condition. Second, the numerical analysis is performed for micro-Poiseuille flow and grooved microchannel flow. The slip velocity and temperature distribution are compared with results of DSMC or Maxwell slip condition and those are shown in good agreement.

• Journal of the Korean Society of Visualization
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• v.1 no.1
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• pp.28-33
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• 2003

This paper presents the visualization method in which 3-dimensional(3D) microchannel flow can be detected using a confocal scanning microscope. By soft-lithography, we fabricated various Bio-MEMS(Micro Electro-Mechanical System) devices such as a disposable microchip for a flow cytometer and a micro-mixer, which have 3D structures. Injecting aqueous fluorescent solution in the microfluidic devices, we measured the flow in a steady state by the confocal scanning microscope. At first, we explain the principle of the confocal scanning microscope. And then we show the results from 3D visualization of microscopic flow structures using the confocal scanning microscope.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.269-274
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• 2008

The present study has been studied on a thermal and flow characteristic of the microchannel waterblock with flow distributions in each channels. Results of a numerical analysis using the CFX-11 are compared with results of an experiment. Numerical analysis and experiment are conducted under a heat transfer rate of 150W, inlet temperature of $20^{\circ}C$ and mass flow rates of $0.7{\sim}2.0\;kg$/min. Base temperature and pressure drop are investigated with standard deviations of mass flow rates in each channels of samples at 0.7 kg/min.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2426-2431
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• 2007

The microchannel waterblock has a good capability in the cooling of electronic devices. The object of this paper is to estiblish the scheme of design for the microchannel waterblock. The effects of flow rate and channel size on the cooling performances are investigated. It was found that the optimum flow rates were ragned from 0.7 lpm to 1.4 lpm. The thermal resistance at 2.0 lpm and 100 W was 0.13 $^{\circ}C$/W. Decrease in the width of channels is more effective for the improvement in the cooling performances of microchannel waterblock than increase in the height of channels. The increase of pressure drop resulted from decrease in the width of channels can be decreased by increasing the hight of channels.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2432-2437
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• 2007

The demand of high speed and miniaturization of electronic devices results in increased power dissipation requirement for thermal management. In this work, the effects of microchannel width, height and liquid flowrate on the cooling performances of microchannel waterblock are investigated experimentally. The microchannel waterblock considered ranged in width from 0.5 to 0.9 mm, with the channel height being nominally 1.7 to 9 times the width in each case. The experiments were conducted using water, over a liquid flow rate ranging from 0.2 to 2.0 lpm. The base temperature, thermal resistance and pressure drop increase with increasing of liquid flow rate. The measured thermal resistances ranged from 0.10 to 0.23 $^{\circ}C$/W for the channel 5.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1921-1923
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• 2001

In this work, an array of resistance temperature detector(RTD) was fabricated inside the microchannel in order to investigate in-situ flow characteristics. A rectangular straight microchannel, integrated with RTD's for temperature sensing and a heat source for generating the temperature gradient along the channel. were fabricated with the dimension of $200{\mu}m(W){\times}{\mu}m(D){\times}$48mm(L), while RTD measured precise temperatures at the inside-channel wall. 4" $525{\pm}25{\mu}m$ thick P-type <100> Si wafer was used as a substrate. For the fabrication of RTDs. 5300$\AA$ thick Pt/Ti layer was sputtered on a Pyrex glass wafer. Finally, glass wafer was bonded with Si wafer by anodic bonding, therefore RTD was located inside the microchannel. The temperature distribution inside the fabricated microchannel was obtained from 4 point probe measurements and Dl water is used as a working fluid. Temperature distribution inside the microchannel was measured as a function of mass flow rate and heat flux. As a result, precise temperatures inside the microchannel could be obtained. In conclusion, this novel temperature distribution measurement system will be very useful to the accurate analysis of the flow characteristics in the microchannel.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1891-1896
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• 2003

The bubble motion during nucleate boiling in a microchannel is investigated numerically. The liquid-vapor interface is tracked by a level set method which is modified to include the effects of phase change at the interface and contact angle at the wall. The computations are made for various channel sizes, liquid flow rates, and contact angles. Based on the numerical results, the bubble growth pattern and its effect on the flow and heat transfer are discussed.

• 한국가시화정보학회:학술대회논문집
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• 2003.11a
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• pp.79-80
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• 2003

This paper presents experimental results on stirring characteristics in a microchannel with structures changed. We fabricated a new chaotic micro mixer and made by a RP(Rapid Rrototyping) technology. Flow visualization for the stirring effect was performed by using pure orator in a reservoir and fluorescent dye in the other. Chaotic mixing was achieved by introducing periodic perturbation in the field of the microchannel flow by means of shaped structures. It was found that the stirring is enormously enhanced at larger bock-height.

• 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.