• Journal of Biomedical Engineering Research
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• v.34 no.4
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• pp.189-196
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• 2013

Dielectrophoresis(DEP) is useful in manipulation and separation of micro-sized particles including biological samples such as bacteria, blood cells, and cancer cells in a micro-fluidic device. Especially, those separation and manipulation techniques using DEP in combination of micro fabrication technique have been researched more and more. Recently, it is revealed that a window structure of insulating layer in microfluidic DEP chip is key role in trap of micro-particles around the window structure. However, the trap phenomenon-driven by DEP force gradient did not fully understand and is still illusive. In this study, we characterize the trap mechanism and efficiency with different shapes of window in a microfluidic DEP chip. To do this characterization, we fabricated 4 different windows shapes such as rhombus, circle, squares, and hexagon inside a micro-fluidic chip, and performed micro-sized particles manipulation experiments as varying the frequency and voltage of AC signal. Moreover, the numerical simulation with the same parameters that were used in the experiment was also performed in order to compare the simulation results and the experimental results. Those comparison shows that both results are closely matched. This study may be helpful in design and development of microfluidic DEP chip for trapping micro-scaled biological particle.

• Journal of Biomedical Engineering Research
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• v.36 no.3
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• pp.61-68
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• 2015

In this paper, we studied the effects of intersection angles of the flow-foucusing type droplet generation device inlet channel on droplet diameter using numerical simulation modeling. We modeled different intersection angles with a fixed continuous channel width, dispersed channels width, orifices width, and expansion channels width. Numerical simulations were performed using COMSOL Multiphysics$^{(R)}$ to solve the incompressible Navier-Stokes equations for a two-phase flow in various flow-focusing geometries. Modeling results showed that an increase of the intersection angle causes an increase in the modification of the dispersed flow rate ($v^{\prime}{_d}$), and the increase of the modification of the continuous flow rate ($v^{\prime}{_c}$) obstructs the dispersed phase fluid flow, thereby reducing the droplet diameter. However, the droplet diameter did not decrease, even when the intersection angle increased. The droplet diameter decreased when the intersection angle was less than $90^{\circ}$, increased at an intersection angle of $90^{\circ}$, and decreased when the intersection angle was more than $90^{\circ}$. Furthermore, when the intermediate energy deceased, there was a decrease in the droplet diameter when the intersection angle increased. Therefore, variations in the droplet diameter can be used to change the intersection angle and fluid flow rate.

• Transactions of Materials Processing
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• v.15 no.9 s.90
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• pp.667-672
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• 2006

Agglutination is one of the most commonly employed reactions in clinical diagnosis. In this paper, we have designed and fabricated nickel mold insert for injection molding of a microfluidic lab-on-a-chip for the purpose of the efficient detection of agglutination. In the presented microfluidic lab-on-a-chip, two inlets for sample blood and reagent, flow guiding microchannels, improved serpentine laminating micromixer(ISLM) and reaction microwells are fully integrated. The ISLM, recently developed by our group, can highly improve mixing of the sample blood and reagent in the microchannel, thereby enhancing reaction of agglutinogens and agglutinins. The reaction microwell was designed to contain large volume of about $25{\mu}l$ of the mixture of sample blood and reagent. The result of agglutination in the reaction microwell could be determined by means of the level of the light transmission. To achieve the cost-effectiveness, the microfluidic lab-on-a-chip was realized by the injection molding of COC(cyclic olefin copolymer) and thermal bonding of two injection molded COC substrates. To define microfeatures in the microfluidic lab-on-a-chip precisely, the nickel mold inserts of lab-on-a-chip for the injection molding were fabricated by combining the UV photolithography with a negative photoresist SU-8 and the nickel electroplating process. The microfluidic lab-on-a-chip developed in this study could be applied to various clinical diagnosis based on agglutination.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.7
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• pp.557-566
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• 2015

The characteristics of a gas-liquid Taylor (slug) flow in a square micro-channel with dimensions of $600{\mu}m{\times}600{\mu}m$ are experimentally investigated in this paper. The test fluids were nitrogen and water. The superficial velocities of the liquid and gas were in the ranges of 0.01 - 3 m/s and 0.1 - 3 m/s, respectively. The bubble and liquid slug lengths, bubble velocities, and bubble frequencies for various inlet conditions were measured by analyzing optical images obtained with a high-speed camera. It was found that the measured values (bubble and liquid slug lengths, bubble velocities) were not in good agreement with the values obtained using empirical models presented in the existing literature. Modified models for the bubble and liquid slug lengths and bubble velocity are suggested and shown to be in good agreement (${\pm}20$) with the measured values. Moreover, the bubble frequency could be predicted well by the relationship between the unit cell length and its velocity.

• Journal of Powder Materials
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• v.23 no.2
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• pp.143-148
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• 2016

A microfluidic reactor with computer-controlled programmable isocratic pumps and online detectors is employed as a combinatorial synthesis system to synthesize and analyze materials for fabricating CdSe quantum dots for various applications. Four reaction condition parameters, namely, the reaction temperature, reaction time, Cd/Se compositional ratio, and precursor concentration, are combined in synthesis condition sets, and the size of the synthesized CdSe quantum dots is determined for each condition. The average time corresponding to each reaction condition for obtaining the ultraviolet-visible absorbance and photoluminescence spectra is approximately 10 min. Using the data from the combinatorial synthesis system, the effects of the reaction conditions on the synthesized CdSe quantum dots are determined. Further, the data is used to determine the relationships between the reaction conditions and the CdSe particle size. This method should aid in determining and selecting the optimal conditions for synthesizing nanoparticles for diverse applications.

• Journal of Powder Materials
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• v.25 no.2
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• pp.132-136
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• 2018

Core/shell CdSe/ZnS quantum dots (QDs) are synthesized by a microfluidic reactor-assisted continuous reactor system. Photoluminescence and absorbance of synthesized CdSe/ZnS core/shell QDs are investigated by fluorescence spectrophotometry and online UV-Vis spectrometry. Three reaction conditions, namely; the shell coating reaction temperature, the shell coating reaction time, and the ZnS/CdSe precursor volume ratio, are combined in the synthesis process. The quantum yield of the synthesized CdSe QDs is determined for each condition. CdSe/ZnS QDs with a higher quantum yield are obtained compared to the discontinuous microfluidic reactor synthesis system. The maximum quantum efficiency is 98.3% when the reaction temperature, reaction time, and ZnS/CdSe ratio are $270^{\circ}C$, 10 s, and 0.05, respectively. Obtained results indicate that a continuous synthesis of the Core/shell CdSe/ZnS QDs with a high quantum efficiency could be achieved by isolating the reaction from the external environment.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.10 s.241
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• pp.1298-1306
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• 2005

In this paper, Part II, we realized the Serpentine Laminating Micromirer (SLM) which was proposed in the accompanying paper, Part I, by means of the injection molding process in mass production. In the SLM, the higher level of chaotic mixing can be achieved by combining two general chaotic mixing mechanisms of splitting/recombination and chaotic advection by the successive arrangement of 'F'-shape mixing units in two layers. Mold inserts for the injection molding process of the SLM were fabricated by SU-8 photolithography and nickel electroplating. The SLM was realized by injection molding of COC (cyclic olefin copolymer) with the fabricated mold inserts and thermal bonding of two injection molded COC substrates. To compare the mixing performance, a T-type micromixer was also fabricated. Mixing performances of micromixers were experimentally characterized in terms of an average mixing color intensity of a pH indicator, phenolphthalein. Experimental results show that the SLM has much better mixing performance than the I-type micromixer and chaotic mixing was successfully achieved from the SLM over the wide range of Reynolds number (Re). The chaotic micromixer, SLM proposed in this study, could be easily integrated in Micro-Total-Analysis- System , Lab-on-a-Chip and so on.

• Journal of the Mineralogical Society of Korea
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• v.18 no.3 s.45
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• pp.227-236
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• 2005

Hydrothermal tourmaline occurs as aggregates or dissemination in the diaspore nodule from an aluminum-rich clay deposit, Milyang, southeastern Korea. Most crystals of tourmaline show complex textures that are finely zoned. The fine-scale chemical zonation of hydrothermal tourmaline reflects the fluctuation conditions that would be expected from fluid mixing in open systems. Oscillatory chemical zoning in tourmaline formed and showed similar patterns, regardless of its crystallographic directions. Mg was enriched in the early stage of crystal growth while Fe was enriched in the later stage, with fluctuations of the ratio of Fe to Mg. Chemical analysis, BSE images, and X-ray compositional maps confirm that the oscillatory Boning in tourmaline is exclusively controlled by the variations of Fe and Mg contents, but the contribution of boron to the zonation is insignificant. The fact that tourmaline altered to diaspore and dickite indicates that tourmaline was unstable with respect to these aluminous minerals as the B, Fe, and Mg activities decreased. Therefore, the aluminum activity may control the stability of tourmaline in the hydrothermal system.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.6
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• pp.1-7
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• 2017

The performance of a MEMS solid propellant thruster was predicted and analyzed through internal ballistics model and CFD analysis. The nozzle throat was $416{\mu}m$, and the area ratio of the nozzle was 1.85. As a result of the internal ballistics model, chamber pressure increased up to 197 bar and the maximum thrust was 3,836 mN. In CFD analysis, the chamber pressure of the internal ballistics model was applied as the operating pressure, and the CFD model was divided into an adiabatic and a heat loss model. As a result, the maximum thrust of the adiabatic model was 14.92% lower than that of the internal ballistics model, and the effect of heat loss was insignificant.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.546-550
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• 2008

In this study, 3-dimensional Computational Fluid Dynamics (CFD) analysis was induced to simulate air flow and particle motion in the axial flow cyclone separator. The commercialized CFD code FLUENT was used to visualize pressure drop and particle collection efficiency inside the cyclone. We simulated 4 cyclone models with different shape of vane, such as turning angle or shape of cross section. For the air flow simulation, we calculated the flow field using standard ${\kappa}-{\varepsilon}$ turbulence viscous model. Each model was simulated with different inlet or outlet boundary conditions. Our major concern for the flow filed simulation was pressure drop across the cyclone. For the particle trajectory simulation, we adopted Euler-Lagrangian approach to track particle motion from inlet to outlet of the cyclone. Particle collection efficiencies of various conditions are calculated by number based collection efficiency. The result showed that the rotation angle of the vane plays major roll to the pressure drop. But the smaller rotation angle of vane causes particle collection efficiency difference with different inlet position.