• Journal of Korean Society of Environmental Engineers
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• v.33 no.3
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• pp.191-195
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• 2011

The measurement and prediction of bacterial transport of bacteria in aquatic systems is of fundamental importance to a variety of fields such as groundwater bioremediation ascending urinary tract infection. The motility of pathogenic bacteria is, however, often missing when considering pathogen translocation prediction. Previously, it was reported that flagellated E. coli can translate upstream under low shear flow conditions. The upstream swimming of flagellated microorganisms depends on hydrodynamic interaction between cell body and surrounding fluid flow. In this study, we used a breathable microfluidic device to image swimming E. coli at a glass surface under low shear flow condition. The tendency of upstream swimming motion was expressed in terms of 'A' value in parabolic equation ($y=Ax^2+Bx+C$). It was observed that high shear flow rate increased the 'A' value as the shear force acting on bacterium increased. Shorter bacterium turned more tightly into the flow as they swim faster and experience less drag force. The result obtained in this study might be relevant in studying the fate and transport of bacterium under low shear flow environment such as irrigation pipe, water distribution system, and urethral catheter.

• Applied Chemistry for Engineering
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• v.35 no.4
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• pp.267-272
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• 2024

This review explores recent advancements in microfluidic crystallization techniques utilizing energy from external sources on a small scale. We focus on four representative types of external sources: ultrasound, laser, microwave, and electric field, emphasizing their impact on crystal formation. This highlights the benefits of using external sources in crystallization, such as improved crystal quality, structure formation, and changes in physical properties. Providing a comprehensive overview of crystallization techniques employing external sources, the paper discusses the potential developments in the field of crystallization through the application of these external energy sources.

• Korean Chemical Engineering Research
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• v.59 no.4
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• pp.626-631
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• 2021

One of the nonlinear electrokinetic phenomena around ion exchange membrane is electroconvective instability which can be found in various electrokinetic applications such as electrodialysis, electrochemical battery, microfluidic analysis platform, etc. Such instability acts as a positive transport mechanism for the electrodialysis via amplifying mass transport rate. On the other hands, in the electrochemical battery and the microfluidic applications, the instability provokes unwanted mass transport. In this research, to control the electroconvective instability, the onset of the instability was analyzed as a function of confinement effect as well as applied voltage. As a result, we figured out that the dynamic behavior of electroconvective instability transited as a sequence of stable regime - static regime - chaotic regime depending on the applied voltage and confinement effect. Furthermore, stability curves about the dynamic transition were numerically determined as well. Conclusively, the confinement effect on electroconvective instability can be applied for effective means to control the electrokinetic chaos.

• Restorative Dentistry and Endodontics
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• v.35 no.5
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• pp.313-320
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• 2010

Objectives: The aim of this study was to examine changes in the dentinal fluid flow (DFF) during desensitizing agent application and to compare permeability after application among the agents. Materials and Methods: A Class 5 cavity was prepared to exposure cervical dentin on an extracted human premolar which was connected to a sub-nanoliter fluid flow measuring device (NFMD) under 20 cm water pressure. DFF was measured from before application of desensitizing agent (Seal&Protect, SP; SuperSeal, SS; BisBlock, BB; Gluma desensitizer, GL; Bi-Fluoride 12, BF) through application procedure to 5 min after application. Results: DFF rate after each desensitizing agent application was significantly reduced when compared to initial DFF rate before application (p < 0.05). SP showed a greater reduction in DFF rate than GL and BF did (p < 0.05). SS and BB showed a greater reduction in DFF rate than BF did (p < 0.05). Conclusions: Characteristic DFF aspect of each desensitizing agent was shown in NFMD during the application procedure.

• 한국가시화정보학회:학술대회논문집
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• 2004.04a
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• pp.19-28
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• 2004

유동장의 특성을 구분할 수 있는 척도는 평균자유행로와 특성거리의 비인 누센수이다. 누센수에 따라서 유장은 연속체영역, 미끄럼영역, 천이영역, 및 자유분자영역으로 나누어진다. 고고도에서 비행체 주위의 유동장, 진공에서의 유동장 등이 비연속체영역 즉 저밀도유동장에 해당된다. 비연속체영역에 해당되는 또 다른 중요한 분야는 미세 유동장이다. 최근에 관심이 대두되고 있는 미세항공기(MAV)와 실리콘혁명 이래 유망한 미래기술중의 하나인 MEMS 장치 주위의 유동장 등이 바로 미세 유동장이다. 비연속체영역에서 유체의 이동 및 전달현상을 기술하기 위하여는 Boltzmann 방정식을 해석하여야한다. Navier-Stokes 방정식을 이용한 기존의 CFD 기법이 적용되지 않는 새로운 유동영역이기 때문이다. 본 발표에서는 Boltzmann 방정식의 유력한 해법인 직접모사(Direct Simulation Monte Carlo)법을 이용한 저밀도 유동장 해석이 소개될 것이다. 또한 직접모사법이 이용되기 어려운 다양한 저속 유동장에 대한 해석결과도 소개될 것이다.

• Composites Research
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• v.35 no.6
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• pp.447-455
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• 2022

Currently, the problem of pollution of the marine environment by microplastics is emerging seriously internationally. In this study, to develop a lightweight portable microplastic collection device, the types and number of microplastics in 21 coastal areas nationwide in Korea were investigated. And CFRP (Carbon Fiber Reinforced Plastic), GFRP (Glass Fiber Reinforced Plastic), ABS (Acrylonitrile Butadiene Styrene copolymer) and aluminum were applied for design and analysis of microplastic collection device to have the durability, corrosion resistance and lightweight. As a result of sample collection and classification from the shore, it was confirmed that microplastics were distributed the most in Hamdeok beach, and the polystyrene was found to be mainly distributed microplastics. Particle information through coastal field survey and CFD (Computational Fluid Dynamics) analysis were used to analyze the flow rate and distribution of particles such as sand and impurities, which were applied to the structural analysis of the cyclone device using the finite element method. As a result of structural analysis considering the particle impact inside the cyclone device, the structural safety was examined as remarkable in the order of CFRP, GFRP, aluminum, and ABS. In the view of weight reduction, CFRP could be reduced in weight by 53%, GFRP by 47%, and ABS by 61% compared to aluminum for the cyclone device.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.1
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• pp.59-63
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• 2017

We present a multi-sample array device based on a pneumatic system. Solenoid valves were used to control a micro valve in a pneumatic system. The use of a compressor together with a vacuum pump ensured that one outlet could supply both compression and vacuum pressure. The multi-sample array device was fabricated using conventional photolithography and PDMS casting. The device was composed of a multiplexer, sample array, and rinsing. The multiplexer could control four sample solutions injecting into the sample array chamber. Sample solution not arrayed was removed by DI-water from the rinsing inlet. To prevent trapping of microbubbles in the channel during injection of sample solution into the device, surfactant was added in PDMS solution to serve as a hydrophilic surface treatment. As a result, the device could be used as a sample array for 64 cases, using four samples and three columns of three chambers.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.5
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• pp.437-441
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• 2014

This paper presents a novel microplatform for high power generation based on reverse electrodialysis. The ideal cation-selective membrane for power generation was realized using geometrically controlled in situ self-assembled nanoparticles. Our proposed membranes can be constructed through a simple and cost-effective process that uses microdroplet control with nanoparticles in a microchannel. Another advantage of our system is that the maximum power and energy conversion efficiency can be improved by changing the geometry of the microchannel and proper selection of the nanoparticle size and material. This proposed platform can be used to supply power sources to other microdevices and contribute to a fundamental understanding of ion transport behavior and the power generation mechanism.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.1
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• pp.63-67
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• 2016

We present a method of fabricating poly (lactic-co-glycolic acid) (PLGA) porous microfibers using a pore template. PLGA microfibers were synthesized using a glass capillary tube in a poly-(dimethylsiloxane) (PDMS) microfluidic chip. Gelatin solution was used as a porous template to prepare pores in microfibers. Two phases of PLGA solutions in different solvents-DMSO (dimethyl sulfoxide) and DCM (dichloromethane)-were used to control the porosity and strength of the porous microfibers. The porosity of the PLGA microfibers differed depending on the ratio of flow rates in the two phases. The porous structure was formed in a spiral shape on the microfiber. The porous structure of the microfiber is expected to improve transfer of oxygen and nutrients, which is important for cell viability in tissue engineering.

• Korean Chemical Engineering Research
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• v.53 no.6
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• pp.740-745
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• 2015

This study investigated the effect of different collection methods on physical properties of pectin hydrogels in microfluidic synthetic approach. The pectin hydrogels were simply produced by the incorporation of calcium ions dissolved in continuous mineral oil. Then, different collection methods, pipetting, tubing, and settling, for harvesting pectin hydrogels were applied. The settling method showed most uniform and monodispersed hydrogels. In the case of settling, a coefficient of variation was 3.46 which was lower than pipetting method (18.60) and tubing method (14.76). Under the settling method, we could control the size of hydrogels, ranging from $30{\mu}m$ to $180{\mu}m$, by simple manipulation of the viscosity of pectin and volumetric flow rate of dispersed and continuous phase. Finally, according to the characteristics of simple encapsulation of biological materials, we envision that the pectin hydrogels can be applied to drug delivery, food, and biocompatible materials.