• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.671-674
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• 2008

We investigate the slippage effect in a micro-channel depending on the surface characteristics; hydrophilic, hydrophobic, and super-hydrophobic wettabilities. The micro-scale grooves are fabricated on the vertical wall to make the super-hydrophobic surfaces, which enable us visualize the flow fields near walls and directly measure the slip length. Velocity profiles are measured using micro-particle image velocimetry (Micro-PIV) and compared those in the hydrophilic glass, hydrophobic PDMS, and super-hydrophobic PDMS micro-channels. To directly measure the velocity in the super-hydrophobic micro-channel, the transverse groove structures are fabricated on the vertical wall in the micro-channel. The velocity profile near the wall shows larger slip length and, if the groove structure is high and wide, the liquid meniscus forms curves into the valley so that the wavy flow is created after the grooves.

• Membrane and Water Treatment
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• v.13 no.6
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• pp.313-320
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• 2022

Theoretical calculation results are presented for the enhancement of the water mass flow rate through the hydrophobic micro/nano pores in the membrane respectively on the micrometer and nanometer scales. The water-pore wall interfacial slippage is considered. When the pore diameter is critically low (less than 1.82nm), the water flow in the nanopore is non-continuum and described by the nanoscale flow equation; Otherwise, the water flow is essentially multiscale consisting of both the adsorbed boundary layer flow and the intermediate continuum water flow, and it is described by the multiscale flow equation. For no wall slippage, the calculated water flow rate through the pore is very close to the classical hydrodynamic theory calculation if the pore diameter (d) is larger than 1.0nm, however it is considerably smaller than the conventional calculation if d is less than 1.0nm because of the non-continuum effect of the water film. When the driving power loss on the pore is larger than the critical value, the wall slippage occurs, and it results in the different scales of the enhancement of the water flow rate through the pore which are strongly dependent on both the pore diameter and the driving power loss on the pore. Both the pressure drop and the critical power loss on the pore for starting the wall slippage are also strongly dependent on the pore diameter.

• Membrane and Water Treatment
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• v.15 no.1
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• pp.31-39
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• 2024

The flow in a nanopore of filtration membrane is often multiscale and consists of both the adsorbed layer flow and the intermediate continuum fluid flow. There is a controversy on which interface the slippage should occur in the nanopore filtration: On the adsorbed layer-pore wall interface or on the adsorbed layer-continuum fluid interface? What is the difference between these two slippage effects? We address these subjects in the present study by using the multiscale flow equations incorporating the slippage on different interfaces. Based on the limiting shear strength model for the slippage, it was found from the calculation results that for the hydrophobic pore wall the slippage surely occurs on the adsorbed layer-pore wall interface, however for the hydrophilic pore wall, the slippage can occur on either of the two interfaces, dependent on the competition between the interfacial shear strength on the adsorbed layer-pore wall interface and that on the adsorbed layer-continuum fluid interface. Since the slippage on the adsorbed layer-pore wall interface can be designed while that on the adsorbed layer-continuum fluid interface can not, the former slippage can result in the flux through the nanopore much higher than the latter slippage by designing a highly hydrophobic pore wall surface. The obtained results are of significant interest to the design and application of the interfacial slippage in nanoporous filtration membranes for both improving the flux and conserving the energy cost.

• The KSFM Journal of Fluid Machinery
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• v.13 no.2
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• pp.5-11
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• 2010

The nanofluidics is characterized by a large surface-to-volume ratio, so that the surface properties strongly affect the flow resistance. We present here the results showing that the effect of wetting properties and the surface roughness may considerably reduce the friction of fluid past the boundaries. For a simple fluid flowing over hydrophilic and hydrophobic surfaces, the influences of surface roughness are investigated by the nonequilibrium molecular dynamics (NEMD) simulations. The fluid slip at near a solid surface highly depends on the wall-fluid interaction. For hydrophobic surfaces, apparent fluid slips are observed on smooth and rough surfaces. The solid wall is modeled as a rough atomic sinusoidal wall. The effects on the boundary condition of the roughness characteristics are given by the period and amplitude of the sinusoidal wall. It was found that the slip velocity for wetting conditions at interface decreases with increasing effects of surface roughness. The results show the surface rougheness and wettability determines the slip or no-slip boundary conditions. The surface roughness geometry shows significant effects on the boundary conditions at the interface.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.03a
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• pp.543-550
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• 1999

Hazardous substances produced from industrial sectors have caused serious contamination of soils and groundwater. The hydrophobic organic compounds in the subsurface are hard to be decomposed, and as they soil on the soil or last as a NAPL they might contaminate the groundwater for a long time. Although we recognize the danger of contaminated subsurface, very little was known about the effective remediation technique. This paper focuses on the remediation of the p-Cresol which contaminated subsurface by applying the surfactant-enhanced description technique. Sorption characteristics of soils and organic compounds are studied, and the applications of surfactant solution are studied for effective rededication. The results from this study could be used as some data for surfactant-enhanced rededication. The flexible-wall permeameter tests are performed in which in-situ remediation is simulated. Results show that triton X-100 at 2% solution disrobes p-Cresol 1.7 times as much as water description in the flexible-wall permeameter tests.

• Bulletin of the Korean Chemical Society
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• v.25 no.3
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• pp.351-356
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• 2004

Selected MPEG-b-PDLLA block copolymers have been synthesized by ring-opening polymerization with systematic variation of the chain lengths of the resident hydrophilic and hydrophobic blocks. The size and shape of the micelles that spontaneously form in solution are then controlled by the characteristics of the block copolymer template. All the materials prepared in this study showed the tunable pore size of 20-80 ${\AA}$ with the increase of hydrophobic chain lengths and up to 660 $m^2$/g of specific surface area. The formation mechanism of these nanoporous structures obtained by controlling the micelle size has been confirmed using both liquid and solid state $^{13}C\;and\;^{29}Si$ NMR techniques. This work verifies the formation mechanism of nanoporous structures in which the pore size and wall thickness are closely dependent on the size of hydrophobic cores and hydrophilic shells of the block copolymer templates.

• Membrane and Water Treatment
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• v.12 no.1
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• pp.37-41
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• 2021

This paper presents the multiscale calculation results of the very fast volume transport in micro/nano cylindrical tubes with the wall slippage. There simultaneously occurs the adsorbed layer flow and the intermediate continuum fluid flow which are respectively on different scales. The modeled fluid is water and the tube wall is somewhat hydrophobic. The calculation shows that the power loss on the tube no more than 1.0 Watt/m can generate the wall slippage even if the fluid-tube wall interfacial shear strength is 1 MPa; The power loss on the scale 104 Watt/m produces the volume flow rate through the tube more than one hundred times higher than the classical hydrodynamic theory calculation even if the fluid-tube wall interfacial shear strength is 1 MPa. When the wall slippage occurs, the volume flow rate through the tube is in direct proportion to the power loss on the tube but in inverse proportion to the fluid-tube wall interfacial shear strength. For low interfacial shear strengths such as no more than 1 kPa, the transport in the tube appears very fast with the magnitude more than 4 orders higher than the classical calculation if the power loss on the tube is on the scale 104 Watt/m.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.847-848
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• 2004

We studied a low density 8CB liquid crystal-hydrophobic aerosil dispersions imbedded in submicron-size cylindrical pores. The nanosize spherical aerosil particles are adsorbed at the pore wall and hinder the planar anchoring. The adsorption is temperature dependent, and an axial to radial molecular configuration transition occurs within the cylindrical pores.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.368-376
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• 2009

Studies on the effect of the wall-ion, wall-water, water-ion and ion-ion interaction on properties of water and ions in nano-channels have been performed through the use of different kinds of ions or different models of potential energy between wall-ion or wall-water. On this paper, we address the effect of water-wall interaction potential on the properties of confined aqueous solution by using the molecular dynamics (MD) simulations. As the interaction potential energies between water and wall we employed the models of the Weeks-Chandler-Andersen (WCA) and Lennard-Jones (LJ). On the MD simulations, 680 water molecules and 20 ions are included between uniformly charged plates that are separated by 2.6 nm. The water molecules are modeled by using the rigid SPC/E model (simple point charge/Extended) and the ions by the charged Lennard-Jones particle model. We compared the results obtained by using WCA potential with those by LJ potential. We also compared the results (e.g. ion density and electro-static potential distributions) in each of the above cases with those provided by solving the Poisson-Boltzmann equation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.6
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• pp.513-523
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• 2014

A fluid transport technique is a key issue for the development of microfluidic systems. In this study, the movement of a droplet on horizontal hydrophilic/hydrophobic surfaces, which is a new concept to transport droplets without external power sources that was recently proposed by the author, was simulated using an in-house solution code(PowerCFD). This code employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with interface capturing method(CICSAM) in a volume of fluid(VOF) scheme for phase interface capturing. The droplet transport mechanism is examined through numerical results that include velocity vectors, pressure contours, and total kinetic energy inside and around the droplet.