• Environmental Engineering Research
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• v.21 no.1
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• pp.1-14
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• 2016

Flocculation is a widely used phase separation technique in industrial unit processes and is typically observed in many natural flow systems. Advances in colloidal chemistry over the past decades has vastly improved our understanding of this phenomenon. However, in many practical applications, process engineering still lags developments in colloidal science thereby creating a gap in knowledge. While significant progress has been made in environmental process engineering research over the past decades, there is still a need to align these two inter-dependent fields of research more closely. This paper provides a comprehensive review of the flocculation mechanism from empirical and theoretical perspective, discuss its practical applications, and examines the need and direction of future research.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.7
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• pp.1276-1281
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• 2010

To analyze the gas discharge phenomena in parallel-plane electrodes, the fully coupled finite element method (FEM) considering secondary electron emission effects in discharge column was adopted in this paper. Two coupled equations of the hydrodynamic diffusion-drift equations for three carriers and the Poisson's equation for electric scalar potential should be solved as a system equation. The proposed method including two secondary electron processes of the photoemission and background ionization has been successfully applied to evaluating the breakdown voltage in parallel-plane electrodes and is verified by comparing its numerical results with the experimental ones. From the obtained results, it is inferred that the proposed numerical scheme will be useful for predicting and understanding streamer transient phenomena.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2696-2699
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• 2008

Microfluidic chips have been frequently utilized to perform biochemical analysis, like cell culture, because they reduce the consumptions of analytes and reagents and automate multi-step analysis processes. It is often critical to monitor temperature in a microchannel for the analyses in order to control a reaction condition of bio or chemical molecules. We propose a novel method to monitor temperature of a microchannel flow by using polydiacetylene (PDA), a conjugated polymer, that has a unique property to transform its color from visible blue to fluorescent red by thermal stress. We inject PDA sensor droplets generated by hydrodynamic instability into a microchannel with a microheater incorporated on the channel bottom. Also, we change the channel temperature by providing the different electric power to the microheater. The results show that the florescence intensity of PDA sensor droplets linearly increases in response to the flow temperature increase within a certain range.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 1999.10a
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• pp.243-252
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• 1999

Recently several research groups using CORMIX, approved by EPA, have been working on the hydrodynamic mixing processes due to the ocean discharges. It provides a useful tool for analyzing near field mixing characteristics through the outfall system. This paper applies CORMIX 1 & 2 to the Pusan Jungang Effluent Outfall System, which is planned to be in the Gamchun harbour and will be completed in 2011. This model output shows the trajectoral variation of dilution and concentration for three cases of outfall system. Dilution differences have been simulated and found the highest dilution condition under the different displacement of outfall system. On the basis of these outputs it will be proposed the optimum outfall system type and location. This approach might contribute on protecting the serious water quality problem due to the ocean discharge.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.47.1-47.1
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• 2019

A gas giant formed in a massive protoplanetary disk via gravitational instability migrates inward due to its gravitational interaction with the disk. Planet migration occurs in various ways depending on the disk structure and internal processes, but previous studies only considered quantitative radiative feedback resulting from mass accretion onto the planet. Allowing for accretion feedback, we perform three-dimensional hydrodynamic simulations with GIZMO to investigate orbital evolution of giant planets in a protoplanetary subject to -cooling. This work shows a planet gains mass due to accretion and gradually opens a gap as it moves inward. The migration in the end halts when the planet clears the gas around its orbit. A more massive planet grows its mass faster and migrates more rapidly, stalling at an orbit farther away from the protostar. Models with a cold disk readily construct a circumplanetary disk and result in high mass growth of the planet. Accretion feedback, in general, reduces the rate of the planet growth and delays migration. We discuss our results with GIZMO in comparison with the previous results with different codes.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.39.2-39.2
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• 2021

To investigate the acceleration of ultra-high energy cosmic rays (UHECRs) in relativistic jets of FR-II galaxies, we simulate high-power jets with jet powers of Q~10^46erg/s in a stratified galaxy cluster halo using a state-of-art relativistic hydrodynamic (RHD) code we have recently developed. With the simulated jet-induced flow profiles, we then perform Monte-Carlo simulations, where the transport of high-energy particles is followed assuming large-angle scatterings in the flow-rest frame. We estimate the energy gains and acceleration times in the acceleration processes by shocks, shear, and turbulence. We present the results and discuss implications on the acceleration of UHECRs in FR II radio jets.

• Journal of the Korean earth science society
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• v.27 no.6
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• pp.659-669
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• 2006

In Kwangyang Bay, the south coast of Korea, surface sediments and sedimentation rates have been investigated to understand the distribution and variation of tidal flat sediments after the construction of sea dyke. The mean grain size of the surface sediments during autumn is coarser, and decrease from winter to summer except for temporarily coarsening in the early summer. The depositional processes are prevalent in spring, while erosional processes are dominant in summer and autumn. This seasonal variation of sedimentary processes show similar results monitored from 2001 to 2003 before the construction of sea dyke. In the northern area of the bay, net annual sedimentation rates show similar results monitored from 2001 to 2003 before the construction of sea dyke. However, in the western area of the bay, net annual sedimentation rates change from erosion-dominated to deposition-dominated environments. It is considered that the western area of the bay is changed to erosion-dominated environments, as a result of the changes of hydrodynamic conditions, caused by sea dyke construction.

• Korean Membrane Journal
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• v.7 no.1
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• pp.1-18
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• 2005

The permeate flux decline due to membrane fouling can be addressed using a variety of theoretical stand-points. Judicious selection of an appropriate theory is a key toward successful prediction of the permeate flux. The essential criterion f3r such a decision appears to be a detailed characterization of the feed solution and membrane properties. Modem theories are capable of accurately predicting several properties of colloidal systems that are important in membrane separation processes from fundamental information pertaining to the particle size, charge, and solution ionic strength. Based on such information, it is relatively straight-forward to determine the properties of the concentrated colloidal dispersion in a polarized layer or the cake layer properties. Incorporation of such information in the framework of the standard theories of membrane filtration, namely, the convective diffusion equation coupled with an appropriate permeate transport model, can lead to reasonably accurate prediction of the permeate flux due to colloidal fouling. The schematic of the essential approach has been delineated in Figure 5. The modern approaches based on appropriate cell models appear to predict the permeate flux behavior in crossflow membrane filtration processes quite accurately without invoking novel theoretical descriptions of particle back transport mechanisms or depending on adjust-able parameters. Such agreements have been observed for a wide range of particle size ranging from small proteins like BSA (diameter ${\~}$6 nm) to latex suspensions (diameter ${\~}1\;{\mu}m$). There we, however, several areas that need further exploration. Some of these include: 1) A clear mechanistic description of the cake formation mechanisms that clearly identifies the disorder to order transition point in different colloidal systems. 2) Determining the structure of a cake layer based on the interparticle and hydrodynamic interactions instead of assuming a fixed geometrical structure on the basis of cell models. 3) Performing well controlled experiments where the cake deposition mechanism can be observed for small colloidal particles (< $1\;{\mu}m$). 4) A clear mechanistic description of the critical operating conditions (for instance, critical pressure) which can minimize the propensity of colloidal membrane fluting. 5) Developing theoretical approaches to account for polydisperse systems that can render the models capable of handing realistic feed solutions typically encountered in diverse applications of membrane filtration.

• Journal of Korean Society on Water Environment
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• v.30 no.5
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• pp.491-502
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• 2014

As meteorology is the driving force for lake thermodynamics and mixing processes, the effects of climate change on the physical limnology and associated ecosystem are emerging issues. The potential impacts of climate change on the physical features of a reservoir include the heat budget and thermodynamic balance across the air-water interface, formation and stability of the thermal stratification, and the timing of turn over. In addition, the changed physical processes may result in alteration of materials and energy flow because the biogeochemical processes of a stratified waterbody is strongly associated with the thermal stability. In this study, a novel modeling framework that consists of an artificial neural network (ANN), a watershed model (SWAT), a reservoir operation model(HEC-ResSim) and a hydrodynamic and water quality model (CE-QUAL-W2) is developed for projecting the effects of climate change on the reservoir water temperature and thermal stability. The results showed that increasing air temperature will cause higher epilimnion temperatures, earlier and more persistent thermal stratification, and increased thermal stability in the future. The Schmidt stability index used to evaluate the stratification strength showed tendency to increase, implying that the climate change may have considerable impacts on the water quality and ecosystem through changing the vertical mixing characteristics of the reservoir.

• KSBB Journal
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• v.30 no.6
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• pp.307-312
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• 2015

Transgenic rice cells using RAmy3D promoter can provide high productivity, and the production of recombinant protein is induced by sugar starvation. In this system, productivity was reduced during the scale-up processes. To ensure the influences of shear stress and oxygen transfer rate, working volume and mixing performances were investigated under various agitation speeds and working volumes. In addition, inoculation methods including suspended cells and filtered cells were compared. Working volumes and shaking speeds were 300, 450 mL and 80, 120 rpm, respectively. Hydrodynamic environment of each condition was measured numerically like mixing time and $k_La$. Good mixing performance and high shear stress were measured at high agitation speed and low volume. The highest level of hCTLA4Ig was 30.7 mg/L at 120 rpm, 300 mL. When conditioned medium was used for inoculation, increased cell growth was noticed during the day 0~4 and decreased slower than filtered cells. Compared with filtered cells, the maximum hCTLA4Ig level reached 37.8 mg/L at 120 rpm, 300 mL and lower protease activity level was observed. In conclusion mixing performance is critical factor for productivity and conditioned medium can have a positive effect on damaged cells caused by hydrodynamic shear stress.