Large-scale calculation of hydrodynamic transport properties for random suspensions of hard-sphere particles

Sangkyun Koo 한국화학공학회 2016 Korean Journal of Chemical Engineering Vol.33 No.8

A numerical method based on fast multipole summation scheme is used to calculate hydrodynamic interactions in random suspensions of non-colloidal hard-sphere particles. The calculation is carried out for suspensions of 1,024 particles randomly placed in periodic unit cell to determine hydrodynamic transport properties such as permeability of a viscous flow through porous medium, effective viscosity of suspension, and sedimentation velocity of the suspended particles. The particle volume fraction φ ranges from 0.01 to 0.25. Effect of particle number N on the transport properties was examined through the numerical calculations with N=64-1,024. It is shown that sedimentation velocity increases with N approaching an estimate for infinite N, and the finite N effect is negligible in effective viscosity and permeability problems. The present scheme is quite useful for obtaining a statistically-averaged quantity for random suspensions. As an example, ensemble-averaged velocity when position of one particle is fixed is numerically obtained in sedimentation problem. The numerical results are shown to be in excellent agreement with theoretical prediction.

Effective viscosity of bidisperse suspensions

Koo Sangkyun,Song Kwang Ho The Korean Society of Rheology 2005 Korea-Australia rheology journal Vol.17 No.1

We determine the effective viscosity of suspensions with bidisperse particle size distribution by modifying an effective-medium theory that was proposed by Acrivos and Chang (1987) for monodisperse suspensions. The modified theory uses a simple model that captures some important effects of multi-particle hydrodynamic interactions. The modifications are described in detail in the present study. Estimations of effective viscosity by the modified theory are compared with the results of prior work for monodisperse and bidisperse suspensions. It is shown that the estimations agree very well with experimental or other calculated results up to approximately 0.45 of normalized particle volume fraction which is the ratio of volume faction to the maximum volume fraction of particles for bidisperse suspensions.

Estimation of hindered settling velocity of suspensions

Sangkyun Koo 한국공업화학회 2009 Journal of Industrial and Engineering Chemistry Vol.15 No.1

Four effective-medium models (EM-I, II, III, IV) are utilized and compared for determining hindered settling velocity of equi-sized particles in a viscous fluid. Among the models, EM-IV model is found to accurately predict the effective viscosity and the hindered settling velocity of monodisperse suspensions. In EM-IV model which was developed for determining the diffusivity of proteins in a biological membrane by Dodd et al. [T.L. Dodd, D. A. Hammer, A.S. Sangani, D.L. Koch, J. Fluid Mech. 293 (1995) 147], the effective-medium region begins at the distance R = a[(1 - S(0))/Φ]1/3 from the origin where the center of the test particle is located, where a is the radius of the particle, f is the volume fraction of the particles in the suspension, and S(0) is the zero wavenumber limit of the structure factor. The estimations by EM-IV model agree very well with the exact calculations and the experimental observations. The hindered settling velocity U of the particles is given, in Richardson–Zaki form, by U/U0 = (1-Φ)5.5, where U0 is the settling velocity for an isolated particle.

Effective viscosity of bidisperse suspensions

송광호,Sangkyun Koo 한국유변학회 2005 Korea-Australia rheology journal Vol.17 No.1

We determine the effective viscosity of suspensions with bidisperse particle size distribution by modifying an effective-medium theory that was proposed by Acrivos and Chang (1987) for monodisperse suspensions. The modified theory uses a simple model that captures some important effects of multi-particle hydrodynamic interactions. The modifications are described in detail in the present study. Estimations of effective viscosity by the modified theory are compared with the results of prior work for monodisperse and bidisperse suspensions. It is shown that the estimations agree very well with experimental or other calculated results up to approximately 0.45 of normalized particle volume fraction which is the ratio of volume faction to the maximum volume fraction of particles for bidisperse suspensions.

Rheological estimation of aggregate size for a colloidal suspension of carbon black particles

Dokyung Kim,Sangkyun Koo 한국유변학회 2020 Korea-Australia rheology journal Vol.32 No.4

Colloidal aggregation is quantitatively characterized by a rheological analysis of the colloidal suspension at various particle concentrations. The rheological analysis is combined with fractal concept to estimate the compactness, size, and size variation with shear stress on colloidal aggregates. The rheological measurement is carried out for a colloidal suspension of 24 nm carbon black particles suspended in ethylene glycol. The particle concentration ranges from 6.0 to 8.5 percent in volume, which is non-dilute regime where colloidal gelation occurs. Elastic modulus behavior with the particle concentration provides fractal dimension of aggregates. With the fractal dimension, concentration-dependent shear stress behavior is used to estimate aggregate size and its variation with shear stress through a rheological modeling. The estimated fractal dimension of aggregate is 2.020 and the average aggregate size exponentially decreases with the shear rate in the range 1152.24 nm at 1 s^-1 to 150.00 nm at 1000 s^-1. These estimations are compared with those from optical measurement using static small-angle X-ray scattering (SAXS) technique. The SAXS analysis gives the fractal dimension of 2.495 and the average aggregate size is 320.56 nm. It is found that the optical measurement gives slightly higher fractal dimension and the aggregate size is numerically close to that predicted one around the shear rate 68.7 s^-1 where steep size reduction turns into being slow.

Application of Scaling Theories to Estimate Particle Aggregation in a Colloidal Suspension

( Soongwan Park ),( Sangkyun Koo ) 한국화학공학회 2022 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.60 No.2

Average aggregate size in particulate suspensions is estimated with scaling theories based on fractal concept and elasticity of colloidal gel. The scaling theories are used to determine structure parameters of the aggregates, i.e., fractal dimension and power-law exponent for aggregate size reduction with shear stress using scaling behavior of elastic modulus and shear yield stress as a function of particle concentration. The structure parameters are utilized to predict aggregate size which varies with shear stress through rheological modeling. Experimentally rheological measurement is conducted for aqueous suspension of zinc oxide particles with average diameter of 110 nm. The predicted aggregate size is about 1135 nm at 1 s^-1 and 739 nm at 1000 s^-1 on the average over the particle concentrations. It has been found that the predicted aggregate size near 0.1 s^-1 agrees with that the measured one by a dynamic light scattering analyzer operated un-sheared.

고분자 분산제 혼합액에 분산된 탄소나노튜브의 응집과 분산액의 탄성 거동

이다은(Daeun Lee),구상균(Sangkyun Koo) 한국고분자학회 2022 폴리머 Vol.46 No.1

다중벽 탄소나노튜브(CNT) 분산액의 탄성적 성질을 이용하여 CNT 입자의 미시적 응집구조에 대해 분석하였다. CNT 입자를 고분자 분산제가 혼합된 에틸렌글리콜에 분산시켜 얻은 분산액에 대해 저장 탄성률과 항복응력의 입자 농도 의존성에 관한 스케일링 이론을 적용하여 응집체의 프랙탈 차원를 비롯한 응집구조 변수들을 구하였다. CNT의 분산이 120 분까지 진행되면서 프랙탈 차원이 분산시간 30분일 때 1.92로부터 120분에서 1.28까지 지속적으로 감소하는 경향을 보임으로써 CNT 응집체가 엉겨 있는 형태에서 1차원적 선의 형태로 변해가는 것으로 나타났다. 다른 미시적 구조 변수들, 유변학적 물성과 전기전도도의 분산시간에 따른 변화도 프랙탈 차원의 변화에 부합하는 결과를 보였다. Aggregates of multi-walled carbon nanotubes (CNT) were microscopically analyzed using elastic properties of their dispersion. Scaling theories based on the dependency of elastic modulus and yield stress on the CNT concentration were applied to the aggregated CNT particles suspended in ethylene glycol mixed with a polymeric dispersant. Using the scaling theories, we obtained structural parameters including fractal dimension of the aggregates. As milling time for CNT dispersion increases up to 120 min, the fractal dimension of the aggregates continuously decreases from 1.92 at 30 min to 1.28 at 120 min. This means that entangled shape of aggregates is turning into one dimensional linear shape as the dispersion time increases. It was found that overall trend of other structural parameters, rheological properties, and electrical conductivity with the dispersion time agreed with that of the fractal dimension.

Study on Factors Influencing the Productivity of Germ-line Chimeras from Embryonic Stem Cells

Sun-Uk Kim,Bon-Sil Koo,Sung-Lan Yu,Tae-Hoon Lee,Sangkyun Jung,Kyung-Kwang Lee,Dae-Yeul Yu 한국실험동물학회 2000 한국실험동물학회 학술발표대회 논문집 Vol.2000 No.-

Benzoyl Peroxide의 반복투여 독성과 생식 및 발생독성

송상환(Sanghwan Song),김수현(Su-Hyon Kim),배희경(Heekyung Bae),김미경(Mikyung Kim),구현주(Hyun Ju Koo),박광식(Kwangsik Park),이상균(Sangkyun Lee),박중훈(Joonghoon Park),최은실(Eun-Sil Choi),이문순(Moon-Soon Lee) 한국독성학회 2003 Toxicological Research Vol.19 No.2

This study was carried out to assess the combined repeated dose, reproduction and developmental toxicities of benzoyl peroxide for OECD SIDS (Screening Information Data Set) program. Male and female Sprague-Dawley rats were exposed to benzoyl peroxide at dose levels of 0, 250, 500 and 1,000 mg/kg/day for 29 days for males and for 41~51 days for females. No deaths were found in all animals including control group during exposure period. No hematological effects attributable to benzoyl peroxide were observed in all treated groups. Significant decrease in the weight of testes and epididymis were observed in males at 1,000 mg/kg/day. In females at 1,000 mg/kg/day, slight histopathological effects in uterus such as epithelial vacuolation or hyperplasia were observed. No treatment-related changes in precoital time and rate of copulation, fertility and gestation period were noted in all treated groups. There was no evidence of teratogenic effect of benzoyl peroxide, but body weight of pups at 1,000 mg/kg/day was significantly decreased. NOAEL for combined repeated dose and reproduction/developmental toxicity was 500 mg/kg/day.