You-Im Chang

Recent development of enhanced oil recovery in China

This paper gives a brief review of the present status (after 1990) of pilot and field test results of polymer flooding, Xanthan gum flooding and combined chemical flooding enhanced oil recovery (EOR) techniques, and their future in China.

The role of hydration force on the stability of the suspension of Saccharomyces cerevisiae–application of the extended DLVO theory

Abstract Including with the term of repulsive hydration force, the extended DLVO theory adopted in the present paper can successfully describe the stability of cell suspension, Saccharomyces cerevisiae THB001, over a wide range of pH and NaCl concentration. By using the experimental results of zeta potential and turbidity measurements, the parameter values of the hydration energy equation are estimated. It is found that, since the turbidity of cell suspension decreases with the increase of NaCl concentration at isoelectric point, hence the hydration energy existed between cells is repulsive and is an inherent surface property of S. cerevisiae THB001.

Deposition of Brownian particles in the presence of energy barriers of DLVO theory: effect of the dimensionless groups

The problem of deposition of colloidal particles onto a collector surface is investigated theoretically using Brownian dynamics simulations. Using the Kuwabara model for the flow field around the collector surface, we examine the effects of the total interaction energy profiles of the DLVO theory on the collection efficiencies. The simulation results show that: (1) the Brownian diffusion effect of particles becomes pronounced when the value of Reynolds number is close to the laminar flow region, (2) a particle size with a minimum collection efficiency exists, and (3) the dimensionless groups, NL0, NDL, NE1 and NE2 which characterize the height of the primary maximum and the depth of the secondary minimum in the total interaction energy curve play a major role in determining the collection efficiency of Brownian particles with low Reynolds numbers. In addition, we compare the present theoretical results with the available experimental data [FitzPatrick J. A. and Spielman L. A. (1973) J. Colloid Interface Sci. 43, 350–369], and find that the simulation results obtained from the present model coincide more closely with the experimental data than those results obtained from the case where the Brownain diffusion effect is neglected.

Prediction of Brownian particle deposition in porous media using the constricted tube model

The deposition of colloidal particles onto the collector surfaces of porous media is investigated using the Brownian dynamics simulation method. The pore structure in a filter bed was characterized by the constricted tube model. The effects of various shapes of the total interaction energy curves of DLVO theory and the effects of different particle diameters on the collection efficiencies of particles are examined. The simulation results show that the particle collection efficiency is strongly dependent on the geometry of the tube and on the shape of the total interaction energy curve. In a comparison with the available experimental measurements of the filter coefficient, it is found that the present model can give a smaller discrepancy than that of the convective diffusion model in the unfavorable deposition region.

The effect of cationic electrolytes on the electrophoretic properties of bacterial cells

Abstract The effect of cationic electrolytes on the surface potential of a bacterial cell has been investigated via zeta potential measurements. It was found that the order of effectiveness of different cationic electrolytes in reducing the zeta potential values (negatively) is Fe 3+ ⪢ Sr 2+ ⪢ Mg 2+ ⪢ Ca 2+ ⪢ Ba 2+ for Bacillus subtilis , and is Fe 3+ ⪢ Ba 2+ ⪢ Ca 2+ ⪢ Sr 2+ ⪢ Mg 2+ for Pseudomonas fluorescenes . The experimental results (zeta potential versus concentration of cation) were applied to calculate the adsorption free energy for these different cationic electrolytes and the available adsorption sites on the bacterial surface by non-linear regression analysis.

Electrostatic interaction between a charge-regulated particle and a solid surface in electrolyte solution : effect of cationic electrolytes

The effect of cations on the electrostatic interaction between a negative charge-regulated particle and a solid surface of constant negative potential in electrolyte solution is analyzed. Here, we assume that the rate of approach of a particle to a solid surface is faster than that of the dissociation of the ionogenic groups on the surface of particle. In other words, the effect of the time-dependent dissociation of ionogenic groups on the surface of a particle is taken into account. The result of the present study reveals that, although the solid surface is negatively charged, the presence of cations in the suspension medium has a negative effect on the rate of adhesion. The qualitative behaviors in the variation of the interaction force between a particle and a solid surface as a function of separation distance between them predicted by a kinetic model and the corresponding equilibrium model and constant charge density model are entirely different. The rate of approach of a particle to a solid surface is on the order (constant charge density model)>(kinetic model)>(equilibrium model).

Divalent cations can increase cell—substrate repulsion at small distances

Abstract The electrostatic interaction between a cell under charge regulation and a solid surface with constant potential is considered. With the ionizable surface groups of the adhesion cell treated as a self-consistent function of the electrostatic potential, numerical examples are given to illustrate the non-linear Poisson—Boltzmann equation. The results show that the presence of divalent cations in the suspension medium will not always reduce the repulsion force during the whole adhesion period. The distance at which the effect of divalent cations exerted on the interaction force changes from positive (reducing the repulsion force) to negative (increasing the repulsion force) is defined as the critical separation distance.

Application of the three-stage shrinking core model in the transport of reactive gas in the porous media

Abstract A model describing the three-stage noncatalytic gas–solid reactions is presented in this paper. With the equations describing the relationship between the fractional conversion of solid reactant and the reaction time scale, two general features are obtained for this three-stage model. The theoretical prediction of the transport of gaseous reactant through the porous media of a fixed bed column using this three-stage model is also presented in this paper.

Effects of fixed-charge distribution and pH on the electrophoretic mobility of biological cells

The electrophoretic mobility of biological cells is investigated theoretically. In particular, the effects of the distribution of the charges in the surface layer and the pH of bulk liquid phase on the mobility of cells are examined. The former includes the fixed charges due to the dissociation of the functional groups and the charges due to the penetrated electrolyte ions. The present analysis extends previous results in that the fixed charges are distributed nonuniformly across the surface layer of a cell. It is found that the distribution of the fixed charges in the surface layer has a significant effect on its electrophoretic mobility. Thus, assuming that the fixed charges are homogeneously distributed in the surface layer of a cell may lead to a significant deviation.

Gravity-induced flocculation of non-Brownian particles

Abstract The theoretical investigation on the rate of gravity-induced flocculation of non-Brownian particles in quiescent media is presented in this paper. Based on the method of trajectory analysis and incorporating gravitational and interparticle forces (as described by DLVO theory), the stability diagrams for this gravity-induced flocculation of dilute colloidal suspension are provided. Depending on the values of the dimensionless parameters of λ (particle size ratio), ν (electromagnetic retardation parameter), κ (ionic strength), N G (the ratio of gravitational forces to van der Waals attractive forces) and N R (the ratio of electrostatic repulsion forces to van der Waals attractive forces), four distinct regions of flocculation are delineated in the stability diagram, (a) flocculation at the primary minimum of the total interaction energy profile; (b) flocculation at the secondary minimum of the total interaction energy profile; (c) an extremely narrow region of simultaneously flocculation at both the primary minimum and the secondary minimum of the total interaction energy profile; (d) a region of deflocculation where colloidal suspension remains stable. Two critical gravitational parameters ( N G ) C i ( i =1, 2) are successfully applied to explain the occurrence of these four flocculation regions. Theoretical calculations of the capture efficiencies corresponding to these four regions are also presented. It is found that the colloidal suspension can be unstable at low and high gravitational forces, but stable at intermediate values of gravitational forces if the electrostatic repulsion is significant.