• Journal of the Korean Chemical Society
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• v.15 no.6
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• pp.303-312
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• 1971

Dependence of the flow behavior of aqueous suspension of Black Hills bentonite on the concentration and the types of electrolytes was stydied. The flow properties were measured with a Couette-type totational viscometer. On addition of monovalent cations, the apparent viscosity determined from the reproducible flow curves (shear rate vs. shear stress) decreased followed by a rise as the ionic concentration further increased. Addition of multivalent cations (di- and tri-) resulted in the viscosity which increased to a maximum then decreased to a constant value. Anions of different chatges produced essentially the same relationship between viscosity and electrolyte concentration. The flow behavior of the electrolyte-containing suspensions was rationalized in terms of the Derjaguin-Landau-Verwey-Overbeek theory of colloidal stability and the generalized theory of viscosity.

• Bulletin of the Korean Chemical Society
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• v.4 no.5
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• pp.212-217
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• 1983

Depending on the range of shear rates, temperatures and concentrations, the potato starch suspension in water behaves as a typical dilatant system. The flow curves of the suspension at various concentrations and temperatures were obtained by using a Couette type rotational viscometer. The flow mechanism of the suspension is explained by a structure model of starch granules in the suspension. Based on the experimental results, a general flow equation for the dilatant system is proposed. By analyzing the temperature dependency of the relaxation time, the activation enthalpy and activation entropy for flow in the starch-water suspension were calculated, the former being about 10 kcal/mol.

• Korea-Australia Rheology Journal
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• v.14 no.4
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• pp.161-174
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• 2002

A new technique for numerical calculation of viscoelastic flow based on the combination of Neural Net-works (NN) and Brownian Dynamics simulation or Stochastic Simulation Technique (SST) is presented in this paper. This method uses a "universal approximator" based on neural network methodology in combination with the kinetic theory of polymeric liquid in which the stress is computed from the molecular configuration rather than from closed form constitutive equations. Thus the new method obviates not only the need for a rheological constitutive equation to describe the fluid (as in the original Calculation Of Non-Newtonian Flows: Finite Elements St Stochastic Simulation Techniques (CONNFFESSIT) idea) but also any kind of finite element-type discretisation of the domain and its boundary for numerical solution of the governing PDE's. As an illustration of the method, the time development of the planar Couette flow is studied for two molecular kinetic models with finite extensibility, namely the Finitely Extensible Nonlinear Elastic (FENE) and FENE-Peterlin (FENE-P) models.P) models.

• Journal of the Korean Chemical Society
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• v.15 no.6
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• pp.293-303
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• 1971

The theological properties of aqueous suspensions of Black Hills bentonite were measured by using a Couette-type viscometer. Three kinds of flow units in aqueous bentonite suspension were postulated. Each has a different average relaxation time, one Newtonian. One of the non-Newtonian types is thixotropic, and the other is non-thixotropic. The thixotropic non-Newtonian unit is transformed to a Newtonian unit by shear stress. If the stress is relieved, the transformed unit returns to its original state. Two flow equations were derived by introducing chemical kinetics consideration for such a transition into the generalized theory of viscous flow. One equation describes the "upcurve," a diagram of rate of sheat versus shear stress, obtained by increasing the rate of shear, and the other relates to the "downcurve" obtained by decreasing the shear rate. The equations satisfactorilly describe the experimental thixotropic hysteresis of bentonite suspensions. The equations also were successfully applied to the flow curves of the suspensions containing various amounts of monovalent electrolyte (KCI).

• Korea-Australia Rheology Journal
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• v.20 no.3
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• pp.143-152
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• 2008

Simulations of solutions of flexible polymer molecules during flow in simple or complex confined geometries are performed. Concentrations from ultradilute up to near the overlap concentration are considered. As concentration increases, the hydrodynamic migration effects observed in dilute solution unidirectional flows (Couette flow, Poiseuille flow) become less prominent, virtually vanishing as the overlap concentration is approached. In a grooved channel geometry, the groove is almost completely depleted of polymer chains at high Weissenberg number in the dilute limit, but at finite concentration this depletion effect is dramatically reduced. Only upon inclusion of hydrodynamic interactions can these phenomena be properly captured.

• Bulletin of the Korean Chemical Society
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• v.17 no.3
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• pp.262-268
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• 1996

Flow properties of all suspensions are controlled by their flow units. The factors effecting on the flow units are the characteristics of the particle itself (surface properties, particle sizes, particle shapes and etc.), the electrostatic interactions among the particles and the influences of the medium in the suspensions. Here, we studied the transition between the flow units with shear rate which can be added to the above factors. For the concentrated starch-water suspensions, by using the Couette type rotational viscometer, we confirmed that at low shear rate, dilatancy is appeared, but it is transformed to thixotropy with increasing shear rate. In order to explain this fact, we derived the following flow equation, representing the transition from dilatancy to thixotropy with shear rate, by assuming the equilibrium between the flow units. f = X1β1s./α1 + 1/(1+Kexp(c0s.2/RT))((1-X1)/α2)sinh-1{(β2)0 s. exp(c2s.2/RT)} + K exp(c0s.2/RT)/(1+K exp(c0s.2/RT))((1-X1)/α3)sinh-1{(β3)0 s. exp(-c3s.2/RT)} By applying this flow equation to the experimental flow curves for the concentrated starch-water suspensions, the flow parameters were obtained. And, by substituting the obtained flow parameters to the flow equation, the theoretical flow curves were reproduced. Also, Ostwald curve was represented by applying the flow equation, and the applicability for stress relaxation was discussed.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.207-212
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• 2001

Electro-Rheological(ER) fluid are suspensions which show an abrupt increase in rheological properties under electric fields. ER effects arise from electrostatic forces between the starch particles dispersed in the electrically insulating silicone oil, induced when an electric field is applied. Yield stress of the fluids were measured on the couette cell type rheometer as a function of electric fields. This paper presents performance analyses of four types of the two parallel-plate. Which have different electrode length and width but same electrode area. On the basis of the pressure drop and flow rate analysis. Four types of the two parallel-plate are designed and manufactured. Using ER fluid, it is possible to directly interface between electric signals and fluid power without moving parts.

• Korea-Australia Rheology Journal
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• v.16 no.3
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• pp.129-134
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• 2004

The aggregation characteristics of red blood cells (RBCs) were measured using a newly developed light-transmission slit rheometer. Conventional methods of RBC disaggregation such as the rotational Couette system were replaced with a pressure-driven slit flow system with a vibrational mechanism. Using a vibration generator, one can disaggregate the RBC aggregates stored in the slit. While shear stress decreases exponentially, instantaneous pressure and the transmitted light intensity were measured over time. Applying an abrupt shearing flow after disaggregation caused a rapid elongation of the RBCs followed by loss of elongation with the decreasing shear stress. While the shear stress is further decreasing, the RBCs start to re-aggregate and the corresponding transmitted intensity increases with time, from which the aggregation indices can be obtained using a curve-fitting program.

• Journal of Ship and Ocean Technology
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• v.4 no.1
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• pp.1-10
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• 2000

A low-order potential based boundary element method is applied for the prediction of the performance of flapped rudders as well as all-movable rudders in steady inflow. In order to obtain a reasonable solution at large angles of attack, the location of the trailing wake sheet is determined by aligning freely with the local flow. The effect of the wake sheet roll-up is also included with use of a high order panel method. The flow in the gap of a flapped rudder is modeled as Couette flow and its effect is introduced into the kinematic boundary conditions for flux at both the inlet and the outlet of the gap. In order to validate the present method, the method is applied for a series of rudders and the computational results on forces and moments are compared with experimental data. The effect of the gap size on the forces and moments is also presented.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.6 s.249
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• pp.578-586
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• 2006

Numerical simulations are carried out to investigate the thermal effects of the gravitational potential on the centrifugal instability of a Taylor-Couette flow, and to further study the detailed flow fields and flow bifurcations to spiral vortices. The effects of centrifugal potential on the centrifugal instability are also investigated in the current study. Spiral vortices have various types of mode depending on Grashof number and Reynolds number. The correlation of Richardson number with the spiral angle of the spiral vortices shows that the structure of the spiral vortices strongly depends on the Richardson number. The heat transfer rate of the inner cylinder increases with increasing Grashof number. It is also confirmed that the torque required to rotate the inner cylinder increases as Grashof number increases.