• Korea-Australia Rheology Journal
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• v.16 no.2
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• pp.101-108
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• 2004

The hemodynamics behavior of the blood flow is influenced by the presence of the arterial stenosis. If the stenosis is present in an artery, normal blood flow is disturbed. In the present study, the characteristics of pulsatile flow in the blood vessel with stenosis are investigated by the finite volume method. For the validation of numerical model, the computation results are compared with the experimental ones of Ojha et al. in the case of 45％ stenosis with a trapezoidal profile. Comparisons between the measured and the computed velocity profiles are favorable to our solutions. Finally, the effects of stenosis severity and wall shear stress are discussed in the present computational analysis. It can be seen, where the non-dimensional peak velocity is displayed for all the stenosis models at a given severity of stenosis, that it is exponentially increased. Although the stenosis and the boundary conditions are all symmetric, the asymmetric flow can be detected in the more than 57％ stenosis. The instability by a three-dimensional symmetry-breaking leads to the asymmetric separation and the intense swirling motion downstream of the stenosis.

• Proceedings of the Korean Society of Rheology Conference
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• 2006.06a
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• pp.191-194
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• 2006

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.1
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• pp.9-16
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• 2014

This paper presents the theoretical analysis of a flow driven by surface tension and gravity in an inclined circular tube. A governing equation is developed for describing the displacement of a non-Newtonian fluid(Power-law model) that continuously flows into a circular tube owing to surface tension, which represents a second-order, nonlinear, non-homogeneous, and ordinary differential form. It was found that quantitatively, the theoretical predictions of the governing equation were in excellent agreement with the solutions of the equation for horizontal tubes and the past experimental data. In addition, the predictions compared very well with the results of the force balance equation for steady.

• Journal of computational fluids engineering
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• v.15 no.4
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• pp.1-8
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• 2010

This article describes the numerical investigation of turbulent blood flow in the stenosed artery bifurcation under periodic acceleration of the human body. Numerical analyses for turbulent blood flow were performed with different magnitude of periodic accelerations using a modified turbulence model which was considering drag reduction of non-Newtonian fluid. The blood was considered to be a non-Newtonian fluid which was based on the power-law viscosity. In order to validate the modified $k-{\varepsilon}$ model, numerical simulations were compared with the standard $k-{\varepsilon}$ model and the Malin's low Reynolds number turbulence model for power-law fluid. As results, the modified $k-{\varepsilon}$ model represents intermediate characteristics between laminar and standard $k-{\varepsilon}$ model, and the modified $k-{\varepsilon}$ model showed good agreements with Malin's verified power law model. Moreover, the computing time and computer resource of the modified $k-{\varepsilon}$ model were reduced about one third than low Reynolds number model including Malin's model.

• Korea-Australia Rheology Journal
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• v.19 no.2
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• pp.89-95
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• 2007

The flow characteristics of chicken blood in a micro-tube with a $100{\mu}m$ diameter are investigated using a micro-Particle Image Velocimetry (PIV) technique. Chicken blood with 40% hematocrit is supplied into the micro-tube using a syringe pump. For comparison, the same experiments are repeated for human blood with 40% hematocrit. Chicken blood flow has a cell-free layer near the tube wall, and this layer's thickness increases with the increased flow speed due to radial migration. As a hemorheological feature, the aggregation index of chicken blood is about 50% less than that of human blood. Therefore, the non-Newtonian fluid features of chicken blood are not very remarkable compared with those of human blood. As the flow rate increases, the blunt velocity profile in the central region of the micro-tube sharpens, and the parabolicshaped shear stress distribution becomes to have a linear profile. The viscosity of both blood samples in a low shear rate condition is overestimated, while the viscosity in a high shear rate range is underestimated due to radial migration and the presence of a cell-depleted layer.

• Preventive Nutrition and Food Science
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• v.22 no.1
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• pp.62-66
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• 2017

This study was conducted to determine the rheological properties of gochujang and chogochujang at different temperatures (25, 35, and $45^{\circ}C$). Rheological properties of the samples were determined using a rotational rheometer at a shear range of 1 to $40s^{-1}$. Gochujang and chogochujang were found to be non-Newtonian fluids according to the Herschel-Bulkley model. Yield stress and consistency coefficient of gochujang at different temperatures were higher than those of chogochujang, whereas the opposite was observed for flow behavior index. Moreover, all rheological properties of gochujang and chogochujang decreased with increasing temperature. The consistency coefficient was related to temperature using an Arrhenius-type relationship. Gochujang (14.48 kJ/mol) had slightly higher activation energy than chogochujang (14.03 kJ/mol).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.6
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• pp.773-778
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• 1997

The present study investigates the effect of the shear rate-dependent thermal conductivity of non-newtonian fluids on the heat transfer enhancement in a 2:1 rectangular duct flow. An axially-constant heat flux and a peripherally-constant temperature boundary conditions(H1) was adopted for a top-wall-heated configuration. The present numerical results of Nusselt numbers for SRDC(Separan) show heat transfer enhancement over those of SRIC. The Nusselt numbers increased linearly as Reynolds numbers increased. The heat transfer enhancement is due to an increased thermal conductivity near the wall, which is attributed to the shear rate-dependence.

• Geotechnical Engineering
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• v.13 no.5
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• pp.125-132
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• 1997

It is observed that debris mitred with a wide range of soil particles and water moves downwards like viscous fluid soon after a landslide has triggered. An Assumption can be made from the field observation that the debris flow behaves as a kind of non(non-Newtoniron) Newtonian fluid which has non linear viscosity. In this study, a series of viscosity tests are carried out to measure rheological properties of debris by using a viscometer with semples taken from a landslide site. It is proved that debris flows behave as Bingham plastic mod el of non-Newtonian fluid. This model can be used predict the movement of debris flows.

• Journal of the Korean Society of Safety
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• v.3 no.1
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• pp.15-19
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• 1988

The falling ball viscometer has been widely used for measuring the viscosity of the Newtonian fluids because of its simple theory and low cost. The use of the falling ball viscometer for measuring the non-Newtonian viscosity has been of interest to rheologists for some years. The analysis of the experimental results in a falling ball viscometer rest on Stokes law which yields the terminal velocity for a sphere moving through an infinite medium of fluids. An attempt to use the falling ball viscometer to measure the non-Newtonian viscosity in the intermediate shear rate ranEe was sucessfully accomplished by combining the direct experimental obserbations with a simple analytical model for the average shear-stress and shear rate at, the surface of a sphere. In the experiments with highly viscoelastic polyacrylamide solutions the terminal velocity was observed to be dependent on the time interval between the dropping of successive balls. The time-dependent phenomenon was used to determine characteristic diffusion times of the concentrated solutions of polyacrylamide.

• Korea-Australia Rheology Journal
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• v.12 no.3_4
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• pp.165-173
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• 2000

Three-dimensional numerical simulation of isothermal/nonisothermal coextrusion process of two immiscible polymers through a rectangular channel has been done using the finite element method. The encapsulation phenomenon with the less viscous layer encapsulating the more viscous layer was investigated with the generalized Newtonian fluids. The interface position around the symmetric plane obtained by numerical simulation nearly coincided with the one observed in experiments, but the degree of encapsulation was less than the one observed experimentally. Open boundary condition method was found to be applied to the simulation of nonisothermal coextrusion process, however, the results are not far from those using the fully developed boundary condition, because the temperature development along the downstream direction is very slow in the case of convection dominated flow. When the inlet velocity is increased, the interface profile does not change in isothermal flow, while it moves upward in nonisothermal situation. The degree of encapsulation decreases along the downstream direction in nonisothermal flow. When the inlet temperature increases compared to the wall temperature, the outlet interface moves downward and the degree of encapsulation increases. The difference of degree of encapsulation between the simulation and the experiments seems to arise from the viscoelastic effect of the materials. It was concluded that the nonisothermal effect alone does not explain the complex coextrusion process and the viscoelastic effect needs to be considered.