• 대한의용생체공학회:의공학회지
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• 제23권4호
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• pp.281-286
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• 2002

심혈관계에서 자주 발생하는 죽상경화증과 혈전의 발생 및 성장에 관한 복잡한 기전을 이해하기 위하여 뇌의 혈액공급을 담당하는 경동맥을 2차원 축대칭으로 모사하여 수치해석하였다. 박동유동 상태에서 경동맥 내에 25%. 50%, 75%의 협착이 형성된 경우에 대하여 혈관내의 속도분포 및 혈류역학적 벽 파라미터들이 고찰되었다. 혈액은 뉴턴유체 및 전단변형률에 따라 점성이 변화하는 비뉴턴유체로 간주되었으며 비뉴턴모델로는 혈액과 유사한 점성치를 나타내는 Carraeu-Yasuda 모델이 적용되었다. 해석 결과 혈관내벽에 작용하는 벽전단응력은 협착이 커질수록 크게 증가하였으며 비뉴턴유체보다 뉴턴유체의 경우에서 벽전단응력이 크게 평가되었다. 벽전단응력 진동지표(OSI)에 의해 시간평균 재부착점이 예측되었는데 비뉴턴유체보다 뉴턴유체의 경우에서 협착 영역으로부터 멀리 떨어진 곳에서 관찰되었다. 시간평균 벽전단응력구배(WSSG)도 협착이 큰 경우에 상당히 크게 나타났는데 비뉴턴유체보다 뉴턴 유체의 경우에 더 큰 값이 나타났다.

• 대한기계학회논문집
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• 제18권3호
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• pp.670-680
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• 1994

The thermophysical properties of Non-Newtonian fluid as the function of the temperature and the concentration are needed in many rheological heat transfer and fluid mechanics problems. The present work investigated the effects of the concentration and the temperature on the thermophysical properties of purely-viscous Non-Newtonian fluids such as the isobaric thermal expansion coefficient, density, zero-shear-rate viscosity, and zero-shear-rate dynamic viscosity within the experimental temperature range from $25^{\circ}C$ to $55^{\circ}C$. The densities of the test fluids were determined as the function of the temperature by utilizing a reference density and the least square equation for the measured isobaric thermal expansion coefficient. As the concentration of purely-viscous Non-Newtonian fluid was increased up to 10,000 wppm, the densities were proportionally increased up to 0.4%. The zero-shear-rate viscosities of test fluids were measured before and after the measurements of the first thermal expansion coefficients and the densities of Non-Newtonian fluid. Even though they were changed up to approximately 22% due to thermal aging and cycling, they had no effects on the thermal expansion coefficients and the densities of Non-Newtonian fluid. The zero-shear-rate dynamic viscosities for purely-viscous Non-Newtonian fluids were compared with the values for distilled water. They showed the similar trend with the zero-shear-rate viscosities due to small differences in the densities for both distilled water and purely-viscous Non-Newtonian fluid.

• Korea-Australia Rheology Journal
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• 제18권3호
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• pp.161-167
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• 2006

This study presents results on the numerical simulation of Newtonian and non-Newtonian flow in a channel obstructed by an asymmetric array of obstacles for clarifying the descriptive ability of current non-Newtonian constitutive equations. Jones and Walters (1989) have performed the corresponding experiment that clearly demonstrates the characteristic difference among the flow patterns of the various liquids. In order to appropriately account for flow properties, the Navier-Stokes, the Carreau viscous and the Leonov equations are employed for Newtonian, shear thinning and extension hardening liquids, respectively. Making use of the tensor-logarithmic formulation of the Leonov model in the computational scheme, we have obtained stable solutions up to relatively high Deborah numbers. The peculiar characteristics of the non-Newtonian liquids such as shear thinning and extension hardening seem to be properly illustrated by the flow modeling. In our opinion, the results show the possibility of current constitutive modeling to appropriately describe non-Newtonian flow phenomena at least qualitatively, even though the model parameters specified for the current computation do not precisely represent material characteristics.

• 대한기계학회논문집
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• 제18권10호
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• pp.2762-2772
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• 1994

Branch flows for Newtonian and non-Newtonian fluids are simulated by the finite volume method. The modified power-law model is employed as a constitutive equation of the non-Newtonian fluids. Numerical analyses are focused on understanding of flow patterns for different values of branch angles, diameter ratios and Reynolds numbers. The numerical results are compared with the existing experimental data. The calculated velocity profiles and pressure variations are in good agreement with available experimental results.

• Korea-Australia Rheology Journal
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• 제15권2호
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• pp.75-82
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• 2003

In this study, with the finite element method we numerically investigate the deformation of liquid drops surrounded by Newtonian or non-Newtonian viscous medium in the axisymmetric contraction flow. 1, 2 or 4 Newtonian or non-Newtonian drops are considered and the truncated power-law model is applied In order to describe non-Newtonian viscous behavior for both fluids. In this type of flow the drop exhibits considerably large deformation, and thus techniques of unstructured mesh generation and auto-remeshing are employed to accurately express the fluid mechanical behavior. We examine the deformation pattern of liquid drops with viscosity dependence different from that of the surrounding medium and also explain their interactions by comparing relative position or speed of drop front.

• 한국유체기계학회 논문집
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• 제17권6호
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• pp.29-37
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• 2014

Non-Newtonian fluid mechanics takes charge of an important role in the oil industries. Especially in the oil well drilling process, the drilling fluid such as mud keeps the drill bit cool and clean during drilling, with suspending drill cuttings and lubricating a drill bit. The purpose of this study is to examine the effect of fluid mud rheological properties to predict different characteristics of non-Newtonian fluid in the mud mixing tank on offshore drilling platforms. In this paper, ANSYS fluent package was used for the simulation to solve the hydrodynamic force and to evaluate mud mixing time. Prediction of the power consumption and the pumping effectiveness has been presented with different operating fluid models as Newtonian and non-Newtonian fluid. The comparison between Newtonain mud model and non-Newtonian mud model is confirmed by the CFD simulation method of drilling mud mixing tank. The results present useful information for the design of the drilling mud mixing tanks and provide some guidance on the use of CFD tool for such non-Newtonian fluid flow.

• KSTLE International Journal
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• 제8권1호
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• pp.16-20
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• 2007

This study introduces a new approach to a falling ball viscometer by using a high speed motion camera to measure the viscosity of both Newtonian and non-Newtonian fluids from the velocity-time data. This method involves capturing continuous photographs of the entire falling motion of the ball as the ball accelerates from the rest to the terminal velocity state. The velocity of a falling ball was determined from the distance traversed by the ball by examining video tape frame by frame using the marked graduations on the surface of the cylinder. Each frame was pre-set at 0.01. Glycerin 74% was used for Newtonian solution, while aqueous solutions of Polyacrylamide and Carboxymethyl Cellulose were for non-Newtonian solutions. The experimental viscosity data were in good agreements with the results obtained from a rotating Brookfield viscometer.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.87-88
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• 2002

To analyze complicated phenomena on the fluid hydrodynamic and the elastic deformation between sliding body surfaces, an analysis to the elastohydrodynamic lubrication of sliding contacts has been developed taking into account the thermal and non-Newtonian effects. The computational technique handled the simultaneous solution of the non-Newtonian hydrodynamic effects, elasticity, the load, the viscosity variation, and temperatures rise. The results included the lubricant pressure profile, film thickness, velocity, shear stress, and temperature distribution, and the sliding frictional force on the surface at various slip conditions. These factors showed a great influence on the behavior resulted in the film shape and pressure distribution. Especially, Non-Newtonian effects and temperature rise by the sliding friction force acted as important roles in the lubrication performance.

• Journal of Mechanical Science and Technology
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• 제16권2호
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• pp.255-261
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• 2002

A newly designed mass-detecting capillary viscometer uses a novel concept to continuously measure non-Newtonian fluids viscosity over a range of shear rates. A single measurement of liquid-mass variation with time replaces the now rate and pressure drop measurements that are usually required by capillary tube viscometers. Using a load cell and a capillary, we measured change in the mass flow rate through a capillary tube with respect to the time, m(t), from which viscosity and shear rate were mathematically calculated. For aqueous polymer solutions, excellent agreement was found between the results from the mass-detecting capillary viscometer and those from a commercially available rotating viscometer. This new method overcomes the drawbacks of conventional capillary viscometers meassuring non-Newtonian fluid viscosity. First, the mass-detecting capillary viscometer can accurately and consistently measure non -Newtonian viscosity over a wide range of shear rate extending as low as 1 s$\^$-1/. Second, this design provides simplicity (i. e., ease of operation, no moving parts), and low cost.

• Elastomers and Composites
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• 제44권3호
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• pp.323-328
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• 2009

고분자 용융 같은 물질의 유변학적인 성질은 전단 흐름에서 복잡한 비 뉴톤 유동 현상을 보인다. 이들 유동성질은 유동단위와 유동부분 사이의 상호작용의 특성에 의하여 결정된다. poly(vinyl alcohol) hydrogel의 비 뉴톤유동 곡선을 cone-plate 레오메타로 여러 온도와 여러 농도 조건에서 얻었다. PVA hydrogel의 유동 곡선을 비 뉴톤 유동식에 적용시켜 유동 파라메타를 얻었다. 유동현상은 전단 속도가 증가함에 따라 전단박화의 틱소트로피 현상을 나타내었다.