A method of isolating surface tension and yield stress effects in a U-shaped scanning capillary-tube viscometer using a Casson model

2002 ◽  
Vol 103 (2-3) ◽  
pp. 205-219 ◽  
Author(s):  
Sangho Kim ◽  
Young I. Cho ◽  
William N. Hogenauer ◽  
Kenneth R. Kensey
Keyword(s):  
Surface Tension ◽  
Yield Stress ◽  
Capillary Tube ◽  
Stress Effects ◽  
Casson Model

scholarly journals Natural convection of Casson fluid in a square enclosure

2020 ◽  
Vol 16 (5) ◽  
pp. 1245-1259
Author(s):  
Mohammad Saeid Aghighi ◽  
Christel Metivier ◽  
Hamed Masoumi
Keyword(s):  
Natural Convection ◽  
Yield Stress ◽  
Casson Fluid ◽  
Small Degree ◽  
Content Type ◽  
Square Enclosure ◽  
Casson Model ◽  
Side Walls ◽  
The Mean ◽  
Viscoplastic Models

PurposeThe purpose of this paper is to analyze the natural convection of a yield stress fluid in a square enclosure with differentially heated side walls. In particular, the Casson model is considered which is a commonly used model.Design/methodology/approachThe coupled conservation equations of mass, momentum and energy related to the two-dimensional steady-state natural convection within square enclosures are solved numerically by using the Galerkin's weighted residual finite element method with quadrilateral, eight nodes elements.FindingsResults highlight a small degree of the shear-thinning in the Casson fluids. It is shown that the yield stress has a stabilizing effect since the convection can stop for yield stress fluids while this is not the case for Newtonian fluids. The heat transfer rate, velocity and Yc obtained with the Casson model have the smallest values compared to other viscoplastic models. Results highlight a weak dependence of Yc with the Rayleigh number: Yc∼Ra0.07. A supercritical bifurcation at the transition between the convective and the conductive regimes is found.Originality/valueThe originality of the present study concerns the comprehensive and detailed solutions of the natural convection of Casson fluids in square enclosures with differentially heated side walls. It is shown that there exists a major difference between the cases of Casson and Bingham models, and hence using the Bingham model for analyzing the viscoplastic behavior of the fluids which follow the Casson model (such as blood) may not be accurate. Finally, a correlation is proposed for the mean Nusselt number Nu¯.

scholarly journals Mathematical Analysis of Non-Newtonian Blood Flow in Stenosis Narrow Arteries

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Somchai Sriyab
Keyword(s):  
Blood Flow ◽  
Skin Friction ◽  
Yield Stress ◽  
Newtonian Fluid ◽  
Mathematical Analysis ◽  
Viscosity Coefficient ◽  
Plasma Viscosity ◽  
Casson Model ◽  
Mild Stenosis ◽  
Normal Artery

The flow of blood in narrow arteries with bell-shaped mild stenosis is investigated that treats blood as non-Newtonian fluid by using the K-L model. When skin friction and resistance of blood flow are normalized with respect to non-Newtonian blood in normal artery, the results present the effect of stenosis length. When skin friction and resistance of blood flow are normalized with respect to Newtonian blood in stenosis artery, the results present the effect of non-Newtonian blood. The effect of stenosis length and effect of non-Newtonian fluid on skin friction are consistent with the Casson model in which the skin friction increases with the increase of ither stenosis length or the yield stress but the skin friction decreases with the increase of plasma viscosity coefficient. The effect of stenosis length and effect of non-Newtonian fluid on resistance of blood flow are contradictory. The resistance of blood flow (when normalized by non-Newtonian blood in normal artery) increases when either the plasma viscosity coefficient or the yield stress increases, but it decreases with the increase of stenosis length. The resistance of blood flow (when normalized by Newtonian blood in stenosis artery) decreases when either the plasma viscosity coefficient or the yield stress increases, but it decreases with the increase of stenosis length.

Capillary Flow of Yield-Stress Fluids in Microchannels

2006 ◽  
Author(s):  
V. Bertola
Keyword(s):  
Yield Stress ◽  
Flow Regime ◽  
Capillary Flow ◽  
Capillary Tube ◽  
Plug Flow ◽  
Wall Slip ◽  
Critical Distance ◽  
Tube Diameter ◽  
Force Balance ◽  
Theoretical Argument

The wicking of a model yield-stress fluid (hair-gel solution in water) in a capillary tube is studied experimentally. By changing the hair-gel concentration in the solution, the yield stress varied from 5 to 20 Pa. A simple force balance between capillary and viscous forces suggests that the fluid should stop flowing as soon as the wall shear stress reaches the yield value, at a critical distance from the inlet which is independent of the tube diameter. However, this theoretical argument is not confirmed by experiments, which show that the fluid moves well beyond the critical distance determined theoretically, and that there is a well-defined effect of the tube diameter. It is proposed that such behavior may be determined by wall slip, which causes the flow to switch from the Poiseuille flow regime to the plug flow regime.

scholarly journals Comparative Analysis of Mathematical Models for Blood Flow in Tapered Constricted Arteries

2012 ◽  
Vol 2012 ◽  
pp. 1-34 ◽  
Author(s):  
D. S. Sankar ◽  
Yazariah Yatim
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Yield Stress ◽  
Flow Rate ◽  
Core Region ◽  
Core Radius ◽  
The Core ◽  
Casson Model ◽  
Longitudinal Impedance ◽  
Two Fluid

Pulsatile flow of blood in narrow tapered arteries with mild overlapping stenosis in the presence of periodic body acceleration is analyzed mathematically, treating it as two-fluid model with the suspension of all the erythrocytes in the core region as non-Newtonian fluid with yield stress and the plasma in the peripheral layer region as Newtonian. The non-Newtonian fluid with yield stress in the core region is assumed as (i) Herschel-Bulkley fluid and (ii) Casson fluid. The expressions for the shear stress, velocity, flow rate, wall shear stress, plug core radius, and longitudinal impedance to flow obtained by Sankar (2010) for two-fluid Herschel-Bulkley model and Sankar and Lee (2011) for two-fluid Casson model are used to compute the data for comparing these fluid models. It is observed that the plug core radius, wall shear stress, and longitudinal impedance to flow are lower for the two-fluid H-B model compared to the corresponding flow quantities of the two-fluid Casson model. It is noted that the plug core radius and longitudinal impedance to flow increases with the increase of the maximum depth of the stenosis. The mean velocity and mean flow rate of two-fluid H-B model are higher than those of the two-fluid Casson model.

scholarly journals Effects of Surface Tension and Yield Stress on Mucus Plug Rupture: A Numerical Study

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Yingying Hu ◽  
Francesco Romanò ◽  
James B. Grotberg
Keyword(s):  
Surface Tension ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Yield Stress ◽  
Pressure Difference ◽  
Rupture Process ◽  
Viscoplastic Fluid ◽  
Air Interface ◽  
Mucus Plug ◽  
Wall Shear

Abstract We study the effects of surface tension and yield stress on mucus plug rupture. A three-dimensional simplified configuration is employed to simulate mucus plug rupture in a collapsed lung airway of the tenth generation. The Herschel–Bulkley model is used to take into account the non-Newtonian viscoplastic fluid properties of mucus. Results show that the maximum wall shear stress greatly changes right prior to the rupture of the mucus plug. The surface tension influences mainly the late stage of the rupture process when the plug deforms greatly and the curvature of the mucus–air interface becomes significant. High surface tension increases the wall shear stress and the time needed to rupture since it produces a resistance to the rupture, as well as strong stress and velocity gradients across the mucus–air interface. The yield stress effects are pronounced mainly at the beginning. High yield stress makes the plug take a long time to yield and slows down the whole rupture process. When the effects induced by the surface tension and yield forces are comparable, dynamical quantities strongly depend on the ratio of the two forces. The pressure difference (the only driving in the study) contributes to wall shear stress much more than yield stress and surface tension per unit length. Wall shear stress is less sensitive to the variation in yield stress than that in surface tension. In general, wall shear stress can be effectively reduced by the smaller pressure difference and surface tension.

scholarly journals Flow onset for a single bubble in a yield-stress fluid

2021 ◽  
Vol 933 ◽  
Author(s):  
Ali Pourzahedi ◽  
Emad Chaparian ◽  
Ali Roustaei ◽  
Ian A. Frigaard
Keyword(s):  
Surface Tension ◽  
Yield Stress ◽  
Computational Methods ◽  
Capillary Number ◽  
Single Bubble ◽  
Two Dimensional ◽  
Bubble Shape ◽  
Static Limit ◽  
Yield Stress Fluid

We use computational methods to determine the minimal yield stress required in order to hold static a buoyant bubble in a yield-stress liquid. The static limit is governed by the bubble shape, the dimensionless surface tension ( $\gamma$ ) and the ratio of the yield stress to the buoyancy stress ( $Y$ ). For a given geometry, bubbles are static for $Y > Y_c$ , which we determine for a range of shapes. Given that surface tension is negligible, long prolate bubbles require larger yield stress to hold static compared with oblate bubbles. Non-zero $\gamma$ increases $Y_c$ and for large $\gamma$ the yield-capillary number ( $Y/\gamma$ ) determines the static boundary. In this limit, although bubble shape is important, bubble orientation is not. Two-dimensional planar and axisymmetric bubbles are studied.

The effect of viscosity, yield stress, and surface tension on the deformation and breakup profiles of fluid filaments stretched at very high velocities

2019 ◽  
Vol 263 ◽  
pp. 130-139 ◽  
Author(s):  
R. Valette ◽  
E. Hachem ◽  
M. Khalloufi ◽  
A.S. Pereira ◽  
M.R. Mackley ◽  
...  
Keyword(s):  
Surface Tension ◽  
Yield Stress ◽  
Very High

scholarly journals Effects of Tube Radius and Surface Tension on Capillary Rise Dynamics of Water/Butanol Mixtures

2021 ◽  
Vol 11 (8) ◽  
pp. 3533
Author(s):  
Seungyeop Baek ◽  
Sungjin Jeong ◽  
Jaedeok Seo ◽  
Sanggon Lee ◽  
Seunghwan Park ◽  
...  
Keyword(s):  
Surface Tension ◽  
High Performance ◽  
Liquid Surface ◽  
Capillary Tube ◽  
Capillary Rise ◽  
Heat Pipes ◽  
Water Mixture ◽  
Tube Radius ◽  
Liquid Surface Tension ◽  
Linear Correlations

Capillary-driven action is an important phenomenon which aids the development of high-performance heat transfer devices, such as microscale heat pipes. This study examines the capillary rise dynamics of n-butanol/water mixture in a single vertical capillary tube with different radii (0.4, 0.6, and 0.85 mm). For liquids, distilled water, n-butanol, and their blends with varying concentrations of butanol (0.3, 0.5, and 0.7 wt.%) were used. The results show that the height and velocity of the capillary rise were dependent on the tube radius and liquid surface tension. The larger the radius and the higher the surface tension, the lower was the equilibrium height (he) and the velocity of rise. The process of capillary rise was segregated into three characteristic regions: purely inertial, inertial + viscous, and purely viscous regions. The early stages (purely inertial and inertial + viscous) represented the characteristic heights h1 and h2, which were dominant in the capillary rise process. There were linear correlations between the characteristic heights (h1, h2, and he), tube radius, and surface tension. Based on these correlations, a linear function was established between each of the three characteristic heights and the consolidated value of tube radius and surface tension (σL/2πr2).

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