Time-dependent rheological behavior of blood at low shear in narrow vertical tubes

1993 ◽  
Vol 265 (2) ◽  
pp. H553-H561 ◽  
Author(s):  
C. Alonso ◽  
A. R. Pries ◽  
P. Gaehtgens
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Shear Flow ◽  
Apparent Viscosity ◽  
Flow Behavior ◽  
Time Dependent ◽  
Flow Conditions ◽  
Wall Shear ◽  
Vertical Tubes ◽  
Low Shear

The time-dependent flow behavior of normal human blood after a sudden reduction of wall shear stress from 5,000 mPa to a low level (2-100 mPa) was studied during perfusion of vertical tubes (internal diam 28-101 microns) at constant driving pressures. Immediately after the implementation of low-shear flow conditions the concentration of red blood cells (RBCs) near the tube wall started to decrease, and marginal plasma spaces developed as a result of the assembly of RBC aggregates. This was associated with a time-dependent increase of flow velocity by up to 200% within 300 s, reflecting a reduction of apparent viscosity. These time-dependent changes of flow behavior increased strongly with decreasing wall shear stress and with increasing tube diameter. A correlation between the width of the marginal plasma layer and relative apparent viscosity was obtained for every condition of tube diameter, wall shear stress, and time. Time-dependent changes of blood rheological properties could be relevant in the circulation, where the blood is exposed to rapid and repeated transitions from high-shear flow conditions in the arterial and capillary system to low-shear conditions in the venous system.

Non-Newtonian Flow Behavior in Microchannels for Emulsion Formation

2006 ◽  
Author(s):  
Ravi Arora ◽  
Eric Daymo ◽  
Anna Lee Tonkovich ◽  
Laura Silva ◽  
Rick Stevenson ◽  
...  
Keyword(s):  
Shear Stress ◽  
Pressure Drop ◽  
Wall Shear Stress ◽  
Power Law ◽  
Flow Behavior ◽  
Scale Up ◽  
High Wall Shear Stress ◽  
Shear Rates ◽  
Wall Shear ◽  
Low Shear

Emulsion formation within microchannels enables smaller mean droplet sizes for new commercial applications such as personal care, medical, and food products among others. When operated at a high flow rate per channel, the resulting emulsion mixture creates a high wall shear stress along the walls of the narrow microchannel. This high fluid-wall shear stress of continuous phase material past a dispersed phase, introduced through a permeable wall, enables the formation of small emulsion droplets — one drop at a time. A challenge to the scale-up of this technology has been to understand the behavior of non-Newtonian fluids under high wall shear stress. A further complication has been the change in fluid properties with composition along the length of the microchannel as the emulsion is formed. Many of the predictive models for non-Newtonian emulsion fluids were derived at low shear rates and have shown excellent agreement between predictions and experiments. The power law relationship for non-Newtonian emulsions obtained at low shear rates breaks down under the high shear environment created by high throughputs in small microchannels. The small dimensions create higher velocity gradients at the wall, resulting in larger apparent viscosity. Extrapolation of the power law obtained in low shear environment may lead to under-predictions of pressure drop in microchannels. This work describes the results of a shear-thinning fluid that generates larger pressure drop in a high-wall shear stress microchannel environment than predicted from traditional correlations.

Wall-shear stress patterns of coherent structures in turbulent duct flow

2009 ◽  
Vol 633 ◽  
pp. 147-158 ◽  
Author(s):  
SEBASTIAN GROSSE ◽  
WOLFGANG SCHRÖDER
Keyword(s):  
Shear Stress ◽  
Stress Distribution ◽  
Wall Shear Stress ◽  
Coherent Structures ◽  
Shear Stress Distribution ◽  
Duct Flow ◽  
Wall Shear Stress Distribution ◽  
Wall Shear ◽  
Turbulent Duct Flow ◽  
Low Shear

The wall-shear stress distribution in turbulent duct flow has been assessed using the micro-pillar shear-stress sensor MPS3. The spatial resolution of the sensor line is 10.8l+(viscous units) and the total field of view of 120l+along the spanwise direction allows to capture characteristic dimensions of the wall-shear stress distribution at sufficiently high resolution. The results show the coexistence of low-shear and high-shear regions representing ‘footprints’ of near-wall coherent structures. The regions of low shear resemble long meandering bands locally interrupted by areas of higher shear stress. Conditional averages of the flow field indicate the existence of nearly streamwise counter-rotating vortices aligned in the streamwise direction. The results further show periods of very strong spanwise wall-shear stress to be related to the occurrence of high streamwise shear regions and momentum transfer towards the wall. These events go along with a spanwise oscillation and a meandering of the low-shear regions.

Analysis of Laminar Mixed Convective Plumes Along Vertical Adiabatic Surfaces

1984 ◽  
Vol 106 (3) ◽  
pp. 552-557 ◽  
Author(s):  
K. V. Rao ◽  
B. F. Armaly ◽  
T. S. Chen
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Leading Edge ◽  
Vertical Surface ◽  
Stream Velocity ◽  
Thermal Source ◽  
Flow Conditions ◽  
Velocity Overshoot ◽  
Wall Shear ◽  
Prandtl Numbers

Laminar mixed forced and free convection from a line thermal source imbedded at the leading edge of an adiabatic vertical surface is analytically investigated for the cases of buoyancy assisting and buoyancy opposing flow conditions. Temperature and velocity distributions in the boundary layer adjacent to the adiabatic surface are presented for the entire range of the buoyancy parameter ξ (x) = Grx/Rex5/2 from the pure forced (ξ(x) = 0) to the pure free (ξ(x) = ∞) convection regime for fluids having Prandtl numbers of 0.7 and 7.0. For buoyancy-assisting flow, the velocity overshoot, the temperature, and the wall shear stress increase as the plume’s strength increases. On the other hand, the velocity overshoot, the wall shear stress, and the temperature decrease as the free-stream velocity increases. For buoyancy opposing flow, the velocity and wall shear stress decrease but the temperature increases as the plume’s strength increases.

scholarly journals Analysis of the wall shear stress in a generic aneurysm under pulsating and transitional flow conditions

2020 ◽  
Vol 61 (2) ◽  
Author(s):  
Andreas Bauer ◽  
Maximilian Bopp ◽  
Suad Jakirlic ◽  
Cameron Tropea ◽  
Axel Joachim Krafft ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Transitional Flow ◽  
Flow Conditions ◽  
Wall Shear

WALL SLIPPAGE IN HIGH-PRESSURE CAPILLARY VISCOMETRY: EFFECTS OF MOLECULAR WEIGHT, COMPOUND COMPOSITION, AND CAPILLARY SURFACE COATING

2019 ◽  
Vol 92 (1) ◽  
pp. 186-197
Author(s):  
Katja Putzig ◽  
E. Haberstroh ◽  
B. Klie ◽  
U. Giese
Keyword(s):  
High Pressure ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Behavior ◽  
Polymer Melt ◽  
Capillary Viscometer ◽  
Molecular Weights ◽  
Rubber Compounds ◽  
Wall Shear ◽  
Wall Slippage

ABSTRACT Flow behavior is of major importance in the extrusion processing of rubber compounds. It is evaluated by means of a series of tests on a high-pressure capillary viscometer (HCV). Adhesion between the polymer melt and the capillary wall is assumed in all current calculation models, although such adhesion does not always pertain to the case of rubber compounds. To date, no uniform model discussed in the literature on the topic extensively describes the wall slippage behavior of rubber compounds. The phenomenon of wall slippage is analyzed by determining the power-law parameters n (flow exponent) and K (consistency factor) from the flow curve in the subcritical flow range. This makes it possible to explicitly calculate first the slip velocity and then the slippage ratio relative to the total volume flow as a function of the given shear rate and temperature. The work is based on the testing of EPDM raw polymers of different molecular weights in the HCV. In addition, EPDM compounds containing either a carbon black or a softener were analyzed with regard to their flow behavior. The rheological analysis was carried out on three variously coated flow channels. It was observed that with attainment of a critical wall shear stress, the wall slippage effect becomes more pronounced; thus, occurrences of flow anomalies such as slip-stick or shark-skin significantly influence processing and flow behavior. Wall slippage effects are noticeable, however, even before the critical wall shear stress is attained.

Achievement of Pentoxifylline for Blood Flow through Stenosed Artery

2012 ◽  
Vol 13 ◽  
pp. 81-89
Author(s):  
Sapna Ratan Shah ◽  
S.U. Siddiqui
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Apparent Viscosity ◽  
Fluid Model ◽  
Plasma Viscosity ◽  
Diabetic Patients ◽  
Newtonian Viscosity ◽  
Stenosed Artery ◽  
Wall Shear

Blood-viscosity reducing drugs like “Pentoxifylline” improve blood flow by making the blood less viscous. The resistance to flow of blood in diabetic patients is higher than in non-diabetic patients. Thus diabetic patients with higher resistance to flow are more prone to high blood pressure. Therefore the resistance to blood flow in case of diabetic patients may be reduced by reducing viscosity of the plasma. Viscosity of plasma can be reducing by giving Pentoxifylline. In this paper an attempt has been made to investigate the blood flow behaviour and significance of non-Newtonian viscosity through a stenosed artery using Bingham Plastic fluid model. Numerical illustrations presented at the end of the paper provide the results for the resistance to flow, apparent viscosity and the wall shear stress through their graphical representations. It has been shown that the resistance to flow, apparent viscosity and wall shear stress increases with the size of the stenosis but these increases are comparatively small due to non-Newtonian behaviour of the blood indicating the usefulness of its rheological character in the functioning of the diseased arterial circulation.

Computational modeling of coupled blood-wall mass transport of LDL: effects of local wall shear stress

2008 ◽  
Vol 294 (2) ◽  
pp. H909-H919 ◽  
Author(s):  
Ufuk Olgac ◽  
Vartan Kurtcuoglu ◽  
Dimos Poulikakos
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Arterial Wall ◽  
Density Lipoprotein ◽  
Filtration Velocity ◽  
Solute Flux ◽  
Ldl Transport ◽  
Low Shear Stress ◽  
Wall Shear ◽  
Low Shear

The work herein represents a novel approach for the modeling of low-density lipoprotein (LDL) transport from the artery lumen into the arterial wall, taking into account the effects of local wall shear stress (WSS) on the endothelial cell layer and its pathways of volume and solute flux. We have simulated LDL transport in an axisymmetric representation of a stenosed coronary artery, where the endothelium is represented by a three-pore model that takes into account the contributions of the vesicular pathway, normal junctions, and leaky junctions also employing the local WSS to yield the overall volume and solute flux. The fraction of leaky junctions is calculated as a function of the local WSS based on published experimental data and is used in conjunction with the pore theory to determine the transport properties of this pathway. We have found elevated levels of solute flux at low shear stress regions because of the presence of a larger number of leaky junctions compared with high shear stress regions. Accordingly, we were able to observe high LDL concentrations in the arterial wall in these low shear stress regions despite increased filtration velocity, indicating that the increase in filtration velocity is not sufficient for the convective removal of LDL.

WALL SLIP EFFECTS MEASURING THE RHEOLOGICAL BEHAVIOR OF ELECTRORHEOLOGICAL (ER) SUSPENSIONS

2012 ◽  
Vol 26 (01) ◽  
pp. 1250006 ◽  
Author(s):  
STEFFEN SCHNEIDER
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Behavior ◽  
Wall Slip ◽  
Hydraulic Test ◽  
Slip Effects ◽  
Measured Flow ◽  
Wall Shear ◽  
Er Fluids ◽  
Electrorheological Suspensions

In this work, a new method to determine the wall shear stress was developed step by step. To determine the wall shear stress, methods of the suspension rheology are being used for the first time to characterize ER fluids. This work focuses on investigations of the flow behavior of electrorheological suspensions in flow channels with different geometries at different electrical field strengths. Careful interpretation of the results with respect to different gap geometries has shown that the measured flow curves should undergo a combination of corrections. As a result it can be shown that wall slip effects can be measured under application like conditions on a hydraulic test bench.

Numerical Simulation of Blood Flow Through Stenosed Vessel

2004 ◽  
Author(s):  
Kimie Onogi ◽  
Kazuhiro Kohge ◽  
Kiyoshi Minemura
Keyword(s):  
Heart Rate ◽  
Blood Flow ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Behavior ◽  
Pressure Change ◽  
Sinusoidal Waveform ◽  
Stenosed Vessel ◽  
Flow Through ◽  
Wall Shear

This article illustrates numerical results on pulsating blood flow through moderately stenosed blood vessel. Two kinds of waveform, that is, a purely sinusoidal waveform and a non-sinusoidal one just like human blood flow are calculated for two cases of heart rate as 60 and 160 (1/s), and resultant flow behavior such as flow velocities, secondary flow, wall shear stress and pressure change are discussed. The abrupt changes in the pressure and wall shear stress occur on the throat of the stenosis, suggesting that this part is easily damaged by the effects when the heart rate is increased.

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