The small shear rate response of electrorheological suspensions. II. Extension beyond the point–dipole limit

1991 ◽  
Vol 94 (9) ◽  
pp. 6170-6178 ◽  
Author(s):  
D. J. Klingenberg ◽  
Frank van Swol ◽  
C. F. Zukoski
Keyword(s):  
Shear Rate ◽  
Point Dipole ◽  
Electrorheological Suspensions ◽  
Small Shear

The Boundary Negative Slippage of Fluid Flowing in Hydrophilic Micro-Channels

2012 ◽  
Vol 594-597 ◽  
pp. 2684-2688 ◽  
Author(s):  
Fu Quan Song ◽  
Ling Yu
Keyword(s):  
Shear Rate ◽  
Slip Length ◽  
Dynamics Simulation ◽  
Low Flow ◽  
Low Permeability ◽  
Threshold Pressure Gradient ◽  
Absolute Value ◽  
Micro Channels ◽  
Small Shear ◽  
Good Agreement

In order to analyze the characteristics of the liquid flow in hydrophilic micro-channels, the negative slippage in the hydrophilic micro-channels were studied by molecular dynamics simulation and experimental research in this paper. The simulation results indicate that there exists negative slippage in the small shear rate. The absolute value of slip length decreases with the augment of shear rate and keeps constant when the shear rate increases to a certain extent. In the condition of same wettability, the slip length is only relative to shear rate of fluids near the wall rather than channel widths. At last, a experiment of deionized water flow in the micro-channel of 10 diameter was carried out. The experimental results have a good agreement with the simulation, and there exists Pseudo Threshold Pressure Gradient(PTPG) under low flow velocity. The negative slippage as the reason of existence of PTPG is analyzed in low permeability porous media

Direct Simulation of Electrorheological Suspensions

2004 ◽  
Author(s):  
Pushpendra Singh ◽  
Nadine Aubry
Keyword(s):  
Stress Tensor ◽  
Electric Fields ◽  
Electrostatic Force ◽  
Dipole Approximation ◽  
Point Dipole ◽  
Maxwell Stress ◽  
Particle Interactions ◽  
Maxwell Stress Tensor ◽  
Point Dipole Approximation ◽  
Electrorheological Suspensions

A numerical scheme based on the distributed Lagrange multiplier method (DLM) is used to study the motion of particles of a dielectric suspensions subjected to uniform and nonuniform electric fields. The Maxwell stress tensor method is used for computing electrostatic forces. In the point dipole approximation the total electrostatic force acting on a particle can be divided into two distinct contributions, one due to dielectrophoresis and the second due to particle-particle interactions. The former is zero when the applied electric field is uniform and the latter depends on the distance between the particles. In the Maxwell stress tensor approach these two contribution appear together. Simulations show that as expected the error in the point dipole approximation decreases, as the distance between the particles increases.

Shear Flow and Large Amplitude Oscillation Shear Study of Solutions of Aggregating Micellar Casein Particles

2008 ◽  
Vol 18 (2) ◽  
pp. 23050-1-23050-7 ◽  
Author(s):  
Anne Pitkowski ◽  
Taco Nicolai ◽  
Dominique Durand
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Shear Flow ◽  
Heating Temperature ◽  
Constant Shear ◽  
Micellar Casein ◽  
Large Amplitude Oscillation ◽  
Increasing Temperature ◽  
Small Shear ◽  
Constant Shear Rate

Abstract Small micellar casein particles were formed in aqueous solutions of native casein after addition of polyphosphate. These so-called submicelles aggregated and gelled with a rate that increased with increasing temperature. The evolution of the viscosity during this process was determined at constant shear rate or shear stress. When applying a small shear stress the viscosity increased strongly until the shear rate became immeasurably slow, but when the applied shear stress exceeded a critical value (σc) the aggregates broke up and the viscosity reached a maximum. At longer times the viscosity decreased rapidly at first, followed by a very slow decrease. σc was independent of the shear rate and heating temperature, but increased strongly with increasing casein concentration. At constant shear rate the stress remained close to σc, but fluctuated irregularly. After cessation of shear flow, gels were formed rapidly. Oscillation shear measurements for σ > σc showed a strongly non-linear response at the time of maximum viscosity.

Analysis of the Yielding Behavior of Electrorheological Suspensions by Controlled Shear Stress Experiments

2006 ◽  
Vol 16 (1) ◽  
pp. 14-18 ◽  
Author(s):  
Vladimír Pavlínek ◽  
Petr Sáha ◽  
José Pérez-González ◽  
Lourdes de Vargas ◽  
Jaroslav Stejskal ◽  
...  
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Yield Stress ◽  
Silicone Oil ◽  
Stress Measurement ◽  
Chain Structure ◽  
Shear Stresses ◽  
Initial Rupture ◽  
Yielding Behavior ◽  
Electrorheological Suspensions

Abstract The yielding behavior of two model electrorheological suspensions of uncoated silica particles and silica coated with polyaniline base in silicone oil using controlled shear rate and controlled shear stress experiments has been analyzed. The results demonstrate that unlike the uncertain dynamic yield stress values estimated from the results obtained in the former mode by extrapolation of the unsteady shear stresses to zero shear rate, the controlled shear stress measurement permits to detect sensitively the region starting from the initial rupture of particle chain structure in the electric field at rest corresponding to a static yield stress τy and ending in total breakage of suspension structure at a breaking stress τb.. The latter quantity can be detected with a good accuracy and proved to be a reliable criterion of the stiffness of ER structure.

Particle Polarization and Nonlinear Effects in Electrorheological Suspensions

MRS Bulletin ◽  
1998 ◽  
Vol 23 (8) ◽  
pp. 30-34 ◽  
Author(s):  
Daniel J. Klingenberg
Keyword(s):  
Electric Field ◽  
Electrostatic Interactions ◽  
Silicone Oil ◽  
Small Deformation ◽  
Nonlinear Effects ◽  
Shear Rates ◽  
Alumina Particles ◽  
Electrostatic Phenomena ◽  
Electrorheological Suspensions ◽  
Small Shear

The phenomenon of electrorheology (ER), described in the guest editors' introduction to this issue, can largely be explained by electrostatic interactions between particles by an externally applied electric field. The purpose of this article is to review particle-polarization mechanisms active in ER suspensions and to highlight some poorly understood electrostatic phenomena that inhibit the commercialization of ER technology.Figure 1 plots the apparent viscosity of a 20-wt% suspension of alumina particles in silicone oil as a function of shear rate for different electric field strengths. The viscosity changes are most pronounced at small deformation rates. At small shear rates the viscosity is proportional to E2 where E is the electric field strength.

Adenosine Diphosphate-Induced Aggregation of Human Platelets in Flow Through Tubes: III. Shear and Extrinsic Fibrinogen-Dependent Effects

1994 ◽  
Vol 71 (01) ◽  
pp. 078-090 ◽  
Author(s):  
H L Goldsmith ◽  
M M Frojmovic ◽  
Susan Braovac ◽  
Fiona McIntosh ◽  
T Wong
Keyword(s):  
Shear Rate ◽  
Single Cells ◽  
Adenosine Diphosphate ◽  
Human Platelets ◽  
Size Analysis ◽  
Fibrinogen Concentration ◽  
Human Fibrinogen ◽  
Shear Rates ◽  
Rate Dependent ◽  
Induced Aggregation

SummaryThe effect of shear rate and fibrinogen concentration on adenosine diphosphate-induced aggregation of suspensions of washed human platelets in Poiseuille flow at 23°C was studied using a previously described double infusion technique and resistive particle counter size analysis (1). Using suspensions of multiple-centrifuged and -washed cells in Tyrodes-albumin [3 × 105 μl−1; (17)] with [fibrinogen] from 0 to 1.2μM, the, rate and extent of aggregation with 0.7 μM ADP in Tyrodes-albumin were measured over a range of mean transit times from 0.2 to 43 s, and at mean tube shear rates, Ḡ, = 41.9, 335 and 1,335 s−1. As measured by the decrease in singlet concentration, aggregation at 1.2 μM fibrinogen increased with increasing Ḡ up to 1,335 s1, in contrast to that previously reported in citratcd plasma, in which aggregation reached a maximum at Ḡ = 335 s−1. Without added fibrinogen, there was no aggregation at Ḡ = 41.9 s1; at Ḡ = 335 s1, there was significant aggregation but with an initial lag time, aggregation increasing further at Ḡ = 1,335 s−1. Without added fibrinogen, aggregation was abolished at all Ḡ upon incubation with the hexapeptide GRGDSP, but was almost unaffected by addition of an F(ab’)2 fragment of an antibody to human fibrinogen. Aggregation in the absence of added fibrinogen was also observed at 37°C. The activation of the multiple-washed platelets was tested using flow cytometry with the fluorescently labelled monoclonal antibodies FITC-PAC1 and FITC-9F9. It was shown that 57% of single cells in unactivated PRT expressed maximal GPIIb-IIIa fibrinogen receptors (MoAb PAC1) and 54% expressed pre-bound fibrinogen (MoAb 9F9), with further increases on ADP activation. However, incubation with GRGDSP and the F(ab’)2 fragment did not inhibit the prebound fibrinogen. Moreover, relatively unactivated cells (8% expressing receptor, 14% prebound fibrinogen), prepared from acidified cPRP by single centrifugation with 50 nM of the stable prostacyclin derivative, ZK 36 374, and resuspension in Tyrodes-albumin at 5 × 104 μl−1, aggregated with 2 and 5 μM ADP at Ḡ = 335 and 1,335 s−1 in the absence of added fibrinogen. We therefore postulate that a protein such as von Willebrand factor, secreted during platelet isolation or in flow at sufficiently high shear rates, may yield the observed shear-rate dependent aggregation without fibrinogen.

Platelet and Shear Rate Promote Tumor Cell Adhesion to Human Endothelial Extracellular Matrix - Absence of a Role for Platelet Cyclooxygenase

1989 ◽  
Vol 61 (03) ◽  
pp. 485-489 ◽  
Author(s):  
Eva Bastida ◽  
Lourdes Almirall ◽  
Antonio Ordinas
Keyword(s):  
Cell Adhesion ◽  
Shear Rate ◽  
Tumor Cell ◽  
Umbilical Vein ◽  
Blood Platelets ◽  
Flow Conditions ◽  
Tumor Cell Adhesion ◽  
Rate Dependent ◽  
Static Conditions

SummaryBlood platelets are thought to be involved in certain aspects of malignant dissemination. To study the role of platelets in tumor cell adherence to vascular endothelium we performed studies under static and flow conditions, measuring tumor cell adhesion in the absence or presence of platelets. We used highly metastatic human adenocarcinoma cells of the lung, cultured human umbilical vein endothelial cells (ECs) and extracellular matrices (ECM) prepared from confluent EC monolayers. Our results indicated that under static conditions platelets do not significantly increase tumor cell adhesion to either intact ECs or to exposed ECM. Conversely, the studies performed under flow conditions using the flat chamber perfusion system indicated that the presence of 2 × 105 pl/μl in the perfusate significantly increased the number of tumor cells adhered to ECM, and that this effect was shear rate dependent. The maximal values of tumor cell adhesion were obtained, in presence of platelets, at a shear rate of 1,300 sec-1. Furthermore, our results with ASA-treated platelets suggest that the role of platelets in enhancing tumor cell adhesion to ECM is independent of the activation of the platelet cyclooxygenase pathway.

The Effect of Red Blood Cells on the ADP-induced Aggregation of Human Platelets in Flow Through Tubes

1990 ◽  
Vol 63 (01) ◽  
pp. 112-121 ◽  
Author(s):  
David N Bell ◽  
Samira Spain ◽  
Harry L Goldsmith
Keyword(s):  
Platelet Aggregation ◽  
Shear Rate ◽  
Red Blood Cells ◽  
Blood Cells ◽  
Platelet Rich Plasma ◽  
Mean Transit Time ◽  
White Blood Cells ◽  
Aggregate Size ◽  
Human Platelets ◽  
Induced Aggregation

SummaryThe effect of red blood cells, rbc, and shear rate on the ADPinduced aggregation of platelets in whole blood, WB, flowing through polyethylene tubing was studied using a previously described technique (1). Effluent WB was collected into 0.5% glutaraldehyde and the red blood cells removed by centrifugation through Percoll. At 23°C the rate of single platelet aggregtion was upt to 9× greater in WB than previously found in platelet-rich plasma (2) at mean tube shear rates Ḡ = 41.9,335, and 1,920 s−1, and at both 0.2 and 1.0 µM ADP. At 0.2 pM ADP, the rate of aggregation was greatest at Ḡ = 41.9 s−1 over the first 1.7 s mean transit time through the flow tube, t, but decreased steadily with time. At Ḡ ≥335 s−1 the rate of aggregation increased between t = 1.7 and 8.6 s; however, aggregate size decreased with increasing shear rate. At 1.0 µM ADP, the initial rate of single platelet aggregation was still highest at Ḡ = 41.9 s1 where large aggregates up to several millimeters in diameter containing rbc formed by t = 43 s. At this ADP concentration, aggregate size was still limited at Ḡ ≥335 s−1 but the rate of single platelet aggregation was markedly greater than at 0.2 pM ADP. By t = 43 s, no single platelets remained and rbc were not incorporated into aggregates. Although aggregate size increased slowly, large aggregates eventually formed. White blood cells were not significantly incorporated into aggregates at any shear rate or ADP concentration. Since the present technique did not induce platelet thromboxane A2 formation or cause cell lysis, these experiments provide evidence for a purely mechanical effect of rbc in augmenting platelet aggregation in WB.

Sign in / Sign up

Export Citation Format

Share Document