Observations of rapidly flowing granular-fluid materials

The rapid shearing of a mixture of cohesionless glass spheres and air or water was studied in an annular, parallel-plate shear cell designed after Savage (1978). Two types of flow were observed. In the first type of flow the entire mass of the granular material was mobilized. At high shear rates the shear and normal stresses were found to be quadratically dependent upon the mean shear rate (at constant volume concentration), in general agreement with the observations of Bagnold (1954) and Savage & Sayed (1984), and the ‘kinetic’ theory of Jenkins & Savage (1983). The stresses were found to be weakly dependent on the volume concentration up to approximately 0.5, and strongly dependent above this concentration. For flows in which water was the interstitial fluid, the ratio of the shear stress to the normal stress was slightly higher (than in air), and the stresses at lower shear rates were found to be more nearly linearly related to the shear rate. It is suggested that these effects are contributed to by the viscous dampening of grain motions by the water. The second type of flow was distinguished by the existence of an internal boundary above which the granular material deformed rapidly, but below which the granular material remained rigidly locked in place. The thickness of the shearing layer was measured to be between 5 and 15 grain diameters. The stress ratio at the bottom of the shearing layer was found to be nearly constant, suggesting the internal boundary is a consequence of the immersed weight of the shearing grains, and may be described by a Coulomb yield criterion. A scaled concentration is proposed to compare similar data obtained using different-sized materials or different apparatus. An intercomparison of the two types of flow studied, along with a comparison between the present experiments and those of Bagnold (1954) and Savage & Sayed (1984), suggests that the nature of the boundaries can have a significant effect upon the dynamics of the entire flow.

Download Full-text

Comparison of antithrombotic efficacy between edoxaban, a direct factor Xa inhibitor, and fondaparinux, an indirect factor Xa inhibitor under low and high shear rates

Thrombosis and Haemostasis ◽

10.1160/th11-07-0451 ◽

2011 ◽

Vol 106 (12) ◽

pp. 1062-1068 ◽

Cited By ~ 10

Author(s):

Naoki Tsuji ◽

Yuko Honda ◽

Chikako Kamisato ◽

Yoshiyuki Morishima ◽

Toshiro Shibano ◽

...

Keyword(s):

Shear Rate ◽

Arterial Thrombosis ◽

Factor Xa ◽

High Shear ◽

Shear Rates ◽

Thrombosis Model ◽

Perfusion Chamber ◽

High Shear Rates ◽

Antithrombotic Effects ◽

Antithrombotic Efficacy

SummaryEdoxaban is an oral, direct factor Xa (FXa) inhibitor under late-phase clinical development. This study compared the antithrombotic efficacy of edoxaban with that of an indirect FXa inhibitor, fondaparinux, in in vivo venous and arterial thrombosis models and in ex vivo perfusion chamber thrombosis model under low and high shear rates in rats. Venous and arterial thrombi were induced by platinum wire insertion into the inferior vena cava and by application of FeCl3 to the carotid artery, respectively. The perfusion chamber thrombus was formed by blood perfusion into a collagen-coated capillary at 150 s-1 (low shear rate) and 1,600 s-1 (high shear rate). Effective doses of edoxaban that reduced thrombus formation by 50% (ED50) in venous and arterial thrombosis models were 0.076 and 0.093 mg/kg/h, respectively. In contrast, ED50 of fondaparinux in the arterial thrombosis model (>10 mg/kg/h) was markedly higher compared to ED50 in the venous thrombosis model (0.021 mg/kg/h). In the perfusion chamber thrombosis model, the ratio of ED50 under high shear rate (1.13 mg/kg/h) to that under low shear rate (0.63 mg/kg/h) for edoxaban was 1.9, whereas that for fondaparinux was more than 66. While the efficacy of fondaparinux markedly decreased in arterial thrombosis and in a high-shear state, edoxaban exerted consistent antithrombotic effects regardless of flow conditions. These results suggest that shear rate is a key factor in different antithrombotic effects between edoxaban and fondaparinux.

Download Full-text

Effects of posture on shear rates in human brachial and superficial femoral arteries

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.01108.2007 ◽

2008 ◽

Vol 294 (4) ◽

pp. H1833-H1839 ◽

Cited By ~ 43

Author(s):

S. C. Newcomer ◽

C. L. Sauder ◽

N. T. Kuipers ◽

M. H. Laughlin ◽

C. A. Ray

Keyword(s):

Shear Rate ◽

Femoral Artery ◽

Brachial Artery ◽

Superficial Femoral Artery ◽

Upright Posture ◽

Brachial Artery Diameter ◽

Shear Rates ◽

Femoral Arteries ◽

Lower Shear ◽

Relative Shear

Shear rate is significantly lower in the superficial femoral compared with the brachial artery in the supine posture. The relative shear rates in these arteries of subjects in the upright posture (seated and/or standing) are unknown. The purpose of this investigation was to test the hypothesis that upright posture (seated and/or standing) would produce greater shear rates in the superficial femoral compared with the brachial artery. To test this hypothesis, Doppler ultrasound was used to measure mean blood velocity (MBV) and diameter in the brachial and superficial femoral arteries of 21 healthy subjects after being in the supine, seated, and standing postures for 10 min. MBV was significantly higher in the brachial compared with the superficial femoral artery during upright postures. Superficial femoral artery diameter was significantly larger than brachial artery diameter. However, posture had no significant effect on either brachial or superficial femoral artery diameter. The calculated shear rate was significantly greater in the brachial (73 ± 5, 91 ± 11, and 97 ± 13 s−1) compared with the superficial femoral (53 ± 4, 39 ± 77, and 44 ± 5 s−1) artery in the supine, seated, and standing postures, respectively. Contrary to our hypothesis, our current findings indicate that mean shear rate is lower in the superficial femoral compared with the brachial artery in the supine, seated, and standing postures. These findings of lower shear rates in the superficial femoral artery may be one mechanism for the higher propensity for atherosclerosis in the arteries of the leg than of the arm.

Download Full-text

Platelet von Willebrand factor: evidence for its involvement in platelet adhesion to collagen

Blood ◽

10.1182/blood.v70.4.1214.bloodjournal7041214 ◽

1987 ◽

Vol 70 (4) ◽

pp. 1214-1217

Author(s):

E Fressinaud ◽

D Baruch ◽

C Rothschild ◽

HR Baumgartner ◽

D Meyer

Keyword(s):

Shear Rate ◽

Von Willebrand Factor ◽

Platelet Adhesion ◽

Von Willebrand Disease ◽

High Shear ◽

Shear Rates ◽

High Shear Rates ◽

Von Willebrand ◽

Willebrand Factor

Although it is well established that plasma von Willebrand Factor (vWF) is essential to platelet adhesion to subendothelium at high shear rates, the role of platelet vWF is less clear. We studied the respective role of both plasma and platelet vWF in mediating platelet adhesion to fibrillar collagen in a parallel-plate perfusion chamber. Reconstituted blood containing RBCs, various mixtures of labeled washed platelets and plasma from controls or five patients with severe von Willebrand disease (vWD), was perfused through the chamber for five minutes at a shear rate of 1,600 s-1. Platelet-collagen interactions were estimated by counting the radioactivity in deposited platelets and by quantitative morphometry. When the perfusate consisted of normal platelets suspended in normal plasma, platelet deposition on the collagen was 24.7 +/- 3.6 X 10(6)/cm2 (mean +/- SEM, n = 6). Significantly less deposition (16 +/- 2.3) was observed when vWD platelets were substituted for normal platelets. In mixtures containing vWD plasma, significantly greater deposition (9 +/- 2.2) was obtained with normal than with vWD platelets (1 +/- 0.4) demonstrating a role for platelet vWF in mediating the deposition of platelets on collagen. Morphometric analysis confirmed these data. Our findings indicate that platelet, as well as plasma, vWF mediates platelet-collagen interactions at a high shear rate.

Download Full-text

The Simulation of Aggregated Colloids Under Flow

MRS Proceedings ◽

10.1557/proc-289-33 ◽

1992 ◽

Vol 289 ◽

Author(s):

John R. Melrose

Keyword(s):

Shear Rate ◽

Large Scale ◽

Shear Thinning ◽

High Shear ◽

Shear Rates ◽

Rouse Model ◽

High Shear Rates ◽

Structural Breakdown ◽

Large Scale Simulations ◽

Low Shear

AbstractAn overview is given of theories of aggregates under flow. These generally assume some sort of structural breakdown as the shear rate is increased. Models vary with both the rigidity of the bonding and the level of treatment of hydrodynamics. Results are presented for simulations of a Rouse model of non-rigid, (i.e. central force) weakly bonded aggregates. In large scale simulations different structures are observed at low and high shear rates. The change from one structure to another is associated with a change in the rate of shear thinning. The model captures low shear rate features of real systems absent in previous models: this feature is ascribed to agglomerate deformations. Quantitatively, the model is two orders of magnitude out from experiment but some scaling is possible.

Download Full-text

Shear Induced Phase Behavior of Polymer Blends by Small Angle Neutron Scattering

MRS Proceedings ◽

10.1557/proc-166-479 ◽

1989 ◽

Vol 166 ◽

Cited By ~ 1

Author(s):

Alan I. Nakatani ◽

Hongdoo Kim ◽

Charles C. Han

Keyword(s):

Neutron Scattering ◽

Polymer Blends ◽

Phase Behavior ◽

Small Angle ◽

Small Angle Neutron Scattering ◽

Large Body ◽

Concentric Cylinder ◽

Shear Rates ◽

Lower Shear ◽

High Shear Rates

ABSTRACTThe phase behavior of polymer blends and solutions can be changed dramatically by a flow field using a variety of flow geometries. Unlike simple binary fluids which require extremely high shear rates to produce only small shifts in the phase boundary, polymer phase behavior may be influenced by as much as 10 degrees with the application of much lower shear rates. However, there is a large body of conflicting data concerning the nature of these shear effects in polymers.Here we report on the effects of shear on the phase behavior of polymer blends by small angle neutron scattering (SANS). Experiments were conducted using a specially constructed, concentric cylinder apparatus for in situ studies of concentrated polymer solutions and melts. Two separate systems will be discussed: 1) a blend of polystyrene and polybutadiene. 2) a blend of polystyrene and poly(vinylmethylether). Both systems exhibit shifts in the phase behavior which indicate shear induced mixing in agreement with previous results obtained by other techniques. These results will be interpreted within the context of existing theories of shear induced phase behavior.

Download Full-text

Shear Rate Moderates Community Diversity in Freshwater Biofilms

Applied and Environmental Microbiology ◽

10.1128/aem.70.12.7426-7435.2004 ◽

2004 ◽

Vol 70 (12) ◽

pp. 7426-7435 ◽

Cited By ~ 107

Author(s):

Alexander H. Rickard ◽

Andrew J. McBain ◽

Amy T. Stead ◽

Peter Gilbert

Keyword(s):

Shear Rate ◽

Denaturing Gradient Gel Electrophoresis ◽

Bacterial Biofilm ◽

Community Diversity ◽

Rrna Gene ◽

High Shear ◽

Shear Rates ◽

High Shear Rates ◽

Static Conditions ◽

Freshwater Biofilms

ABSTRACT The development of freshwater multispecies biofilms at solid-liquid interfaces occurs both in quiescent waters and under conditions of high shear rates. However, the influence of hydrodynamic shear rates on bacterial biofilm diversity is poorly understood. We hypothesized that different shear rates would significantly influence biofilm diversity and alter the relative proportions of coaggregating and autoaggregating community isolates. In order to study this hypothesis, freshwater biofilms were developed at five shear rates (<0.1 to 305 S−1) in a rotating concentric cylinder reactor fed with untreated potable water. Eubacterial diversity was assessed by denaturing gradient gel electrophoresis (DGGE) and culturing on R2A agar. Fifty morphologically distinct biofilm strains and 16 planktonic strains were isolated by culturing and identified by partial 16S rRNA gene sequencing, and their relatedness was determined by the construction of a neighbor-joining phylogenetic tree. Phylogenetic and DGGE analyses showed an inverse relationship between shear rate and bacterial diversity. An in vitro aggregation assay was used to assess the relative proportions of coaggregating and autoaggregating species from each biofilm. The highest proportion of autoaggregating bacteria was present at high shear rates (198 to 305 S−1). The intermediate shear rate (122 S−1) selected for the highest proportion of coaggregating bacteria (47%, or 17 of a possible 36 coaggregation interactions). Under static conditions (<0.1 S−1), 41 (33%) of a possible 125 coaggregation interactions were positive. Few coaggregation (3.3%) or autoaggregation (25%) interactions occurred between the 16 planktonic strains. In conclusion, these data show that shear rates affect biofilm diversity as well as the relative proportions of aggregating bacteria.

Download Full-text

Heat Transfer in Fully-Developed, Laminar Flows of Dissipative Pseudoplastic and Dilatant Fluids in Circular Conduits

Journal of Heat Transfer ◽

10.1115/1.4049387 ◽

2020 ◽

Author(s):

Massimo Capobianchi ◽

Richard Cangelosi ◽

Patrick McGah

Keyword(s):

Shear Rate ◽

Flow Curve ◽

Numerical Study ◽

Constant Heat Flux ◽

Laminar Flows ◽

Rate Parameter ◽

Constant Heat ◽

Shear Rates ◽

Nusselt Numbers ◽

Entire Flow

Abstract This paper reports the results of a numerical study that determined the Nusselt number for hydrodynamically and thermally fully-developed, laminar, dissipative flows of pseudoplastic and dilatant fluids through circular conduits. Two boundary conditions were considered, constant heat flux and constant temperature. Constitutive equations were used that describe the entire flow curve, from the zero-shear rate through the infinite-shear rate Newtonian regions, so that computed Nusselt numbers are valid for whatever shear rates may exist in the flow field. Nusselt numbers are reported as a function of a dimensionless shear rate parameter that establishes the region of the flow curve where the system is operating, and are shown to be bound by the Newtonian and power law values. The conditions required for the system to perform at these asymptotic limits are quantified.

Download Full-text

SHEARING EFFECTS ON THE ELECTRORHEOLOGICAL RESPONSE

International Journal of Modern Physics B ◽

10.1142/s0217979201005453 ◽

2001 ◽

Vol 15 (06n07) ◽

pp. 930-937 ◽

Cited By ~ 6

Author(s):

K. TANAKA ◽

S. HASHIMOTO ◽

T. TAKENOUCHI ◽

I. SUGIMOTO ◽

A. KUBONO ◽

...

Keyword(s):

Shear Rate ◽

Electric Field ◽

Transient Response ◽

Stress Responses ◽

Experimental Conditions ◽

Transient Stress ◽

Shear Rates ◽

Lower Shear ◽

Mason Number ◽

The Individual

The steady and transient stress responses were investigated from lower shear rates to higher shear rates at a given strength of the electric field, and the individual experimental conditions were reduced to Mason number ( M n). The electro-rheological response was found in the region with higher M n of the order of 10, and the transient response became faster as the shear rate increased. These results show that the effect of chance of collision among the polarized particles would play an important role even in the region.

Download Full-text

Macroscopic rheology of non-Brownian suspensions at high shear rates: the influence of solid volume fraction and non-Newtonian behaviour of the liquid phase

Rheologica Acta ◽

10.1007/s00397-021-01320-1 ◽

2021 ◽

Author(s):

Patrick Wilms ◽

Jörg Hinrichs ◽

Reinhard Kohlus

Keyword(s):

Liquid Phase ◽

Shear Rate ◽

Volume Fraction ◽

Solid Volume Fraction ◽

Shear Thinning ◽

High Shear ◽

Rate Dependency ◽

Shear Rates ◽

Liquid Phases ◽

High Shear Rates

AbstractModelling the macroscopic rheology of non-Brownian suspensions is complicated by the non-linear behaviour that originates from the interaction between solid particles and the liquid phase. In this contribution, a model is presented that describes suspension rheology as a function of solid volume fraction and shear rate dependency of both the liquid phase, as well as the suspension as a whole. It is experimentally validated using rotational rheometry ($$\varphi$$ φ ≤ 0.40) and capillary rheometry (0.55 ≤ $$\varphi$$ φ ≤ 0.60) at shear rates > 50 s−1. A modified Krieger-Dougherty relation was used to describe the influence of solid volume fraction on the consistency coefficient, $$K$$ K , and was fitted to suspensions with a shear thinning liquid phase, i.e. having a flow index, $$n$$ n , of 0.50. With the calculated fit parameters, it was possible to predict the consistency coefficients of suspensions with a large variation in the shear rate dependency of the liquid phase ($$n$$ n = 0.20–1.00). With increasing solid volume fraction, the flow indices of the suspensions were found to decrease for Newtonian and mildly shear thinning liquid phases ($$n$$ n ≥0.50), whereas they were found to increase for strongly shear thinning liquid phases ($$n$$ n ≤0.27). It is hypothesized that this is related to interparticle friction and the relative contribution of friction forces to the viscosity of the suspension. The proposed model is a step towards the prediction of the flow curves of concentrated suspensions with non-Newtonian liquid phases at high shear rates.

Download Full-text