High Shear Rate Flow Research Articles

Influence of Planar Elongation Strain on Flow-Induced Structure and Flow Instability of CTAB/NaSal Aqueous Solution

An aqueous solution of CTAB/NaSal forms wormlike micelles and shows viscoelastic properties. It also shows flow-induced structure and flow instability in high shear rate flows. In this study, the occurrences of flow-induced structure and flow instability in planar elongational flows in a 4-roll mill flow cell were examined. An empirical formula of planar elongation strain as a function of elapsed time was proposed by results of particle trace velocimetry technique. In the planar elongational flow, the fluid was observed to become turbid, caused by the structure change, beyond a certain elongation rate. Subsequently, the elastic recoil was observed and simultaneously the turbid region disappeared. The change of turbidity is closely related to the planar elongation strain and the occurrence of the elastic recoil is related with a certain critical elastic energy. Furthermore, both critical rate and critical strain of the occurrence of these phenomena are considerably low in the planar elongation flow as compared with the shear flow.

Mechanism of Periodical Fluid Oscillation Induced by Separating High Shear Rate Flow in Side Branch of Right-Angle Branch

In the previous study, it has been clarified in the right-angle branch that the periodical oscillation flow is induced in the side branch and the Strouhal number based on the variables in the side branch is independent of the Reynolds number, the flow division ratio, and the radius of the side branch. This periodical oscillation appears along the boundary between two pairs of vortices with the opposite rotation at the cross section of the side branch across the separation flow. In the present study, another source of the periodical oscillation is experimentally clarified that the high shear rate flow is induced along the separation shearing layer between the separation flow of low velocity and the main flow with high velocity along the distal wall in the side branch since the high shear rate along this separation shearing layer is several times as large as that in the upstream trunk or in the downstream region of the side branch.

C216 高せん断流れに対応する画像変形を用いたPIV

In this paper, a window-deformation PIV was proposed in order to measure high shear-rate flows. For proper deformation, an appropriate velocity gradient tensor must be obtained. In the present approach, a method to extrapolate the velocity gradient from the region with higher reliability velocity was proposed. As a result of evaluation by using artificial images, it was found that the proposed method can be measure high-shear rate flows with little outliers.

RHEOLOGICAL BEHAVIOR AND TIME‐DEPENDENT CHARACTERIZATION OF ICE CREAM MIX WITH DIFFERENT SALEP CONTENT

ABSTRACT The effect of salep concentration on the rheological characteristics of ice cream mixes (0.5–1.5% salep content), prepared from nonfat cow's milk and sugar, was studied using a controlled stress rheometer. The flow curves and time‐dependent flow properties of the ice cream mixes were assessed at different temperatures. The ice cream mixes’ samples showed slightly thixotropic behavior, which was reduced as the salep content decreased. The forward and backward measurements of the flow curves of ice cream mixes were modeled with the power law model. The ice cream mixes showed pseudoplastic flow behavior after destruction of the thixotropic structure. In mixes that were first presheared at a high shear rate flow properties could also be described by the power law model. The second‐order structural kinetic, first‐order stress decay and Weltman models were applied to model the time‐dependent flow properties of the ice cream mixes. Among these, the first‐order stress decay model was found to fit well the experimental data.

Capillary rheometry for polymer melts revisited

Capillary rheometry provides an efficient access to high shear rate flow properties relevant for processing. An automated gas driven capillary rheometer developed at BASF enables accurate measurements at imposed wall shear stress, thus supplementing instruments operating at imposed flow rate. A simplified treatment of dissipative heating based on the assumption of a radially flat temperature profile is outlined and justified by means of finite element simulations. The combined treatment of dissipation and pressure dependent viscosity yields relations to treat throttling experiments at imposed flow rate. Throttle pressure coefficients from a long die and an orifice agree for LDPE but significantly differ for PαMSAN. The effect is explained on the basis of identical pressure coefficients for shear and elongational flows, with regard to a constant stress, however. The effect of melt compressibility is negligible in practical capillary rheometry if the temperature and pressure coefficients of the melt density are by an order of magnitude smaller than those of the viscosity. Gas pressure driven instruments allow an effective determination of wall slip velocities from Mooney plots. This is of advantage for the investigation of the mechanism of additives or processing aids. Furthermore, imposed pressure experiments are pertinent to investigate the spurt effect of HDPE and to demonstrate that two different slip processes contribute to the apparent flow curve above spurt.

Figuring with subnanometer-level accuracy by numerically controlled elastic emission machining

A numerically controlled elastic emission machining (EEM) system has been developed to fabricate ultraprecise optical components, particularly in x-ray optics. Nozzle-type EEM heads, by which a high shear-rate flow of ultrapure water can be generated on the work surface, have been newly proposed to transport the fine powder particles to the processing surface. Using this type of EEM head, the obtainable spatial resolution in figure correction can be changed by selecting the suitable aperture size of the nozzle according to the required spatial frequency. As a result of test figuring, 1 nm level peak-to-valley (p–v) accuracy is achieved throughout the entire spatial wavelength range longer than 0.3 mm. In addition, the microroughness of the processed surface is certified to also be approximately 1 nm (p–v).

Quasi-Steady Bingham Biplastic Analysis of Electrorheological and Magnetorheological Dampers

Electrorheological (ER)and magnetorheological (MR)fluids are characterized by an increase in dynamic yield stress upon application of a magnetic field. The Bingham plastic model has proven useful in modeling flow mode dampers utilizing ER and MR fluids. However, certain MR fluids can exhibit shear thinning behavior, wherein the fluid’s apparent plastic viscosity decreases at high shear rates. The Bingham plastic model does not account for such behavior, resulting in overprediction of equivalent viscous damping. We present a Bingham biplastic model that can account for both shear thinning and shear thickening behaviors. This approach assumes a bilinear post yield viscosity, with a critical shear rate specifying the region of high shear rate flow. Furthermore, the model introduces non-dimensional terms to account for the additional parameters associated with shear thinning and thickening. A comparison is made between Bingham plastic and Bingham biplastic force responses to constant velocity input, and equivalent viscous damping is examined with respect to nondimensional parameters.

2D Maxwell model

A polymer is considered to be an ensemble of elastic elements with friction between them. Newton's law relating shear stress and strain is assumed to be valid even at high shear rate flow of the polymer, but the viscosity is assumed to be dependent on variables other than the shear rate. In particular, it is assumed to be dependent on the deformation of the elastic elements. The case of isothermal, incompressible flow of a polymer through a duct, whose cross-sectional height (x 3 direction) is much larger than its cross-sectional width (x 2 direction), is analyzed. The assumptions of the theory indicate a dependence of viscosity on the deformation of the elastic elements. For a linear material, Hooke's Law gives the relation between the shear deformation of the elements and the shear stress; so the dependence of the viscosity on the pressure gradient can be found. Application of Newton's law then enables the velocity profile and other flow properties to be found in terms of this variable. For a nonlinear material, a power-series relation between the shear deformation of the elements and the shear stress is assumed. We show how to find the parameters in this series by a simple curve fitting procedure beginning from linear behavior. Once this dependence of the viscosity on the pressure gradient is found, the application of Newton's law enables the velocity profile and other flow properties to be found.

A mitogen-activated protein kinase-dependent signaling pathway in the activation of platelet integrin alpha IIbbeta3.

We have recently shown that the platelet integrin alpha(IIb)beta(3) is activated by von Willebrand factor (vWF) binding to its platelet receptor, glycoprotein Ib-IX (GPIb-IX), via the protein kinase G (PKG) signaling pathway. Here we show that GPIb-IX-mediated activation of integrin alpha(IIb)beta(3) is inhibited by dominant negative mutants of Raf-1 and MEK1 in a reconstituted integrin activation model in Chinese hamster ovary (CHO) cells and that the integrin-dependent platelet aggregation induced by either vWF or low dose thrombin is inhibited by MEK inhibitors PD98059 and U0126. Thus, mitogen-activated protein kinase (MAPK) pathway is important in GPIb-IX-dependent activation of platelet integrin alpha(IIb)beta(3). Furthermore, vWF binding to GPIb-IX induces phosphorylation of Thr-202/Tyr-204 of extracellular signal-regulated kinase 2 (ERK2). GPIb-IX-induced ERK2 phosphorylation is inhibited by PKG inhibitors and enhanced by overexpression of recombinant PKG. PKG activators also induce ERK phosphorylation, indicating that activation of MAPK pathway is downstream from PKG. Thus, our data delineate a novel integrin activation pathway in which ligand binding to GPIb-IX activates PKG that stimulates MAPK pathway, leading to integrin activation.

A novel interpretation of the role of von Willebrand factor in thrombotic microangiopathies based on platelet adhesion studies at high shear rate flow

Clinical manifestations of thrombotic microangiopathies (TMA) are secondary to platelet aggregation and thrombotic occlusion of the microvasculature of the affected organs. Abnormalities in von Willebrand factor (vWF) in these patients were considered instrumental in promoting the process leading to microvascular thrombosis. We evaluated the capacity of plasma in these patients to induce adhesion of normal platelets and thrombus formation under conditions of controlled fluid shear stress. We also studied vWF multimeric distribution to establish whether abnormalities of this glycoprotein correlate with platelet adhesion and thrombus formation. Plasma from patients in the acute phase and remission showed the same capacity to induce platelet adhesion and thrombus formation at a low level of shear rate (600 sec-1) as plasma from control subjects. At a high shear rate (1,500 sec-1), platelet adhesion and thrombus dimensions were significantly increased (P < 0.05) by plasma from patients with TMA compared with controls. The capacity to enhance thrombus formation at high shear stress was present during the acute phase and disease remission and did not correlate with the presence of unusually large vWF multimers. Increased thrombus formation with patient plasma is completely normalized by blocking the interaction of vWF with the platelet receptors, glycoprotein (GP)Ib and GPIIb-IIIa, suggesting that the phenomenon is completely mediated by vWF. Our results suggest the possibility of an intrinsically altered vWF molecule in these patients that is probably more effective than normal vWF in mediating platelet adhesion and thrombus formation.

A molecular dynamics study of a short-chain polyethylene melt.: II. Transient response upon onset of shear

Using nonequilibrium molecular dynamics simulation, we have studied the response of a C 100H 202 model polyethylene melt to a step change from equilibrium to a constant, high shear rate flow. The transient shear stress exhibits pronounced overshoot at the strain value predicted by the reptation model, in striking similarity to melts of longer, entangled polymer governed by reptation motion. The Doi–Edwards theory is found to be applicable but only by taking into account the shear-rate-dependence of the terminal relaxation time (which is also consistent with the calculated shear-rate-dependence of the xx component of melt’s self-diffusion tensor). We also analyze the molecular origins of stress overshoot behavior in short polymer chains by decomposing the shear stress and normal stress differences into the contributions from various molecular interactions and by examining the shear-induced ordering in the C 100H 202 melt.

Transient rheology of a polyethylene melt under shear.

Using nonequilibrium molecular dynamics simulation, we have studied the response of a C100 model polymer melt to a step change from equilibrium to a constant, high shear rate flow. The transient shear stress of the model polymer melt exhibits pronounced overshoot at the strain value predicted by the reptation model, in striking similarity to melts of longer, entangled polymer governed by reptation motion. At the maximum of shear stress overshoot, the molecular orientational order and the alignment angle are found to be midway between those characteristic of Newtonian flow and full alignment with the flow. The Doi-Edwards theory is found to be applicable but only by taking into account the shear-rate-dependence of the terminal relaxation time. We further analyze the molecular origins of such behavior in short polymer chains by decomposing the total stress into the contributions from various molecular interactions.

Rheological Properties of Low-Gel-Loading Borate Fracture Gels

Summary This paper presents a study of hydration, crosslinking, and rheological properties of 15- to 25-lbm/1,000-gal optimized borate-crosslinked guar fluids. Hydration and crosslinking properties of fluids were measured in a new turbulent flow-loop viscometer to simulate the high shear mixing of fracture fluids in surface equipment and the pumping of the fluids down tubulars. Fluids were then heated and measured in laminar flow to simulate fluid flow in a fracture. The effects of conditioning crosslinked fluids in high shear rate flow on laminar flow properties were observed. Hydration rates were measured for guar at different levels of shear history. Optimum shear levels and times for hydration were observed for the time-dependent base gel fluids. The properties of the crosslinked fluid were critically dependent upon the base gel fluid state of hydration before crosslinking. Properly crosslinked fluids did not shear-thin back to base gel levels but maintained significant viscosity even at high shear levels. Power-law index values were measured for low-polymer borate fluids with a three-viscometer method that uses constant shear rates. Lower values of n′ were found for the new fluids compared with conventional borate fluids with similar polymer loadings. Proppant transport properties were qualitatively observed in a transparent slot model showing good transport for both an optimized 25-lbm/1,000-gal borate fluid and a conventional 35-lbm/1,000-gal borate fluid.

Numerical Analysis Visco-Elastic Flow for Multi-mode Giesekus Model under High Shear Rate Flow.

In this work, we carry out a numerical analysis of visco-elastic flow for the multi-mode Giesekus model under high shear rate flow. In the previous work, we proposed a new numerical scheme that is suited for the analysis of visco-elastic fluids. This scheme employs the MUSCL (Monotone Upstream-centered Scheme Conservation for Law)-TVD (Total Variation Diminishing) and the GSMAC (Generalized Simplified Maker and Cell)-FEM (Finite Element Method) for the numerical analysis of the constitutive equation and the momentum equation, respectively. Hence, we analyze the flow through the contraction plane for the multi-mode Giesekus model using this scheme. In this analysis, eight relaxation modes are considered. The results of this analysis are good agreement with the experimental data under low shear rate flow and the results are stable under high shear rate flow.

The Role of the Elasticity of the Lubricant in Rotor Dynamics

An analysis is presented to find the effect of the elasticity of the lubricant in polymer containing multigrade oils on the performance of a dynamically loaded rotor, supported by short journal bearings. This paper solves for the loci of the center of a journal, subjected to unsteady loading, using Newtonian and viscoelastic lubricants. The viscoelastic fluid is described by a relatively new rheological equation which has been shown to be successful in predicting the experimental trends of various unsteady high shear rate flows. The analysis is a perturbation solution for low Deborah numbers where the stress relaxation process is a first-order effect. The results show an improvement in the performance of viscoelastic lubricants over Newtonian lubricants. Under an unsteady load, the journal center orbits show reduced eccentricity and travel of the journal due to the elasticity of the fluid. It implies that lubricants with a longer relaxation time can be developed where the viscosity and viscous losses can ...

Rheology of melts and magmatic suspensions: 1. Design and calibration of concentric cylinder viscometer with application to rhyolitic magma

Accurate rheological data for silicate melts and crystal‐melt, melt‐vapor, and crystal‐melt‐vapor suspensions of both natural compositions and simple binary and ternary systems are useful in constraining theories of momentum transport in magmatic systems and theories of melt structure. Data addressing these problems are presented in a series of papers of which this is the first. A high‐torque wide‐gap concentric cylinder viscometer has been constructed and used for characterization of the rheometric properties of rhyolitic magma under conditions of varying temperature (1100°–1350°C) and shear rate (0.05–13 s−1) at 105 Pa total pressure. Two natural rhyolitic starting materials were used in these experiments. Four independent temperature‐shear rate cycles were performed on composition RlA (∼76% SiO2) and two independent cycles on composition R2A (∼74% SiO2). Each run had a small (3–8 vol %) fraction of vapor present during viscometric testing. A power law model of the form τ = m (T) n(T) was found to fit the data. The temperature dependencies of m and n are m (т = a exp (b/T) and n (T) = c + dT, where a, b, c, and d are constants for fixed melt composition and bubble content. The viscosity function is given by η = a exp (b/T) c−1 + d T. Representative values of the constants for composition R2A are a = 5.579 ± 0.034 × 10−7 Pa s−n, b = 41491 ± 9.5 K, c = 3.039 ± 0.003 and d = −1.516 ± 0.002 K−1. The power law index coefficient n increases as temperature increases in the range 1100°–1350°C due to both volumetric expansion of vapor bubbles with increasing temperature and because of the effects of high shear rate on vapor bubble shapes. The Capillary number (Ca = ηa/ϕ), the ratio of stress tending to distort bubbles and stress tending to maintain sphericity, is high for these experiments, indicating substantial deviations from bubble sphericity. The activation energy for viscous flow, defined according to ∂1nn/∂(1/T) = b ‐ dT21nϒ, depends strongly and monotonically on shear rate. The Weissenberg effect, a phenomenon indicative of the presence of nonzero normal stresses has been observed. Melt climbs along the inner rotating rotor due to a positive first normal stress difference defined according to τΘΘ ‐ τrr = ‐Ψ1 r Θ2, where ‐Ψ1 is the first normal stress coefficient. Based on a plot of climb height Ch versus rotor angular frequency ω, ‐Ψ1 is found to be ∼2.5 × 103 Pa s2. Viscoelastic effects may be important in certain high shear rate flows of petrologic significance in which the Deborah number, defined according to De = Ψ1 /2η, is of order unity. To our knowledge, this is the first reported measurement of a normal stress coefficient for magma.

High shear rate flow behavior of xanthan gum dispersions

The high shear rate flow behavior of aqueous xanthan gum dispersions of 0.05, 0.10, 0.25, 0.50 and 1.0% w/w concentration, was determined at 5, 15, 25 and 35°C by capillary rheometry. Viscosity declined with increasing shear rates and approached a constant infinite shear viscosity, over a shear rate range of 1000–250 000/s. This viscosity decline was modeled using non-linear regression to relate apparent viscosity to shear stress and infinite shear viscosity. Arrhenius and Huggins models were then used to describe the variation of infinite shear viscosity with temperature and concentration respectively. Multiple regression was used to express the logarithm of infinite shear viscosity as a function of the logarithm of concentration and reciprocal of the absolute temperature. Examination of the data revealed that xanthan solution viscosities at high rates of shear were less dependent on gum concentration than on solvent viscosity.

Deformation and haemolysis of red cells in shear flow

Many in vitro experiments are performed to investigate mechanical damage to red blood cells. A theoretical interpretation of such experiments involving high shear-rate flows is presented here. Since haemolysis affects individual cells attention is concentrated on a single cell. The model chosen for analysis is an ellipsoid in a uniform shear flow. The small size of the cell ensures a small particle-based Reynolds number and hence the applicability of existing solutions for slow flow past an ellipsoid. Assuming a flexible elastic membrane the resulting stresses and displacements are calculated for low shear-rates. Passing to higher shear-rates the behaviour of Rand’s viscoelastic membrane breakdown model when subjected to the calculated stresses is investigated. The non-uniform rate of cell rotation produces a prediction of steady growth of strain, without increase of applied stress, until haemolysis occurs. When cell shapes predicted for low shear-rates are compared with observations there is adequate agreement and a qualitative explanation of other observed phenomena may be given. The predicted times to haemolysis are evaluated for various shear-rates and compared with published experimental results giving order of magnitude agreement.