High Shear Rate Flow Research Articles

Numerical study of ultra-large von Willebrand factor multimers in coagulopathy.

An excessive von Willebrand factor (VWF) secretion, coupled with a moderate to severe deficiency of ADAMTS13 activity, serves as a linking mechanism between inflammation to thrombosis. The former facilitates platelet adhesion to the vessel wall and the latter is required to cleave VWF multimers. As a result, the ultra-large VWF (UL-VWF) multimers released by Weibel-Palade bodies remain uncleaved. In this study, using a computational model based on first principles, we quantitatively show how the uncleaved UL-VWF multimers interact with the blood cells to initiate microthrombosis. We observed that platelets first adhere to unfolded and stretched uncleaved UL-VWF multimers anchored to the microvessel wall. By the end of this initial adhesion phase, the UL-VWF multimers and platelets make a mesh-like trap in which the red blood cells increasingly accumulate to initiate a gradually growing microthrombosis. Although high-shear rate and blood flow velocity are required to activate platelets and unfold the UL-VWFs, during the initial adhesion phase, the blood velocity drastically drops after thrombosis, and as a result, the wall shear stress is elevated near UL-VWF roots, and the pressure drops up to 6 times of the healthy condition. As the time passes, these trends progressively continue until the microthrombosis fully develops and the effective size of the microthrombosis and these flow quantities remain almost constant. Our findings quantitatively demonstrate the potential role of UL-VWF in coagulopathy.

Tribology and rheology of potato protein and pectin mixtures and Maillard conjugates

AbstractThis study aimed to compare the tribological and rheological properties of plant proteins versus their mixtures or conjugates with polysaccharides. We hypothesize that combining potato proteins (Po) with pectin (Pe) at various concentrations (0.5–5.0 wt%, ratios 1:1 and 1:2 w/w) will improve the lubrication performance of plant proteins by virtue of viscosity modification and boundary lubrication. Po showed shear thinning behavior with limited concentration‐dependence in boundary and mixed lubricity. Pe on the other hand showed pronounced concentration‐dependent flow and lubrication behavior delivering favorable boundary and viscous lubricity. Pe dominated the lubrication and high shear rate flow behavior in Po + Pe mixtures, governed mainly by the concentration of Pe and the hydrodynamic volume rather than the total concentration of the biopolymers. Maillard reaction (≤33% degree of conjugation) led to more negatively‐charged protein‐polysaccharide conjugates versus the sole biopolymers (p < 0.05). The conjugation decreased the second plateau shear viscosity of the Po + Pe mixtures and led to improvement in boundary and mixed lubricity when a reduced entrainment speed parameter was used. Findings from this study may inspire future studies combining plant proteins with polysaccharides to enhance their lubrication behavior and eventually improve the textural properties of plant‐based foods.

Experimental investigation of the effect of rotation rate and current speed on the dynamic response of riserless rotating drill string

Dynamic responses of rotating riserless drill string were investigated by varying rotation rate and current speed. Rotation rate ranged from 20 to 180 r/min, current speed ranged from 0.1 to 0.8 m/s, corresponding to Reynolds number of 1600–12,800 and rotation Reynolds number of 134–1206. Results show that the vibration energy of the rotating drill string is concentrated in rotation frequency, and its frequency doublings are stable in time series; equilibrium deflections are consistent in cross-flow (CF) and in-line (IL) directions and trajectory shows an oval-shape in still water. IL dominant frequency of rotating drilling string coupling VIV decreases, while CF dominant frequency and overall section dominant frequency increase with rotation rate. Vibration frequency transitions from high to low and its bandwidth increases in high shear-rate flow. Equilibrium deflection and vibration amplitude are higher than those of non-rotating drill string when Re ≤ 2400 due to the strong coupling of rotation and current. Rotation reduces mode participation, vibration envelopes are deflected to one side with both traveling and standing waves coexisting. Vibration amplitude reaches a maximum due to multiple resonances. Therefore, rotation rate near natural frequency should be avoided, and the rotation interference effect at low reduced velocity should not be overlooked.

The Impact of Different Arrangements of Molecular Chains in Terms of Low and High Shear Rate's Viscosities on Heat and Mass Flow of Nonnewtonian Shear thinning Fluids.

Non-newtonian fluids, especially shear thinning fluids, have several applications in the polymer industry, food industry, and even everyday life. The viscosity of shear thinning fluids is decreased by two or three orders of magnitude due to the alignment of the molecules in order when the shear rate is increased, and it cannot be ignored in the case of polymer processing and lubrication problems. So, the effects of viscosities at the low and high shear rates on the heat and mass boundary layer flow of shear thinning fluid over moving belts are investigated in this study. For this purpose the generalized Carreau model of viscosity relate to shear rate is used in the momentum equation. The Carreau model contains the five parameters: low shear rate viscosity, high shear rate viscosity, viscosity curvature, consistency index, and flow behavior index. For the heat flow, the expression of the thermal conductivity model similar to the viscosity equation due to the non-Newtonian nature of the fluid is used in the energy equation. On the mathematical model of the problem, boundary layer approximations are applied and then simplified by applying the similarity transformations to get the solution. The solution of the simplified equations is obtained by numerical technique RK-shooting method. The results are compared with existing results for limited cases and found good agreement. The results in the form of velocity and temperature profiles under the impact of all the viscosity's parameters are obtained and displayed in graphical form. Moreover, the boundary layer parameters such as the thickness of the regions, momentum thickness, and displacement thickness are calculated to understand the structure of the boundary layer flow of fluid. The velocity and temperature of the fluid are decreased and increased respectively by all viscosity's parameters of the model. So, the results of the boundary layer fluid flow under rheological parameters will not only help engineers to design superior chemical equipment but also help improve the economy and efficiency of the overall process.

Rheological Characterization of Non-Newtonian Mixtures by Pressure Pipe Tests

The rheological behavior of non-Newtonian fluids in turbulent conditions is an important topic in several fields of engineering. Nevertheless, this topic was not deeply investigated in the past due to the complexity of the experimental tests for the assessment of the constitutive parameters. Pressure pipe tests on Herschel-Bulkley mixtures were proven to be suitable for exploring turbulent conditions, but discrepancies with the results of tests performed in laminar flow were detected. These contradictions could be attributed to the inconsistencies of the Herschel-Bulkley model (HB) for high shear rate flows, proven by Hallbom and Klein, who suggested a more general “yield plastic” model (HK). Hence, in this study, a procedure for the estimation of the rheological parameters of both HB and HK models in pressure pipe tests is defined and rated on a complete set of experiments. The HK model performed much better than HB model in the turbulent range and slightly better than the HB model in the laminar range, confirming the consistency of the “yield plastic” model. The rheological parameters obtained by the proposed procedure were used to numerically model a dam-break propagation of a non-Newtonian fluid, showing significant differences in terms of process evolution depending on the constitutive model.

Predicting Mixing and Compaction Temperatures of Polymer Modified Bitumen

Despite many advantages of using polymer additives in bitumen, there are several challenges bordering on standards and specifications with regards to their utilization. One of these challenges is related with specifying the required heating or mixing and compaction temperatures of the polymer modified bitumen. The standard method (ASTM D 2493) aims to determine mixing and compaction temperatures of the base or unmodified bitumen. Nevertheless, the application of this method in the case of polymer modified bitumen led to very high temperatures which may not be appropriate for PMB. In this paper, some alternative methods named as the high shear rate and steady shear flow method suggested in the literature have been examined and tested for 50/70 and 160/220 penetration grade bitumen samples involving an elastomeric type of additive. A suggested method has also been proposed to overcome the complexities in the implementation of the alternative methods.

Numerical Investigation of the Effects of Red Blood Cell Cytoplasmic Viscosity Contrasts on Single Cell and Bulk Transport Behaviour

In-silico cellular models of blood are invaluable to gain understanding about the many interesting properties that blood exhibits. However, numerical investigations that focus on the effects of cytoplasmic viscosity in these models are not very prevalent. We present a parallelised method to implement cytoplasmic viscosity for HemoCell, an open-source cellular model based on immersed boundary lattice Boltzmann methods, using an efficient ray-casting algorithm. The effects of the implementation are investigated with single-cell simulations focusing on the deformation in shear flow, the migration due to wall induced lift forces, the characteristic response time in periodic stretching and pair collisions between red blood cells and platelets. Collective transport phenomena are also investigated in many-cell simulations in a pressure driven channel flow. The simulations indicate that the addition of a viscosity contrast between internal and external fluids significantly affects the deformability of a red blood cell, which is most pronounced during very short time-scale events. Therefore, modelling the cytoplasmic viscosity contrast is important in scenarios with high velocity deformation, typically high shear rate flows.

Effect of molecular weight, branching and temperature on dynamics of polypropylene melts at very high shear rates

Dynamics of linear polypropylene (L-PP) and long-chain branched polypropylene (LCB-PP) miscible blends, having weight average molecular weight between 64 and 78 kg/mol, was investigated via high shear rate rheology. Results obtained were compared with the corresponding data for L-PP. High-shear rate secondary Newtonian plateaus, η∞, were identified at three different temperatures for well entangled L-PP/LCB-PP blends above shear rates of 2·106 1/s and their dependence on weight average molecular weight, Mw, was successfully related as η∞(T)=K∞(T)·Mwn with the exponent n = 1.010. Interestingly, the temperature dependant proportionality constant K∞ was found to be about 10–20% lower for the blend in comparison with the pure L-PP whereas the parameter n was found to be the same for both systems. The average values of high-shear rate flow activation energy, E∞, for the blends was found to be slightly lower than for pure L-PP and comparable with low-shear rate flow activation energy of PP like oligomer squalane (C30H62; 2,6,10,15,19,23-hexamethyltetracosane). This suggests that polymer chains are fully disentangled at very high shear rates and chain branching can enhance the flow in this regime due to smaller coil size and higher availability of the free volume (i.e. lower monomeric friction coefficient) in comparison with their linear counterparts.

Effect of molecular weight on secondary Newtonian plateau at high shear rates for linear isotactic melt blown polypropylenes

In this work, three melt blown grades of isotactic linear polypropylenes, with weight average molecular weights between 56 250–75 850 g/mol, have been characterized at 230 °C over a very wide shear rate range (10–107 1/s) by using conventional rotational and twin bore capillary rheometry equipped with novel orifice die, and by an instrumented capillary nozzle on an injection molding machine. A low shear rate primary Newtonian plateau, a pseudoplastic region and a well developed secondary Newtonian plateau (occurring between 2·106−7·106 1/s) were identified for all the polypropylene melts. Flow activation energy at low (E0) and high (E∞ ) shear rates was found to be 56.590 kJ/mol and 25.204 kJ/mol, respectively. Considering the typical value of pressure sensitivity coefficient for polypropylene melt, β = 20.00 GPa−1, and measured flow activation energy at the secondary Newtonian plateau, E∞ = 25.204 kJ/mol, it was found that the effect of viscous dissipation and pressure is mutually cancelled, i.e. that the measured viscosity data can be considered as the true material property within the whole applied shear rate range. For the first time, it has been revealed that the secondary Newtonian viscosity, η∞, depends linearly on the weight average molecular weight, Mw, in log-log scale as η∞=1.19·10−6Mw1.084. The observed slope close to 1 between η∞ and Mw suggests that polymer chains in the melt are disentangled at the secondary Newtonian plateau region. This conclusion is supported by the experimental observation that the high shear rate flow activation energy E∞ for given PP melts is comparable with the flow activation energy of PP like oligomer (squalane, C30H62; 2,6,10,15,19,23-hexamethyltetracosane). The measured flow data were fitted by six different viscosity models, from which two, namely Modified Carreau and Quemada models, were suggested here for the first time. It has been found that the accuracy of utilized models to describe the measured data is the highest for the newly suggested models and decreases in the following order: Modified Quemada model, Modified Carreau model, Carreau-Yasuda model, Cross model, Generalized Quemada model and Carreau model.

Time-periodic Electroosmotic Flow of Non-newtonian Fluids in Microchannels

The alternating current electroosmotic flow of a non-Newtonian power-law fluid is studied in a circular microchannel. A numerical method is employed to solve the non-linear Poisson-Boltzmann and the momentum equations. The main parameters which affect the flow field are the flow behavior index, the dimensionless zeta potential and the dimensionless frequency. At very low dimensionless frequencies (slow oscillatory motion, small channel size, or large effective viscosity), the plug-like velocity profiles similar to steady-state electroosmotic flow are observed at nearly all times. At very high dimensionless frequencies, the flow is shown to be restricted to a thin region near the channel wall, while the bulk fluid remains essentially stationary. Velocity distributions of pseudoplastics and dilatants may be widened at low values of the dimensionless frequency depending on the dimensionless zeta potential; at high dimensionless frequencies, however, both fluids represent enhanced velocity magnitudes with the dimensionless zeta potential. In the case of high shear rate and/or suddenly-started flows, pseudoplastics tend to produce higher velocities than dilatants. These two kinds of fluids may produce same velocity profiles relying on the value of the dimensionless zeta potential as well as the ratio of their flow behavior indexes.

Matrix metalloproteinase-2 enhances platelet deposition on collagen under flow conditions.

Platelets contain and release matrix metalloproteinase-2 (MMP-2) that in turn potentiates platelet aggregation. Platelet deposition on a damaged vascular wall is the first, crucial, step leading to thrombosis. Little is known about the effects of MMP-2 on platelet activation and adhesion under flow conditions. We studied the effect of MMP-2 on shear-dependent platelet activation using the O'Brien filtration system, and on platelet deposition using a parallel-plate perfusion chamber. Preincubation of human whole blood with active MMP-2 (50 ng/ml, i.e. 0.78 nM) shortened filter closure time (from 51.8 ± 3.6 sec to 40 ± 2.7 sec, p<0.05) and increased retained platelets (from 72.3 ± 2.3% to 81.1 ± 1.8%, p<0.05) in the O'Brien system, an effect prevented by a specific MMP-2 inhibitor. High shear stress induced the release of MMP-2 from platelets, while TIMP-2 levels were not significantly reduced, therefore, the MMP-2/TIMP-2 ratio increased significantly showing enhanced MMP-2 activity. Preincubation of whole blood with active MMP-2 (0.5 to 50 ng/ml, i.e 0.0078 to 0.78 nM) increased dose-dependently human platelet deposition on collagen under high shear-rate flow conditions (3000 sec⁻¹) (maximum +47.0 ± 11.9%, p<0.05, with 50 ng/ml), while pre-incubation with a MMP-2 inhibitor reduced platelet deposition. In real-time microscopy studies, increased deposition of platelets on collagen induced by MMP-2 started 85 sec from the beginning of perfusion, and was abolished by a GPIIb/IIIa antagonist, while MMP-2 had no effect on platelet deposition on fibrinogen or VWF. Confocal microscopy showed that MMP-2 enhances thrombus volume (+20.0 ± 3.0% vs control) rather than adhesion. In conclusion, we show that MMP-2 potentiates shear-induced platelet activation by enhancing thrombus formation.

Carreau fluid model for blood flow through a tapered artery with a stenosis

In present article, we have studied the blood flow through tapered artery with stenosis. The non-Newtonian nature of blood in small arteries is analyzed mathematically by considering the blood as Carreau fluid. Carreau fluid is a type of generalized Newtonian fluid. At low shear rate Carreau fluids behaves as a Newtonian fluid n=1 and at high shear rate as power law fluid. For n<1 Carreau fluid gives pseudoplastic(non-Newtonian), or shear-thinning fluids have a lower apparent viscosity at higher shear rates and for n>1 Carreau fluid behaves as Dilatant(non-Newtonian), or shear-thickening fluids increase in apparent viscosity at higher shear rates. All three cases are appropriate for blood flow in arteries because the assumption of Newtonian behavior of blood is acceptable for high shear rate flow, i.e. the case of flow through larger arteries. It is not, however, valid when the shear rate is low as is the flow in smaller arteries and in the downstream of the stenosis. It has been pointed out that in some diseased conditions, blood exhibits remarkable non-Newtonian properties. The representation for the blood flow is through an axially non-symmetrical but radially symmetric stenosis. Symmetry of the distribution of the wall shear stress and resistive impedance and their growth with the developing stenosis is another important feature of our analysis. Analytical solutions has been evaluated for velocity, resistance impedance, wall shear stress and shear stress at the stenosis throat. The graphical results of different types of tapered arteries (i.e converging tapering, diverging tapering, non-tapered artery) have been examined for different parameters of interest.

High shear rate flow in a linear stroke magnetorheological energy absorber

To provide adaptive stroking load in the crew seats of ground vehicles to protect crew from blast or impact loads, a magnetorheological energy absorber (MREA) or shock absorber was developed. The MREA provides appropriate levels of controllable stroking load for different occupant weights and peak acceleration because the viscous stroking load generated by the MREA force increases with velocity squared, thereby reducing its controllable range at high piston velocity. Therefore, MREA behavior at high piston velocity is analyzed and validated experimentally in order to investigate the effects of velocity and magnetic field on MREA performance. The analysis used to predict the MREA force as a function of piston velocity squared and applied field is presented. A conical fairing is mounted to the piston head of the MREA in order reduce predicted inlet flow loss by 9% at nominal velocity of 8 m/s, which resulted in a viscous force reduction of nominally 4%. The MREA behavior is experimentally measured using a high speed servo-hydraulic testing system for speeds up to 8 m/s. The measured MREA force is used to validate the analysis, which captures the transient force quite accurately, although the peak force is under-predicted at the peak speed of 8 m/s.

Matrix metalloproteinase-2 of human carotid atherosclerotic plaques promotes platelet activation

Purified active matrix metalloproteinase-2 (MMP-2) is able to promote platelet aggregation. We aimed to assess the role of MMP-2 expressed in atherosclerotic plaques in the platelet-activating potential of human carotid plaques and its correlation with ischaemic events. Carotid plaques from 81 patients undergoing endarterectomy were tested for pro-MMP-2 and TIMP-2 content by zymography and ELISA. Plaque extracts were incubated with gel-filtered platelets from healthy volunteers for 2 minutes before the addition of a subthreshold concentration of thrombin receptor activating peptide-6 (TRAP-6) and aggregation was assessed. Moreover, platelet deposition on plaque extracts immobilised on plastic coverslips under high shear-rate flow conditions was measured. Forty-three plaque extracts (53%) potentiated platelet aggregation (+233 ± 26.8%), an effect prevented by three different specific MMP-2 inhibitors (inhibitor II, TIMP-2, moAb anti-MMP-2). The pro-MMP-2/TIMP-2 ratio of plaques potentiating platelet aggregation was significantly higher than that of plaques not potentiating it (3.67 ± 1.21 vs 1.01 ± 0.43, p<0.05). Moreover, the platelet aggregation-potentiating effect, the active-MMP-2 content and the active MMP-2/pro-MMP-2 ratio of plaque extracts were significantly higher in plaques from patients who developed a subsequent major cardiovascular event. In conclusion, atherosclerotic plaques exert a prothrombotic effect by potentiating platelet activation due to their content of MMP-2; an elevated MMP-2 activity in plaques is associated with a higher rate of subsequent ischaemic cerebrovascular events.

Rheological characterization of galactomannans extracted from seeds of Caesalpinia pulcherrima

The galactomannan from the seeds of Caesalpinia pulcherrima L. was isolated and purified by precipitation method using alcohol to get C. pulcherrima (CP) gum. CP gum was studied for its physicochemical and rheological properties. The composition of CP gum was found to contain mannose:galactose:glucose:xylose in a proportion of 2.8:1:0.1:0.08, with M/G ratio 2.80. The molecular weight (Mw) for CP gum was obtained to be approximately 2.72×106Da by static light scattering measurements and 2.79×106Da using Mark–Houwink relationship. The intrinsic viscosity by Huggins and Kraemer plots using capillary viscometry was obtained as 12–12.5dl/g. The rheological behavior of aqueous galactomannan solutions was studied at 25°C, using steady-shear and dynamic oscillatory measurements. The various concentrations of CP gum exhibits shear thinning non Newtonian behavior at high shear rate and Newtonian flow at low shear rate. Experimental data in steady shear has been correlated and found a better fitting with the Cross and Carreau models. A graph of the specific viscosity at zero shear rate (ηsp0) against coil overlap parameter (C[η]) was plotted and the slope of the lines in dilute and semi-dilute regions were found to be 1.23 and 4.1 respectively. The critical concentration (C*) was found to be about 3.8/[η]. The linear viscoelastic region for CP gum solutions presented nature as that of macromolecular solutions. At all shear rates and frequencies, ηap and η* had almost similar magnitudes, which shows its reasonable agreement with the Cox–Merz rule. The present investigation shows the suitability of CP gum as a pharmaceutical aid application like viscosity modifier, release retardants, binders.

Cilostazol down-regulates the height of mural platelet thrombi formed under a high-shear rate flow in the absence of ADAMTS13 activity

Cilostazol is an anti-platelet drug that reversibly inhibits phosphodiesterase III (PDE-III), which is ubiquitously expressed in platelets and various tissues. PDE-III converts cyclic adenosine monophosphate (cAMP) to 5'-AMP and up-regulates the intracellular concentration of cAMP, a potent inhibitor of platelet aggregation. Unlike other anti-platelet drugs, cilostazol is unique because patients receiving this drug do not have a significantly prolonged bleeding time, but the reasons for this difference are still unknown. In this study, we have examined how cilostazol inhibits platelet thrombus formation using anti-coagulated normal whole blood in which the platelets were labeled with a fluorescent dye in comparison with the anti-GPIIb/IIIa agent, tirofiban. We used an in vitro assay to examine mural platelet thrombus growth on a collagen surface under a high-shear rate flow in the absence of ADAMTS13 activity. These experimental conditions mimic the blood flow in patients with thrombotic thrombocytopenic purpura. Using this model, we clearly determined that cilostazol down-regulates the height of mural platelet thrombi formed on a collagen surface in a dose-dependent manner, without affecting the surface coverage. The concentration of cilostazol used in this study was relatively high (60–120μM) compared to clinically relevant concentrations (1–3μM), which may be due to the in vivo synergistic effects of PDE-III present in other tissues aside from platelets. Cilostazol does not affect the initial formation of platelet thrombi, but does inhibit the height of thrombi. These results showed a sharp contrast to tirofiban, and address why cilostazol does not significantly prolong bleeding time, despite its strong anti-platelet activity.

Measurement of pollen clump release and breakup in the vicinity of ragweed (A. confertiflora) staminate flowers

Pollen dispersal is fundamental in a plant's reproductive ecology and as a result of fragmentation of the landscape, questions have been raised on how isolated plant populations can still exchange genetic information. A common mechanism for gene exchange is wind pollination (anemophily). A successful anemophilous species native to North America is ragweed (Ambrosia), a weed that is hard to eradicate after it takes root on crop fields and its pollen causes very strong allergenic effects (hay fever). Despite the extremely clumpy nature of ragweed pollen that should limit its long distance dispersal, ragweed has spread rapidly across the world during the last century while maintaining a high genetic diversity. One of the reasons for its success may be prolific pollen production as well as an efficient pollen clump release and breakup mechanism. Efficient pollen entrainment and dispersal into the atmosphere is highly influenced by flow field characteristics as pollen released into the atmosphere initially encounters flow structures created by the plant's morphology. Here, the flow field in the wake of a mature ragweed spike having multiple staminate flowers as well as pollen release was studied using Particle Image Velocimetry and high-speed, inline holographic cinematography. The latter enabled to track the pollen in a 3D volume. The spike was set up in a wind tunnel and exposed to wind speeds ranging from 1 to 2 m/s. Results indicated that ragweed pollen was released in multiple sized clumps containing tens to several thousand single grains. Clumps were both “pulled apart” at the point of entrainment while exiting the flowers as well as broke up in smaller sized clumps in high shear rate flow regions not far from the spike. In addition, the largest clumps that did not travel far, deposited in the vicinity of the spike, breaking apart into many small clumps upon deposition. Based on our results, initial release and dispersal of ragweed pollen clumps is characterized by three concomitant mechanisms of clump breakup occurring at entrainment, in mid-air and on deposition, which make it perfectly suited to disperse pollen over a wide range of spatial scales.

Rheological measurements of large particles in high shear rate flows

This paper presents experimental measurements of the rheological behavior of liquid-solid mixtures at moderate Stokes and Reynolds numbers. The experiments were performed in a coaxial rheometer that was designed to minimize the effects of secondary flows. By changing the shear rate, particle size, and liquid viscosity, the Reynolds numbers based on shear rate and particle diameter ranged from 20 to 800 (Stokes numbers from 3 to 90), which is higher than examined in earlier rheometric studies. Prior studies have suggested that as the shear rate is increased, particle-particle collisions also increase resulting in a shear stress that depends non-linearly on the shear rate. However, over the range of conditions that were examined in this study, the shear stress showed a linear dependence on the shear rate. Hence, the effective relative viscosity is independent of the Reynolds and Stokes numbers and a non-linear function of the solid fraction. The present work also includes a series of rough-wall experiments that show the relative effective viscosity is also independent of the shear rate and larger than in the smooth wall experiments. In addition, measurements were made of the near-wall particle velocities, which demonstrate the presence of slip at the wall for the smooth-walled experiments. The depletion layer thickness, a region next to the walls where the solid fraction decreases, was calculated based on these measurements. The relative effective viscosities in the current work are larger than found in low-Reynolds number suspension studies but are comparable with a few granular suspension studies from which the relative effective viscosities can be inferred.

A Model of Slurry Flow in a Fracture

Abstract An accurate calculation of slurry flow in a fracture is an important issue for fracture design. A model taking into account particle dynamics on a micro-level has been developed. The model shows that the slurry dynamics, to a significant extent, is governed by particle fluctuations generated in a high shear-rate flow. Particles migrate from high shear-rate zones at the fracture walls towards the fracture centre. Thus, a slurry flow is characterized by non-uniform concentration across a fracture. Low solids concentration near the walls leads to reduction of slurry-wall friction compared to that predicted by a model not taking particle migration into account. Reduction in the friction leads to a significant decrease in the pressure gradient and the net pressure, respectively. Introduction Hydraulic fracturing is a complicated but well-studied technology for well stimulation(1). There are a number of computational codes for calculating technological parameters of a fracturing procedure. Such codes solve equations describing slurry hydrodynamics coupled with equations modelling formation fracturing. Since the percentage of fracturing job failures is high (above 30%), it is important to enhance the accuracy of modelling of different components of hydraulic fracturing to make this procedure a more reliable operation. In the current research, we suggest a model of slurry flow in a fracture taking into account an important effect of proppant migration to the fracture centre. Model Slurry flow moving in a fracture is usually characterized by a high mean shear rate (up to γm = um/w= 200 1/s), where um is the mean (superficial) slurry velocity and w is the fracture width. In our analysis, we will consider a steady-state slurry flow in a channel of a constant width. We also neglect impact of fluid leakoff into the formation on slurry dynamics. Many fracturing fluids used in practice are characterized by the power-law rheology. Engineers usually employ a known solution of the Navier-Stokes equation for power-law slurry(1) obtained by assuming that particles have the same velocity as a fluid and that the concentration of solids is uniformly distributed across a fracture. Lattice-Bolzmann computations have shown that in a high shear rate slurry, flow particles fluctuate(2). For the present study, the kinetic theory of granular flows(3) was employed for flow modelling. The kinetic theory assumes that particles collide with each other moving like ideal gas molecules and the velocity distribution of particle fluctuations is Maxwellian. The key parameter of this approach is the granular temperature determining intensity of particle fluctuations: Equation 1 Available in Full Paper. where &amp;lt; υ2s&amp;gt; is the mean-square fluctuation velocity of a particle. An equation of a granular energy balance for a flat channel is written as(4): Equation 2 Available in Full Paper.

Transient rheological behavior of lyotropic (acetyl)(ethyl)cellulose/m-cresol solutions

The chiroptical properties and transient rheological behavior of (acetyl)(ethyl)cellulose (AEC) m-cresol liquid crystalline solutions have been investigated. Chiroptical properties were manipulated through (i) increasing degree of acetylation of ethyl cellulose (EC), and (ii) blending AEC with EC. At the same average degree of acetylation (DA), the chiroptical properties of pure AEC were different from those of the EC/AEC mixtures. However, at the same DA, the AEC and mixed AEC/EC solutions showed similar steady state flow and oscillatory behaviors, but the transient behaviors were different. At high flow rates the mixed AEC/EC solutions exhibited double recoil after cessation of steady-state flow, whereas the AEC solutions showed double recoil only in the high DA AEC solutions. All solutions, pure and mixed, had the same stress relaxation behavior. Both pitch and handedness affected the transient behavior. After cessation of high shear rate flow, the rate of modulus evolution decreased with increasing pitch, and was faster in right-handed mesophases than in left-handed ones at a similar pitch.