Shear-thinning Suspensions Research Articles

Using Ultrasound Imaging To Identify Flow Reattachment In Shear-Thinning Suspensions

The current study explores ultrasound imaging velocimetry (UIV) as an alternative method for capturing flow fields in shear-thinning suspensions. In particular, UIV is used here together with pressure measurements to identify the reattachment point and to correlate the point's location with the pressure recovery downstream of an axisymmetric expansion. Four fluids are investigated: pure water, as well as three 1750ppm xanthum-gum-in-water solutions mixed with non-reactive mineral micro-particles at 0%, 15% and 30% volume fractions. Wall-pressure measurements were collected through taps located at 0 to 13 throat diameters downstream of the expansion with subsequent UIV measurements collected from 0.5 to 5 throat diameters downstream of the expansion. Pressure-tap measurements for the tested suspensions demonstrate 80% to 100% total pressure recovery achieved at approximately 4 to 5 throat diameters downstream from the throat. Furthermore, all four fluids exhibit total pressure recoveries within 10% of Borda-Carnot prediction. Despite similar pressure recoveries, UIV revealed different reattachment lengths for the tested fluids. Water exhibited a reattachment length of approximately four throat diameters, which is expected within the tested turbulent regime, while the xanthum-gum solution exhibited a delayed reattachment beyond the field-of-view when the effective Reynolds number is O(100). Pipe-wall velocity measurements suggest that the dense suspensions exhibit similar reattachment lengths to that of water despite expectations that the dense suspensions would behave similar to the pure xanthum-gum solution given: the similar Reynolds number between the pure xanthum-gum solution and the tested dense suspensions; and previous work done by Barnes et al. (2024) and others revealing shear-layer stabilization within dense suspensions. It is suspected that increased diffusion within the suspension mitigates the shear layer's ability to convect downstream, but improved measurements are required to state this conclusively.

Modeling the impact of the temperature profile on the sedimentation process for shear thinning suspensions in the annulus of oil well

The particle settling phenomena were broadly studied in the literature experimentally and numerically. To the best of our knowledge, previous works do not consider the temperature effect on the suspension rheology and, consequently, the influence over the settling velocity. Motivated by the problem of the sedimentation in confined drilling fluids exposed to a geothermal temperature gradient, this work proposed a continuum model for the sedimentation process of weighting agents in non-Newtonian suspensions based on the Mixture Theory. A temperature-dependent correction for the suspension consistency index was proposed and the results were discussed for different temperature profile cases, including uniform temperature profile, linear and geothermal profiles. Numerical simulations were performed, using the Finite Volume technique. Results for the solids concentration along the column for up to five years were discussed as well as the solids concentration evolution for selected points along the column. The results showed that the temperature gradient significantly impacts the settling velocity and the evolution of sedimentation regions. The main affected zones were the free settling and the sediment zones, which can alter directly parameters of interest for applications in oil wells, such as the height of sediment.

Development of an adaptive coaxial concrete rheometer and rheological characterisation of fresh concrete

Abstract The accessibility to rheological parameters for concrete is becoming more and more relevant. This is mainly related to the constantly emerging challenges, such as not only the development of high-strength concretes is progressing very fast but also the simulation of the flow behaviour is of high importance. The main problem, however, is that the rheological characterisation of fresh concrete is not possible via commercial rheometers. The so-called concrete rheometers provide valuable relative values for comparing different concretes, but they cannot measure absolute values. Therefore, we developed an adaptive coaxial concrete rheometer (ACCR) that allows the measurement of fresh concrete with particles up to d max = 5.5 mm {d}_{{\rm{\max }}}=5.5\hspace{.5em}{\rm{mm}} . The comparison of the ACCR with a commercial rheometer showed very good agreement for selected test materials (Newtonian fluid, shear thinning fluid, suspension, and yield stress fluid), so that self-compacting concrete was subsequently measured. Since these measurements showed a very high reproducibility, the rheological properties of the fresh concrete could be determined with high accuracy. The common flow models (Bingham (B), Herschel–Bulkley, modified Bingham (MB) models) were also tested for their applicability, with the Bingham and the modified Bingham model proving to be the best suitable ones.

Experimental insights into elasto-inertial transitions in Taylor-Couette flows.

Since the seminal work of Taylor in 1923, Taylor-Couette (TC) flow has served as a paradigm to study hydrodynamic instabilities and bifurcation phenomena. Transitions of Newtonian TC flows to inertial turbulence have been extensively studied and are well understood, while in the past few years, there has been an increasing interest in TC flows of complex, viscoelastic fluids. The transitions to elastic turbulence (ET) or elasto-inertial turbulence (EIT) have revealed fascinating dynamics and flow states; depending on the rheological properties of the fluids, a broad spectrum of transitions has been reported, including rotating standing waves, flame patterns (FP), and diwhirls (DW). The nature of these transitions and the relationship between ET and EIT are not fully understood. In this review, we discuss experimental efforts on TC flows of viscoelastic fluids. We outline the experimental methods employed and the non-dimensional parameters of interest, followed by an overview of inertia, elasticity and elasto-inertia-driven transitions to turbulence and their modulation through shear thinning or particle suspensions. The published experimental data are collated, and a map of flow transitions to EIT as a function of the key fluid parameters is provided, alongside perspectives for the future work. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (part 1)'.

Effect of previous sedimentation time in filtration rate for shear-thinning suspensions

In oil well drilling, the Annular Pressure Build-up (APB) phenomena may lead to several damages in the formation and, in some cases, the well losing. Open shoes are generally used to mitigate this phenomenon, in which some spaces are maintained opened under the wall coating, at the well bottom. After the fluid expansion and pressure raising, the confined fluid flows directly to the rock formation. The sedimentation of the weighting material in the drilling mud in confined annular regions provides a thicker cake which may clog the shoe, turning the mitigation process inefficient. This research aims to study the effect of previous sedimentation and temperature on the filtrate volume and the mud cake properties for shear-thinning suspensions. To study the particles settlement, the falling dynamics were monitored by an online microscope coupled in a sedimentation test apparatus. Filtration experiments with and without previous sedimentation were performed. It was possible to conclude from experimental data that, for non-Newtonian fluids, filtration and sedimentation rates are increased with previous sedimentation. The main responsible factor is the presence of agglomerated particles vertically chained, increasing the permeability of the sedimentation cake. The observed mechanics are favorable to the annular pressure relief.

Printable Ink Development for Molten Salt Battery Electrodes

Thermal batteries are important power sources in applications requiring a long shelf life, fast activation, and reliable power delivery. They operate at high temperatures and utilize molten salt electrolytes, typically eutectic mixtures, which are inert solids at ambient temperatures and provide fast ionic conductivity above the melting point of the salt. The size, energy density, and mechanical properties of thermal batteries are limited by the current manufacturing processes, which are slow and labor-intensive. The development of printable, coated-film electrodes and components will lead to batteries with increased energy density, a more efficient production process, and form factor flexibility.The electrolyte salt (LiCl-KCl eutectic) and MgO separator materials are combined in a single ‘electrolyte binder’ mixture (EB). Slurries were prepared with the EB using DMSO as the carrier solvent and additional dissolved LiCl as a binder for the printed film. The slurries show a large change in viscosity as a portion of the electrolyte dissolves during the mixing process. The initial coarse slurry mixture quickly increases in apparent viscosity before smoothing out into highly shear-thinning suspension with a small overall particle size (<25 µm). The slurries can be easily printed directly on coated cathode substrates, using a slot-die or tape casting coating method. After drying, the film provides a stable separator layer, which can be cut or punched into the desired form and assembled into battery cells. Micro-CT imaging shows the resulting multi-layer film with a distinct cathode layer, and separator layers with a final dry film thickness on the order of 220 µm.Thermal analysis data indicates that neither the modified salt content nor the dissolution and re-crystallization process significantly alter the melting behavior of the electrolyte salts and separator coatings when compared to the standard thermal battery separator mixtures. Thermogravimetric analysis (TGA) indicates that the solvent is sufficiently removed from the printed films during the drying process, and differential scanning calorimetry (DSC) measurements show that the melting point of the electrolyte in the coated separator film shifts by less than 5ºC, in comparison to the standard LiCl-KCl eutectic mixture. Single-cell electrochemical tests using the combined multi-layer separator/cathode films yielded voltages of >1.9 V delivering a capacity >100 mAh/g and with a lower internal resistance than standard thermal battery cells.Figure 1. Cross-sectional micro-CT image of printed multi-layer electrode, consisting of carbon fiber support with cathode film and separator/electrolyte overcoat. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government. SAND No. SAND2020-5349 A Figure 1

Turbulent coarse-particle suspension flow: Measurement and modelling

Solid-liquid suspension flows are widely encountered in industrial applications. In many of these flows, the carrier fluid exhibits shear-thinning behaviour and the solids have a broad size distribution. Shear-thinning suspensions can occur in laminar or weakly turbulent regimes due to their high viscosity. This paper presents a DNS-DEM model for weakly turbulent coarse-particle suspension flows. Although our interest is in shear-thinning suspensions, we aim firstly to develop a liquid-solid model in a Newtonian fluid to remove the uncertainty in particle-fluid interaction in non-Newtonian suspensions. Matching experiments were conducted for validation. The predicted mixture velocity and concentration profiles are in good agreement with experiments, and discrepancies are mostly less than 10%. The mean velocity profiles are significantly damped by coarse particles and particle phase generally exhibits a higher fluctuation. This DNS-DEM modelling approach is viable for simulating these flows and will form the basis of future work on shear-thinning suspension flow.

Absolute Rheological Measurements of Model Suspensions: Influence and Correction of Wall Slip Prevention Measures.

Since suspensions (e.g., in food, cement, or cosmetics industries) tend to show wall slip, the application of structured measuring surfaces in rheometers is widespread. Usually, for parallel-plate geometries, the tip-to-tip distance is used for calculation of absolute rheological values, which implies that there is no flow behind this distance. However, several studies show that this is not true. Therefore, the measuring gap needs to be corrected by adding the effective gap extension to the prescribed gap height in order to obtain absolute rheological properties. In this paper, we determine the effective gap extension for different structures and fluids (Newtonian, shear thinning, and model suspensions that can be adjusted to the behavior of real fluids) and compare the corrected values to reference data. We observe that for Newtonian fluids a gap- and material-independent correction function can be derived for every measuring system, which is also applicable to suspensions, but not to shear thinning fluids. Since this relation appears to be mainly dependent on the characteristics of flow behaviour, we show that the calibration of structured measuring systems is possible with Newtonian fluids and then can be transferred to suspensions up to a certain particle content.

Additive Manufacturing of Optical Quality Germania-Silica Glasses.

Direct ink writing (DIW) three-dimensional (3D) printing provides a revolutionary approach to fabricating components with gradients in material properties. Herein, we report a method for generating colloidal germania feedstock and germania-silica inks for the production of optical quality germania-silica (GeO2-SiO2) glasses by DIW, making available a new material composition for the development of multimaterial and functionally graded optical quality glasses and ceramics by additive manufacturing. Colloidal germania and silica particles are prepared by a base-catalyzed sol-gel method and converted to printable shear-thinning suspensions with desired viscoelastic properties for DIW. The volatile solvents are then evaporated, and the green bodies are calcined and sintered to produce transparent, crack-free glasses. Chemical and structural evolution of GeO2-SiO2 glasses is confirmed by nuclear magnetic resonance, X-ray diffraction, and Raman spectroscopy. UV-vis transmission and optical homogeneity measurements reveal comparable performance of the 3D printed GeO2-SiO2 glasses to glasses produced using conventional approaches and improved performance over 3D printed TiO2-SiO2 inks. Moreover, because GeO2-SiO2 inks are compatible with DIW technology, they offer exciting options for forming new materials with patterned compositions such as gradients in the refractive index that cannot be achieved with conventional manufacturing approaches.

Porous gravity currents: Axisymmetric propagation in horizontally graded medium and a review of similarity solutions

Abstract We present an investigation on the combined effect of fluid rheology and permeability variations on the propagation of porous gravity currents in axisymmetric geometry. The fluid is taken to be of power-law type with behaviour index n and the permeability to depend from the distance from the source as a power-law function of exponent β. The model represents the injection of a current of non-Newtonian fluid along a vertical bore hole in porous media with space-dependent properties. The injection is either instantaneous ( α = 0 ) or continuous (α > 0). A self-similar solution describing the rate of propagation and the profile of the current is derived under the assumption of small aspect ratio between the current average thickness and length. The limitations on model parameters imposed by the model assumptions are discussed in depth, considering currents of increasing/decreasing velocity, thickness, and aspect ratio, and the sensitivity of the radius, thickness, and aspect ratio to model parameters. Several critical values of α and β discriminating between opposite tendencies are thus determined. Experimental validation is performed using shear-thinning suspensions and Newtonian mixtures in different regimes. A box filled with ballotini of different diameter is used to reproduce the current, with observations from the side and bottom. Most experimental results for the radius and profile of the current agree well with the self-similar solution except at the beginning of the process, due to the limitations of the 2-D assumption and to boundary effects near the injection zone. The results for this specific case corroborate a general model for currents with constant or time-varying volume of power-law fluids propagating in porous domains of plane or radial geometry, with uniform or varying permeability, and the possible effect of channelization. All results obtained in the present and previous papers for the key parameters governing the dynamics of power-law gravity currents are summarized and compared to infer the combinations of parameters leading to the fastest/lowest rate of propagation, and of variation of thickness and aspect ratio.

Study on the stability of a shear-thinning suspension used in oil well drilling

In order to avoid solid-liquid gravitational separation of particles in the drilling fluid and cuttings generated in this process, the oil industry has been developing drilling fluids with shear-thinning and thixotropic characteristics. In case of operational stops in the drilling process, the intense sedimentation of these particles can damage the equipment used and the well. In this context, this study simulated an operational stop to obtain information about stability of solids in a paraffin-based suspension with time-dependent shear-thinning behavior, which has already been used in current drilling processes. A long-term test using gamma-ray attenuation technique identified the separation dynamics of a set of micrometric particles belonging to and incorporated into the drilling fluid during operation. This test verified the typical regions of gravitational sedimentation and, through constant concentration curves, indicated that the sedimentation process did not occur at a constant rate. This study also proposed a constitutive equation for pressure on solids.

Processing, microstructure and thermoluminescence response of biomorphic yttrium oxide ceramics

The present work reports a fast-direct bio-prototyping process using Luffa Cylindrica vegetable sponge to produce biomorphic yttrium oxide ceramics with reticulated-porous architecture and thermoluminescence response. Processing parameters as rheology of yttrium oxide suspensions, bio-template surface treatment and thermal decomposition of bio-template were investigated. Shear thinning suspensions of 30vol% yttrium oxide with apparent viscosity of 243mPa.s provided a successful impregnation of samples, whereby bio-templates with smooth ceramic layer and hierarchical reticulated architecture were formed. By thermal treatment at 1600°C for 2h biomorphic yttrium oxide ceramics with porous microstructure and TL response at 150°C and λ=550nm were produced. The proposed fast-direct bio-prototyping process is suitable for the production of ceramic components with complex shape and demonstrates potential for general applicability to any bio-template.

The influences of particle–particle interaction and viscosity of carrier fluid on characteristics of silica and calcium carbonate suspensions-coated Twaron® composite

ABSTRACTThe effects of particle–particle interaction and viscosity of carrier fluid on steady and dynamic rheological responses and quasi-static penetration resistance of Twaron® fabrics treated with shear thickening and shear thinning suspensions have been investigated. The suspensions have been made by mechanically dispersing 60 nm silica (SiO2) and calcium carbonate (CaCO3) nanoparticles in poly ethylene glycol (PEG) with molecular weights of 200 and 400 g/mol. The CaCO3 suspensions display shear thinning behaviour along with the total dominance of the elastic state over the viscous state while the SiO2 suspensions exhibit shear thickening behaviour with the emergence of both the elastic and viscous states. With the increase of molecular weight of PEG, viscosity, viscoelastic modules and instability of the suspensions increase and critical shear rate and frequency of transition to elastic state diminish. The PEG200 and PEG400-contained SiO2 suspensions-treated Twaron® composites at 35 wt.% have quasi-static penetration resistances which are nearly 2.63 and 2.48 times and maximum absorbed energies which are about 1.54 and 1.55 times higher, respectively, than those of the corresponding CaCO3 ones. However, the influence of increasing the PEG's molecular weight is not as considerable as the effect of particle–particle interaction on the enhancement of penetration resistance performance.

Wplyw dodatku mocznika, azotanu sodu i glikolu etylenowego na wlasciwosci reologiczne kleikow skrobi kukurydzianej

The effects of the additives used in starch adhesives production on the pasting process and rheological properties of native corn starch were investigated. Suspensions of the starch of Indentata variety (6 %) prepared in distilled water or aqueous solutions of urea (2.5 %), sodium nitrate(V) (2.5 %) and ethylene glycol (1.5 %) were subjected to a controlled pasting in RVA viscometer. The obtained pastes were placed in a measuring cylinder of HAAKE rheometer and the viscosity measurements were performed using controlled shear rate (CR) mode at shear rates of 0—600 s-1. The paste smears were analyzed under a microscope after staining with Lugol's solution. It was found that the addition of urea caused a reduction in the pasting temperature, change in the shape of pasting curve as well as 30 % increase in the final viscosity (Table 1). The addition of sodium nitrate(V) led to an increase in the pasting time, decrease of the viscosity drop and reduced viscosity increase during cooling (Fig. 1). The influence of ethylene glycol additive on the pasting process was less significant than that of urea and sodium nitrate(V). Corn starch forms pastes or shear thinning suspensions with a distinct change in the rheological properties over time.

Radial gravity currents in vertically graded porous media: Theory and experiments for Newtonian and power-law fluids

This study theoretically and experimentally explores the behaviour of axisymmetric gravity currents of Newtonian and power-law fluids in inhomogeneous porous media. Systematic heterogeneity along the vertical is represented by a power-law permeability variation governed by the parameter ω, mimicking trends in natural media. A self-similar solution describing (i) the rate of propagation and (ii) the profile of the current is derived by considering a current of volume proportional to time raised to a non-negative power α. Four critical values of α are determined: the first two affect the time dependency of the radius, height and average gradient of the current on flow behaviour index n and ω; the third one dictates if the current accelerates or decelerates; the fourth one governs the asymptotic validity of the thin current approximation. Experimental validation is performed using shear-thinning suspensions and Newtonian mixtures in constant- and variable-flux regimes. A stratified porous medium composed of four uniform strata of glass beads with different diameters is used for this purpose. The experimental results for the radius and profile of the current agree well with the self-similar solution except at the beginning of the process, due to the limitations of the 1-D assumption and to boundary effects near the injection zone. An uncertainty analysis indicates that the rheological fluid behaviour and the variation in permeability significantly affect the propagation of the current.

Imaging the Microscopic Structure of Shear Thinning and Thickening Colloidal Suspensions

The viscosity of colloidal suspensions varies with shear rate, an important effect encountered in many natural and industrial processes. Although this non-Newtonian behavior is believed to arise from the arrangement of suspended particles and their mutual interactions, microscopic particle dynamics are difficult to measure. By combining fast confocal microscopy with simultaneous force measurements, we systematically investigate a suspension's structure as it transitions through regimes of different flow signatures. Our measurements of the microscopic single-particle dynamics show that shear thinning results from the decreased relative contribution of entropic forces and that shear thickening arises from particle clustering induced by hydrodynamic lubrication forces. This combination of techniques illustrates an approach that complements current methods for determining the microscopic origins of non-Newtonian flow behavior in complex fluids.

A Physical Model for Yield Plastic Fluids

This article presents the theoretical basis for the yield plastic rheological model for shear-thinning mineral suspensions. The standard structural model is modified to allow for the hypothesis that the average interparticle bond strength increases as the structure (aggregates) breaks down. The resulting model is algebraically simple and contains the Newtonian, Bingham, and Casson models as special cases. If minor stresses are considered, the model will also describe suspensions with a low shear rate viscosity plateau (i.e., Carreau-type suspensions). The yield plastic model accurately describes the flow behavior of most shear-thinning suspensions and is consistent with the observed behavior in rheometers and pipelines.

Effect of pH on deagglomeration and rheology/morphology of aqueous suspensions of goethite nanopowder

The kinetics of deagglomeration in diluted suspensions of goethite nanopowder, as well as the rheology and morphology of the resulting suspensions, strongly depends on pH. At pH 3, nanopowder can be dispersed as separate nanoparticles, and the resulting suspension is Newtonian, with the viscosity only marginally higher than the viscosity of water. At pH between 5 and 12, nanoparticles tend to reaggregate and form weak aggregates/flocs. Morphology changes from a Newtonian suspension of primary nanoparticles to a non-Newtonian, shear-thinning suspension of large, porous, interconnected flocs with the yield stress reaching a maximum at an isoelectric point. The effect of pH on morphology and rheology is reversible, and as pH is reduced to 3, the suspension becomes Newtonian, with viscosity marginally higher than the viscosity of water. The rheological models based on DLVO theory do not allow prediction of the effect of pH on viscosity and yield stress, but the flow curves of goethite suspensions can be described by a fractal model with five adjustable parameters.

Dynamics of shear-thinning suspensions of core–shell structured latex particles

The rheological behavior and microstructure of shear-thinning suspensions of core–shell structured carboxylated latex particles were examined. The steady shear viscosity of the suspension increased with increasing dissociation of the carboxyl groups or increasing particle concentration, however the critical shear stress σ c and inter-particle distance ξ of the microstructure did not change. With increasing particle diameter, σ c increased and ξ decreased. These results were consistent with a Brownian hard sphere model, in which competition exists between the bulk mass transfer due to the applied field and diffusion of the particles. We confirmed that σ c depends on ξ, as expressed by σ c = 3 k T / 4 π ξ 3 . This relationship is consistent with the dynamics of a Brownian hard sphere model with particle diameter ξ. Thus the dynamics of shear-thinning suspensions of core–shell particles can be explained by a Brownian thermodynamic model.

Geometrical Aspects During Formation of Compact Aggregates of Red Blood Cells

In the past forty years considerable progress has been achieved on the knowledge of human blood as a non-Newtonian shear-thinning suspension, whose initial state, that is at rest (stasis) or at very low shear rates, has a gel-like internal structure which is destroyed as shear stress increases. The main goal of this communication is to describe the role of geometrical aspects during RBC (red blood cell) aggregate formation, growth and compaction on naturally aggregate (porcine blood) and non-aggregate (bovine blood) samples. We consider how these aspects coupled with tension equilibrium are decisive to transform red cell linear roleaux to three-dimensional aggregates or clusters. Geometrical aspects are also crucial on the compaction of red blood cell aggregates. These densely packed aggregates could precipitate out of blood- either as dangerous deposits on arterial walls, or as clots which travel in suspension until they block some crucial capillary.