Thixotropic Effects Research Articles

The Effect of Thixotropy on Pressure Losses in a Pipe

Drilling fluids are designed to be shear-thinning for limiting pressure losses when subjected to high bulk velocities and yet be sufficiently viscous to transport solid material under low bulk velocity conditions. They also form a gel when left at rest, to keep weighting materials and drill-cuttings in suspension. Because of this design, they also have a thixotropic behavior. As the shear history influences the shear properties of thixotropic fluids, the pressure losses experienced in a tube, after a change in diameter, are influenced over a much longer distance than just what would be expected from solely entrance effects. In this paper, we consider several rheological behaviors that are relevant for characterizing drilling fluids: Collins–Graves, Herschel–Bulkley, Robertson–Stiff, Heinz–Casson, Carreau and Quemada. We develop a generic solution for modelling the viscous pressure gradient in a circular pipe under the influence of thixotropic effects and we apply this model to configurations with change in diameters. It is found that the choice of a rheological behavior should be guided by the actual response of the fluid, especially in a turbulent flow regime, and not chosen a priori. Furthermore, thixotropy may influence pressure gradients over long distances when there are changes of diameter in a hydraulic circuit. This fact is important to consider when designing pipe rheometers.

Investigation of Roll-to-Roll Gravure Printing for Printed Electronics with Fine Features

Gravure printing is known to be cost competitive in manufacturing of printed electronic devices due to its capability to mass produce at lower costs. Current standard of gravure printed feature sizes is in a range of around 50 μm down to sub-10 μm, predominantly through small scale setups and specialized engraving. However, reliance on gravure cell design limits the scalability of printing over a large area due to the setup cost. In this study, ink viscoelastic behavior was modified to improve replication of gravure printed features over a large printing area of 300 mm web-width without a reduction in gravure cell dimension. Fine lines were printed using a high viscosity ink with a good replication of the nominal line width. Control over the printed features was performed through the variation of printing speed and the alteration of ink viscosity. The effects of ink viscosity and printing speed on the printed ink particle distribution and size were also examined. New methodologies of characterizing ink transfer were also developed to help understand the ink transfer processes: mass transfer and particle transfer. A deeper understanding of the thixotropic effect and shear recovery behavior of inks was achieved through simulations of shearing conditions.

Thixotropy effects on drilling hydraulics

Thixotropy is the reversible breakdown of fluid microstructure when sheared. The microstructure achieves a new steady-state once shearing stops. Drilling fluids are thixotropic due to their rheological makeup which means that fluid microstructure has a time-dependent response to changes in applied shear rate. In contrast to the literature focusing on the time-independent nature of drilling fluid, few studies have focused on the time-dependent response and even fewer have considered cuttings transport while doing so. The purpose of this study is to investigate the fundamental relationship between thixotropy and drilling hydraulics. An algorithm is developed to model thixotropy using flow history. The results show that the addition of drill cuttings does not directly affect the thixotropic behavior, rather the steady-state response is impacted which consequently changes the thixotropic response. Since the fluid microstructure takes time to respond to shear rate variations, viscosity lags behind shear rate variations causing annular pressure loss to fluctuate. The magnitude of pressure fluctuations is inversely proportional to characteristic time and directly proportional to stretching exponent. At smaller characteristic time coupled with smaller stretching exponent, high yield stress deteriorates cuttings transport. For larger values of characteristic time and stretching exponent, a clear trend is not observed, and further investigation is recommended. Nevertheless, when the thixotropic behavior of drilling fluid is considered, the results show that high flow rates and yield stresses do not guarantee efficient hole cleaning. Out of the two industrial fluid samples discussed, WBM yields higher pressure fluctuations and better cuttings transport compared to OBM. Since the proposed algorithm does not differentiate between the types of drilling fluids, this is due to WBM's smaller characteristic time and larger stretching exponent. It is suggested that a fluid exhibiting a slower response to shear rate changes causes higher pressure fluctuations and better cuttings transport.

The influence of thixotropy on the magnetorheological property of oil-based ferrofluid

A Fe3O4 hydrocarbon oil-based ferrofluid was synthesized and its magnetorheological behavior was investigated. The ferrofluid exhibits shear thinning behavior under different magnetic fields and a significant hysteresis effect was observed from the viscosity-shear rate flow curves due to the thixotropy of ferrofluid. The thixotropic behavior is induced by the presence and evolution of the microstructures in the ferrofluid. Moreover, the experimental results demonstrate that the viscosity of the ferrofluid decreases with increasing magnetic field when the magnetic field is below 81 mT. This is followed by an abrupt increase in the viscosity when the magnetic field increases to 124 mT. However, the viscosity again decreases as the magnetic field continue to increase beyond 124 mT. We reveal the negative correlations between viscosity and magnetic fields. The unusual magnetorheological behavior of the ferrofluid is due to the joint effect of thixotropy and magnetic fields. These findings provide a new perspective on the rheological behaviors of ferrofluids that takes the thixotropic effect into consideration.

Advanced Constitutive Modeling of the Thixotropic Elasto-Visco-Plastic Behavior of Blood: Description of the Model and Rheological Predictions.

This work focuses on the advanced modeling of the thixotropic nature of blood, coupled with an elasto-visco-plastic formulation by invoking a consistent and validated model for TEVP materials. The proposed model has been verified for the adequate description of the rheological behavior of suspensions, introducing a scalar variable that describes dynamically the level of internal microstructure of rouleaux at any instance, capturing accurately the aggregation and disaggregation mechanisms of the RBCs. Also, a non-linear fitting is adopted for the definition of the model’s parameters on limited available experimental data of steady and transient rheometric flows of blood samples. We present the predictability of the new model in various steady and transient rheometric flows, including startup shear, rectangular shear steps, shear cessation, triangular shear steps and LAOS tests. Our model provides predictions for the elasto-thixotropic mechanism in startup shear flows, demonstrating a non-monotonic relationship of the thixotropic index on the shear-rate. The intermittent shear step test reveals the dynamics of the structural reconstruction, which in turn is associated with the aggregation process. Moreover, our model offers robust predictions for less examined tests such as uniaxial elongation, in which normal stress was found to have considerable contribution. Apart from the integrated modeling of blood rheological complexity, our implementation is adequate for multi-dimensional simulations due to its tensorial formalism accomplished with a single time scale for the thixotropic effects, resulting in a low computational cost compared to other TEVP models.

Pasting, viscoelastic and rheological characterization of gluten free (cereals, legume and underutilized) flours with reference to wheat flour.

In this study, the rheological properties of dough prepared from gluten free flours (rice, sorghum, moong, water chestnut and unripe banana) and wheat dough were determined. Pasting properties and viscoelastic properties were analyzed using rheometer and dough rheology experiment was performed on texture analyzer. Water chestnut flour exhibited highest peak viscocity (22.6Pas), trough viscosity (12.1), breakdown viscosity (10.5Pas) and final viscosity (14.92Pas) than others while unripe banana flour showed highest setback viscosity (4.54Pas). Pasting temperature was found to be highest for sorghum followed by wheat and others. The highest elastic (G') and loss (G″) module were obtained for moong flour. Wheat and gluten free flours were found to exhibit thixotropic effect. Moong flour dough was found to be the stickiest (dough stickiness 57.83g) followed by WCF, UBF, wheat, rice and sorghum. Similar trend was observed for dough strength. These flours can be proved as key materials for the gluten-free products market and can provide additional inexpensive advantage to the food processing industry.

The non-homogeneous flow of a thixotropic fluid around a sphere

The non-homogeneous flow of a thixotropic fluid around a settling sphere is simulated. A four-parameter Moore model is used for a generic thixotropic fluid and discontinuous Galerkin method is employed to solve the structure-kinetics equation coupled with the conservation equations of mass and momentum. Depending on the normalized falling velocity U*, which compares the time scale of structure formation and destruction, flow solutions are divided into three different regimes, which are attributed to an interplay of three competing factors: Brownian structure recovery, shear-induced structure breakdown, and the convection of microstructures. At small U*( ≪ 1), where the Brownian structure recovery is predominant, the thixotropic effect is negligible and flow solutions are not too dissimilar to that of a Newtonian fluid. As U* increases, a remarkable structural gradient is observed and the structure profile around the settling sphere is determined by the balance of all three competing factors. For large enough U*( ≫ 1), where the Brownian structure recovery becomes negligible, the balance between shear-induced structure breakdown and the convection plays a decisive role in determining flow profile. To quantify the interplay of three factors, the drag coefficient Cs of the sphere is investigated for ranges of U*. With this framework, the effect of the destruction parameter, the confinement ratio, and a possible nonlinearity in the model-form on the non-homogeneous flow of a thixotropy fluid have been addressed.

Unique rheological behavior of detonation nanodiamond hydrosols: The nature of sol-gel transition

The paper describes the data on unusual rheological properties of detonation nanodiamonds (DND) hydrosols and presents the fractal model explaining such behavior. The hydrosols of DND with particles size of 4–5 nm and concentration range of 1.1–7.3 wt% with negative (ζ < 0) and positive (ζ > 0) electrokinetic potentials have been studied by rotational viscometry, small-angle X-ray scattering, nuclear magnetic resonance and Cryo Electron Tomography. Remarkable hysteresis of viscosity and thixotropic effect demonstrate the sol-gel transition at very low concentrations of the DND: 4–5 wt% for ζ > 0 and 5–6 wt% for ζ < 0. The transition is accompanied by increase of loss (viscosity) modulus by two orders of magnitude and the storage (elasticity) modulus started to be detected also. The experimental results have been explained in the frame of percolation theory based on the network formation due to faceted DND particles interactions.

Improvement of Strength Parameters of Foam Ceramics for Energy-Efficient Enclosing Structures

Studies of the influence of vibration impact on the strength of foam-ceramic raw material, produced on the basis of chemically modified natural silicites, are presented. The natural oscillation frequencies of mineral particles are established, taking into account their size, density and ultimate shear stress of raw suspensions. It is shown that the coincidence of the natural and forced oscillations of the particles leads to an increase in the thixotropic effect. Using the technology of a controlled «sol-gel» transition in the structure of raw material, swelling under the influence of vibration load, samples of the material were obtained with a higher-quality macrostructure without the use of binders. Indicators of compressive strength and average density of raw and ceramics are given.

Insights in thixotropic concrete pumping by a Poiseuille flow extension

AbstractThixotropy is a reversible time-dependent phenomenon in fluids, in which an internal structure grows due to flocculation and breaks down under shear action. Numerous fluids are thixotropic,e.g.concretes and cementitious suspensions. Pumping of concrete is an important application. Since current approaches omit thixotropic effects, we aim to develop a simple theoretical model to evaluate or understand the significance of thixotropy on the concrete pumping behaviour. We therefore extended Poiseuille flow for thixotropic concretes and reformulated it in a dimensionless form to gain insights. After a validation, the results and significance are elaborated and concluded.Results showed that for increasing thixotropy and decreasing flow rates, the plug radius, wall shear rate and pumping pressure loss increase. Even though all thixotropy mechanisms may not be covered, a simple model is delivered to interpret or predict the effect of thixotropy on the pumping behaviour of cementitious suspensions. The dimensionless formulations via the Bingham numberBnand related discharge diagrams are sufficiently elegant for computational implementation and very insightful to distinguish a thixotropic flow regime. The model could be extended for more complicated thixotropies, irreversible time-dependent effects or even other pumping related phenomena.

Determination of the Sensitivity and Thixotropic Effects of Clay Soil for Selected Sites in Diwaniya City - Iraq

This paper is conducted to determine the sensitivity and thixotropic effects of clay soil for selected sites in Diwaniya city which are: (Dawr Aldubbat, Al-Zawra square, 14 Ramadan square, Al'iiskan Alaqadim and Military square). The main aim of this investigation is to study the sensitivity and thixotropy of clay soil, and determination and classification of soils to (Insensitive), (slightly to very sensitive) and (slightly to extra quick)) relying on special test methods in sensitivity and thixotropic phenomena. The experimental tests that were done including geotechnical, chemical and mineralogical tests to natural soils and special tests were for the identification and classification of sensitivity of soils. The results of sensitivity of soils test displayed low to medium for all the types of the soils in the study area. The results of the thixotropic strength ratio test showed a small increase in thixotropic strength ratio values with time. The results of Atterberg limits test indicated that increasing the proportion of the clay causes an increase in the plasticity index of the soil. While the results of the liquidity index varied from 0.24 to 0.70, which reflects the low sensitivity of the clay soil in the study area.

A Novel Preparation Process for Magnetorheological Fluid with High Working Temperature

We report the preparation of a magnetorheological fluid with a high working temperature by using fluorocarbon surfactant and titanate coupling agent as additives at appropriate contents determined by a series of experiments. The sedimentation ratio, apparent viscosity, and yield stress are measured to evaluate the performance of the prepared magnetorheological fluid. Results indicate that AES dispersants, titanate coupling agents, and fluorocarbon surfactants all have improved dispersion properties, and that the compounding fluorocarbon surfactants and titanate coupling agent can further improve the settlement stability of magnetorheological fluid, with 7 % one-week settlement rate. Diatomite has a good thixotropic effect, and the antisettling effect enhanced with increased content. The types of carrier fluid have no significant effect on the performance of MR fluids. The prepared MR fluid can also work at 180 °C, which is higher than most commercial fluids, and the shear yield stress can reach 50 kPa.

Multiscale Nature of Thixotropy and Rheological Hysteresis in Attractive Colloidal Suspensions under Shear.

Colloids with short range attractions self-assemble into sample-spanning structures, whose dynamic nature results in a thermokinematic memory of the deformation history, also referred to as "thixotropy." Here, we study the origins of the thixotropic effect in these time- and rate-dependent materials by investigating hysteresis across different length scales: from particle-level local measurements of coordination number (microscale), to the appearance of density and velocity fluctuations (mesoscale), and up to the shear stress response to an imposed deformation (macroscale). The characteristic time constants at each scale become progressively shorter, and hysteretic effects become more significant as we increase the strength of the interparticle attraction. There are also strong correlations between the thixotropic effects we observe at each scale.

Investigation of Rheological Behaviour of Liquid and Semi-solid Magnesium Alloys of Mg–Zn–Al, Mg–Zn–RE Groups

In this study, in order to obtain more comprehensive characteristics of the magnesium alloys, rheological measurements were performed for the liquid and semi-solid state, taking into account the effect of thixotropy of the magnesium alloys tested. The hysteresis loop plotted shows the thixotropy of two examined alloys.

Normal and oblique drop impact of yield stress fluids with thixotropic effects

Normal and oblique drop impact on a solid surface is numerically analysed for yield stress fluids. A rich diversity of results are generated as a consequence of the exploration of the inertial, elastic, plastic and thixotropic features of the process, as well as the inclination of the solid surface. We show that drops of more thixotropic fluids have a higher tendency to bounce in the normal impact, and to roll or to bounce in the case of an oblique drop impact. Concerning elasticity, we found a critical value for the elastic Ohnesorge number above which no bouncing takes place. Experimental findings such as the fact that the stored energy due to the elasticity of the fluid drop plays a role similar to the stored energy of an interfacial nature in inelastic fluid drops are corroborated in the present study.

The influence of osteopathic correction on the viscoelastic characteristics of the lower leg muscles

Introduction.To date there is a lack of studies dedicated to the objectification of the palpation data obtained by a specialist during the osteopathic examination. The issue of the evidence of the results of osteopathic correction still remains important. Search for instrumental methods allowing to register and to measure various palpation phenomena and manifestations of somatic dysfunctions is very relevant for the development of osteopathy as a science. It is also very important to find objective characteristics of these methods.Goal of research— to study viscoelastic characteristics of the soft tissues of the lower legs by palpation and instrumental methods before and after osteopathic correction.Materials and methods.22 volunteers (12 women and 10 men) aged 18–23 years without complaints of the musculoskeletal system were examined. Osteopathic diagnostics and measurement of the viscoelastic properties of muscles were carried out by the method of vibration viscoelastometry before and after osteopathic correction.Results.Correlation analysis by Spearman showed that the subjective assessment of an osteopath positively correlated with both elasticity (r=0,43, p&lt;0,05) and viscosity of soft issues (r=0,29, p&lt;0,05). For the gastrocnemius muscle, this pattern was even more pronounced — for elasticity r=0,51, p&lt;0,05, for viscosity =0,34, p&lt;0,05. After osteopathic correction no changes in the elasticity of the soft tissues were observed. The viscosity of the tissues reduced, but in the projection of the gastrocnemius muscle, these changes were not statistically significant (p=0,12), whereas in the projection of the soleus muscle statistically significant changes (p=0,034) were observed.Conclusion.Changes in the viscoelastic properties of tissues demonstrated that the effects of osteopathic correction with the use of myofascial mobilization techniques, articulation mobilization techniques, and lymphatic drainage techniques were not obvious. The elasticity of soft tissues of the lower legs did not change, while the viscosity decreased, especially in the projection of the soleus muscles. This effect of the osteopathic correction can be associated with the effect of thixotropy — the transformation of gel-like intercellular substance into sol. Thus, the research showed that vibration viscoelastometry can be used for the objectifi cation of the condition of soft tissues and of the effects of osteopathic correction.

Thixotropic yielding behaviors of ferrofluids

The thixotropic yield behaviors of ferrofluids with different particle volume concentrations were studied through a series tests under constant stresses for sufficiently long times. A lubrication oil based ferrofluid was prepared and a diluted sample was acquired by mixing the initial ferrofluid sample with carrier fluid according to a ratio of 1:3. The particle volume concentration of the samples was estimated through the magnetization curves as 7.8% and 1.9%. A critical bifurcation stress can be observed through the time evolution of the initial ferrofluid sample under moderate magnetic fields, over which the viscosity curves tend to infinity. For the diluted ferrofluid sample, no viscosity bifurcation can be observed even under the minimum stress values. Similar viscosity bifurcation phenomenon for initial samples can be seen from the curves under different magnetic field strengths or temperatures. The experimental results indicate that the yield process of ferrofluids is thixotropic and significantly influenced by the shear history. The microscopic mechanism behind the thixotropic yield behaviors of ferrofluids is discussed and analyzed. A non-linear structural model was presented to describe the time evolution of viscosity in ferrofluids under different magnetic field strength. The comparison between the fitting results and experimental data indicates that the thixotropic yielding behaviors of ferrofluids can be predicted in some extent. These findings provide a new perspective on the yielding behaviors of ferrofluids which takes the thixotropic effect into consideration.

Thixotropic Hardening of Fao Clay

Fao region is characterized by weak soft silty clay to clayey silt thick layer which extends to a depth of about 20 m. The construction of some structures on such soils may needs piles. During the installation of driven piles, the soil geotechnical properties are exposed to significant changes result due to shearing under large shear strains. These changes significantly decrease the shear strength of the virgin soil due to the destruction of soil structure caused by remolding. The degradation of shear strength is usually followed by strength regaining which is called “Thixotropy”. In this study, the thixotropic effect on Fao clay was investigated. Many disturbed and undisturbed soil samples were brought from Fao region. Some of the soil samples were thoroughly remolded in the laboratory in its natural water content and molded as direct shear specimens. More than 180 specimens were prepared and tested over 36 weeks in order to accurately assess the percentage of strength regaining with time passing. The results show that soil remolding causes about a 45 % reduction in shear strength in comparing with the shear strength of the intact soil. This reduced percent in shear strength was almost fully regained after 25 weeks due to thixotropic effect.&#x0D;

On the thixotropic effect of turbulence

As a follow-up research of the work on the natural viscosity of turbulence of Huang et al. [Journal of Turbulence (2003)], here we investigate the thixotropic effect of a turbulent Newtonian fluid on the basis of the ensemble-averaged Navier–Stokes equation. In view of the natural viscosity, we show that in homogeneous isotropic turbulence the turbulent Newtonian fluid behaves like a thixotropic fluid, exhibiting the thixotropic effect with its natural viscosity decreasing with time.

Stability of oil well olefin drilling fluids: solid–liquid sedimentation and rheological characterization

Oil wells drilling processes are a crucial step in petroleum exploration and drilling fluids are an important player in this operation. Both solid–liquid sedimentation stability and appropriate rheological characteristics are significant and desirable aspects for drilling fluid. In this context, this study aimed at analyzing the stability of olefin drilling fluids, differentiated by calcium carbonate additive, related to solid–fluid interaction sedimentation and rheological behavior. Rheology, gravitational, and batch sedimentation experimental tests were performed as both time and function position. A low viscosity viscometer was used for the rheological characterization, and gamma-ray attenuation, a nondestructive technique, was applied to quantify the local volumetric solids concentration in sedimentary regions. The results showed a shear-thinning behavior and thixotropic effects in these fluids and the influence of calcium carbonate in the sedimentation profile. The thickened suspension showed higher values of apparent viscosity and lower sedimentation rates than the non-thickened system. Thus, the formulation of drilling fluids affected the solid–liquid separation process and the rheological behavior of suspensions; and, for that sense, it should be appropriated for drilling exploration.