Showing papers in "Applied Rheology in 2008"
TL;DR: In this article, it was shown that the critical shear rate and shear stress increase with the solid content and depend on the fractal dimension of flocs which implies that thixotropic effects are all the more important as the sludge is thick.
Abstract: Abstract Sewage sludge presents a dual rheological behaviour with an abrupt change between the two regimes. Using a new technique of reconstruction of the velocity profile, the behaviour can be modelled by a unique equation including liquid and solid components but also a structural parameter. It is also rigorously demonstrated that the only one rheological behaviour in steady state in the liquid regime is a truncated power-law which can be defined only for a shear rate and a shear stress higher than a critical value, γ̇c and τc. Moreover, the critical shear rate and shear stress increase with the solid content and depend on the fractal dimension of flocs which implies that thixotropic effects are all the more important as the sludge is thick and fresh.
61 citations
TL;DR: In this article, a new procedure is described to convert the vane torque and rotational velocity data into shear stress vs shear rate relationships, based on considering locally the sheared material as a Bingham fluid and computing a characteristic shear rates from Couette analogy.
Abstract: A new procedure is described to convert the vane torque and rotational velocity data into shear stress vs shear rate relationships. The basis of the procedure consists in considering locally the sheared material as a Bingham fluid and computing a characteristic shear rate from Couette analogy. The approach is first applied to experimental vane data of Newtonian fluid, then used to process vane experimental data of non-Newtonian and yield stress materials. Results, which are favourably compared with torsional flow, show that the approach correctly predicts the rheological behaviour of the materials investigated.
39 citations
TL;DR: In this article, the influence of VMA on the rheological properties of the material at cement scale level is investigated, in particular, the change in the thixotropic properties due to the inclu- sion of VMAs is investigated.
Abstract: © Appl. Rheol. 18 (2008) 45604-1 - 45604-8 Abstract: Water soluble polymers such as cellulosic or starch ethers are often included in the mix-design of Self Com- pacting Concretes (SCCs) in order to improve their stability and robustness. The stability, including resistance to liquid-solid separation and sedimentation, may be attributed to the increase of the viscosity of the liquid phase due to the thickening effect of the polymer. The later is then referred to as a Viscosity-Modifying Admixture (VMA). In the present study, we consider the influence of VMAs on the rheological properties of the material at cement scale level. In particular, the change in the thixotropic properties of the cement paste due to the inclu- sion of VMA is investigated. It is found that addition of VMA significantly enhances rebuild-up kinetics at rest following shearing at high shear rate. The influence of VMA on the steady state rheological properties is also considered. As reported in the literature, the yield stress is found to monotonically increase with VMA content, while the consistency presents a minimum indicating the existence of an optimum value of the VMA for which the workability of the cement paste is maximum. Zusammenfassung: Wasserlosliche Polymere wie Zellulose- oder Starkeether werden haufig in die Herstellung von Mischungen mit selbstverfestigendem Beton miteinbezogen, um deren Stabilitat und Robustheit zu verbessern. Die Stabilitat, einschlieslich des Widerstandes zur Flussigphasen-Feststoffphasentrennung und zur Sedimentation, kann der Viskositatserhohung der flussigen Phase aufgrund des Verhartungseffektes des Polymers zugeschrieben wer- den. Dieser Zusatz fur den Verhartungseffekt wird als viskositatsmodifizierende Beimischung (VMA) bezeich- net. In dieser Arbeit wird der Einfluss von VMAs auf die rheologischen Eigenschaften des Materials im Zement- zustand betrachtet. Insbesondere wird die Anderung der thixotropen Eigenschaften des Zements aufgrund der VMA-Inklusionen untersucht. Die Zugabe von VMA erhoht wesentlich die Wiederherstellungskinetik im Ruhe- zustand nach einer Scherung mit einer hohen Schergeschwindigkeit. Der Einfluss von VMA auf die stationaren Eigenschaften wird ebenfalls untersucht. Im Einklang mit Literaturangaben nimmt die Fliesspannung mono- ton mit dem VMA-Inhalt zu. Die Konsistenz nimmt dabei ein Minimum an, was die Existenz eines optimalen VMA-Wertes fur die optimale Verwendung der Zementpaste andeutet. Resume:
31 citations
TL;DR: In this paper, a methodology is presented to invert the flow equation of a Herschel-Bulkley fluid in Couette concentric cylinder geometry, thus enabling simultaneous computation of the true shear rates, γ̇HB, and of the three Herschel Bulkley rheological parameters.
Abstract: Abstract A methodology is presented to invert the flow equation of a Herschel-Bulkley fluid in Couette concentric cylinder geometry, thus enabling simultaneous computation of the true shear rates, γ̇HB, and of the three Herschel-Bulkley rheological parameters. The errors made when these rheological parameters are computed using Newtonian shear rates, γ̇N, as it is normal practice by research and industry personnel, can then be estimated. Quantification of these errors has been performed using narrow gap viscometer data from literature, with most of them taken with oil-field rheometers. The results indicate that significant differences exist between the yield stress and the flow behavior index computed using γ̇HB versus the parameters obtained using γ̇N and this is an outcome of the higher γ̇HB values. Predicted true shear rates and rheological parameters are in very good agreement with results reported by other investigators, who have followed different approaches to invert the flow equation, both for yield-pseudoplastic and power-law fluids.
28 citations
TL;DR: In this article, an extended version of the Poiseuille formula for shear-thickening materials with a yields stress, described by the modified Bingham equation, is applied to flow-tests with self-compacting concrete.
Abstract: In practice, while placing concrete in a formwork by pumping, the pressure generated by the pump is not controlled. In order to enhance the safety on the worksite, and in view of the current economic and ecologic arguments., it would be useful to dispose of an equation able to predict pressure losses based on the rheological properties of the concrete and the pipe configuration. This paper describes the derivation of an extended version of the Poiseuille formula, for shear-thickening materials with a yields stress, described by the modified Bingham equation. This formula is applied to flow-tests with self-compacting concrete. The results prove the applicability of this extended Poiseuille formula, showing that the flow is occurring in laminar regime, with no significant wall slip.
25 citations
TL;DR: In this article, the rheologies of a shear-frozen commercial ice cream and of a model ice cream foam have been studied at -5 degrees C and other temperatures by capillary rheometry on a commercial manufacturing line and in a multi-pass Rheometer, respectively.
Abstract: The rheologies of a shear-frozen commercial ice cream and of a model ice cream foam have been studied at -5 degrees C and other temperatures by capillary rheometry on a commercial manufacturing line and in a Multi-Pass Rheometer, respectively. Both were 50 vol% aerated emulsions of milk fat in an aqueous sucrose solution, but the model ice cream foam was without ice crystals. The data indicate significant wall slip effects which have been analysed using the classical Mooney method, the Jastrzebski variant and one based on Tikhonov regularization. The latter approach yields 'most convincing results', including a previously unreported region of shear thickening at very high shear rates of similar to 3000 s(-1) for the model ice cream foam, when the capillary number indicates a possible transition in the flow around bubbles from domination by interfacial effects to viscous effects. Viscous heating effects were observed at relatively low shear rates for the commercial ice cream, but not the model ice cream foam. This was attributed to the melting of the ice crystal phase in the commercial ice cream, and, hence, absent from the model ice cream foam.
24 citations
TL;DR: In this article, the yield stresses of five samples (two highly concentrated emulsions, two Kaolin dispersions and mayonnaise) were determined in two ways: steady shear experiments were performed over a range of incrementally decreasing shear rates.
Abstract: Abstract The yield stresses of five samples (two highly concentrated emulsions, two Kaolin dispersions and mayonnaise) were determined in two ways. In one case, steady shear experiments were performed over a range of incrementally decreasing shear rates. The resulting flow curves, plotted as shear stress against shear rate, clearly showed the existence of a yield stress for each sample, the Herschel-Bulkley model being fitted to obtain values. In the second case, oscillatory amplitude sweeps were performed at three frequencies, and the “dynamic yield stress” was defined as the stress at which deviation from linearity occurred; this procedure has often been used to determine the yield stress of emulsions. It was found that the dynamic yield stress is frequency dependent, and cannot therefore be thought of as physically meaningful material property. At no frequency did the dynamic yield stress correlate with the yield stress obtained from the flow curves.
23 citations
TL;DR: In this article, an Ultrasonic Velocity Profiling technique (UVP) in combination with a pressure difference (PD) measurement was tested to provide in-line measurement of rheological parameters.
Abstract: The rheological behaviour of non-Newtonian, highly concentrated and non-transparent fluids used in industry have so far been analysed using commercially available instruments, such as conventional rotational rheometers and tube viscometers. When dealing with the prediction of non-Newtonian flows in pipes, pipe fittings and open channels, most of the models used are empirical in nature. The fact that the fluids or slurries that are used normally are opaque, effectively narrows down the variety of applicable in-line rheometers even further, as these instruments are normally based on laser or visible light techniques, such as Laser Doppler Anemometry. In this research, an Ultrasonic Velocity Profiling technique (UVP), in combination with a pressure difference (PD) measurement, was tested to provide in-line measurement of rheological parameters. The main objective of this research was to evaluate the capabilities of the UVP-PD technique for rheological characterisation of different concentrations of non-transparent non-Newtonian slurries. Kaolin, bentonite, Carboxymethyl Cellulose (CMC) and water solutions were used as model non-Newtonian mining slurries. Results determined by the UVP-PD method were compared with results obtained by off-line rheometry and in-line tube viscometry. The agreement between the UVP-PD method, tube viscometry and conventional rheometry was found to be within 15 % for all of the highly concentrated mineral suspensions investigated over a given range of shear rates. This method, if used in combination with a pressure difference technique (PD), has been found to have a significant potential in the development process of new in-line rheometers for process control within the mining industry.
22 citations
TL;DR: In this paper, the authors give an overview of the temperature dependent behavior of the ER effect for these fluids and describe the basic principles how this is explained, and provide information as a basis for a polarization model in several dimensions.
Abstract: Abstract Electrorheological fluids (ERF) change viscosity when an electric field is applied. A special type of ERF consists of polyurethane particles which are doped with Li+ and /or Zn2+ cations and suspended in silicone oil. This article gives an overview of the temperature dependent behavior of the ER effect for these fluids and describes the basic principles how this is explained. Chemical analyses provide information as a basis for a polarization model in several dimensions down to molecular size.
18 citations
TL;DR: In this paper, the apparent flow curve measured from inclined plane flows coincides with the apparent rheogram from classical rheometer tests and the flow curve obtained from local Couette flow measurements with magnetic resonance imaging (MRI).
Abstract: Abstract We show that the rheological characteristics of a fresh cement paste can be determined from inclined plane tests. The apparent flow curve measured from inclined plane flows coincides with the apparent rheogram from classical rheometer tests and the flow curve obtained from local Couette flow measurements with magnetic resonance imaging (MRI). In order to describe the thixotropic properties of these fluids we suggest to use a simple model, the four parameters of which may be determined from specific, practical, inclined plane experiments.
15 citations
TL;DR: In this article, two approaches for determining the entrance pressure drop in capillary rheometry were compared with low-density polyethylene and polystyrene melts as test fluids.
Abstract: Abstract Two approaches for determining the entrance pressure drop in capillary rheometry were compared with low-density polyethylene and polystyrene melts as test fluids. Direct measurements with the orifice die were found to yield higher values for the entrance pressure drop, and hence lower values for the wall shear stress, than the Bagley correction method. This was postulated to be caused by the sticking of the melt to the wall of the outlet region of the orifice die. The additional pressure drop created in the outlet region of the orifice die, when the flowing material fills it completely, was also evaluated by means of numerical flow simulation.
TL;DR: In this paper, a first order kinetic equation to describe structural changes in asphalt has been incorporated with the non-linear rheological model of White- Metzner, and the resulting set of governing equations was solved numerically to describe the rheology of asphalt.
Abstract: Abstract Rheological behavior of asphalt is strongly affected by loading conditions, temperature and environment. One of the main challenges in understanding the rheology of asphalt is to relate the chemical constituents and the micro-structure of asphalt on one hand to its rheological behavior on the other hand. In this work, nonlinear rheological behaviour of asphalt was investigated using a structural rheological model. A first order kinetic equation to describe structural changes in asphalt has been incorporated with the nonlinear rheological model of White- Metzner. The resulting set of governing equations was solved numerically to describe the rheology of asphalts. Different modes of rheological testing and asphalts with different compositions were considered. An analysis and comparison of model behaviour with experimental data from the literature is carried out in both stress growth at constant shear rate and oscillatory shear modes. A strategy is proposed for the estimation and tuning of the model parameters based on available experimental data and literature. Qualitatively, the model can capture the rheological behaviour of non-Newtonian fluids such as asphalt under different modes of rheological testing. Quantitative analysis from this work shows that the model describes the rheological behaviour of asphalt for the temperature range of 20 – 60ºC. It is demonstrated that a single set of equations tuned with the steady shear experimental data can be used to predict the nonlinear rheological behaviour of asphalts. In addition, it is shown that the model parameters can be related to the chemical composition of asphalts.
TL;DR: In this paper, the influence on the particle transport of the non-Newtonian and Newtonian properties of the blood as well as the influence of the heart rate was studied and a analytical model was developed and the calculation of particle trajectories was presented and evaluated.
Abstract: Abstract Investigations on the behaviour of superparamagnetic nanoparticles under the influence of a high gradient magnetic field in the vascular system is required for a better under-standing of magnetic drug targeting. The influence on the particle transport of the non-Newtonian and Newtonian properties of blood as well as the influence of the heart rate was therefore studied. A analytical model was developed and the calculation of particle trajectories is presented and evaluated. The results show that the non-Newtonian properties of the blood have a positive influence on the number of retended nanoparticles. The calculations also showed that the number of retained nanoparticles was lower in oscillatory flow profile than in steady flow. The influence of the heart rate can be neglected for Womersley numbers smaller than 1.5.
TL;DR: The reason for this can only be understood in the context of historic development as discussed by the authors, where technical fibre flows are normally flocky, but have theoretically mainly been treated as individual fibre flows.
Abstract: Technical fibre flows are normally flocky, but have theoretically mainly been treated as individual fibre flows. The reason for this can only be understood in the context of historic development. I ...
TL;DR: In this paper, the origin of technical fiber flow research was traced to the beginning of the 19th century, and was followed through its formative years at the first half of the 20th century up to about WWII.
Abstract: Technical fibre flows are normally flocky but have theoretically mainly been treated as individual fibre flows. The reason for this can only be understood through the subject's historic development. In Part 1 of this investigation the origin of fibre flow research was traced to the beginning of the 19th century, and was followed through its formative years at the first half of the 20th century up to about WWII. This second and final part takes us up to about the 1960s when the present main theoretical research tradition had been firmly established. An example of an alternative approach is given. Finally, some suggestions for future work are advanced. In Appendix methods of characterising the inner geometry of technical fibre suspensions are discussed.
TL;DR: In this article, a novel thixotropic model is defined that incorporates s aging, and conditions under which viscosity changes due to thixotropy and aging are unambiguously defined.
Abstract: Complex fluids exhibit time-dependent changes in viscosity that have been ascribed to both thixotropy and aging. However, there is no consensu s for which phenomenon is the origin of which changes. A novel thixotropic model is defined that incorporate s aging. Conditions under which viscosity changes a re due to thixotropy and aging are unambiguously defined. Viscosity changes in a complex fluid during a period of rest after destructuring exhibit a bifurcation at a crit ical volume fraction φc2 . For volume fractions less than φc2 the viscosity remains finite in the limit t→∞ . For volume fractions above critical the viscosity grows without limit, so aging occurs at rest. At constant shear rate the re is no bifurcation, whereas under constant shear stress the model predicts a new bifurcation in the viscosity a t a critical stress σB , identical to the yield stress σy observed under steady conditions. The divergence of the visc osity for σ ≤ σB is best defined as aging. However, for σ > σB , where the viscosity remains finite, it seems pref erable to use the concepts of restructuring and des tructuring, rather than aging and rejuvenation. Nevertheless, w hen a stress σA ( ≤ σB) is applied during aging, slower aging is predicted and discussed as true rejuvenation. Plast ic behaviour is predicted under steady conditions w hen σ > σB. The Herschel-Bulkley model fits the flow curve for stresses close to σB, whereas the Bingham model gives a better fit for σ >> σB. Finally, the model's predictions are shown to be consistent with experimental data from the literature for the transient behaviour of lapon ite gels.
TL;DR: In this article, the design of the stress controlled rheometer with its main parameters has been described in detail, which enables direct measurements of even small yield stresses in ferrofluids as well as large effects like they are found in magnetorheological fluids.
Abstract: Abstract Investigations of rheological properties of ferrofluids have shown strong changes of the viscosity in magnetic fluids with an applied magnetic field. The change of the viscosity – the magnetoviscous effect – can theoretically be described with chain and structure formation under the influence of a magnetic field. Moreover, the formation of these structures leads to the appearance of viscoelastic effects or other non-Newtonian features like yield stress in ferrofluids with an applied magnetic field. With a shear rate controlled rheometer – as it as been used in former experiments – the yield stress could not be investigated directly. Therefore the results concerning a field dependent yield stress based on an extrapolation of shear controlled measurements. For the direct investigations of the yield stress, a dedicated stress controlled rheometer is required, allowing direct investigations of the magnitude and field dependence of this effect. In this work the design of the stress controlled rheometer with its main parameters has been described in detail. The rheological investigations with differently composed fluids show that the stress controlled rheometer enables direct measurements of even small yield stresses in ferrofluids as well as large effects like they are found in magnetorheological fluids (MRF).
TL;DR: In this paper, the authors present a Web of Science Record created on 2010-11-30, modified on 2016-08-09 and used for the publication of this paper.
Abstract: Reference EPFL-ARTICLE-159920doi:10.1016/j.jnnfm.2009.01.003View record in Web of Science Record created on 2010-11-30, modified on 2016-08-09
TL;DR: In this paper, the authors used dynamic mechanical functions under different deformational and temperature conditions, as a means for rheological characterization of nanocomposites, and showed that the nano-scale traits are clearly reflected in substantial stiffness at low strains and, unexpectedly, dwindling energy loss with increasig filler content and/or decreasing temperature.
Abstract: Abstract Rheological properties of elastomeric nanocomposites with organically modified Montmorillonite clays, as possible replacements or supplements to classical active fillers, such as carbon black or silica, have been intensively studied in recent years. Possessing large specific surface areas acquired through the melt-mixing processes of elastomeric intercalation and subsequent filler exfoliation, the clay particles have indeed proved to be highly eligible reinforcing and thermally stabilizing ingredients for application in elastomers. In fact, their performance has shown to be in many respects superior to that of classical fillers, particularly owing to some unusual, though beneficial, exhibited properties. Namely, apart from uncommonly high surface activity, manifested by creation of a host of van der Waals type secondary linkages with elastomer molecules, the main curiosity of clay filler is its dissipative action. Using dynamic mechanical functions under different deformational and temperature conditions, as means for rheological characterization of nanocomposites, the foregoing nano-scale traits are clearly reflected in substantial stiffness at low strains and, unexpectedly, dwindling energy loss with increasig filler content and/or decreasing temperature. Besides, rheological analysis of this kind, together with appropriate theoretical grounds, has enabled elucidation of peculiar conduct, as well as macroscopic insight into the very nature of secondary interactions in elastomers.
TL;DR: Novel Trends in Rheology II as discussed by the authors is the most recent edition of the series, which was organized at the Tomas Bata University in Zlín, Czech Republic with more than 200 pages.
Abstract: rina Chaloupkova and Martin Zatloukal who belong to Prof. Petr Saha research group at Tomas Bata University in Zlin; Prof. Ivan Machac from University of Pardubice – president of the Czech Society of Rheology; Prof. Frantisek Rieger from Czech Technical University in Prague; Jana Mikesova from Institute of Macromolecular Chemistry, Petr Filip and Radek Pivokonsky from Institute of Hydrodynamics) as well as industry (Jiri Vlcek, president of Compuplast International Inc., Czech Republic; Karen Xiao, Brampton Engineering, Canada; Johan De Witte, 3M Belgium N.V.-Dyneon, Belgium; Dietmar Boettner, TI Automotive, Germany; Biran Toure, Nexans Research Centre, France). We also would like to thank our sponsors (3M Belgium N.V.-Dyneon; Malvern Instruments; Compuplast International; Amedis) for the financial support. The conference has been hosted at the Tomas Bata University in Zlín, Zlín, Czech Republic and the conference proceedings have been published in a book entitled 'Novel Trends in Rheology II' with more than 200 pages, having the following ISBN: 978-80-7318-591-6. The next meeting of this series (Novel Trends in Rheology III) will be organized in summer 2009 and specific attention will be paid to applied rheology and polymer processing.
TL;DR: In this article, an evolution equation for the Cauchy stress tensor is proposed to take elastic, viscous and plastic characteristics of complex fluids simultaneously into account, in particular, hypoplasticity is incorporated to account for the plastic features.
Abstract: Abstract In the present study, an evolution equation for the Cauchy stress tensor is proposed to take elastic, viscous and plastic characteristics of complex fluids simultaneously into account. In particular, hypoplasticity is incorporated to account for the plastic features. The stress model is applied to investigate time-dependent flows of an elasto-visco-plastic fluid driven by an oscillating boundary with/without an additional stationary boundary to study the cyclic responses and the model performance. Numerical simulations show that while different degrees of elastic and viscous effects can be captured by varying the model parameters, plastic deformation plays a significant role in the velocity distribution, and can be simulated appropriately by use of hypoplasticity. The stress model is capable of accounting for the combined elastic, viscous and plastic features of complex materials in transient motions, and applications may be found in geomorphic fluid motions like granular and debris flows, and flows involving polymers.
TL;DR: In this article, small micellar casein particles were formed in aqueous solutions of native casein after addition of polyphosphate and aggregated and gelled with a rate that increased with increasing temperature.
Abstract: Abstract Small micellar casein particles were formed in aqueous solutions of native casein after addition of polyphosphate. These so-called submicelles aggregated and gelled with a rate that increased with increasing temperature. The evolution of the viscosity during this process was determined at constant shear rate or shear stress. When applying a small shear stress the viscosity increased strongly until the shear rate became immeasurably slow, but when the applied shear stress exceeded a critical value (σc) the aggregates broke up and the viscosity reached a maximum. At longer times the viscosity decreased rapidly at first, followed by a very slow decrease. σc was independent of the shear rate and heating temperature, but increased strongly with increasing casein concentration. At constant shear rate the stress remained close to σc, but fluctuated irregularly. After cessation of shear flow, gels were formed rapidly. Oscillation shear measurements for σ > σc showed a strongly non-linear response at the time of maximum viscosity.
TL;DR: In this article, the authors considered the motion generated by the collapse of a dam-retaining mud, itself modeled as a power-law fluid, and derived an equation of motion in a non-dimensional form and solved analytically with the shallow-water assumption in a dry and smooth horizontal channel.
Abstract: Abstract The main characteristics of geological flows such as debris flows, avalanches and lahars is due to the relative importance of viscous versus inertial forces in the momentum balance. This paper considers the motion generated by the collapse of a dam-retaining mud, itself modeled as a power-law fluid. The equation of motion is derived in a non-dimensional form and solved analytically with the shallow-water assumption in a dry and smooth horizontal channel. Notably indicated are flow regimes and the effect of the reservoir length as well as the effect of mud rheology on flow development. Then, a parametric study of this model is produced and the effect of mud shear-thinning on flow development is pointed out.
TL;DR: In this paper, the authors developed a fluid dynamic model that predicts the shear and pressure distributions in the compound during its processing in a metering nip based on process parameters and rheological results.
Abstract: Abstract This is a study of three-phase foam rheology to qualify penetration in to backing webs during frothed carpet compounds applications. Transient viscosity as a function of shear rate under a short time period is proposed to characterize flow of these compounds in response to a rapidly changing shear field during their application. We developed a fluid dynamic model that predicts the shear and pressure distributions in the compound during its processing in a metering nip based on process parameters and rheological results. We tested frothed compound formulations that are empirically known to be “penetrating” and “non-penetrating” based on the choice of soap (frothing surfactant). Formulated at the same froth density, penetrating to carpet backing compounds had large froth bubbles, relatively low transient shear viscosity and showed increasing foam breakdown due to shear when compared to non-penetrating compounds. Such frothed compounds readily collapse under shear and have relatively low dynamic stability, so the transition from a three-phased (air/aqueous/solid) to a two-phased (water/solid) system occurs much easier and faster during application. The model predicts the shear rate development and a small difference in the pressure distributions in the applicator nip between these formulations, but reduction in drainage for the non-penetrating formulation.
TL;DR: In this article, a survey of applicable methods for characterization of electrorheological suspensions as well as appropriate correction methods is provided, and the viscosity dependence on temperature under an applied electrical or magnetic field is investigated.
Abstract: The focus of previous research activities in the field of electrorheological fluids (ERF) has mostly been on new technical applications or on characterization using a single method. Comparisons between different results are hampered somewhat because standardized methods to characterize electrorheological fluids’ behavior have been lacking. This thesis provides a survey of applicable methods for characterization of electrorheological suspensions as well as appropriate correction methods. To date, the viscosity dependence on temperature under an applied electrical or magnetic field has only been investigated for homogeneous electrorheological fluids [1] and magnetorheological suspensions [2]. In this study, electrorheological suspensions were considered. In the absence of an applied electrical field, the
TL;DR: In this article, the effect of small addition of a surfactant in the turbulent flow of water depends on the structure and concentration of the additive, temperature of the solution and turbulence intensity, possible flow disturbance by a mechanical obstacle and the content of ions in water.
Abstract: Abstract Effectiveness of drag reduction by small addition of a surfactant in the turbulent flow of water depends on the structure and concentration of the additive, temperature of the solution and turbulence intensity, possible flow disturbance by a mechanical obstacle and the content of ions in water, but also on the age of the surfactant solution. We show how important aging effects are in connection with total surfactant concentration, in particular how rheological parameters of the drag reducing solution change with time.