| 1. |
- Björkman, Ulf
(författare)
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THE NON-NEWTONIAN FLUID MECHANICS OF TECHNICAL FIBRE SUSPENSIONS : COMPRESSIVE FLOWS
- 2009
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Ingår i: Applied Rheology. - 1430-6395 .- 1617-8106. ; 19:4
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Tidskriftsartikel (refereegranskat)abstract
- The flow of non-Newtonian technical fibre suspensions (paper pulps) through a number of contractions is analysed and compared. Traditionally technical fibre flows are modelled as flow of fibres in a suspending medium. Here they are treated as crowded flows of fibre flocs from which the liquid may be squeezed in and out from. Compressive flows are common in the fibre-based process industry. They can e.g. be found in the head-box of a paper machine, in extruder nozzles in polymer technology, in the stirrer zone of mixers, etc. Traditionally such flows are analysed in elongational flow terms. Here it will be demonstrated that elongational and compressive flows for technical fibres suspensions differ qualitatively. The nature of technical fibre flocs is also discussed. For historic reasons they have come to be regarded as the outcome of a flocculation process of electrostatic-colloidal and/or mechanical-entanglement type. It will be shown that such a process is unnecessary for technical fibre suspensions and that these flocs are qualitatively different, viz. frozen-developed dissipative structures of the flocky fibre flow from which they originate. It will also be demonstrated that technical fibre flocs, in contrast with flocs of the chemically flocked type, are basically non-coherent, i.e. not kept together by themselves. It is this non-coherence that makes a compressive approach fruitful, for these economically important flows. An attempt to explain the reasons behind the present state of fibre flow theory is presented. The ambition is to stop to the present inproductive tradition in technical fibre flow.
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| 2. |
- Björkman, Ulf
(författare)
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The nonlinear history of fibre flow research. Part 1 : Background and beginning
- 2008
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Ingår i: Applied Rheology. - : Walter de Gruyter GmbH. - 1430-6395 .- 1617-8106. ; 18:2
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Tidskriftsartikel (refereegranskat)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. In Part 1 of this historic investigation the roots of fibre flow research are traced to the beginning of the 19th century. The subsequent development is followed through its formative period in the first half of the 20th century up to about WW2. Part 2 will continue up to about 1960s when the present main tradition had been well established. In Part 2, an example of an alternative approach will also be given, and some proposals for future development presented.
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| 3. |
- Björkman, Ulf
(författare)
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The nonlinear history of fibre flow research. Part 2 : Continuation, reflections and suggestions
- 2008
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Ingår i: Applied Rheology. - : Walter de Gruyter GmbH. - 1430-6395 .- 1617-8106. ; 18:3
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Tidskriftsartikel (refereegranskat)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.
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| 4. |
- Eriksson, I, et al.
(författare)
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Evaluation of a helical ribbon impeller as a viscosity measuring device for fluid foods with particles
- 2002
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Ingår i: Applied Rheology. - 1430-6395. ; 12, s. 303-308
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Tidskriftsartikel (refereegranskat)abstract
- The traditional methods of measuring viscosity with rotational viscometers, i.e. cone-plate and concentric cylinder systems, are often not suitable for suspensions. To be able to measure viscosity on suspensions mixer viscometers have been developed. In this study a new design of a helical ribbon impeller has been evaluated and the Metzner-Otto approach has been used to calibrate the impeller. Different kinds of food products were studied. The Metzner-Otto parameter obtained from tomato products was lower than those obtained from starch products. The study showed that the Metzner-Otto parameter varied but seemed rather to be dependent on the composition of the food material than on the flow behaviour index. The impeller could handle high concentration of quite large particles. This type of helical ribbon impeller viscometer is thus recommended for rheological studies of suspensions with high concentration of particles.
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| 5. |
- Gram, Annika, et al.
(författare)
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Particle motion in fluid : Analytical and Numerical Study
- 2016
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Ingår i: Applied Rheology. - : Kerschensteiner Verlag GmbH. - 1430-6395 .- 1617-8106. ; 26:2
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Tidskriftsartikel (refereegranskat)abstract
- Particle motion in fluid is discussed for one-particle systems as well as for dense suspensions, such as cementitious materials. The difference in large particle motion between larger particles and behaviour of fines (<125 μm) is explained, motion of one particle is shown by numerical simulation. It is concluded and highlighted that it is the particular motion of the fines that to a large extent contribute to the rheological properties of a suspension. It is also shown why larger ellipsoidal particles do not necessarily contribute to the increase of viscosity.
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| 6. |
- Hamedi, Naser, et al.
(författare)
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Application of CFD–Based Correction Factors to Increase the Accuracy of Flow Curve Determination in a Couette Rheometer
- 2016
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Ingår i: Applied Rheology. - 1430-6395. ; 26:3
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Tidskriftsartikel (refereegranskat)abstract
- The measurement and the investigation of the errors in a Couette rheometer have been a topic of considerable interest in many rheometric studies. In the present study, a more accurate predictor-corrector method based on CFD and the analytical solution of the problem is described. Comparing to the previous CFD-based method, in addition to considering the effect of the end parts, the presented correction factors also take into account the effect of the wide gap into a single coefficient. The correction factors are computed for both Newtonian and non-Newtonian fluids in wide and narrow gap rheometry. Results showed that the shear rate distribution across the gap is highly non-linear in non-Newtonian wide gap rheometry. Moreover, for very shear thinning fluid i.e. n < 0.4 in narrow gap rheometry, there is a need to apply correction factor to the calculated fluid properties. Comparing the presented CFD approach and the current approach, the correction factor can be enhanced up to 16% depending on the fluid behavior and the gap distance.
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| 7. |
- Håkansson, Ulf, et al.
(författare)
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In-line rheometry of micro cement based grouts : A promising new industrial application of the ultrasound based UVP+PD method
- 2012
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Ingår i: Applied Rheology. - 1430-6395 .- 1617-8106. ; 22:4, s. 1023-1034
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of the viscosity of non-Newtonian fluids and suspensions having a solid volume fraction of about 30% or more is of major interest from an industrial point of view. Cement paste and cement grouts for injection grouting applications, with water to cement ratios typically in the range of 0.4 and 0.6 - 0.8 by weight, are two examples of industrial fluid systems. Few in-line techniques are available on the market that can be used for these fluid systems and under realistic field conditions. The so-called UVP+PD in-line rheometry method combining the Ultrasound Velocity Profiling (UVP) technique with Pressure Difference (PD) measurements is a promising new tool for industrial applications. This paper presents an initial pre-study that aims to demonstrate the feasibility of the UVP+PD method using cement grouts for process monitoring and control of grouting applications under realistic field conditions. The UVP+PD method was tested and found successful for continuous inline measurements of concentrated micro cement-based grouts with water/cement ratios of 0.6 and 0.8. The test set-up consisted of a combination of an experimental " flow loop" and a conventional field grouting rig - UNIGROUT, from Atlas Copco. The rheological properties were determined, directly in-line and the parameters obtained were subsequently compared with off-line measurements using a conventional rotational rheometer.
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| 8. |
- Kotze, Reinhardt, et al.
(författare)
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Optimization of the UVP+PD rheometric method for flow behavior monitoring of industrial fluid suspensions
- 2012
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Ingår i: Applied Rheology. - 1430-6395 .- 1617-8106. ; 22:4, s. 2-
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Tidskriftsartikel (refereegranskat)abstract
- Ultrasonic Velocity Profiling (UVP) is a powerful technique for velocity profile measurements in research and engineering applications as it is the only available method that is cost-effective, relatively easy to implement and applicable to opaque fluid suspensions, which are frequently found in industry. UVP can also be combined with Pressure Drop (PD) measurements in order to obtain rheological parameters of non-Newtonian fluids by fitting theoretical rheological models to a single velocity profile measurement. The flow properties of complex fluids are almost exclusively obtained today using commercially available instruments, such as conventional rotational rheometers or tube (capillary) viscometers. Since these methods are time-consuming and unsuitable for real-time process monitoring, the UVP+PD methodology becomes a very attractive alternative for in-line flow behavior monitoring as well as quality control in industrial applications. However, the accuracy of the UVP+PD methodology is highly dependent on the shape and magnitude of the measured velocity profiles and there are still a few problems remaining with current instrumentation and methods in order to achieve the robustness and accuracy required in industrial applications. The main objective of this research work was to optimize an UVP+PD system by implementing new transducer technology and signal processing techniques for more accurate velocity profile measurements as well as rheological characterization of complex fluids under industrial/realistic conditions. The new methodology was evaluated in two different pipe diameters (22.5 and 52.8mm) and tested with three different non-Newtonian fluids in order to obtain a wide range of rheological parameters. Results were also compared to conventional rotational rheometry and tube viscometry. It was found that rheological parameters obtained from accurate velocity data across the pipe radius, especially close to pipe walls where the velocity gradient is high, showed better agreement to conventional rheometry than when compared to results obtained using profiles measured with conventional UVP instrumentation and commercial software (Met-Flow SA Version 3.0). The UVP+PD method is now more robust and accurate. The main challenge remaining is to successfully implement a complete non-invasive system in industrial processes that is able to achieve real-time and accurate complex flow monitoring of non-Newtonian fluid suspensions.
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| 9. |
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| 10. |
- Nowak, J., et al.
(författare)
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Consequences of Sheep Blood Used as Diluting Agent for the Magnetoviscous Effect in Biocompatible Ferrofluids
- 2015
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Ingår i: Applied Rheology. - 1430-6395 .- 1617-8106. ; 25:5, s. 20-27
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic nanoparticles suspended in suitable carrier liquids can be adopted for use in biomedicine. For this to be achieved, the biocompatibility of these ferrofluids needs to be ascertained. In cancer treatment, potential applications currently under investigation include, e.g. drug targeting by using magneticfields and the destruction of diseased cells by applying alternating magnetic fields, which cause heating of magnetic nanoparticles. To enable the use of ferrofluids in the actual biomedical context, detailed knowledge of the flow characteristics is essential to ensure safe treatment. From ferrofluids used in the engineering context, a rise of viscosity when a magnetic field is applied the magnetoviscous effect is well known. This effect, which leads to an increased viscosity and profound alteration of a fluid's rheological behavior, has also been demonstrated for biocompatible ferrofluids used in the aforementioned applications. In biomedical applications, ferrofluids will be diluted in the blood stream. Therefore, the interaction between whole blood and the ferrofluid has to be investigated. This is the focus of the current experimental study, which makes use of two different ferrofluids diluted in sheep blood to gain a deeper understanding of the fluid mixtures primarily regarding the relative change in viscosity if an external magnetic field is applied. The results demonstrate a strong interaction between blood cells and structures formed by the magnetic nanoparticles and show a high deviation of results compared to ferrofluids diluted in water. These findings have to be taken into account for future research and applications of similar biocompatible fluids to guarantee safe and effective use in living organisms.
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