| 1. |
- Walther, Bernhard, et al.
(författare)
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Drop deformation dynamics and gel kinetics in a co-flowing water-in-oil system
- 2005
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 286:1, s. 378-386
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Tidskriftsartikel (refereegranskat)abstract
- Drop deformation and superimposed gel kinetics were studied in a fast continuous-flow process for a water-in-oil system. Highly monodisperse drops were generated in a double capillary and then deformed passing through a narrowing rectangular channel geometry. Nongelling deformation experiments were used to establish the process and compare it with existing theories. Thereafter, temperature induced drop gelation was included to study its effect on deformation and gel kinetics on short timescales and at high temperature gradients. The disperse phase was a ?-carrageenan solution with additional sodium and potassium ions for gelation experiments. Sunflower oil was used for the continuous phases. Nongelling experiments showed that shear forces are able to deform drops into ellipsoids. A comparison with the small deformation theory by Taylor was surprisingly good even when drop deformation and flow conditions were not in steady state. Superimposed gelation on the deformation process showed clearly the impact of the altered rheological properties of the dispersed and continuous phase. Deformation first increased on cooling the continuous phase until the onset of gel formation, where a pronounced decrease in deformation due to increasing droplet viscosity/viscoelasticity was observed. Drop deformation analyses were then used to detect differences in gelation kinetics at high cooling rate within process times as short as 1.8 s. © 2005 Elsevier Inc. All rights reserved.
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| 2. |
- Walther, Bernhard, et al.
(författare)
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Flow processing and gel formation : A promising combination for the design of the shape of gelatin drops
- 2002
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Ingår i: Food Hydrocolloids. - 0268-005X .- 1873-7137. ; 16:6, s. 633-643
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Tidskriftsartikel (refereegranskat)abstract
- This investigation is a model study on how drops can be structured by a combination of flow processing and gel formation. Different drop shapes were created by subjecting gelatin drops to various flow conditions. At the same time, temperature induced gel formation of the drops fixed the shape. Elongated drops and drops of complex form were created. The flow to shape the gelatin drops was generated in a 4-Roll Mill (4RM) and silicon oil was used as the continuous phase. During processing in the 4RM, the drops were allowed to follow two different streamlines and thereby being subjected to purely elongational and a mixture of shear and elongational flow. The drop size varied between 1.5 and 2.8 mm. The gelatin drops were temperature conditioned before the experiment to 60 °C and the silicon oil to 5 °C. The drops were cooled via the cold oil phase during the flow process, and gel formation was induced. A gel strength strong enough to resist further deformation was achieved at different fixation zones in the 4RM, and this depended on the process parameters of flow type, flow rate, drop size and gelatin concentration. The shape created was directly related to the fixation zone. There was a broad freedom to combine different parameter values to fix a drop in a certain fixation zone. The mechanism behind the various drop shapes is explained in terms of elongation, relaxation, pinching and gel formation in relation to flow pattern and time in the 4RM. Elongation is a major contribution to the mechanism in the case of elongated shapes, while elongation followed by relaxation and pinching are the dominant determinants in the creation of complex shapes. © 2002 Elsevier Science Ltd. All rights reserved.
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| 3. |
- Wiklund, Johan, et al.
(författare)
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In-line rheometry of particulate suspensions by pulsed ultrasound velocimetry combined with pressure difference method
- 2012
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Ingår i: Applied Rheology. - 1617-8106 .- 1430-6395. ; 22:4, s. Article Number: 42232-5
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Tidskriftsartikel (refereegranskat)abstract
- The in-line rheometer concept based on the combination of the ultrasonic velocity profiling (UVP) technique and pressure difference (PD) measurements was utilized for investigating the influence of particle concentration and size distribution on the rheology of particulate suspensions in pipe flow under realistic industrial process conditions. Well defined model suspensions were used, consisting of 11 mu m and 90 mu m diameter polyamide particles suspended in rapeseed oil at concentrations ranging from 1 to 25 % by volume. The variation of concentration and particle size distribution had the expected effects on the shear viscositiy of the investigated uni-modal and bimodal suspensions. The in-line results showed that the investigated suspensions exhibit Sisko flow behavior and demonstrated that the UVP+PD method can be used to determine the flow behavior of complex fluids and suspensions, even at high solid concentrations, under industrial conditions in-line. The obtained in-line results were in good agreement with measurement data obtained using a conventional rotational controlled-stress rheometer. Limitations of commercially available transducer technology were identified and other possible sources of inaccuracy of the UVP+PD method were investigated. Several improvements of the UVP+PD measurement method were proposed.
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