| 1. |
- Gevert, Börje Sten, 1956, et al.
(författare)
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Hydro processing rape seed oil with gas oil for diesel fuel
- 2009
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Ingår i: Abstract of Papers of the American Chemical Society. - 0065-7727. - 9780841224414
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Konferensbidrag (refereegranskat)abstract
- The work was divided into two different series of light gas oil (LLGO) and heavy gas oil (HGO). The rapeseed oil was blended with the gas oils in the following concentrations: 10%, 20% and 30%. The pressure was maintained constant. The flow rate, temperature were varied. It is possible to blend rape seed oil into HGO and LLGO in the production of low sulfur diesel fuel. The conversion of the rapeseed oil to hydrocarbon was higher when blended into LLGO compared to HGO. Low reaction temperatures and high flow rates give less amount of conversion of the rape seed oil.
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| 2. |
- Claesson, Julia, 1985
(författare)
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An experimental study of the flow of concentrated pulp suspension through a sudden expansion and over a backward facing step
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Large amounts of pulp suspensions are handled in the pulp and paper industry annually. In order to produce the final product, paper, a lot of energy is required, e.g. for pumping and drying the suspensions. The lack of knowledge of the flow and fluid properties of pulp suspensions, however, aggravates the optimization of the design and the operation of process equipment. Pulp suspensions are two-phase solid liquid mixtures that consist of fibers and water. Already at a consistency of 1%, coherent networks are formed that affect the flow structure. Valid rheology models that capture the two-phase effects have not been developed yet due to the difficulties in describing pulp suspension in all flow regimes.The aim of this study was to make progress with the understanding of the nature of the flow and fiber interaction by experimentally studying concentrated pulp suspensions flowing through a sudden expansion as well as over a backward facing step. These two simple flow geometries were chosen because of their potential to generate complex flow structures, including several flow regimes as well as recirculation flow, separating flows and free mixing layers. The flow structures of the suspensions that flow through a sudden expansion were studied with Ultrasonic Velocity Profiling technique (UVP) and the flow over a backward facing step was studied with Laser Doppler Anemometry (LDA). Both measurement techniques were successfully used in the study of pulp suspensions at consistencies up to 3% at various flow rates. From the results of the flow through a sudden expansion it was concluded that the dimensions of the formed jet were influenced by the velocity and the consistency of the pulp suspensions. This proves that a similarity solution could not describe the suspensions at the velocities studied. Conclusions from the flow over a backward facing step show that greater consistency or a drop in velocity decrease the reattachment length in all suspensions except those with a consistency lower than 1.5%. The reason for the change in reattachment length seems to be related to the flow regime valid in the separation boundary layer. The results from both studies indicate that pulp suspensions are best described by rheology models that include a yield stress, but the available models cannot capture the flow structure over the whole flow range investigated. Therefore new models, probably including two-phase effects, need to be derived.
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| 3. |
- Claesson, Julia, 1985, et al.
(författare)
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An experimental study of the turbulent mixing layer in concentrated fiber suspensions.
- 2012
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Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 27:5, s. 940-946
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Tidskriftsartikel (refereegranskat)abstract
- Turbulence structures in a free mixing layer after a backward-facing step were studied in concentrated pulp suspensions (0.5-3% by weight) using Laser Doppler Anemometry (LDA) at two predetermined average inflow velocities (0.9 and 1.8 m/s). Both average and fluctuating velocities were investigated and the findings were compared with measurements in water. The experimental findings show that both the average velocities and the RMS velocities in the mixing layer decreased with an increase in concentration. Furthermore, by analyzing the energy spectra at the center of the mixing layer, it was possible to extract the inertial sub-range of pulp suspensions with a concentration of 0.5% at the lower inflow velocity and in suspensions up to a concentration of 1% at the higher inflow velocity. At higher concentrations the turbulence was damped by the fiber network and no turbulence structures could be extracted. The energy content at lower frequencies was higher in the pulp suspensions than in the experiments in pure water.
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| 4. |
- Claesson, Julia, 1985
(författare)
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Experimental and numerical studies of the flow of pulp suspensions
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Large amounts of pulp suspensions are handled in the pulp and paper industry daily. In order to produce the final product, paper, a lot of energy is required, e.g. for pumping, mixing and screening the suspensions. A lack of knowledge about the flow and fluid properties of pulp suspensions, however, aggravates the optimization of the design and the operation of process equipment. The aim of this research is to advance the understanding of the nature of fiber flow and fiber interaction by experimentally studying pulp suspensions at a consistency of 0.5 to 3%. These pulp suspensions were studied in flows through a sudden expansion, over a backward-facing step and along a flat plate. These simple flow geometries were chosen because of their potential to generate complex flow structures, including several flow regimes. Flow structures were studied with Ultrasonic Velocity Profiling technique (UVP) and Laser Doppler Anemometry (LDA). The experimental data was later used to develop a model that describes the local yield stress of the pulp suspension. The results show that jet dimensions are influenced by the consistency and velocity of the pulp suspension. In simulations, it was found that the size of the yield stress, i.e. fiber network strength, is the main parameter that affects the jet length. From these findings, a model that describes the local yield stress of pulp suspensions at a consistency higher than 1% was derived and connected to a single-phase rheology model. Validation of the model shows that it captures the trends in the experimental data. In studies of pulp suspensions after a backward-facing step, it was found that the reattachment length decreased with an increase in suspension consistency or a decrease in flow rate, except at the lowest consistency. It was also found that the reattachment length may be affected by the fluid regime at the separation point at the end of the step. In the study of the development of the near-wall boundary layer, width was found to increase with a decrease in consistency or an increase in velocity. An additional finding was that a constant boundary layer thickness was reached after 20 mm, regardless of the consistency or the velocity of the pulp suspension in the flow pipe.
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| 5. |
- Claesson, Julia, 1985, et al.
(författare)
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Flow of concentrated fiber suspensions over a backward facing step studied using LDA
- 2012
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Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 27:3, s. 653-661
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Tidskriftsartikel (refereegranskat)abstract
- Laser Doppler Anemometry (LDA) was used to study the flow structures of pulp suspensions over a backward facing step at two step heights (5 and 10 mm). Experiments were conducted at four consistencies (1, 1.5, 2 and 3%) and two pre-determined free stream velocities (1.3 and 1.8 m/s). The flow structures in the suspensions were compared with measurements made in water. The experimental results showed that it was possible to measure recirculation flow, mixing layers, reattaching flows as well as different flow regimes with LDA. Further measurements in turbulent concentrated pulp flows are needed to distinguish and characterize turbulent structures. Results show that the reattachment length decreased along with a decrease in velocity or an increase in consistency in pulp suspensions with a consistency of at least 1.5%. At 1% a decrease in velocity gave an increase in the reattachment length probably due to a change in the flow regime from laminar to transition or turbulent.
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| 6. |
- Claesson, Julia, 1985, et al.
(författare)
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Measurement and Analysis of Flow of Concentrated Fiber Suspensions through a 2-D Sudden Expansion Using UVP
- 2013
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Ingår i: AICHE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 59:3, s. 1012-1021
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Tidskriftsartikel (refereegranskat)abstract
- The ultrasound velocity profiling technique (UVP) was used to study flow structures after a two-dimensional (2-D) 1: 11 sudden expansion of pulp fiber suspensions at varied average velocities (1-2.2 m/s) and concentrations (1.8 and 2.8 wt %). One advantage of studying jet geometry is the potential to investigate the main flow structures away from walls. Measurements done at the same percent of the total jet length, at constant concentration, show that an increase in flow rate gave a faster decrease in centerline velocity and a quicker increase in jet width. Increasing the concentration, at the same jet length, the centerline velocity was more stable and the width of the mixing layer increased more rapidly. Comparisons with CFD simulations in the laminar regime, using the Bingham plastic model, show that the main flow structures were captured if the yield stress used in the simulations is approximately 20% of the measured using a rheometer.
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| 7. |
- Claesson, Julia, 1985, et al.
(författare)
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Modeling the effect of fiber orientation on local yield stress in flow of pulp suspensions
- 2014
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Ingår i: Nordic Pulp and Paper Research Journal. - : Walter de Gruyter GmbH. - 2000-0669 .- 0283-2631. ; 29:3, s. 444-452
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Tidskriftsartikel (refereegranskat)abstract
- A model that takes into account the local yield stress in pulp suspensions (2-3%) was derived. In this model the yield stress was assumed to decrease due to a reduction in the number of contact points between fibers in a network when the fibers are oriented in the shear field. The local yield stress described by the number of contact points multiplied by the friction force in the fiber connections was implemented in a CFD solver to describe the yield stress in the non-Newtonian single-phase Bingham model. Model results were compared with experimental UVP data from a study performed earlier on the flow of pulp suspensions at two concentrations after a sudden expansion. First model parameters were estimated with experimental data from a case with a concentration of 1.8% and an inflow velocity of 1.2 m/s. Then the model was used to predict five other cases. The proposed model was able to capture both the decrease in centerline velocity and the increase in the width of the jets at higher inflow velocities. At low inflow velocities the predicted jet lengths were too short compared to the experimental measured jet length due to under prediction of fiber alignment.
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| 8. |
- Claesson, Julia, 1985, et al.
(författare)
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The development of a near-wall boundary layer over a flat plate in concentrated pulp fiber suspensions
- 2013
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Ingår i: Nordic Pulp and Paper Research Journal. - : Walter de Gruyter GmbH. - 2000-0669 .- 0283-2631. ; 28:3, s. 399-406
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Tidskriftsartikel (refereegranskat)abstract
- The development of a boundary layer over a flat plate placed in a square pipe was studied in pulp suspensions at concentrations of 0.5, 1 and 1.8% at flow velocities of 0.24-0.96 m/s. Laser Doppler Anemometry (LDA) was used to measure velocities in the boundary layer from y=0-3 mm at x=0, 5, 10, 20 and 30 mm, where x=0 mm was the position where the flow met the plate. During the measurement time the pressure drop over the plate was also measured and it was concluded that the flow was in the rolling friction regime. The results of boundary layer thickness show that an increase in velocity or a decrease in concentration gave a thicker boundary layer in contrast to a laminar Newtonian boundary layer. In a power law fluid, boundary layer thickness decreases with an increase in shear thinning or velocity. Furthermore, in the pulp suspensions, a boundary layer with a constant thickness was reached 20 mm from the plate edge in contrast to a Newtonian and a shear thinning boundary layer which continued to increase along the plate. The difference in boundary layer development is believed to depend on the two-phase effects in pulp suspensions.
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| 9. |
- Fock, Helena, 1979, et al.
(författare)
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Near wall effects in the plug flow of pulp suspensions
- 2011
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Ingår i: Canadian Journal of Chemical Engineering. - : Wiley. - 1939-019X .- 0008-4034. ; 89:5, s. 1207-1216
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Tidskriftsartikel (refereegranskat)abstract
- Experimental data by the authors are further analysed to gain a more detailed understanding of the mechanisms of the plug flow and near-wall behaviour in the pipe flow of pulp suspensions at concentrations up to 4.7% by weight. The results indicate two-phase flow effects near the wall, one being that the apparent viscosity is higher than that of water. Another is that the wall shear stress estimated with the pressure drop data and a force balance is much higher than the one obtained with the measured velocity profile, indicating the presence of mechanical friction forces.
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