Time filter

Source Type

Hyensjo M.,Metso Paper Karlstad AB | Dahlkild A.,KTH Royal Institute of Technology | Vikstrom T.,Metso Paper Sundsvall AB
Paper Conference and Trade Show 2010, PaperCon 2010 | Year: 2010

The fibre orientation state evolution is evaluated by the fully 3D convection-dispersion equation, i.e. the Fokker-Planck equation. This is solved along various streamlines in the contraction with vane inserts so that effects of wakes and boundary layers could be studied across a jet. As an input to the fibre orientation model the turbulent flow field is solved by Computational Fluid Dynamics (CFD) with second-order closure of the turbulence model. Parameter values for the rotational dispersion coefficient of three hypotheses reported in studies are tested for an independent experimental case. After the contraction the anisotropy profile across the flow, has a variation in anisotropy value in different regions, identified as the boundary layer, the undisturbed region and wakes. The numerical result predicts these regions by comparison to the experimental result with the fully 3D approach of the fibre orientation state applied.

Helena F.,Mid Sweden University | Per E.,Mid Sweden University | Granfeldt T.,Metso Paper Sundsvall AB | Logenius L.,Mid Sweden University
16th International Symposium on Wood, Fiber and Pulping Chemistry - Proceedings, ISWFPC | Year: 2011

To predict the brightness reduction in a chemithermomechanical process as well as the bleachability of pulps produced from different species of wood raw materials there are, at present, no shortcuts available. Pulps have to be manufactured in pilot or mill scale and bleached; evaluating and predicting the bleachability has consequently been very resource consuming and thus expensive - until now! Due to this, we have used a laboratory method based on 60 × 60 mm wood shavings making it possible to predict the bleachability of primarily chemithermomechanical pulps but also other mechanical pulps. Our experiments showed that retention time and impregnation temperature appears to have no impact on the final brightness of birch shavings. When being subjected to a simulated chemithermomechanical pulp process, eucalyptus exhibited an increase in chromophore content before the bleaching stage. In addition, eucalyptus suffered from severe alkaline darkening. After the bleaching stage, the alkaline darkening diminished. A higher retention temperature resulted in lower brightness of the eucalyptus shavings compared to when using a lower retention temperature. Birch reached the highest final brightness levels and had a higher overall yield too.

Claesson J.,Chalmers University of Technology | Wikstrom T.,Metso Paper Sundsvall AB | Rasmuson A.,Chalmers University of Technology
Nordic Pulp and Paper Research Journal | Year: 2013

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.

Fock H.,Chalmers University of Technology | Claesson J.,Chalmers University of Technology | Rasmuson A.,Chalmers University of Technology | Wikstrom T.,Metso Paper Sundsvall AB
Canadian Journal of Chemical Engineering | Year: 2011

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. © 2011 Canadian Society for Chemical Engineering.

Claesson J.,Chalmers University of Technology | Rasmuson A.,Chalmers University of Technology | Wiklund J.,Swedish Institute for Food and Biotechnology | Wikstrom T.,Metso Paper Sundsvall AB
AIChE Journal | Year: 2013

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. © 2012 American Institute of Chemical Engineers (AIChE).

Fock H.,Chalmers University of Technology | Rasmuson A.,Chalmers University of Technology | Wikstrom T.,Metso Paper Sundsvall AB
Nordic Pulp and Paper Research Journal | Year: 2010

The mixing of solid-liquid systems exhibiting non-Newtonian flow behaviour is studied using CFD. It is shown how transient variations in the local solids concentration can be included by adding a scalar transport equation for concentration and introducing a Theological model that is dependent on the local concentration. As an example, the transient behaviour of an agitated pulp stock chest subjected to variations in inlet pulp concentration is treated. In the chests, the mixing of the pulp suspension is important for decreasing the amplitude of the variations in the outlet flow from the chests, and this mixing is highly dependent on the local fibre concentration in the chest. The pulp suspension was modelled as a Bingham fluid, with a yield stress related to the local fibre concentration. It is shown that the change in the local fibre concentration affects the cavern formation, thus also affecting the mixing efficiency of the tank. The flow pattern obtained in the transient simulation, including the fibre concentration variation, indicates that there are areas that will remain unchanged over time. It is also shown that the yield stress level strongly affects the efficiency of the chest. Results of CFD model simulations agree fairly well with in-line fibre concentration measurements of the inlet and outlet flow from an industrial chest.

Claesson J.,Chalmers University of Technology | Wikstrom T.,Metso Paper Sundsvall AB | Rasmuson A.,Chalmers University of Technology
Nordic Pulp and Paper Research Journal | Year: 2012

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.

Claesson J.,Chalmers University of Technology | Wikstrom T.,Metso Paper Sundsvall AB | Rasmuson A.,Chalmers University of Technology
Nordic Pulp and Paper Research Journal | Year: 2012

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.

Melander O.,Metso Paper Sundsvall AB | Rasmuson A.,Chalmers University of Technology
Drying Technology | Year: 2011

A 3D two-phase flow drying model for medium density fiber-board (MDF) fibers was developed and implemented in the Ansys-CFX commercial CFD software. The model was validated against measurement data [1] with satisfactory results. A parameter study was done to study the effects of dryer temperature and mass loading of fibers. A realistic dryer geometry has been simulated and it has been demonstrated that the model can capture 2D and 3D flow phenomena that affect the drying results. The simulation results can be used to determine suitable ways for improving dryer efficiency. © 2011 Taylor & Francis Group. LLC.

Loading Metso Paper Sundsvall AB collaborators
Loading Metso Paper Sundsvall AB collaborators