Modeling pulp fiber suspension rheology

Understanding the flow behaviour of pulp suspensions is very important in the design and operation of process equipment and paper mills. Pulp suspension flow is an opaque two-phase flow system, consisting of water and pulp fibres that aggregate and form coherent networks, resulting in very complex flow behaviour above a certain concentration. An Ultrasound Velocity profiling (UVP) technique was used in this study to investigate pipe flow of pulp suspensions in the near wall region. The study was performed at two concentrations and at four bulk velocities. The results showed that the mean velocity profiles exhibit a distinct plug at the centre of the pipe surrounded by a sharp velocity gradient. The plug size increases when the concentration increases or the bulk velocity decreases. The demodulated echo amplitude profile indicates a concentration profile in the near wall area, with a decreasing amount of fibres close to the pipe wall.

Rheologica Acta, 2012

This paper reports thixotropy in concentrated pulp fibre suspensions and studies their transient flow behaviour using conventional rheometry coupled with a velocimetry technique. Specifically, an ultrasonic Doppler velocimeter is used in conjunction with a rate-controlled rheometer to deduce the local velocity profiles of pulp fibre suspensions. Pulp suspensions are found to exhibit a plateau in their flow curves where a slight increase in the shear stress generates a jump in the corresponding shear rate, implying the occurrence of shear banding. The velocity profiles were found to be discontinuous in the vicinity of the yielding radius where the Herschel-Bulkley model failed to predict the flow. Shear history and the time of rest prior to the measurement were found to play a significant role on the rheology and the local velocity profiles of pulp suspensions.

2014

Computational Fluid Dynamics (CFD) tools can be ap plied successfully to predict the turbulent pipe flow of pulp suspensions. This s trategy allows to avoid the design of industrial equipment based on empirical correlation s. The present work investigated the turbulent pipe flow of concentrated Eucalyptus pulp suspensions. The numerical study was performed using the ANSYS FLUENT ® CFD software [ANSYS FLUENT ® 13.0.0, ANSYS FLUENT Inc., 2010]. A pseudo-homogeneous approach w as applied in this work. The nonNewtonian behavior of the pulp suspensions was intr oduced into the CFD code by considering the pulp viscosity as a function of a l ocal shear rate. Additionally, the model took into account a presence of a water annulus at the p ipe wall surrounding the flow core. The Chang-Hsieh-Chen [1,2] low-Re k-ε turbulence model was selected in this study as th e one allowing to account for a drag reduction effect in the pulp suspension flow as already show n in the previous work of the auth...

2002

We investigate the dynamics of a flexible, elastic fibre, suspended in a fluid and subjected to a 3D shear flow. Simulations are performed using the "Immersed Boundary Method," and are distinguished by their ability to capture the hydrodynamic interaction between the fluid and fibre, as well as the detailed structure of the individual fibres. Suspensions of flexible fibres are encountered in many industrial problems, although we focus in this work on the application to wood pulp fibre suspensions.

In the pulp and paper industry, the design of industrial equipment based on empirical correlations can be avoided using Computational Fluid Dynamics (CFD) tools. The present study aims at investigation of the turbulent pipe flow of concentrated Eucalyptus pulp suspension using the ANSYS FLUENT® CFD software package. The modelling strategy was a pseudohomogeneous approach. The non-Newtonian behavior of the pulp suspension was introduced into the CFD code considering its viscosity as a function of a shear rate. Additionally, the existence of a water annulus at the pipe wall surrounding the core flow was taken into account. Four low-Reynolds k-ε turbulence models were selected in the present study aiming at describing the presence of a drag reduction effect. All the models used were able to reproduce the drag reduction effect. Additionally the Lam-Bremhorst model was modified taking into account alterations applied successfully by other authors for the turbulent flow of polymer solutions. A good correspondence between the peculiar S-shaped profile near the wall, for the dimensionless velocity, reported in literature for these systems and those obtained numerically was achieved. The approach followed was validated by comparing the numerical results of pressure drop with those from literature.

Procedia Engineering, 2015

The 7th World Congress on Particle Technology (WCPT7) Application of different low-Reynolds k-ε turbulence models to model the flow of concentrated pulp suspensions in pipes

Proceedings 16th Annual International Symposium on High Performance Computing Systems and Applications, 2002

We investigate the dynamics of a flexible, elastic fibre, suspended in a fluid and subjected to a 3D shear flow. Simulations are performed using the "Immersed Boundary Method," and are distinguished by their ability to capture the hydrodynamic interaction between the fluid and fibre, as well as the detailed structure of the individual fibres. Suspensions of flexible fibres are encountered in many industrial problems, although we focus in this work on the application to wood pulp fibre suspensions.

Computational Fluid Dynamics (CFD) tools can be applied successfully to predict the turbulent pipe flow of pulp suspensions. This strategy allows to avoid the design of industrial equipment based on empirical correlations. The present work investigated the turbulent pipe flow of concentrated Eucalyptus pulp suspensions. The numerical study was performed using the ANSYS FLUENT ® CFD software [ANSYS FLUENT ® 13.0.0, ANSYS FLUENT Inc., 2010]. A pseudo-homogeneous approach was applied in this work. The non-Newtonian behavior of the pulp suspensions was introduced into the CFD code by considering the pulp viscosity as a function of a local shear rate. Additionally, the model took into account a presence of a water annulus at the pipe wall surrounding the flow core. The Chang-Hsieh-Chen [1,2] low-Re k-ε turbulence model was selected in this study as the one allowing to account for a drag reduction effect in the pulp suspension flow as already shown in the previous work of the authors [3]. Moreover, as referred in [2] the CHC turbulence model is more universal than the other low-Re models since its constants are the same as those conventionally used for the standard k-ε model. The applicability of the CHC model to reproduce the drag reduction effect has been tested with a damping function adopted from the work of Malin [4] who studied the pipe flow of a power-law fluid. In order to better fit the available reference experimental data the damping function proposed in has been modified by varying its parameters. A good correspondence between the velocity profiles reported in literature and those obtained numerically was achieved. As the key indicator of the model appropriateness the pressure drop values obtained experimentally were used.

Journal of Fluids Engineering-transactions of The Asme, 2017

The present paper describes a study of Freon R11 hydrate deposition in a turbulent flow of water. Eulerian-Eulerian CFD model was built in order to study the process numerically, the model was validated with experimental data from the multiphase flow loop. Different mechanisms for particulate stress were studied in the work in terms of their performance results, compared to experimental data. The model considered an expression for variable hydrate particle size which was validated in a series of population balance numerical experiments.