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Licentiate seminar

A model for Simulation of Fiber Suspension Flows


Defendant Main Advisor Extra Advisor Date
David Hammarström Anders Dahlkild Jari Hämäläinen 2004-06-11

Opponent
Tomas Wikström, Metso Paper Inc., Sundsvall

Evaluation committee

Abstract

Abstract The fiber suspensions in the production line from wood to paper are subjected to many types of chemical and mechanical processes, in which the flow of the suspension is of vital importance. The flow of the suspension determines the degree of uniformity of the fibers through the processing, which in return affects the properties of the fiber suspension. In order to optimise the process, thorough knowledge of the suspension flow is necessary, both on the level of suspension, fiber networks and individual fibers. Knowledge of the fiber suspension behaviour combined with commercial CFD simulation provides an efficient design method for any unit operation in the papermaking process. This work concentrates on macroscopic modeling of the behaviour of fiber suspensions from 0.5-5% dry content, pure fiber suspensions without fillers or additives. Any mechanisms causing the characteristic behaviour of the pulp suspension have not been included, they are only included through their influence on the suspension parameters. Excluded mechanisms are, for instance, the fiber-fiber coupling mechanisms that are the reason for the formation of fiber networks and parts of fiber network, flocs. By combining a rheology model for the bulk suspension, a wall function that accounts for the slip layer and finally introducing turbulence, a model has been created that is able to simulate the flow of most fiber suspensions. The flow of the suspension is not constrained to any particular flow conditions; the models discussed in this work aim at describing the behaviour of the suspension for all flow rates and flow types. The models are developed under simple flow conditions, where all variables can be controlled, but the models are intended for usage within the industry-based flows in real pulp and papermaking applications. Keywords: rheology, fiber, suspension, CFD, model, wall, slip, turbulence
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