Abstract:

The instantaneous flow behaviors, i.e., the average velocity, turbulent kinetic energy and turbulent dissipation of diluted pulp at different planes, were simulated using the granular Eulerian multiphase model that combines the standard k-εturbulence model with sliding-grid algorithm (SG)technique in FLUENT.The characteristics of pulp flow in the dilution-zone and S-type dischargers with different structures, type-Ⅰ,Ⅱ and Ⅲ, at the bottom of high consistency bleaching tower were analyzed.To validate the model, the image separation and filtration for fiber and water tracer were performed in the particle image velocity (PIV)system and the velocities of fiber and water were measured.The comparison between the experimental data measured by PIV system and the CFD (computational fluid dynamics)simulations indicated that the Eulerian and standard k-ε turbulence models gave a better description for the flow patterns in the dilution-zone of the tower, which provide a good guidance for further study on the discharger.Among the dischargers, the one with type-Ⅰ structure (the ellipse section of 38 mm×50 mm)provides uniform falling of high consistency pulp and rapid discharging for diluted pulp in the dilution zone, in which the turbulent kinetic energy and turbulent dissipation of diluted pulp are greater than those in type-Ⅱ and Ⅲ dischargers, so it is more appropriate for pulp discharging at the bottom of the tower.