Concentric Mixing Of Softwood Pulp And Water, 2004 Paper Summit, Spring Technical & International Environmental Conference, (including Papermakers; Process Control, Electrical & Information; Product & Product Quality)

Concentric mixing experiments with velocity ratios of up to 6 have been completed using softwood thick stock pulp (0.9 – 4.0 % consistency). By increasing the velocity ratio from 1 to 6 (ratio of inner:outer jet velocity), the inner jet mixing region changes from snake-like to cone-like, the jet spreads faster, and the downstream mixing region is more uniform as quantified by local consistency measurements. With the increased velocity ratio, the process transforms from large-scale low-intensity toward small-scale high-intensity mixing and microscale turbulence, yielding a well-mixed blend. This is evidence that once the fiber network strength is overcome by shear stress and turbulence, the mixture behaves as a conventional Newtonian fluid in turbulent flow. Increased thick stock turbulence is found to have a minor effect on the mixing process. Turbulent numerical modeling with the standard k-ε turbulence model shows reasonable qualitative agreement with the experimental data.