In-line jet mixing of liquid–pulp–fibre suspensions: Effect of concentration and velocities

Abstract Mixing quality of liquid injection into the main stream was evaluated after 90°-tee mixers for both water and softwood kraft pulp suspensions over a range of mass concentrations (0–3.0%), mainstream pipe velocities (0.5–5.0 m/s), side-stream jet velocities (1.0–12.7 m/s) and jet-to-pipe diameter ratios (0.05–0.208) using electrical resistance tomography (ERT). The degree of mixing was determined from measurements in cross-sectional planes along the pipeline based on a modified mixing index derived from the coefficient of variation ( CoV ) of individual conductivity values in each image pixel. The results show significant differences in jet mixing of a Newtonian fluid (water) in the turbulent flow regime and non-Newtonian pulp suspensions due to the complex rheology of the pulp suspensions and different flow regimes, which play important roles in determining the degree of mixing in pulp suspensions.