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

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.

► In-line jet mixing was investigated for both water and pulp fibre suspensions.
► Mixing in water improved with increasing jet-to-pipe velocity ratio.
► Suspension mixing depended on mainstream velocity due to its influence on flow regime.
► For a dilute suspension, mixing improved with increasing jet velocity.
► At higher concentration, optimum mixing was achieved when jet penetrated to centre of pipe.