In‐line jet mixing of liquid‐pulp‐fiber suspensions: Effect of fiber properties,flow regime,and jet penetration

Mixing effectiveness was determined experimentally for side jet injection into pipe flow for water and pulp suspensions for a range of fiber mass concentrations (0–3.0%), mainstream velocities (0.5–5.0 m/s), and side‐stream velocities (1.0–12.7 m/s). The mixing quality was measured in cross‐sectional planes along the pipe using electrical resistance tomography and quantified by a modified mixing index, derived from the coefficient of variation of conductivity. Mixing depended strongly on the flow regime and jet penetration. For turbulent flow, the criteria for in‐line jet mixing in water are applicable to the mixing in suspensions, with small differences likely due to differences in fiber network strength and influences of fiber‐turbulence interactions in modifying turbulent structures in the bulk. When a suspension flows as a plug, however, the mixing differs greatly from that in water, depending on the fiber network strength in the core of the pipe. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1420–1430, 2013