Mechanical Engineering, Chemical and Biological Engineering
Journal or Book Title
We completed concentric mixing experiments with velocity ratios of up to 6 using hardwood pulp of 1.0%, 1.9%, and 2.9% consistency and water. By increasing the velocity ratio (ratio of inner:outer jet velocity), we found the inner jet spread angle to be larger and the downstream mixing region uniform. Furthermore, local consistency measurements show a flattening of the concentration profile with increasing velocity ratio, confirming mixing improves as velocity ratio increases. For the fiber stock tested, mixing was significantly dependent on the stock consistency when the velocity ratio is small (Rv ≅ 1). This result indicates that the fluid streams do not deliver the shear stress and turbulence required to fully dislodge the fiber network. Mixing results from hydrodynamic instabilities and macroscale variations, which lead to downstream nonuniformities. At higher velocity ratios when the flow is turbulent, mixing is significantly affected by the velocity ratio, but there is no clear indication that mixing is affected by the stock consistency. These trends are 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. Mixing at high velocity ratio results from microscale turbulence that leads to a relatively uniform downstream mixture.
Giorges, Aklilu T.G.; White, David E.; and Heindel, Theodore J., "Concentric mixing of hardwood pulp and water" (2004). Mechanical Engineering Publications. 354.