Campus Units

Mechanical Engineering, Chemical and Biological Engineering

Document Type

Article

Publication Version

Published Version

Publication Date

5-2004

Journal or Book Title

TAPPI Journal

Volume

3

Issue

5

Abstract

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.

Comments

This article is published as Giorges, A.T.G., White, D.E., and Heindel, T.J., “Concentric Mixing of Hardwood Pulp and Water,” TAPPI Journal 3, no. 5 (online exclusive) (2004). Posted with permission.

Copyright Owner

TAPPI

Language

en

File Format

application/pdf

Published Version

Share

COinS