The sedimentation of papermaking fibers

The motion of F-18 radioactively labeled papermaking fibers settling in the midst of a suspension of nonradioactive fibers has been studied using positron emission tomography (PET). Various fractions were separated from the whole-pulp suspension, radioactively labeled, and reintroduced into the original suspension. Tracer concentration profiles were measured dynamically throughout the sedimenting structure over the first 2 h of settling. These profiles were then used in conjunction with the Eulerian volume-averaged two-phase flow equations to estimate the permeability and solid-phase stress functions for this suspension. Good agreement was found between the experimental data and the numerical model using particular functional forms for permeability and solid stress. The general approach outlined here can be used to examine the networking characteristics of different mixed suspensions of fibers. (c) 2006 American Institute of Chemical Engineers AIChE J, 52: 2697-2706,2006.