FIBER PASSAGE THROUGH A SINGLE SCREEN APERTURE

Fibre passage was examined for the case of flow through a narrow apert ure under conditions similar to pulp screening. An expression for fibr e passage, quantified by passage ratio, was derived in terms of the up stream fibre concentration profile. Fibre concentration profiles were measured for nylon fibres with lengths, L, equal to 1, 2, and 3 mm, an d shown to be zero at the wall, to increase linearly with distance fro m the wall to approximately L/3, and to remain constant beyond L/3. As suming fibres follow the fluid streamlines, passage ratio was calculat ed and compared with experiment for a broad range of fibre lengths, sl ot widths, W, average slot fluid velocities, V-s, and average cross-fl ow fluid velocities, V-u. Short fibre passage (L/W less than or equal to 2), was governed by the fibre concentration profile alone. Long fib re passage (L/W > 2), was largely governed by the concentration profil e; however, at low V-s/V-u the experimentally measured passage ratio w as less than that predicted by the concentration profile, and at high V-s/V-u the experimental measurements were greater than predicted.