An estimate of the axial dispersion during flow through a compressible wood-chip bed

Abstract

In this work, we present a methodology to characterise the axial dispersion of a solute during steady-flow through a compressible bed of wood chips under mechanical load. We use a non-invasive imaging technique, namely electrical resistance tomography (ERT), to visualise the uniaxial displacement of a salt solution. Here we demonstrate that under two limiting cases the porosity of the porous bed varies slowly in the flow-direction and to the lowest order can be considered a constant. This simplified the optimisation routine we used to match the experimental data to the numerical results of the advection–diffusion equation. Using this, a methodology to estimate the axial dispersion is given by a minimisation scheme. In the experimental portion of the work we measure the axial dispersion of a bed of hemlock wood chips at three different kappa numbers κ, and compacted to three different compaction pressures p_c. We find that the dispersion D_e in the axial direction varies as a function of the porosity ε, according to , where a = 7.2 × 10⁻⁴ m²/s and b = −3.8 for hemlock wood chips. © 2011 Canadian Society for Chemical Engineering