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

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 $D_{{\rm e}} = a\varepsilon {}^{b} $ , where a  = 7.2 × 10 −4  m 2 /s and b  = −3.8 for hemlock wood chips. © 2011 Canadian Society for Chemical Engineering