Rate dependence of permeability in clean and soil contaminated prepared cane

This paper reports an investigation into the effects of soil contamination and superficial flow velocity on the permeability response of prepared sugar cane. Permeability is expressed as a function of void ratio, mass ratio of soil to organic fibre, and superficial flow velocity. When soil is added to a fixed volume of cane, soil reduces the overall permeability by reducing the void space available for juice flow. A net reduction in permeability occurs despite the apparently higher permeability of the solid soil particles relative to the highly microporous fibrovascular bundles. Significantly, the dependence of pressure gradient upon flow velocity is found to be less than unity, contrary to the flow laws of Darcy and Forchheimer. An explanation for this non-linear behaviour is given in terms of the collapse of cell walls in the fibrovascular bundles at high flow and pressure gradients and the partial expression of the soil and bagacillo fine fractions.