Intrinsic and relative permeability for flow of humid air in unsaturated apple tissues

Abstract

Knowledge of intrinsic and relative permeabilities is important when studying pressure driven mass transport in unsaturated porous media. Little information is available on intrinsic and relative permeabilities of biomaterials. In this study, an experimental procedure was developed to determine intrinsic and relative permeabilities for the flow of humid air in porous apple tissues. Experiments were completed in two steps. In the first step, apple tissues were freeze-dried to remove moisture without changing the sample’s original pore structure. Dry air was passed through the sample and Darcy’s law was used to determine intrinsic permeability, K, as a function of porosity. In the second step, moist air was forced through partially saturated apple tissues to determine the air permeability, K g. The humid air was in thermodynamic equilibrium with the apple tissues to obtain an equivalent immiscible condition. The air relative permeability k rg was then calculated based on the value of the air permeability K g and the intrinsic permeability K. The intrinsic permeability for apple tissue varied from 8.89 × 10 −13 to 4.57 × 10 −11 m 2 for porosity ranging from 0.33 to 0.77. The porosity dependency of intrinsic permeability can be described by the Kozeny–Carman model. The gas relative permeability k rg was correlated to saturation by an empirical model.