Unsaturated fluid transport in swelling poroviscoelastic biopolymers

The hybrid mixture theory was used to obtain the two-scale unsaturated transport and thermomechanical equations for biopolymers. The two-scale laws of conservation of mass, momentum, energy and entropy were utilized, the constitutive theory was formulated and the entropy inequality was exploited to obtain various equilibrium, near-equilibrium and non-equilibrium relations. The system was treated as poroviscoelastic with the viscoelastic biopolymers interacting with the viscous water and oil phases at pore-scale via hydrophilic and hydrophobic forces. The gas phase exchanged mass with the liquid water due to evaporation/condensation away from equilibrium. The exploitation of entropy inequality resulted in temporally non-local generalized Darcy[U+05F3]s laws for the liquid phases, near-equilibrium swelling and capillary pressure relations, generalized stress relations, near-equilibrium Gibbs free energy relation and the rate of evaporation relation. The generalized Darcy[U+05F3]s law relations include novel integral terms with long-memory effects. These can describe the effect of biopolymer-fluid interaction on both Darcian and non-Darcian modes of fluid transport depending upon the state of the biopolymers (glassy, rubbery or glass-transition). The resulting transport laws for various phases include the cross-effect terms in the form of volume fraction gradients. The unsaturated generalized Darcy[U+05F3]s law relations were validated by making comparison to the experimental data on moisture transport, heat penetration and pressure development during frying of potato cylinders.