Catálogo de publicaciones - libros

An alternative formulation of the model for chemical osmosis in clay membranes is presented. It is shown that it exhibits the correct behaviour for limiting values of the reflection coefficient. The model results compare reasonably well with experimental data and a method is developed to obtain analytical solutions that agree in most cases with results derived from numerical simulations.

A permeameter was developed for measurement of coupled flow phenomena in clayey materials. Results are presented on streaming potentials in a Na-bentonite induced by hydraulic flow of electrolyte solutions. Transport coefficients are derived from the experiments, assuming the theory of irreversible thermodynamics to be applicable. Hydraulic and electro-osmotic conductivities are consistent with data reported elsewhere. However the electrical conductivity of the clay is substantially lower. This is ascribed to the high compaction of the clay resulting in overlap of double layers

It is known that when the concentration of background electrolyte in a charged porous medium increases, the permeability of the porous medium also increases. In this paper, a set of coupled governing equations is derived that describe Navier-Stokes flow of a pore fluid through a charged porous medium (i.e. flow in the presence of a diffuse double-layer). The set of coupled partial differential equations describe the transport of the individual ions along their electrochemical potential gradient, the transport of the pore fluid together with the ions in solution, and the voltage distribution through the porous medium, while simultaneously maintaining electro-neutrality of the system. The governing equations are solved for an example problem. By using this approach, new insight is gained into the origin of permeability changes arising from changes in the background electrolyte concentration.

Compact bone is a well-organised, multi-level porous structure. Strain-derived fluid flow likely steers the activity of cells within the bone matrix, which in turn orchestrate the concerted activity of bone resorbing and bone forming cells at the surface. We present a model of the strain-driven bone remodelling proces, which could explain the mechanically optimised structure of compact bone.

Liquid phase transport in heterogeneous media such as gels and biopolymers may induce very large strains. These produces internal mechanical stresses that interact with water transport mechanisms. We analyze transfers in porous media saturated with an ionic solution using the linear thermodynamics of irreversible processes. The interaction between mass transfer and stress/strain is analyzed using free energy. A large number of coefficients appears and we proposed theoretical and experimental method for their determination. A validation of the model is given in the simplified case of osmotic dehydration of Agar gel.

The influence of flow on the crystallization of polymers is divided into four different regimes, using a molecular description of polymer rheology: (1) close- to equilibrium configurations, (2) orientated chains, (3) weak chain stretching, and (4) strong chain stretching where the chain conformation can be affected. It can be shown that these regimes correlate well with the different morphologies observed in flow induced crystallization experiments. An explanation for the change in nucleation dynamics can be given based on kinetic and/or thermodynamic processes depending on the orientation and stretch of the polymer chains. The different morphologies are characterized by Minkowski functionals, and their development in time are described by the so-called Schneider rate equations.

When subjected to a mechanical loading, the solid phase of a saturated porous medium undergoes a dissolution due to strain-stress concentration effects along the fluid-solid interface. Through a micromechanical analysis, the mechanical affinity is shown to be the driving force of the local dissolution. For cracked porous media, the elastic free energy is a dominant component of this driving force. This allows to predict dissolution-induced creep in such materials.

A simplified quintuple model for the description of freezing and thawing processes in gas and liquid saturated porous materials is investigated by using a continuum mechanical approach based on the Theory of Porous Media (TPM). The porous solid consists of two phases, namely a granular or structured porous matrix and an ice phase. The liquid phase is divided in bulk water in the macro pores and gel water in the micro pores. In contrast to the bulk water the gel water is substantially affected by the surface of the solid. This phenomenon is already apparent by the fact that this water is frozen by homogeneous nucleation.

An approach based on the theory of mixtures with the concept of molar volume fractions and on the basic principles of continuum mechanics and macroscopic thermodynamics is introduced to model soil freezing of solute saturated soil.

In this paper we discuss a pore scale model for crystal precipitation and dissolution in porous media. We consider weak solutions in general domains and dissolution/precipitation fronts in thin strips. The latter yields an upscaled transport—reaction model.