Abstract
The aim of this paper is to propose a method to determine the chemical potential of two miscible components of a solution in porous media, particularly in the case of an unsaturated soil. It is limited to the capillary state; the equilibrium of the liquid phase in the soil is determined by gas–liquid interfaces whose geometry obeys Laplace’s law. Deduction of the chemical potential of the two components from the chemical potential of pure water is based on the assumption that, for the same volume occupied by the fluid phase in the porous medium, the geometry of the fluid phase is independent of the composition of the solution.The expressions of the chemical potentials of the two components were established. They show the superposition of two effects: the effect of interfacial forces and the effect of the presence of the other component. A study of the water–alcohol solution in a clayey silty sand soil was then conducted to alcohol mole fractions between 0 and 0.15 and water content in the 5%–15% range. In this field, the chemical potential of the water was seen to be affected by the capillary effects below a water content of 10%. Above that, its variation as a function of the mole fraction of alcohol differed little from that of the potential of the water in a free solution. The chemical potential of the alcohol was little affected by the capillary effects.
Highlights
Thermodynamic modelling of unsaturated soils in areas such as environmental geomechanics, agronomy, etc., implies knowledge of the state of the various components of the liquid phase
The aim of this paper is to propose a method to determine the chemical potential of the components of a solution of two miscible liquids in porous media, in the case of unsaturated soil
The assumption behind the assessment of chemical potentials of the components of a binary solution in a porous medium from the chemical potential of pure water is that, for the same volume occupied by the fluid phase in the porous medium, the geometry of the fluid phase is independent of the composition of the solution
Summary
Thermodynamic modelling of unsaturated soils in areas such as environmental geomechanics, agronomy, etc., implies knowledge of the state of the various components of the liquid phase. In a previous publication,[10] it was shown that the experimental techniques available, i.e. tensiometry and the use of saturated salt solutions, make it possible to establish the relationship between chemical potential and water content when the liquid phase of the porous medium is composed of pure water. This relationship has been established in the isothermal case for media having various structures: soils, gels and food products. The water–alcohol solution will be considered as a case study
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