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Paradoxes and Realities in Unsaturated Flow Theory
Author(s) -
Gray William G.,
Hassanizadeh S. Majid
Publication year - 1991
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/91wr01259
Subject(s) - capillary pressure , wetting , hydrostatic equilibrium , relative permeability , thermodynamics , flow (mathematics) , hysteresis , mechanics , capillary action , two phase flow , saturation (graph theory) , mathematics , hydrostatic pressure , conservation of mass , physics , geotechnical engineering , geology , porous medium , quantum mechanics , combinatorics , porosity
In currently applied theory of unsaturated flow, paradoxes exist concerning the equation of state for the water phase, the idea of a water phase at negative absolute pressure, the applicability of the hydrostatic pressure gradient at equilibrium, and the lack of explicit inclusion of interface effects in the problem formulation. The theory of unsaturated flow presented here eliminates those paradoxes and indicates that the hysteresis in capillary pressure and relative permeability may be accounted for by allowing these quantities to depend on interfacial area as well as saturation. The wettability potential is shown to be a thermodynamic function which is important in describing unsaturated flow processes. The momentum balance equation for the interface between the air and water phases also contributes to a systematic and tractable set of equations which describe unsaturated flow.