Coupled transports in heterogeneous media

An external electric field, a pressure gradient, and a concentration gradient are simultaneously acting on a dilute electrolyte flowing through a charged porous medium or a charged fracture. A general theoretical presentation is summarized, and the coupling tensors between the three previous macroscopic gradients are systematically computed for a number of dimensionless parameters and for a large variety of geometries. The numerical results are presented and discussed. The influences of the zeta potential, of the double-layer thickness, and of geometrical parameters, such as the porosity for porous media and the surface roughness for fractures, are investigated. The dispersion of the coupling coefficients can be significantly reduced when a characteristic length scale Lambda, applicable to every configuration, is used. Moreover, in this representation, the numerical data are close to the predictions derived from generalized analytical solutions for circular and plane Poiseuille flows. (C) 2001 Academic Press.