Coupled transports in heterogeneous media

An external electric field, a pressure gradient, and a concentration gradie nt are simultaneously acting on a dilute electrolyte flowing through a char ged porous medium or a charged fracture. A general theoretical presentation is summarized, and the coupling tensors between the three previous macrosc opic gradients are systematically computed for a number of dimensionless pa rameters and for a large variety of geometries. The numerical results are p resented and discussed. The influences of the zeta potential, of the double -layer thickness, and of geometrical parameters, such as the porosity for p orous 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.