THE ENTROPY CONDITION FOR THE DYNAMICS OF NONLINEAR MULTICOMPONENT SORPTION IN POROUS-MEDIA

Relations are developed which describe the condition imposed by the second law of thermodynamics (i.e. the entropy condition) on the dynamics of nonlinear sorption in porous media. The relations extend previous work to ion exchange, to systems where sorption causes variations in fluid velocity, to chemically reacting systems, and to systems involving dissolution/precipitation phenomena. The correspondence between the entropy condition and other criteria for the existence for various types of coherent concentration fronts is investigated and several relations are proven. The entropy conditions is used to extend results of other investigators concerning the existence of self-sharpening, square root broadening, and proportionate-pattern fronts. A method incorporating entropy considerations is developed for determining shapes of constant-pattern fronts in multicomponent sorption when transport resistances are present. The method has several advantages over existing methods when the single-solute isotherms are known accurately but the multicomponent isotherms are imprecisely represented. © 1989.