Simultaneous Flow of Water and Salt Through Unsaturated Porous Media: I. Rate Equations

The thermodynamic theory of irreversible proceses was used as a basis in developing two rate equations for the simultaneous movement of potassium chloride and water through porous media under isothermal conditions. The two rate equations are urn:x-wiley:03615995:saj2sssaj196503615995002900020010x:equation:saj2sssaj196503615995002900020010x-math-0001 where T is Kelvin temperature, J w and J s are flux of water and salt, ΔP and ΔC s are the pressure and salt concentration differences across the sample, C̄ s is the mean salt concentration, r is the concentration ratio, v̄ w is the partial molar or specific volume of matric water, depending upon units selected for measuring J w and R, L ww and L ss are the direct transfer coefficients for water and salt, and L sw and L ws are the interaction or linked transfer coefficients. The equations were tested under conditions of flow through unsaturated kaolinite and Millville silt loam at constant temperatures of 15, 25, 35C. The results showed that the interaction coefficients, L ws and L sw , were equal, suggesting that the Onsager theorem was met in both kaolinite and soil systems at the temperatures, pressure, and concentrations used.