Irreversible thermodynamic coupling between heat and matter fluxes across a gas/liquid interface

Abstract

The governing equation for irreversible thermodynamic coupling phenomena, the dissipation function, is derived for a generalized gas/liquid interface following two routes and is shown to differ significantly from previous results (L. F. Phillips, Geophys. Res. Lett, 1991, 18, 1221; J. Chem. Soc., Faraday Trans., 1991, 87, 2187). The magnitude and direction of the coupled heat–mass effect is then computed for an idealized interface based on results from the kinetic theory of evaporation and condensation. The characteristic parameter for the coupling behaviour is the heat of transfer (q^*_i), the ratio of the conductive heat to mass flux arising from the cross-terms in the irreversible thermodynamic formulation. q^*_i for interfacial transport is shown to have a value of –0.43RT for both liquid–vapour and liquid–gas mixture systems. The coupled or cross-effect mass flux forced by the temperature field occurs from the cold fluid to the warm, counter to the conductive heat flux. This work suggests that the coupled mass fluxes across a gas/liquid interface are generally weaker than the direct, pressure-driven mass fluxes and are much smaller, by approximately a factor of 20, and in the opposite direction from earlier model predictions.