Steady-state heat and matter transfer at a non-uniform phase boundary

Fluxes of heat and matter are calculated by applying Onsager's irreversible thermodynamics to a macroscopic system which comprises a number of layers with differing transfer coefficients for heat and matter. It is shown that Eq. (1), which was previously derived for transport through a single uniform layer, applies to the composite system when suitably averaged values of transfer coefficients are used. The results are applied to calculations of the rate of CO2 transfer at a model air-sea interface which specifically includes the transition zone over which the medium changes from gas to liquid.