Second law analysis of combined heat and mass transfer in internal and external flows

Abstract

The control volume method is used to establish the rate of entropy generation due to heat and mass transfer in a fluid stream, accompanied by fluid friction. We show that unless the intensive form of the Gibbs equation is used, in recognition of the assumption of local thermodynamic equilibrium, errors arise in this analysis. These involve the incorrect use of the absolute mass flux instead of the diffusion flux and the appearance of a spurious coupling term between heat and mass transfer. The results are applied to examples of simultaneous heat and mass transfer in internal and external flows.