Entropy generation in a binary gas mixture in the presence of thermal and solutal mixed convection

Steady-state, laminar, fully-developed mixed convection of a binary non-reacting gas mixture flowing upwards in a vertical parallel-plate channel has been investigated from the point of view of the second law of thermodynamics. Analytical expressions are derived for the entropy generation rate for two combinations of boundary conditions: uniform wall temperature with uniform wall concentration (UWT-UWC) and uniform wall heat flux with uniform wall concentration (UHF-UWC). These expressions include three sources of irreversibility: heat conduction, fluid friction and species diffusion. In the UWT-UWC case, the entropy generation rate depends on the thermal and solutal boundary conditions and the mean velocity while in the UHF-UWC case it also depends on the streamwise coordinate. For humid air, the contribution of fluid friction is negligible for both cases while heat conduction and species diffusion effects appear to be of comparable orders of magnitude.