Combination of the first and second law of thermodynamics has been utilized in analysing the convective heat transfer in a rectangular packed duct. Raschig ring type of packing in the air flow passage is used to enhance the heat transfer from uniformly heated front wall to air when the other walls are adiabatic. The packing increases wall to fluid heat transfer considerably, hence reduce the entropy generation due to the heat transfer across a finite temperature difference. However, the entropy generation due to fluid flow friction increases. The net entropy generations resulting from the above effects provide a new criterion in analysing the system. Using the Ergun equation for pressure drop estimation, an expression for the volumetric rate of entropy generation has been derived for a vertical 0.675 m long packed duct (H/W = 0.31). This expression has been displayed graphically to show the influences of physical and geometric parameters on the entropy generation. Introduction of packing proves to be a thermodynamically sound augmentation technique of convective heat transfer.