In this study, we analyze the thermal hydraulic effects of pitched and flat impeller blades in a mixing vessel for different numbers of revolutions and various power levels of heaters in the blades. The installation of electric heaters inside blades expands the role of the blades from only mechanical effects to include thermal effects due to heat transfer between the blades and the fluid. At a constant blade geometry, the heat transfer rate depends on the temperature gradient between the blades and the fluid and the total convective heat transfer coefficient. Rotation of the heating blades causes hydraulic irreversibility clue to friction and the blade geometry as well as thermal irreversibility due to temperature gradients. In this case, unsteady convection generates unsteady total fluid entropy, especially thermally generated fluid entropy. Analyzing the causes of the increased total fluid entropy generated by blades indicates possible ways to minimize losses caused by thermal and hydraulic irreversibility and to maximize the efficiency of similar irreversible heating systems. (C) 2013 Elsevier Ltd. All rights reserved.