The working fluid was conveyed by a volumetric pump to an holding tank and it entered the test section equipped with copper fin electrodes which were connected to a power supply, type HP 6671A, working in the ranges 0–8 V and 0–220 A. This setup allowed investigating the heat transfer performance of the tubes under the prescribed condition of heat generated by Joule effect in the wall. By neglecting the changes in the local wall resistivity due to the cold working process, changes in the geometry and the effect of heat conduction in the wall, this heating condition well approximated the constant heat flux boundary condition at the fluid–wall interface.