Thermal interaction between the streams of laminar flow double-pipe heat exchangers is investigated theoretically by accounting for axial conduction along the wall separating the fluids. In a countercurrent arrangement, thermal coupling is demonstrated to have a definite influence on all the more important heat transfer parameters, such as the wall temperature, the heat flux density, the local entropy production rate, and the Nusselt number distributions. The overall performance of the device is considered under a second law point of view, and a complete parametric study is carried out
