Abstract: A numerical simulation of a double pipe heat exchanger is carried out to comprehend the effects of the outlet positions and tilt angles on the performance of convective heat transfer.Parameters including profiles of temperature at the selected cross-sections and distributions of both Nusselt number(Nu),and convective heat transfer coefficients (α) are obtained.Results show that the outlet position impacts on total heat flux,whereas the effect of the tilt angle is slight.Temperature dramatically varies within the thermal boundary layer;however,there is a slight variation in wall temperature of the double tube.α increases with increasing Reynolds number(Nu) ranging from 2 650 to 10 800.Compution results of Nu agree with the data obtained by the semi-empirical analytic solutions to Kays and Leung.