Abstract: An experimental investigation of air flow and heat transfer in three types of converging-diverging tubes is presented in this study. They have the same diameter, rib height and pitch, but the different lengths of the converging and diverging sections and their joint ways. The experimental results indicate that the heat transfer is enhanced when the length of converging section increases. A 12.4% increase of Nusselt number is observed and a 6.8% increase of friction coefficient is seen for the developed tube jointed linearly (DTL).Also a 5.27% increase of Nusselt number is observed and a 46.5% increase of friction coefficient is seen for the developed tube jointed convexly (DTC). The comparison results of Webb’s method show the DTL is better than OT in the range 1.5×10⁴～4×10⁴, but the DTC is not better than it.