This work experimentally investigates the characteristics of convective heat transfer and pressure drop of water flow in the annulus-side of horizontal double pipe heat exchangers. Twelve heat exchangers of counter-flow configurations are constructed with/without Single Segmental Perforated Baffles (SSPBs), which are fabricated with different holes spacing, void, cut, pitch ratios and inclination angle. The experiments are performed for annulus-side Reynolds number from 1380 to 5700, and for Prandtl number from 5.82 to 7.86. The results revealed that increasing SSPBs holes spacing and void ratios and inclination angle and decreasing SSPBs cut and pitch ratios increase the annulus average Nusselt number (View the MathML source) as well as friction factor (fan). The thermal performance index (TPI ) is calculated to compare the thermal performance of perforated baffled double pipe heat exchangers with un-baffled one. It is observed that increasing SSPBs holes spacing ratio and inclination angle, and decreasing SSPBs void ratio, cut ratio and pitch ratio enhances the thermal performance index. Finally, correlations for View the MathML source in addition to fan for concentric tube heat exchangers with SSPBs as a function of the investigated parameters are obtained.