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. Eight heat exchangers of counter-flow configurations are constructed with/without Single Segmental Perforated Baffles (SSPBs), which are fabricated with different void, cut and pitch ratios. 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 void ratio and inclination angle, and decreasing SSPBs cut and pitch ratios increases the annulus average Nusselt number (¯Nu_an) as well as friction factor (f_an). Furthermore, there is a slight increase in ¯Nu_an with decreasing the annulus-fluid inlet temperature, while its effect on f_an can be neglected. 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 inclination angle and decreasing SSPBs void, cut and pitch ratios enhances the TPI. Finally, correlations for ¯Nu_an in addition to f_an for concentric tube heat exchangers with SSPBs as a function of the investigated parameters are obtained.