This study investigates the performance characteristics of a shell-tube heat exchanger using three techniques to improve heat transfer rate: baffles, nanofluids, and semicircular tubes (SCTs). The experiments are done using six heat exchangers of SCTs with different base spacing ratios (), alumina/water nanofluid loaded on the shell side with different nanoparticle loadings (), and single-segmental baffles mounted with cut ratio (=16.5%), and pitch ratio (=1.47). The results show that when SCTs are used instead of CCTs, the heat transfer coefficient and friction factor are greater, and they increase when the SCT spacing ratio increases. The ¯Nu_sh and f_sh of nanofluids are greater than the base fluid at the same flow condition, and they grow as φ increases. Besides, the inclusion of nanoparticles in water on the shell side has a greater influence on these increases with SCTs than CCTs. The hydrothermal performance index (HTPI) is evaluated using the Stanton number of the shell side and f_sh ratios. The maximum obtained HTPI is 3.19 for a shell-SCT heat exchanger with baffles of =16.5%, =1.47, alumina/water nanofluid concentration of φ=1.5%, and SCTs of =55.1%. Finally, correlations are provided to predict ¯Nu_sh, f_sh, and the HTPI of the tested heat exchangers.