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 ¯Nush and fsh 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 fsh 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 ¯Nush, fsh, and the HTPI of the tested heat exchangers.