Experimental and numerical investigations of three variants of internal cooling configurations—dimples only, ribs only, and ribs with dimples have been explored at process conditions (96 °C and 207 bar) with sCO2 as the coolant. The designs were chosen based on advanced internal cooling features typically used for air-breathing gas turbines. The experimental study described utilizes additively manufactured square channels with the cooling features over a range of Reynolds number from 80,000 to 250,000. Nusselt number is experimentally calculated utilizing the Wilson Plot method and three heat transfer characteristics—augmentation in Nusselt number, friction factor, and overall thermal performance factor (TPF) are reported. To explore the effect of surface roughness introduced due to additive manufacturing, two baseline flow cases are considered—a conventional smooth tube and an additively manufactured square tube. A companion computational fluid dynamics (CFD) simulation is also performed for the corresponding cooling configurations reported in the experiments using the Reynolds-averaged Navier–Stokes (RANS) based turbulence model. Both experimental and computational results show increasing Nusselt number augmentation as higher Reynolds numbers are approached, whereas prior work on internal cooling of air-breathing gas turbines predict a decay in the heat transfer enhancement as Reynolds number increases. Comparing cooling features, it is observed that the “ribs only” and “ribs with dimples” configurations exhibit higher Nusselt number augmentation at all Reynolds numbers compared with the “dimples only” and the “no features” configurations. However, the frictional losses are almost an order of magnitude higher in the presence of ribs.